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Comparative osteology of Mastodonsaurus giganteus (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen)

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Comparative osteology of Mastodonsaurus giganteus (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen)

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Comparative osteology of Mastodonsaurus giganteus (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen) With 4 plates and 54 textfigures Abstract Mastodonsaurus giganteus, the most abundant and giant amphibian of the German Letten-keuper, is revised. The study is based on the excellently preserved and very rich material which was excavated during road construction in 1977 near Kupferzell, Northern Baden-Württemberg. It is shown that there exists only one diagnosable species of Mastodonsaurus, to which all Lettenkeuper material can be attributed. All finds from other horizons must be referred to as Mastodonsauridae gen. et sp. indet. because of their fragmentary status. A sec-ond, definitely diagnostic genus of this family is Heptasaurus from the higher Middle and Upper Buntsandstein. Finally a diagnosis of the family Mastodonsauridae is provided. A detailed osteological description of Mastodonsaurus giganteus reveals numerous un-known or formerly inadequately understood features, yielding data on various hitherto poor-ly known regions of the skeleton. The sutures of the skull roof, which could be studied in de-tail, are significantly different from the schemes presented by previous authors. The endocra-nium and mandible are further points of particular interest. The palatoquadrate contributes a significant part to the formation of the endocranium by an extensive and complicated epi-pterygoid. The neurocranium is dominated by the exoccipital, otic, and several portions of the sphenethmoid. For the first time the stapes is found in articulation and uncompressed. The mandible is slender and bears a massive postglenoid area, and the symphyseal area is extend-ed to accommodate giant tusks. The prearticular forms a pronounced process anterior to the glenoid facet. The axial skeleton is strongly ossified. It consists of massive, cylindrical intercentra that tend to be lower towards the tail and which have a dorsal incisure for the chorda, further it contains paired pleurocentra which are set in facets of the neural arch and intercentrum, and finally it bears low neural arches possessing posteriorly inclined, short and unfinished proces-sus spinosi and broad, laterally extended transverse processes. The costal apparatus is wide, bearing broadened ribs in the anterior and middle part of the trunk which are strengthened by two different uncinate processes. While in the trunk these processes disappear tailwards, the tail base and anterior tail proper again bear wide ribs with marked processes.
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Stuttgarter Beiträge zur Naturkunde
Serie B (Geologie und Paläontologie)
Herausgeber:
Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart
Comparative osteology of Mastodonsaurus giganteus
(Jaeger, 1828) from the Middle Triassic
(Lettenkeuper: Longobardian) of Germany
(Baden-Württemberg, Bayern, Thüringen)
By Rainer R. Schoch, Stuttgart
With 4 plates and 54 textfigures
Abstract
Mastodonsaurus giganteus, the most abundant and giant amphibian of the German Letten-
keuper, is revised. The study is based on the excellently preserved and very rich material
which was excavated during road construction in 1977 near Kupferzell, Northern Baden-
Württemberg. It is shown that there exists only one diagnosable species of Mastodonsaurus,
to which all Lettenkeuper material can be attributed. All finds from other horizons must be
referred to as Mastodonsauridae gen. et sp. indet. because of their fragmentary status. A sec-
ond, definitely diagnostic genus of this family is Heptasaurus from the higher Middle and
Upper Buntsandstein. Finally a diagnosis of the family Mastodonsauridae is provided.
A detailed osteological description of Mastodonsaurus giganteus reveals numerous un-
known or formerly inadequately understood features, yielding data on various hitherto poor-
ly known regions of the skeleton. The sutures of the skull roof, which could be studied in de-
tail, are significantly different from the schemes presented by previous authors. The endocra-
nium and mandible are further points of particular interest. The palatoquadrate contributes a
significant part to the formation of the endocranium by an extensive and complicated epi-
pterygoid. The neurocranium is dominated by the exoccipital, otic, and several portions of the
sphenethmoid. For the first time the stapes is found in articulation and uncompressed. The
mandible is slender and bears a massive postglenoid area, and the symphyseal area is extend-
ed to accommodate giant tusks. The prearticular forms a pronounced process anterior to the
glenoid facet.
The axial skeleton is strongly ossified. It consists of massive, cylindrical intercentra that
tend to be lower towards the tail and which have a dorsal incisure for the chorda, further it
contains paired pleurocentra which are set in facets of the neural arch and intercentrum, and
finally it bears low neural arches possessing posteriorly inclined, short and unfinished proces-
sus spinosi and broad, laterally extended transverse processes. The costal apparatus is wide,
bearing broadened ribs in the anterior and middle part of the trunk which are strengthened by
two different uncinate processes. While in the trunk these processes disappear tailwards, the
tail base and anterior tail proper again bear wide ribs with marked processes.
Stuttgarter Beitr. Naturk. Ser. B Nr. 278 175 pp., 4 pls., 54 figs. Stuttgart, 30. 12. 1999
Doctoral dissertation Univ. Tübingen 1998.
The girdles and appendages are well represented in the Kupferzell material, with the excep-
tion of the pes; because of their disarticulated state their original arrangement has to be recon-
structed. The dermal bones of the pectoral girdle consist of broad and flattened claviculae and
a wide, rhomboidal interclavicle which has, as is typical of capitosaurs, a stilette-like anterior
process with a broadened tip. The ontogeny of the cleithrum and scapulocoracoid is docu-
mented in detail. Scapula and coracoid are separate at first, but later in development fuse to
give a compound ossification, whose coracoid portion tends to increase in area. In addition
the geometry and surface of the glenoid facet changes during ontogeny. The humerus is rela-
tively slender and long, yet poorly differentiated with respect to most other temnospondyls.
Only in the largest specimens are there definite epicondyles and a faint supinator process. Ra-
dius and ulna are well differentiated and elongate, and the manus consists mainly of slender
metacarpals and phalanges. In the pelvic girdle the ilium is slender and low, with an acetabu-
lum that enlarged during later development. The ischium is small and remains poorly differ-
entiated. In larger specimens it appears to fuse with the pubis which is still unknown as isolat-
ed element. The femur is slender, elongate, and differentiated, whereas the lower leg gains less
than half the length of the upper leg and has a rudimentary structure.
Finally open questions and problems regarding the reconstruction of the whole skeleton
are discussed. This involves a clarification of the methods used and a discussion of the lines of
evidence. A complete yet still partially provisional restoration of the skeleton of Mastodon-
saurus giganteus gives an animal similar to a gigantic salamander. Mastodonsaurus was most
similar to cryptobranchid salamanders in its bodily proportions such as the relative length of
the trunk and tail, as well as the considerable breadth and flattness of the rib cage.
Zusammenfassung
Mastodonsaurus giganteus, das häufigste und größte Amphib der europäischen Mitteltrias,
wird eingehend revidiert. Die Untersuchung geht aus von dem hervorragend erhaltenen und
sehr umfangreichen Material, das beim Autobahnbau 1977 bei Kupferzell geborgen wurde.
Im Lettenkeuper existiert nur eine diagnostizierbare Art von Mastodonsaurus, während die
fragmentarischen Funde aus anderen Formationen lediglich der Familie Mastodonsauridae
zugeordnet werden können. Die zweite, gegenwärtig faßbare Gattung dieser Familie ist Hep-
tasaurus, die auf den höheren Mittleren und Oberen Buntsandstein beschränkt bleibt. Die ta-
xonomische Revision schließt mit einer Diagnose der Mastodonsauridae.
Im Rahmen einer detaillierten osteologischen Untersuchung von Mastodonsaurus gigante-
us werden zahlreiche neue Merkmale beschrieben und viele, bisher unzureichend verstandene
Regionen des Skeletts vorgestellt und rekonstruiert. Die Suturen im Schädeldach können
dank der guten Erhaltung der Kupferzeller Funde erstmals genau erfaßt werden; sie weichen
in einigen Punkten erheblich von den Schemata früherer Bearbeiter ab. Das Endocranium und
die Mandibel von Mastodonsaurus bilden weitere Schwerpunkte. Das Palatoquadratum ist
mit einem ausgedehnten und kompliziert gebauten Epipterygoid wesentlich an der Gestal-
tung des Endocranium beteiligt. Im knöchernen Neurocranium dominieren das Exoccipitale,
das Oticum sowie verschiedene Portionen des Sphenethmoid; der Stapes wird erstmals un-
verdrückt und in Artikulation vorgefunden und vorgestellt. Im Unterkiefer, der sehr niedrig
ist und eine massive, langgestreckte Postglenoid-Region besitzt, dominieren riesige Fangzäh-
ne in der verbreiterten Symphyse. Ein hoher, allometrisch positiv wachsender Fortsatz des
Praearticulare bildet eine knöcherne Sperre unmittelbar vor dem Unterkiefergelenk.
Das Axialskelett ist stark verknöchert. Es besteht aus massiven, kurz-zylindrischen Inter-
centra, die zur Cauda hin niedriger werden und eine Inzisur für die Chorda aufweisen, wei-
terhin enthält es paarige Pleurocentra, die in Facetten des Neuralbogens und des Intercentrum
eingelassen sind, und schließlich die Bögen selbst, die niedrig sind, mit nach hinten geneigten
Dornfortsätzen und breit nach lateral vorgreifenden Transversalfortsätzen. Der Rippenkorb
ist breit, im vorderen und mittleren Rumpf aus kräftigen Rippen bestehend, die mehrere Un-
cinat-Fortsätze tragen können. Diese werden im hinteren Rumpfabschnitt kürzer und ver-
schwinden schließlich ganz, während im Schwanzskelett die Rippen erneut größer sind und
auch dort blatt- bis stilettförmige Uncinat-Fortsätze tragen.
Die Gürtel und Extremitäten sind bis auf das Fußskelett gut dokumentiert, müssen jedoch
weitgehend anhand disartikulierter Reste rekonstruiert werden. Der hautknöcherne Schulter-
gürtel besteht aus breiten, großflächigen Claviculae und einer breitrhombischen Interclavicu-
2stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
la, die den für Capitosaurier typischen, vorne verbreiterten anterioren Fortsatz trägt. Die On-
togenese des Cleithrum sowie der ersatzknöchernen Elemente läßt sich im Detail verfolgen.
Die Scapula und das Coracoid sind anfangs getrennt und verschmelzen später suturlos, wobei
sich der Coracoid-Anteil stark medial ausdehnt. Auch die Glenoidfacette erweitert und ver-
kompliziert sich im Zuge der späteren Ontogenese. Der Humerus ist anfangs verhältnismäßig
schlank, insgesamt relativ lang und bis in das hohe Alter von rudimentärer Gestalt verglichen
mit den meisten anderen Temnospondylen; erst bei den größten Individuen bilden sich die
Condyli an seinem Distalende sowie ein schwacher Supinatorfortsatz. Radius und Ulna sind
lang und differenziert, und das Handskelett besteht aus überwiegend schlanken Metacarpalia
und Phalangen. Im Beckengürtel findet sich ein niedriges und schlankes Ilium, dessen Anteil
am Acetabulum sich im Alter vergrößert. Das Ischium ist klein und bleibt zeitlebens wenig
differenziert; bei größeren Tieren scheint es mit dem Pubis, das bisher isoliert nicht bekannt
ist, verschmolzen zu sein. Das Femur ist schlank, langgestreckt und differenziert, während Ti-
bia und Fibula weniger als halb so lang werden und rudimentär bleiben.
Die Untersuchung schließt mit der Besprechung offener Fragen und Probleme bei der Re-
konstruktion des Gesamtskeletts. Dabei werden getrennt nach einzelnen Regionen die we-
sentlichen Schritte bei der Rekonstruktion des Rumpfes und der Extremitäten behandelt.
Eine in Abschnitten sicherlich noch vorläufige Gesamtrekonstruktion ergibt für Mastodon-
saurus giganteus die Gestalt eines Salamander-artig langgestreckten Tieres, die in einigen
Punkten – etwa der relativen Länge von Rumpf und Schwanz, der Breite des Brustkorbes und
dem hohen Grad der Abflachung – dem Habitus rezenter Asiatischer Riesensalamander
(Cryptobranchiden) am nächsten kommt.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Outline of study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Stratigraphical range and geographical occurrence . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Lithology and fauna of the Kupferzell Fossil-Lagerstätte . . . . . . . . . . . . . . . . . . . . 12
1.4. Material examined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.1. Mastodonsaurus giganteus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.2. Temnospondyl material studied for comparative purposes . . . . . . . . . . . . . . 18
1.5. Institutional abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2. Taxonomy of Mastodonsaurus giganteus (J
AEGER
, 1828) . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1. Discovery and first assignment of finds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2. Identification of the Kupferzell specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3. Taxonomic status of Mastodonsauridae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3. Comparative osteology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1. Cranial anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1.1. General structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.1.2. Skull roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.3. Palatal dermal elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.1.4. Occiput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.1.5. Palatoquadrate ossifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.1.6. Neurocranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.1.7. Mandible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.2. Postcranial anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.2.1. Historical sketch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.2.2. General structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.2.3. Axial skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.2.4. Appendicular skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4. Reconstruction of skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
4.2. Problems and open questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.3. Lines of evidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
4.4. Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
4.4.1. Threedimensional structure of mandible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
4.4.2. The structure of the occiput and its articulation with the atlas . . . . . . . . . . . 141
schoch, mastodonsaurus giganteus 3
4.4.3. Structure of the vertebral segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
4.4.4. The sequence of intercentra through the axial skeleton . . . . . . . . . . . . . . . . . 143
4.4.5. The sequence of rib types through the axial skeleton . . . . . . . . . . . . . . . . . . 145
4.4.6. Structure and length of the tail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
4.4.7. Appendicular skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
4.4.8. The skeleton as a whole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Glossary of anatomical terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
1. Introduction
In 1824, G. F. J
AEGER
was the first to mention finds of giant bones from Triassic
strata resembling those of salamanders. These were collected in an alum mine at
Gaildorf near Schwäbisch Hall in northern Baden-Württemberg. J
AEGER
’s brief note
– written in Latin – was succeeded by a more informative and illustrated account on
the material (J
AEGER
1828), and basing on a tooth and a piece of a large occiput he
erected two genera – Mastodonsaurus and Salamandroides. The first name, a greek
translation for ‘wart-toothed lizard’, referred to the worn-off tip of a giant tooth
from Gaildorf, while the second pointed at the resemblance to extant amphibians,
notably salamanders, which have similar-shaped occipital condyles.
Several publications, most of them being brief notes, followed (for details see syn-
onymy list), among them the first diagnostic characterization of this species which is
now called Mastodonsaurus giganteus. O
WEN
(1841) compared the Gaildorf materi-
al with teeth encountered in the Upper Triassic Warwick Sandstone of Southern
England. His studies of dental fine structure were an important contribution to the
understanding of early tetrapod teeth, as he was the first to publish on the labyrin-
thic infolding of the dentine and enamel. This culminated in the birth of the name
‘Labyrinthodontes’, giving rise to a long-used, though nowadays somewhat outdat-
ed expression for certain large early tetrapods (labyrinthodonts). M
EYER
in M
EYER
& P
LIENINGER
(1844) replied to O
WEN
by emphasizing his earlier yet unpublished
discovery of the labyrinthic infolding in Mastodonsaurus, and he believed the animal
to be a reptile (‘Saurus’) rather than an amphibian (‘Batrachus’). M
EYER
therefore
supported the name Mastodonsaurus in favour of Salamandroides (cf. J
AEGER
1828;
A
LBERTI
1834), Batrachosaurus (M
UENSTER
1834), or Labyrinthodon (O
WEN
1841).
Even though M
EYER
was wrong in his understanding of Mastodonsaurus as an am-
niote (as we may translate his concept into modern terms), he and P
LIENINGER
(1844) gave a first detailed overview on the morphology of the skull and certain pres-
acral bones. M
EYER
in particular added an interesting discussion in which he com-
pared the cranial anatomy of Mastodonsaurus with many Recent forms; these inves-
tigations doubtlessly stand as a masterpiece of early comparative anatomy until the
present day, and they are unparalleled by all subsequent authors.
Q
UENSTEDT
(1850), following earlier arguments of J
AEGER
(1828) and others, fi-
nally explicitly argued for the amphibian nature of the labyrinthodont finds. It re-
mains unclear whether the weight of Q
UENSTEDT
’s and O
WEN
’s authorities, or the
strength of their arguments at the end resulted in the broad consensus on this ques-
tion recognised after 1870.
E. F
RAAS
(1889), F. v. H
UENE
(1922), W
EPFER
(1922a, b, 1923 a), and finally P
FAN
-
NENSTIEL
(1932) successively added new and more detailed information on cranial
4stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 5
Fig. 1. Skull of Mastodonsaurus giganteus (J
AEGER
, 1828) in dorsal view (SMNS 54675; see
also plate 2). Note the pronounced sculpturing of the dermal bones, the asymmetri-
cal sutures, and the characteristic shape and large size of the orbits. The small open-
ings anterior to the nares accommodated large tusks located on the mandibular sym-
physis.
and postcranial anatomy of the genus Mastodonsaurus (sensu lato), referring to ma-
terial from Gaildorf and other Lettenkeuper localities (M. giganteus), as well as new
material from the Upper Buntsandstein (M. cappelensis W
EPFER
, 1923), which was
later assigned to the new genus Heptasaurus (S
ÄVE
-S
ÖDERBERGH
1935).
Quite recently, rich and exceptionally well preserved material of Mastodonsaurus
giganteus was discovered near the small town Kupferzell in Hohenlohe, northern
Württemberg, during road works (Bundesautobahn 6, Heilbronn-Nürnberg) which
transsected fossiliferous Lettenkeuper strata in spring, 1977. However, without the
trained eyes of the engaged amateur collector J
OHANN
G. W
EGELE
, as well as the
skilled and determined acting of the curator Dr. R
UPERT
W
ILD
(and many other in-
dividuals then employed at the Staatliches Museum für Naturkunde Stuttgart) the
finds would not have been recovered in this quantity and completeness. The excava-
tion yielded more than twenty good skulls and thousands of single bones from all
parts of the body. The quality of this material is optimally suited not only for a rede-
scription of Mastodonsaurus, but also for detailed studies on the structure of the
skeleton of large temnospondyls in general. It is fortunate that this historically so
important species can be the focus of a detailed reinvestigation of stereospondyl am-
phibians, which form an important yet still little understood element in Triassic ter-
restrial ecosystems.
1.1. Outline of study
This study has three main interests: (1) a taxonomic clarification of all Middle Eu-
ropean finds attributed to Mastodonsaurus giganteus, with particular emphasis on
the taxonomy of the Kupferzell finds, (2) a detailed analysis of the osteology of Mas-
todonsaurus giganteus regarding all regions of the skeleton, with comments on ta-
phonomy, preservation, and the problems related to disarticulation, and (3) a recon-
struction of the skeleton, based on direct anatomical evidence, taphonomic evidence,
and indirect evidence from the nearest fossil relatives of Mastodonsaurus.
The three sections are ordered as follows: the taxonomy section first clarifies the
status of Mastodonsaurus giganteus and the Mastodonsauridae, thereby establishing
a basis on which the succeeding sections operate. The osteological study forms the
main part; it is subdivided into an introductive part which discusses the general
structure of a particular structural unit, then continues with a detailed treatment of
the anatomy of its components, and finally reviews the subject by focussing on some
of the most conspicuous general structures, by which the single elements are inte-
grated into the architectural frame. Finally a 3-d reconstruction of the skeleton is at-
tempted, based on the osteological description and drawings, whereby single bones
are successively added to the reconstructed region.
1.2. Stratigraphical range and geographical occurrence
The discovery of Mastodonsaurus giganteus dates back to a time of an awaking
and intensive interest in the geology of Württemberg and neighbouring regions. Nu-
merous practising geologists, miners, and not least various well-educated laymen be-
gan to work in the field (see reviews by W
EBER
1990, 1992 a, b). Württemberg be-
came particularly famous at the beginning of the last century as a fossil-bearing re-
gion, but only by the activity of the aforementioned people it became what H
UENE
later termed a “classical saurian country” (W
ILD
1980a).
6stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
The horizons rich in vertebrate fossils range from the Lower Triassic (Buntsand-
stein) up to the Upper Jurassic (Malm), and the peculiar southwest German geomor-
phology permits broad outcropping of all stratigraphic units (fig. 2). There is a gen-
eral dip to the southeast. The main lithological units form slightly tilted plains each
of which ends in an escarpment to the northwest. The landscape thus morphologi-
cally differentiated by erosional steps is therefore aptly called Schichtstufenland in
German.
The Buntsandstein has its most extended outcrop in the northern Schwarzwald
mountains; farther to the south it is restricted to the eastern margin of this mountain
range.The Buntsandstein forms the lowermost unit of the Schichtstufenland which
develops to the east and southeast. The following two steps in the landscape are
formed by the escarpments of Muschelkalk and Keuper which overlay the Bunt-
sandstein. The sequence of steps is continued by the escarpments of Lower and Mid-
dle Jurassic further southeast. The most spectacular step is then formed by the high
and steep escarpment of the Upper Jurassic limestones of the Schwäbische Alb.
The main localities at which remains of the giant amphibian family Mastodonsau-
ridae have been found are distributed on the outcroppings of two particularly fossi-
liferous stratigraphical units, the Upper Buntsandstein (Olenekian/Anisian
boundary) and the Lettenkeuper (Upper Ladinian: Longobardian). The localities
of the former are aligned along the margins of the Vosges, Schwarzwald, Odenwald,
and Spessart mountains, whereas the localities of the latter (and only these are con-
cerned by the present study) are situated especially in the vast outcrop in Hohen-
lohe, a region in northern Württemberg.
The Mastodonsauridae first appear in the Upper Buntsandstein at the eastern
margin of the Schwarzwald mountain range (figs. 2, 3), as summarised recently by
K
AMPHAUSEN
& O
RTLAM
(1993). Even small bone fragments of mastodonsaurids
are easily identified by their great thickness and the peculiar type of sculpturing; in
larger fragments the advanced morphology, especially of the skull, is an unequivocal
sign. To date, the family Mastodonsauridae encompasses two genera, Heptasaurus
and Mastodonsaurus, which are separated by a considerable stratigraphical interval.
Heptasaurus is abundant in the Pflanzensandstein topping the Violetter Horizont
(VH) 5, below the Röttone (so4, Uppermost Buntsandstein), and most probably al-
so occurs in equivalent horizons of the Prims Mulde, north of the Hunsrück moun-
tains (S
CHMIDT
1960; J
UX
& P
FLUG
1958; J
UX
1962, 1966; S
ANDER
& G
EE
1994). As
far as can be said at this preliminary stage, all of these finds are attributable to Hep-
tasaurus cappelensis, which was first described by W
EPFER
(1923 a) as a second spe-
cies of Mastodonsaurus. An assemblage of almost fourty specimens, recovered
between the villages Kappel and Niedereschach, between Villingen-Schwenningen
and Rottweil, became famous (W
EPFER
1922a, b).
Through the marine Muschelkalk sequence mastodonsaurid bones are found
sporadically, particularly in the topmost part of the sequence, the Obere Terebratel-
bank (mo3). The finds designated as Mastodonsaurus silesiacus (K
UNISCH
1885) from
the Lower Muschelkalk of Southern Poland are, as S
CHROEDER
(1913) noted, more
reasonably attributed to Parotosuchus (Capitosaurus) sp. (Z
ITTEL
1887–90).
Definite mastodonsaurid fragments from the Oberer Muschelkalk consist of large
labyrinthodont teeth, dermal skull roof fragments, vertebrae, and ribs. In theory, the
enormous size of the tusks is diagnostic for the genus, although a similar capitosaur
genus (Eryosuchus) with comparably large tusks appears in the Ural Forelands
schoch, mastodonsaurus giganteus 7
8stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Fig. 2. Geographical occurrences of the Mastodonsauridae in southern Germany, and
stratigraphical position of finds. Famous localities mapped onto geological setting.
(O
CHEV
1972). However, by means of the above listed features, most of the larger
finds are rather safely assigned to the Mastodonsauridae. The fragmentary nature of
all these finds does not permit a clear assignment to Mastodonsaurus giganteus, the
abundant and only Lettenkeuper mastodonsaurid species, but the very large size and
high degree of ossification speaks in favour of Mastodonsaurus rather than Hepta-
saurus.
The Grenzbonebed usually bears many remains of Mastodonsaurus, which of-
ten stem from animals of the size exclusively gained by the species M. giganteus (i.e.
a skull length of more than 60 cm). R
EIF
(1971) and H
AGDORN
& R
EIF
(1988) stud-
ied the composition and formation of these bonebeds and showed that they may
contain very different faunal components. Remains of Mastodonsaurus thus appear
therein in concert with marine, lacustrine, and terrestrial forms (H
AGDORN
& S
I
-
MON
1985).
Almost throughout the Lettenkeuper sequence (representing the deeper upper
Ladinian stage), Mastodonsaurus giganteus occurs abundantly, and complete skulls
were found in several stratigraphical horizons (fig. 4). H
AGDORN
& R
EIF
(1988)
compiled data on the occurrence of Mastodonsaurus in the Lettenkeuper, adding to
earlier studies of P
LIENINGER
in M
EYER
& P
LIENINGER
(1844) and F
RAAS
(1889).
The Lettenkeuper sediments of Württemberg and Franken and aspects of their pa-
laeontology were studied by Z
ELLER
(1908), W
AGNER
(1913), P
ROSI
(1922), P
ATZELT
(1964), B
RUNNER
(1973, 1977), U
RLICHS
(1982), H
AGDORN
(1980 a, b, 1988), and
W
EBER
(1992 a, b, 1996).
The Grenzbonebed is followed by the Vi t r i o l s chiefer, which consists of dark
grey marls occasionally enriched in alum. It was mined in the 18th century, after
the metal salts had long been used for colouring clothes in the vicinity of the out-
crops (H
AGDORN
& S
IMON
1985). There is a dissensus about the proper strati-
graphical belonging of the mined sequence at Gaildorf (W
EBER
1992a; H
AGDORN
1988), where the first spectacular finds of Mastodonsaurus were made between
1820 and 1860.
In the following section light grey marls and dolomites alternate (Estherien-
Schichten). Both sediments sporadically contain teeth, but Mastodonsaurus partic-
ularly occurs in a bonebed situated within the Estherien-Schichten, which otherwise
contains many shark teeth and remains of rauisuchians (R
EIF
1974; H
AGDORN
& S
I
-
MON
1985). W
EBER
(1992a) argued for the Gaildorf Fossil-Lagerstätte to belong to
this horizon, referring to sections studied by K
URR
(1852) and Q
UENSTEDT
(1880).
H
AGDORN
(1988) instead pointed out the lack of coal (which occurs in Gaildorf) in
the Lower Lettenkeuper, and concluded that the famous mine was rather built in the
Untere Graue Mergel (see below).
The Gaildorf Fossil-Lagerstätte [see F
RAAS
(1889), H
AGDORN
(1988), and W
EBER
(1992 a) for details] is peculiar in the presence of articulated specimens, which usual-
ly are very rare in other Lettenkeuper horizons. Hence the Gaildorf specimens con-
stitute an important source of anatomical information. The preservation of verte-
brates in this horizon is very variable, but usually distortion is strong exceeding that
of localities such as Kupferzell-Bauersbach and Vellberg-Eschenau (see below).
The Hauptsandstein is the major gross-fraction unit in the Lettenkeuper se-
quence. Its thickness varies considerably, as its base is erosional, and in certain re-
gions it directly overlies the Oberer Muschelkalk, although in reworking horizons
indicating the former presence of the Vitriolschiefer, Blaubank, dolomites, and Es-
schoch, mastodonsaurus giganteus 9
therien-Schichten. In many other regions the Hauptsandstein however is represent-
ed by argillaceous shales. The base of larger sandstone bodies frequently contains a
bonebed enriched in labyrinthodont teeth, suggesting the presence of Mastodonsau-
rus.
The top of the Hauptsandstein may be locally overlain by grey to black shales,
which in the Rothenacker Wald (Markgröningen) yielded a near-complete skull of
Mastodonsaurus giganteus in 1867 (SMNS 4774). A field excursion performed by T.
A
IGNER
(Tübingen) and A. E
TZOLD
(Freiburg) recently discovered a disarticulated
partial skeleton of Mastodonsaurus in a grey shale equivalent to the Hauptsandstein
(Baresel quarry, Vaihingen an der Enz), now also housed in Stuttgart (SMNS 80479).
The next horizon is a locally dark, rigid carbonate layer (Alberti-Bank) bearing
scales of actinopterygian fishes, dipnoan teeth, thecodont teeth, and bones of Masto-
donsaurus (especially in the Serrolepis-Bank, see H
AGDORN
& R
EIF
1988).
Further above, the Sandige Pflanzenschiefer, a variably argillaceous shale
enriched in plant fragments, may be locally rich in vertebrate fossils. At Michelbach
an der Bilz, south of Schwäbisch Hall, several partially articulated amphibian skele-
tons, among them one partial skeleton of Mastodonsaurus, a plagiosaurid, and two
trematosaurid specimens were found (H
AGDORN
1980 a; unpublished data).
The Upper Lettenkeuper starts with a calcareous to dolomitic section, the An-
thrakonitbank, whose top often bears a bonebed. The following, much thicker
unit is however richer in large and well-preserved vertebrate remains: the Untere
Graue Mergel near a thickness of 2 m, and are mainly brown to green marls and
clays, interrupted by thin carbonate layers. Since the last century especially finds of
Mastodonsaurus and plagiosaurs have been made, most of them being housed in the
collections at Stuttgart and Tübingen. During the ongoing construction of the Au-
tobahn Heilbronn-Nürnberg the Untere Graue Mergel were cut at several sites in
Hohenlohe. Two of them, one close to the village Bauersbach (Gemeinde Kupfer-
zell), and one near to the Heidehöfe (Wolpertshausen), revealed particularly rich
vertebrate faunas.
A large excavation at the Kupferzell site, carried out by the SMNS and with the
help of amateur collectors (J. G. W
EGELE
, R. M
UNDLOS
, and J. T
ÖPFER
) gave numer-
ous specimens of Mastodonsaurus giganteus, and about 30,000 disarticulated bones,
teeth, and coprolithes (W
ILD
1978 a-c, 1980 a-b, 1981; S
CHOCH
& W
ILD
1999 a; and
section 1.3 herein) (fig. 5). H. H
AGDORN
collected a range of valuable specimens at
the Wolpertshausen locality, now housed in the Muschelkalk Museum Ingelfingen.
An additional site where Untere Graue Mergel are particularly fossiliferous is the
Schumann quarry near Vellberg-Eschenau, where also well-preserved skulls and
partially articulated skeletons of Mastodonsaurus have been found in the last decades
(K
UGLER
& B
ARTHOLOMÄ
1985; R. W
ILD
, pers. comm.). The Untere Graue Mergel
were studied in detail by U
RLICHS
(1982) who compared various sections, especially
in the area of Kupferzell, including those at the excavation site.
The Hohenecker Kalk, confined to the Ludwigsburg region and famous for
the occurrence of Neusticosaurus pusillus, also yielded the two large specimens of
Mastodonsaurus acuminatus F
RAAS
, 1889, which are shown to be junior synonyms
of M. giganteus here. The finds in this horizon are usually strongly flattened and dis-
torted. Equivalent horizons in the Lettenkeuper of eastern Thüringen (Molsdorf
near Arnstadt) have also yielded a suite of cranial and postcranial remains of Masto-
donsaurus giganteus (S
CHMIDT
1931).
10 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
A locality close to this site, between the villages Molsdorf and Thörey, which has
been recently opened by road works, gave numerous bones of Mastodonsaurus, pla-
giosaurs, and nothosaurs in several horizons. One of them appears to be an equiva-
lent of the Lingula-Dolomit, as already presumed by S
CHMIDT
(1931). In Bedheim
(Hildburghausen, southern Thüringen), R
ÜHLE VON
L
ILIENSTERN
(1935) reported a
find of Mastodonsaurus acuminatus from a sandstone in the uppermost Lettenkeup-
er sequence, slightly below the Grenzdolomit. W
ERNEBURG
has recently (1994) re-
viewed the faunistic and stratigraphical data on this site.
schoch, mastodonsaurus giganteus 11
Fig. 3. Stratigraphical range of the Mastodonsauridae in the German Triassic, based on a re-
cent survey of available material and information. Modified from B
RUNNER
(1973).
The subsequent entire Gipskeuper sequence (lower Mittelkeuper, km1), is poor
in mastodonsaurid finds except for labyrinthodont teeth, such as those found in
Gaildorf (H
AGDORN
& S
IMON
1985). Recently, C. K
LUG
(Tübingen) collected ver-
tebral intercentra of a mastodonsaurid from the Quarzitbank, at the top of the
Dunkle Mergel (Ladinian/Carnian boundary).
The Schilfsandstein section (higher Mittelkeuper, km2) again is particularly
rich in temnospondyl amphibians, especially the stereospondyls Cyclotosaurus and
Metoposaurus (M
EYER
& P
LIENINGER
1844; Q
UENSTEDT
1850; F
RAAS
1913). Besides
the last definite trematosaurid find worldwide (Hyperokynodon keuperinus, see
H
ELLRUNG
1987 and S
CHOCH
, M
ILNER
& H
ELLRUNG
in preparation), the Schilf-
sandstein has also revealed a snout fragment of a mastodonsaurid (F
RAAS
1913). Al-
though a clear assignment of this find is at this stage not possible, a stratigraphical
range of the genus Mastodonsaurus well into the Mittelkeuper cannot be ruled out.
1.3. Lithology and fauna of the Kupferzell Fossil-Lagerstätte
U
RLICHS
(1982) described the local lithology and commented on aspects of inver-
tebrate palaeontology and palaeobotany at Kupferzell. According to his findings, li-
thology and fossil content vary considerably within the excavated area. The richest
samples were found in the southern part of the area, and there also the vertebrate-
bearing strata reached their maximal thickness (figs. 4, 5).
The Untere Graue Mergel form a horizon of variable thickness, which is largely
grey to brown in colour, with a rather limited content of vertebrate fossils in gener-
al. Only in its topmost part, immediately below the Anoplophora-Dolomite, an en-
richment in vertebrate bones, sometimes even articulated skeletons, is recorded. A
similar situation is known in the Schumann quarry near Vellberg-Eschenau, differ-
ing in that preservation is generally better in Kupferzell, and the result of compac-
tion less pronounced. In both localities, three different fossil-bearing horizons have
been recorded (from bottom to top): (1) greenish-grey clay, (2) brown clay or marl,
whose base sometimes attains the appearance of a bonebed, and (3) yellow carbo-
nates (fig. 5).
The greenish layer in Kupferzell contains a large number of well-preserved yet of-
ten isolated bones. The majority of finds was made in this horizon. Although disar-
ticulated, the bones are generally not worn-off or damaged. In addition, numerous
complete skulls of Mastodonsaurus have been found in this layer, including some
disarticulated specimens such as the giant specimen (SMNS 81310) or the medium-
sized, partially articulated specimen (SMNS 80913). In Vellberg-Eschenau the
greenish layer is thinner and less rich in fossils; in addition most of the bones are iso-
lated and some suggest wearing from a longer transport, which has only rarely been
observed among the Kupferzell finds.
The brown clay is characterized by a lower concentration of finds, which are
however more clearly articulated or only partially disarticulated as compared with
those in the greenish layer. This is most obvious in the case of completely articulat-
ed plagiosaurid skeletons. In Vellberg-Eschenau the single bones are frequently frag-
mented, though still being partially articulated.
The carbonates, which form the basal layer of the Anoplophora-Dolomite, only
rarely bear fossils in Kupferzell, such as a partial skeleton of Nothosaurus mirabi-
lis. In the Schumann quarry instead, this horizon may locally contain articulated
12 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 13
Fig. 4. Lithological section through the Lettenkeuper (Unterkeuper, Erfurt Formation) in
the Hohenlohe region, northern Baden-Württemberg (modified after B
RUNNER
1973). High concentration of mastodonsaurid bones in horizons indicated by bold
letters.
skeletons of Mastodonsaurus, and also one rauisuchian was found (R. W
ILD
pers.
comm.).
Ongoing studies reveal that the following vertebrates definitely occur at Kupfer-
zell; most of them have meanwhile been identified from other Lettenkeuper local-
ities as well (fig. 6). Most amphibians belong to the Stereospondyli; an overview on
the current systematic concept of this group is given in fig. 7.
1. Pisces
Chondrichthyes: Hybodus sp., Acrodus sp., etc. (R. B
ÖTTCHER
and D. S
EEGIS
,
pers. comm.);
Actinopterygii: Serrolepis sp., Gyrolepis sp. (W
ILD
1980a);
Actinistia: gen. et sp. indet. (R. B
ÖTTCHER
and D. S
EEGIS
, pers. comm.);
Dipnoi: Ptychoceratodus serratus (S
CHULTZE
1981).
2. Amphibia
Plagiosauridae: Plagiosuchus pustuliferus (W
ILD
1980a; H
ELLRUNG
, in prep.)
Gerrothorax n. sp. (H
ELLRUNG
, in prep.);
Capitosauridae: Kupferzellia wildi (W
ILD
1980a; S
CHOCH
1997a);
Mastodonsauridae: Mastodonsaurus giganteus (W
ILD
1980a; S
CHOCH
1997a);
Trematosauridae: Bukobaja cf. enigmatica (SMNS 56252, 57003,
80968, 84122–84126) (see O
CHEV
1972);
Almasauridae: n. g. n. sp. (SMNS 55385);
Chroniosuchia: n. g. n. sp. (SMNS 81698).
3. Reptilia
Prolacertilia: Tanystropheus cf. conspicuus (W
ILD
1980a);
Lepidosauria: gen. et sp. indet. (W
ILD
, pers. comm.);
Sauropterygia: Nothosaurus n. sp.(W
ILD
1980a; pers. comm.);
Neusticosaurus cf. pusillus (W
ILD
1980a);
Rauisuchia: n. g. n. sp. (W
ILD
1980a-c; G
OWER
, in press).
4. Synapsida
Cynodontia: Gomphodontidae indet. (W
ILD
1980; S
UES
& H
OPSON
,in
prep.).
1.4. Material examined
All studied material was found in the Lettenkeuper of southern Germany. The
examined specimens were for the largest part excavated during spring 1977 at Kup-
ferzell, and they were prepared in the time since by employees of the SMNS, par-
ticularly by Dr. R. W
ILD
and Mrs. B. W
ILD
, J. G
INDER
, T
H
. R
ATHGEBER
, N.
A
DORF
, as well as J. G. W
EGELE
(Waldenburg). The specimens were almost
throughout catalogued by R. W
ILD
and the author, with the assistance of D. M
ETZ
-
GER
, M. R
ÜCKLIN
, F. G
ROSSMANN
, and B. G
REENWOOD
, then practical students at
the SMNS.
A small part of the material was collected and catalogued in the last century and
early part of this century; these specimens are almost throughout from the Gaildorf
mine, the Rothenacker Wald near Markgröningen, or from Hoheneck near Lud-
wigsburg. Of these, several finds from Gaildorf are lost, while certain others suffered
considerable damage and had to be restored in the erly 1970s (see below).
1.4.1. Mastodonsaurus giganteus
1. SMNS 4698. Complete skull with mandibles (60cm). Locality: Locus typicus. Hori-
zon: Stratum typicum. References: M
EYER
& P
LIENINGER
(1844: 11, pl. 6fig. 1, pl. 7 fig. 1),
F
RAAS
(1889: Schädel I), H
UENE
(1922).
14 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 15
2. SMNS 54679. Complete skull with mandibles (60cm), damaged and restored in many
regions. Locality: Locus typicus. Horizon: Stratum typicum. References: M
EYER
& P
LIE
-
NINGER
(1844: 11), F
RAAS
(1889: Schädel II).
3. SMNS 4707. Large, complete skull with mandibles (74cm) and anterior part of verte-
bral column (9 intercentra). Condition rather poor, most sutures are invisible and dermal bone
surface worn off. Locality: Locus typicus. Horizon: Stratum typicum. References: M
EYER
&
P
LIENINGER
(1844: first specimen, p. 11), F
RAAS
(1889: Schädel III).
4. SMNS 4938. Tip of snout (estimated length 65cm), poor condition. Locality: Locus
typicus. Horizon: Stratum typicum.
5. SMNS 4774. A near-complete skull (75 cm), partially restored, with particularly coarse
sculpturing. Locality: Rothenacker Wald near Markgröningen, Baden-Württemberg. Hori-
zon: Hauptsandstein. References: F
RAAS
(1889: Schädel IV)
6. SMNS 740. Medium-sized palate (52cm) exposed in ventral view. Locality: Hoheneck
near Ludwigsburg, Baden-Württemberg. Horizon: Hohenecker Kalk. References: F
RAAS
(1889: 105, pl. 7: M. acuminatus).
7. SMNS 4194. Large skull roof (66cm) in ventral view. Locality: Hoheneck near Lud-
wigsburg, Baden-Württemberg. Horizon: Hohenecker Kalk. References: F
RAAS
(1889: 105,
pl. 8, fig. 1: M. acuminatus).
8. SMNS 54675. Complete skull (60,5cm), almost undistorted, with perfectly preserved
braincase. Locality: Kupferzell. Horizon: Untere Graue Mergel, green layer. References:
W
ILD
(1978, 1981: figs. 4, 5).
Fig. 5. Lithology of the fossiliferous horizons at the Kupferzell excavation site. Based on a
recent compilation of unpublished stratigraphical data, some of them provided by
courtesy of R. W
ILD
and M. U
RLICHS
. See W
ILD
(1980a), U
RLICHS
(1982), and
S
CHOCH
& W
ILD
(1999a) for further information.
16 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Fig. 6. Synopsis of the temnospondyl amphibian fauna in the Lettenkeuper. Based largely on new finds. Occurrence and relative fre-
quency in different Lettenkeuper horizons are mapped; broad bars indicate high frequency of diagnostic finds. The differ-
ences in frequency among plagiosaurids is especially notable. Further details are provided by S
CHOCH
& W
ILD
(1999a).
9. SMNS 54677. Complete skull (51cm) with mandible in articulation (figs. 8, 17). Local-
ity: Kupferzell. Horizon: Untere Graue Mergel, brown layer. References: W
ILD
(1980).
10. SMNS 54678. Complete skull (54,5 cm) (figs. 12, 13). Locality: Kupferzell. Horizon:
Untere Graue Mergel, green layer. References: Z
IEGLER
(1986: fig. 150).
11. SMNS 80249. Posterior rim of skull (? 70cm) with well-preserved braincase . (Local-
ity: Kupferzell. Horizon: Untere Graue Mergel, green layer.
12. SMNS 80704. Complete skull (55cm) with mandible. Locality: Kupferzell. Horizon:
Untere Graue Mergel, green layer.
13. SMNS 80878. Near-complete skull (about 65cm) with parts of mandible. Locality:
Kupferzell. Horizon: Untere Graue Mergel, brown layer.
14. SMNS 80887. Snout fragment (? 60cm). Locality: Kupferzell. Horizon: Untere
Graue Mergel, green layer.
15. SMNS 80889. Complete skull (59cm) with mandible, partly dislocated right side. Lo-
cality: Kupferzell. Horizon: Untere Graue Mergel, green layer.
16. SMNS 80890. Postorbital part of skull (about 40 cm skull length). Locality: Kupfer-
zell. Horizon: Untere Graue Mergel, green layer.
17. SMNS 80905. Partial, disarticulated skull (about 45 cm skull length). Locality: Kup-
ferzell. Horizon: Untere Graue Mergel, green layer.
18. SMNS 80913. Fragmentary skull (75cm total length) with 28 presacral vertebrae. Lo-
cality: Kupferzell. Horizon: Untere Graue Mergel, green layer.
19. SMNS 81310. Catalogued and frequently referred to as “Riesenexemplar von Kup-
ferzell”. Complete mandible (145 cm) with few remnants of the palate and a total of 28 presa-
cral and 6 caudal vertebrae, 6–8 neural arches, 20 pleurocentra, and about 40, largely complete
ribs from all regions in the axial skeleton. All elements were found in close proximity, and in
association with a much smaller specimen of Mastodonsaurus giganteus, as well as several iso-
lated, giant teeth of Mastodonsaurus. Locality: Kupferzell. Horizon: Untere Graue Mergel,
green layer.
20. SMNS 81368. Posterior part of palate, with attachment sites for braincase elements.
Locality: Kupferzell. Horizon: Untere Graue Mergel, green layer.
Isolated cranial material consists of the following, rich body of specimens: 7 premaxillae, 3
maxillae, 4 jugals, 3 quadratojugals, 4 squamosals, 10 tabulars, 7 postparietals, 6 supratempo-
rals, 5 postorbitals, 5 postfrontals, 5 parietals, 3frontals, 5 nasals, 3 lacrimals, 3 prefrontals, 20
quadrata, 31 exoccipitals, 14 pterygoids, 10 parasphenoids (often fragmentary), 12 stapes, 15
epipterygoids, 2 palatines, and 2 ectopterygoids. There are several entirely unprepared skulls,
and a large number of unprepared disarticulated cranial elements in the Stuttgart collection.
Further, 9 complete and prepared mandible halves are housed in the SMNS (54675, 56634,
80871, 80872, 80874, 80879, 80880, 80881, 80882). About 40further fragments from all regions
of the lower jaw have been investigated for this study.
Postcranial material. 1. Gaildorf (Locus typicus, stratum typicum): SMNS 4698 [20
vertebrae, mentioned by P
LIENINGER
in M
EYER
& P
LIENINGER
(1844) and F
RAAS
(1889)],
SMNS 56630 [the one figured in part by M
EYER
& P
LIENINGER
1844, and referred to by
F
RAAS
(1889) and H
UENE
(1922)], SMNS 4706 [left clavicle with ulna and part of manus,
figured by F
RAAS
(1889), right clavicle with badly preserved phalanges and carpal elements,
fragmentary interclavicle, both scapulocoracoids, 1 radius, and about 10 presacral vertebrae].
In addition the Gaildorf material of the SMNS encompasses 10 ribs, 3 ilia, 1fibula, 2 interclav-
icles, and one large clavicle. The GPIT possesses additional specimens: (1) three intercentra,
neural arches, and rib fragments in articulation, and (2) various isolated presacral intercentra.
2. 1977 Kupferzell excavation (Untere Graue Mergel, almost throughout green layer, infor-
mation by courtesy of R. W
ILD
and M. U
RLICHS
): About 120 prepared and catalogued, isolat-
ed presacral intercentra are housed in the SMNS. In addition there are at least 25 caudal inter-
centra prepared, 20 pleurocentra, 30 mostly very fragmentary neural arches, and 114 isolated
ribs from all regions of the body. The appendicular skeleton is also well-represented: 13 cleith-
ra, 25 claviculae, 29 interclaviculae (the numerous fragments not counted), 12 scapulocora-
coids, 12 humeri, 5 radii, 3 ulnae, 10 phalanges, 19 ilia, 10 ischia, 8femora, 1 tibia, and 1fibula.
3. 1989 excavation at Vellberg-Eschenau (Untere Graue Mergel): 20 giant intercentra of a
specimen of which the skull is in the private collection of Mr. B
ERNER
(Heilbronn).
schoch, mastodonsaurus giganteus 17
1.4.2. Temnospondyl material studied for comparative purposes
A large suite of temnospondyl taxa housed in different institutions was examined,
the number of studied specimens given in brackets.
AMNH: Edops craigi (cast of holotype), Trimerorhachis insignis (15), Isodectes sp. (1), Iso-
dectes (Saurerpeton) obtusus (3), Eryops megacephalus (12), Stanocephalosaurus birdi (1).
BPI: Rhinesuchus sp.(5), Rhineceps nyasaensis (1), Uranocentrodon senekalensis (2), Broo-
mistega sp.(1), Lydekkerina huxleyi (2), Eolydekkerina magna (1), Kestrosaurus dreyeri (2),
Parotosuchus africanus (1).
GPIT: Dvinosaurus sp., cast (1), Trimerorhachis sp. (5), Eryops sp. (4), Sclerocephalus sp.
(5), Cheliderpeton latirostre (2), Archegosaurus decheni (2), Parotosuchus nasutus, cast (1),
Heptasaurus cappelensis (1 original, 1 cast),
IGWH: Trematosaurus brauni (38), Parotosuchus nasutus (23).
PIN: Dvinosaurus primus (2), Thoosuchus jakovlevi (6), Prothoosuchus samariensis (2),
Angusaurus dentatus (1), Benthosuchus sushkini (5), B. uralensis (1), Wetlugasaurus angusti-
frons (2), W. samaransis (1), Parotosuchus orientalis (1), P. orenburgensis (1), Eryosuchus anti-
quus (1), E. tverdochlebovi (1), E. garjainovi (8), giant Eryosuchus sp. from the Bukobay For-
mation of Kazakhstan (1), Mastodonsaurus torvus (1), Cyclotosaurus sp. (1), “Cyclotosaurus”
sp. from Arizona, cast (1), Bukobaja enigmatica (1).
SAM: Lydekkerina huxleyi (3), Rhinesuchus sp. (1), Phrynosuchus whaitsi (1),
Cyclotosaurus albertyni (1).
SMF: Parotosuchus nasutus (2), P. helgolandiae (cast), Lyrocephaliscus euri (2), Benthosu-
chus sushkini (1).
SMNK: Sclerocephalus haeuseri (1), Heptasaurus cappelensis (remains of about 12 speci-
mens), Eocyclotosaurus sp. (1).
SMNS: Sclerocephalus haeuseri (12), Cheliderpeton latirostre (2), Archegosaurus decheni
(2), Lydekkerina sp. (1), Benthosuchus sp. (1), Thoosuchus jakovlevi (1), Trematosaurus brau-
ni (4), Hyperokynodon keuperinus (2), Parotosuchus nasutus (3), Heptasaurus cappelensis (5),
Eocyclotosaurus woschmidti (1), E. lehmani, cast (1), Eocyclotosaurus n. sp. from Arizona, cast
(1), Stenotosaurus semiclausus (1), Meyerosuchus fuerstenberganus, cast (1), Odenwaldia hei-
delbergensis, cast (1), Kupferzellia wildi (18), Cyclotosaurus robustus (3), C. posthumus (1), C.
mordax (6).
UCMP: Trimerorhachis insignis (13), Zatrachys serratus (11), Eryops sp. (2), Wellesaurus
peabodyi (12), Eocyclotosaurus n. sp. (6).
1.5. Institutional abbreviations
AMNH: American Museum of Natural History, New York
BPI: Bernard Price Institute of Palaeontology, Johannesburg
GPIT: Institut und Museum für Geologie und Paläontologie, Tübingen
IGWH: Institut für Geologische Wissenschaften und Geiseltalmuseum, Halle
MMI: Muschelkalk Museum, Ingelfingen
PIN: Paleontological Institut of the Russian Academy of Sciences, Moscow
SAM: South African Museum, Cape Town
SMF: Naturkundemuseum Senckenberg, Frankfurt
SMNK: Staatliches Museum für Naturkunde in Karlsruhe, Karlsruhe
SMNS : Staatliches Museum für Naturkunde in Stuttgart, Stuttgart
UCMP: University of California Museum of Paleontology, Berkeley.
18 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
2. Taxonomy of Mastodonsaurus giganteus (J
AEGER
, 1828)
2.1. Discovery and first assignment of Mastodonsaurus
In the early 1820s, two particular finds supposed to have come from the alum
mine at Gaildorf attracted the attention of Professor G
EORG
F
RIEDRICH
J
AEGER
, lat-
er curator of the Königlich-Württembergisches Naturaliencabinet, the forerunner of
the Staatliches Museum für Naturkunde in Stuttgart. According to his own words,
the two specimens had been found almost side by side (“os occipitis . . . communis
cum dente simul allato situs”). In 1828 he specified, that the tooth was brought to
him by Mr. Z
OBEL
, the occiput by Prof. S
CHÜBLER
(who then taught Geology at the
Eberhard-Karls University of Tübingen), and additional material, which now also is
assigned to Mastodonsaurus, found by Mr. H
EHL
and Mr. D
IETRICH
respectively, the
latter was the owner of the alum mine at Gaildorf.
schoch, mastodonsaurus giganteus 19
Fig. 7. Systematic position of the family Mastodonsauridae within the suborder Stereo-
spondyli (Tetrapoda: Temnospondyli). Trematosaurids were dominant freshwater
to marine dwellers in the Lower Triassic, while capitosauroids managed to become
the most frequent and widespread stereospondyls by the Middle Triassic. The Cy-
clotosauridae and Metoposauridae are the last stereospondyls to be found in Eu-
rope, both being known by the Schilfsandstein (Middle Carnian).
It is somewhat obscure whether all material was found in the same mine and at the
same time, as J
AEGER
’s note in 1824 suggests, or if the names he cites mean that the
specimens where found at different times by different people. K
URR
(1850) and re-
cently W
EBER
(1992 a) noted that the Gaildorf mine was the only site from which de-
finitive finds of Mastodonsaurus had become known in these early days; this is the
most convincing evidence in favour of J
AEGER
’s (1824) original statement.
Concerning the taxonomic assignment of the finds, J
AEGER
(1824) further wrote:
“Maxime distinguitur condylis ad modum prominentibus, quales nulli, quantum
equidem scio, reptilium generi, excepto forte Proteo mexicano competunt”. Obvi-
ously he had made comparisons with various extant reptiles and thereby had hooked
at one particular feature, the double occipital condyle of Mastodonsaurus. By this
character it differed from all reptiles known to him, but brought the ‘Mexican
Proteus’ to his mind, by which he probably referred to the ambystomatid salaman-
der Ambystoma mexicanum. He therewith pre-dated the findings of O
WEN
(1841,
1842) and Q
UENSTEDT
(1850) on the amphibian nature of Mastodonsaurus, only that
he used a different argumentation and based his comparison on a different extant
taxon. (In fact, by comparing Mastodonsaurus with an aquatic salamander he came
much closer to the current concept than any of his successors, although we cannot
be sure about his reasons.) This explains his choice of Salamandroides as generic
name for the occiput, which later became a junior synonym of Mastodonsaurus.
J
AEGER
(1824) concludes: “Pro certo itaque habere licet, . . . vero Monitoribus
forte affinis strato profundiori peculiaria esse, quod . . ... etiam reliquias foveret, si os
occipitis, quod utique probabile est, non ejusdem [sic] animalis esset”. [J
AEGER
here-
in stresses the resemblance of the giant Gaildorf tooth with those of large Recent va-
ranids (e.g. the monitor). Finally, he argues, the occiput might turn out to be from a
different animal than the tooth, an alternative “which is particularly probable”.]
2.2. Identification of the Kupferzell specimens
The only two capitosauroid species definitely present at the Kupferzell excavation
site are the small-growing capitosaurid Kupferzellia and the large to giant mastodon-
saurid Mastodonsaurus. The anatomy of these two forms differs conspicuously in
the skull and mandible so even minor fragments may be readily distinguished (for
details see S
CHOCH
1997a). A well-defined yet only fragmentarily known form has
clear trematosaurid affinities, and is also represented by numerous characteristic
intercentra (see section 1.3). Finally the find of a small almasaurid-like temnospon-
dyl in the Untere Graue Mergel of the Schumann quarry in Vellberg-Eschenau (M
O
-
RALES
1988) demonstrates that additional stereospondyls might still be hidden in the
large unprepared sample from Kupferzell. Both the trematosaurid and almasaurid
cannot be confused with either Mastodonsaurus or Kupferzellia, because their crani-
al morphology is too distinct. This involves major differences in dermal sculpturing,
proportions of skull roof bones in nearly all regions, and the structure of the palate;
hence even small skull fragments are readily distinguished by that way.
The mastodonsaurid is identified by the enormous size of most finds, and gener-
ally the large extent of ossification. The dermal sculpturing is coarse in the sense that
the ridges are broad and well-defined, applying even and in particular to the small-
est specimens. Furthermore, even small finds are recognised by means of their pecu-
liar cranial morphology: the skull forms a narrow, isoceles triangle with large orbits
20 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
at midlevel, the symphyseal tusks penetrate the tip of the snout, the parasphenoid
and pterygoid are massive ossifications meeting in a long suture much different from
that of Kupferzellia, and the large size and shape of the interpterygoid vacuities.
There are also numerous differences in the mandible (long postglenoid area, large
and anteriorly extended Meckelian window, symphyseal region: postsymphyseal
teeth) between Mastodonsaurus and Kupferzellia (S
CHOCH
1997a).
The following valid species attributable to the Mastodonsauridae have been erect-
ed and described :
1. Mastodonsaurus giganteus (J
AEGER
, 1828) (M
EYER
& P
LIENINGER
1844; F
RAAS
1889; H
UENE
1922): Lettenkeuper of northern Württemberg (Land Baden-
Württemberg), Mainfranken (Freistaat Bayern), and north of the Thüringer Wald
(Freistaat Thüringen). A junior synonym is M. acuminatus F
RAAS
1889from the
Lettenkeuper of Hoheneck in Baden-Württemberg and Molsdorf in Thüringen
(S
CHMIDT
1931; R
ÜHLE VON
L
ILIENSTERN
1935; W
ERNEBURG
1994). See fig. 3 for
stratigraphical range.
2. Heptasaurus cappelensis (W
EPFER
, 1923) (see W
EPFER
1922 a, b; P
FANNENSTIEL
1932; S
ÄVE
-S
ÖDERBERGH
1935): Oberer Buntsandstein (Lower Anisian) of Vosges,
Schwarzwald, and Mainfranken. Synonyms are possibly Mastodonsaurus vaslenen-
sis M
EYER
, 1847–55 and M. ingens T
RUSHEIM
, 1937. See fig. 3 for stratigraphical
range.
3. Mastodonsaurus torvus K
ONZHUKOVA
, 1955 from the Orenburgskaya Oblast
and Bashkirstan (Bashkortostan) in the Russian Federation and northern Kazakh-
stan. This form is in some aspects similar to Heptasaurus cappelensis (e.g., width of
jugals), but has orbital windows of similar shape as in M. giganteus and attains the
size of large specimens of this species (M.A. S
HISHKIN
, pers. comm.; pers.exam. of
various specimens in the PIN). The available finds are throughout very fragmentary,
so that a reasonable comparison with the two German genera is impossible thus far;
a provisional assignment to Mastodonsaurus, paying tribute to the closer resem-
blance of the East European mastodonsaurid to this giant form, may be sufficient.
The Kupferzell mastodonsaurid material is throughout similar to Mastodonsaurus
giganteus from Gaildorf and Markgröningen. The range of morphological variation
in the Kupferzell specimens is fairly broad and continuous, strongly suggesting the
presence of only one species. Re-examination of the type material of M. acuminatus
revealed that the differences to the Gaildorf material mentioned by F
RAAS
are the re-
sult of extreme compaction in the latter. The variability in the Kupferzell skulls
ranges from narrow-cheeked forms similar to M. acuminatus to very broad-cheeked
specimens. The material from Molsdorf, attributed to M. acuminatus by S
CHMIDT
(1931) for stratigraphical rea-sons, is likewise throughout assigned here to M. gigan-
teus.
Heptasaurus cappelensis, the only other valid German mastodonsaurid species to
date, differs from all mentioned specimens by smaller orbits and a markedly broad-
er snout tip. Correlated with the smaller size of the orbit is the greater width of the
jugal and the frontal. An unequivocal assignment of all mastodonsaurid material
from Kupferzell to Mastodonsaurus giganteus (J
AEGER
, 1828) is thus possible.
schoch, mastodonsaurus giganteus 21
2.3. Taxonomic status of Mastodonsaurus giganteus (J
AEGER
, 1828)
Amphibia L
INNAEUS
, 1758
Temnospondyli Z
ITTEL
, 1890 [emend. M
ILNER
, 1993]
Stereospondyli M
ILNER
, 1994 [non W
ATSON
, 1919]
Capitosauroidea S
ÄVE
-S
ÖDERBERGH
, 1935 [lapsus: -“oidae”]
Mastodonsauridae W
ATSON
, 1919 [non L
YDEKKER
, 1885]
Mastodonsaurus giganteus (J
AEGER
, 1828)
p. 38, tab. 5, figs. 1–2
v 1824 animal ignotus J
AEGER
, p. 11–12
v 1828 Mastodonsaurus J
AEGER
, p. 35; nomen imperfectum
v*1828 Salamandroides giganteus J
AEGER
, p. 38
1832 Mastodonsaurus jaegeri M
EYER
, p. 208
v 1833 Mastodonotsaurus [sic] J
AEGER
, p. 86; printing mistake
v 1833 Salamandroides J
AEGER
, p. 86
v 1834 Salamandroides jaegeri A
LBERTI
, p. 120; first revisor
v 1838 Mastodonsaurus salamandroides J
AEGER
, p. 547
1841 Labyrinthodon jaegeri O
WEN
, p. 227
1842 Labyrinthodon salamandroides O
WEN
, p. 512
1842 Mastodonsaurus salamandroides R
OEMER
, p. 96
v 1844 Mastodonsaurus jaegeri M
EYER
, p.11, plts. 6–7
v 1844 Mastodonsaurus jaegeri P
LIENINGER
, p. 57, plts. 3–7
1845 Labyrinthodon jaegeri O
WEN
, p.195
? 1847–55 Xestorrhytias perrini M
EYER
, p. 81, pl. 62, fig. 5 (partim !)
v 1847–55 Mastodonsaurus jaegeri M
EYER
, p. 89
v 1850 Mastodonsaurus giganteus Q
UENSTEDT
, p. 2
v 1864 Mastodonsaurus jaegeri A
LBERTI
, p. 255
1874a Mastodonsaurus giganteus M
IALL
, p. 151
1874b Mastodonsaurus giganteus M
IALL
, p. 433
v 1889 Mastodonsaurus giganteus F
RAAS
, p. 32, pls. 1–5
v 1889 Mastodonsaurus acuminatus F
RAAS
, p. 104, pls. 7, 8
1890 Mastodonsaurus jaegeri L
YDEKKER
, p. 142
v 1919 Mastodonsaurus giganteus W
ATSON
, p. 36, fig. 22
v 1922 Mastodonsaurus giganteus H
UENE
, p. 400, figs. 1–12
v 1928 Mastodonsaurus giganteus S
CHMIDT
, p. 371, figs. 1047–1049
v 1928 Mastodonsaurus acuminatus S
CHMIDT
, p. 373, fig. 1050 a
1931 Mastodonsaurus acuminatus S
CHMIDT
, p. 237, figs. 1–5, pls. 1–3
1932 Mastodonsaurus giganteus P
FANNENSTIEL
, p. 1
1935 Mastodonsaurus acuminatus R
ÜHLE VON
L
ILIENSTERN
, p. 177
1935 Mastodonsaurus giganteus S
ÄVE
S
ÖDERBERGH
, p. 81
1942 Mastodonsaurus giganteus N
ILSSON
, p. 95
1944 Mastodonsaurus giganteus N
ILSSON
, p. 5, fig. 2
1947 Mastodonsaurus giganteus R
OMER
, p. 230, figs. 12, 13, 38, 39
1955 Mastodonsaurus giganteus P
IVETEAU
& D
ECHASEAUX
, p. 151
1955 Mastodonsaurus giganteus K
ONZHUKOVA
, p. 62
1956 Mastodonsaurus giganteus H
UENE
, p. 94, figs. 130, 131
1958a Mastodonsaurus giganteus O
CHEV
, p. 100
1958b Mastodonsaurus giganteus O
CHEV
, p. 487
1964 Mastodonsaurus giganteus S
HISHKIN
, p. 95
v 1965 Mastodonsaurus jaegeri W
ELLES
& C
OSGRIFF
, p. 12
1966 Mastodonsaurus giganteus O
CHEV
, p.159
1972 Mastodonsaurus jaegeri O
CHEV
, p.176
v 1974 Mastodonsaurus jaegeri P
ATON
, p. 281, fig. 18
v 1980 Mastodonsaurus sp. W
ILD
, p. 16, fig. 3
v 1981 Mastodonsaurus sp. W
ILD
, p. 49, fig. 4, 5
22 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
1994 Mastodonsaurus acuminatus W
ERNEBURG
, p. 128, fig. 8
v 1997 Mastodonsaurus jaegeri S
CHOCH
, p. 245
v 1999a Mastodonsaurus giganteus S
CHOCH
& W
ILD
, p. 2, figs. 3–4, 6
v 1999b Mastodonsaurus giganteus S
CHOCH
& W
ILD
, p. 3
Holotype: GPIT 1824, an occiput of a large specimen.
Remarks: 1. The nomenclatural situation of this species, its valid name, and the state of all
objective synonyms are to be reviewed and discussed elsewhere. The binomen Mastodonsau-
rus giganteus (J
AEGER
, 1828) is used throughout the present study.
2. GPIT 1824 is clearly diagnostic of Mastodonsaurus giganteus (cf. W
ELLES
& C
OSGRIFF
1965!). I came to this conclusion by personal examination of nearly all known large stereo-
spondyl species (see list of material investigated). GPIT 1824 comprises the posteriormost
part of the parasphenoid and large parts of the exoccipitals including the occipital condyles.
The skull length of this specimen is estimated to approximately 75 cm. The large condylar fa-
cets, their shape, and the posterior region of the parasphenoid are particularly diagnostic of
Mastodonsaurus giganteus. The presence of a tripartite fossa parasphenoidalis (S
CHOCH
1997a) is unique to this species. In addition, the mode of contact between the pterygoid and
exocciptal is characteristic of the Lettenkeuper mastodonsaurid. By these features, the occiput
differs from all studied specimens of Heptasaurus, Eryosuchus, and Parotosuchus – i.e., those
forms, which are structurally closest to Mastodonsaurus. SMNS 55911, the giant tooth, is
probably from the same species as the occiput, although clearly from a much larger specimen.
This is evident from complete finds (e.g. SMNS 80878, 80913) in which specimens matching
the size of the occiput have teeth reaching only half the length of that in SMNS 55911.
J
AEGER
’s giant tooth is certainly not diagnostic, as large labyrinthodont teeth are common to
all capitosauroids; in addition, the Kazakhian form Eryosuchus garjainovi, which is known to
reach a skull length of one metre, may bear even larger teeth (pers. exam.).
The aforementioned arguments are based on careful re-examination of the original materi-
al and invalidate the remarks of W
ELLES
& C
OSGRIFF
(1965) who considered the occiput un-
diagnostic. Unfortunately they did neither examine this specimen, nor study mastodonsaurid
morphology on the basis of any of then available Gaildorf specimens housed in Stuttgart,
Tübingen, and Yale.
Locus typicus: Alum mine at Gaildorf in Hohenlohe, northern Baden-Württemberg,
southwestern Germany. K
URR
(1852), Q
UENSTEDT
(1880), H
AGDORN
(1988), and W
EBER
(1992a) have commented on the geological setting of this site. This mine was exploited
between 1763 and 1895 (W
EBER
1996). Its owner Mr. D
IETRICH
, a trader at Gaildorf, repeat-
edly sent specimens (SMNS 4698, 4707, 4938, and 54679) to the collections in Stuttgart and
Tübingen, following J
AEGER
(1828) and M
EYER
& P
LIENINGER
(1844).
Stratum typicum: The “Gaildorfer Alaunschiefer”, a black, pyrite-bearing horizon of
some 25 cm magnitude (K
URR
1852). Several authors have commented and discussed on this
particular site and stratum (op. cit.), but no agreement has been achieved on the exact strati-
graphic position of this bed. A recent review is given by W
EBER
(1996), who suggests a be-
longing to the Estherien-Schichten 3 (higher Lower Lettenkeuper). Alternative views are held
by R. W
ILD
(pers. comm.: Vitriolschiefer) and H. H
AGDORN
(1988: Untere Graue Mergel);
see fig. 4.
Geographical occurrence: In many localities throughout Baden-Württemberg,
Bayern (Rothenburg o. d. T., see M
UENSTER
1834), and in Thüringen (S
CHMIDT
1931; R
ÜHLE
VON
L
ILIENSTERN
1935); see fig. 2.
Stratigraphical range: Fairly complete, diagnostic skull fragments are known from the
Grenzbonebed (from quarries in the Crailsheim region) through the Hohenecker Kalk (Lud-
wigsburg, Molsdorf), which covers nearly the whole Lettenkeuper sequence (figs. 3, 4).
Isolated, large postcranial and lower jaw bones are occasionally found in the Obere Te-
rebratelbank, Uppermost Muschelkalk (e.g. in Crailsheim). These specimens are conspicu-
ously larger than those of Heptasaurus from the Oberer Buntsandstein (W
EPFER
1922a,
1923a), and are therefore attributable to Mastodonsaurus. However, the find of Mastodonsau-
rus ingens T
RUSHEIM
, 1937, which is by its stratigraphical position usually suggestive of Hep-
tasaurus, demonstrates that giant mastodonsaurids were present in the Middle European Ba-
sin already by Anisian time.
schoch, mastodonsaurus giganteus 23
24 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Fig. 8. Diagnostic features of the Mastodonsauridae (normal letters) and the genus Masto-
donsaurus (bold letters) mapped onto a drawing of the skull roof and palate of
Mastodonsaurus giganteus. Figure based on SMNS 54677.
Diagnosis
Mastodonsaurus giganteus (J
AEGER
, 1828) is characterized by the following
unique features (fig. 8):
1. Orbits are very large (orbit length/ skull length = 0.24), the interorbital width is
much narrower than the width of orbit, and the anterior end of the orbit is point-
ed.
2. Tripartite posterior rim of the basal plate (fossa parasphenoidalis).
3. Palatine ramus (pterygoid) stout and thickened by medial ridge and constricting
interpterygoid vacuities laterally; quadrate ramus short and directed completely
transversely; basal plate of parasphenoid broadened in its most posterolateral
part.
4. Epipterygoid large and stout, with long anterior portion and a prominent proces-
sus lamellosus, and in contact to six cranial elements; in large specimens confluent
with other regions of the palatoquadrate.
5. Processus hamatus (prearticular) very high and massive, forming an extended fa-
cet continuous with the glenoid area of the articular.
The following features are characteristic of, but not unique to M. giganteus:
6. The thoracal intercentra 3 –26 form complete, nearly equally thick disks. This fea-
ture is however variable, as a broad study of individual variation in Mastodonsau-
rus giganteus revealed (this paper).
7. Anterior trunk ribs with stout processus uncinati and an additional proximal pro-
cessus each (Sclerocephalus, Cheliderpeton, Eryosuchus).
Status of the Mastodonsauridae
The family name was introduced by L
YDEKKER
(1885) and later confined to the
type genus Mastodonsaurus by W
ATSON
(1919). L
YDEKKER
had summarized various
temnospondyl genera under this heading, which are from our present knowledge
only distantly related, e.g. the classical Keuper forms Mastodonsaurus, Capitosaurus
(Cyclotosaurus), and Metopias (Metoposaurus). W
ATSON
instead, who studied the
Gaildorf specimens personally, already recognised some unique features of Masto-
donsaurus, wherein he was principally followed by S
ÄVE
-S
ÖDERBERGH
(1935),
R
OMER
(1947), and H
UENE
(1956). This concept has been upheld ever since (R
OMER
1966; S
HISHKIN
1964; O
CHEV
1966, 1972; P
ATON
1974; C
ARROLL
1988; K
AMPHAU
-
SEN
1989).
S
ÄVE
-S
ÖDERBERGH
(1935: 79) regarded Mastodonsaurus cappelensis W
EPFER
,
1923 more closely related to Capitosaurus than to Mastodonsaurus and consequent-
ly erected an own genus Heptasaurus. R
OMER
(1947) and H
UENE
(1956) instead fa-
voured Mastodonsaurus cappelensis, but this finally became obsolete (C
ARROLL
1988; K
AMPHAUSEN
1989).
The Mastodonsauridae, conceived here to encompass the genera Mastodonsaurus
and Heptasaurus only, are characterized by several unique features. These render the
taxon a monophyletic group in traditional as well as the Hennigian sense.
The following unique characters are shared by Mastodonsaurus giganteus and
Heptasaurus cappelensis (fig. 8):
1. Skull forms isoceles triangle, snout and median series very narrow.
2. Tip of snout elongated anterior to the nares.
3. Premaxillae pierced by large symphyseal tusks, anterior but not medial to the
schoch, mastodonsaurus giganteus 25
nares and distinctly lateral to the lyrae; in the palate there is a paired apertura
praemaxillaris, separated by a broad contact between premaxillae and vomers.
4. Orbits large, reaching more than 1/5 the lenght of the skull. Their shape is sagit-
tally oval, and the anterior and lateral margins are frequently irregular and
strongly convex.
5. Postorbital, prefrontal, and parietal much elongated anterior to the pineal fora-
men; this gives a particularly large postorbital, which is unparalleled by other
stereospondyls.
The parietal is much longer anterior to the pineal foramen than posterior to it.
[This feature was regarded by S
HISHKIN
(1973) as characteristic of the Colostei-
formes, a group supposed to enclose only brachyopids, trimerorhachids, and co-
losteids.]
Characters typical of, but not unique to the Mastodonsauridae are:
6. The degree of ossification is very high (a feature also found in Buettneria perfec-
ta, Parotosuchus orenburgensis, and Eryosuchus garjainovi (all pers. exam.).
7. The parasphenoid-pterygoid suture is very long, giving a roughly triangular
basicranial region, and posteriorly constricted interpterygoid vacuities (similar
morphologies are present in Eryosuchus, Cyclotosaurus, and Eocyclotosaurus
(all pers. exam.).
8. The cultriform process (parasphenoid) is strongly keeled (also present in Cyclo-
tosaurus, Eocyclotosaurus, and the Trematosauridae; all pers. exam.).
9. The large tusks in the palate and symphysis reach giant size; this feature is only
paralleled by Eryosuchus garjainovi O
CHEV
, 1972 (pers. exam.).
10. Lateral line sulci are very wide, especially in the anterior portion of the snout
(this feature is also expressed in large specimens of Eryosuchus and the brachyo-
poid Batrachosuchus; all pers. exam.).
11. Fenestra Meckeli long and slender, 1/5 mandibular length (also in Eocyclotosau-
rus sp. from the Moenkopi Formation, Arizona, and Cyclotosaurus posthumus
from the Middle Stubensandstein of Germany).
Assignment of other finds referred to Mastodonsaurus
The following species and fragmentary specimens have been originally or at some
stage assigned to Mastodonsaurus, but thereafter turned out to be either synonyms
of other species, or nomina dubia.
Mastodonsauridae [non Mastodonsaurus]:
Mastodonsaurus vaslenensis M
EYER
, 1847–55 is clearly a mastodonsaurid and
probably conspecific with Heptasaurus cappelensis (W
EPFER
, 1923). However, as
this find is lost since World War II, and moreover lacks definite diagnostic fea-
tures of Heptasaurus cappelensis, it cannot be taken as senior synonym of the lat-
ter, which thus retains validity.
Mastodonsaurus keuperinus F
RAAS
, 1889 is clearly a mastodonsaurid. This applies,
however, only to the snout fragment, which differs markedly from all co-occur-
ing stereospondyl amphibians (Cyclotosaurus, Metoposaurus, Hyperokynodon) in
the presence and position of the tusk holes in the premaxilla, the position of the
naris, as well as the breadth and position of the lateral line sulci.
26 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Mastodonsaurus ingens T
RUSHEIM
, 1937 is probably also a junior synonym of
Heptasaurus cappelensis (W
EPFER
, 1923), but this must await re-investigation of
W
EPFER
’s original material (S
CHOCH
in preparation).
Parotosuchus mechernichensis (J
UX
& P
FLUG
, 1958) is clearly not a Cyclotosaurus,
as its first describers thought, but a mastodonsaurid. It comprises a posterior skull
table, with the orbits partially visible and the squamosal embayment partially pre-
served. According to all observed diagnostic features, definite mastodonsaurid
characters are present (size of the orbits, proportion of frontals and jugals, and
length of the parietal and supratemporal). It bears greatest similarities with Hep-
tasaurus, and I herewith suggest to provisionally classify it as Heptasaurus cf. cap-
pelensis.
Mentosaurus waltheri R
OEPKE
, 1930 is quite probably a mastodonsaurid. The
interclavicle is very large, but undiagnostic, whereas the sculpturing and propor-
tions of the mandible are typical of the family. The missing hamate process and
postglenoid area, however, render a definite assignment difficult.
Capitosauridae:
Mastodonsaurus robustus Q
UENSTEDT
, 1850 is a synonym of Cyclotosaurus robus-
tus (Q
UENSTEDT
, 1850).
Mastodonsaurus cyclotis Q
UENSTEDT
, 1850 (implicitly) is a synonym of Cycloto-
saurus robustus (Q
UENSTEDT
, 1850), referring to the same material as M. robustus.
Nomina dubia are:
Mastodonsaurus meyeri M
UENSTER
, 1834 is clearly a nomen dubium. It consists of
a single labyrinthodont tooth that might stem from any of the larger stereospon-
dyl taxa occurring in the Mittelkeuper.
Mastodonsaurus andriani M
UENSTER
, 1843 bears the same problems as the afore-
mentioned taxon.
Mastodonsaurus durus C
OPE
, 1866 is clearly a nomen dubium. It might belong to
a metoposaurid rather than a capitosauroid, as W
ELLES
& C
OSGRIFF
(1965) point
out, although this is only inferred from its stratigraphical and geographical posi-
tion.
Mastodonsaurus silesiacus K
UNISCH
, 1885 is a nomen dubium. It bears resem-
blance to advanced capitosaurids, such as Tatrasuchus kulczyckii or Kupferzellia
wildi, might however as well stem from a more primitive capitosauroid form such
as Parotosuchus nasutus.
Mastodonsaurus fuerstenberganus (M
EYER
, 1847–55) (spelled M. fürstenbergensis
by Z
ITTEL
1890, but referred to the same specimen) was assigned to a new genus
erected for it, Meyerosuchus, by K
AMPHAUSEN
1989). I consider this to be a no-
men dubium, as it lacks any definitely diagnostic features; an assignment to Ste-
notosaurus or Eocyclotosaurus would be equally plausible by the structure of the
anterior palate, although these two genera are regarded as only distant relatives by
K
AMPHAUSEN
(1989).
Mastodonsaurus lavisi (S
EELEY
, 1876) is a nomen dubium, based on indeterminate
material. The associated, very fragmentary specimens, however, bear close resem-
blance to M. giganteus, especially the circum-orbital elements (P
ATON
1974: figs.
5, 7b).
schoch, mastodonsaurus giganteus 27
28 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Fig. 9. Skull roof of Mastodonsaurus giganteus with anatomical terms mapped. Note the
differences in the geometry of sutures, such as the failure of the supratemporal to
contact the postfrontal on the right side. Figure based on SMNS 54678 (see also
plate 3).
Capitosauroidea:
Mastodonsaurus weigelti W
AGNER
, 1935 is considered a junior synonym of Paro-
tosuchus nasutus (M
EYER
, 1858) (see W
ELLES
& C
OSGRIFF
1956: 65).
Mastodonsaurus sp.(S
CHMIDT
1928) is an undiagnostic mandible fragment from
the Middle Buntsandstein of Altensteig. It does not bear any definite mastodon-
saurid features, but instead possesses additional teeth posterior to the symphyseal
tusks, which is entirely untypical of the Mastodonsauridae.
3. Comparative osteology
3.1. Cranial anatomy
3.1.1. General structure
The skull of Mastodonsaurus giganteus is one of the most attractive exhibition
items of any Triassic fossil collection. It strikes by its flatness, the elongated snout
with the threehundred teeth, and the very large orbits which suggest enormous eyes.
The skeleton reminds of a crocodile yet the structure is too different even to misguid
a layman.
Mastodonsaurus is different in many aspects from all Recent tetrapods, which is
especially apparent in the cranium. Instead, it is much closer to the primitive condi-
tion of tetrapods (H
ENNIG
1983; S
CHULTZE
& A
RSENAULT
1985; P
ANCHEN
&
S
MITHSON
1987; J
ANVIER
1997; C
LACK
1998). The main differences are found in the
palate, which characterizes the genus as an advanced temnospondyl, having wide
interpterygoid vacuities.
The composition of the skull roof is readily compared to that of Ichthyostega sp.
(J
ARVIK
1996), with minor differences in the proportions of elements (figs. 9, 10).
The mandible is slightly more distinct from that of the earliest tetrapods, especially
in possessing a large Meckelian window on its lingual side, and in the presence of a
conspicuous retroarticular process. The palate and occiput of Mastodonsaurus clear-
ly deviate in several aspects from the plesiomorphic pattern: the pterygoids and par-
asphenoid are anteriorly separated by extensive interpterygoid vacuities, the basi-
pterygoid articulation is lost and, instead, extensive sutures exist in this region
between pterygoids, parasphenoid, and the exoccipitals. In the occiput the exoccip-
itals are the only enchondral bones, making up widely separate, paired condyles of
enormous size. The sculpturing of the dermal bones in Mastodonsaurus is also very
characteristic. This particular type of bone surface, consisting of polygonally ar-
ranged ridges, is found almost as a rule in basal tetrapods and clearly is a ground-
plan feature. Among Recent groups it occurs only in large, hyperossified anurans
and, moreover, rather frequently in crocodiles.
The skull of Mastodonsaurus has immediately apparent unique features (figs. 8, 9).
The outline of the head forms an elongated, isoceles triangle. Its margins taper fairly
continuously towards the narrow, bluntly ending snout. Irrespective of the gigantic
size of the skull, the orbital fenestrae are very large, nearing 1/4 of the skull length.
Moreover, the outline of the orbit is ir-regular in forming an elongated oval which is
markedly pointed anteriorly (M
EYER
& P
LIENINGER
1844; F
RAAS
1889). A similar
orbit shape occurs only in distant taxa such as baphetids (B
EAUMONT
1977) and pro-
colophonids (I
VACHNENKO
1987). Consequently the jugals, postfrontals, and pre-
frontals cover much smaller areas than in related taxa. Mastodonsaurus is further pe-
schoch, mastodonsaurus giganteus 29
culiar in the large extent of skeletal ossification. This concerns most regions of the
cranium, including the braincase. The neurocranium of Kupferzell Mastodonsaurus
is beautifully preserved and thanks to the attentive treatment by the preparators at
Stuttgart it offers a unique possibility to study the complete cranial osteology.
The threedimensional structure of the skull is very characteristic. In contrast to
most other capitosaurs, the orbits are not raised above the flat skull table. The height
of the skull increases continually but only very slightly from the snout to the occi-
put. Squamosals and tabulars comprise the most elevated regions of the head. On top
of the skull table proper there is almost no relief, with the exception of the anterior
part of the supratemporals where a weak depression may be found in some speci-
mens. Besides sculpturing, the only relief is produced by the wide supraorbital sulci
of the lateralis system.
3.1.2. Skull roof
The skull roof is throughout made up of very thick dermal ossifications which con-
tact one another by means of complex, serrated sutures. The sculpturing is intense and
frequently overprints these sutures, although co-ossification remains the exception
(figs. 9, 11). Overprinting by sculpturing is the main reason for the difficulty to find
most sutures in the Gaildorf specimens, a fact which had long precluded a comparison
of Mastodonsaurus giganteus to other labyrinthodonts. M
EYER
(1847–55) and F
RAAS
(1889) gave provisional images of the proportion of the skull roofing elements which
they probably gathered from irregularities in sculpturing. M
EYER
’s illustration is fair-
ly diagrammatic yet generally sound (1847–55: pl. 61, fig. 4), whereas F
RAAS
’ (1889:
fig. 1) interpretation of the posterior skull table departs clearly from the situation
found in the originals. In the Kupferzell material practically all sutures can be studied
in great detail. The cranial anatomy of Mastodonsaurus giganteus provided here there-
fore relies predominantly on material from this locality.
Transsection reveals that the dermal bones of Mastodonsaurus contain countless
tiny pores and channels. B
YSTROW
(1935) studied sections of Benthosuchus bones
and carefully described a similar situation in that comparatively small capitosaur.
Characteristically the pores occur in the lower two thirds of the element, whereas
the upper, most shallow portion consists of numerous parallel sheets of bone. These
uppermost layers produce the prominent sculpturing ridges by means of intensified
growth at discrete points. Following B
YSTROW
, the pores are arranged in a complex-
ly internested channel system. He distinguished several types of channels which are
also observable in the various specimens from Kupferzell. The arrangement of the
pores is most characteristic as it corresponds with the sculpturing pattern: foramina
occur in the pits and grooves mainly. The deepest part of each of these grooves usu-
ally contains a large pore, and in elongated grooves there is a whole series of pores of
different size.
Preservation
The skull roofing elements are throughout very well preserved in the Kupferzell
material. The sculpturing is uncrushed and not affected by wearing such as some ex-
posed palate elements were. Only in one specimen the skull roofing bones have a
surface apparently affected by dissolution. This specimen was found “palate-up” in
the grey marl with the skull roof sticking to the bottom and the occiput being un-
30 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
crushed. Among the occipital dermal bones, compaction has resulted in a displace-
ment of tabulars and postparietals against the exoccipitals. Sometimes the columnae
verticales and the paroccipital processes are also entirely mashed, leaving a com-
pletely fragmented, anatomically unresolvable fabric. Three major types of mechan-
ical destruction are observed in skull roofing bones.
1. Major fractures with large-scale displacement of fragments but preservation of
most anatomical details:
transverse fractures in the long elements of the snout (frontal, nasal, lacrimal);
squamosal and tabular with radial fractures whose origin being in the most ex-
posed areas;
displacement along sutures occurs only in the most exposed areas (tabular,
postparietal, or in marginal elements which connect skull roof to palate (jugal,
maxilla, quadratojugal).
schoch, mastodonsaurus giganteus 31
Fig. 10. The skull roof in selected temnospondyl amphibians, not to scale. Throughout the
group, the number of dermal bones and the general pattern of sutures is remarkably
conservative, although there is a wide range of proportions. All diagrams are based
on personal observations.
Bentho- Tremato- Lettenkeuper Metopo-
suchus saurus almasaurid saurus
Paroto- Mastodon- Kupfer- Cycloto-
suchus saurus zellia saurus
2. Fine fractures:
oblique fractures arranged in various systems that overcross one another affect
most dermal bones.
3. Distortion of dermal bones:
tabular and squamosal (surrounding squamosal embayment);
vertically oriented parts of dermal elements (lamina ascendens pterygoidei,
lamina descendens squamosi);
well-ossified ventral parts of tabular and postparietal contacting processes of
exoccipital (columna verticalis, paroccipital process);
dorsal process of jugal rotated into a steeper angle with the palatal plane.
Taphonomy
Taphonomic evidence is mainly gathered from finds of isolated skull roof bones
and the record of partially disarticulated specimens (e.g. SMNS 80913). The collect-
ing of taphonomic data at the excavation site was constrained by the short time
interval in which excavation was possible. The amount of excellent material recov-
ered and the possibility to collect numerous taphonomic data from the finds them-
selves, however, are nevertheless a most lucky and highly exceptional situation.
The most likely areas to fall apart in the skull roof of Mastodonsaurus are accord-
ingly the cheek and tooth-bearing margin. On the contrary, the posterior skull table
appears to be the most stable region. This is not clearly apparent from the topogra-
phy of sutures, but was controlled by the binding effect of the braincase which is at-
tached at several points to the median roofing series and the supratemporal. In the
snout region the median series also is the most stable region. The premaxillae, nasals,
and frontals are often found in concert, whereas lacrimal plus maxilla and prefrontal
more easily disintegrate. Lacrimal, maxilla, and palatine together make up another
fairly stable unit, whereas the jugal and postorbital very often are dislocated. These
data are preliminary conclusions from ongoing studies on the body of taphonomic
evidence available from the Kupferzell excavation. I am indebted to Dr. R. W
ILD
for
his comments on the settings of certain specimens, and his generous donation of nu-
merous slides which he photographed on his own during the excavation.
Premaxilla
The tip of the snout is especially well ossified. Strong tooth arcades and the olfac-
tory passage are located in close proximity to each other. The premaxilla supports
the median roofing series by a broad suture with the nasal. Its three main branches
are: (1) the dental ramus (dental shelf) which forms the tooth-bearing anterior mar-
gin of the skull, (2) the alary process that connects the skull roof with its margin, and
(3) the processus vomeralis which connects the dental shelf to the vomer (figs. 12,
15).
The dental shelf is ventrally entirely flat and widens medially, and on top of it the
labyrinthodont teeth are borne in acrodont fashion. The dentition is heterogenous
but generally stronger than that of other capitosaurs. The four medialmost teeth
which are arranged in a transverse row are the largest. Further posterolaterally, to-
wards the maxilla, tooth size decreases markedly. Altogether 18 to 19 teeth are
present. Their bases are elongated perpendicular to the longitudinal axis of the ar-
cade. Throughout the smaller teeth are arranged equidistantly, with the tooth bases
32 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
almost in contact. These laterally extended tooth bases cover the dental shelf almost
completely. The surface of the shelf itself is concave transversely, a feature typical of
all marginal tooth arcades (premaxilla, maxilla, dentary). All tooth crowns are bent
lingually, irrespective of their size.
The processus vomeralis is a posteromedian outgrowth of the dental shelf which
separates the symphysial tusks. It firmly connects the medially broadened dental
shelf to the vomer; the suture may disappear in large specimens. The width of the
processus vomeralis is solely determined by the position of the symphyseal fangs, as
exemplified by comparison to other capitosaurs. The general structure of the snout
is not influenced by these particular differences and thus rather uniform throughout
the group. The premaxillar symphysis is sometimes co-ossified. The processus vom-
eralis is ventrally convex and cylindrical in transverse section. Its surface is smooth
and covered only by very fine striations which supposedly trace connective fibre or-
ientation.
The symphyseal tusks of Mastodonsaurus are extraordinarily large and always
penetrate the skull roof. The position of these rather unusual fenestrations is differ-
ent among the capitosaurs possessing them. In Mastodonsaurus and Eocyclotosaurus
they sit anterior to the nares, tunnelling the alary processes, whereas in Cyclotosau-
rus they penetrate the nasals medial to the nares (F
RAAS
1889; K
AMPHAUSEN
1989).
However, the size and proper position of these fenestrae is variable in the Kupferzell
specimens. Their size is not strictly correlated with skull size.
Sculpturing covers the whole alary process as well as the dorsomedial wall of the
dental shelf. It consists of a network of ill-defined, broad and rounded ridges. The
depressions increase in size towards the posterodorsal portion of the alary process.
There is a clear size difference between the sulcus supraorbitalis and the depressions
in its proximity, a feature not found in smaller capitosaurs, where a distinction
between the actual lateral line sulci and mere ornamentation is sometimes difficult
(S
CHOCH
1997a).
Nasal
The nasal of capitosaurs is a very conservative element, and in Mastodonsaurus it
is only striking by its narrowness (fig. 9). The length of the nasal and frontal is gen-
erally relatively greater in capitosaurs as compared to plesiomorphic taxa such as
Sclerocephalus or Eryops (S
AWI N
1941; B
OY
1988) and more similar to that of the ac-
tinodontid-grade Cheliderpeton and Intasuchus, and the very Rhinesuchus-like “ar-
chegosaurs” Melosaurus and Konzhukovia (K
ONZHUKOVA
1955; G
UBIN
1984; B
OY
1993; W
ERNEBURG
& S
CHNEIDER
1996). The tendency in capitosaurs to form a con-
servative naso-frontal suture type is further very conspicuous: the frontals are medi-
ally wedged between the nasals and converge towards a point in the midline. The na-
sals in turn are set in between the prefrontals and frontals posteriorly. Laterally they
contact the lacrimals, anterolaterally the maxillae, and anteriorly the premaxillae.
Rather unusual in capitosaurs is the long nasomaxillar suture, resulting from the rel-
atively short lacrimal.
The shape of the nasal is that of an elongated rectangle which widens in its middle
third. The sculpturing of the element is very characteristic. It is divided into two un-
equally large areas by the wide sulcus supraorbitalis. Throughout the radially ar-
ranged ridges have their centre at the margin of the sulcus.
The anterolateral, sculptured region bears a network of small, polygonal ridges
schoch, mastodonsaurus giganteus 33
which are arranged radially, the centre being at the edge of the flexura medialis of the
sulcus. The sulcus supraorbitalis forms a very broad, shallow groove which has a
largely smooth surface. Only sporadically there occur small foramina, situated in
slight depressions within the sulcus. The margin of the sulcus is bordered by sculp-
turing ridges, and there is a zone immediately next to the first ridges which is cov-
ered by very fine, short stripes. Ventrally the nasal is attached to the anteriormost
ethmoid region of the neurocranium. This may eventually ossify completely, being
attached with its roof laterally to the planar inner surface of the nasal.
Frontal
The frontals of Mastodonsaurus giganteus are especially slender elements, and
clearly differ from those of all other capitosaurs by this feature (figs. 9, 10). Lateral-
ly they form the intermediate part of the orbital rim, separating the prefrontal and
postfrontal to an extent untypical even of capitosaurs. Because of the enormous size
of the orbits the frontals are laterally slightly constricted. In their median extension
they are markedly longer than the nasals and thereby the longest bones of the medi-
al series. Their shape is that of elongated rectangles, the sutures with prefrontals be-
ing largely serrated and irregular though. In many specimens the frontal reaches well
double the length of the parietal, by which the species differs clearly from Heptasau-
rus. The frontal contacts the nasal anteriorly, the prefrontal along its anterolateral
margin, the postfrontal posterolaterally, and the parietal posteriorly. Typically, the
anterior frontal sutures converge towards the midline, where their anteriormost ex-
tension is reached. This converging is, however, subject to variation, interestingly to
a larger degree than it is in other capitosaurs.
Sculpturing on the frontal is dominated by long and slender ridges, as well as the
very impressive supraorbital canal of the lateral sense. The latter is relatively very
wide, about half the breadth of the frontal itself, and slightly increase in width ante-
riorly. Its course parallels the medial rim of the orbit, therefore bending anterolater-
ally in the posterior third of the frontal.
The ventral surface of the frontals forms a plane and is nearly smooth, with the ex-
ception of faint traces left by the attachment site of the braincase. This contact is su-
tural in most specimens and maximally continuous along the entire width and length
of the sphenethmoid. There are no descending processes formed by the frontals,
such as typical of the parietals throughout capitosaurs, or on the frontals such as in
Cyclotosaurus robustus (F
RAAS
1913). The sphenethmoid always expands over al-
most the entire width of the elements in the interorbital region. Anteriorly, the ex-
tension of sphenethmoid ossification varies considerably, but roughened ventral sur-
face of the frontals suggests a tight contact to the braincase irrespective of its state of
mineralization.
Parietal
Mastodonsaurus is characterized by an elongate parietal which exceeds the length
of the postparietal and prefrontal by far. This is most uncommon among capitosaurs,
but an abundant feature in plesiomorphic temnospondyls (figs. 8–10). In contrast to
all these, the frontal and nasal of Mastodonsaurus are still distinctly longer than the
parietal. In most specimens it contacts the following bones: the frontal anteriorly,
the postfrontal anterolaterally, the supratemporal laterally, and the postparietal pos-
34 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
teriorly. In addition, a common suture with the postorbital may eventually be estab-
lished in cases where the postfrontal is posteriorly small.
The position of the pineal foramen is in the posterior third of the parietal which is
an unusual feature for capitosaurs, and advanced temnospondyls in general (S
HISH
-
KIN
1973). This posterior position results from the relative elongation of otic, late-
rosphenoid, and epipterygoid regions in the endocranium. By this, Mastodonsaurus
giganteus differs from other basal tetrapods with a similarly elongated parietal, such
as the Colosteidae, Trimerorhachidae, and Brachyopidae (W
ATSON
1956; S
HISHKIN
1973; S
MITHSON
1982).
Like in other medial elements, the sutures with the lateral neighbours and the me-
dial counterpart are generally smoother than those with the anterior or posterior ele-
ments. Ventrally, the parietal is attached to the middle part of the roof of the sphen-
ethmoid. This is accomplished by means of elongated sagittal crests that are borne
by the otherwise smooth ventral side of parietal.
Postparietal
The postparietal is one of the morphologically most invariable elements in ca-
pitosaurs. It differs largely in its relative size, but hardly varies in morphology (fig.
10). It forms the posteromedial edge of the skull roof, connecting to the exoccipi-
tal by means of a slender descending outgrowth, the lamina supraoccipitalis. The
roofing part is roughly quadrangular in outline and exceeds only slightly the width
of the parietal to which it connects by an externally variably shaped suture line.
The supratemporal also shares a variable, but in general rather short suture with it
which is straight, and finally the relatively large tabular connects to it by means of
a serrate suture posterolaterally. Finally the posterior margin of the skull roof is
clearly concave in dorsal view, which is a widespread feature among temnospon-
dyls.
Ventrally, the columna verticalis (exoccipital) firmly connects to the rather short
descending process of the postparietal. The occipital part of the postparietal is very
well ossified and slopes posteroventrally, being markedly thickened in medially. The
whole occipital area is very much roughened, suggesting fleshy insertion of epaxial
musculature. The dermal sculpturing consists of equally-sized, quadrangular poly-
gons, which fail to connect to those of the neighbouring elements. The internal side
of the bone is smooth except for the ventral suture surface of the processus supraoc-
cipitalis.
Lacrimal
The lacrimal bridges the long space between the jugal and the anterior part of the
snout, connecting the maxilla with the nasal and the prefrontal. It bears the supraor-
bital and infraorbital canals of the lateralis system, which are of huge size in this re-
gion (figs. 8, 9). Most of the dorsal surface of the lacrimal is in fact dominated by the
impressions of these canals, so that only a small area in the posterior corner is sculp-
tured in the typical way. The lacrimal does neither border the orbit nor the naris. It
connects, however, to the palatine by means of a short and stout column, which
tightly connects the palatine tusk region to the roof. This column has not been re-
ported in other capitosaurs and may be a particular device of this genus or species,
whose snout region is among the most flattened in temnospondyls.
schoch, mastodonsaurus giganteus 35
Unlike the prefrontal, this bone does not differ in morphology or size as com-
pared to other capitosaurs. It is about as long as the prefrontal, and only slightly nar-
rower than the nasal. The contact to the latter comprises about ‚ of the entire length
of the bone. The lateralis canals occupy each about half of the width of the bone,
whereby the supraorbital canal is straight though widens anteriorly, and the infraor-
bital canal curves in sigmoid fashion to give the flexura lacrimalis.
Prefrontal
The huge size and anterior extension of the orbital fenestra affects the posterior
morphology of the prefrontal, whereas the anterior portion does not differ from the
general structure of other, narrow-snouted capitosaurs (figs. 9–10). The element is
however, most different in proportion from that of typical capitosaurids and ben-
thosuchids. As pointed out before, the preorbital region of Mastodonsaurus is much
abbreviated with respect to other genera, and this is most obvious in the prefrontal.
The peculiar shape of the mastodonsaur skull is particularly due to the unique struc-
ture of the prefrontal region: moderately wide mid-level, very large orbits, and a nar-
row yet rather short snout.
The prefrontal wedges in between the medial and marginal series of the skull roof,
and in Mastodonsaurus giganteus is basically a triangular element with a pronounced
posterior indentation. The latter has the shape of an isoceles, wide triangle, making
up 1/3 of the orbital window. In particular the posterior margin is much thickened
and the area immediately anterior to this is the most elevated and clearly sculptured
region. The supraorbital canal passes right through the imaginal centre of the bone.
Thereby the canal widens conspicuously and carves into the otherwise markedly
sculptured, planar dorsal surface of the bone. The canal leaves the prefrontal in its
anterior third laterally to run through the lacrimal, and the suture between these ele-
ments abruptly curves in medial direction at this point. The internal side of the pre-
frontal is smooth with the exception of the rim of the orbital window that may be ce-
vered by fine stripes in some specimens. In addition in the posterior third of the ele-
ment, there is a deep groove which runs and deepens anteriorly, finally terminating
in a large foramen.
Postfrontal
The postfrontal is widely separated from the prefrontal (which it contacts in all
plesiomorphic capitosaurs and temnospondyls in general), and this to an extent un-
paralleled among capitosaurs (fig. 10). The element forms part of the posteromedial
border of the orbit, and it wedges in between the postorbital, supratemporal, and pa-
rietal. In few cases a failure to contact the supratemporal is observed, and the parie-
tal then has a moderately long suture with the generally large postorbital. The shape
of the postfrontal is constrained by the narrow skull, the large orbit, and the rather
long postorbital skull table to which it contributes only a minor component though.
It forms an elongate oval or rectangle, does not constrict the parietal anteriorly, and
forms at best half of the concave posterior border of the orbital window. The sculp-
turing is overprinted rather than interrupted by the supraorbital canal which is very
weak and frequently terminates before it leaves the bone posteriorly. It consists of
asymmetrical polygons which open posterolaterally and converge towards the orbi-
tal rim. The internal face of the bone is smooth, but may carry a weakly developed
depression in the posterior part.
36 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 37
Fig. 11. Two dermal skull roofing elements of Mastodonsaurus giganteus, the postorbital
(above) and supratemporal (below). The pronounced ornamentation on the dorsal
surface (left side) is typical of bones and osteoderms growing in a relatively shallow
position within the dermis. The inner or ventral surface is smooth with the excep-
tion of muscle scars and foramina for nutritive vessels, nerves, and tendons.
Postorbital
This is the dominant element in the postorbital region (figs. 8, 9). It is much long-
er than in many other capitosaurs, and its structure differs significantly from that
figured by F
RAAS
(1889), to which most authors referred. The shape of the bone is
more like in Eryosuchus or Benthosuchus than in most Parotosuchus species or Cy-
clotosaurus. It attains the outline of a nearly symmetrical pentagon with the symme-
try axis orientated roughly sagittally.
Unique for Mastodonsaurus giganteus though is the length of the postorbital; it
deeply wedges in between the supratemporal and squamosal. S
HISHKIN
(1980) was
mistaken in assuming that there was no anterolateral process of the postorbital,
which may indeed be very pronounced in this species; his interpretation relied on
the false illustration of F
RAAS
(1889).
The sculpturing is arranged radially, consisting of distally widening and enlarging
polygons. Instead the orbital rim is thickened and has a marked slope towards inside
the orbit. The internal side of the bone is mostly smooth.
Supratemporal
The supratemoporal covers one of the most variable regions in the temnospondyl
skull roof, but unlike more plesiomorphic genera [e.g. Sclerocephalus, see B
OY
(1972,
1988)] there is never an additional element (intertemporal) present. However, the
bone may eventually fail to contact the postfrontal (fig. 9), a situation sometimes
found in temnospondyls for which individual variation is known (B
OY
1972). The
supratemporal is peculiar in being remarkably narrow and proportionately small in
Mastodonsaurus. Generally it has an asymmetric-hexagonal shape, with straight and
unserrated sutures. The dermal sculpturing is well-defined. It consists of radially ar-
ranged polygons that tend to be elongated anteriorly, and which are strongly devel-
oped at the suture with the postorbital, overprinting the latter frequently. The tem-
poral canal of the lateral sense is variably expressed, but in any case terminates slight-
ly posterior to the central point of the bone. On the ventral side, the supratemporal
bears a transverse ridge in its posterior third, and in addition to this several pores or
larger foramina may be present. The anterior part of the bone has sometimes a weak
depression on the internal side.
Tabular
This element forms the well-ossified posterolateral cornerpiece of the skull table,
and it holds a key position regarding the architecture of this region. It contacts the
squamosal anteromedial to the otic notch by means of a broad and serrated suture
(fig. 9). The contact with the supratemporal is straight, whereas that with the post-
parietal varies but often is markedly curved and serrated. The tabular never contacts
the squamosal posterior to the otic notch (as it does in Cyclotosaurus, Eocyclotosau-
rus, and various other capitosaurs), largely because of the poorly developed crista
falciformis. The distal end of the tabular is, however, very strongly ossified and of
stout appearance, and in contrast to most plesiomorphic capitosaurs is directed lat-
erally rather than posteriorly (cf. Benthosuchus, Wetlugasaurus, Parotosuchus nasu-
tus, P. orenburgensis, etc). It resembles closest the tabular in Parotosuchus pronus and
Eryosuchus garjainovi, but in Mastodonsaurus may be highly variable in shape.
38 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
The ventral side of the bone bears a ventromedially directed process, the proces-
sus paroticus, which is blade-like, with widened anterior and posterior surfaces. It
meets the exoccipital in a broad, serrated suture, thereby binding the occipital con-
dyle to the lateral corner of the roof. Medially the parotic process frames the su-
praoccipital fenestra, which in Mastodonsaurus is very high and roughly triangular.
The ventral surface of the tabular is complicated, being roughened especially in the
area posterolateral to the base of the parotic process. Anterior to this base, which
terminates in a sharp crest (crista tabularis externa), there is a large muscle impres-
sion.
Maxilla
The maxilla forms a large, completely dentigerous shelf bearing in between 85 and
100 throughout uniform teeth. For most of its length it is narrow and rather thin,
with a convex dorsolateral surface and a flattened dentate shelf. The suture to the ec-
topterygoid and palatine is set in a marked and broad furrow that corresponds with
the tooth arcade of the dentary. The tooth shelf in particular is remarkably thin, and
posteriorly forms a sheet borne by the jugal ventral process and the quadratojugal
(fig. 13).
The maxilla makes a well-defined contribution to the skull roof, especially anteri-
or to the lacrimal, where it contacts the nasal. Further it borders the naris posterolat-
erally, although this part is overgrown by the dermal portion of the septomaxilla.
There the maxilla contacts both the palatine and vomer, in the choanal region slight-
ly broadening medially on the palatal side. For most of its length it forms the lateral
rim of the skull, and by its structure and sculpturing (fine ridges only) it is distinct
from all other roofing elements. It contacts the quadratojugal posteriorly, but often
the immediate contact zone is broken.
The teeth are for most of its length of almost similar size and morphology. The
tooth bases are characteristically anteroposteriorly compressed, giving flattened an-
terior and posterior surfaces. Obviously this is a device to gain a very dense tooth ar-
cade. The tooth crowns are only very slightly bent medially, and are of conical shape.
Carinae, such as described for Cyclotosaurus hemprichi (K
UHN
1941), are not ob-
served.
Jugal
A most characteristic element in the skull roof of Mastodonsaurus giganteus is the
jugal, which has a concavely curved lateral margin, where it slopes towards the max-
illa. It medially borders the large, oval orbital window (fig. 9). In transverse section
the bone is convex towards the lateral side, with the dorsal and roofing part being a
laterally slightly sloping plate. The jugal wedges in between the maxilla and palatine
(and ectopterygoid, respectively) on the ventral side, and further forms the posteri-
or edge of the marginal tooth arcade (fig. 13). The dentigerous, rather thin-walled
elements are framed by this ventral process of the bone, and it has even a well-de-
fined, ventrally triangular face on the palatal side.
Squamosal
The cheek is amongst the most elevated and strongly ossified regions in the head,
a part which is largely formed by the squamosal. This element gives the posterior
schoch, mastodonsaurus giganteus 39
skull its characteristic shape (fig. 9). It connects the skull table to the margin, forms
the largest part of the roof of the upper adductor chamber, and its posterior slope
helps supporting the musculature of the neck and/or the depressor mandibulae. Its
most elevated region is the posterior margin and the squamosal embayment (otic
notch), of which it forms about one half. The posterior rim bears a pronounced
crest, the crista falciformis. This is most similar to Parotosuchus nasutus and Eryosu-
chus garjainovi in not being posteriorly much extended and therefore far separate
from the tabular. However, this is a condition which underlies particular develop-
mental change, and the otic notch may near closure in large specimens. The resulting
morphology is, however, quite different from that of Cyclotosaurus or similar forms.
The sculpturing of the squamosal is arranged radial from the frame of the otic
notch, and the polygons tend to increase in length thereby. In addition, the ridges
tend to become thinner yet higher distally, and are confluent with similar such ridg-
es on the jugal, quadratojugal, and postorbital. In the whole anterior cheek region it
is often difficult to identify the sutures because of this strong overprinting. On the
ventral side the roofing part of the squamosal is roughened in several areas, especial-
ly posteriorly near the apex of the strongly convex, elevated region. The posteriorly
sloping occipital portion is formed by the lamina ascendens of the squamosal, which
is thin-walled and overlaps the pterygoid and quadratojugal ventrally.
Quadratojugal
The subtemporal window is laterally framed by the quadratojugal, which forms
the posterolateral corner of the skull roof and integrates the quadrate trochlea into
the framework of the palate, cheek, and occiput (figs. 9, 13). The quadratojugal is
very massive and quite tightly set in a frame made by the jugal, squamosal, and pter-
ygoid. It has only a minor occipital component that is significantly overlapped by
the squamosal, but forms out a stout ventral process that abuts laterally against the
quadrate. This process thins anteriorly where it curves to parallel the skull margin
and finally merges into the main plane of the element anteriorly. Posteriorly, on the
occipital face, the quadratojugal is pierced by a large paraquadrate foramen, and
there again the lateral margin bears a prominent crest.
The sculpturing is of a similar type as that of the squamosal and jugal, and the cen-
tre of divergence is at the lateral margin of the roofing portion of the bone. The
internal side reveals the large degree of overlapping by the squamosal, but is other-
wise rather smooth. The subtemporal window is bordered laterally completely by
this bone, which tends to curve convexely, especially in the largest specimens. The
quadratojugal transsects the palatal plane, and terminates in a bulge lateral to the
subtemporal fenestra. There is no contact to the maxilla, a feature found among most
capitosaurs and paralleled in several other, more distant basal tetrapod clades.
Orbital windows
The orbits of Mastodonsaurus giganteus have long been known to be of peculiar
size, morphology, and structure (M
EYER
& P
LIENINGER
1844; F
RAAS
1889). The
length of these windows is about ‚ skull length, and their shape is long-oval with a
pronounced anterior, triangular extension (figs. 1, 8, 9). P
ATON
(1974) was mistaken
in stating that this anterior extension was an artifact of preparation in the Gaildorf
specimens, a fact proved by the Kupferzell material.
40 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
Because of the huge size of these windows, the morphology of the bones anterior,
lateral, and medial to the orbits is partially significantly different from that of other
capitosaurs. In particular, the prefrontals are much shorter posteriorly, the jugals and
frontals are very narrow. The rim of the window is unsculptured and thickened. It
may be entirely smooth or covered by numerous fine stripes.
The paradox that the cranial morphology of Mastodonsaurus appears immature
though the species is larger than any other temnospondyl has often struck scientists.
The notion of such an immature morphology (e.g., large eyes in small skulls, which
make surrounding elements appear rudimentary and juvenile) is sometimes trans-
ferred to large animals which have a similar morphology for entirely different rea-
sons.
Naris and septomaxilla
The nares of Mastodonsaurus giganteus are proportionately relatively small,
which is expectable from the large size of the skull. They are widely separated, sit-
ting close to the margin of the skull, but slightly more posterior in position as com-
pared to most other capitosaurids (fig. 12). The outline of the naris is very character-
istic in being longitudinally oval with slightly pointed anterior and posterior ends.
schoch, mastodonsaurus giganteus 41
Fig. 12. Two growth stages of the preorbital region in Mastodonsaurus giganteus. The septo-
maxilla has two portions, a lateral one which participates in the bordering of the nar-
is, and a medial and internal one, which supported the narial duct as in Recent sala-
manders.
The posterolateral portion may be slightly extended in most specimens, a feature
found in Wellesaurus, Kupferzellia, and Cyclotosaurus, as well (W
ELLES
& C
OSGRIFF
1965; S
CHOCH
1997a).
As the snout is very much flattened, the naris forms only a slit (in transverse sec-
tion) which leads into the very narrow and straight narial ductus. This passage is me-
dially and ventrally constricted by the thickened roof for the vomerine tusk sockets.
The ductus consequently narrows to one half of its anterior diameter and curves
markedly laterally to end in the small, rounded choana proprieta, which then opens
ventrally towards the reniform choana palatalis. There is no trace of an ossified na-
sal capsule, and also no attachment site for parts of the cartilaginous capsule are
found. In any case the whole structure of the narial region suggests that the nasal
capsules were underdeveloped with respect to most temnospondyls, and especially
if compared with apparently terrestrial and lung-breathing forms as Eryops (S
AWI N
1941), Zatrachys (B
OY
1989; S
CHOCH
1997a).
Surprisingly though, a definite septomaxilla is present in the naris of Mastodon-
saurus giganteus. It is integrated into the dermal skull roof at the posterolateral rim
of the naris, where it forms a concave-convexe stripe of well-sculptured bone (fig.
12). This element has a posteromedial process which points into the narial passage.
This process is very thin and narrows medially, and is only present in larger speci-
mens. It is unclear whether it actually floored the passage (which is suggested by
preservation) or pointed, in half upright posture, into the otherwise unossified part
of the narial duct.
Review on the structure of the skull roof
The skull of Mastodonsaurus is composed of extraordinarily massive, planar ele-
ments which differ considerably in size but are throughout similar in thickness.
There is only one temnospondyl genus with a comparable amount of ossification at
nearly the same size, namely Eryosuchus from Kazakhstan (O
CHEV
1966, 1972; pers.
exam).
The arrangement of sutures partially matches the topography of the endocranium
(figs. 19–20). In addition, the proportions of the medial and temporal series are cor-
related with those of the otic, epipterygoid, and sphenethmoid ossifications. This is
important for comparing the cranium with those of other capitosaurs in which the
braincases are sufficiently known. The posterior rim, formed by postparietals and
tabulars, is thickened and forms a descending occipital lamella.
The sutures are tight due to a pronounced serration along all spatial axes: the
superficially visible suture is continued into the depth to interfingering bone layers
of both elements (fig. 11). The result is an entirely akinetic cranium, a condition
which is clearly derived among early tetrapods.
Mastodonsaurus has an overall very flat skull which lacks a pronounced slope an-
terior to the orbits. It is most similar to the capitosaurids Wellesaurus peabodyi
(W
ELLES
& C
OSGRIFF
1965), Eryosuchus garjainovi (O
CHEV
1972), and Parotosu-
chus pronus (H
OWIE
1970) in this respect, and it differs clearly from that of Cycloto-
saurus, all other Parotosuchus species, Eocyclotosaurus, and Benthosuchus (B
YSTROW
& E
FREMOV
1940).
42 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 43
Fig. 13. The skull of Mastodonsaurus giganteus in ventral view (SMNS 54675). Characteris-
tic are the two dental arcades, the large tusks in the anterior palate, and the strongly
sutured and elongated basicranium.
3.1.3. Palatal dermal elements
The structure of the palate of Mastodonsaurus is in all aspects that of what has
been conceived an advanced capitosaur (R
OMER
1947; W
ATSON
1951, 1962). The
interpterygoid vacuities are very large, having more than half the skull length and to-
gether two thirds the skull width (figs. 13–14). They do not completely match the
position of the orbits, because they are constricted by the stout palatine rami of the
pterygoids posterolaterally. The cultriform process of the parasphenoid is narrow
and rather weakly ossified.
Jaw articulation, occipital condyles, braincase, and marginal tooth arcade are to be
firmly integrated by the palatal dermal bones. A predominant role in this context
play the parasphenoid and pterygoids (fig. 13). As the occipital and quadrate con-
dyles are extraordinarily massive in larger capitosaurs, the pterygoids and para-
sphenoids tend to be very stout in these.
The dentition of the mastodonsaur palate is especially generalised and uniform. It
consists largely of two parallel rows which roughly indicate the gape of the animal.
The outer row is formed by the teeth of the maxilla and premaxilla and contours the
outline of the snout. It is separated from the inner row by a narrow groove posteri-
orly and by the choana and the symphyseal tusks anteriorly. In two regions a spe-
cialised tooth pair of the inner row grows to large size to form palatal fangs. These
are situated posterior and anterior to the choana. Besides the described tooth arcades
there are no tooth-bearing regions. The ventral surfaces of the pterygoids and para-
sphenoid which in many basal tetrapods are vaulted and dentigerous, are instead
smooth and flattened in Mastodonsaurus.
Preservation
The palate is usually somewhat more affected by compaction than the skull roof.
This does however not concern the teeth which generally are neatly preserved in situ
in upright position and without major fractures. Empty tooth sockets are obviously
not the result of taphonomic decay. There are basically two types of significant
preservational bias affecting the palate of Mastodonsaurus in the Kupferzell materi-
al:
1. Major fractures have lead in certain well-defined regions to slight displacements
of structural units. Such fractures occur in the following regions:
transversely in the posterior third of the basal plate of the parasphenoid (and
sometimes the quadrate ramus of the pterygoid);
obliquely in the palatine ramus of the pterygoid (close to or along its suture with
the ectopterygoid);
transversely in the cultriform process (in various regions, but most frequently
transversely along its contact with the basal plate);
obliquely along the sutures of the quadrate trochlea, tending to isolate this struc-
ture;
transversely in the narrowest regions of the palatine;
along the suture between maxilla and palatine and ectopterygoid.
2. Dissolution is rare and confined to the most exposed regions such as the sagit-
tal crest of the parasphenoid. This crest frequently appears to have been “worn off”
for still unclear reasons. As the preparation was carried out throughout very cau-
tiously, an early diagenetic partial dissolution of bone seems to be more probable.
44 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
schoch, mastodonsaurus giganteus 45
Fig. 14. Palates of selected temnospondyls, exemplifying the proportion of the pterygoid,
parasphenoid, and interpterygoid vacuities. Not to scale. Balanerpeton and Trime-
rorhachis are primitive forms, which have large pterygoids and extensive tooth
patches on the palatal elements. Sclerocephalus is a stem-stereospondyl, representing
a moderately advanced temnospondyl condition. Mastodonsaurus is an extreme
variation of the latter, with a strongly ossified and akinetic skull.
Except for one skull, all crania were found in roof-up position, with the palate stick-
ing in a slightly more finegrained layer. The preservation of fine structures such as
sutural surfaces, attachment sites for cartilage and musculature, and nutritive forami-
na is nevertheless throughout excellent.
Vomer
The ventral snout region is dominated by large tusk pairs of vomer and dentary,
an almost continuous row of small “circum-vomerine” teeth, and the palatine tusks
(figs. 13, 15). This is the typical condition throughout capitosaurs; somewhat similar
situations are found in Ichthyostega (J
ARVIK
1996: fig. 25) and Trimerorhachis (C
ASE
1935); see fig. 14. Mastodonsaurus is peculiar among capitosaurs in having extreme-
ly large fangs whose bases occupy a considerable area. Generally the tooth sockets
have about twice the size of those in other large capitosaurs. The only exception is a
still undescribed giant Eryosuchus-like form from Kazakhstan (M.A. S
HISHKIN
,
pers. comm).
The vomer is the main supporting structure of the snout floor, firmly connecting
the tooth-bearing margins of the skull to the ossified floor of the braincase (para-
sphenoid). The choana, a small, slit-like internal opening of the olfactory passage, is
wedged in between the giant fangs of palatine and vomer sagittally and between the
maxillar and vomerine tooth arcades transversely. The vomer is a long-rectangular
plate which increases in thickness anteriorly. It contacts the following elements: the
premaxilla anteriorly, the maxilla laterally, the palatine posterolaterally, and the cul-
triform process (parasphenoid) posteriorly. The latter contact is established by
broad posteromedial processes (pr. parasphenoidales) that form a frame into which
the parasphenoid is set in firmly. In Mastodonsaurus the processus parasphenoidales
do not unite in the midline, so that the cultriform process is exposed ventrally. This
is the condition found throughout true capitosaurids (sensu R
OMER
1947), i.e. ex-
cluding Benthosuchus, Wetlugasaurus, and the Trematosauridae (B
YSTROW
& E
FRE
-
MOV
1940). The parasphenoid hence separates the vomers in the midline up to the
dentigerous region at their anterior rim where they meet in a tight suture. The ex-
posed area of the cultriform process characteristically forms a countersunk, anteri-
orly deepening drain (fodina vomeralis). This drain bifurcates as it enters the canal
formed by the vomers. It is bordered by a thickened margin of the vomers that may
eventually form a shallow bulge. Further, the canal ends shortly anterior to the
transverse vomerine tooth row in a single exit foramen. The median suture between
the vomers, which is established along only 1/3 the whole length of the vomers, is
serrated and sometimes even co-ossified. The parasphenoid process is thick at its
base and compressed-oval in cross-section, but narrows posteriorly to form a thin
sheet which moves into a more steep angle relative to the palatal plane as it nears its
posterior end.
The symphysial tusks of the dentary are framed by an anteromedial and an ante-
rolateral process of the vomer. The former (pr. fenestralis) contacts the posteromedi-
al process of the premaxilla (pr. vomeralis), whereas the latter (pr. subnarialis) binds
the vomer tightly to the medial wall of the premaxillar dental shelf (fig. 15). The
aperturae praemaxillares are entirely separated by vomer and premaxilla whose su-
ture is longer than the diameter of each of the aperturae. The anterior rim of the
vomers is massive and declines gradually from the base of the transverse tooth row
towards the apertural region. The latter is most similar to those of capitosaurids
(Parotosuchus, Eryosuchus, Cyclotosaurus) in the morphology of the transversely el-
ongated depression in which the aperturae proper are situated.
The ventral surface of the bone is flat and covered with numerous pores occurring
in a broad string that runs medial to the circumvomerine tooth arcade. These pores
46 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
open posteriorly, suggesting an intense vascularization of the base of the tooth ar-
cade. The cultriform process further overlaps the vomer dorsally, reaching almost up
to the fenestral process. It sits in a depression on the dorsal side of the vomer such as
known in Benthosuchus sushkini (B
YSTROW
& E
FREMOV
1940: fig. 8). The dorsal
surface of the vomer is otherwise smooth and without clear relief.
The vomerine tusk pair is situated at the anterolateral corner of the ventral side of
the vomer, next to the region where vomer, premaxilla, and maxilla meet. The long
axes of the tusk bases are oriented perpendicular to the long axis of the vomerine
tooth arcade. This suggests that the large fangs are developmentally a derivate of the
proper vomerine tooth arcade and have just greatly become enlarged. The vomerine
tusks are larger than those of the palatine and only slightly smaller than the dentary
symphyseal tusks. They occupy half the anterior width of the vomer. The rims of
their empty sockets are slightly elevated, and the vomer is dorsally fused to the lac-
rimal in this region.
The circumvomerine tooth arcade consists of (1) a transverse row of 10–11 small
teeth (dentes postfenestrales), (2) the tusk pair, (3) a sagittal row of 15–17 small teeth
schoch, mastodonsaurus giganteus 47
Fig. 15. Anterior portion of the palate in Mastodonsaurus giganteus (SMNS 54678). The
large symphyseal tusks penetrated the premaxillae through paired openings anteri-
or to the vomerine tusks. A second row of teeth, internal to the premaxillar-maxillar
dental arcade, is a characteristic feature of most stereospondyls. In Mastodonsaurus
the contrast between the tiny marginal teeth and the giant tusks is conspicuous.
(dentes parachoanales). The postfenestral and parachoanal tooth rows bear the
smallest teeth in the jaws of Mastodonsaurus. They are uniform, equidistant, and
have medially and posteriorly bent crowns. Their tooth sockets are slightly raised
above the vomerine surface, and the postfenestral tooth row has a straight, well-de-
fined base raised above the flat surface of the vomer.
The sutures with the premaxilla and maxilla run lateral to the vomerine tusks,
where the latter two bones contact at about midlength. The vomero-maxillar suture
converges posteromedially towards the rim of the choana. Finally the suture with
the palatine is curved and relatively longer than in the more plesiomorphic capito-
saurids, separating the palatine from the vomerine parachoanal tooth rows, it first
runs posteriorly and then bends medially where the palatine forms the entire antero-
lateral rim of the interpterygoid vacuity, finally abutting against the parasphenoid
process of the vomer medially.
Choanal region
In plesiomorphic genera such as Lydekkerina, Benthosuchus, or Wetlugasaurus
the choana forms an elongate oval, situated between the vomerine and palatine tusks
and bordered by parasagittal tooth rows on both sides. In Parotosuchus the choana
is merely a narrow and long slit, whereas in Cyclotosaurus it is instead very short and
round to subcircular. Intermediate choanal shapes are possessed by Eryosuchus,
Wellesaurus, and Mastodonsaurus.
The choanal region of Mastodonsaurus giganteus is reniform with its long axis
aligned parallel to the maxillar tooth row. It is bordered by the vomer medially and
anteromedially, the maxilla laterally, and the palatine posteriorly (fig. 15). The ante-
rior end is rounded and broader than the posterior one which is constricted lateral-
ly. At least in Mastodonsaurus, two different openings have to be distinguished: (1)
the reniform rim outlined by the palatal elements at the level of their plane ventral
surfaces (choana palatalis, chpa), and (2) the proper opening of the olfactory passage
towards the dorsal portion of the snout (choana proprieta, chpr). The former is 1/3
longer than the latter and constitutes the structure usually referred to as choana in
temnospondyls. Further, the choana palatalis lies in the same plane as the ventral sur-
face of the vomer, whereas the choana proprieta is aligned with a plane clearly in-
clined towards the palatal plane. The medial frame of the choanal region is straight
vertical, thus both palatal and proprietal openings end exactly at the same medial lev-
el. Instead, the lateral and posterior walls of the choana palatalis are curved and in-
cline rather shallowly to finally form in the rim of the choana proprieta which is dis-
tinctly further anteromedial.
The morphology of the choana proprieta is similar to that in the figure M
EYER
(1847–55) gave of the giant, now lost Mastodonsaurus skull from Gaildorf. The
choana palatalis is most similar to that of Eryosuchus, Wellesaurus in being only
moderately long, and it differs conspicuously from the broad choana of Kupferzel-
lia and Cyclotosaurus. In small forms such as Kupferzellia or Eocyclotosaurus, there
is no internal opening (choana proprieta) because of the low extent of ossification.
Parasphenoid
The parasphenoid is the longest and most differentiated component of the dermal
palatal ossifications. It differs markedly in thickness and structure in its various re-
48 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
gions. By its structure it can be readily divided into two architecturally different
components: the basal plate and the cultriform process. The former is an elongated
trapezoidal plate which floors the hindbrain and auditory capsules and firmly con-
nects the pterygoids and exoccipitals (fig. 13). Its thickness increases markedly to-
wards the extensive sutures with the latter two bone pairs. The cultriform process
instead is a slender and rather delicate structure, strut-like in ventral view and rough-
ly U-shaped in transverse cross-section. It connects the basal plate, of which it ap-
pears to form an anterior outgrowth, with the vomer. There is, however, develop-
mental evidence according to which a separate origin of the two parasphenoidal
units can be assumed (L
EBEDKINA
1979; S
CHOCH
1992).
The basal plate forms a well-ossified block in which the pterygoids and exoccipi-
tals meet; it therefore constitutes the main integrating unit in the posterior palate.
The resistance against forces from the quadrate and occipital condyles is certainly as
important as the tight contact to the floor of the braincase cartilages and bones. As
in basal tetrapods in general, the parasphenoid is almost the exclusive bearer of the
endocranium. Also primitive for tetrapods is a basicranial articulation of which the
basal plate forms part (R
OMER
1947; W
ATSON
1962; B
EAUMONT
1977; P
ANCHEN
1980; J
ARVIK
1996). In the plesiomorphic state there is no suture, but instead an elab-
orate joint between pterygoid and parasphenoid. This condition is found in plesio-
morphic temnospondyls like Edops and Trimerorhachis (R
OMER
& W
ITTER
1942;
W
ATSON
1956), and may even be present in advanced forms such as Platyoposaurus
(K
ONZHUKOVA
1955). Capitosaurs instead are characterised by a completely flattend
basal plate which contacts the pterygoids along extended sutures. In large genera like
Mastodonsaurus or Cyclotosaurus this suture is extremely long and the morphology
of the palatal elements strongly altered with respect to other capitosaurs. R
OMER
(1947), amongst numerous others, stressed this and took the morphology of the bas-
icranial region as main guide in his phylogenetic reasoning. Others (O
CHEV
1966;
S
HISHKIN
1980) on the contrary emphasised this region because they believed it be
subject to manifold convergences. Any of these ways, the basal plate is a predomi-
nant structure that merits special attention. Its dorsal surface is, after the study of the
braincase itself, most significant for the reconstruction of the position of endocrani-
al elements.
Mastodonsaurus giganteus possesses a particularly extended basal plate which has
elongated and very tightly fitting, partially co-ossified sutures with the pterygoids
(fig. 13). These sutures run posterolaterally, giving the basal plate a roughly trape-
zoidal outline. In the posterior fourth of its length, the basal plate extends laterally
to give an extended contact to the exoccipital. The pterygoid instead has only a short
suture with the latter. There are clear differences to Cyclotosaurus or Eocyclotosau-
rus which have superficially similar, elongated basal plates. These genera lack the de-
scribed posterolateral extension of the basal plate and instead the pterygoid contacts
the exoccipital there by means of a pronounced posterior process.
The ventral surface of the basal plate is entirely smooth and forms a marked lon-
gitudinal bowl that continues for a short distance onto the base of the cultriform
process. Such a depression is present in all capitosaurs, but is more clearly estab-
lished in plesiomorphic forms such as Parotosuchus orenburgensis. The continuation
of the depression onto the basal plate is instead confined to large genera such as Cy-
clotosaurus and Mastodonsaurus, among the advanced capitosaurs. The narrow ante-
riormost portion of the basal plate continues gradually into the base of the cultri-
schoch, mastodonsaurus giganteus 49
form process, its lateral margins curving faintly. The suture with the pterygoid con-
stitutes a plane that slopes weakly in lateral direction. The surface of this plane is
roughened, with numerous small interfingering processes alternating from both
sides. The large area and structure of this suture suggests a tight fitting, the result is
an entirely akinetic basicranial region. Along the posterior margin the basal plate is
firmly connected to the exoccipitals; its medialmost part slightly projects behind the
level of this suture and separates the exoccipitals. Such a posterior portion is usually
covered by paired ‘muscular pockets’ (W
ATSON
1962) supposed to form origin sites
for hypaxial musculature. In Mastodonsaurus these fossae are very variable in size,
position, and expression. In any case they are not as predominant as in most other
capitosaurs, and especially their length is minimal as compared to Parotosuchus, Ly-
dekkerina, and Rhinesuchus (S
CHROEDER
1913; B
ROILI
& S
CHRÖDER
1937a, b; W
AT
-
SON
1962). A definite crista muscularis, that is a sharp-cut transverse edge bordering
the posterior sunk area (termed by B
YSTROW
& E
FREMOV
1940) is not throughout
present.
The dorsal side of the basal plate has a rugose surface and is attached to several os-
sified units of the endocranium (fig. 18). These are, from anterior backwards, (1) the
laterosphenoid portion, (2) the basisphenoid region, (3) the otics, (4) the exoccipi-
tals, and (5) the basioccipital ossification. All of these leave well-defined attachment
areas, between which the surface is markedly smoother. The basal plate itself bears a
complex system of crests and depressions, which are from posterior to anterior: (a)
the medial crista basioccipitalis, (b) the paired cristae paroccipitales, (c) the paired
cristae parapterygoideae, and (d) the paired cristae laterosphenoidales at the base of
the cultriform process. Cristae paroccipitales and parapterygoideae converge to-
wards a common point where they form a slightly raised point. This point is almost
exactly at midlength of the basal plate in Mastodonsaurus.
The well-ossified laterosphenoid region of the braincase is tightly set in the region
between the cristae laterosphenoidales, as transverse section revealed. The crests be-
come higher but thin anteriorly, keeping their width roughly. Anteriorly they bear
the sphenethmoid proper, which is not separable from the laterosphenoid ossifica-
tion. The unpaired laterosphenoid unit is easily distinguished from its ventral sup-
portings by the finer structure, the lighter colour, and the larger extent of compac-
tion. This portion of the basal plate is fairly smooth and was probably not directly
covered by cartilage. There are two pairs of foramina situated lateral to the cristae
laterosphenoidales. B
YSTROW
& E
FREMOV
(1940: fig. 10) homologised these forami-
na as palatine ramus (the outer) and internal carotid ramus proper (the inner) of the
carotid artery. The single entrance foramen was supposed to be at the posterolateral
corner of the basal plate, anterior to the suture with the exoccipital. S
HISHKIN
(1968)
and B
OY
(1988) agreed with this concept by homologizing similar foramina in other
eryopoid species. In Mastodonsaurus the position of the exit foramina is very simi-
lar to that in Benthosuchus sushkini, whereas the proper entrance foramen is more
difficult to localise, and perhaps may be variable in position. The basal plate of Mas-
todonsaurus differs from that of plesiomorphic capitosaurs by its anterior extension
particularly. This is most evident by the relative position of markers, such as (1) the
crista parapterygoidea, (2) the conical recess, and (3) the internal carotid foramen.
Whereas in Benthosuchus, Wetlugasaurus, Parotosuchus, and Kupferzellia they are
arranged sagittally very close to each other, in Wellesaurus and particularly Masto-
donsaurus there is a long distance between the former two and the lattermost of
50 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
these points. The epipterygoid, basisphenoid, and laterosphenoid regions are conse-
quently longer. The floor of the laterosphenoid region (the dorsum sellae region)
ends medial to the attachment of the basisphenoid. Whereas the former is an entire-
ly unpaired element, the latter is separated partially by it and its attachment areas on
the basal plate are far distanced. These areas are roughly triangular, and have about
2/3 the extension of the epipterygoid cross-section at this level. The epipterygoid
does only have a very narrow attachment site on the basal plate, otherwise expand-
ing on top of the basipterygoid ramus of the pterygoid exclusively. Medial to the
epipterygoid, and slightly posterolateral to the basisphenoid, there is a short crest
which attaches to the otic ossification (the crista basipterygoidea of the otic). Thus
the epipterygoid, otic, and sphenethmoid-laterosphenoid ossifications are closely
packed in this region; whether this situation is unique for Mastodonsaurus or simply
an expanded yet topographically otherwise primitive state is yet to be elucidated.
The floor of the auditory capsule was apparently entirely cartilaginous and at-
tached only at certain points to the basal plate. Such a contact is evident from rough
markers on the bottom of a depression bordered by the parapterygoid crest, the
epipterygoid, and the basisphenoid. This bowl-shaped depression is exactly medial
to the conical recess, forming the apex of the floor of the auditory capsule. The par-
apterygoid crests are almost straight transverse, such as in Kupferzellia and
Wellesaurus, but unlike in Benthosuchus. In Mastodonsaurus they meet in the mid-
line where they form a slightly elevated medial crest, into which the paroccipital
crests converge, as well. The cristae parapterygoideae have a rather complex surface:
strictly speaking they bifurcate laterally by splitting into an anterior and posterior
portion. The anterior part runs strictly transverse and continues into the gradually
widening base of the epipterygoid. That means that parasphenoid and pterygoid are
indeed co-ossified in this region. The posterior part runs slightly posterolateral,
forming the posterior wall of the chamber of the stapes. Anterior and posterior parts
of the crest are separated by a laterally widening groove, out of which a prominent
boss rises close to the point of bifurcation. This is the site to which the ventral pro-
cess of the stapes is attached, as cross-section clearly shows. The crista paroccipital-
is rises from the posterior portion of the crista parapterygoidea. It widens postero-
laterally to give a large suture for the attachment of the subtympanic process of the
exoccipital.
The posterior part of the basal plate is demarcated by the prominent, anteromedi-
ally curved cristae paroccipitales which together outline a semicircle. The height of
these crests increases posterolaterally, where they form stout attachment areas for
the otics and exoccipitals. Inside this semicircle the surface of the plate forms a de-
pression (fossa basioccipitalis of B
YSTROW
& E
FREMOV
1940) which is sagittally
elongate and ends bluntly at the transverse posterior margin. In Mastodonsaurus this
bowl is partially subdivided by a crest that originates at the midpoint of the posteri-
or margin (where it is highest) and runs about half the length of the bowl, continu-
ally shallowing towards there. The entire surface of these crests and the bowl con-
tains grooves and ridges which converge towards the apex of the semicircle formed
by the paroccipital crests. Well-preserved specimens suggest that the entire surface
of the fossa basioccipitalis was covered by cartilage. The ossification of this cartilage
follows a pattern already known from other capitosaur genera (e.g. Eryosuchus tver-
dochlebovi, O
CHEV
1972). According to the topography of this cartilage a homolog-
ization with the basioccipital is rather straightforward (S
AWI N
1941). The first por-
schoch, mastodonsaurus giganteus 51
tions to ossify are the regions lateral to the crista basioccipitalis, and they may even-
tually attach to the submedullar processes of the exoccipitals. Only in some speci-
mens the extent of ossification is larger, comprising a large part of the fossa basioc-
ciptalis. Characteristically, ossification of this region is recognised as a fine cover by
a granular substance which easily disintegrates. Only the paired anlagen lateral to the
crista basioccipitalis reach a bodily structure, rising markedly above the surface of
the bowl. These paired anlagen are very similar in shape and position to the lateral
portions of the basioccipital in Eryops (S
AWI N
1941: pl. 7, fig. B).
The cultriform process comprises more than 2/3 the length of the skull. It forms
the largest part of the medial border of the interpterygoid vacuities. The spheneth-
moid element, which is variable in its extent of ossification, is completely floored by
the cultriform process. This contact is established by the cristae sphenethmoidales
which are outgrowths of the dorsolateral margins of the element. The sphenethmoid
is set in the space delimited by these cristae, and its side walls connect to these almost
without a visible suture.
Ventrally, the cultriform process bears a ridge which rises from the converging lat-
eral margins at about the posterior third of the length of the orbits, and persists up
to the level of their anterior end. The height and surface structure of this ridge is var-
iable, it is however clearly different from the sagittal crests present in various other
capitosaurs (Thoosuchus, Parotosuchus oreburgensis, Eocyclotosaurus, Cyclotosau-
rus). Rather it resembles the more cylindrical rod-like cultriform process typical of
Parotosuchus nasutus (S
CHROEDER
1913). The base of the process is ventrally mark-
edly depressed. Instead, the anterior third of the element is slightly convex posteri-
orly and gradually becomes concave, as the process is framed laterally by the vom-
ers. The transverse cross-section of the element is U-shaped posteriorly, V-shaped
about at midlength, and finally transversely oval to flat in the anterior third.
Palatine
The interpterygoid vacuities are laterally framed and separated from the marginal
tooth arcades by the palatine and ectopterygoid. In Mastodonsaurus these bones are
comparatively slender and thin (fig. 13). Posteriorly the palatine tooth row is separ-
ated from the vacuity by only a narrow stripe of planar and smooth bone. There the
interpterygoid vacuities reach their widest measure. The palatine is an intercalated
strut which (1) connects the vomer posterolaterally to the skull margin, (2) borders
the choana posteriorly, (3) bears a pair of prominent tusks, and (4) forms part in the
supporting of the continuous inner tooth arcade. It connects to four bones: to the
maxilla laterally, the vomer anteromedially, the pterygoid posteromedially, and the
ectopterygoid posteriorly. Among those the contact to the pterygoid is typical of ca-
pitosaurs, in which the palatine ramus of the pterygoid is reduced anteriorly. The
proper contact is established by means of an elongated and slender posteromedial
process of the palatine; the ectopterygoid is thereby completely excluded from the
bordering of the interpterygoid vacuities.
The palatine tooth arcade altogether comprises in between 25 and 30 teeth of dif-
ferent size. Basically three regions can be arbitrarily distinguished (from posterior
forewards): (1) a posterior row of 20–25 similar-sized and equidistant, (2) a pair of
large tusks, and (3) three to six tiny teeth of the parachoanal tooth row. The teeth of
the first and third groups are set in almost without a clear base, but instead rise di-
52 stuttgarter beiträge zur naturkunde Ser. B, Nr. 278
rectly from the flat plane of the ventral surface. Only the lateral and medial margins
of the tooth sockets are slightly raised above this surface. The latter is otherwise en-
tirely smooth. The medial margin of the palatine is in its middle part rounded but
otherwise forms a rather thin sheet of bone. The anteriormost tooth pair is very
large, forming the posteriormost of the palatal tusk pairs. It is situated well posteri-
or to the choana palatalis, whose posterior part is formed entirely by the palatine.
Medial to the tusk pair the palatine is very wide, forming almost the complete an-
terior rim of the interpterygoid vacuities by means of a medial protuberance which
is sutured to the vomer in serrated fashion. The anteriormost part of the interptery-
goid vacuity is very narrow because of the broadening of the palatine in this region
which is at the level of the posterior tusk. The suture with the maxilla runs antero-
medially, at about midlength of the choana palatalis towards which it converges.
Dorsally the palatine contacts the lacrimal by a posteriorly directed spine which it
meets in a horizontal, flat suture, a contact which was first observed and named in
Benthosuchus sushkini (B
YSTROW
& E
FREMOV
1940).
Ectopterygoid
This element is almost of the same length as the palatine, but clearly forms the
larger part of the continuous tooth arcade borne by these bones. The ectopterygoid
contacts the maxilla laterally, the palatine anteriorly, the pterygoid posterolaterally,
and the jugal posterodorsally (fig. 13). It is excluded from the rim of the subtempo-
ral window by a large ventral process of the jugal. The ectopterygoid is along most
of its length equally wide, throughout being narrower than the palatine. It bears in
between 39 and 43 teeth of similar size and morphology. The tooth sockets are char-
acteristically laterally expanded and sagittally compressed.
The ectopterygoid is among the palatal elements the thinnest and least stabilised
bone, basically it forms a sheet which largely overgrows other, more firmly integrat-
ed components of the palate and skull roof. The suture with the pterygoid is long
and slightly serrate. The anterior half of the element overlaps the pterygoid, which is
reversed posteriorly. The ectopterygoid itself overlaps the ventral process of the ju-
gal extensively, leaving only a small triangular area of the latter exposed ventrally (in-
sula jugalis). Most of the dorsal side of the ectopterygoid is, moreover, attached to
the medial margin of the fissura maxillaris of the jugal. The suture with the maxilla is
the longest contact and along the entire length the maxilla provides the underlapping
base for the ectopterygoid. The furrow separating the ectopterygoid and maxillary
tooth rows is entirely made up by the maxilla.
Pterygoid
In the primitive condition of the Tetrapoda the pterygoid (= entopterygoid + der-
mometapterygoid?) is a tooth-bearing element among others (ectopterygoid, pala-
tine, vomer) which serves both the purposes of stabilisation and mobility (basicrani-
al articulation). In capitosaurs the pterygoid has lost both the tooth arcades and the
movable basipterygoid joint. Instead, it appears to predominantly guarantee maxi-
mum stability there. It has lost contact to the vomer entirely and the suture with the
palatine is largely modified with respect to the plesiomorphic condition: only the
posteriormost part of the palatine is reached. As a result of this anterior reduction,
the interpterygoid vacuities are very large in capitosaurs.
schoch, mastodonsaurus giganteus 53
By its architecture the pterygoid is basically a four-rayed strut which connects the
upper jaws with the quadrate condyles, the cheek region, the occipital condyles, and
the floor of the braincase (fig. 13). It therewith contacts all major ossified units of the
posterior skull. These four rays are (from anterior backwards, in clockwise rota-
tion): (1) the palatine ramus, (2) the basipterygoid ramus, (3) the quadrate ramus, and
(4) the lamina ascendens, which actually is a dorsal, sheet-like prolongation of the
latter (fig. 17).
The largest and most strengthened ramus is the palatine branch that connects the
basal plate with the palatine, jugal, and ectopterygoid. It is stout and markedly wid-
ened in Mastodonsaurus (figs. 8, 13), by its extent differing from all other capito-
saurs, even the closely related Heptasaurus. The column of the palatine ramus is
formed by a broad, cylindrical rod which runs parasagittally, close to the medial
margin of this unit. This rod continues anteriorly, by slightly bending into a more
lateral direction, to form the margin of the interpterygoid vacuities. Posteriorly the
column reaches towards the base of the quadrate branch near to the suture with the
basal plate. The lateral parts of the palatine process form a flat yet well-ossified sheet
which is covered by only minor striations. Anterolaterally, the branch becomes
markedly wider, which culminates in a small posterolateral lappet, until the process
bends medially again to align with the anterior embayment of the subtemporal win-
dow.
The basipterygoid branch is – even compared to the state found in most capito-
saurs – relatively short. It is plesiomorphically the bearer of the basicranial articu-
lation, but in capitosaurs connects by means of a long suture to the basal plate. On
the dorsal side the basipterygoid branch bears the large attachment facet for the
epipterygoid footplate. It rises anterior to a rounded hollow, the conical recess. In
most other capitosaurs the epipterygoid facet is restricted to the region anterior to
this recess. In Mastodonsaurus and Eryosuchus, however, the attachment area is
greatly expanded (S
CHOCH
1997a) and even extends lateral to the conical recess,
connecting to the base of the lamina ascendens. Medial to the base of the epiptery-
goid a narrow bony sheet is borne which connects the pterygoid to the otic. The
suture with the basal plate is an almost horizontal plane, with the basal plate over-
lapping the pterygoid ventrally. The quadrate ramus is relatively short but stout in
Mastodonsaurus, by which this form is again similar to Eryosuchus and Cyclotosau-
rus. It connects the quadrate trochlea with both the exoccipital and basal plate. Un-
like in plesiomorphic capitosaurs such as Wetlugasaurus and Rhinesuchus it is
oriented nearly transversely. Typically the quadrate ramus forms a curved bony
sheet that slopes posterodorsally where it forms a marked edge, then bending ante-
rodorsally to contact the quadrate and quadratojugal in the occiput. The suture
with the quadrate is large and apparently very tight. The surface of this suture is
curved concavely, and the contact is tightened by the already described complex al-
ternate indentation.
The lamina ascendens is an extended dorsal outgrowth of the quadrate ramus.</