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Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs. The derived genera Dakosaurus and Geosaurus exhibit a macroevolutionary trend towards extreme hypercarnivory, underpinned by a diverse array of craniodental adaptations, including denticulate serrated (ziphodont) dentition. A comparative analysis of serrations in Metriorhynchidae shows that known Dakosaurus species had conspicuous denticles, in contrast to the microscopic denticles of Geosaurus. A new tooth from the Nusplingen Plattenkalk of Germany provides evidence for a previously unknown large species of Geosaurus. Metriorhynchid specimens from the upper Kimmeridgian–lower Tithonian of Southern Germany show that ziphodont species of Dakosaurus and Geosaurus co-occurred in the Nusplingen and Solnhofen Seas. Although these genera are similarly denticulate, they diverge in overall crown morphology. Therefore, resource/niche partitioning via craniodental differentiation is posited as maintaining two contemporaneous genera of highly predatory metriorhynchids. Additionally, the new generic name Torvoneustes is proposed for “Geosaurus” carpenteri, the only known metriorhynchid with false-ziphodont dentition. A cladistic analysis shows that ziphodont dentition may have evolved independently in Dakosaurus and Geosaurus, or been acquired earlier by their common ancestor and secondarily lost in Torvoneustes and related taxa.
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The evolution of extreme hypercarnivory in Metriorhynchidae
(Mesoeucrocodylia: Thalattosuchia) based on evidence from microscopic
denticle morphology
MARCO BRANDALISE DE ANDRADE
a
; MARK T. YOUNG
ab
; JULIA B. DESOJO
c
; STEPHEN L.
BRUSATTE
de
a
Department of Earth Sciences, Faculty of Sciences, University of Bristol, Bristol, England, United
Kingdom
b
Department of Palaeontology, Natural History Museum, London, United Kingdom
c
Museo
Argentino de Ciencias Naturales 'Bernardino Rivadavia', Buenos Aires, Argentina
d
Division of
Paleontology, American Museum of Natural History, New York, New York, U.S.A.
e
Department of
Earth and Environmental Sciences, Columbia University, New York, New York, U.S.A.
Online publication date: 15 September 2010
To cite this Article DE ANDRADE, MARCO BRANDALISE , YOUNG, MARK T. , DESOJO, JULIA B. and BRUSATTE,
STEPHEN L.(2010) 'The evolution of extreme hypercarnivory in Metriorhynchidae (Mesoeucrocodylia: Thalattosuchia)
based on evidence from microscopic denticle morphology', Journal of Vertebrate Paleontology, 30: 5, 1451 — 1465
To link to this Article: DOI: 10.1080/02724634.2010.501442
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Journal of Vertebrate Paleontology 30(5):1451–1465, September 2010
© 2010 by the Society of Vertebrate Paleontology
ARTICLE
THE EVOLUTION OF EXTREME HYPERCARNIVORY IN METRIORHYNCHIDAE
(MESOEUCROCODYLIA: THALATTOSUCHIA) BASED ON EVIDENCE FROM MICROSCOPIC
DENTICLE MORPHOLOGY
MARCO BRANDALISE DE ANDRADE,
*,1
MARK T. YOUNG,
1,2
JULIA B. DESOJO,
3
and STEPHEN L. BRUSATTE
4,5
1
Department of Earth Sciences, Faculty of Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, England,
BS8 1RJ, United Kingdom, marcobranda@yahoo.com.br; Marco.B.Andrade@bristol.ac.uk;
2
Department of Palaeontology, Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom,
zoologika@gmail.com;
3
Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia,’ Angel Gallardo 470, C1405DRJ, Buenos Aires, Argentina,
CONICET, julideso@macn.gov.ar;
4
Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024,
U.S.A., sbrusatte@amnh.org;
5
Department of Earth and Environmental Sciences, Columbia University, New York, New York 10025, U.S.A.
ABSTRACT—Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs. The derived genera
Dakosaurus and Geosaurus exhibit a macroevolutionary trend towards extreme hypercarnivory, underpinned by a diverse
array of craniodental adaptations, including denticulate serrated (ziphodont) dentition. A comparative analysis of serrations
in Metriorhynchidae shows that known Dakosaurus species had conspicuous denticles, in contrast to the microscopic denti-
cles of Geosaurus. A new tooth from the Nusplingen Plattenkalk of Germany provides evidence for a previously unknown
large species of Geosaurus. Metriorhynchid specimens from the upper Kimmeridgian–lower Tithonian of Southern Germany
show that ziphodont species of Dakosaurus and Geosaurus co-occurred in the Nusplingen and Solnhofen Seas. Although
these genera are similarly denticulate, they diverge in overall crown morphology. Therefore, resource/niche partitioning via
craniodental differentiation is posited as maintaining two contemporaneous genera of highly predatory metriorhynchids. Ad-
ditionally, the new generic name Torvoneustes is proposed for Geosaurus carpenteri, the only known metriorhynchid with
false-ziphodont dentition. A cladistic analysis shows that ziphodont dentition may have evolved independently in Dakosaurus
and Geosaurus, or been acquired earlier by their common ancestor and secondarily lost in Torvoneustes and related taxa.
INTRODUCTION
During the Mesozoic numerous clades of reptiles secondar-
ily returned to the oceans and evolved a fully pelagic lifestyle.
One such clade is the Metriorhynchidae, a peculiar group of
extinct marine crocodylians that lived from the Middle Juras-
sic to the Early Cretaceous (171–136 Ma). Although metri-
orhynchids were some of the first fossil reptiles to be discov-
ered, investigation of large-scale evolutionary patterns within the
group began only recently (see Young et al., 2010; also Pierce
et al. 2009a, 2009b). Metriorhynchids, particularly Geosaurus and
Dakosaurus, are recognized as fierce pelagic predators (e.g., Gas-
parini et al., 2006; Young and Andrade, 2009), and the only ma-
rine crocodylomorphs to possess true ziphodont (i.e., serrated)
teeth. This morphology, also present in other crurotarsans and
theropods dinosaurs, offers important biologic and phylogenetic
signals, because it can be functionally related to food selec-
tion/acquisition and diet.
Here we use several lines of evidence to study the evolution
of extreme strategies of carnivory within metriorhynchids. We
describe a distinctive new metriorhynchid tooth from the Late
Jurassic of Germany, and use this specimen as a springboard
for detailed description and comparison of metriorhynchid denti-
tions. We focus on microscopic features of metriorhynchid teeth,
having analyzed several specimens with scanning electron mi-
*
Corresponding author.
croscopy (SEM). This allows for careful description of the size
and form of denticles among different taxa, and the identification
of possible subtle differences between taxa that are often lumped
together as ‘ziphodont.’ With detailed information on tooth and
denticle morphology available, a more integrated comprehension
of high-order predation in marine crocodylomorphs is possible.
In particular, we use this new information to explore (a) preva-
lence of ziphodonty in metriorhynchids; (b) whether ziphodonty
evolved multiple times in the group; (c) the stratigraphic distri-
bution of ziphodont forms; and (d) possible ecological niche par-
titioning in co-existing, hyperpredatory metriorhynchid taxa due
to different tooth morphologies.
Institutional AbbreviationsBMM,B
¨
urgermeister-M
¨
uller-
Museum, Solnhofen, Germany; BRSMG, Bristol City Mu-
seum and Art Gallery, Bristol, England; BSPG, Bayerische
Staatssammlung f
¨
ur Pal
¨
aontologie und Geologie, M
¨
unchen,
Germany; JME, Jura Museum, Eichst
¨
att, Germany; MOZ,
Museo “Professor J. Olsacher”, Zapala Argentina; NHM, Nat-
ural History Museum, London, England; SMNS, Staatliches Mu-
seum f
¨
ur Naturkunde Stuttgart, Germany.
Metriorhynchids and Ziphodonty in Context
Metriorhynchids arguably represent the greatest divergence
from the ‘classic’ crocodylian bauplan (taxonomy sensu Mar-
tin and Benton, 2008), and exhibit greater marine specializa-
tions than any other archosaur clade. Such adaptations in-
clude hydrofoil-like forelimbs, a hypocercal tail, and loss of
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1452 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
osteoderm cover (e.g., Fraas, 1902; Young et al., 2010). As in
most semi-aquatic/aquatic crocodylians, the majority of metri-
orhynchids were mainly piscivorous (e.g., Massare, 1987; An-
drade and Young, 2008; Young and Andrade, 2009; Pierce et al.,
2009b). In these taxa, teeth are essentially conical and lack
any type of carinae or keel, although the enamel surface may
be intensely ornamented (e.g., Cricosaurus). However, in both
Geosaurus and Dakosaurus (Geosaurinae), tooth crowns are
ziphodont, a condition that contrasts with all other thalattosuchi-
ans, as well as most other pelagic predators (e.g., Gasparini et al.,
2006; Pol and Gasparini, 2009; Young and Andrade, 2009).
Ziphodont (or true-ziphodont) dentitions—defined as denti-
tions where all teeth possess denticulated carinae, comprised
of true denticles (see Langston, 1975; Prasad and Broin, 2002;
Andrade and Bertini, 2008a)—are fairly common in terrestrial
crocodylian groups (e.g., Baurusuchidae, Sebecia, Pristichamp-
sidae). They provide important clues on ecology, because they
can be readily linked to diet and feeding behavior. The ser-
rated carinae are related to more efficient processing of me-
chanically hard prey items, by acting as cutting edges that re-
duce the energy required to propagate cracks in hard food
(Purslow, 1991; Freeman and Weins, 1997; Evans and Sanson,
1998). Teeth with denticulate carinae (true-ziphodonty) facili-
tate slicing and cutting (Frazzetta, 1988; Abler, 1992). Further-
more, Abler (1992) demonstrated that, at least for the preda-
tory dinosaur Tyrannosaurus, denticles aided puncture and grip.
Overall, teeth equipped with denticulated carinae require less
energy to penetrate food, making larger and tougher organisms
more energetically feasible prey items, expanding the range of
potential prey in a particular environment. Ziphodonty there-
fore represents an evident adaptation to high-order carnivory, al-
lowing equipped taxa to maximize their efficiency as predators.
Therefore, it is not surprising to recognize that many high-order
carnivores possess denticulated carinae (e.g., Massare, 1987).
Among marine tetrapods, serrated carinae was only reported
for mosasaurs and a few ichthyosaurs (Temnodontosaurus, Lep-
topterygius), although it remains unclear if these structures are
composed of keels (false-ziphodonty) or true denticles.
Terrestrial crocodylians are generally believed to have evolved
the ziphodont condition many times (e.g., Langston, 1975; Prasad
and Broin, 2002), but less is known about the development of
serrated teeth in marine forms. Currently, teeth with denticu-
lated carinae have been reported for three species of Geosaurus
(Tithonian–early Valanginian) and two species of Dakosaurus
(late Kimmeridgian–early Berriasian). These include Geosaurus
giganteus (Von S
¨
ommerring, 1816), G. grandis (Wagner, 1852),
G. lapparenti (Debelmas and Strannoloubsky, 1957), Dakosaurus
maximus (Plieninger, 1846), and D. andiniensis Vignaud and Gas-
parini, 1996, (see Gasparini et al., 2006; Pol and Gasparini, 2009;
Young and Andrade, 2009). The new German tooth described
here (SMNS 81834), preliminarily placed in Geosaurus by Young
and Andrade (2009), also possess finely serrated ziphodont cari-
nae. Further examples include other isolated teeth (e.g., NHM
R.486, NHM 47989), currently assigned to Dakosaurus (Table 1).
The rise of ziphodont metriorhynchids represented a major
event in the evolutionary history of the group, and provides valu-
able clues on the rise of high-order carnivory within archosaurs
and in marine ecosystems. Unfortunately, the form, distribution,
and evolution of dental characters associated with high-order car-
nivory in metriorhynchids have only been explored in a cursory
manner (Gasparini et al., 2006; Pol and Gasparini, 2009; Young
and Andrade, 2009; Young et al., 2010).
MATERIALS AND METHODS
A number of specimens were analyzed by means of scanning
electron microscopy (SEM), producing either secondary electron
TABLE 1. Stratigraphy of metriorhynchids from the upper Kimmeridgian–lower Tithonian of southern Germany.
German zone Formation Ammonite zone Localities
Taxa (using the revised taxonomy of Young
and Andrade, 2009)
Malm Zeta 3 M
¨
ornsheim
Formation
Uppermost
hybonotum-zone
Daiting Cricosaurus elegans
a
(BSPG AS I 504)
Rhacheosaurus gracilis (Lost holotype, lost holotype of C.
medius)
Geosaurus giganteus
b
(NHM R.1229, NHM R.1230)
Geosaurus grandis
2
(BSPG AS I VI 1)
Malm Zeta 2b Solnhofen
Formation
Upper
hybonotum-zone
Solnhofen Cricosaurus elegans
a
(NHM 43005)
Geosaurus giganteus
b
(NHM 37016–37020)
Lower
hybonotum-zone
Eichst
¨
att Rhacheosaurus gracilis (NHM R.3948)
Cricosaurus elegans
a
(NHM 37006)
Schernfeld Dakosaurus maximus (JME-SOS4577, JME-SOS2535)
Zandt Rhacheosaurus gracilis (Broili, 1932)
Malm Zeta 1 Painten Formation beckeri-zone,
ulmense-subzone
Painten Cricosaurus sp. (BMM uncategorized)
Mergelst
¨
atten
Formation
beckeri-zone,
ulmense-subzone
Schnaitheim Dakosaurus maximus (Lost holotype, NHM 33186, NHM
35766, NHM 35835–7)
Cf. Geosaurus (SMNS 51494)
Staufen Dakosaurus maximus (SMNS 8203)
Nusplingen
Plattenkalk
beckeri-zone,
ulmense-subzone
Nusplingen Dakosaurus maximus (SMNS 81793)
Cricosaurus suevicus
a
(SMNS 3808, SMNS 90513)
Geosaurus sp.
b
(SMNS 81834)
R
¨
ogling Formation beckeri-zone,
setatum-subzone
Schamhaupten Dakosaurus maximus (JME uncategorized—M.
K
¨
olbl-Ebert, pers. comm., 2008)
For data on the geological subdivision of southern Germany see F
¨
ursich et al. (2007) and Schweigert and Garassino (2003) and references therein.
Malm Zeta 1 is the uppermost Kimmeridgian, whereas Malm Zeta 2–3 are the lowermost Tithonian. Type specimens in bold.
a
There is a potential synonymy between Cricosaurus elegans and C. suevicus. Note that currently all specimens attributed to C. suevicus are restricted
to Malm Zeta 1, whereas those of C. elegans are known from Malm Zeta 2–3.
b
There is a potential synonymy between Geosaurus giganteus and G. grandis. Geosaurus grandis is known from only the M
¨
ornsheim Formation,
whereas G. giganteus is known from Malm Zeta 2–3. The Nusplingen species, which is a posterior maxillary tooth, is very similar in form (but bigger)
to Geosaurus specimens in Malm Zeta 2–3.
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1453
FIGURE 1. Dentition in Geosaurus giganteus, as seen in NHM R.1229, type specimen. A, General aspect of skull. BC, Detail of teeth at mid-
dentition, at the right side, showing the occlusion pattern and general crown morphology. D, Oblique view of crowns at the right side, where it is
possible to note the facets and carinae. E, Oblique close up of teeth at the left side, where serrations in the carinae are barely perceptible. F,Life
reconstruction of Geosaurus. Solid bar equals 10 mm. Life reconstruction in F by Dmitry Bogdanov.
(SE-SEM) or backscatter electron (BSE) images, as well as com-
mon optical microscopic techniques. All SEM analyses were con-
ducted at the Electron Microbeam Facility (University of Bris-
tol), under the advice of S. Kearns.
The use of SE-SEM provides images of better quality, but
require gold-coating the specimen, whereas BSE-SEM avoids
such damage to the fossil. As a result, BSE-SEM was applied to
the majority of the specimens, whereas an isolated tooth from
Geosaurus grandis was analyzed through SE-SEM. The dentition
of Geosaurus giganteus, solely represented by in situ teeth in the
two known skulls (NHM R.1229 and NHM 37020), could only
be imaged by light microscopy, and were registered by means of
macrophotography (Fig. 1).
The new tooth, SMNS 81834 (Fig. 2), is a critical specimen
due to is fine preservation and size. It is part of a larger sample
of teeth collected by G. Schweigert during an SMNS excavation
(May 9, 2000) in the Hoelderi Horizon (uppermost Kimmerid-
gian) of the Nusplingen Plattenkalk, Southwestern Germany.
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1454 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
TABLE 2. Measurements (minimum/maximum) for selected teeth of Dakosaurus and Geosaurus,asplottedinFigure7.
Denticle measurements
Denticle density Denticle size
Species Length Height Width (denticles/5 mm) difference index Type
Dakosaurus maximus
(NHM 35766)
300/425 300/330 600/675 16/17 1.06 Macroziphodont
Dakosaurus andiniensis
(MOZ 6146P)
330/500 150/200 700/800 9.5/13 Macroziphodont
Dakosaurus indet.
(NHM R.486)
100/160 200/270 24.9/28.5 1.14 Microziphodont
Geosaurus grandis
(BSPG AS-VI-1)
150/270 150/165 210/270 28.1 1.00 Microziphodont
Geosaurus indet.
(SMNS 81834)
100/200 100/135 200/320 33.3/41.7 1.25 Microziphodont
Batrachotomus kupferzellensis
(SMNS 91050)
240/345 210/450 490/700 20.8/21.4 1.03 Macroziphodont
Erythrosuchus africanus
(NHM R.3592)
334/449 862/987 11.6 Macroziphodont
Nicrosaurus kapffi
(NHM 38068)
231/435 430/693 295/374 14.1/18.6 1.32 Macroziphodont
Phytosaurus sp.
(NHM R.5950)
332/457 669/902 492/701 11.9/12.3 1.03 Macroziphodont
Note that various non-metriorhynchid taxa, with typical true ziphodont teeth, are used for comparison. Microziphodont dentition will typically have
carinae with denticles not exceeding 300 µm, in most or all its dimensions. Denticle density (denticles/5 mm) in selected ziphodont crocodylian tooth-
crowns (measurements taken at the middle of the crown). Denticle size difference index is the ratio of the number of denticles per given length unit
of the mesial and distal carina, taken from the same tooth. Data for D. andiniensis from Pol and Gasparini (2009). All measurements in µm. Type
specimens in bold.
This tooth displays a highly characteristic crown morphology
(e.g., ‘tri-faceted’ labial surface), which is otherwise only seen in
Geosaurus giganteus and G. grandis (see Young and Andrade,
2009). Other teeth from the same sample include SMNS 9808,
SMNS 51494, SMNS 80148, and SMNS 80480. These, however,
lack any macroscopic characteristics that can be used to relate
them to Geosaurus (see below), but also exhibit ziphodonty.
Because they are comparatively robust and weakly compressed,
they are preliminarily identified as cf. Dakosaurus, and otherwise
excluded from the present study.
Specimen SMNS 81834 and other isolated ziphodont metri-
orhynchid teeth were analyzed with the aid of scanning elec-
tron microscopy (SEM), including the following specimens: (1)
Geosaurus grandis (BSPG AS-VI-1 [Fig. 3]; Daiting, Germany;
lower Tithonian); (2) Dakosaurus maximus (NHM 35766 [Fig. 4];
Schnaitheim, Germany; upper Kimmeridgian); (3) Dakosaurus
indet. (NHM R.486 [Fig. 5]; Oxford, England; upper Callo-
vian to lower Oxfordian). Additionally, the false-ziphodont
Geosaurus carpenteri (BRSMG Ce17365 [Fig. 6]; Westbury,
England; upper Kimmeridgian) yielded a comparative view of
the tooth morphology of a non-ziphodont metriorhinchid. Fi-
nally, the Lower/Middle Triassic archosauriform Erythrosuchus,
upper Middle Triassic ziphodont ‘rauisuchian’ Batrachotomus,
and Late Triassic phytosaurs (Nicrosaurus and Phytosaurus)pro-
vided comparative data on terrestrial and semi-aquatic non-
crocodylian taxa (see Table 2).
In order to quantify denticle size, parameters such as length,
width, and height were measured (Table 2) from SEM images,
following Sankey et al. (2002). Microscopic images from carinae
(SEM) were mostly taken at mid-section, where denticles were
best defined and preserved. Due to the small number of speci-
mens and reduced sampling available, only maximum, minimum,
and median values were calculated. Height measurements of den-
ticles must be treated with particular caution, because (a) the
identification of the base of each denticle is subjective, due to
the gradual transition with the crown surface, presence of a keel
and proximity to other denticles; and (b) wear and/or breaks af-
fect height measurements with greater impact that the width or
length of the denticles (see Figs. 1–4). It must be noted that ex-
treme measurements were not necessarily taken from the same
denticle; therefore the denticle with the smallest length in a taxon
is not necessarily the same with the smallest height or width. For
the purposes of this study, the full range of size for each particu-
lar taxon is considered relevant to differentiate microscopic from
macroscopic serrations, not the average values. Serration den-
sity (sensu Farlow and Brinkman, 1987) was measured as close to
the mid-crown point on the carinae as possible (as recommended
by Farlow and Brinkman, 1987; Farlow et al., 1991; Smith et al.,
2005). The final denticle size metric used is denticle size differ-
ence index (DSDI sensu Rauhut and Werner, 1995). This metric
is the ratio of the number of denticles per given length unit of the
mesial and distal carinae. Total body length for metriorhynchids
either follows data known from specimens (e.g., Fraas, 1901) or
estimated length, as in Young (2009).
COMPARATIVE DESCRIPTION
The tooth SMNS 81834 is a well-preserved crown, with the
basal section of the root present (Fig. 2B). The crown itself is
relatively large in comparison to the teeth of most other thalat-
tosuchians (e.g., Pelagosaurus, Cricosaurus); it is 31.7 mm long
apicobasally and its base is 16.0 mm wide mesiodistally (longer
axis). Based on comparison to complete dentitions of G. gigan-
teus (NHM R.1229, NHM 37020) and G. grandis (BSPG AS-VI-
1), SMNS 81834 appears to be a posterior tooth of either the
maxillary or dentary series, and clearly is not a premaxillary or
an anterior dentary tooth. In G. giganteus, anterior teeth tend
to be slender (height/base = 2.77–2.33:1), whereas proportionally
lower crowns (height/base < 2:1) are located at the mid-posterior
region of the tooth row. SMNS 81834 has a height/base ratio of
1.98:1, consistent with our interpretation as a posterior tooth. In
absolute size, SMNS 81834 is larger than most crowns found in G.
giganteus (the largest crown is 35 by 16 mm, a dentary crown oc-
cluding against the premaxillary-maxillary notch of NHM 37020),
and certainly much larger than all crowns of posterior teeth. Al-
though it is difficult to produce a proper size estimate of the indi-
vidual to which SMNS 81834 belonged, it seems fair to consider
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1455
FIGURE 2. Geosaurus sp. SMNS 81834, from the Nusplingen Plattenkalk (upper Kimmeridgian), Late Jurassic of Germany, a single tri-faceted
crown exposed at the labial surface. A, General view of the specimen, with main structures and cross-section made evident in schematic drawing
(right). B, Oblique view of the crown, where the typical facets of German Geosaurus are evident. C, Low angle images of the crown, taken from the
base of the tooth, showing that enamel wrinkles that cross the crown from mesial to distal edges, forming bands. D, Macrophotograph of crown in
oblique (mesial?) view showing the carina, where denticles are barely perceptible. E, Microscopy images of the carina in different views, showing that
the serrations are composed by microscopic true denticles. F, Denticles in close view, where the presence of a keel is evident. White pointers indicate a
double denticle. Electron microscopy obtained through the use of backscatter secondary image (BSE). Note that it is not possible to establish whether
the carina analyzed is mesial or distal, because SMNS 81834 is partially embedded in matrix and only one carina is fully exposed. Solid bar in AD
equals 10 mm.
this animal approximately twice the size of the largest known
specimens of G. giganteus.
The tooth is strongly mediolaterally compressed, single cusped,
and the preserved section of the root is undivided. No constric-
tion is present at the crown/root junction, but the boundary is ev-
ident through color and texture, due to termination of enamel.
The crown is laminar and curved lingually. In labial view, the
crown widens constantly, assuming a triangular profile, some-
what reminiscent of Carcharodon teeth, rather than the teeth of
dinosaurs or other ziphodont crocodylians. On the labial face,
three facets (planar surfaces) on the crown surface are clearly
identifiable, progressing from base to apex. The central facet
is widest at the base of the crown, and wider than the lateral
facets; its mesiodistal width diminishes towards the apex and be-
comes more convex along the last quarter of its length. The lat-
eral facets are symmetrical and have the same width along the
entire crown. The entire lingual surface is slightly more convex
than the labial surface, due to the presence of facets on the later.
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1456 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
The apex is damaged: the outer layer of enamel and dentine
has been removed, but it is currently unclear if this is a fracture
resulting from predatory behavior or damage related to taphon-
omy or preparation.
The crown is serrated, but serrations are microscopic. As the
specimen is partially embedded in matrix, only one carina is ex-
posed. Unfortunately, as the position of this tooth in the den-
tal series is unknown, it is not possible to determine if the ca-
rina is mesial or distal. However, observation of Geosaurus teeth
suggests that there are no significant differences in the morphol-
ogy of mesial/distal carinae in the group (BSPG AS-VI-1, NHM
R.1229, and NHM 37020).
The exposed carina of SMNS 81834 differs markedly from
the false-ziphodont (sensu Prasad and Broin, 2002) dentition
of Geosaurus carpenteri (Fig. 6), in which serrations (but not
true denticles) are created on the surface of the carinal keel by
the conspicuous superficial ornamentation of enamel. In SMNS
81834, carinae are comprised of both denticles and a keel, as in
true ziphodont teeth (Andrade and Bertini, 2008a). Several true
denticles are present at the mesial and distal borders (6.66–8.35
denticles/mm), creating well-defined carinae. In comparison with
other ziphodont metriorhynchids, Geosaurus grandis (see Table
2) possesses a smaller number of denticles per unit length (5.62
denticles/mm), whereas species of Dakosaurus have even fewer
(1.9–3.4 denticles/mm). In SMNS 81834, the carinae extend from
the base to apex of the crown. Overall, denticles have a simi-
lar height (isometric), but shape varies substantially (poorly iso-
morphic). Furthermore, the size and shape of the interdenticular
spaces are also variable. In a few cases, denticles are positioned
extremely close together and are fused, creating larger ‘double’
denticles (Fig. 2), a condition fairly common in other ziphodont
crocodylians (e.g., Geosaurus grandis; Fig. 3). However, some of
the size differences observed in the denticles of SMNS 81834 can
be recognized as the result of wear or breaks. There are only cari-
nae on the mesial and distal edges of the tooth, with no split or
supernumerary carinae (sensu Beatty and Heckert, 2009), or ac-
cessory ridges.
The individual denticles of SMNS 81834 are small, with max-
imum measurements of 200 µm × 320 µm × 135 µm (length,
width, and height, respectively), with dimensions reasonably sim-
ilar to those of Geosaurus grandis (see Table 2). The ‘rauisuchian’
Batrachotomus, in comparison, has much larger denticles, as
do Kimmeridgian-Berriasian species of Dakosaurus (see Ta-
ble 2). However, the Oxfordian Dakosaurus indet. has a max-
imum denticle length (160 µm) and width (270 µm) similar to
the ones found in Geosaurus (height not sampled). The DSDI
for SMNS 81834 is 1.25, which is high, when compared to
other Kimmeridgian-Tithonian geosaurines (which have a DSDI
around 1.0; see Table 2). In all Geosaurus teeth, denticles never
reach 350 µm in width, and will typically have a length/height
below 250 µm. Therefore, SMNS 81834 is the largest Geosaurus
crown known to date, and is the only with denticle widths
marginally surpassing 300 µm. The profile of the denticles is
rounded in lingual view, but the serrations bear a sharp cutting
edge (the keel) on the distal and mesial margins (Fig. 2C). This
morphology is also observed in Geosaurus grandis (Fig. 3C–D),
Dakosaurus maximus (Fig. 4), Dakosaurus indet. (Fig. 5), and
Dakosaurus andiniensis (see Pol and Gasparini, 2009). The false-
ziphodont Geosaurus carpenteri also has a keel, but because
it lacks true denticles, its morphology can only be considered as
analogous (Fig. 6).
Although both the labial and lingual surfaces of the crown of
SMNS 81834 are smooth, faint ornamentation is present on both
surfaces, which is only visible under SEM. The ornamentation
is comprised of low hills and valleys, subcircular to elliptical in
shape, formed by low and poorly marked enamel foldings. Most
elongated foldings are apicobasal in orientation, and resemble
the enamel foldings present in G. grandis (Fig. 3) and G. gigan-
teus. None of these foldings form the accessory ridges/keels, com-
mon in teleosaurids, goniopholidids, or pholidosaurids (M.B.A.,
pers. observ.), as well as some theropod dinosaurs that have
teeth that superficially resemble those of crocodylians (e.g.,
spinosaurids: Charig and Milner, 1997; Ceratosaurus:Madsenand
Welles, 2000). Cingula and accessory cusps/denticles are absent,
as in all thalattosuchians.
Enamel wrinkles (sensu Brusatte et al., 2007) are present at
least on the labial surface of the crown, extending perpendicu-
lar to the apicobasal axis of the crown. They flank the denticles
and curve towards the root as they continue across the labial
surface. The wrinkles are more evident on the two smaller lat-
eral facets, but are also present across the medial facet, form-
ing even fainter enamel bands (sensu Brusatte et al., 2007).
It is not possible to verify that these bands completely en-
circle the crown, due to the presence of matrix. These wrin-
kles/bands are fewer in number and not as conspicuous as those
seen in some theropod dinosaurs (see Brusatte et al., 2007).
Enamel bands are also known to be present on the posterior-most
maxillary teeth of Dakosaurus andiniensis (Pol and Gasparini,
2009) and Geosaurus giganteus (NHM 37020). As discussed by
Brusatte et al. (2007), enamel wrinkles and bands may be rem-
nants of tooth growth and/or a mechanical adaptation for tooth
strengthening.
Characterization of Macro- and Microziphodont Dentitions
Small to large serrations in the teeth of crocodylomorphs are
often reported, particularly in fully terrestrial lineages (e.g., Bau-
rusuchidae, Peirosauridae, Sebecidae, Sphagesauridae, Trema-
tochampsidae, Pristichampsus, Araripesuchus, “Sphenosuchia”).
In all documented cases, the denticles are macroscopic and their
presence can be recognized without the aid of special equip-
ment (although proper recognition of morphology and differenti-
ation from non-ziphodont serrations demand the use of SEM; see
Prasad and Broin, 2002; Andrade and Bertini, 2008a). Geosaurus
is the only crocodylian taxon previously reported to have a true
ziphodont carina with microscopic denticles (see Young and An-
drade, 2009). Before the present study, other crurotarsans with
serrated teeth (e.g., Batrachotomus, Baurusuchus, Mariliasuchus)
generally have denticles with much greater dimensions than 300
µm (Riff and Kellner, 2001; Prasad and Broin, 2002; Andrade and
Bertini, 2008a; Pinheiro et al., 2008), and serrated carinae can be
promptly identified.
The SEM analysis presented here show that SMNS
81834, Geosaurus giganteus, G. grandis, and the Oxfordian
Dakosaurus teeth (NHM R.486, NHM 47989) have denticles
of microscopic dimensions. In all such cases, these dimensions
rarely surpass 300 µm (see Fig. 7; Table 2). Therefore, specimens
having microscopic denticles can be easily misidentified as non-
ziphodont upon simple macroscopic examination. This raises the
possibility that microscopic examination of teeth in collections
worldwide may reveal further examples of such microscopic ser-
rations in taxa previously thought to be non-ziphodont. Despite
size being a continuous variable, it is therefore of practical use
to characterize the microscopic serrations as ‘microziphodont,’
which are currently known in SMNS 81834, Geosaurus gigan-
teus (Young and Andrade, 2009), Geosaurus grandis (BSPG
AS-VI-1), and the Oxfordian “Dakosaurus” (NHM R.486).
Microziphodont teeth are here defined as teeth with denticles
in the carinae that are microscopic, and whose dimensions
(length, width, height) typically do not exceed 300 µm. Mi-
croziphodont dentitions are those with all teeth corresponding
to these parameters. Macroziphodont teeth and dentitions, on
the other hand, are characterized by the presence of conspicuous
serrations, clearly visible microscopy, where true denticles are
present and typically exceeding 300 µm in most dimensions;
this is the most common morphology among crocodylians and,
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1457
FIGURE 3. Dentition in Geosaurus grandis BSPG AS-VI-1, holotype, as shown in SEM. A, Skull in dorsal view. B, Carinae and denticles in occlusal
view. C, Carinae and denticles in lateral view. D, Denticles in oblique view, with close details showing the presence of a conspicuous continuous keel
running along the carina, both between denticles (left) and on top of each denticle (right), as indicated by white pointers. Solid bar in A equals 10 mm.
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1458 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
FIGURE 4. Ziphodont dentition in Dakosaurus maximus. A, General view of the skull and dentition, as seen in SMNS 8203, neotype. B, Close view
of NHM 35766, a typical D. maximus crown, used in this study to access carinal morphology. C, BSE microscopy of NHM 35766, showing morphology
of carina, in lateral (top) and occlusal (bottom) views, with detail of denticles in occlusal view (right). D, Life reconstruction of Dakosaurus maximus.
Note the robustness of denticles. Solid bar in AB equals 10 mm; graduated bar in C equals 200 µm. Life reconstruction in D by Dmitry Bogdanov.
possibly, in Crurotarsi. Currently, no crurotarsan species has
been observed with a dentition, including both macro- and
microziphodont teeth. Nonetheless, it is not necessary to create
a new nomenclature to refer to this combination, because
the identification of the ziphodont condition is immediate.
Therefore such pattern will be consistent with the concept of
macroziphodont dentition.
Microscopic denticles may pack closely in the carinae, re-
sulting in high denticle density, which occurs in all known mi-
croziphodont taxa. However, high density alone does not imply
in microscopic denticles, and can occur in macroziphodont taxa
(e.g., Batrachotomus has denticle density >20/5 mm, but denticle
width >400 µm; Table 2).
PHYLOGENETIC ANALYSIS
Until recently, the evolutionary relationships within Metri-
orhynchidae were understudied (Mueller-T
¨
owe, 2005; Gasparini
et al., 2006; Young, 2007; Wilkinson et al., 2008; Jouve, 2009;
Pol and Gasparini, 2009). Currently, the most complete anal-
ysis includes all known valid metriorhynchid taxa (Young and
Andrade, 2009). With a global phylogeny now available, it is
possible to investigate the character evolution and morpholog-
ical change associated with extreme marine hypercarnivory, es-
pecially concerning the microscopic and macroscopic dental fea-
tures discussed in this paper.
The phylogenetic analysis herein follows Young and An-
drade (2009), with the addition of SMNS 81834, and the
lower Oxfordian Geosaurus (NHM 36336, NHM 36339) and
Dakosaurus (NHM R.486, NHM 47989) teeth mentioned by
Young and Andrade (2009) (see Appendix 1). However, as
only metriorhynchids are of interest here, Teleidosaurus calva-
dosii, Cricosaurus suevicus,andRhacheosaurus gracilis were used
as outgroups and no non-metriorhynchoid crocodylians are in-
cluded. The phylogenetic analysis was run in using TNT v1.1
(Willi Hennig Society Edition) (Goloboff et al., 2008). Tree space
was searched using a heuristic search algorithm with TBR branch
swapping and 1000 random addition replicates. The analysis was
FIGURE 5. Ziphodont dentition in Dakosaurus indet. from the Oxford Clay Formation (NHM R.486). A, Close view of the crown in labial (left)
and lingual (right) views. B, Details of carinae and denticles in BSE microscopy. Solid bar equals 10 mm; graduated bar equals 200 µm.
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1459
FIGURE 6. Dentition in Torvoneustes car-
penteri (Wilkinson et al., 2008), comb. nov.
A, Oblique view skull of BRSMG Ce17365,
holotype, where the robust dentition with pro-
portionally large teeth is evident. B, Crown
BRSMG Cd7203, in close view. C, BSE mi-
croscopy of BRSMG Cd7203, where it is pos-
sible to see the false-ziphodont serrations at
the carina, in occlusal view. Solid bar equals
10 mm; graduated bar equals 500 µm.
then subjected to the advanced methods in TNT, namely, sec-
torial search, tree fusion, ratchet, and drift. Nodal support was
evaluated using two methods. Firstly, non-parametric bootstrap-
ping (Felsenstein, 1985) with 500 replicates, each with 100 ran-
dom addition sequences, was conducted using heuristic search-
ing with TBR branch swapping. In addition, double-decay anal-
FIGURE 7. Data plot for ranges of minimum and maximum values
for denticle length and width in ziphodont metriorhynchids, compared
against terrestrial crurotarsans (see Table 2). Note that macro- and
microziphodont teeth group in different areas of the graph, and the val-
ues for Geosaurus sp. (SMNS 81834) plot close to Geosaurus grandis.
Although NHM R.480 also shares microziphodont carinae, crown mor-
phology is clearly the same as in other species of Dakosaurus. Ranges
in dashed line. Square = marine microziphodont taxa; cross = marine
macroziphodont taxa; circle = terrestrial macroziphodont taxa (basal
Crurotarsi).
ysis (Wilkinson et al., 2000) was calculated using RadCon v.1.1.6
(Thorely and Page, 2000). Ten replicates using heuristic search-
ing with TBR branch swapping was employed.
The analysis returned a single most parsimonious cladogram
(length = 111 steps, CI = 0.903, RI = 0.902, RC = 0.781) (Fig.
8). It is clear that SMNS 81834 is more closely related to G. gi-
ganteus and G. grandis than to any other metriorhynchid species,
supporting taxonomic assignment of the tooth to Geosaurus.
Within Metriorhynchidae, two monophyletic clades of ziphodont
taxa are recovered: the genus Geosaurus (G. grandis, G. gigan-
teus, G. lapparenti and the Nusplingen specimen) and the genus
Dakosaurus.
Geosaurus carpenteri, the ‘Portomaggiore croc’ (see
Leonardi, 1956; Kotsakis and Nicosia, 1980), and a few isolated
teeth assigned to Geosaurus (NHM 36336, NHM 36339) clus-
ter separately as a putative third lineage, sister taxon to true
Geosaurus. Most of these specimens differ from Geosaurus
and Dakosaurus in tooth morphology (e.g., false-ziphodont and
conical dentition in G. carpenteri;Fig.6),butthefragmentary
nature of the remains prevents further assessment of their
characteristics, particularly in the case of the ‘Portomaggiore
croc,’ where dentition is unknown. This clade exhibits weak
nodal support, and its position is poorly corroborated (double
decay index = 1; bootstrap <50%) relative to Geosaurus and
Dakosaurus. Furthermore, previous analyses show that there
is currently no consensus for the placement of G. carpenteri
(formerly Dakosaurus carpenteri) into either of these genera
(compare Wilkinson et al., 2008; Young and Andrade, 2009).
Unfortunately, character optimization regarding acquisition
of ziphodont carinae is ambiguous. It remains unclear whether
denticulated carinae evolved early at the base of the Geosauri-
nae clade, and was subsequently lost in G. carpenteri,orif
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1460 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
FIGURE 8. Reduced phylogeny based on Young and Andrade (2009), and including new metriorhyncnid ziphodont teeth. The phylogeny is cali-
brated with the stratigraphical record, and firmly places SMNS 818384 within Geosaurus. Ziphodont taxa (white squares) may have either microscopic
(small squares) or macroscopic (large squares) denticles. Note that ghost lineages extend the range of Geosaurus and Dakosaurus into the early Ox-
fordian. Currently, Geosaurus is restricted to the Late Jurassic–Early Cretaceous of Europe. Nodal support values as follows: double decay index
above 1 (italicized); bootstrap above 50% (bold).
it evolved independently in Geosaurus and Dakosaurus. How-
ever, as Geosaurus and Dakosaurus exhibit different ziphodont
morphologies when examined in detail, multiple acquisition of
ziphodonty in metriorhynchids may be a more likely hypothesis.
DISCUSSION
Taxonomic Implications
The detailed description of microscopic and macroscopic mor-
phology of metriorhynchid dentitions and the phylogenetic anal-
ysis herein imply some taxonomic amendments. Three major
points deserve attention. First, we can show that SMNS 81834
is referable to Geosaurus, and represents both the largest known
tooth and the oldest material currently assignable to this genus.
Second, we provide a modified diagnosis of Geosaurus,which
excludes all material with false-ziphodont/non-ziphodont denti-
tions, and/or with well-ornamented teeth. Third, relying on this
new diagnosis, we provide a new generic name for the highly
autapomorphic, false-ziphodont Geosaurus carpenteri,ataxon
whose phylogenetic relationships have proven controversial (i.e.,
divergent phylogenetic hypotheses of Wilkinson et al., 2008, and
Young and Andrade, 2009).
SYSTEMATIC PALEONTOLOGY
CROCODYLOMORPHA Walker, 1970
CROCODYLIA Gmelin, 1789 (sensu Martin and Benton, 2008;
= Crocodyliformes Benton and Clark, 1988)
THALATTOSUCHIA Fraas, 1901 (sensu Young and Andrade,
2009)
METRIORHYNCHIDAE Fitzinger, 1843 (sensu Young and
Andrade, 2009)
GEOSAURINAE Lydekker, 1889 (sensu Young and Andrade,
2009)
GEOSAURUS Cuvier, 1824 (sensu Young and Andrade, 2009)
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1461
Amended Diagnosis—Metriorhynchid thalattosuchian pos-
sessing the following combination of characters: brevirostrine to
short mesorostrine snout; maxillary crowns moderately enlarged;
cranial bones smooth, lacking conspicuous ornamentation; pre-
frontal teardrop-shaped, with the inflexion point directed pos-
teriorly approximately 70
from the anteroposterior axis of the
skull; acute angle formed by the lateral and medial processes of
the frontal; antorbital fossa present and much longer than higher;
lacrimal-prefrontal fossa present, with a crest along the sutu-
ral contact (adapted from Young and Andrade, 2009); strongly
lateromedially compressed teeth, with crowns that may be tri-
faceted or not; all teeth possessing denticulate carinae with true
microscopic denticles; crowns with a continuous keel at mesial
and distal edges; enamel surface at labial/lingual facets lacks con-
spicuous ornamentation or apicobasal accessory ridges (this pa-
per).
GEOSAURUS sp.
Material—SMNS 81834: isolated tooth partially embedded in
matrix (Fig. 2).
Locality and Horizon—Nusplingen, Zollernalbkreis, Baden-
W
¨
urttemberg, Germany. Hoelderi horizon, Nusplingen
Plattenkalk—Malm Zeta 1 (German zone), beckeri tethys
ammonite-zone (upper Kimmeridgian, Upper Jurassic; Grawe-
Baumeister et al., 2000).
TORVONEUSTES, gen. nov.
Type SpeciesTorvoneustes carpenteri (Wilkinson et al., 2008)
comb. nov.
Etymology—‘Savage swimmer.’ Torvus- is Latin for ‘savage,’
whereas neustes is Ancient Greek for ‘swimmer.’ The generic
named acknowledges the morphology of skull, postcrania, and
dentition, which indicate a large and robust marine predator, as
indicated in its original description by Wilkinson et al. (2008).
Diagnosis—As for the only known species.
TORVONEUSTES CARPENTERI (Wilkinson et al., 2008)
comb. nov.
(Fig. 6)
Metriorhynchus superciliosus (de Blainville, 1853): Grange and
Benton, 1996:497, figs. 3–9.
Dakosaurus carpenteri Wilkinson et al., 2008: Grange and Ben-
ton, 1996:1307, figs. 2–10.
Geosaurus carpenteri (Wilkinson et al., 2008): Young and An-
drade, 2009; Young et al., 2010.
Holotype—BRSMG Ce17365: incomplete skull (Fig. 6).
Type Locality—Westbury, Wiltshire, England (lower Kim-
meridge Clay Formation). Mutabilis to eudoxus ammonite zones
(Upper Kimmeridgian, Upper Jurassic).
Etymology—Carpenter’s savage swimmer.
Referred Specimens—BRSMG Cd 7203: isolated postcranial
and mandibular remains (see Wilkinson et al., 2008).
Amended Diagnosis—Metriorhynchid thalattosuchian distin-
guished from other species of Dakosaurus, Geosaurus,and
Metriorhynchus, by the following combination of characters: the
supratemporal fossae are enlarged and project further forward
than in other species; teeth somewhat smaller than those of
other species of Dakosaurus, but larger than those of all species
of Metriorhynchus; robust cranium, lacking ornamentation; pre-
frontal makes a greater angle with the long axis of the skull
than in Dakosaurus (50 degrees), but less than in species of
Metriorhynchus (60–70 degrees); number of teeth in each jaw
ramus estimated at 14, similar to D. maximus and D. andinien-
sis (12–16), and far fewer than in any species of Metriorhynchus
(typically 22–29) (adapted from Wilkinson et al., 2008); acute an-
gle formed by the lateral and medial processes of the frontal;
small antorbital fenestra present, enclosed within an oblique an-
torbital fossa; lacrimal-prefrontal fossa present (modified from
Young and Andrade, 2009); teeth large, robust, mostly conical,
but with little mediolateral compression; intensely ornamented
crowns, and carinae formed by a keel with false-serrations (i.e.,
created by conspicuous superficial ornamentation of the enamel;
false-ziphodont); anteromedial process of the frontal triangular,
projecting anteriorly, reaching the same relative position as the
anterior border of the orbit; mandibular symphysis longer than
wide, terminating prior to the antorbital fossa (this paper).
Taxonomic Comment—Unfortunately, our phylogenetic anal-
ysis found only feeble nodal support for an expanded clade con-
taining Torvoneustes carpenteri, the ‘Portomaggiore croc’ (see
Leonardi, 1956; Kotsakis and Nicosia, 1980) and the early Ox-
fordian “Geosaurus teeth NHM 36336 and NHM 36339 (Fig. 8).
Therefore, whether these latter specimens can be referred to
Tor-
voneustes remains uncertain. These specimens, however, cannot
be considered as part of either Geosaurus or Dakosaurus.
Updated Dental Description—The teeth of Torvoneustes car-
penteri are single cusped and conical, with slight mediolaterally
compression (although newly erupted crowns can be mediolater-
ally compressed; BRSMG Cd7203). No constriction is present at
the crown/root junctions, but the boundary is evident due to color
and texture. No facets are evident on either the labial or lingual
faces. Crowns are intensely ornamented. The enamel on the pre-
maxillary, maxillary, and dentary crowns have fine apicobasally
aligned ridges that become coarser away from the smooth apex.
Grange and Benton (1996:505) considered the highly polished
apices of the crowns to have been formed by tooth-to-food abra-
sion, in particular from hard prey. Furthermore, Young et al.
(2010) consider the crowns of T. carpenteri to be indicative of
Massare’s (1987) ‘general guild,’ supporting the hypothesis of
feeding on hard prey items. With an estimated 14 teeth per upper
tooth-row (Wilkinson et al., 2008), Torvoneustes has one of the
shortest tooth-rows of any metriorhynchid. Moreover, along with
Geosaurus and Dakosaurus, the apicobasal length of the premax-
illary, maxillary, and dentary crowns in T. carpenteri exceed 20
mm (reaching a maximum of 32 mm in BRSMG Ce17365). All
other metriorhynchid genera have teeth <20 mm in apicobasal
length (M.T.Y., pers. observ.).
The teeth of the holotype bear false serrations (false-ziphodont
carinae, sensu Prasad and Broin, 2002), but these are micro-
scopic and could only be identified with the use of SEM. In this
type of morphology, the ‘serrations’ are created on the surface
of the carinal keel by the conspicuous superficial ornamentation
of enamel (Fig. 6). False-ziphodonty is rare in Thalattosuchia:
prior to its discovery in T. carpenteri, it was only reported in the
teleosaurid genus Machimosaurus (see Prasad and Broin, 2002).
No true denticles are present on the carinae of Torvoneustes,and
split or supernumerary carinae were not found on any tooth.
Metriorhynchid Ziphodont Morphotypes
The general pattern of shared dental features seen in the differ-
ent species of ziphodont metriorhynchids is consistent through-
out the group (Wagner, 1858; Fraas, 1902; Debelmas and Stran-
noloubsky, 1957; Pol and Gasparini, 2009; Young and Andrade,
2009). As seen above, the only marine crocodylians possess-
ing ziphodont teeth are Dakosaurus and Geosaurus, both of
which can be diagnosed by tooth morphology alone. Further-
more, by examining crown morphology and denticle size, it is
possible to recognize four well-delimited ‘groups’ within these
genera, which are here proposed as morphotypes. These mor-
photypes enable the identification of isolated marine crocodylian
teeth—particularly ziphodont teeth—allowing revision of mate-
rial currently preserved in collections, or new material as it is re-
covered from the field.
Other metriorhynchid teeth are not included below, because
they are not ziphodont, and workers should follow previous
nomenclatural proposals when describing or identifying such
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1462 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 5, 2010
teeth (Prasad and Broin, 2002; Andrade and Bertini, 2008a). In
most cases, non-ziphodont taxa have conical, curved teeth, with
well-ornamented crowns. Unfortunately, this description applies
to many taxa, and is of little taxonomic value.
The proposed morphotypes for recognition of ziphodont ma-
rine crocodylians are as follows.
Morphotype 1—Crowns poorly compressed mediolaterally,
but very robust, without conspicuous ornamentation; carinae
with macroscopic denticles (>300 µm; macroziphodont). No
faceting on labial or lingual surface of the crowns. Currently in-
cludes Dakosaurus maximus (Fig. 4) and D. andiniensis (Gas-
parini et al., 2006; Pol and Gasparini, 2009).
Morphotype 2—Crowns poorly compressed mediolaterally,
but very robust, without conspicuous ornamentation; carinae
with microscopic denticles (<300 µm; microziphodont). No
faceting on labial or lingual surface of the crowns. Cur-
rently includes Dakosaurus indet. NHM R.486 (Oxfordian
Dakosaurus”; Fig. 5).
Morphotype 3—Crowns strongly compressed mediolaterally,
without conspicuous ornamentation; carinae with microscopic
denticles (<300 µm; microziphodont). Labial surface of the
crowns exhibits strong tri-faceting. Currently includes Geosaurus
giganteus, G. grandis (“Solnhofen Geosaurus”), and Geosaurus
sp. SMNS 81834 (Fig. 2).
Morphotype 4—Crowns strongly compressed mediolaterally,
without conspicuous ornamentation; carinae with microscopic
denticles (<300 µm; microziphodont). No faceting on labial or
lingual surface of the crowns. Currently includes Geosaurus lap-
parenti (Valanginian).
Inferred Diet for Geosaurus and Dakosaurus
Morphology provides a reasonable proxy for identification of
diet, and it is especially important to consider functionally re-
lated characters such as type of carina, denticle morphology and
density, tooth crown shape, proportional mandible depth, and
presence or absence of grinding areas and worn teeth (e.g., Van
Valkenburgh and Molnar, 2002; Pol, 2003; Van Valkenburgh
et al., 2004; Andrade and Bertini, 2008a).
Dakosaurus and Geosaurus possess the proportionally short-
est and deepest rostra (Gasparini et al., 2006; Pol and Gasparini,
2009; Young and Andrade, 2009) among thalattosuchians, and
also proportionally deep mandibles. They also lack grinding areas
on tooth crowns, although broken teeth are common (expected in
predators; see Van Valkenburgh, 1988). These factors, along with
tooth crown morphology, and presence of true serrations and a
keel, are consistent with a hypercarnivorous diet (i.e., composed
at least 70% by meat; Van Valkenburgh, 1988, 2007; Holliday and
Steppan, 2004). The ziphodont dentition, along with other fea-
tures of gross morphology (see Young et al., 2010), indicate that
Geosaurus and Dakosaurus were well adapted not only to hyper-
carnivory, but to extreme strict carnivory, whereas piscivory was
probably not their main dietary strategy (although fish could have
been an important part of their diet).
Body size is likely to have influenced prey selection in
Geosaurus and Dakosaurus, which were larger (estimated size 4
m) than their close relatives and most other putative predators
in their environment (4 m), such as Cricosaurus (see Young,
2009). In terrestrial ecosystems there is a positive relation be-
tween prey and predator size, allowing the inclusion of prey
larger than the predator itself (Van Valkenburgh and Molnar,
2002; Van Valkenburgh et al., 2004). Although energetic con-
straints of marine and terrestrial predators may differ from their
terrestrial counterparts, tooth morphology and the larger size of
ziphodont metriorhynchids are consistent with selection of pro-
portionally large prey (including both vertebrates and inverte-
brates). Further, it has been shown that short-snouted metri-
orhynchids were biomechanically fit to perform the ‘death roll’
(Pierce et al., 2009b; Young et al., 2010), a feeding strategy that
increases efficiency with predator size at an exponential rate, be-
ing particularly useful in the killing and dismemberment of large
prey (see Fish et al., 2007, and references within).
The single non-ziphodont metriorhynchid to reach a compa-
rablesizetoGeosaurus and Dakosaurus is Torvoneustes (see
Wilkinson et al., 2008; Young, 2009), which is convergent on these
genera by possessing a false-ziphodont dentition, and was also
able to perform the ‘death roll.’ The presence of false serrations
in the enamel ornamentation of Torvoneustes is a clear conver-
gence towards extreme hypercarnivory, allowing a diet of large
prey, although its proportionally shorter and blunter teeth were
not as well suited for the penetration or slicing action that its
ziphodont relatives were able to inflict (see Young et al., 2010).
Stratigraphic Range of Metriorhynchid Ziphodonty
Isolated Dakosaurus tooth crowns have long been known
(e.g., Lydekker, 1888), but the confirmation that NHM R.486
is microziphodont extends the range of ziphodonty in metri-
orhynchids back into the Oxford Clay Formation (upper
Callovian–lower Oxfordian). The extension of ziphodont metri-
orhynchids further back in time makes these crocodylomorphs
the earliest known examples of both true- and false-ziphodonty
in secondarily pelagic tetrapods. Nonetheless, the range of
macroziphodonty in the genus seems to be substantially shorter
(upper Kimmeridgian to the lower Berriasian). Unfortunately,
there are no reliably known specimens of Dakosaurus (sensu
Young and Andrade, 2009) from sediments younger than the
lower Berriasian, preventing further extension of the ziphodonty
range in the genus.
The new tooth, SMNS 81834, is the oldest known true (i.e.,
ziphodont) Geosaurus. The description of SMNS 81834 directly
extends the range of ziphodonty in this genus, from the lower
Tithonian (G. giganteus, G. grandis) to the upper Kimmeridgian.
Geosaurus lapparenti is the youngest known geosaurine (lower
Valanginian), and is the last known occurrence of ziphodonty
in Metriorhynchidae (although ziphodonty persisted in terres-
trial crocodylians through the Upper Cretaceous, Paleogene, and
Neogene). When the phylogenetic relationships of Geosaurinae
are calibrated against stratigraphy, further extension of lineages
occurs through addition of ghost ranges. Considering material un-
equivocally assigned to Dakosaurus, this genus spanned at least
15.7 million years. The fossil record of Geosaurus currently spans
only 11 million years, but it is substantially increased if ghost
ranges are taken into consideration. Combined, the total record
of ziphodont metriorhynchids spreads over some 23 million years.
The distribution of ziphodonty in time (early Oxfordin to
early Valanginian) implies that two pivotal lineages of ziphodont
metriorhynchids co-existed in time for at least 16 million years.
This is surprising, as in terrestrial paleoecosystems, apex preda-
tors tend to persist for much shorter periods of time (e.g.,
6 million years in canids; see Van Valkenburgh et al., 2004;
Van Valkenburgh, 2007). Additionally, the distribution of mi-
croziphodonty in time (20 million years) is surprisingly longer
than macroziphodonty (currently restricted to the Dakosaurus
lineage; 10 million years). Therefore, microziphodonty is re-
vealed to be the most resilient pattern in metriorhynchid history,
contrasting with the pattern seen in terrestrial taxa.
Co-occurrence of Geosaurus and Dakosaurus,andNiche
Partitioning in the Nusplingen Sea
Prior to the discovery of SMNS 81834, the only known co-
occurrence of Geosaurus and Dakosaurus was in the Solnhofen
Formation (lower Tithonian; Table 1). The new tooth shows
that the two genera also co-existed in the Nusplingen Sea
(Mergelst
¨
atten Formation; lower Tithonian). The co-occurrence
of large-sized ziphodont species of Dakosaurus and Geosaurus
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ANDRADE ET AL.—EXTREME HYPERCARNIVORY IN METRIORHYNCHIDS 1463
in these two seas is remarkable, especially because they shared
features of gross morphology that relate to high-order carnivory
(i.e., body size, aquatic adaptations, binocular vision). Dental fea-
tures, on the other hand, may explain how two large predators
were able to co-exist in multiple seas during much of the Late
Jurassic.
Although both Geosaurus and Dakosaurus possess ziphodont
teeth, their overall crown morphologies are distinct both micro-
scopically and macroscopically. Dakosaurus is the only exam-
ple of a marine ziphodont crocodylian with robust and recurved
crowns, comparable with large theropod dinosaurs such as Tyran-
nosaurus. Geosaurus has slender to triangular, blade-like crowns,
reminiscent of Carcharodon. Mechanical testing by Abler (1992)
determined that the primary function of Tyrannosaurus denticles
is to puncture and grip, and that slicing and cutting roles were
secondary, whereas Carcharodon teeth are optimized for slicing
and cutting. Taking Tyrannosaurus and Carcharodon as models
for, respectively, Dakosaurus and Geosaurus, different biologi-
cal functions (and diets) can be deduced for these crocodylian
taxa. Furthermore, denticles in Geosaurus are rounder, joining
smoothly the crown surface, and can be proportionally narrower
than the denticles of Solnhofen/Nusplingen Dakosaurus,which
potentially reduces the drawing force necessary to cut.
The mid-crown denticle density measurements also differ be-
tween Geosaurus and Kimmeridgian-Berriasian Dakosaurus. In
the later they are within the range observed in many clades
of large theropod dinosaurs (<20 denticles/5 mm, e.g., Smith
et al., 2005; Brusatte and Sereno, 2007; Sereno and Brusatte
2008), baurusuchid crocodilians (e.g., Riff and Kellner, 2001; Pin-
heiro et al., 2008), rauisuchians (e.g., Peyer et al., 2008), phy-
tosaurs, and Erythrosuchus (Table 2). In contrast, mid-crown
densities of Kimmeridgian-Tithonian Geosaurus and the Oxfor-
dian Dakosaurus are similar to those of small- to medium-sized
theropod dinosaurs (>20 denticles/5 mm; e.g., Smith et al., 2005)
and terrestrial crocodilians (e.g., Company et al., 2005). Many
taxa with coarse denticle density morphology are well suited
to deliver high bite forces or endure impact feeding (e.g., Ray-
field et al., 2001; Rayfield, 2004), including Dakosaurus (Young
et al., 2010). On the contrary, it is generally thought that thero-
pod dinosaurs with higher denticle densities possessed propor-
tionally lower bite forces (e.g., Therrien et al., 2005). Therefore,
the higher denticle density in Geosaurus indicates that this taxon
was not as adapted as Dakosaurus for high bite force (or impact
feeding).
In sum, although Geosaurus and Dakosaurus were both able
to feed on large-bodied prey, differences in their dentitions (den-
ticle size, crown morphology, mid-crown density) indicate spe-
cialization towards ‘softer’ and ‘harder’ diets, respectively. These
differences may have enabled niche partitioning, and thus the
co-existence of these two large predators. Dakosaurus, equipped
with robust and recurved crowns, was biomechanically able to
withstand high bite forces, and may have included armored
prey in its diet (e.g., teleosaurids, thick-shelled ammonites).
Geosaurus, on the other hand, would have possessed a lower bite
force, but the dentition, arranged as opposing blades, enabled
this taxon to slice through fleshy prey more efficiently (Young
et al., 2010). By abstaining from a diet of armored/shelled prey,
Geosaurus would have reduced the hindrances of tooth breakage
against heavy bones/shells (Van Valkenburgh, 1988).
CONCLUSIONS
Ziphodont teeth in metriorhynchids exhibit variability in both
macroscopic (crown morphology) and microscopic (denticle size
and density) features. Many of these features are subtle, and are
often overlooked or entirely impossible to identify without the
use of SEM or optical resources. However, when identified, these
characters are useful in distinguishing isolated material and can
be utilized in broader discussions of phylogeny, macroevolution-
ary trends, functional morphology, and paleoecology.
Based on its possession of derived characters, the new tooth
from the Nusplingen Plattenkalk (SMNS 81834) unequivocally
pertains to a large species of the genus Geosaurus (sensu Young
and Andrade, 2009). It is now evident that
Geosaurus inhabited
the Nusplingen Sea, not only Dakosaurus as previously thought.
SMNS 81834 is currently the oldest specimen assignable to a
ziphodont species of Geosaurus, whereas SEM analysis indi-
cates that other ziphodont metriorhynchids were already present
by the Oxfordian. Ziphodont metriorhynchid lineages persisted
for longer than previously thought and co-existed in individual
ecosystems, seemingly enabled by niche partitioning due to dif-
ferences in craniodental morphology. Unfortunately, it is still un-
clear whether ziphodonty in Dakosaurus and Geosaurus is ho-
mologous or evolved independently. Further, the false-ziphodont
Geosauruscarpenteri diverged in tooth morphology from both
these lineages, and is reassigned to a new genus, Torvoneustes.
ACKNOWLEDGMENTS
We thank R. Schoch (SMNS) for access to SMNS specimens,
particularly SMNS 81834, and O. Rauhut (BSPG), S. Chap-
man and P. Barrett (NHM), and R. F. Vaughan and R. Barnett
(BRSMG) for access to specimens under their care; S. Kearns
for his guidance on SEM, and S. Powell (BRSUG) for advice on
image treatment; M. K
¨
olbl-Ebert (JME) and E. Robert (Univer-
sit
´
e Joseph Fourier) for information regarding their collection;
and D. Bogdanov for the life reconstructions in Figures 4 and 7.
We thank B. Beatty, E. Rayfield (BRSUG), D. Schwarz-wings
(Museum f
¨
ur Naturkunde Berlin), and an anonymous referee for
their comments, and F. R. O’Keefe and M. Wilson for their edito-
rial assistance, which greatly contributed to improve the original
manuscript.
M.B.A. receives financial support from Conselho Nacional
de Desenvolvimento Cientifico e Tecnol
´
ogico (CNPq, Proc. No.
200381/2006–10), Brazil. Direct examination of Stuttgart and
Munich specimens was only possible with the support of the
Sylvester Bradley Fund to M.B.A. and Alexander von Humboldt
Foundation to J.B.D. M.T.Y. receives support from the Natu-
ral Environment Research Council (grant NER/S/A/2006/14058),
UK, and the NHM. S.L.B. is supported by an NSF Graduate Re-
search Fellowship (Columbia University), his tenure in the UK
was supported by the Marshall Scholarship, and his specimen
visits were funded by the Jurassic Foundation, Paleontological
Society, SYNTHESYS (DE-TAF-4368, FR-TAF-3918), and the
University of Bristol Bob Savage Memorial Fund. SYNTHESYS
(http://www.synthesys.info/) is financed by the European Com-
munity Research Infrastructure Action under the FP6 ‘Structur-
ing the European Research Area Programme.’
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tion of G. giganteus (Thalattosuchia: Metriorhynchidae) from the
Upper Jurassic of Bayern, Germany. Zoological Journal of the Lin-
nean Society 157:551–585.
Young, M. T., S. L. Brusatte, M. Ruta, and M. B. Andrade. 2010. The evo-
lution of Metriorhynchoidea (Mesoeucrocodylia, Thalattosuchia):
an integrated approach using geometric morphometrics, analysis of
disparity and biomechanics. Zoological Journal of the Linnean So-
ciety 158:801–859.
Submitted July 29, 2009; accepted February 10, 2010.
APPENDIX 1. Phylogenetic analysis after Young and Andrade
(2009), with the addition of the following codings for new taxa.
Nusplingen Geosaurus indet. (SMNS 81834)
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English (lower Oxfordian) Geosaurus/Torvoneustes teeth (NHM
36336, NHM 36339)
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English (upper Callovian–lower Oxfordian) Dakosaurus teeth
(NHM 47989, NHM R.486)
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... Thalattosuchia was a species-rich and geographically widespread clade of marine and freshwater crocodylomorphs that were particularly abundant between the late Early Jurassic and the Late Jurassic when they regulated the trophic structure of near-shore as well as deep-water settings (e.g., Andrade et al. 2010;Young et al. 2013a;Wilberg 2015;Foffa et al. 2018cFoffa et al. , 2019Johnson et al. 2018;Martin et al. 2018). Thalattosuchian fossils are particularly abundant in western Europe, often preserving complete skeletons (e.g., Eudes-Deslongchamps 1867-1869Fraas 1902;Andrews 1913). ...
... When the crown is observed in labial view, it is noticeably wider at the base narrowing apically, creating a sub-triangular profile. The labial surface lacks apicobasal planar surfaces (i.e., "facets"), three labial facets are autapomorphic for the geosaurinan genera Geosaurus and Ieldraan (Young and Andrade 2009;Andrade et al. 2010;Foffa et al. 2018b). ...
... As such, they are best observed with good lighting or optical aids (Fig. 5). The ornamentation differs from the densely packed and high-relief ridges observed in Torvoneustes and members of the "E-clade" (Andrade et al. 2010;Young et al. 2013b;Barrientos-Lara et al. 2016;Abel et al. 2020), and the smooth enamel lacking ridges in Dakosaurus andiniensis (Pol and Gasparini 2009), D. maximus and Geosaurus giganteus (Andrade et al. 2010). ...
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Metriorhynchid crocodylomorphs were an important component in shallow marine ecosystems during the Middle Jurassic to Early Cretaceous in the European archipelago. While metriorhynchids are well known from western European countries, their central and eastern European record is poor and usually limited to isolated or fragmentary specimens which often hinders a precise taxonomic assignment. However, isolated elements such as tooth crowns, have been found to provide informative taxonomic identifications. Here we describe two isolated metriorhynchid tooth crowns from the upper Valanginian (Lower Cretaceous) of the Štramberk area, Czech Republic. Our assessment of the specimens, including multivariate analysis of dental measurements and surface enamel structures, indicates that the crowns belong to two distinct geosaurin taxa (Plesiosuchina? indet. and Torvoneustes? sp.) with different feeding adaptations. The specimens represent the first evidence of Metriorhynchidae from the Czech Republic and some of the youngest metriorhynchid specimens worldwide.
... The geosaurin Dakosaurus maximus is a common faunal element in upper Kimmeridgian and lowermost Tithonian localities (e.g. Nusplingen, Heidenheim, Wattendorf, Painten, Kelheim; Fraas 1901Fraas , 1902Frickhinger 1994;Andrade et al. 2010;Young et al. 2012;Sachs et al. 2019). In the older localities the records of Geosaurus and Geosaurinae indet. ...
... are scarce and based on isolated teeth (e.g. Andrade et al. 2010;Sachs et al. 2019); however, there seems to be a co-occurrence of geosaurin taxa during the late Kimmeridgian (e.g. Nusplingen and Torleite formations; Fig. 1). ...
... Geosaurus is recorded in the upper part of the Altm€ uhltal Formation (Solnhofen; Fig. 1) and the M€ ornsheim Formation records the co-occurrence of two species of Geosaurus (e.g. Zittel 1890;Ammon 1906;Broili 1931Broili , 1932Frickhinger 1994;Andrade et al. 2010;Young et al. 2012; Fig. 1). In the Altm€ uhltal and M€ ornsheim formations the co-occurrence of rhacheosaurins is documented by Rhacheosaurus and Cricosaurus (e.g. ...
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Cricosaurus represents one of the most important radiations within Metriorhynchidae, a specialized marine clade of Crocodylomorpha that flourished in marine environments from the Middle Jurassic until the Early Cretaceous. Here, we describe a new species of Cricosaurus, Cricosaurus rauhuti sp. nov., from the Mörnsheim Formation (lower Tithonian) of southern Germany. The specimen is the first three-dimensionally preserved Cricosaurus from this realm, and it is represented by a partially preserved cranium and lower jaw that has autapomorphic characters that distinguish it from any other species of Cricosaurus. The phylogenetic analysis shows that the new species is more closely related to some non-European forms from the Late Jurassic and one taxon from the Valanginian of Germany (all 3D-preserved) than to other Late Jurassic Cricosaurus from southern Germany (all 2D-preserved). Our exploratory analyses confirm that this is not a preservation bias. For the first time, this shows that there are two clades of Cricosaurus present during the Late Jurassic in Germany. Furthermore, it provides additional evidence of a close faunal relationship between Europe and South America in the Late Jurassic, as also evidenced by the fossil record of other marine reptiles. Finally, the distribution of metriorhynchids in localities of the Solnhofen Archipelago suggests a change in the taxic diversity of the region during the early Tithonian, which might be the result of environmental changes in the Solnhofen Archipelago. http://zoobank.org/urn:lsid:zoobank.org:pub:488705BF-AEAD-4F02-BB4E-429E3117BCD1
... In Europe, abundant and well-preserved fossils of Late Jurassic marine reptiles are known from the Kimmeridge Clay Formation (Kimmeridgian) of the United Kingdom (e.g., Owen 1842; Seeley , 1875Lydekker 1889;Andrews 1921;Tarlo 1960;Brown 1981;Brown et al. 1986;Tay lor and Cruickshank 1993;Sassoon et al. 2012;Young et al. 2013b;Benson et al. 2013;Benson and Bowdler 2014;Pérez-García 2015b, c;Püntener et al. 2015;Anquetin and Chapman 2016;Moon and Kirton 2018), the Reuchenette Formation (Kimmeridgian) of Switzerland (e.g., Rütimeyer 1873;Bräm 1965;Meyer 1994;Comment et al. 2015;Püntener et al. 2015Püntener et al. , 2017aSullivan and Joyce 2017;Raselli and Anquetin 2019;Anquetin and Püntener 2020), the "Soln-hofen Limestone" (Tithonian) of Southern Ger many (e.g., Meyer 1839a; Parsons and Williams 1961;Gaffney 1975b; Bardet and Fernández 2000;Dupret 2004;Young and de Andrade 2009;de Andrade et al. 2010;Young et al. 2012;Anquetin and Joyce 2014;Arratia et al. 2015;Anquetin et al. 2017;Bever and Norell 2017), several Kimmeridgian and Tithonian localities of France (e.g., Thiollière 1850;Meyer 1860;Lortet 1892;Rieppel 1980;Broin 1994;Lapparent de Broin et al. 1996; Bardet et al. 1997;Pérez-García 2015b) and Iberia (e.g., Lapparent de Broin and Murelaga 1999;Pérez-García and Ortega 2011;Pérez-García 2015c), as well as several fossil-bearing horizons spanning the Volgian (Tithonian-lowermost Berriasian) of European Russia (e.g., Zverkov et al. 2015aZverkov et al. , b, 2018Arkhangelsky et al. 2018;Zverkov and Efimov 2019;Zverkov and Prilepskaya 2019) and the Slottsmøya Member of the Aghardfjellet Formation of Spitsbergen (e.g., Druckenmiller et al. 2012;Knutsen et al. 2012a-c;Roberts et al. 2014Roberts et al. , 2020Delsett et al. 2019). ...
... These include lingually curved and subcircular to indistinctly labiolingually compressed cross sections near the base of the crowns; indistinctly blunt apices; well-developed and continuous carinae; no constriction at the crown/root junction; and ornamentation that includes a combination of structural elements restricted to particular segments of the tooth crowns. When metriorhynchids with such dental morpho logy and general characteristics of enamel structural elements are considered, MZ VIII Vr-72 shares the presence of short, apicobasally oriented ridges/ridglets limited to the basal part of their crowns and changing apically into an indistinct to conspicuous vermicular pattern with some taxa, such as the geosaurines Suchodus brachyrhynchus (Eudes-Deslongchamps, 1868b), Torvoneustes spp., and Tyrannoneustes lythrodectikos Young, de Andrade, Brusatte, Saka moto, and Liston, 2013a, and the metrio rhynchines Gracilineustes leedsi Andrews, 1913, andMetriorhynchus super ciliosus (Blainville, 1853) (Andrade et al. 2010;Young et al. 2013a, b). All of these taxa, however, appear to lack the smoother mid-section that is present in most teeth of MZ VIII Vr-72, in which the lingual surface is exposed. ...
... We were not given permission to examine the microscopic anatomy of the dentition of MZ VIII Vr-72 and so were unable to describe its carinal morphology, which is also used in thalattosuchian taxonomy (e.g., Andrade et al. 2010) and could possibly provide additional data important for determining the taxonomic affinity of the specimen. ...
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Marine reptiles from the Upper Jurassic of Central Europe are rare and often fragmentary, which hinders their precise taxonomic identification and their placement in a palaeobiogeographic context. Recent fieldwork in the Kimmeridgian of Krzyżanowice, Poland, a locality known from turtle remains originally discovered in the 1960s, has reportedly provided additional fossils thought to indicate the presence of a more diverse marine reptile assemblage, including giant pliosaurids, plesiosauroids, and thalattosuchians. Based on its taxonomic composition, the marine tetrapod fauna from Krzyżanowice was argued to represent part of the “Matyja-Wierzbowski Line”—a newly proposed palaeobiogeographic belt comprising faunal components transitional between those of the Boreal and Mediterranean marine provinces. Here, we provide a detailed re-description of the marine reptile material from Krzyżanowice and reassess its taxonomy. The turtle remains are proposed to represent a “plesiochelyid” thalassochelydian (Craspedochelys? sp.) and the plesiosauroid vertebral centrum likely belongs to a cryptoclidid. However, qualitative assessment and quantitative analysis of the jaws originally referred to the colossal pliosaurid Pliosaurus clearly demonstrate a metriorhynchid thalattosuchian affinity. Furthermore, these metriorhynchid jaws were likely found at a different, currently indeterminate, locality. A tooth crown previously identified as belonging to the thalattosuchian Machimosaurus is here considered to represent an indeterminate vertebrate. The revised taxonomy of the marine reptiles from Krzyżanowice, as well as the uncertain provenance of the metriorhynchid specimen reported from the locality, cast doubt on the palaeobiogeographic significance of the assemblage.
... However, it was the metriorhynchid subclade that reached the zenith of aquatic specialization, evolving pelagic adaptations such as flipper-like forelimbs, a highly regionalized caudal vertebral column with a hypocercal tail, loss of osteoderms, preorbital salt exocrine glands and compact inner ear semicircular canals (e.g. Fraas, 1902;von Arthaber, 1906;Andrews, 1913;Fernández & Gasparini, 2000Young et al., 2010;Herrera et al., 2013a, b;Sachs et al., 2019a;Schwab et al., 2020). It has also been suggested that metriorhynchids evolved a non-homeothermic mode of endothermy and were viviparous (see: Herrera et al., 2015a;Séon et al., 2020). ...
... The first time 'Havre snout' was considered to be the lectotype was by Vignaud (1995) in his unpublished PhD thesis. Young et al. (2010) followed Vignaud (1995) in considering the 'Havre snout' as the lectotype of Me. geoffroyii. Young et al. (2010) Owen (1842) The taxonomy proposed by Owen (1842) Talking about Cuvier, he added: 'il a créé plusieurs monstruosités anatomiques, en construisant une espèce avec des pièces de deux autres; ainsi son Crocodile à long museau, avec des mâchoires longues, en effet, réunies au crâne du Crocodile à museau moins long' ('he [Cuvier] created several anatomical monstrosities, by constructing one species with parts of two others; thus his long snout crocodile, with long jaws, indeed, joined to the skull of the crocodile with a shorter snout'). ...
... Young et al. (2010) followed Vignaud (1995) in considering the 'Havre snout' as the lectotype of Me. geoffroyii. Young et al. (2010) Owen (1842) The taxonomy proposed by Owen (1842) Talking about Cuvier, he added: 'il a créé plusieurs monstruosités anatomiques, en construisant une espèce avec des pièces de deux autres; ainsi son Crocodile à long museau, avec des mâchoires longues, en effet, réunies au crâne du Crocodile à museau moins long' ('he [Cuvier] created several anatomical monstrosities, by constructing one species with parts of two others; thus his long snout crocodile, with long jaws, indeed, joined to the skull of the crocodile with a shorter snout'). Blainville is thus the first one to note that Cuvier's 'Honfleur crocodile' species were chimeras. ...
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Metriorhynchidae was a clade of extinct crocodylomorphs that adapted to a pelagic lifestyle, becoming a key component of Mesozoic lagoonal and coastal marine ecosystems. The type genus Metriorhynchus is one of the best-known genera of Mesozoic crocodylomorphs, and since the mid-19th century, the ‘concept’ of Metriorhynchus has become associated with the referred species Me. superciliosus. Historically Metriorhynchus has been the most species-rich genus in Metriorhynchidae, with most Middle Jurassic species and many Late Jurassic species referred to the genus at some point in their history. However, the type species Me. geoffroyii has largely been omitted in the literature. Its type series is a chimera of multiple metriorhynchid species, and a type specimen has never been designated. Moreover, phylogenetic analyses have repeatedly shown that the 19th–20th century concept of Metriorhynchus is not monophyletic – to the point where only referring every metriorhynchid species, and some basal metriorhynchoids, to the genus would render it monophyletic. Herein we designate a lectotype for Me. geoffroyii, re-describe it and restrict the genus Metriorhynchus to the type species. We also establish the new genus Thalattosuchus for Me. superciliosus, thereby cutting the ‘Gordian knot’ of Metriorhynchus with Th. superciliosus.
... Larson and Sidor, 1999;Carvalho et al., 2007;Larson and Sues, 2007;Geroto and Bertini, 2019). Denticulated carinae are a common feature among many crocodyliform taxa, as they appear in notosuchians, peirosaurids, Theriosuchus, paralligatorids, basal tethysuchians and thalattosuchians (e.g., Gasparini et al., 1991;De Lapparent De Broin, 2002;Schwarz and Salisbury, 2005;Sereno and Larsson, 2009;Andrade et al., 2010;Brochu, 2013;Adams, 2014). There are several similar characteristics between UFRJ-DG 659RD and other crocodyliform teeth, such as the almost conical morphology of the crown and the denticulated carinae seen in the caniniforms of peirosaurids (Gasparini, 1982;Carvalho et al., 2004;2007;Hendrickx, pers. ...
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Several studies have used isolated crocodyliform and theropod teeth as an important tool for taxonomic identification, as they can often be the only record of some taxa. The objective of this paper is the description and identification of the isolated crocodyliform and theropod teeth in order to clarify which taxa inhabited the western portion of the Potiguar Basin during mid-Cretaceous. The material consists of six tooth crowns from Açu Formation (Albian–Cenomanian), Potiguar Basin, northeastern Brazil. The crowns were identified by a set of qualitative (morphological comparisons and cladistics) and quantitative analyses. UFRJ-DG 659Rd was identified through morphological comparison as a peirosaurid crocodyliform due to its true ziphodont condition, enamel with an irregular texture, and faint lingual fluting. Five of the tooth crowns were identified as abelisaurid theropods based on the results of the cladistic analysis and morphological comparison, with the quantitative analysis supporting this result only for two of the five teeth. This result represents the first report of peirosaurids and abelisaurids in Potiguar Basin, and possibly one of the oldest abelisaurid records in Brazil.
... The question whether there were one or multiple species of Cricosaurus species from the late Kimmeridgian-early Tithonian of Southern Germany, or just one, has been discussed in the literature. Andrade et al. (2010) noted that there was a potential synonymy between C. elegans and C. suevicus and stated that all specimens referred to C. suevicus at that time were from Malm Zeta 1 (upper Kimmeridgian), while those referred to C. elegans were known from Malm Zeta 2-3 (lower Tithonian). As such, there was a question as to the validity of the specific separation, or whether these where chronospecies or an anagenic lineage. ...
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Herein we describe a new and exceptionally well-preserved skeleton of the metriorhynchid thalattosuchian Cricosaurus from the upper Kimmeridgian Torleite Formation of Painten in Bavaria (Southern Germany). The specimen is articulated, shows soft-tissue preservation, and represents one of the most complete metriorhynchid skeletons known. The exceptional preservation allows us to explore the morphological variation of the tail region in the Metriorhynchidae, a part of the skeleton that has long been neglected. Based on our description and phylogenetic analyses, we name this specimen Cricosaurus albersdoerferi sp. nov. Our phylogenetic analyses recover a Cricosaurus subclade composed of four species from Southern Germany and one from Argentina. We provide revised diagnoses for the Southern German members of this subclade, revealing the presence of at least four closely-related Cricosaurus species in the late Kimmeridgian-early Tithonian of Southern Germany. Interestingly, within this subclade there is evidence of rapid change in tail construction and feeding ecology. However, there is no evidence of sympatry between these taxa, and the two species known from the same ammonite subzone are exclusively found in different northern-Tethys lagoons. Most interesting, however, is the variation in the skulls, dorsal neural spines, the tail displacement units, and flukes between these different species. This previously unexplored variation within Metriorhynchidae hints to differences in locomotory abilities between different species.
... Surprisingly the Cretaceous-Palaeogene boundary does not appear to be associated with any changes in mean body size. In all cases, even with ghost ranges reconstructed, we may miss earlier unpreserved portions of the records of lineages 40 . ...
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... These differences in tissue arrangements have previously been discussed in relation to functional advantages (e.g. [20,[22][23][24][25][26][27][28][29][30]). The functional significance of serration types is especially important given that morphologies commonly associated with hypercarnivory (e.g. ...
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