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A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
Boletín de la Sociedad Geológica Mexicana
/ 2017 /
87
BOL. SOC. GEOL. MEX. 2017
VOL. 69 NO. 1
P. 87 ‒ 134
RESUMEN
Se describe el esqueleto casi completo de un
nuevo plesiosaurio polycotílido. El ejemplar
procede de las calizas laminares de Valle-
cillo del noreste de México y fue asignada
estratigráficamente a la parte temprana del
Cretácico Tardío. En las porciones mejor
preservadas de las partes blandas se iden-
tificaron estructuras milimétricas, alarga-
das transversalmente de forma rectangular
a trapezoidal, y con orden longitudinal. En
la solapa, el borde posterior de la piel pre-
serva fibra y escamas, ordenadas en filas y
perpendiculares al borde de salida. Se iden-
tificó una capa de tejido subdermal, la que
es particularmente gruesa en la base de la
cola y debe haber contribuido al contorno hi-
drodinámico en forma de gota del animal,
formándose una entidad entre el cuerpo y la
cola. De acuerdo con el contorno y los teji-
dos blandos, se presume que la velocidad del
animal debe de haberse aproximada a la de
una tortuga laúd. La enigmática osteología
del paladar, intermedio entre Dolichorhyn-
chops y Trinacromerum, la morfología única
de los cinturones y propodiales, igual que las
vértebras gastrales medialmente convergentes,
permiten asignar el nuevo espécimen a un
nuevo género y especie de los Polycotilidae,
Mauriciosaurus fernandezi gen. et sp. nov.
Palabras clave: Paleontología de
vertebrados, Plesiosauria, Poly-
cotylidae, Cretácico Tardío, nor-
este de México, preservación de
partes blandas, paleoecología.
ABSTRACT
A nearly complete skeleton of a poly-
cotylid plesiosaur is described from
the early Late Cretaceous laminat-
ed limestones at Vallecillo, northeast
Mexico. It shows extensive soft tissue
preservation. In some exceedingly
well preserved areas there are trans-
versely elongate rectangular to trap-
ezoid millimetric scale-like structures
arranged in longitudinal rows. The
trailing edge skin flap preserves fibers
and scale rows perpendicular to the
trailing edge. A thick layer of subder-
mal tissue is present, especially along
the tail base. It was responsible for
the hydrodynamic drop-shaped body
contour, with the body and tail form-
ing a single unit. The body shape
determined from the preserved soft
tissues suggests a swimming speed
similar to extant leatherback turtles.
Based on the unique osteology of the
palate, which is intermediate between
Dolichorhynchops and Trinacromerum,
and according to the unique mor-
phology of the girdles and propodi-
als as well as the medially converging
gastralia, the new specimen is placed
in a new genus and species of Poly-
cotylidae, Mauriciosaurus fernandezi
gen. et sp. nov.
Keywords: Vertebrate palaeon-
tology, Plesiosauria, Polycotyli-
dae, Late Cretaceous, northeast
Mexico, soft tissue preserva-
tion, palaeoecology.
Manuscript received: December 4, 2016
Corrected manuscript received: December 29, 2016
Manuscript accepted: December 31, 2016
Eberhard Frey
dinofrey@aol.com
Staatliches Museum für Naturkunde Karl-
sruhe, Geowissenschaftliche Abteilung, Erb-
prinzenstraße 13, 76133 Karlsruhe, Germany.
Eric W. A. Mulder
Museum Natura Docet Wonderryck Twente,
Oldenzaalsestraat 39, 7591 GL Denekamp,
the Netherlands.
Wolfgang Stinnesbeck
Universität Heidelberg, Institut für Geowis-
senschaften, Im Neuenheimer Feld 234-236,
69120 Heidelberg, Germany.
Héctor E. Rivera-Sylva
José Manuel Padilla-Gutiérrez
Arturo Homero González-González
Museo del Desierto, Carlos Abedrop Dávila
3745, Centro Metropolitano, Parque Las
Maravillas, 25022 Saltillo, Mexico.
ABSTRACT
Eberhard Frey, Eric W.A. Mulder, Wolfgang Stinnesbeck, Héctor E. Rivera-Sylva,
José Manuel Padilla-Gutiérrez, Arturo Homero González-González
A new polycotylid plesiosaur with extensive soft tissue preservation
from the early Late Cretaceous of northeast Mexico
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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INTRODUCTION
1. Introduction
Plesiosauria are one of the dominant groups of
Mesozoic marine reptiles. Besides the enigmatic
Pistosaurus and its allies of Middle to late Triassic
age, two ‘suborders’ are distinguished in tradition-
al systematics, the either long- or short-necked
Plesiosauroidea and the exclusively short-necked
Pliosauroidea (Carpenter, 1997; Druckenmiller
and Russell, 2008; Ketchum and Benson, 2010;
O’Keefe, 2001). A body with a rounded triangu-
lar or oval cross-section and a tail, whose length is
shorter than the body, are the main features that
characterize all Plesiosauria. Plesiosaurs swam
with four hydrofoil-shaped ippers of almost equal
size with dorsoventrally attened limb bones, a
unique pattern of aquatic locomotion. Among
Plesiosauria, ipper size varies with respect to
body size (Ellis, 2003; Hampe, 1992). The skele-
tal anatomy of these predatory marine reptiles is
known from numerous excellently preserved spec-
imens, and much is known about their life style,
but little about their reproduction and ontogeny
(Noé, 1999; O’Keefe and Carrano, 2005; O’Keefe
and Chiappe, 2011; Taylor, 1986). The diet of
elasmosauroids and pliosauroids is evidenced by
rare fossil stomach contents and the body cavity of
some specimens also contains gastroliths, the role
of which is still debated (Brown, 1904; Cicimurri
and Everhart, 2001; Cope, 1872; Martill, 1992;
McHenry et al., 2005; Taylor, 1993). While sub-
aqueous ight is generally accepted as the main
mode of locomotion, the mode of ipper opera-
tion remains debated as the role of the tail (Frey
and Riess, 1982; Godfrey, 1984; Halstead, 1989;
Lingham-Soliar, 2000; Robinson, 1975; Sanders et
al., 2004; Taylor, 1981). Reconstructions of plesio-
saurs with a tail n are based on a single specimen
of Seeleyosaurus guilelmiimperatoris (Dames, 1895)
from the Early Jurassic of Holzmaden (South
Germany). This specimen shows a black expand-
ed substance dorsal to the posterior quarter of the
posterior vertebral column. However, Großmann
(Großmann, 2006) states that after a detailed study
of the specimen that this tail n is likely to have
been fabricated. There is discussion on whether
plesiosaurs could crawl on land, as do sea turtles
and pinnipeds, and on how fast they could swim
(Taylor, 1986). The discovery of a pregnant fe-
male of a polycotylid plesiosauroid, a longirostrine
group of Late Cretaceous plesiosaurs, provides ev-
idence that Plesiosauria were viviparous and did
not need to emerge on land for the purpose of egg
laying (O’Keefe and Chiappe, 2011).
Despite numerous complete and fully articulated
skeletons being available, there is a lack of soft
tissues in the fossil record of Plesiosauria. Even
in localities where soft tissue preservation is well
known from other vertebrates in the assemblage
there is no unequivocal record of soft tissue for
plesiosaurs. In one single Holzmaden specimen of
Hydrorion brachypterygius in the collection of the Ge-
ologisch-Paläontologisches Institut at Tübingen,
Germany (GPIT/RE/3185), a black substance
trailing the proximal half of the posterior margin
of the front ns is preserved suggesting a skinny
exible trailing edge (Großmann, 2006; Robinson,
1975). Besides the tail n (Dames, 1895) this rep-
resents the only record of soft tissue preservation
in plesiosaurs. Information on the body shape of
plesiosaurs and the surface structure of their skin
remains a mystery.
Polycotylid plesiosaurs are a cosmopolitan taxon
with a temporal range extending from the Early
Aptian to the Late Maastrichtian (Druckenmiller
and Russell, 2009). One of the currently oldest
representatives, the Australian Umoonasaurus dem-
oscyllus (Kear et al., 2006), is no longer referred
to Polycotylidae by most authors (Druckenmiller
and Russell, 2009). The same is true for Edgaro-
saurus muddi from the Late Albian Thermopolis
Shale of the United States which, according to
many authors, lies outside Polycotylidae (Albright
III et al., 2007a; Benson et al., 2013; Schumacher,
2007; Schumacher et al., 2016) Two specimens,
AM 6206-6298 and SAM P36356, both from
the Aptian or Albian Bulldog shale of Australia
(Kear, 2006), have not been formally named. The
earliest polycotylid from North America, TMP
95.87.01, comes from the Albian Clearwater For-
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
89Boletín de la Sociedad Geológica Mexicana
/ 2017 /
89
INTRODUCTION
Figure 1 Geographical position of the town of Vallecillo. The new polycotylid comes from the quarry field in the close vicinity of
Vallecillo. The exact quarry of provenance cannot be reconstructed, because the slabs were already loaded on a truck.
mation of Alberta, Canada, and is also unnamed.
Thus, the earliest named polycotylids are those
reported from the Cenomanian of North Amer-
ica [Eopolycotylus rankini, (Albright III et al., 2007a),
Palmulasaurus quadratus, (Albright III et al., 2007a,
b), Pahasapasaurus haasi, (Schumacher, 2007)] and
Morocco [Thililua longicollis, (Bardet et al., 2003)].
The geologically youngest polycotylid has no for-
mal name or collection number and comes from
New Zealand (Kear, 2006: p. 847, Figure 2E). The
geologically youngest named species, Sulcusuchus
erraini comes from near the Campanian/Maas-
trichtian boundary of Argentina (Gasparini and
Fuente, 2000).
This report describes a new genus and species of
polycotylid plesiosaur (collection number INAH
CPC RFG 2544 P.F.1) from the Late Cretaceous
of northeast Mexico. The specimen comes from
laminated limestones cropping out around the
town of Vallecillo (26°39’N 99°59’W), about 100
km north of the City of Monterrey, Nuevo León
(Figure 1). The skeleton is complete, fully articu-
lated and represents the rst plesiosaur preserving
dermal surface structures in ne detail. The spec-
imen was discovered in summer 2011 by a group
of workmen in an active limestone quarry in the
vicinity of Vallecillo.
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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MATERIAL AND METHOD / GEOLOGICAL
SETTING
2. Material and method
The material comprises a single specimen pre-
served in nely laminated, micritic limestone.
Photographs were taken with an Olympus TG 1
(“Tough”) and an Olympus E 620 with a Zuiko
Digital 14 – 42 mm lens, 1:3.5 – 5.6 and a Zuiko
Digital Macro 35 mm lens, 1:3.5. Low angle light
photography was performed with an infrared con-
trolled Olympus Electronic Flash FL 36R. Pho-
tographs were traced with CorelDraw X6. The
drawings were designed using the same program.
The specimen was investigated under natural and
articial low angle illumination.
3. Geological setting
The new specimen comes from the Cenomanian
to Turonian Agua Nueva Formation, a dominant-
ly carbonate unit comprising thick sequences of
cyclic limestone and shale that are widely distrib-
uted in northeastern Mexico. These strata were
deposited in a moderately deep shelf of low relief,
which were developed along the western coast of
the Gulf of Mexico extending as far as the West-
ern Interior of the United States of America and
Gulf of Mexico Basin (Goldhammer and Johnson,
2001; Ifrim, 2006; Muir, 1936; Sohl et al., 1991).
The Agua Nueva Formation is generally poor in
macrofossils (Sohl et al., 1991), but it includes a unit
of thin-bedded laminated limestone and marl (plat-
tenkalk) with abundant and exquisitely preserved
vertebrates of latest Cenomanian to earliest Turo-
nian age. The fauna includes a diverse assemblage
of shes (selachians, crossopterygians, pycnodon-
tiforms, aspidorhynchiforms, teleosts) and marine
reptiles (Mosasauroidea and Chelonia). Many of
the fossils exhibit soft tissue preservation (Buchy et
al., 2007; Ifrim et al., 2005). Until now, Plesiosau-
ria are represented by a single tooth (Blanco-Piñón
et al., 2005; Blanco-Piñón and Alvarado-Ortega,
2007; Blanco and Alvarado-Ortega, 2006; Blanco
and Cavin, 2003; Buchy et al., 2005; Giersch, 2014;
Ifrim, 2006). This assemblage is known mainly
from around the small town of Vallecillo, but sim-
ilar coeval lithologies and fossiliferous horizons are
known from other areas in northeastern Mexico,
including Monterrey, Arteaga and Ciudad Victo-
ria (Ifrim et al., 2008; Stinnesbeck and Frey, 2014).
The Vallecillo-type plattenkalk is thus widespread
and covers an area of at least 10000 square kilo-
meters. It formed on an open shelf environment
under anoxic conditions caused by global Oceanic
Anoxic Event 2 OAE 2 (Ifrim et al., 2011, 2008;
Ifrim and Stinnesbeck, 2008; Schlanger and Jen-
kyns, 1976). The polycotylid presented here is the
rst virtually complete plesiosaur of the Late Cre-
taceous of Vallecillo, and the rst complete poly-
cotylid from Mexico.
At Vallecillo, the plattenkalk section of thin-bed-
ded and millimetrically laminated platy marl is 7.7
m thick and contains abundant planktic foramin-
ifera, inoceramid bivalves, ammonites and crus-
taceans (Stramentum) which provide a precise and
detailed biostratigraphic zonation from the latest
Cenomanian Inoceramus pictus pictus Zone to late
Early Turonian (Mammites nodosoides Vascoceratid
- Mytiloides kossmati assemblage) (Ifrim and Stinnes-
beck, 2008). The invertebrate assemblage, the bio-
stratigraphy, as well as sedimentological aspects,
have been described in detail by Ifrim (2006).
The slab containing the polycotylid plesiosaur de-
scribed here is associated with a specimen of Mam-
mites nodosoides, indicating that it is from the late
Early Turonian interval of the Vallecillo section.
The Vallecillo plattenkalk is a Konservat-Lager-
stätte deposited in an open marine environment
several hundred kilometres from the North Amer-
ican coastline, near the southern opening of the
Western Interior Seaway into to the Paleogulf of
Mexico (Figure 2). The excellent preservation of
vertebrate fossils is explained by the absence of
traction currents and storm waves on the sea oor,
combined with dysoxic to anoxic conditions on the
substrate resulting in the absence of carnivores,
scavengers, and infaunal benthos. Inoceramids are
the only abundant benthic element in the macro-
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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GEOLOGICAL SETTING / PRESERVATION
and microfauna and may have adapted to the
hostile low-oxygen conditions by sheltering che-
moautotrophic microbes as symbionts (e.g., Fischer
and Bottjer, 1995; Ifrim et al., 2011; MacLeod and
Hoppe, 1992).
4. Preservation
The complete and fully articulated polycotylid
plesiosauroid, is accessible through the Museo
del Desierto, Saltillo, Coahuila Mexico under the
INAH (Instituto Nacional de Antropología e His-
toria) collection number CPC RFG 2544 P.F.1. It
is preserved on 28 slabs that t closely together
(Figure 3). The specimen has a length of 1.9 me-
ters, a ipper span of 1.15 meters and is exposed
in ventral aspect. Besides a substantial part of the
left coracoid, only small sections of the skeleton
are missing: a slab immediately craniomedially to
the left pubic plate, the distal half of the right fore
ipper, the distal third of the left hind ipper, a
segment of the mid part of the right hind ipper
and the tip of the tail (Figure 3A). These elements
were lost when the quarry workmen excavated
the specimen. The propodials and all girdle bones
show slight impaction and/or deformation cracks.
The vertebrae, mandible, epipodials, metapodi-
als and phalanges are somewhat deformed due to
compaction.
The postcervical vertebral column is nearly
straight, but the neck is strongly curved to the
Figure 2 Geographical position of Vallecillo N.L. during the Turonian. Note that the Western Interior Seaway is connected with the
Paleogulf of Mexico (modified from Bhattacharya and MacEachern, 2009).
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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PRESERVATION
Figure 3 : Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. A) Photograph of the specimen after preparation, B) interpretative line
drawing. Note the massive tail base and the dorsal skin preserved between the ribs.
right such that the skull is orientated at an angle
of about 85° to the long axis of the trunk and tail
skeleton (Figure 3). The skull is exposed in ven-
tral aspect with the mandible in articulation (Fig-
ures 3, 4 A, B). The mandibular rami have been
distorted because the left is positioned vertically
with only its ventral edge visible, while the right
ramus shows its ventrolateral aspect. The palate is
exposed between the mandibular rami and shows
only minor compaction fractures. The cranium
and mandible are slightly twisted sinistrally where-
by the mandible was sheared to the left by about
5° against the long axis of the cranium but with
the jaw articulations remaining in contact. Fifteen
teeth are visible on the right side of the rostrum,
two of which likely belong to the premaxilla. Nine
teeth are preserved on the left side, of which two
belong to the premaxilla. However, tooth positions
can only be positively identied on the right max-
illa, the alveolar ange of which is fully exposed.
Only a few fragments of the left maxilla are visible
medially adjacent to the left splenial and lateral to
the left margin of the mandible (Figure 4 A, B).
The enamel of all preserved teeth as well as some
apices of the crowns has been largely scratched
away during preparation.
All vertebrae posterior to the atlas-axis system are
seen in ventrolateral view such that the neural
spines are visible in lateral aspect (Figures 3, 5, 6).
The anterior and posterior margins of the neu-
ral spines contact each other and dene the neck
curvature. The neural spines have been distorted
dextrally at their bases due to compression. The
torsion of the cervical series begins immediately
posterior to the atlas-axis, which is slightly disartic-
ulated but is still in contact with the occipital con-
dyle (Figures 3, 4 A, B). This torsion persists to the
cervicothoracic transition at the base of the neck.
The ribcage has collapsed posteriorly and the ven-
tral termini of the ribs overlie each other (Figures
3, 8). There is no trace of a lateral movement of
the ribs, implying that vertebrocostal articulation
must was maintained on burial. The gastralia are
only slightly disarticulated in a few places but the
entire gastral basket has been attened by com-
paction so that the ventral termini of the gastralia
now extend beyond the ribcage and protrude be-
yond the lateral margin of the preserved skin on
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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PRESERVATION
the left side of the trunk (Figure 6).
Like the gastralia, the ventral bones of both girdles
lie at in one plane (Figures 3, 8). While the me-
dian suture of the coracoids, as far as preserved,
is in tight contact, the pubic symphysis has slight-
ly separated, but the ischia maintain their in situ
Figure 4 : Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. A) skull as preserved in ventrolateral aspect, B) interpretative line
drawing, C) reconstruction of the skull in ventral aspect.
contact. The dorsal elements of both girdles are
disarticulated but still lie close to their original in
situ position (Figures 3, 8). The ventral elements
of both girdles have been deformed around the
underlying bones (Figure 6). Both scapulae, the ex-
ternal face of which is exposed, have symmetrical-
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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PRESERVATION / SYSTEMATIC
PALEONTOLOGY
ly rotated anterolaterally but retain contact with
the coracoids with their anteroproximal corner at
the glenoid fossa (Figures 3, 8). The anteromedial
corners of both scapulae lie adjacent to the cer-
vical vertebrae. The scapular processes of both
scapulae face laterally. Both ilia have rotated pos-
teriorly at the posterior acetabular contact. They
lie along the lateral margin of the ischia with their
medial face exposed (Figures 3, 8).
All four ippers extend laterally. While both hu-
meri face laterally at an angle of ~90° to the long
axis of the trunk, the femora are orientated cau-
dolaterally at an angle of ~ 60° (Figure 3). The
metapodial and digital elements are slightly curved
posteriorly. The curvature is stronger in the front
than in the hind ippers. The incomplete right
front ipper shows the strongest curvature of all
four (Figure 3). Adjacent to the posterodistal cor-
ner of the left humerus there are two disk-shaped
bones, possibly parts of the interclavicles (Figure
9).
The soft tissue has a reddish-brown color and is
preserved along the right side of the postorbital
part of the skull, and from there it continues along
the right side of the neck (Figure 3). On the left
side of the neck the soft tissue is restricted to the
cervicothoracic transition (Figure 15). On both
sides of the trunk, soft tissue is preserved at the
shoulder girdle and the anks with a width of be-
tween 50 mm and 70 mm. It continues along the
pelvic girdle without any constriction onto the tail
base (Figures 3, 8). Here, the soft tissue reaches a
maximum thickness of 170 mm immediately pos-
terior to the ischiadic plates and from there gradu-
ally converges towards the end of the tail. Patches
of a grey matter, which are apparently related to
the soft tissue, are preserved along the right side
of the body and at both sides of the tail. Wrinkled
dark coating, which likely represents the visceral
skin surface or the peritoneum, is visible between
the ribs and the central elements of the gastralia
(Figure 14). Soft tissue is also preserved along the
ipper (Figures 3, 16). The humerus and proximal
podials of both front ippers are surrounded by
the reddish-brown substance. The soft tissue at the
left front ipper expands posteriorly to about one
fourth of the width of the ipper and terminates
at about in the mid-length of the manus. There is
soft tissue preserved that extends to the tip of the
IVth digit of the right hind ipper, and is one third
the width of the ipper (Figures 3, 12).
5. Systematic paleontology
Plesiosauria de Blainville, 1835
Plesiosauroidea Welles, 1943
Leptocleidia Ketchum and Benson, 2010
Polycotylidae Williston, 1908
Mauriciosaurus gen. nov
Mauriciosaurus fernandezi sp. nov.
Derivation of name: Genus and species name
in honor of Mauricio Fernández Garza, who not
only made the specimen accessible for scientic re-
search, but also secures all future work in the quar-
ry area at Vallecillo and supports public education
in Earth- and biological sciences predominantly in
the state of Nuevo León.
Holotype: A nearly complete and articulated
skeleton with extensive soft tissue preservation
(Figure 3) with the INAH (Instituto Nacional de
Antropología e Historia) registration number CPC
RFG 2544 P.F.1. The specimen is housed and on
display in the Museo Papalote Verde, Monterrey.
Type locality: Vallecillo (26°39’N 99°59’W),
western quarry eld (Figure 1)
Type horizon: Vallecillo Member of the
Aguas Nuevas Formation (Early Turonian, Late
Cretaceous).
The specimen is referred to Polycotylidae accord-
ing to the following combination of features:
Family: Polycotylidae (Albright III et al., 2007a;
Benson et al., 2013; O’Keefe, 2001; Schumacher et
al., 2016; Williston, 1908)
1. Pterygoids with anterior processes emerging
from the middle of the anterior pterygoid
body (Figure 4).
2. Pterygoid body with a shallow oval depression
(“dished” according to O’Keefe, 2001) lateral
A new polycotylid plesiosaur from the early Late Cretaceous of northeast Mexico
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SYSTEMATIC PALEONTOLOGY
to posterior interpterygoid vacuities meeting
posterior to the posterior interpterygoidal va-
cuities (Figure 4).
3. Mandibular symphysis long (measuring at
least one fourth of the entire mandibular
length; Table 1; Figure 4).
4. Number of cervical vertebrae reduced (when
compared with other Leptocleidia).
5. Humerus shorter but posterodistally slightly
more expanded than femur (Figures 10, 12).
6. Shaft of humerus with subtle sigmoid curva-
ture (Figure 12).
7. Supernumerary ossications in epipodial rows
(Figures 10 – 12).
8. Phalange digits one through four interlocking
(Figures 10 – 12).
9. Pterygoids meet atop the parasphenoid clos-
ing the posterior interpterygoideal vacuities
(Figure 4).
5.1. DIAGNOSIS FOR THE GENUS AND SPECIES
1. Dish-like depression restricted to the anterior
half of the pterygoideal plates. The depres-
sion is posteriorly open, merging with a relief
of prominent ridges that are arranged in a
W-conguration covering the posterior half
of the pterygoideal corpus (Figure 4). This re-
lief is perfectly preserved in three dimensions
and it resembles that of Polycotylus (Schum-
acher et al., 2016), but is more complex in
Mauriciosaurus.
2. Anterior pterygoid rods expand at union with
the vomers to three times the width of the
basal third of the processes (Figure 4).
3. Parasphenoid with a deeply concave ventral
face and concave lateral margins in the mid-
dle part of the bone; anterior process bifurcat-
ed (Figure 4) without any trace of a median
protuberance.
4. Posterior interpterygoidal vacuities narrow,
longitudinally oval with a slight anterior ex-
pansion (Figure 4).
5. At least 42 tooth positions on either side of the
upper jaw.
6. No posterior or medial perforations in the
Table 1. Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1;
measurements of the skull in mm.
Measurements of the skull in mm
Length of left mandibular ramus 420
Length of right mandibular ramus 425
Length of symphysis 175
Mandibular width at caudal end of
symphysis 70
Ratio mandibular/symphyseal length approx. 45%
coracoids (Figure 8). This could be due to the
juvenile stage of the specimen, but given the
fact that this animal probably had at least half
the length of an adult, one should expect at
least to the a trace of such perforations.
7. Average length/width ratio of phalanges of
digit III is 1.77. The polycotylid standard
would be 1.5 (Table 5; Albright III et al.,
2007a).
8. Gastralia converging medially, forming a me-
dian plate-like structure (Figure 9). A similar
structure has been described for Cryptoclidus
(Brown, 1981), but not for any polycotylid.
5.2. NOMENCLATURAL ACTS
The electronic edition of this article conforms to
the requirements of the amended International
Code of Zoological Nomenclature, and hence the
new names contained herein are available under
that Code from the electronic edition of this ar-
ticle. This published work and the nomenclatural
acts it contains have been registered in ZooBank,
the online registration system for the ICZN. The
ZooBank LSIDs (Life Science Identiers) can be
resolved and the associated information viewed
through any standard web browser by appending
the LSID to the prex “http://zoobank.org/” (In-
ternational Commission on Zoological Nomencla-
ture, ICZN, 2017). The LSID for this publication
is: urn:lsid:zoobank.org:act:DF54BB6D-73DE-
4BEC-8723-A9B7B4A888B9 for the genus
and urn:lsid:zoobank.org:act:8D331E82-25B5-
4E81-98F8-AFE7086E7693 for the species..
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The electronic edition of this work was pub-
lished in a journal with an ISSN, and has been
archived and is available from the following dig-
ital repositories: PubMed Central, LOCKSS
urn:lsid:zoobank.org:pub:2B15EAB5-9688-
4DF3-8149-77217E598238.
6. Osteology
SKULL (FIGURE 4)
Both mandibular rami overlie the ventral surface
of the skull, which is slightly twisted to the left side
around its long axis in a way that the skull is vis-
ible in ventrolateral view. The mandible remains
in articulation but has been sheared to the left in
anterior direction. Therefore, the entire alveolar
ange of the right premaxillomaxillary complex
is exposed, whereby most of the medial part of
the left premaxilla is only preserved as an external
mould (Figure 4 A). Of the left maxilla only frag-
ments of the mid part of the alveolar margin are
visible. The tip of the rostrum is missing. Due to
compaction many of the bones are crushed, which
makes the reconstruction of their outline dicult
or impossible.
MANDIBLE (FIGURE 4; TABLE 1)
Dentary: With the exception of its anterior ter-
minus, the right dentary is preserved for its entire
length, while the left one is only half preserved.
The right dentary terminates at the level of the
posterior margin of the pterygoideal corpus. The
dentaries converge at an angle of ~10° towards
the dentary symphysis, which forms about 50 %
of the mandibular symphysis that posteriorly ter-
minates at the twelfth maxillary tooth position.
The dentary part of the symphysis measures one
sixth of the dentary length. At the symphysis the
lateral margin of the dentary is slightly convex an-
teriorly terminating in an acute anterior tip. Pos-
terior to the dentary symphysis the lateral margin
of the bone is slightly concave, and levels with the
posterior terminus of the maxilla. Ultimately, it
becomes convex again paralleling the squamosal.
The medial margin of the dentary parallels the
lateral margin. The bone surface of the dentaries
appears slightly sculptured with irregular shallow
longitudinal striae, but much of the surface struc-
ture of the bones has been scratched away during
preparation.
Splenial: Both splenials are preserved over their
entire length. The right one is seen in ventrolat-
eral and the left one in ventromedial view due to
the slight torsion of the skull (Figure 4). The sple-
nial symphysis forms the posterior 50 % of the
mandibular symphysis with an apertural angle of
about 10° at the anterolateral margin and about
15° at the anteromedial one. The splenial symphy-
sis measures about one fth of the longitudinal ex-
pansion of each bone. The lateral margins of the
splenials lie in articulation with the medial margin
of the dentaries following their curvature. The
ventral face of each splenial slightly converges in
posterior direction with the medial margin run-
ning sub-parallel to the lateral one. The ventro-
lateral part of each splenial terminates at level of
the middle of the maxillary arches 15 mm anterior
to the posterior margin of the pterygoid where it
forms a posteriorly directed U-shaped suture with
the angular. The medial ange of the splenial is
only visible on the left mandibular ramus, but ap-
pears to terminate at the level of the anterior base
of the jugal and contacts the surangular with a
sigmoidal suture. A faint striation of the bone sur-
face has been partially destroyed by unprofessional
preparation.
Angular: Both angulars are preserved (Figure 4).
The right one shows its lateral, the left one its me-
dial aspect. The lateral face measures about one
fourth of the length of the anteriorly adjacent
splenial and is slightly laterally convex. The dor-
sal and ventral margins are parallel to each other.
The anterior margin of the lateral face shows an
anteriorly open U-shaped incision that matches its
equivalent on the posterior margin of the splen-
ial. The posterior terminus of the left splenial is
slightly eroded but likely was evenly rounded as
is seen on the right splenial. The medial face of
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each angular is concave. Each bone contacts a
surangular with its regularly concave dorsal mar-
gin, which runs near parallel to the ventral one.
The curvature of the angular gradually increas-
es posteriorly. Each angular contacts the vertical
posterior margin of the surangular in a posteriorly
open V-shaped suture. At their anterior ends, the
angulars appear to underlie the splenials for a few
millimeters forming a squamate suture. Again the
bone surface is badly scratched.
Surangular (Figure 4): The right surangular ex-
poses its lateral, the left one its medial face. The
lateral face of each bone has about two thirds the
length of the lateral face of the angular, while its
medial face has three times the length of the lat-
eral face, covering the suture between angular and
splenial medially. While the anterior two thirds of
the medial ange of the surangulars are straight
and parallel-sided, the posterior third of the bone
curves medially, thereby slightly diverging in pos-
terior direction. The surface of the bone appears
smooth.
Articular (Figure 4): Only the left articular can
be seen on the left mandibular ramus, where it
is mostly overlain by the angular and surangular.
Only the posterior-most terminus of the retroar-
ticular process and the dorsomedial tip of the
posterior cotylar process of the glenoid fossa are
visible. The original shape of the bone cannot be
determined.
CRANIUM (FIGURE 4)
Premaxilla: Only the lateral margin of the right
premaxilla is preserved as a slender seam of bone,
which is broken dorsally to the alveolar ange,
which is now missing. Medial to the preserved re-
main of the premaxilla there is an internal mold
of the internal surface of the alveolar ange,
which is smooth and convex in all directions, with
the transverse convexity being strongest. Posterior-
ly the lateral premaxillary wall overlaps the later-
al margin of the maxilla reaching the level of the
third visible maxillary alveolus. This overlap likely
represents the lateral part of the suture with the
maxilla, while the ventral part is missing. Howev-
er, the damaged anterior margin of the alveolar
ange of the maxilla suggests that the premaxillo-
maxillary suture was transverse at least in its later-
al third. The remnants of three premaxillary teeth
lie adjacent to the right premaxilla. Two teeth that
are topographically referred to the left premaxilla
are preserved to the left side of the left dentary.
There were at least four widely spaced premaxil-
lary teeth.
Maxilla: The entire alveolar ange of the right
maxilla is preserved. Anteriorly the bone termi-
nates at the level of the middle of the dentary
symphysis, posteriorly it forms an obliquely direct-
ed suture with the jugal, and tapering to a point-
ed terminus. The maxillosquamosal suture covers
about one third of the squamosal as exposed. Al-
together 32 tooth positions are identied on the
right maxilla. Alveolae numbers 5, 12 to 21, 23
and 30 to 32 contain slightly recurved conical
teeth. Of the left maxilla, the posterior two thirds
of the palatinal part are preserved, the posterior
third of which are mostly overlain by the left sple-
nial. A few fragments of the middle part of the lat-
eral-most portion of the alveolar ange are visible
adjacent to the lateral margin of the left dentary.
The remnants of seven teeth from the left maxilla
are preserved but they cannot be assigned to their
respective tooth positions.
Vomer: Only two insignicant portions of the
vomers are preserved between the medial mar-
gin of the palatinal part of the left maxilla and
the right splenial. Neither the overall shape of the
bone nor its posterior or anterior extension can be
reliably reconstructed. As preserved the vomer ter-
minates posteriorly at the level of maxillary tooth
position 22 and separates the anterior processes of
the pterygoids.
Palatine: Only fragments of the palatines are
preserved. The left palatine preserves the entire
transverse extent, but only the medial half is pre-
pared and exposed. The lateral half of the right
palatine is overlain by the right splenial. Most like-
ly the palatines had sub-triangular outlines. An-
teriorly they taper between the palatinal part of
the maxilla and the anterior process of the pter-
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ygoid. The medial margin of the palatines forms
a laterally convex loose contact with the anterior
process of the pterygoids. Close to the posterior
base of the anterior process of the pterygoid, the
suture curves laterally and accommodates a low
lateral process of the pterygoid. Two thirds of this
suture is preserved on the right side. The lateral
margins of the palatines contact the medial mar-
gin of the palatinal part of the maxillae. However,
the middle two thirds of the palatinomaxillary su-
ture on the left side of the cranium are obscured
by matrix. The posterior margin of the palatines
is poorly preserved and thus is dicult to recon-
struct. Evidently they closely approached the ec-
topterygoids approximately in the middle of the
posterior margin of the palatines, but the contact
is not preserved. Medially and laterally there is a
concavity that forms the anterior margin of the
adductor chamber.
Pterygoid: The pterygoid consists of a rounded
irregularly pentagonal corpus and an anterior pro-
cess, which is one fth longer than the corpus and
anteriorly reaches the level of maxillary tooth po-
sition 18. The corpus expands anteriorly until the
level of the maxillary tooth position 32. The later-
al margin of the corpus is sigmoidal being laterally
convex in its anterior two thirds and concave in its
posterior third. The caudolateral margin lies ad-
jacent with the medial terminus of the squamosal
and is inclined medially at an angle of 130° with
the lateral margin and it is straight. The posterior
margin of the pterygoid is sigmoidal, about four
times as wide as the caudolateral margin, and is
one third the length of the corpus. The pterygoids
meet in the median line posterior to the paras-
phenoid. The pterygoidoparasphenoidal suture is
W-shaped. The contact of the medial margin of
the corpus of the pterygoid is sigmoidal between
the posteromedial corner of the pterygoid and the
foramen pterygoideum, the posterior half of the
suture being laterally convex. The anterior one
is laterally concave. Immediately anterior to the
foramen pterygoideum there is a short triangular
recess, which continues anteriorly in an elongate
concavity conuent with the medial margin of the
anterior processes of the pterygoids. It borders a
large interpterygoideal vacuity. The anterior ter-
minus of the parasphenoid marks the base of the
anterior process of the pterygoid. The lateral and
medial margins of this process are concave with
the narrowest point lying in the basal third of the
process. Further anteriorly the lateral and medi-
al margins of the process diverge to about three
times its minimum diameter. The lateral margin
contacts the pars palatinalis of the maxilla, the
anterior terminus borders the foramen incisiv-
ium and the medial one the vomer. The corpus
of the pterygoid has a relief of prominent ridges
arranged in a W-conguration and opening ante-
riorly with a tubercle close to the posterior margin
of the bone.
Parasphenoid: The parasphenoid is bot-
tle-shaped with a W-shaped posterior margin and
the neck of the bottle lying between the expand-
ed anterior third of the posterior interpterygoide-
al foramina facing anteriorly. The neck of the
parasphenoid is about half as wide as the maxi-
mum width of its corpus. Its ventral face is deeply
concave. Two short triangular processes form the
parasphenoidal rostrum and protrude into the fo-
ramina pterygoidea. Further anteriorly the paras-
phenoid expands to a bifurcated process, which
reaches the width of the corpus at its anterior ter-
minus. The anterior margin of the parasphenoid
is deeply concave forming the posterior margin
of the interpterygoidal vacuity. The ventral face
of the corpus of the parasphenoid is deeply con-
cave in its posterior third and gradually shallows
anteriorly.
Occipitals: The basioccipital and the otoccipitals
are only identied by the topographical position
of their fragments, which do not permit a con-
dent reconstruction of these bones.
Postorbital: This boot-shaped postorbital is visi-
ble between the left palatine and the left jugal. The
peduncle faces anteriorly and contacts the pala-
tine. The corpus of the postorbital as preserved
and contacts the jugal. This latter contact is three
times the width of the peduncular contact with
the palatine. The medial and lateral margins of
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the postorbital appear deeply concave, but from
the state of preservation the outline of the bone
remains uncertain.
Ectopterygoid: Both ectopterygoids are poor-
ly preserved. The right one is visible in lateral,
the left one in medial aspect. The ectopterygoid
is trapezoidal in outline with the medial margin
being about one third as long as the lateral visible
one. The lateral-most part of the ectopterygoid
is obscured by the right mandibular ramus. The
anterior and posterior margins of the ectoptery-
goid are concave. The ectopterygoid contacts the
pterygoid at the transition from the corpus to the
anterior process. The suture is medially convex
and even.
Squamosal: Both squamosals are present but
badly preserved. Although none of the margins is
complete, it is assumed in analogy to other ple-
siosaurs that each bone likely had a wide convex
posterior margin and formed at least the posteri-
or half of the roof of the adductor chamber. It
is likely that the supratemporal fenestra was short
and narrow.
Quadrate: A fragment of possibly the left quad-
rate is preserved. It contacts the right mandibular
ramus where the jaw articulation should be. The
possibility that this fragment represents a fragment
of the right squamosal instead cannot be excluded
because of the incomplete preservation. The mar-
gins of the fragment are too damaged to allow for
a reconstruction of the bone outline.
PALATAL VACUITIES (FIGURE 4)
Vomeral foramen [foramen incisivium according
to Buchy et al., (2006), “internal naris” according
to (O’Keefe, 2001)]: Only the left vomeral fora-
men is preserved. It has a longitudinal diameter of
about 5 mm and is three times as long as it is wide.
It is posteriorly bordered by the anterior terminus
of the anterior pterygoidal process, laterally by the
medial margin of the left maxilla and medially by
the lateral margin of the vomer. The outline of the
vomeral foramen was most likely an elongate oval.
Anterior interpterygoidal vacuity: Anterior-
ly bordered by the vomer, laterally by the anteri-
or pterygoideal processes and posteriorly by the
parasphenoid, this long oval vacuity is by far the
largest palatal aperture of the specimen. Its length
is dicult to reconstruct because the posterior
portion of the vomer is missing and likely covered
the anterior processes of the pterygoids. It ap-
pears likely that this vacuity extended from max-
illary tooth positions 23 through 32. Its maximum
width level with tooth position 31 covers one third
of the palate at the same level. It is hypothesized
by some authors that this vacuity represents the
choana (Buchy et al., 2006). Inside the interpter-
ygoideal vacuity there are fragments of the skull
roof that cannot be further identied. Presumably
they come from the frontoparietal area.
Posterior interpterygoidal vacuities: The
pterygoid foramina are laterally bordered by the
pterygoid and medially by the parasphenoid. The
vacuities are twice as long as they are wide and set
o by raised margin. They are about one fourth
the length of the parasphenoid.
DENTITION (FIGURE 4)
All preserved teeth show a height/width ratio of
the crown of about 4:1 independent from their
respective diameter. They have conical and mod-
erately recurved pointed tips. A few crowns show
coarsely striated enamel. However, due to the
preparation scratch marks no details of the enam-
el sculpture remain. Because of the bad preser-
vation and insucient preparation, arrangement
and size of the teeth are only assessable from an
extrapolation based on the few teeth with pre-
served crowns, the diameter at the tooth cervix or
the diameter of the alveoli.
The dentition is isodont, despite the smallest teeth
being about one quarter the size of the largest
(Figure 5 C). The badly preserved margin of the
upper jaw indicates that the teeth in the anterior
half of the preorbital rostrum are separated by an
interalveolar space that is a little larger than the re-
spective alveolar diameter. Only three small likely
fragmentary teeth were identied there with cer-
tainty (tooth positions 1, 8, 11). The bulk of the
small replacement teeth or tooth fragments occur
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in the posterior half of the preorbital part of the
rostrum. The dental margin of the posterior third
of the maxilla is very badly preserved and recon-
struction would be too speculative. However the
alveoli are visible in dierent stages of abrasion
and the three posterior-most tooth positions ap-
pear widely spaced with interalveolar spaces that
are three times the diameter of the respective
alveoli.
Altogether there are at least 42 tooth positions in
the upper jaw including the ones we reconstruct-
ed on minimum assumption. Because of the miss-
ing premaxillomaxillary suture any comment on
the distribution of the teeth is impossible. That
many of the teeth are spread out laterally sug-
gests that the teeth from the upper and lower jaw
interdigitated.
AXIAL SKELETON (FIGURES 3, 5, 6; TABLE 2)
The vertebral column is preserved in full articula-
tion, but the trunk region is partially obscured by
the bones of the girdles.
Cervical vertebrae: 21 cervical vertebrae are
visible (Figures 3, 5). Although the atlas/axis sys-
tem lies in a mass of broken bone, it is identied
with condence (Figure 5). The atlas is in articula-
tion with the occiput and is posteriorly followed by
the axis. All cervical vertebrae are slightly procoe-
lous and have a length/width ratio of 2:3. Verte-
brae XIII to XXI are visible in ventrolateral aspect
because there that part of the cervical vertebral
column has been twisted to the right. The centra
of the cervical vertebrae I through XII are visible
in ventral aspect, exposing the paired foramina,
which are considered diagnostic for Sauroptery-
gia (Rieppel, 1997). There is a blunt median keel
between the foramina (Figure 6). From cervi-
cal vertebra XII to cervical vertebra XVIII, this
keel abruptly changes into a median depression,
anked by a pair of sharp ridges. The depression
is one-third the width of the respective centrum.
Cervical vertebrae XVIII through XXI also have
a blunt median ridge anked by a paired of foram-
ina. The diameter of the cervical vertebrae grad-
ually increases by approximately one third from
the anterior-most to the posterior-most. The cer-
vical ribs are single headed and articulate at a long
oval facet on the ventrolateral face of the centra.
The articular facet has a length/width ratio of 2:1
and it extends over the posterior two thirds of the
length of the respective cervical centrum.
The cervical neural arches are tilted laterally (Fig-
ures 5, 6). This indicates that these neural arches
are not fused to the cervical centra due to the ju-
venile stage of the animal. From cervical vertebra
VI through XVII the neural spines including their
respective peduncles are visible from the right side.
The height of the rst visible neural spine is one-
third the width of the respective vertebral body.
Posteriorly the height of the neural spines grad-
ually increases with respect to the width of the
vertebral body until a ratio of 1:1 is reached in
cervical vertebra XVII. While the neural spines
of the anterior-most cervical vertebrae are vertical
with almost parallel anterior and posterior mar-
gins, those of vertebrae XII through XVII are
inclined posteriorly. This inclination begins with
about 3° at vertebra XII and increases to about
15° at vertebra XVII. In all inclined neural spines
the anterior margin is convex and the posterior
one concave, but both remain almost parallel. In
the cervical vertebrae XIII through XVIII, there
is a bulge at the base of the anterior margin that
protrudes anteriorly between the postzygapophy-
ses of the preceding cervical vertebra, suggesting
the presence of a zygosphene / zygantrum artic-
ulation. The bulge covers the ventral half of the
anterior margins of the respective neural spines
and is tentatively identied as the base of a zy-
gantrum (Figure 6). The dorsal margin of all the
neural spines is very slightly convex and bears a
sharp and low laterally facing ridge.
The postzygapophyses are visible on all preserved
neural spines of the cervical vertebral column
with the exception of vertebra XVII, where the
postzygapophyses are missing. They arise from a
blunt elevation beginning on the middle of the
lateral face of the neural spines. The postzyga-
pophyses extend posteriorly beyond the posterior
margin of the respective neural spine for about
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Figure 5 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Cervical vertebral column; A) photograph of the cervical vertebral
column, B) interpretative line drawing.
one third the longitudinal extent of the respective
neural spine, whereas the articular faces continue
anteriorly over one half of the lateral face of the
neural spines. The articular facets of the postzy-
gapophyses are inclined slightly lateroventrally,
and in cervical XVII slightly caudoventrally, too.
Prezygapohyses are only visible in the cervicals X,
XI, and XIV to XVI (Figures 5, 6). In the three
latter vertebrae the prezygapophyses protrude be-
yond the anterior margin of the respective neural
spine over the full length of its articular facet and
terminate anteriorly in a notch on the lateral face
of the possible zygosphene, which is only visible in
cervical vertebrae VII and IX (Figure 5 d). In cer-
vicals X and XI, the prezygapophyses overlie only
the posterior two thirds of the preceding vertebra
and do not terminate in a notch. In all others the
prezygapophyses are at least partially covered by
the cervical ribs. The same holds true for the pe-
duncles of the neural arches of which only patches
are seen. Otherwise the neural arches and spines
would not have disarticulated from their respective
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Figure 6 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Detail of cervical vertebral column, section from cervical vertebra VII
through XII; A) photograph of the section, B) interpretative line drawing. Abbreviations: ns = neural spine, na = neural arch, cr = cervical
rib.
centra in one line held together solely by the zyga-
pophyseal articulations.
The articular heads of the cervical ribs II through
XII have the same longitudinal diameter as the
distal ends of the ribs. From vertebra XIII until
XXI the lateral margin of the cervical ribs in-
creases in length by about one third due to a
posteriorly orientated process that terminates in
a sharp point (Figure 5). The middle part of the
rib is constricted, whereas the constriction is more
expressed longitudinally with the exception of the
posterior-most cervical rib. At the constriction, the
longitudinal extension of the cervical ribs declines
to about two thirds of the length of the articular
facet. The aspect ratio of the cervical ribs changes
from 1:1 in the most anterior ones to 1:2 in cer-
vical vertebra XX (Figure 5). The cervical rib of
vertebra XX is about ve times longer than it is
wide. This cervical is transitional to the thoracic
vertebrae.
Thoracic vertebral column (Table 2): Only 17 tho-
racic vertebrae are visible, because three are cov-
ered by the coracoids (Figure 8). Three vertebrae
are covered by the ventral pelvic plates (Figures
3, 8). One of these must represent a sacral from
its position relative to the ilium. However, it is not
clear which sacral it is. Thus the animal had at
least 23 thoracic vertebrae. Thoracic vertebrae
VII through XI are covered by the coracoids, and
XV and XVI by the gastralia (Figures 3, 8). The
outline of those vertebral bodies covered by the
coracoids is visible through the latter bones (Fig-
ure 8). Like the cervicals the centra of the thoracic
vertebrae have a length / width ratio of 2:3 (Table
2, Figure 7). The thoracic vertebrae are platycoe-
lous and show a pair of foramina on the ventral
face. A pair of low but sharp ridges runs medial to
the foramina in longitudinal direction. The ante-
rior and posterior articular faces are ventrally sur-
rounded by a sharp circumference, which merges
with a shallow constriction that is the narrowest in
about the middle of the vertebral centrum. Here,
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Table 2. Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Counts and measurements of the vertebral column in millimetres; the
numbering of the posteriors is Arabic, because posterior vertebra I cannot be identified with certainty (see also text). Note also that
the number of thoracic vertebrae is at least 23. Because the height of the vertebrae cannot be measured for comparison the length/
width ratio is given here under the premise that in polycotylids the width of a centrum approximately equals its height (Schumacher
et al., 2016).
cervical total: 21
number centrum length centrum width length/ width ratio height of neural spine length cervical rib
atlas 13 16 0.62 ? none
axis 14 22 0.63 ??
III 14 21 0.66 ? ?
IV 17 21 0.81 ? ?
V 17 26 0.65 ? ?
VI 17 26 0.65 ? 14
VII 20 26 0.76 ? 15
VIII 18 25 0.72 ? 15
IX 20 27 0.74 ? 15
X 20 30 0.66 ? 22
XI 20 34 0.58 ? ?
XII 20 36 0.55 21 22
XIII 18 ? ? 24 23
XIV 20 37 0.74 25 26
XV 20 37 0.74 30 28
XVI 17 ? ? 30 30
XVII 20 ? ? 30 35
XVII 20 38 0.52 30 36
XIX 22 ? ? 30 42
XX 20 38 0.52 30 ?
XXI 24 ? ? ? ?
thoracic total: 20 sacral/ caudal total: 25
number centrum length centrum width length/width ratio number centrum length centrum width length/width
ratio
I25 ? ? 127 41 0.66
II 24 ? ? 2 27 41 0.66
III 20 ? ? 3 26 39 0.66
IV 25 ? ? 4 ? 39 0.66
V 22 54 0.4 5 ? 39 ?
VI ? ? ? 6 ? 39 ?
VII ? ? ? 7 25 38 0.66
VIII ? ? ? 8 20 38 0.52
IX 27 ? ? 9 20 39 0.51
X 24 ? ? 10 20 37 0.54
XI 30 ? ? 11 20 34 0.59
XII 25 53 0.47 12 20 32 0.62
XIII 27 53 0.51 13 ? 29 ?
XIV 29 50 0.58 14 20 29 0.69
XV 25 ? ? 15 18 26 0.69
XVI ? 50 ? 16 15 21 0.71
XVII ? 46 ? 17 21 20 1.05
XVIII 29 43 0.67 18 21 18 1.16
XIX 27 43 0.63 19 12
??
XX 27 ? ? 20 18
??
XXI ? ? ? 21 15
??
XXII ? ? ? 22 20
??
XXIII ? ? ? 23 14
??
24 ?
??
Counts and measurements of the vertebrae in mm
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the centrum is about one fth narrower than at the
articular faces (Table 2, Figure 7). A pair of blunt
ventrolateral longitudinal keels connects both ar-
ticular circumferences and borders a ventral face,
which is slightly concave in all directions and is
two third the width of the centrum. Immediately
medial to each ventrolateral keel there is a small,
mostly long oval vertebral foramen nutritivum,
which is only visible on those vertebrae that are
exposed (Figure 8).
Sacral and caudal vertebral column (Table 2): The
number of sacrals cannot be identied with cer-
tainty because they are covered by the ischia, and
therefore, the exact border between the sacral and
caudal vertebrae remains unclear. Consequently,
the caudals have been designated Arabic num-
bers. The caudal vertebral column consists of at
least 15 vertebrae, in which case there are three
sacrals. The posterior six caudals lie along an
oblique break and thus lack their left lateral faces.
The number of missing caudals, can thus only
be estimated to a maximum of ten, which coin-
cides with other polycotylids. All caudal vertebrae
are exposed in ventral aspect. The rst vertebra
posterior to the ischium is regarded as caudal 1.
With a length/width ratio of 1:3 this vertebra is
one quarter shorter than the preceding one. The
ventral margin of the posterior vertebral articula-
tion facet of the rst caudal is concave in the mid-
dle suggesting a slight opisthocoely. All following
caudals have planar intervertebral articulations.
While their length remains about constant, their
width gradually decreases posteriorly. The poste-
rior-most preserved vertebrae are twice as long as
they are wide. Like the trunk vertebrae the basal six
caudal vertebrae have a sharp, ridge-like circum-
ference and a constriction around the middle of
their centra, where the diameter of the vertebral
bodies decreases to three fths of the diameter at
the anterior articular face. From caudal vertebrae
7 to 13, the constrictions slightly deepen and the
circumferences at the intervertebral articulations
become more rounded. The articular facets for the
hemal arches are limited to the anterior margin
of the respective posterior vertebra. The facets are
visible on caudals 2, 3 and 5 through 8.
Figure 7 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. The scatter plot of the length/width ratio indices of the vertebrae shows
a typical polycotylid pattern (Schumacher et al., 2016).
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Thoracic ribs (Figure 8): 20 pairs of thoracic ribs
are reconstructed by extrapolation from those ribs
visible on either side of the thoracic vertebral col-
umn. With the exception of the rst left thoracic
rib, which is morphologically transitional between
the cervical and the following thoracic ribs, none
of the ribs is completely visible, because they are
all overlain by the ventral girdle plates and the gas-
tralia. With the exception of the ribs IV and V
of the right side of the body all ribs are regularly
curved posterodistally. The distal half of thoracic
rib IV and the middle section of rib V are straight.
The ribs gradually increase in length from thorac-
ic segment I through IX, where they reach their
maximum length. They remain of approximately
equal size until thoracic segment XIII and then
gradually decrease in length towards the sacral re-
gion, where they measure probably one fourth to
one third the size of the longest thoracic ribs. The
diameter of the thoracic ribs is largest in the third
pair, the head of which is one third higher than
that of the longest thoracic ribs. In all following
visible ribs the diameter remains nearly constant.
Those that are partially visible between the left
pelvic plates are about one third thinner than the
preceding ribs.
Figure 8 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Detail of the trunk including the girdles; A) photograph, B) interpretive
line drawing; abbreviations: cv = cervical vertebra, thv = thoracic vertebra, cav = caudal vertebra.
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In all ribs, the capitula and tubercula are conuent
and together form single articular facets. There-
fore, though invisible, the par- and diapophyses
must be fused to synapophyses. The costal artic-
ular facet is slightly concave in the thoracic pairs
of ribs III through XII. In the thoracic ribs I and
II these facets are convex and posterior to tho-
racic segment XII the costal articular facets are
at where exposed. Thoracic rib III on the left
side shows a sharply triangular cross-section at
its articular head with a rounded internal face, a
sharp external edge and a concave anterior face.
This concavity may be due to compression and is
not seen in any other rib with an articular head
exposed.
In medial direction the corpus of the ribs diverg-
es to an o-set ventrolaterally facing, transversely
oval and concave articular facet for the vertebro-
costal contact, which has twice the diameter of the
corpus in the middle part of the shaft. Where the
ribs are abraded, the medullary cavity is visible.
This cavity, which is sharply separated from the
compacta, has about half the diameter of the re-
spective part of the rib shaft.
GASTRALIA (FIGURES 8, 9)
The gastralia basket is preserved mostly in situ (Fig-
ures 8, 9). Deformation occurred when the gastral
basket collapsed and was later crushed over the
underlying bones during early diagenesis. There
are six transversely oriented gastralia converging
in medial direction. The widely V-shaped un-
paired medial gastral ossicles contact each other
to form a medial plate. The anterior-most two are
about one third wider than the posteriorly follow-
ing three. Due to a gap in the slab (Figure 8) the
medial parts of these gastral ossicles are missing;
they were reconstructed according to the diame-
ters at the medial fractures and mirrored. Later-
ally adjacent to the medial gastral ossicles, there
is a transversely orientated series of lateral gastral
ossicles. The arrangement of these lateral gastral
ossicles is dierent in all gastralia.
The anterior-most gastrale has two medial ossi-
cles opening anteriorly at a reconstructed angle of
about 150°. The posterior of the two lies in close
contact or overlaps the median gastral ossicle of
gastral ribs II and III. Laterally adjacent to the an-
terior of the two follows a pair of spindle-shaped
lateral gastral ossicles that are half as long as one
arm of the respective medial gastral ossicle. Later-
ally, there is one more lateral gastral ossicle, which
has three times the length of the spindle-shaped
one but is the same thickness. It curves posteriorly
and terminates in a sharply rounded caudolateral-
ly facing tip.
Gastral ribs II and III share one medial gastral os-
sicle, which, like the next following two or three
open posteriorly at a reconstructed angle of 120
to 140°. Gastrale III consists of four pairs of spin-
dle-shaped lateral gastral ossicles that contact each
other in a transversely directed suture. The suture
between lateral gastral ossicles III and IV is in-
clined caudolaterally at an acute angle of about
20°. The lateral-most gastral ossicle is curved cau-
dolaterally and terminates in a sharp caudolater-
ally facing tip. Gastral rib III also consists of four
paired lateral gastral ossicles in a similar arrange-
ment as in gastral rib II. However, lateral gastral
ossicle III is half as wide as ossicles I and II and
anteriorly overlapped by lateral gastral ossicle IV,
which curves caudolaterally, ending in a sharp
posteriorly facing tip. The medial face of lateral
gastral ossicle IV articulates with the lateral face
of lateral gastral ossicle II.
Gastral rib IV has the most massive medial gas-
tral ossicle likely having been about twice as thick
as the others. There are three pairs of lateral gas-
tral ossicles. The medial two are spindle-shaped.
The lateral of the two is one third shorter than
the medial one. The third and lateral-most gastral
ossicle of the gastral rib is only half as thick as
the other two but about twice as long as the me-
dially adjacent one. Lateral gastral ossicle III con-
tacts the second along its entire anterior face. The
medial terminus of the third lateral gastral ossicle
contacts the lateral face of the rst in an oblique
suture. Lateral gastral ossicle III curves caudola-
terally and terminates in a sharp tip.
Gastral ribs V and VI share one medial gastral
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ossicle. Likely, there was a second one posteriorly
adjacent, which might have underlain the medial
gastral ossicle. In this case the lateral gastral ossi-
cles would have formed forming the base if the
anterior edge of gastral rib ve represented the
lateral arms of medial gastral ossicle VI. However,
the median part is missing.
Gastral rib V consists of a paired bundle of three
basal lateral gastral spindle-shaped ossicles, the
anterior of which, number one, might represent
the lateral termini of medial gastral ossicle VI.
The caudolaterally following lateral gastral ossicle
II is twice as long as the rst and laterally contacts
lateral gastral ossicle IV. The third lateral gastral
ossicle lies posteriorly adjacent to lateral gastral
ossicle II and it measures four fth of the latter.
Lateral gastral ossicle III medially contacts medial
gastral ossicle V and the rst lateral gastral ossi-
cle of gastrale VI. Lateral gastral ossicle IV is also
spindle-shaped and has about the same length as
the third. The lateral-most gastral ossicle, which is
as long as the second, curves posteriorly and ter-
minates in a sharp tip.
The sixth gastral rib has only two lateral gastral
ossicles. The medial one is an elongating trapezoi-
dal in outline and articulates with the caudolateral
face of medial gastral ossicle V. The lateral-most
second gastral ossicle is one fth longer than the
rst and sharply curves posteriorly in its distal fth
terminating in a slim and pointed posteriorly di-
rected tip.
GIRDLES (FIGURES 8, 10; TABLE 3)
SHOULDER GIRDLE (FIGURES 8, 10; TABLE 3)
The shoulder girdle as preserved consists of a
fragmentary interclavicle, a pair of scapulae and
a pair of coracoids. The coracoid is three times
the size of the scapula. Remnants of the clavicles
are also preserved, but were damaged during col-
lection and preparation. The preserved remains
are barely ossied due to the immaturity of the
animal. The outline of the bones can thus only
be tentatively restored (Figures 8, 10). The cora-
coid is trapezoidal in outline. Its maximum length
is about twice the minimum width. The contra-
lateral coracoids contact each other along their
medial margin in a serrated suture, which diverges
at the anterior-most terminus of the bones. The
anterolateral margin of the coracoid is convex
with the convexity strongest in the medial third
of the anterolateral margin. In posterior direc-
tion this margin becomes almost straight, whereas
the anterolateral margin forms an acute angle of
approximately 50° with the medial margin. The
coracoidal part of the fossa glenoidea, which is
barely visible, occupies the posterior-most fourth
of the anterolateral margin of the coracoid. The
lateral margin is concave. Anteriorly it is delimited
by a small laterally facing protuberance that marks
the posterior extension of the fossa glenoidea. Be-
cause of the juvenile status of the individual there
are no further anterior extensions that interlock
with the clavicles in adults. Posteriorly, the lateral
margin of the coracoid turns medially at an angle
of about 90° and merges with the posterior mar-
gin, which is convex and set o by a low rim that
commences on the lateral extremity of the poste-
rior margin and terminates at the suture with the
contralateral coracoid. The external surface of the
coracoid is otherwise smooth. The angle between
the posterior and the medial margins comprises
about 120°.
These features may reect the early ontogenetic
status of the specimen. Parts of the clavicles and
the interclavicle are now missing because of the
crude method of collection.
The scapula is about half as long as the coracoid
and has an evenly convex medial margin, which
anteriorly expands into a low ventral process. The
anterior margin of the scapula is strongly convex
and angled sharply against the medial margin at
about 90°. The anterior margin of the scapula is
set o by a low ridge that probably demarcated
a cartilaginous extension. The lateral margin of
the scapula is slightly concave. In the middle third
of this margin arises the dorsal scapular process,
which most likely was orientated dorsolaterally
during life. The dorsal scapular process is almost
as wide as the corpus of the scapula in its middle
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part and is inclined posteriorly against the corpus
of the scapula at an angle of about 45°. The slight-
ly convex dorsal margin of the dorsal scapular
process is about one third wider than the base of
the process. Evidently this process was not yet fully
mineralized. The posterior margin of the scapula
is set of from the corpus by a low ridge, and is
strongly convex in its middle third, but medially
and laterally bares a shallow concavity. This medi-
al concavity articulates with the proximal edge of
the coracoid and the lateral one forms the scapu-
lar part of the fossa glenoidea. The external face
of the scapula shows a blunt straight ridge that
reaches from the lateral third of the anterior mar-
gin of the bone to its caudolateral corner. Along
this ridge the lateral part of the scapula with the
dorsal process was angled against the medial part
of the corpus. Because there is no break along the
ridge either the bending angle was very shallow, or,
more likely, the scapula suered some plastic dia-
genetic deformation. Otherwise the external face
of the scapula is smooth.
Table 3. Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Measurements of the girdles in mm.
Figure 9 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Gastral basket reconstructed according to the best preserved elements.
Because of the near in situ position of the lateral termini of the gastralia and the lining-up of the ossicles the median convergence is
unlikely to be a taphonomic artefact a diagenetic artefact.
shoulder girdle left right pelvic girdle left right
scapula corpus length 120 130 ilium shaft length 103 103
max. dorsal width 53 65 acetabular width 35 34
width at glenoid fossa 55 ? spinal width 10 10
caudal margin 95 ? ischium length through shaft 135 130
depth of notch 39 ? acetabular width 50 52
clavicle no data width of caudal
chord 135 115
interclavicle no data pubis length through shaft 140 142
coracoid max. length 224 224 width at acetabulum 52 55
max. width 125 ? max. width of plate 175 170
Measurements of the girdles in mm
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Anteriorly adjacent to the left scapula there is a
sub-rectangular bone likely representing the cen-
tral part of the left clavicle. It articulates with the
medial third of the craniomedial articulation face
of the scapula. The medial margin of this frag-
ment likely represents the original margin of the
clavicle. The anterior margin of the fragment is
irregularly broken while the lateral margin dips
below the matrix. The original shape of the clav-
icle cannot be determined. Only an insignicant
fragment, likely of the right clavicle, is identied,
but it has no contact with the scapula, and thus
might be part of the interclavicle.
PELVIC GIRDLE (FIGURES 8, 10, TABLE 3)
The elements of the pelvic girdle are almost pre-
served in their correct position, the ilia being
crushed caudolaterally during diagenesis (Figure
8). The pubis is the largest of the pelvic elements
being one third larger than the ischium and about
six times larger than the ilium. The craniomedial
margin of the pubic plate is semi-circular in out-
line and slightly expanded. A rim that parallels
this margin suggests a cartilaginous extension of
the bone in life, which explains the separation of
contralateral pubic bones as preserved. The pubis
becomes thickest close to its posteromedial corner.
The posteromedial and caudolateral margins of
the pubis are deeply concave and converge to a
posteriorly facing peduncle that has one-fourth the
width of the pubic plate. Anterior to the postero-
medial margin there is a recess in the external sur-
face that is boarded by a deeply concave, rounded
step on the external surface of the bone. The me-
dial third of the posterior margin of this peduncle
is angled against the lateral two-thirds at about
130°. The medial part represents the contact sur-
face with the ischium, the lateral part forms the
pubic part of the acetabulum.
The plate of the ischium is orientated medially
with a convex medial margin becoming lateral-
ly directed in its posterior third. In the anterior
third the contralateral ischia diverge at an angle
of about 10°. Posteriorly the divergent angle is ap-
proximately 45°. The medial articular facet of the
ischia reaches its maximum thickness in the ante-
rior third. The anterior and caudolateral margins
of the ischium are concave, the concavity of the
anterior margin being deeper than of that poste-
rior one and only two thirds as long. In the middle
third of the posteromedial margin of the ischium
there is a slight convexity. Both anterior and pos-
terior margins, in lateral direction, converge into
a peduncle that is orientated at an angle of about
46° anteriorly against the long axis of the animal.
The anterolaterally facing articular facet of the
peduncle has one-fourth the length of the medial
margin of the ischum. The craniomedial third of
the face articulates with the pubis, the lateral two-
thirds from the ischiadic part of the acetabulum.
The ilium is elongate with a rounded triangular
outline with the apex facing posteromedially. Its
length is four times the width at its acetabular
base, which is anteriorly convex. Both the lateral
and medial margins converge posteriorly as pre-
served and merge with the posterior terminus of
the ilium, which is sharply convex. The lateral
margin of the ilium is gently convex. The medial
margin is bipartite with the basal two thirds being
slightly convex and the apical third being slightly
concave. The anteriorly oriented basal part is the
thickest and formed the roof of the acetabulum
prior to a diagenetic collapse of the pelvic girdle.
APPENDICULAR SKELETON (FIGURES 11 – 13; TABLE
4)
PECTORAL LIMBS (FIGURE 11; TABLE 4)
The reconstruction of the pectoral limbs is main-
ly based on the left forelimb, which is better pre-
served than the right.
Humerus: The slightly sigmoidally curved shaft
of the humerus is longitudinally oval in cross-sec-
tion with a length/ height ratio of approximately
1.6. Towards the caput humeri the shaft becomes
almost circular in cross-section. The humeral head
is low and regularly rounded with a nely wrinkled
surface suggesting a cartilaginous coating in life.
Immediately distal to the anterior margin of the
humeral head there is a low and blunt deltoid tu-
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REFERENCES
berosity that extends about one-seventh the length
of the humerus. A low elevation on the posterior
margin of the humeral shaft may represent the
insertion tubercle for the m. coracobrachialis (Robin-
son, 1975). From the middle of the shaft in distal
direction the anterior and posterior margins of the
humerus diverge to about twice the longitudinal
diameter. While the anterior supracotylar ridge
only slightly curves anteriorly, the posterior one
shows a deep convexity at its base. The posteri-
or supracotylar ridge forms an angle of approx-
imately 120° with the humeral shaft and merges
with the distal articular face in a regularly rounded
ange. The distal articular face is at and sepa-
rated from the shaft by a blunt ridge that merges
with the anterior and the posterior extremity of
the humeral shaft. The articular facets for radius
and ulna are separated by a very low interarticular
rim that forms the distal-most extremity of the hu-
merus. The articular facets for ulna and pisiform
are conuent and together they are of equal size
as that for the radius. Both articular faces include
an angle of about 170°. While the articulation
facet with the radius is straight, that of the ulna/
pisiform complex is slightly convex.
Radius and ulna: All articular facets of radius
and ulna lie in articulation with their neighboring
bones. However, there is a gap between radius,
ulna and pisiform as well as the humerus.
The radius has a length/width ratio of 0.7, is about
twice the size of the ulna and roughly pentagonal
in outline. The regularly convex proximal articular
face with the humerus is the longest. The curva-
ture of the proximal articular face of the radius
does not match its humeral counterpart. Howev-
er, the radial articular face of the humerus is still
covered by matrix so that the actual shape of the
facet cannot be reconstructed. The slightly convex
anterior margin of the radius forms a right angle
with the proximal articulation facet and includes
an angle of about 100° with the slightly concave
articular facet with the radial one. The articular
facet between radius and radial has three fourth
the length of the radiohumeral one. Both articu-
lar facets run nearly parallel to each other. The
contact between radius and intermedium extends
over one fourth of the longitudinal expansion of
the radius, is slightly concave and forms an angle
of 120° with both the radioradial and the straight
radioulnar articular facets, which are of equal
length. The radioulnar articulation is slightly con-
cave and over its entire length it contacts the ulna.
The ulna has a length/width ratio of 0.83, is
Figure 10 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1.
Reconstruction of the girdles in ventral aspect; A) shoulder girdle
with likely confluent coracoscapular foramina, B) pelvic girdle
with likely large areas of cartilage that may have separated the
contralateral obturator foramina; dotted lines and light grey =
reconstructed. Note the ischia that are as long as they are wide,
and the rounded pubic bones. These features may be aligned
with the early ontogenetic status of the specimen. Parts of the
clavicles and the interclavicle were lost during collection.
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roughly hexagonal in outline with the regularly
convex ulnohumeral articulation face being the
longest margin of the bone. The convex articular
face is covered by wrinkles. The convexity matches
the respective concavity of articulation facet of the
humerus, but is separated from it by a gap. The
ulnoradial facet forms a notch that accommodates
the respective facet on the radius. It has one-third
the length of the ulnohumeral facet. Both include
an angle of about 110°. The articular facet with
the intermedium is straight. It has two-thirds the
length of the ulnohumeral facet and lies at an
angle of 110° to the ulnoradial facet and at an
angle of 120° with the slightly convex ulnoulnar
facet, which is a little shorter than the ulnointer-
medial facet. The posterior margin of the ulna is
formed by the tiny straight articular face with the
fourth proximal carpal. This facet is half as long
as the ulnointermedial facet and the two describe
an angle of about 110°. The articular facet with
the pisiform is straight, equals the length of the
ulnointermedial facet and is orientated at an angle
of 110° against the posterior margin of the bone.
Carpalia: All carpalia lie in close contact to each
other, suggesting that the articular facets were cov-
ered by a thin layer of cartilage during life.
The pisiform is trapezoidal with an almost straight
articular facet with the posterior margin of the
ulna. The posterior margin of the pisiform is also
straight, and is the same length as the articular
facet with the ulna. Both posterior and anterior
margins of the bone converge distally at an angle
of about 20°. The asymmetrically convex prox-
imal margin of the pisiform is about one third
Figure 11 Mauriciosaurus fernandezi CPC RFG 2544 P.F.1. Left pectoral limb in ventral aspect; A) photograph, B) interpretative line
drawing.
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longer than its evenly convex distal margin. The
strongest convexity of the proximal margin of the
pisiform lies in its anterior third.
The supernumerary carpal element is also trap-
ezoidal. The articular face with the ulna consists
of two low convexities that are separated from
each other by a sharp notch. The anterior convex-
ity merges with the proximal articular facet with
Table 4. Mauriciosaurus fernandezi; measurements of the extremities in mm; abbreviations: dc = distal carpal, dt = distal tarsal.
right left left right
humerus shaft length 170 180 femur shaft length 185 180
max. width
humeral head 48 55
max. width
femoral head 55 55
max. distal width 105 ?max. distal with 100 85
ulna longitudinal 35 45 tibia longitudinal 43
proximodistal 25 25 proximodistal 30
radius longitudinal 30 35 fibula longitudinal 42
proximodistal 25 25 proximodistal 30
extrazeugo-podial
element longitudinal 15 20
extrazeugo-podial
element 1 longitudinal 8 12
proximodistal 17 20 proximodistal 10 14
extrazeugo-podial
element 2 longitudinal 20 22
proximodistal 23 20
extrazeugo-podial
element 3 longitudinal 9 15
proximodistal 13 10
radiale longitudinal ? 35 tibiale longitudinal 34 30
proximodistal ? 15 proximodistal 19 17
intermedium longitudinal ? 25 intermedium longitudinal 24 25
proximodistal ? 20 proximodistal 22 19
ulnare longitudinal ? 24 fibulare longitudinal 27 25
proximodistal ? 20 proximodistal 20 20
dc I longitudinal ? 25 dt I longitudinal 22 21
proximodistal ? 15 proximodistal 18 15
dc II+III longitudinal ? 20 dt II+III longitudinal 20 17
proximodistal ? 15 proximodistal 18 16
dc IV longitudinal ? 18 dt IV longitudinal 18 16
proximodistal ? ?proximodistal 21 18
total length proximodistal ? 510 proximodistal 505 510
manus length proximodistal ? 300 proximodistal 280 28
Measurements of the extremities in mm
front flipper hind flipper
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the pisiform. The posterior half of the articular
facet with the pisiform is slightly concave and ter-
minates in a caudoproximally orientated tubercle.
The sinusoidal proximal articular facet of the su-
pernumerary element measures two thirds of the
length of the sinusoidal posterior margin, in which
the concavity lies in the proximal half of the bone.
Posterior and anterior margins are of equal lengths
and diverge distally at an angle of about 30°. The
distal margin along which the supernumerary el-
ement articulates with the ulnare is about as long
as its posterior margin. Where the supernumerary
element contacts the ulnare, its margin is concave,
whereas the posterior two thirds of the distal mar-
gin of the former are slightly convex. Along the
convexity there is a posteriorly diverging articular
gap. Both the proximal and distal margins parallel
each other.
The radiale is longitudinally elongated pentagonal
with a length/width ratio of about 0.4. With its
anterior margin the bone articulates with the radi-
us, which is about three times as big as the radiale.
The slightly convex anterior margin of the radiale
is the longest of all margins of the bone and al-
most parallels the posterior margin, which is a little
shorter than the anterior one and slightly concave
along its contact with distal carpal I. The proxi-
mal fourth of the posterior margin of the radiale is
straight and curves proximally against the concav-
ity at an angle of about 7°. Distally the posterior
margin of the radiale terminates in a blunt process
that matches a respective notch on the anterior
margin of distal carpal I. The anterior face of the
radiale is regularly convex. The posterior face con-
sists of two straight articular facets of equal length
that include an angle of about 55° with each other.
The anterolaterally orientated facet of these two is
angled in 55° against the anterior margin of the
radiale and articulates with the anterior face of the
intermedium. The caudolaterally orientated part
of the posterior margin bridges the gap between
the anterior face of the intermedium and proxi-
mal face of distal carpal I.
The intermedium is hexagonal. The straight an-
teroproximally facing intermedioulnar articula-
tion parallels the posterodistally facing margin of
the ulna, leaving a small interarticular gap, inside
which the dorsal margin of the intermedioradial
articulation facet is visible. Thus the articular sur-
face of the slightly compacted intermedioanterior
articulation is exposed. The intermedioulnar ar-
ticulation is about two-thirds the length of the in-
termedioradial articulation and describes an angle
of about 70° with the former and thus is facing
proximoposteriorly. The intermedioulnar articula-
tion faces posteriorly and is as large as the interme-
dioradial articulation.
The ulnare is longitudinally rounded in outline
with a length/width ratio of 1.2. There are no
clearly dened articular facets along its anterior,
proximal and posterior margins. The anterior
margin of the bone contacts the intermedium in
a tiny section while the proximal margin of the
ulnare matches the slightly concave posterodistal
margin of the ulna.
Caudoproximally the pisiforme contacts the
ulnare in a shallow concave craniodistally facing
articular facet. The posterior and distal margins
of the ulnare are slightly concave, the caudodor-
sal corner of the bone having been lost. The dis-
tal articular facet is about one third longer than
the posterior one. Both facets include an angle of
about 100°. The same angle is included between
the posterior articular facet of the ulnare and its
carniodistally facing margin. The distal concavity
likely articulated with metacarpal (mc) V, but this
area was destroyed while the slab was broken.
All three distal carpals (dc) are visible in the left
pectoral limb. dc I is rounded rectangular in out-
line with a length/width ratio of 0.6. The proxi-
mal, anterior and posterior margins of the bone
are evenly convex, while the distal one is straight
and about one sixth shorter than the proximal
one. With its proximal margin dc I contacts both
the accessory carpal element and the radiale; with
its distal margin it contacts mc I and II/III. With
its posterior margin dc I articulates with dc II/III,
which is rounded quadrangular in outline with a
length/width ratio of 0.75. The proximodistal ex-
tension of dc II/III is a little larger than that of
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dc I, but cranioposteriorly it is about half as long.
Like in dc II/III all margins meet approximate-
ly in right angle, with the proximal and posterior
margins being concave and with the anterior and
distal margins being convex. The distal margin
shows the strongest convexity. The caudoproximal
corner of dc II/III is marked by a short, straight
facet that is one-fth the length of the posterior
facet of dc II/III. The proximal concavity of the
bone precisely matches the distal convexity of the
intermedium, while the posterior concavity ts the
convex anterior margin of dc III. The convex an-
terior margin of dc II/III contacts the posterior
margin of dc I in one point. Likely the distal mar-
gin of dc II/III articulated with mc II and III, but
this contact is obscured by a fracture in the slab.
With a size of about one third the size of dc I, dc
IV is the smallest of the preserved distal carpals.
As preserved the bone is irregularly pentagonal in
outline. The proximal, anterior and posterior mar-
gins are slightly convex. The distal margin of dc IV,
which has a length/width ratio of 0.75, is situated
on the edge of a crack and thus is slightly abraded.
The proximal articular facet is about half as long
as the anterior and posterior margins. With the
anterior margin the proximal articular facet forms
an angle of about 100°, with the posterior one an
angle of about 120°. The distal margin has three
times the length of the proximal margin, which
contacts the distal margin of the intermedium in
its posterior third. The anterior margin of dc IV
articulates with the posterior margin of dc II/III.
Distally, dc IV articulates with mc III and IV. Like-
ly, there was a contact with the anterior margin of
mc IV, but the relevant area is destroyed.
Metacarpalia: With the exception of mc I the prox-
imal ends of the metacarpalia are now missing as
is much of their corpora. From what is preserved a
length/width ratio of about 2 is reconstructed for
all metacarpalia (Table 5). Nothing more can be
said about their shape.
Phalanges: The phalangeal formula of the manus
is 9-12-11 (preserved) -12 (preserved) -11 with the
incomplete digits II and IV being the longest. With
the exception of the distal-most ones, the phalan-
ges are uniformly hourglass-shaped with almost
straight interphalangeal articulations. The length
width ratio of the phalanges of all digits III is 1.77.
In each phalanx, the minimum transverse section
at the medial constriction is about two thirds of
the extension of the proximal articular facet. The
distal articular facet is about one fth smaller than
the proximal facet. The ultimate phalanges show
a rounded tapering tip and a slightly convex prox-
imal articular facet that does not precisely match
its counterpart on the penultimate phalanx. The
phalanges in the proximal half of the manus are
arranged in oblique rows directed posterodistally.
The interphalangeal articulations lie in the con-
striction of the posteriorly following phalanges. In
distal direction, the interphalangeal articulation
lines gradually line up with each other and in the
distal fth of the manus from a straight line.
PELVIC LIMBS (FIGURES 12, 13)
Femur: The femur resembles the humerus in out-
line with its longitudinally oval cross-section and
a length/width ratio of approximately 1.8, but
it is a little smaller in all dimensions and it has a
straight shaft. At the caput femoris, the shaft be-
comes almost circular in cross-section. At the frill
of the articular facet, the bone expands by about
one fth. The anatomical neck of the caput fem-
oris is a shallow circumference distally adjacent to
it. The third trochanter forms a shallow elevation
on the posterior face of the femur. It commences
distally to the anatomical neck and extends distally
for about one third of the shaft. The caput femoris
is low and regularly rounded. Its surface bears ne
wrinkles, which during life were probably covered
by a cartilaginous cap.
From the middle of the shaft the anterior and
posterior margins of the femur gradually diverge
distally. At the distal articular face the bone has
about twice the longitudinal diameter of the mid-
shaft. The posterior face of the femur is more con-
vex than the anterior face. Therefore, the evenly
rounded distal articular facet extends further pos-
teriorly with respect to the long axis of the shaft
than anteriorly. The posterior face of the femur in-
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Table 5. Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1; measurements of metapodials and phalanges in mm. The average
length/width ratio of the phalanges (ph) is 1.77.
average
ray III ph 1 ph 2 ph 3 ph 4 ph 5 ph 6 ph 7 ph 8 ph 9 ph 10 ph 11 ph 1 ph 2
length 21 21 22 20 17 16 14 13 14 9 ? 25 27
width 10 10 12 12 10 10 7965? 1415
ratio 2.1 2.1 1.8 1.7 1.7 1.6 2 1.4 2.3 1.8 ? 1.7 1.8
hind left
ray III ph 1 ph 2 ph 3 ph 4 ph 5 ph 6 ph 7 ph 8 ph 9 ph 10 ph 1 ph 2 ph 3
length 27 ? ? ? ? `23 20 17 17 16 23 23 22
width 16 ? ? ? ? 13 11 10 10 8 10 9 11
ratio 1.6 ? ? ? ? 2.1 1.8 1.7 1.7 2 2.3 2.6 2
1.77Average length/width ratio total
1.85 1.8
1.86 2.3
Measurements of metapodials and phalanges in mm
front left average front right
hind right
Figure 12 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Left pelvic limb in ventral aspect; A) photograph, B) interpretative line
drawing.
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cludes an angle of about 120° and merges with the
distal articular face in a regularly rounded ange.
A blunt ridge separates the at distal articular face
from the shaft. This ridge merges with the ante-
rior and the posterior extremity of the femoral
shaft. The articular facets for tibia and bula are
conuent with no trace of an intercondylar ridge.
The femur is separated from the distal elements of
the hind limb by a considerable gap containing a
goethitic substance.
Tibia and bula: The tibia is irregularly oval in
outline with the anterior margin being about one
third longer than the posterior ones. The length/
width ratio of the bone is about 0.7. All facets are
regularly convex and conuent. The tibia lies level
with the anterior half of the distal femoral artic-
ular face, but it is separated from the latter by a
gap that is half the proximodistal dimension of the
tibia. With its posterior extremity the tibia contacts
the anteroproximal half of the anterior convexity
of the bula. Distally, the tibia loosely articulates
with tibiale and intermedium in one point.
The bula is irregularly oval as well but has only
a little more than half the longitudinal extension
than the tibia (length/width ratio: 0.7). Like in the
tibia all articular faces are convex and conuent.
The bula lies posteriorly adjacent to the tibia and
like the latter is separated from the distal articular
face of the femur by a gap. With its craniodistal
convexity the bula contacts the intermedium in
one point, while the posterior two thirds of the dis-
tal convexity match a concavity on the proximal
margin of the bulare.
Supernumerary epipodial elements: Tw o
sesamoidal supernumerary elements are preserved
posterior to the bula. The most anteriorly posi-
tioned of the two is rounded triangular in outline
with the apex facing distally. The anterior and pos-
terior margins are about on fourth longer than the
proximal margin, which lies in line with that of
the bula. The anterior supernumerary element
touches the posterior extremity of the bula. With
its caudoproximal corner the anterior supernu-
merary element contacts the posterior one, while
its distal extremity touches yet another supernu-
merary element, which lies posteriorly adjacent
to the bulare. The posterior supernumerary ele-
ment is oval and one-third the size of the anterior
supernumerary element. Its proximodistal diame-
ter is twice the length of the cranioposterior. The
bone articulates with the anterior supernumerary
element with its distal extremity.
Tarsalia: Four elements form the proximal row
of the tarsals: tibiale (= astragalus), intermedium,
bulare and a supernumerary element. The tibiale
is an irregularly oval bone, which is twice as long
longitudinally than transversely. All articular fac-
ets are convex, but the proximal one bears a tiny
notch in its posterior third. Anteriorly, the tibiale
extends over two thirds of the distal margin of the
tibia and with its posterior extremity it contacts the
intermedium. The distal convexity articulates with
the anterior concave margin of dt I.
The intermedium is one third shorter than the tib-
iale but has the same proximodistal extension. All
articular margins are convex and conuent giving
the bone an oval outline, the proximal margin are
more convex than the distal one. The proximal
margin of the intermedium touches the posterodis-
tal corner of the tibia and the craniodistal corner
of the bula, respectively. The posterior extremity
of the intermedium articulates with the anterior
one of the bulare. Its distal margin touches the
proximal convexities of dt II/III and IV.
The bulare is the same size as the intermedium,
but is roughly pentagonal in outline. Its anterior
margin is concave and articulates with the poste-
rior half of the distal margin of the bula. The
anteroproximal margin of the bulare is almost
straight and includes an angle of about 120° with
the anterior margin. At its anterior extremity the
anteroproximal facet terminates in a sharply con-
vex process that merges with the distal convexity
at an angle of 90°. The posterior margin of the
bulare is one third longer than the anterior one
and posteriorly merges with the shallowly convex
posterior margin at an angle of about 90°. The
caudoproximal facet of the bulare is straight and
meets with the posterior margin at an angle of
about 120°. The posterior and the caudoproximal
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facets are of equal length and together they are as
long as the anterior margin. With its distal mar-
gin, the bulare contacts dt IV and mt V in one
point, respectively. The caudoproximal margin of
the bone articulates with the posterior margin of
a supernumerary epipodial element that is trap-
ezoidal in outline, it has one third the size of the
bulare and bridges the gap between the bulare,
the bula and the anterior supernumerary ele-
ment posterior to the bula. The proximal margin
of the tarsal supernumerary element is about half
the size of the distal margin.
There are three distal tarsals, which are arranged
in a row distally adjacent to the proximal row of
tarsalia. Dt I is approximately trapezoidal and
about one fourth smaller than the tibiale. The an-
terior margin of dt I is the longest of all margins;
it is concave and rmly articulates with the tibiale.
The anterior, distal and posterior margins are all
convex and conuent at the corners. The distal
margin is about one third smaller than the prox-
imal one. The anterior margin of dt I is as long
as the distal one with which it includes an angle
of about 100°. The angle between the anterior
margin and the proximal articular facet is about
80°. The posterior margin of dt I is strongly con-
vex and is half the length of the proximal margin.
With its distal margin dt I contacts mt I, with its
posterodistal corner mt II. The posterior extrem-
ity of dt I articulates with the anterior margin of
dt II/III, which is irregularly oval in outline and
one fourth smaller than dt I. The proximal margin
of dt II/III is convex and punctually contacts the
distal convexities of tibiale and intermedium. The
distal margin of the bone is divided into two facets
of almost equal length. Both are convex and only
separated by a slightly more convex part of the
distal margin, which protrudes between the proxi-
mal articular faces of mt II and III. The posterior
extremity of dt II/III contacts dt IV in a single
point.
In longitudinal direction, dt IV is one third shorter
than dt II/III, but a little larger proximodistally.
The outline of dt IV is marked by slightly convex
posterior and distal margins. The other margins
are conuent and evenly convex, forming a near-
ly circular outline. The proximal margin of dt IV
touches the intermedium and bulare in a point,
respectively. The posterior concavity, which equals
the distal one in length, articulates with mt IV and
the posterior one with the proximal two thirds of
the anterior face of mt V.
Metatarsals: All ve metatarsals are preserved
in articulation. Mt I is the shortest being about one
third shorter than mt III-V. In cranioposterior di-
rection, mt I is about one fourth shorter than in the
proximodistal direction. The narrowest point of
the shaft lies in the middle of the bone and is bare-
ly visible. Both the proximal and distal articular
surfaces are slightly convex and articulate loosely
with dt I proximally and with the basal phalanx
of digit I distally. The posterior margin of mt I
lies in close contact with mt II. The latter bone is
about one quarter longer proximodistally than mt
I and shows a proximally orientated process that
interdigitates with dt I and dt II/III. The circum-
ference of the shaft is mostly obscured by matrix.
The distal articular face is slightly convex. Mt II-V
are approximately twice as long proximodistally as
they are anteroposteriorly. The mid-shaft circum-
ference has one-fourth the width of the proximal
articular facet. The proximal articular faces of all
metatarsalia are slightly convex as are the distal ar-
ticular facets of mt I, II and V. Those of mt II and
IV are slightly concave. The articulation surfaces
between mt I-IV and the basal phalanges of the
digits I-IV form a line which is inclined against the
long axis of the body by about 5°. With one third
of its anterior margin mt V contacts the proximal
third of the posterior margin of mt IV.
Phalanges: The phalangeal formula of the pes is
6 (preserved) -12-14-14-11 with the digit IV being
the longest. With the exception of the distal-most
ones, the phalanges are hourglass-shaped with al-
most straight interphalangeal articulations, as in
the manus. The length/width ratio of the pha-
langes of all digits III is 1.77 (Table 5). The min-
imum transverse section at constriction is about
two thirds of the extension of the proximal articu-
lar facet and the distal articular facet is about one
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fth smaller than the proximal one. The ultimate
phalanges, where preserved, they show a rounded
tapering tip and a slightly convex proximal artic-
ular facet that does not precisely match the distal
articular face of the penultimate phalanx. The
two proximal-most phalanges of the digits I-IV
are arranged in oblique rows with a posterodistal
direction, and with minimal overlap. An exception
is digit V, which overlaps the posterior margins
of the phalanges in digit IV by one third of their
posterior proximal face. Further distally the incli-
nation of the line of the interphalangeal articu-
lations gradually approaches the situation seen in
the manus, where the interphalangeal articulation
lies within the constriction of the posteriorly fol-
lowing phalanges. In distal direction, the interpha-
langeal articulation surfaces gradually line up with
each other and in the distal fth of the pes they
form a straight line, as is the case in the manus,
which is about one fourth larger than the pes.
SOFT TISSUES (FIGURES 2, 14 – 18)
There are ve types of soft tissue preservation
in the specimen: (1) a glossy black material that
is restricted to the body cavity (Figure 14), (2) a
dark grey material organized in transverse bars on
the right side of the neck base (Figure 15), (3) an
amorphous reddish substance along the neck and
tail, as well as in the proximal areas of the ippers
and along the posterior margin of the left hind
limb (Figures 13, 15 - 18), (4) a reddish-grey mate-
rial ornamented with shallow, but sharp transverse
and longitudinal furrows along the trunk and the
base of the left hind limb (Figures 15, 17), and (5)
a light to dark grey glossy amorphous substance
restricted to the tail base left and right hand side of
the caudal vertebral column (Figure 18).
The amorphous to granular, sometimes nely
striated glossy black material is restricted to the
dorsal wall of the body cavity (Figures 2, 14). It
coats the internal face of the dorsal half of the
ribs, the space between them and the ventral face
of the respective centra. Neither the gastralia nor
the external faces of the ribs show such a coat-
ing. The material is especially well preserved on
the right side of the body cavity. There are two
taphonomic options that would explain this mate-
rial: (1) it represents the bituminous remnants of
the putreed intestines that liquidized inside the
body cavity under anoxic conditions that now coat
the dorsal wall of the thorax. (2) The material rep-
resents the remains of a pigmented visceral peri-
toneum. In case of (1) it should be expected that
the liquidized organic matter concentrates in the
dorsal arcades of the ribcage along the thoracic
vertebral column. However, the black substance is
equally thin inside the entire body cavity includ-
ing the medial sections of the ribs and the ventral
faces of the centra; in places it shows a brous or
wrinkled relief inconsistent with a liquid mass of
organic matter. Therefore, it appears more likely
that the black lining represents the visceral peri-
toneum that likely was heavily pigmented with
melanocytes. A pigmented visceral peritoneum
especially coating the dorsal part of the abdomi-
nal cavity is known from a variety of diurnal squa-
mates that inhabit desert or high altitude habitats
and is thought to screen solar radiation and block
UV radiation from damaging the reproductive
systems (Greer, 1989; Porter, 1967). However, a
peritoneum pigmented with melanin also occurs
in poultry (Wang et al., 2012), and a number of te-
leosts, where it even represents a diagnostic feature
(e. g. Page and Burr, 2011). However, the function
of a black peritoneum in chickens and teleosts is
unknown. Plesiosaurs, at least those that prefera-
bly cruised close to the water surface were exposed
to massive sun radiation and could have beneted
from a melanistic visceral peritoneum especially in
early ontogenetic stages.
In order to do a geochemical analysis, we were
allowed to remove a very small piece from the
substance. A test with EDAX probing yielded the
typical absorption bands for Goethite Fe3O(OH),
a mineral that preferably precipitates under dys-
oxic conditions and temperatures around 25°C
(Schweitzer et al., 2013). For further investigations
the sample was too small and further sampling was
not permitted.
To the right hand side of the base of the cervical
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vertebral column along the ventral termini of the
left cervical ribs there is a sequence of approxi-
mately rectangular structures ve to ten millime-
tres long by two mm wide preserved in a dark-grey
substance. Rarely, they are square. Some are or-
ganized in transverse bands (Figure 15). Where
preserved the structures are densely packed and
organized in longitudinal rows. They are especial-
ly well preserved at the cervicothoracic transition,
where they occur within a pale reddish substance.
In places they are preserved as internal molds.
Along the anterior margin of the scapula and
lateral of the clavicle there are conuent patches
of a light-grey mass. The transverse rectangular
structures also occur along the body anks, where
they are either preserved in a dark-grey substance
or as internal molds (Figure 16). In some places
the rectangular structures are organized in almost
parallel-sided longitudinal rows that are interrupt-
ed by areas of amorphous grey and red substance.
In the space between the right femur and ilium
similar rectangular structures occur in the same
preservation styles, also interrupted by large areas
with amorphous red and grey substances (Figure
17). Along the body wall, the structures are pre-
dominantly rectangular and measure about ve
millimeters transversely and one to two millime-
ters longitudinally. Many are arranged in oblique,
parallel-sided rows extending from craniomedially
to terminolaterally. Towards the external margin
of the soft tissue the structures become circular
or oval. In the angle between femur and ilium the
Figure 13 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Right pelvic limb in ventral aspect; A) photograph, B) interpretative line
drawing.
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lines bordering the structures become increasingly
perpendicular to the trailing edge of hind ipper.
In the transitional zone they diverge anteriorly
and the structures preserved between the lines are
trapezoidal reaching sizes up to 12 x 14 millime-
ters. In distal directions the longitudinal parallel
lines become exceedingly ner and their distance
decreases to about one millimeter or less. Lines
of sub-circular structures are occasionally found
between them. No such structures are visible
in the tail. All soft tissue types detected here are
amorphous.
The structures described above appear too regular
to represent the results of taphonomic eects such
as shrinking or autolysis. Artefacts of preparation
can also be excluded. The structures can be inter-
preted as remnants of squamae mostly from the
ventral and the lateral skin of neck and body. The
regular squamation likely consisted of vaulted
squamae, orientated transversely a size of about
12 x 2 millimeters. They were arranged in paral-
lel-sided longitudinal rows that may have covered
the entire belly. At the base of the ippers this pat-
tern becomes radially arranged, forming a exible
folding zone. The trailing ap of the ippers was
most likely covered by longitudinal rows of small,
millimetric, sub-circular squamae giving the skin
exibility.
The amorphous reddish substance along neck and
tail and as well in some patches along the sides of
the trunk are approximately 100 – 150 mm wide
with sharp lateral margins clearly set o from the
surrounding sediment (Figures 3, 16). This mate-
rial very likely is a decay product of skin and the
subdermal tissue. The thickness of the substance
suggests that either the skin of the ventral side of
the body was still exible and not particularly de-
composed, when the gastral basket collapsed into
the body cavity (Figure 19 B), or the subdermal tis-
sue was thicker than in most extant reptiles, espe-
cially squamates. The subdermal tissue may have
been rich in adipose tissue as is the case in many
modern marine Mammalia where it streamlines
the body. Possibly both factors contributed to the
Figure 14 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Soft tissue preservation inside the body cavity; the yellow broken line
outlines the black, glossy coating of the right thoracic cavity. Note that the internal faces of the ribs are covered by the substance but
not the external faces of the gastralia.
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preservation of the amorphous reddish substance
as preserved. In the distal area of the ippers the
amorphous reddish substance is not only visible
between the bones but also as a patch at the pos-
terior margin of the left humerus and as a seam
along the posterior margin of the right hind ip-
per (Figures 3, 11 A, 13). This seam has one-third
the depth of the bony core of the ipper and from
the middle of the posterior margin of the femur
curves into the lateral wall of the tail. This pro-
vides strong evidence for plesiosaur ippers having
a exible trailing edge and used as hydrofoils (Frey
and Riess, 1982; Godfrey, 1984; Halstead, 1989;
Lingham-Soliar, 2000; Robinson, 1975; Sanders et
al., 2004; Taylor, 1981). Furthermore, the propo-
dials of the ippers were integrated in the body
contour by a posterior skin fold that merged with
the lateral body wall.
There are patches of a dark reddish or dark-grey
substance that is thicker than the amorphous red-
dish substance, especially in the posterior third of
the trunk, the base of the right hind ipper and
the tail base. These areas are characterized by a
pattern of ne crisscross running furrows that are
mostly straight or slightly curved (Figure 18). The
areas between the furrows are roughly rectangu-
lar or trapezoidal in outline with a smooth sur-
face. Because these structures are preserved only
on the external surface, they are assumed to be
epidermal, but there is no evidence for scute-like
Figure 15 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1.
Soft tissue preservation at the left side of the neck base; A)
photograph, B) interpretative line drawing; abbreviations: cv =
cervical vertebra, cr = cervical rib.
Figure 16 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1.
Soft tissue preservation along the left side of the trunk; A)
photograph, B) interpretative line drawing. Note the transversely
rectangular squamae are arranged in longitudinal rows.
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structures.
A light to dark grey amorphous and glossy sub-
stance is preserved on both sides of the vertebral
column of the tail, especially on the right side
(Figure 18). It is bordered laterally by the above
described amorphous reddish or dark-grey sub-
stance. Occasionally this substance shows an irreg-
ular brous texture and is evidently responsible for
the conical shape of the tail and its massive base. In
many lizards, e.g. the fat tailed geckos, the posterior
adipose tissue is subdermal (Delome et al., 2012;
Derickson, 1976). In crocodiles, the posterior ad-
ipose tissue is deposited in the tail base between
the m. ilioischiocaudalis and m. caudofemoralis
(Frey, 1988). Topographically these tissues in both
groups of reptiles coincide with the grey masses
preserved in the tail base of Mauriciosaurus. Provid-
ed these grey masses represent remains of adipose
tissue, the deposit likely was subdermal, because
the muscle masses of the tail are delimited by the
dimensions of the transverse processes, the neu-
ral spines and the hemal arches, which are small
in Mauriciosaurus, suggesting a weak musculariza-
tion of the tail. Therefore it appears plausible that
the tail base of Mauriciosaurus was stabilized and
shaped mainly by contour fat in a way that the
outline of the trunk continued onto the tail.
7. Comparative anatomy
7.1. COEVAL POLYCOTYLIDS
About seven genera of Polycotylidae are described
and accepted (e. g. Albright III et al., 2007b, 2007c;
Druckenmiller and Russell, 2009; Ketchum and
Benson, 2011, 2010).
According to Druckenmiller and Russell (2009),
seven genera in eight species and two un-named
taxa occur during the Late Cenomanian and Early
Turonian, and thus are about coeval with Mauricio-
saurus fernandezi. Two of these, Manemergus (Buchy
et al., 2005) and Thililua (Bardet et al., 2003) have
been found only in the Early Turonian of Moroc-
co. The rostrum of Manemergus is dorsally concave,
while that of Thililua is laterally compressed, with
vertically festooned jaw margins and a convex
ventral margin of the mandible level below the
anterior margin of the orbit. In contrast, the ros-
trum of Mauriciosaurus is straight and rounded in
cross-section, the jaw margins are straight and the
ventral margin of the mandible is evenly convex.
The dentition in both African species is anisodont.
Furthermore, Mauriciosaurus has less than half as
many cervical vertebrae as Thililua.
Figure 17 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1.
Soft tissue preservation, at the posterior base of the right pelvic
limb; A) photograph, B) interpretative line drawing. Note that
the trailing flap continues on the tail base. Also note the fibrous
structures perpendicular to the more distal part of the trailing
edge.
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COMPARATIVE ANATOMY
Palmulasaurus (Albright III et al., 2007c), previous-
ly described as Palmula (Albright III et al., 2007a)
is reported with one species, P. quadratus, from the
early Late Cenomanian of South Dakota (Schum-
acher and Bell, 1999; Von Loh and Bell, 1998) and
the Late Cenomanian of Japan (Sato and Storrs,
2000). Pahaspasaurus haasi from the early late Ceno-
manian of South Dakota is probably congeneric
with Palmulasaurus (Schumacher et al., 2016). In
Mauriciosaurus, the mandibular alveolae are invis-
ible and it is therefore impossible to determine to
which pair of alveoli the splenials extended ante-
riorly. However, when comparing the anterior ex-
tent of the splenials quantitatively, they appear to
Figure 18 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. Soft tissue preservation in the tail; A) photograph, B) interpretative line
drawing. Note the massive tail base and the light-grey glossy substance on both sides of the vertebral column.
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COMPARATIVE ANATOMY
be signicantly shorter and wider than in Palmu-
lasaurus. Additionally, Mauriciosaurus has a straight
lateral mandibular face, whereas the mandible of
Palmulasaurus shows lateral interalveolar depres-
sions. Palmulasaurus has 19 thoracic and 11 caudal
vertebrae, each with a large nutritive foramen on
the dorsolateral face of the centrum (Albright III
et al., 2007a). Mauriciosaurus has 21 thoracic and at
least 13 caudal vertebrae. In Mauriciosaurus there
is no epipodial foramen between the rounded
epiepipodials. For Palmulasaurus, isomorph polyg-
onal epiepipodials are diagnostic and epipodial
foramina are present. The average length/width
ratio of 1.77 (Table 5) is smaller than that of Pal-
mulasaurus, where this ratio is 1.9 [Figures 11-13;
Table 3 (Albright III et al., 2007a)]. The morpho-
logical dierences of the pelvic bones of Mauri-
ciosaurus and Palmulasaurus are due to dierent
ontogenetic stages.
A fourth species which to date is restricted to the
Early Turonian of Utah (top-most Dakota For-
mation) is Eopolycotylus rankini (Albright III et al.,
2007b). This species diers from Mauriciosaurus in
the more massive teeth, the participation of the
splenials in the ventral face of the mandibular
symphysis, which is about 30 % (Albright III et al.,
2007b) instead of 50 % in Mauriciosaurus, thoracic
vertebrae that are about one fourth shorter than
the cervical ones, a coracoid with a prominent an-
terior process and a number of foramina along its
medial margin, foramina also in a scapula where
the glenoid process is almost as wide as the later-
al one. The curved ilium of Eopolycotylus has only
about half the length of the ischium, while on the
humerus there is a tuberosity, which is missing in
Mauriciosaurus posterior to the caput.
The Turonian genus Trinacromerum and the Early
Conacian genus Dolichorhynchops, which both are
reported to reach the Campanian-Maastrichtian
boundary, are also distinct from Mauriciosaurus.
The dish-like depression in the pterygoids of Mau-
riciosaurus is restricted to the anterior half of the
ventral face of the corpus. They open posteriorly,
merging with a relief of prominent ridges arranged
in a W-conguration covering the posterior half
of the pterygoideal corpus, similar to Polycotylus
(Figure 4). In Trinacromerum this depression is elon-
gate ovoid (O’Keefe, 2004; Williston, 1908). In
Trinacromerum the posterior fourth of the ventrolat-
eral margins of the pterygoids rise to a sharp ridge
that posteriorly terminates in an elongate process
(O’Keefe, 2004; Williston, 1908). Mauriciosaurus
bears a pair of prominent tubercles on the ventral
face of the pterygoids adjacent to their posterior
margins. The anterior pterygoid rods in Mauri-
ciosaurus expand in their anterior halves to three
times the width of the basal third of the process-
es. Similarly, in Trinacromerum, these rods expand
to about twice the width of the basal third of the
bone (O’Keefe, 2004; Williston, 1908). The pter-
ygoids in Mauriciosaurus meet atop the parasphe-
noid, almost closing the posterior interpterygoidal
vacuities (Figure 4). In Trinacromerum these vacuities
are wide because of the concave lateral margins
of the parasphenoid, which also lacks the ventral
depression of this bone in Mauriciosaurus, and the
concave medial margin of the caudal half of the
pterygoids. Like the parasphenoid of Mauriciosau-
rus, that of Trinacromerum terminates in an anterior
bifurcation (O’Keefe, 2004; Williston, 1908). With
about 42 tooth positions, Mauriciosaurus has more
premaxillomaxillary teeth than Trinacromerum with
a premaxillomaxillary tooth count of about 30 in
T. osborni and about 38 in T. willistoni (Riggs, 1944).
The vertebral centra of Mauriciosaurus are laterally
and ventrally constricted and not cylindrical as in
Trinacromerum (Albright III et al., 2007a; Carpen-
ter, 1997). The distal margin of the propodials of
Mauriciosaurus is evenly rounded. In Trinacromerum
they show a distinct articular facet for the anteri-
or epipodial (Albright III et al., 2007b; Williston,
1908). The primary epipodials of Mauriciosaurus
are distinctly wider than long and not as equidi-
mensional as in Trinacromerum (Schumacher and
Everhart, 2005). The average length/width ratio
of the phalanges of Mauriciosaurus is 1.77 and thus
similar to Trinacromerum (Schumacher and Ever-
hart, 2005). Posterior and medial perforations of
the coracoid are present in Trinacromerum (O’Keefe,
2004; Williston, 1908), but not in Mauriciosaurus.
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COMPARATIVE ANATOMY
Dolichorhynchops diers from Mauriciosaurus in hav-
ing a bean-shaped dish-like depression, which oc-
cupies the entire ventral face of the corpus of the
pterygoids (O’Keefe, 2008, 2001; Sato et al., 2011).
Dolichorhynchops lacks the prominent tubercles of
Mauriciosaurus on the ventral face of the pterygoids
adjacent to their caudal margins (O’Keefe, 2008,
2004, 2001; Sato et al., 2011). In Dolichorhynchops
the anterior pterygoid rods taper anteriorly and
slightly curve medially at their tips (O’Keefe, 2001,
2004, 2008; Sato et al., 2011), unlike the expanded
pterygoid rods in Mauriciosaurus. The lateral mar-
gins of the parasphenoids of Dolichorhynchops are
concave and border a wide posterior interpalati-
nal vacuity like in Trinacromerum. Similar to Mau-
riciosaurus the ventral face of the parasphenoid of
Dolichorhynchops is concave, but to a lesser extent
(O’Keefe, 2008). The parasphenoid of Dolichorhyn-
chops anteriorly terminates in a blunt process, while
that of Mauriciosaurus is bifurcated (O’Keefe, 2001,
2004, 2008; Sato et al., 2011). Mauriciosaurus has
more teeth in the upper jaw than Dolichorhynchops,
where the tooth count of the premaxillomaxillary
complex ranges between 26 and 30 in adults and
26 or 27 in juveniles (O’Keefe, 2008; Sato, 2005).
The caudal centra bear anterior and posterior ar-
ticular faces for the heamal arches suggesting that
they articulated with two caudals (Albright III et al.,
2007a; Carpenter, 1997; Schumacher and Ever-
hart, 2005). In Dolichorhynchops the distal margins
of the propodials resemble those of Mauriciosaurus
in being almost evenly rounded. The facets for the
epipodials are faintly visible (O’Keefe, 2008). The
average phalangeal length/width ratio of Dolicho-
rhynchops is 1.45 (Schumacher et al., 2016). In Mau-
riciosaurus it is 1.77, which could suggest a more
primitive condition (Albright III et al., 2007a). In
contrast to Mauriciosaurus, Dolichorhynchops possesses
posterior and medial perforations of the coracoid.
One outstanding feature of Mauriciosaurus is the
gastralia basket with the gastralia converging to
a center. A taphonomic eect is unlikely, because
there is no displacement of bones in the abdom-
inal area. Gastral baskets are rarely preserved in
polycotylids, and when they are, mostly they are
decayed e.g. (Carpenter et al., 2010; Schumacher et
al., 2016). Therefore, little is known about the mor-
phology of this structure. Most reconstructions are
analogues to the gastralia arrangements in other
plesiosaurs. For the moment, Mauriciosaurus is the
only plesiosaur with this arrangement of gastralia,
which could thus be regarded as diagnostic feature
unique to Mauriciosaurus.
7.2. COMPARISON WITH NON-COEVAL
POLYCOTYLIDS
Pahasapasaurus haasi (Schumacher, 2007) report-
ed from the early Late Cenomanian Graneros
Formation in western South Dakota diers from
Mauriciosaurus in the following diagnostic features
(Schumacher, 2007): it lacks an anterior interpter-
ygoidal vacuity, the pterygoids have a common
median suture anterior to the parasphenoid that
bears a longitudinal ventral keel which is absent
in Mauriciosaurus. The teeth are massive; the lateral
margin of the anterior half of the jaws is undu-
lating due to the laterally bulging tooth sockets.
Furthermore, the alveolar margin is elevated. All
epipodials have foramina. The distal margins of
the propodials show three distinct facets and are
not smoothly convex as in Mauriciosaurus.
Georgiasaurus penzensis (Ochev, 1977, 1976; Storrs et
al., 2000) from the Santonian of the Penza region
(the formation was not specied), about 700 km
southeast of Moscow, diers from Mauriciosaurus
in its massive teeth and the degree of participa-
tion of the splenials in forming just one tenth of
the mandibular symphysis. Such a dentition and
symphysis are also seen in a polycotylid described
by Arkhangelsky et al. (2007) from the Campanian
the middle Volga Region (SGU 104a/37, -38) and
there stated to be closely related with Georgiasaurus.
One single species of the genus Polycotylus, P. latip-
innis, is known from the Early Campanian of
North America, namely from the Niobrara Chalk
of Kansas and the Moreville Chalk Formation of
Alabama (Cope, 1869; O’Keefe, 2004; Schumach-
er et al., 2016). The cervical and trunk vertebrae
of Late Cretaceous polycotylids referred to the
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COMPARATIVE ANATOMY / DISCUSSION
genus Polycotylus (Trinacromerum) from the Late Cre-
taceous Russian districts Orenburg and Saratov
(Bobolubow, 1912) are doubtful and thus not valid.
Polycotylus diers from Mauriciosaurus in having 26
instead of 21 cervical vertebrae (Storrs, 1999).
The latest of the named polycotylids is Sulcusuchus
erraini, Gasparini and Spalletti 1990 from the Late
Campanian – Early Maastrichtian La Colonía
Formation, Cerro Bosta, Southern Argentina. De-
spite the fact that the specimen consists only of
a fragmentary skull and mandible, according to
the emended diagnosis given by O’Gorman and
Gasparini, 2013, it preserves the following unique
diagnostic features that are not found in Mau-
riciosaurus: there are deep and wide anterior and
mandibular grooves, the parasphenoid has a keel
on its ventral side, the basioccipital tubercle pro-
trudes posteriorly to the posterior terminus of the
occipital condyle, and there is a wide notch on the
posterior margin of the pterygoids. The anterior
part of the body of the parasphenoid protrudes
between the posteromedial margins of the wings
of the pterygoids and together with them it forms
a at barely sculptured plate.
Mauriciosaurus fernandezi is identied as a polycoty-
line polycotylid based on its slightly sigmoidal hu-
meri with a length/width ratio of 1.65 (Figure 11;
Table 3), a missing antebrachial foramen (Figure
11), three distal tarsals (Figures 12, 13), primary
epipodials which are distinctly wider than long
(Figure 11; Table 3), and more than twenty trunk
vertebrae (Figure 8) (Albright III et al., 2007a).
Of all polycotylids, Mauriciosaurus most resembles
Dolichorhynchops, but also shares many characters
with Trinacromerum. The phalangeal length/width
ratio appears more primitive than in Dolichorhyn-
chops and Trinacromerum and more resembles that
of Palmulasaurus. The enigmatic construction of
the gastral basket may represent an autapomor-
phy of Mauriciosaurus fernandezi and is certainly not
depending on the ontogenetic stage. We therefore
consider it appropriate to erect a new genus for
this enigmatic polycotylid that inhabited the Pa-
leogulf of Mexico.
8. Discussion
8.1. TAPHONOMY
The thick soft tissue in the trunk and tail region
of Mauriciosaurus suggests the presence of a layer
of subdermal adipose tissue, also known as con-
tour fat (Figures 3, 16 – 18). This adipose tissue,
combined with a thin epidermis with thin kera-
tinous scales, is probably the reason why dermal
structures of plesiosaurs are so rarely preserved.
The putrefaction process of the subdermal adi-
pose tissue would rapidly lead to a delamination
and disruption of the thin epidermis. In order to
explain the excellent preservation of Mauriciosaurus
the following scenario is proposed that is consis-
tent with the preserved remains, the sediment and
the depositional setting.
After death, Mauriciosaurus must have rapidly sunk
into the soft water-soaked lime mud sediment,
with its back rst (Figure 19 A). This is concluded
from the position of the ribs, which have rotated
not laterally, but posteriorly in their vertebral ar-
ticulations during the collapse of the body and
subsequent compaction (Figure 4, 8). At least the
dorsal half of the polycotylid must have been con-
tained by sediment as is suggested by the thickness
of the soft tissue (Figure 19 A). The immediate en-
closure of the fresh carcass by soft water-soaked
sediment formed a chemical reaction chamber in
which the adipose tissue could become saponied
into mortuary wax or adipocere (Figure 19 B).
Adipocere is a waxy substance that forms under
anoxic conditions at temperatures of between 21
°C and 37 °C and thus matches the palaeoenvi-
ronmental conditions reconstructed for the Val-
lecillo limestone (Ifrim et al., 2008; Topper et al.,
2011). The adipocere likely helped to conserve the
thin epidermis of the entire dorsal skin of the ple-
siosaurs and the contours of its body (Kahana et
al., 1999). The belly, however, was exposed to the
hostile oxygen-decient bottom water (Figure 19
A). Therefore the exposed skin of the ventral face
of the body decayed prior to the nal embedding
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DISCUSSION
and thus left no trace on the skeleton (Figure 19
B). The preserved parts are all marginal or around
the ippers. Due to early diagenetic compaction
the previously vaulted gastralia basket was pressed
at in such a way that the lateral extremities of the
gastralia now protrude laterally beyond the pre-
served soft tissue seam (Figures 8, 19 B).
The extensive soft tissue preservation of the Val-
lecillo polycotylid Mauriciosaurus fernandezi suggests
that at least polycotylids, but probably all plesio-
saurs, had a thin epidermis with an extremely low
fossilization potential. The body appears to have
been stream-lined by subdermal adipose tissue
that was especially massive at the tail base. This
adipose armor precluded a mobility of most of the
weakly muscularised tail, probably excluding the
very tip. This weak muscularization is evidenced
by the low hemal arches and the short transverse
processes that, in extant reptiles, mark the diam-
eter of the hypaxial muscle masses. The neural
spines which would yield a hint on the dimensions
of the epaxial muscle mass are not visible. Appar-
ently the tail was also mostly immobile especially
at its base. Both tail and trunk formed a drop-
shaped, stream-lined unit that was propelled with
the four ippers.
8.2. INDIVIDUAL AGE
Little is known about the ontogeny of plesiosaurs,
especially polycotylids. The only fetal skeleton
known is completely disarticulated (O’Keefe and
Chiappe, 2011). Neonates and early ontogenetic
stages of polycotylids are hitherto unknown, but
there are some records of juveniles and subadults
(Buchy et al., 2005; Schumacher et al., 2016). The
following features suggest that Mauriciosaurus fer-
nandezi must have died at an early ontogenetic
stage:
1. The neurocentral sutures are unfused, as is vis-
ible in the cervicals (Albright III et al., 2007a).
2. The coracoids lack anterior clavicular exten-
sions. They are simple in shape with little pos-
terolateral and no posteromedial expansion
(Figures 8, 10).
3. The ventral girdle bones are extremely thin.
4. The scapulae lack a dorsal process (O’Keefe
and Byrd, 2012).
5. The ischia are short and only three times as
long as they are wide (Figures 8, 10; Schum-
acher et al., 2016).
6. A wide gap between the propodials and
epipodials suggests extensive cartilage (Figures
11-13).
Figure 19 Mauriciosaurus fernandezi INAH CPC RFG 2544 P.F.1. ; model for the taphonomy: A) Schematic mid-trunk cross-section
through the carcass in the embedding position after sinking into a soft, water-soaked substrate; note that the belly is not embedded
with the gastralia. B) The part of the trunk exposed to the open water decayed and collapsed and the gastralia basket spread. The
subdermal adipose tissue has transformed into adipocere preserving the delicate epidermal structures. In a third phase the ribs rotated
posteriorly around their vertebral articulations due to the semi-consolidated surrounding sediment, as is seen in Figure 3.
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DISCUSSION
7. The small size of the specimen.
These immature features mostly concern the lo-
comotor apparatus and are contrasted by densely
packed carpals, tarsals and metapodials, as well as
by the presence of a fourth supernumerary epipo-
dial. There is also almost no space for cartilage be-
tween the interphalangeal joints (Figures 11-13).
The palatinal roof is almost fully mineralized and
thus shows features of a subadult. This pattern
suggests that ontogenetic mineralization of the
skull and distal elements of the limbs preceded
that of the vertebral column (closing of the neuro-
central suture (Albright III et al., 2007a). The rapid
mineralization of the skull is best explained by the
enhancement of bite force as early as possible
during ontogeny, similar to pliosaurid plesiosaurs
(Kear, 2007). The early mineralization of the epi-,
meso-, meta- and acropodials suggests that the
main thrust-generating structure was stabilized as
soon as possible, prior to the mineralization of the
elbow joint and that of the ventral girdle plates,
where the locomotor muscles attached. This dis-
crepancy may be explained by a high frequency
and low amplitude of underwater ight that would
require less power. The dimensional relationship
of the ippers with respect to the body in Mauri-
ciosaurus conrms the suggestion of O´Keefe and
Chiappe (2011) of an isometric growth of poly-
cotylids. Mauriciosaurus died in the open sea about
500 km from the nearest shoreline. Other juvenile
polycotylid are also reported from marine environ-
ments but shallow water coastal habitats (Buchy et
al., 2005; Schumacher et al., 2016). Mauriciosaurus
is the rst juvenile polycotylid reported from a
deep shelf oshore habitat.
8.3 LOCOMOTION AND POSSIBLE DIET
The limbs of Mauriciosaurus fernandezi had strong-
ly muscularised propodials and a exible trailing
edge (Dames, 1895; McHenry et al., 2005) as con-
cluded from the soft tissue adjacent to the posterior
edge of the left pelvic limb. Hydrofoil locomotion
models are therefore viable for all four limbs. Due
to the immobile trunk and tail, all maneuvers
could only have been provided by the limbs and
neck. The latter was reinforced, as in all plesio-
saurs, by a chain of overlapping cervical ribs that
prevented extreme bending but allowed enough
movement to seize prey, which in the case of Mau-
riciosaurus likely consisted of small items because of
the slender rostrum and the small, pointed teeth.
These anatomical features, and the fact that the
thickest part of the trunk and tail unit lies in its an-
terior third, suggest swimming speeds comparable
to that of modern sea turtles. Among these, the
leatherback (Dermochelys coriacea), the fastest swim-
ming sea turtle, travels at an average velocity of
about 7 kph (Eckert, 2002) and shows a hydrody-
namic carapace, the outline of which strikingly re-
sembles the body outline of Mauriciosaurus (Figure
20). This swimming speed falls within the range
of swimming speeds reconstructed for Mesozoic
marine reptiles (Massare, 1988). Nonetheless, the
long and slim limbs that likely all participated in
thrust generation, may have allowed for higher ve-
Figure 20 Comparison of the body outline of Mauriciosaurus
fernandezi and Dermochelys coriacea. A) Schematic outline
reconstruction of Mauriciosaurus fernandezi CPC RFG 2544 P.F.1.
based on soft tissue evidence in ventral aspect. Note that trunk
and tail form a functional unit with a drop-shaped outline with
the thickest diameter lying anterior to the mid-section of the
body. B) Outline sketch of a Leatherback Turtle (Dermochelys
coriacea). Note that the drop-shaped outline of the carapace
strikingly resembles the trunk-tail complex of Mauriciosaurus.
The more slender body of the plesiosaur and the four-winged
thrust system suggests a swimming speed greater than 7 km/h
(1.9 m/s), which is the travel speed of a Leatherback Turtle.
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DISCUSSION / CONCLUSIONS /
ACKNOWLEDGEMENTS / REFERENCES
locities (Carpenter et al., 2010). According to the
conservative body construction of Plesiosauria
and the dimensions of the tail with respect to the
body, it is reasonable to assume that Plesiosauria
may have shared a drop-shaped body with a ba-
sically immobile fat tail that formed a functional
unit with the trunk.
10. Conclusions
Mauriciosaurus fernandezi is an enigmatic polycoty-
line plesiosaur from the Paleogulf of Mexico. The
species shows a mosaic of characters comprising
diagnostic features from both Dolichorhynchops and
Trinacromerum with a closer similarity to Dolicho-
rhynchops, but also features of more basal polycoty-
lids. Many of the enigmatic features are likely due
to the early ontogenetic stage of the individual.
Maturization of the cranial bones and the bones
distal to the propodials preceded that of the axial
skeleton and the vertebral column, resulting in an
early enhancement of the feeding and locomotor
apparatus. The extensive soft tissue preservation
suggests a streamlined body contour with a fat tail
base. The shape of the body thus resembles that
of sea turtles. The soft tissue also allows for a re-
construction of the aspect ratio of the ippers of
about 3.9, suggesting a high frequency – low am-
plitude stroke. This supports the assumption that
polycotylids were the fastest swimming plesiosaurs
(Carpenter et al., 2010; Massare, 1988). The body
surface was covered with transversely orientated
rectangular scutes arranged in transverse and lon-
gitudinal rows in the neck, body and tail. These
structures could have helped to reduce drag at
least at swimming speeds relevant for polycotylids
(e. g. Dean and Bhushan, 2010; Saravi and Cheng,
2013; Supriadi et al., 2015) the body cavity was
probably lined with a black peritoneum. Mauri-
ciosaurus fernandezi is the best preserved ‘soft tissue
plesiosaur’ worldwide and therefore contributes
substantially to our knowledge on the anatomy
and locomotion of plesiosaurs, especially consid-
ering that this young juvenile roamed the open sea
more than 500 km away from the nearest shore.
11. Acknowledgements
Our special thanks go to Ing. Mauricio Fernández
Garza for securing the specimen for the scientic
community, allowing us to describe it, and donat-
ing it to the Museo Papalote Verde in Monterrey
(Nuevo León). This publication would not have
been possible without the support of the Deutsche
Forschungsgemeinschaft (DFG). Dominik Schus-
ter (Karlsruhe) assisted with the literature data-
base and the measurement. We are very grateful to
Bruce A. Schuhmacher (Hays Kansas), Bruce M.
Rothschild (Rootstown, Ohio) R. Ewan Fordyce
(Otago) and Robin O´Keefe (Huntington, West
Virginia), who provided excellent reviews in an
earlier version of this manuscript that substantial-
ly helped to improve the scientic content of the
paper especially with respect to taxonomy. We cor-
dially thank David M. Martill (Portsmouth) and
Michael Maisch (Albstadt/Tailngen) for their
extremely constructive reviews of the nal version
of the papers. We also cordially thank Dr. Antoni
Camprubí, Francisco Vega, Oscar Monzon and
Sandra Ramos Amézquita (Mexico City) for their
fantastic editing work.
12. References
Albright III, L.B., Gillette, D.D., Titus, A.L., 2007a,
Plesiosaurs from the Upper Cretaceous
(Cenomanian-Turonian) Tropic Shale of
southern Utah, part 2: Polycotylidae: Journal
of Vertebrate Paleontology, 27, 41–58.
Albright III, L.B., Gillette, D.D., Titus, A.L., 2007b,
Plesiosaurs from the Upper Cretaceous
(Cenomanian–Turonian) Tropic Shale
of Southern Utah, part 2: Polycotylidae;
replacement names for the preoccupied
genus Palmula and the subfamily Palmulainae:
Journal of Vertebrate Paleontology, 27,
41–58.
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