Provenance and Anatomy of Genyodectes serus, a Large-Toothed Ceratosaur (Dinosauria:

Theropoda) from Patagonia

Author(s): Oliver W. M. Rauhut
Source: Journal of Vertebrate Paleontology, Vol. 24, No. 4 (Dec. 10, 2004), pp. 894-902
Published by: Taylor & Francis, Ltd. on behalf of The Society of Vertebrate Paleontology
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Journal of Vertebrate Paleontology 24(4):894-902, December 2004
© 2004 by the Society of Vertebrate Paleontology

PROVENANCE AND ANATOMY OF GENYODECTES SERUS, A LARGE-TOOTHED

CERATOSAUR (DINOSAURIA: THEROPODA) FROM PATAGONIA

OLIVER W. M. RAUHUT*
Institut for Paliontologie, Museum fuir Naturkunde der Humboldt Universitat, InvalidenstraBe 43, 101
Museo Paleontol6gico Egidio Feruglio, Av. Fontana 140, 9100 Trelew, Argentina, owmrauhut@h

ABSTRACT-The type material of Genyodectes serus, the first unquestionable non-avian theropod din
described from South America, is redescribed in detail and its provenance and systematic position are dis
though no detailed information about the provenance of the specimen exists, it is probably derived from the l
of the Cerro Barcino Formation (Chubut Group; Aptian-Albian) at Cafiad6n Grande, central Chubut Provi
tina. Genyodectes is characterized by closely-spaced premaxillary teeth that are arranged in an overlapping
pattern and extremely transversely compressed maxillary teeth, the longest of which exceed the minimal h
dentary in apicobasal length. Although systematic information is limited by the fragmentary nature of the m
combination of fused interdental plates, maxillary and dentary teeth with a pronounced flat or even slightly c
adjacent to the serrated carinae, premaxillary teeth that are considerably shorter than the maxillary teeth
compressed and very long maxillary teeth indicates neoceratosaurian and, more specifically, ceratosaurid af
Genyodectes. Thus, this taxon adds a further lineage of neoceratosaurs to the already diverse South Americ
this group.

INTRODUCTION The type material of Genyodectes has recently been remov

from the artificial matrix in which it was exhibited at the Mus
In 1901, A. S. Woodward Idescribed a partial snout of a thero-
de La Plata and reprepared. This has revealed new informatio
pod dinosaur from Chubut Province, Argentina, as a new genus
regarding the internal surfaces of the jaws, which were pre
and species, Genyodectes serus. With the possible exception of a
ously still largely covered in matrix. Thus, the holotype of t
probable theropod tooth included in the type material of Lon-
first South American theropod is here redescribed and its g
cosaurus (Ameghino, 1899; Coria and Salgado, 1996), this was
graphic provenance, stratigraphic age, and systematic positi
the first unquestionable non-avian theropod described from
are discussed in the light of our much improved knowledge
South America. Up to the late 1970s, it remained the most com-
South American theropods and theropods in general.
plete theropod specimen known from this continent (Bonaparte
1978), with the exception of the probably theropodan herre-
rasaurids (Reig, 1963; Benedetto, 1973; Novas, 1993; Sereno and
Novas 1993). This specimen is thus of considerable historical PROVENANCE OF THE MATERIAL
interest, but its systematic position and phylogenetic relation-
An important and so far unsolved problem concerning
ships have remained enigmatic, mainly due to the fragmentary
dectes is the exact geographic and especially stratigraph
nature of the type and only known specimen. Originally
enance thought
of the specimen. Woodward (1901: 179) noted t
to be a megalosaurid (Huene, 1929), von Huene later
material came(1932)
from a "red sandstone in the Cafiad6n Grande,
tentatively referred Genyodectes to the Dinodontidae
Chubut". (=Huene
Tyran- (1929) gave more precise, but partially contra-
nosauridae), and this view was accepted by most ofdictory
the few other On p. 5 he stated, referring to the locality:
information.
authors who took this genus into consideration"Cafiad6n
(e.g. Maleev,
Grande of the Rio Chubut, not very far from
1974). However, Molnar (1990) argued that Genyodectes does
Gaiman" (translated by OR). However, no Mesozoic sediments
not show any tyrannosaur synapomorphies and crop thusout considered
within some 50 km of the town of Gaiman, and this
it Theropoda incertae sedis. Paul (1988) noted that Genyodectes
information is not in accordance with other accounts of the prov-
probably represents an abelisaurid and tentatively enance
suggestedof thethat
specimen. On a later page, Huene (pp. 17-18)
it might be the same as Abelisaurus, but gave no detailed
discussed thejusti-
provenance of Genyodectes in more detail and
fication for this. Similarly, Bonaparte (1996) noted
even some simi-
gave approximate coordinates for the locality (44030' S,
larities between the snout of Genyodectes and abelisaurids, butW), which is within the area between the Rio
slightly east of 700
concluded that the material "provides limited information
Senguer and to theat-
Rio Chubut, where Santiago Roth, who col-
tempt a serious interpretation of the systematics" (p. the
lected 93) specimen
of this sometime between 1896 and 1898, mainly
taxon.
worked (Reguero, pers. com. 2002). This is also in accordance
In the last twenty years, our knowledge of South American
with other information on the locality that the material came
theropod faunas has increased dramatically. One of the
frommost
(Roth, 1908; Ameghino and Torcelli, 1934:fig. 22). It thus
important results of the work on Cretaceous theropodsseemsfrom
most likely that Genyodectes was found in the area be-
South America is the recognition of a highly diverse group of
tween Laguna del Mate and Manantial Pelado, some 70 km
basal theropods, the neoceratosaurs, as one of the most impor-of the town of Paso de Indios. In fact, a valley with the
southwest
tant Cretaceous theropod groups in the Southern Hemisphere
name Cafiad6n Grande is situated only some 20 km to the east of
(e.g. Bonaparte, 1991, 1996; Novas, 1997; Coria andthe
Salgado,
Laguna del Mate, and it seems very likely that the material
2000; Coria et al., 2002). is derived from this location (Fig. 1). Unfortunately, no detailed
geological map of this area exists, but according to the general
geological map of the province of Chubut (Lizuain et al., 1995),
the only Mesozoic sedimentary unit cropping out in this area is
* Present address: Bayerische Staatssammlung fOir Paliontologie,the Chubut Group (Hauterivian-Cenomanian; Fig. 1), and no
Richard-Wagner-Strasse 10, 80333 Miinchen, Germany; o.rauhut@lrz. uppermost Cretaceous units are found in this part of the prov-
uni-muenchen.de ince (Lizuain et al., 1995; Page et al., 1999; Puerta, pers. comm.

894

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 RAUHUT-PATAGONIAN CERATOSAUR 895

SanDept.
Mendoza Tehuelches Lag. de la
Chile Argentina 10km . Bombilla
La Pampa Buenos Aires

Neuquen0 , /rand & L/g. del Mate

SRio Negro I .d lM a /4

chubut Indios
,/ Dept.
Paso de

- - - - - - - - - - - - - - - -

CSanta 23
500 km Dept. Sarmiento
Rio Senguerl
FIGURE 1. Probable locality of the type specimen of Genyodectes serus. Hatched are

2002). Just northwest of the Cafiad6nrales, Buenos in

Grande, Aires, Argentina;
the SierraMLP,
del Museo de La Plata, La
Cerro Negro, the outcropping units of the Plata,Chubut
Argentina;Group
MWC, Museum
includeof Western Colorado, Fruita,
the lowermost Los Adobes FormationColorado, U.S.A.; QG, National Museum of Natural History,
(Hauterivian-Barremian)
and the lower two units of the Cerro Barcino Formation, the Harare, Zimbabwe.
Puesto la Paloma (Barremian-Aptian) and Cerro Castafio (Ap-
tian-Albian) members (Nullo, 1983). It is thus very likely that the
SYSTEMATIC PALEONTOLOGY
type locality of Genyodectes is located in one of these units.
Within these units, the Cerro Castafio Member of the Cerro
Barcino Formation is the most likely candidate to have yielded DINOSAURIA Owen, 1842
the material, because it is the most fossiliferous unit within the SAURISCHIA Seeley, 1887
lower parts of the Chubut Group and contains frequent red sand- THEROPODA Marsh, 1881
stones (pers. obs.). Furthermore, no vertebrate fossils have been CERATOSAURIA Marsh, 1884
reported from the Los Adobes Formation so far and the La ?CERATOSAURIDAE Marsh, 1884
Paloma Member of the Cerro Barcino Formation in the area of
Comment-The
Paso de Indios is dominated by gray to greenish sediments. The Ceratosauridae-created by Marsh (1884) to
include
interpretation of the fossil coming from the Cerro Castafio Mem-Ceratosaurus and potentially its closest relatives-has not
beenwho
ber is also in accordance with information from Roth (1908), formally defined phylogenetically yet. Although it is pre-
noted that the specimen came from a "dinosaur sandstone". mature to give such a formal definition at present, the name is
used
Some of his illustrations of this dinosaur sandstone in the here for a clade containing all ceratosaurs that are more
prov-
ince of Chubut (Roth, 1908:pl. 11, 12, 13) show sections closely
of the related to Ceratosaurus than to abelisaurids.
Cerro Barcino Formation along the Chubut river between the
towns of Los Altares and Paso de Indios (pers. obs.), which are GENYODECTES SERUS Woodward, 1901
now considered to belong to the Cerro Castafio Member (Page
Holotype-MLP
et al., 1999; Manassero et al., 2000). Thus, an Aptian-Albian age 26-39, partial snout, including both nearly
for this fossil is likely (Page et al., 1999). complete premaxillae, fragments of both maxillae, both den-
It might be noted that, according to Huene (1929, p. 17), Roth
taries, all with teeth, parts of both supradentaries, and fragments
(1908) provided a photograph of the locality on his pl. 14, of
butthe
this
left splenial.
is not obvious from Roth's text. However, the general aspect Locality
of and Horizon-Cafiad6n Grande, Departamento
the "dinosaur sandstone" on this photograph is in general Pasoacor-
de Indios, Chubut Province, Argentina. ?Cerro Castafio
dance with the Cerro Castafio Member of the Cerro Barcino Member, Cerro Barcino Formation; Aptian-Albian, Lower Cre-
Formation. taceous.

Institutional Abbreviations-BM, Museum fuir Naturkunde Diagnosis-Differs from all theropods with the poss
ception of Ceratosaurus in that the premaxillary teeth
der Humboldt Universitit, Berlin, Germany; BSP, Bayerische
Staatssammlung ftir Palaontologie und historische Geologie,
ranged in an overlapping en-echelon pattern and the
Munich, Germany; MACN, Museo Argentino de Ciencias maxillary
Natu- tooth crowns are longer apicobasally than the

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896 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 4, 2004

dorsoventral depth of the mandible. Differs from although parts of this are preserved on the left s
Ceratosaurus
in the presence of four, as opposed to three, premaxillary
supradentaries, teeth.
only short sections of the posterior p
served. The left splenial is represented only by sca
DESCRIPTION ments affixed to the inner side of the dentary by ma
Premaxillae-The premaxillae (Fig. 2) are massive
Preservation-Generally, the snout elementseach of Genyodectes
other along a symphysis in their anterior third t
of the snout that
are rather poorly preserved, although the semi-articulated stateis broadly U-shaped in ventral vie
in which the material was obviously found, and narial
the fact premaxillary
that most body is approximately as high as
mm)
of the teeth are still in place, indicate that this and to
is due bears
recentfour teeth (Fig. 2A, B, D). The late
erosion rather than to taphonomic processes. pierced by several large foramina above the alveolar
Both premaxillae
were preserved in articulation, but were notalong fusedthe in anterior
life, as margin (Fig. 2A, C, D). Dorsally
indicated by a slight anteroventral displacementside bends
of the medially
right pre- to form an anteroventral shelf
maxilla. Likewise, the maxillae were found in fossa
articulation
(Fig. 2A, with
C). The broken base of the nasal pr
teroposteriorly
the premaxilla, but were affixed to the latter only by matrix. In long but transversely narrow, with a
the lower jaw, the supradentaries are only veryterior
slightly edge and a posterior, plate-like portion. Th
displaced,
and, as far as can be made out, the fragments of process
the leftwassplenial
obviously rather small, but nothing can b
seem to be in their original position relative toitsthe
exact size orAll
dentary. shape because it is missing and the
the elements of the right side of the skull show connection
signs ofwith slightthe premaxillary body is damaged on
deformation, whereas the left side seems to be Medially,
undeformed. the interdental plates are fused without
The left premaxilla is almost complete, lackingsuture,
only forming
the nasala medial alveolar border that is on
lower than
process and the subnarial process. The right premaxilla the lateral border (Fig. 2B). The parade
is missing
delimiting
both processes and parts of its posterodorsal border. It isthe interdental plates from the premaxil
fur-
thermore slightly compressed, making the inturn developed
along the only as a faint step that curves down abr
narial
fossa less marked than on the left side. Both riorly
maxillae behind
are onlythe premaxillary symphysis (Fig. 2B
represented by their anterior alveolar borders, striations
and neither on the theinterdental plates, as are found in
ascending process nor the rim of the antorbital(Sampson
fenestra are et al.,
pre- 1996), are not present. Dorsally, di
this paradental
served. Both dentaries lack only their thin posteriormost portion,shelf, one small, round foramen is p

FIGURE 2. Genyodectes serus, holotype, MLP 26-39. Articulated premaxillae in A, left lateral view (stereop
(stereopair), C, anterior view, and D, right lateral view. Abbreviations: g, groove; idp, interdental plates; m, cont
Scale bars equal 5 cm.

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 RAUHUT-PATAGONIAN CERATOSAUR 897

each tooth. In the posterodorsal

than in Carnotaurus part(MACN CH 894). of The anterior
theendmedial of the si
below the narial shelf, a short,
dentary is slightlybroad,
expanded dorsally, anteroventrally
so that the tooth row is
groove seems to be present, notably concave
althoughbehind the third dentary
it mighttooth, whereas themerel
artifact of preservation (Fig. 2B).
portion containing the anteriormost three teeth dips very slightly
The suture with the maxilla is4A,developed
anteriorly (Fig. C, D). The ventral border isas a over
straight broad,
slightly rugose surface thatmost of itsfaces posterolaterally
length and gradually curves dorsally anteriorly to (Fi
Whereas this surface blends meet theinto
dorsal borderthe
at nearly alateral
right angle. In the side
left dentary,along
curve dorsally, it is set off from
the ventral margin flexes theventrallylatter ventrally
towards the posterior end of b
nounced rounded step. the tooth row, and thus the dentary expands posteriorly (Fig. 4A,
Maxillae-Not much can be said
B). Posteriorly, bothabout
dentaries are toothe
damaged to maxillae,
determine the ow
nature of the mandibular
their fragmentary preservation. Of fenestra.
the left maxilla, 19
the alveolar border, containingThe lateral 5 side1/2 alveoli
of the dentary is very and 225 dorso-
slightly convex m
right maxilla, containing 6 1/2with
ventrally, alveoli,
the exception of are preserved.
the posteriormost expanded part,
which is planar.
The lateral side of the maxflla seemsAnteriorly, toseveral
belarge foramina are found
smooth, wi
few small foramina above (Fig.the
4A, C). alveolar
Beginning at the 5th border (Fig.
alveolus, a notable 3A
longitudi-
sign of the border of the nalantorbital
groove runs over thefossa is present
bone posteriorly, at approximately onone-
served parts, indicating that
third ofthis the height border
of the bone from was the placed
alveolar border rat
(Fig
above the alveolar border. 4A).Medially,
This groove is deeper the and moreinterdental
sharply bordered ventrally p
fused (Fig. 3B, D), as in the premaxillae.
but gradually shallows dorsally. Several The large,paradent
slit-like foramin
(Madsen, 1976), which is only
seem to bepreserved
placed along its ventral on a slightly
border, very moresma
widely
the anterior end of the leftspaced than maxilla
the teeth. (Fig. 3D), is some
above the medial alveolar border.
Medially, a shallow The contact
and very with widening
gradually posteriorly the
illa consists of a broad medial surface,
Meckelian groove which
is present, placed just below isthe slightl
mid-height o
anteriorly and very slightlythe bone medially
(Fig. 4B, D). This groovedirected,narrows and becomesand slightly
a r
teriorly directed lateraldeeper
lip (Fig.
in its 3D).
anteriormost The
part, and maxillae
its tip bends sharply ventrally
slightly from their (Fig. 4B). Although
articulation with thisthe
area is premaxillae,
not well preserved in either
an
parallel, as is the case in some element, it theropods (e.g.,
seems that the groove widens Allosaur
considerably dorsoven-
sen, 1976). trally towards the posterior end of the tooth row and here thu
Dentary-As is the case with the bones of the skull, the den- leaves only a thin lateral wall of the bone below the dorsal al-
taries are rather massive (Fig. 4). In dorsal view, the better- veolar part. As in the upper jaw, the interdental plates are fuse
preserved left dentary is slightly flexed medially, although less so without any visible suture and only set off from the main body b

FIGURE 3. Genyodectes serus, holotype, MLP 26-39. Right maxilla in A, lateral and B, medial view. Left maxilla in C, lateral and D,
(stereopair). Abbreviations: idp, interdental plates; pds, paradental shelf; pm, contact with the premaxilla. Scale bars equal 5 cm.

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898 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 4, 2004

FIGURE 4. Genyodectes serus, holotype, MLP 26-39. Left dentary in A, lateral (stereopair) and B, medial v
lateral and D, medial view. Abbreviations: g, groove; idp, interdental plates; mg, Meckelian groove; sd, supr
5 cm.

a low paradental shelf (Fig. 4B, D). Anteriorly,ally. Its anterior

this shelfextent
risescannot
in be ascertained because only small
a smooth curve to meet the alveolar border just partsatare the
preserved on both sides.
posterior
end of the first alveolus. No foramina are visible at the base of Splenial-Not much can be said about this bone. It was ap-
this shelf below the alveoli. With a maximum height of 22 parently
mm in a thin plate of bone that ended anterodorsally in a sharp
the anterior mid-part of the bone, the dentary interdentaltip
plates
just below the supradentary behind the seventh tooth position
are considerably lower than those in the maxilla. As noted by From this tip it seems to have expanded rapidly pos-
(Fig. 4B).
Woodward (1901), no clearly defined symphyseal facet is teriorly presentand probably covered most of the large posterior part of
on the anterior part of the medial side of the dentary,the but it
Meckelian groove medially.
seems most probable that the symphysis was restricted to aDentition-Although
nar- the exact number of teeth can only be
row vertical zone at the slightly oblique anteriormost margin ascertained
of for the premaxillae (4), in comparison with other
the dentary. theropods and based on the estimation of the number of teeth in
The preserved length of the more complete left dentary is ca. the dentary, it seems likely that the maxillary tooth count did not
335 mm, its maximum anterior height is ca. 76 mm and its mini- exceed 15. As noted above, there were probably no more than 14
mal height ca. 67 mm. The left dentary preserves 10 alveoli over teeth in the dentary. The teeth do not show the alternating pat-
a preserved alveolar border of 230 mm, whereas the right den- tern of fully and partially erupted teeth seen in other theropods
tary exhibits 11 tooth position over a length of 260 mm. Given (e.g. Tyrannosaurus; Molnar, 1991), but largely seem to represent
the morphology towards the posterior break of the dentary, it is the same tooth generation (Figs. 2-4). Clearly erupting teeth
very likely that the total number of teeth did not exceed 14. without a larger functional tooth laterally are only found in the
Supradentary-The supradentary is a long, slender rod of second alveolus of the right maxilla, the third alveolus of the left,
bone, about half the height of the dentary interdental plates (Fig. and possibly the fourth alveolus of the right dentary (although in
4B, D). It covers the upper half of the interdental plates medi- the latter, the larger tooth might simply be missing). In addition,

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 RAUHUT-PATAGONIAN CERATOSAUR 899

erupting teeth with the functional tooth

teeth have at least not experiencedlateral to them
any major displacement is the
fact that
ent in the third alveolus of the their roots fit
left their respective alveoli
premaxilla at the eroded
(Fig. 2B
third alveolus in the left maxilla
dorsal surface of (although
the maxillary fragments. here the lar
The tooth crowns seem toby
is missing, its presence is indicated increasea
in size from the first
large to the
alveolus
the erupting tooth). third maxillary tooth and then remain subequal in size to at least
The premaxillary teeth are very
the fifth or sixth closely spaced
maxillary tooth (Fig. 3A, C). Theand eve
first crown of
lap each other considerably in
the left labial
maxilla view70-75
is approximately (Fig.
mm long, 2A, D).
whereas the
teeth on either side seem to longest
be preserved
of subequal
crown, the fifth oflength,
the right maxilla,
althou
is more
of the tip are missing in than all80but mm long;one (in which
as reconstructed, this crown theis 95 mmtiplong,
glued on the wrong way round). The premaxillary
which seems a reasonable tooth
estimate for its total length. Thus, the
are considerably shorter (ca. 65-75
longest maxillary toothmm)
crowns areand stouter
longer than the height of th the
of the maxillary teeth. They corresponding
are slightlypart of the dentary. The maxillary crowns are
asymmetrical, w
distal carina being displaced symmetrical and very strongly
labially, compressed labiolingually
especially in the (Fig. a
most two teeth. 5A), more so than the premaxillary teeth or the maxillary teeth
The maxillary crowns are considerably larger than the premax- of most theropods. Unfortunately, the fact that the bases of all
illary crowns, although their exact size is hard to ascertainteethsince are damaged, probably by expansion of mineral infillings of
many teeth are missing the tip or are reconstructed in somethe part.
pulpa cavity, makes a quantification of this labio-lingual flat-
However, the size of the tooth crowns seems to be real, and not and a comparison with published measurements (Farlow
tening
an artifact of loosening and displacement of the teeth within et al., 1991) impossible. In most crowns, an unusual flat area is
their alveoli. Although the crowns are badly fractured, making present adjacent to the mesial and distal carinae (Fig. 5A), an
interpretations difficult, serrations on the distal carina area reachthat is usually convex in most theropods. The maxillary
down to almost the alveolar border in the third and fourth tooth teeth are also rather tightly spaced, with less than half the me-
of the right maxilla and the crown-root boundary is not visible siodistal
in length of a tooth separating two subsequent teeth.
any of the preserved crowns, indicating that it was placed at, In all
or crowns of the upper jaw, both the apical half of the
directly below the alveolar border. Another indication that theand all of the distal carinae are serrated. There are ap-
mesial

FIGURE 5. Genyodectes serus, holotype, MLP 26-39. Dentition. A, medial view of the 5th right maxillary tooth (stereopair). B, C, ant
three teeth of the right dentary in B, lateral and C, medial view (stereopairs). D, E, sixth and seventh right dentary teeth in D, lateral and
view (stereopairs). Scale bars equal 1 cm.

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900 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 4, 2004

proximately 12 denticles per 5 mm mesially and distally. high, it isThe

almost as long as high and thus differs from the pre-
denticles are chisel-shaped, perpendicular to the long maxillae
axis of in the
abelisaurids, which are higher than long (Bonaparte
carina and do not show any grooves extending fromand Novas,
their 1985; Bonaparte et al., 1990; Sampson et al., 1998).
bases
onto the crown. Furthermore, Genyodectes lacks several abelisaurid synapomor-
The dentary tooth crowns are considerably shorter than those
phies, such as the strong external sculpturing of the external skull
of the maxillary teeth. They rapidly increase in size from the
bones (Sampson et al., 1998) and the presence of longitudinal
striations on the interdental plates (Sampson et al., 1996; Car-
small first (ca. 40 mm in the right dentary) to the third crown
rano et al., 2002). One derived character that Genyodectes shares
(Figs. 4, 5B, C) and then remain of subequal size (approximately
60 mm) up to at least the seventh tooth. Only the two anterior-
with abelisaurids is the presence of a longitudinal groove that is
most crowns are asymmetrical, similar to those in the premaxilla
deeper ventrally than dorsally on the dentary. However, the dis-
tribution of this character needs further elucidation before its
(Fig. 5B, C). The third crown seems to be transitional, and from
the fourth onwards, the teeth are more or less symmetrical. The
systematic value can be evaluated.
dentary crowns are less strongly compressed transversely than Nevertheless, several characters indicate neoceratosaurian
the maxillary crowns, but show the same flat areas adjacentand,
to more precisely, ceratosaurid relationships. First, the pres-
ence
the carinae (Fig. 5D, E). Denticle density and morphology are as of a flat or even slightly concave area adjacent to the mar-
in the upper teeth. ginal carinae in the lateral teeth is a character shared with both
Ceratosaurus (USNM 4735, MWC 1, UMNH V 5278) and at
DISCUSSION least some abelisaurids (Majungatholus: FMNH PR 2100). In
other theropods, this area is usually slightly to strongly mesio-
On the basis of the above description, it is clear thatconvex,
distally Genyo- especially at the anterior carina, and thus this
dectes differs from all other theropod dinosaurs fromseems
character South to represent a neoceratosaurian synapomorphy.
America for which cranial material is known. Furthermore, Completely fused interdental plates are found in Ceratosaurus
based on the characters given in the diagnosis, it can (Gilmore,
currently1920; beMadsen and Welles, 2000) and abelisauroids
distinguished from all other theropods and thus (Bonaparte, should be1991; con-Sampson et al., 1998; Carrano et al., 2002),
sidered a valid taxon, despite the poor preservation of the
whereas theyholo-
are separate in basal sauropodomorphs (Plateosau-
type. However, determining its systematic position rus:
is MB
muchR. 1937),
more basal theropods (e.g. Syntarsus: QG 193; Dilo-
problematic. Unfortunately, the extremely fragmentary phosaurus: Welles,
nature1984), basal tetanurans (e.g. Buckland, 1824;
of the type of Genyodectes prohibits a formal phylogenetic Currie and Zhao,
analy- 1993; Zhao and Currie, 1993; Allain, 2002) and
sis, and so this discussion will focus on an evaluation basal coelurosaurs
of previ- (Compsognathus: BSP AS.I. 563; Ostrom,
ously proposed affinities and the distribution of important 1978). Althoughchar- fused interdental plates are not uncommon in
acters seen in Genyodectes within theropods. theropods, being also present in Torvosaurus (Britt, 1991), ad-
Huene (1932:243, translated by OR) referred Genyodectes vanced allosauroids to (Stromer, 1931; Madsen, 1976), and some
the Dinodontidae (= Tyrannosauridae) simply oncoelurosaurs the basis(Currie,
that 1995), the distribution of unfused interden-
"according to the teeth and size, it fits with thetaldinodontids".plates indicates that this is the plesiomorphic character state.
This assignment was accepted by several other Thus, authors in the(e.g.,
light of all available evidence, the presence of fused
Maleev, 1974), although no detailed justificationinterdental has everplates beenin Genyodectes is most parsimoniously ex-
published. Genyodectes shows premaxillary tooth crowns
plained that
as a synapomorphy shared with neoceratosaurs.
are considerably smaller than the maxillary crowns, Another
a tyranno-
noteworthy character in the teeth of Genyodectes is
saurid synapomorphy (Holtz, 2001). However, as the pointed
extremeout by
transverse flattening of the lateral maxillary crowns.
Molnar (1990), the premaxillary crowns are notSimilarly D-shaped in teeth are only found in Ceratosaurus (USNM
flattened
cross-section, which is another tyrannosaurid synapomorphy 4735, MWC 1, UMNH V 5278) and advanced carcharodontosau-
(Holtz, 2001). More importantly, a considerable size rids difference
(Stromer, 1931; Sereno et al., 1996). However, the teeth of
between the premaxillary and maxillary crowns is carcharodontosaurids
also found in differ from those of Genyodectes in the
Ceratosaurus. In the type of Ceratosaurus dentisulcatus, presence of downpointing
the long- grooves at the bases of the marginal
est premaxillary crown is an estimated 63 mm denticles in length (Stromer,
(the 1931) and the presence of pronounced
longest completely preserved crown only 49 mm), whereas
enamel wrinkles theon the crown (Sereno et al., 1996).
longest preserved maxillary crown is 93 mm long Another (Madsen character
and shared with Ceratosaurus is the extreme
Welles, 2000). Likewise, an isolated premaxillarylength tooth of of
thethemaxillary tooth crowns. In Ceratosaurus dentisul-
type of Ceratosaurus magnicornis (MWC 1) has catus, an estimated
the longest maxillary crown is 93 mm long, which corre-
crown length of ca. 50 mm, while the maxillary crowns sponds to measure
the minimal height of the dentary (Madsen and Welles,
up to 80 mm. Furthermore, the strongly transversely 2000).compressed
Likewise, in the type of Ceratosaurus nasicornis (USNM
maxillary crowns of Genyodectes are very unlike the 4735;rather
Gilmore, stout
1920), with a length of approximately 70 mm, the
crowns of tyrannosaurids (Currie et al., 1990). Thus, longestthere is no crown in the maxilla exceeds the minimal
preserved
convincing evidence for referring Genyodectes to the of
height Tyranno-
the mandible, given as 63 mm at the fifth dentary tooth
sauridae. by Gilmore (1920). Thus, only in Genyodectes and Ceratosaurus,
Little evidence has been brought forward for the proposed does the length of the longest maxillary crowns exceed the mini-
abelisaurid relationships of Genyodectes as well. Paul (1988:283)
mal height of the dentary, and this character might represent a
noted that "the teeth have the long length and slender build synapomorphy of these two taxa.
characteristic of abelisaurs" and Bonaparte (1996:93) stated thatThus, although the information is limited, and most possible
"the distance between the alveolar border and the lower rimsynapomorphies
of are ambiguous, the character combination ex-
the narial opening is rather large and resembles the abelisaurid
hibited by the jaws of Genyodectes indicates ceratosaurid rela-
snout condition". However, the teeth in Carnotaurus (MACN tionships for this taxon. Possible ceratosaurid synapomorphies
Ch 894; Bonaparte et al., 1990), Majungatholus (FMNH include
PR strongly labiolingually compressed maxillary tooth
2100; Sampson et al., 1998), and at least some other abelisaurids
crowns, maxillary crowns that exceed the minimal height of the
(Lamanna et al., 2002) are rather short and not as flattened dentary in length, and a significant size difference between the
transversely as is the case in Genyodectes; the teeth of Abelisau-
premaxillary and maxillary crowns (with the possible exception
rus are unknown (Bonaparte and Novas, 1985). Likewise, of al-the anteriormost maxillary teeth).
though the premaxillary body below the nares in Genyodectes is Thus, Genyodectes adds a further lineage of neoceratosaurs to

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 RAUHUT-PATAGONIAN CERATOSAUR 901

(Theropoda-Ceratosauria)
the already diverse Cretaceous record of thisfrom groupthe Cretaceous of Patagonia, Ar-
in South
America. Our knowledge of Early gentina. Gaia 15:89-102.
Cretaceous theropod faunas
of South America is still poor, Currie,
and P. J. 1995. Newthis
thus information on the anatomy
record ofand a relationships
basal of
Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal of
neoceratosaur from most probably Lower Cretaceous sediments
Vertebrate Paleontology 15:576-591.
is of significance. Together with the possible abelisaur Liga-
Currie, P. J., J. K. Rigby, and R. E. Sloan. 1990. Theropod teeth from the
bueno from the Hauterivian-Barremian La Amarga
Judith River Formation Formation
of southern Alberta, Canada; pp. 107-125 in
of Neuqudn (Bonaparte, 1996) andK.fragmentary abelisaurid re- Ap-
Carpenter and P. J. Currie (eds.), Dinosaur systematics.
mains from the Barremian La Paloma member of the Cerro
proaches and perspectives. Cambridge University Press, Cambridge.
Barcino Formation (Rauhut et al., 2003), this record hints at P.
Currie, anJ., and X.-J. Zhao. 1993. A new carnosaur (Dinosauria,
early diversification of neoceratosaurs in South America, well
Theropoda) from the Jurassic of Xinjiang, People's Republic of
China. Canadian Journal of Earth Sciences 30:2037-2081.
before the Late Cretaceous (see also Lamanna et al., 2002).
Gilmore, C. W. 1920. Osteology of the carnivorous Dinosauria in the
ACKNOWLEDGMENTS United States National Museum, with special reference to the gen-
era Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the
United
Special thanks are due to Zulma Gasparini and States National
Marcelo Museum 110:1-154.
Holtz,
Reguero for loan of the type of Genyodectes and theT. R. Jr. 2001. The phylogeny and taxonomy of the Tyrannosau-
permission
to reprepare the material. Marcelo Reguero is ridae; pp. 64-83 in D. H. Tanke and K. Carpenter (eds.), Mesozoic
furthermore
thanked for his invaluable information on the activities of S. vertebrate life. Indiana University Press, Bloomington and India-
napolis.
Roth between 1896 and 1898 and the probable provenance of the
Huene, F. von 1929. Los Saurisquios y Ornitisquios del Cretaiceo Argen-
material. Matthew Lamanna provided valuable additional infor- tino. Anales del Museo de La Plata (serie 2) 3:1-196.
mation regarding this point. Pablo Puerta's working experience Huene, F. von. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Ent-
in Chubut Province also proved to be extremely helpful in track- wicklung und Geschichte. Monographien zur Geologie und Palae-
ing down the original locality. Laura Reiner skillfully carriedontologieout (Serie 1) 4:1-361.
the extraction of the material from the artificial matrix and its Lamanna, M. C., R. D. Martinez and J. B. Smith. 2002. A definitive
preparation. This work benefited from discussions with Matthew abelisaurid theropod dinosaur from the early Late Cretaceous of
Lamanna, Matthew Carrano and Adriana L6pez-Arbarello. Patagonia. Journal of Vertebrate Paleontology 22:58-69.
Lizuain, A., D. Ragona and A. Folguera. 1995. Mapa Geol6gico de la
Adriana is furthermore thanked for critical comments on an ear-
lier version of the manuscript, and the paper greatly benefited Provincia del Chubut, Reptiblica Argentina, 1:750.000. Secretarfa de
from critical reviews by Matthew Lamanna, Matthew Carrano, Mineria, Direcci6n Nacional del Servicio Geol6gico, Buenos Aires.
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