ArticlePDF Available

Abstract and Figures

Heterodontosauridae is a morphologically divergent group of dinosaurs that has recently been interpreted as one of the most basal clades of Ornithischia. Heterodontosaurid remains were previously known from the Early Jurassic of southern Africa, but recent discoveries and studies have significantly increased the geographical and temporal range for this clade. Here, we report a new ornithischian dinosaur from the Middle Jurassic Cañadón Asfalto Formation in central Patagonia, Argentina. This new taxon, Manidens condorensis gen. et sp. nov., includes well-preserved craniomandibular and postcranial remains and represents the only diagnostic ornithischian specimen yet discovered in the Jurassic of South America so far. Derived features of its anatomy indicate that Manidens belongs to Heterodontosauridae, as the sister taxon of Heterodontosaurus and other South African heterodontosaurids. The presence of posterior dentary teeth with high crowns but lacking extensive wear facets in Manidens suggests that this form represents an intermediate stage in the development of the remarkable adaptations to herbivory described for Heterodontosaurus. The dentition of Manidens condorensis also has autapomorphies, such as asymmetrically arranged denticles in posterior teeth and a mesially projected denticle in the posteriormost teeth. At an estimated total length of 60-75 cm, Manidens furthermore confirms the small size of basal heterodontosaurids.
Content may be subject to copyright.
A Middle Jurassic heterodontosaurid dinosaur
from Patagonia and the evolution of heterodontosaurids
Diego Pol &Oliver W. M. Rauhut &Marcos Becerra
Received: 9 October 2010 / Revised: 28 February 2011 / Accepted: 3 March 2011
#Springer-Verlag 2011
Abstract Heterodontosauridae is a morphologically diver-
gent group of dinosaurs that has recently been interpreted as
one of the most basal clades of Ornithischia. Heterodonto-
saurid remains were previously known from the Early Jurassic
of southern Africa, but recent discoveries and studies have
significantly increased the geographical and temporal range for
this clade. Here, we report a new ornithischian dinosaur from
the Middle Jurassic Cañadón Asfalto Formation in central
Patagonia, Argentina. This new taxon, Manidens condorensis
gen. et sp. nov., includes well-preserved craniomandibular
and postcranial remains and represents the only diagnostic
ornithischian specimen yet discovered in the Jurassic of
South America so far. Derived features of its anatomy
indicate that Manidens belongs to Heterodontosauridae, as
the sister taxon of Heterodontosaurus and other South
African heterodontosaurids. The presence of posterior dentary
teeth with high crowns but lacking extensive wear facets in
Manidens suggests that this form represents an intermediate
stage in the development of the remarkable adaptations to
herbivory described for Heterodontosaurus. The dentition of
Manidens condorensis also has autapomorphies, such as
asymmetrically arranged denticles in posterior teeth and a
mesially projected denticle in the posteriormost teeth. At an
estimated total length of 6075 cm, Manidens furthermore
confirms the small size of basal heterodontosaurids.
Keywords Ornithschia .Gondwana .Jurassic .Cañadón
Asfalto Formation .Heterodontosauridae
The fossil record of ornithischian dinosaurs starts in the
Late Triassic (Casamiquela 1967) and extends up to the end
of the Cretaceous. However, the first 70 million years of
ornithischian evolution are still poorly known (Butler et al.
2006,2008a; Irmis et al. 2007), and our knowledge of early
ornithschians is so far based almost entirely on fossils from
a small number of geological units, such as the Elliot
Formation of southern Africa (Knoll 2005; Butler et al.
2007; Irmis and Knoll 2008; Rauhut and Lopez-Arbarello
2008). One of the most conspicuous groups in Early
Jurassic ornithischian assemblages is the Heterodontosauridae.
Whilst it was long thought to represent an early and highly
specialized lineage of derived clades of ornithischian
dinosaurs, such as ornithopods (e.g. Sereno 1986,1999;
Weishampel and Witmer 1990;Normanetal.2004a)or
marginocephalians (Xu et al. 2006), recent research has
reinterpreted this group as one of the most basal and
Communicated by Robert Reisz
Electronic supplementary material The online version of this article
(doi:10.1007/s00114-011-0780-5) contains supplementary material,
which is available to authorized users.
D. Pol (*)
CONICET, Museo Paleontológico Egidio Feruglio,
Fontana 140,
9100 Trelew, Argentina
O. W. M. Rauhut
Bayerische Staatssammlung für Paläontologie und
Geologie and Department of Earth and Environmental Sciences,
LMU München, Richard-Wagner-Str. 10,
80333 Munich, Germany
M. Becerra
Departamento de Ciencias Geológicas,
Universidad de Buenos Aires,
Ciudad Universitaria Pab. II,
Ciudad Autónoma de Buenos Aires C1428EHA, Argentina
DOI 10.1007/s00114-011-0780-5
successful radiation of ornithischians (Butler et al. 2007,
2008a). Furthermore, recent studies have demonstrated that
this group was more widely distributed both geographically
and stratigraphically than previously thought (Norman and
Barrett 2002, Zheng et al. 2009, Butler et al. 2010). These
studies have suddenly placed heterodontosaurids in a key
position for understanding the origin and early evolution of
ornithischian dinosaurs.
The Jurassic record of ornithischian dinosaurs from
Gondwana is of special interest for our understanding of the
early evolution of the group because basal members of the
major lineages are found in the Late TriassicEarly Jurassic of
southern Gondwana, indicating that the group as a whole
might have originated here (Rauhut and Lopez-Arbarello
2008). However, the Jurassic ornithischian fossil record from
Gondwana is currently restricted to the Early Jurassic of the
Upper Elliot Formation of southern Africa (Knoll 2005)and
the Late Jurassic Tendaguru Formation of Tanzania (Aberhan
et al. 2002;Maier2003; Rauhut and Lopez-Arbarello 2008).
Apart from these units, Gondwanan ornithischians are only
known from isolated remains (Barrett et al. 2008; Rauhut
and Lopez-Arbarello 2008) and footprints (e.g. Moreno et al.
2004) that do not provide information for our understanding
of the evolution of the group during the Jurassic.
The Cañadón Asfalto Formation of Chubut Province,
Argentina, has yielded the most diverse and important
Middle Jurassic terrestrial biota of Gondwana (Escapa et al.
2008). Vertebrate groups reported so far include basal
members of every major lineage of terrestrial vertebrates to
be expected in the Jurassic (Escapa et al. 2008), including a
wealth of dinosaur remains (Bonaparte 1979,1986; Rauhut
2003a,2005; Escapa et al. 2008), pterosaurs (Rauhut et al.
2001; Cordoniú et al. 2010), turtles (Sterli 2008), mammals
(Martin and Rauhut, 2005; Rauhut et al. 2002; Rougier et
al. 2007a,b) and anurans (Báez and Nicoli 2008). Until
recently, the dinosaur fauna was exclusively composed of
sauropod and theropod saurischians, with only a single
reported non-diagnostic specimen of an ornithischian
(Rauhut and Lopez-Arbarello 2008). Here, we describe
diagnostic ornithischian remains from a partially articulated
skeleton found in this unit and evaluate its phylogenetic
relationships and its significance for understanding the
evolution of heterodontosaurid dinosaurs.
Systematic palaeontology
Dinosauria Owen, 1842
Ornithischia Seeley, 1887
Heterodontosauridae Kuhn, 1966
Manidens condorensis gen. et sp. nov.
Etymology The genus name Manidens, from manus (Latin,
hand) and dens (Latin, tooth), refers to the similarity of the
posteriormost tooth to the human hand. The specific epithet
condorensis refers to the nearby village of Cerro Cóndor,
Chubut Province, Argentina.
Holotype MPEF-PV 3211 (Museo Paleontológico Egidio
Feruglio, Trelew, Argentina), partial associated skeleton,
including most elements of the skull and lower jaws,
cervical, dorsal and sacral vertebrae, left scapula and
coracoids, and almost complete pelvic girdles.
Referred material MPEF-PV 1719, 1786, 1718, 3810, 3811
isolated posterior teeth, from the same locality and horizon
as the holotype.
Locality and horizon Queso Rallado locality within the
Cañadón Asfalto Formation, 2.3 km west of the village of
Cerro Cóndor, Chubut Province, Argentina. The bone-
bearing layer is a silicified mudstone within a series of
lacustrine mudstones and limestones (Rougier et al. 2007b).
Further locality information is given in the Electronic
supplementary material (ESM) and stratigraphic informa-
tion can be found in Rougier et al. (2007b). GPS
coordinates of this locality are deposited in the MPEF
collections and are available upon request. The age of the
Cañadón Asfalto Formation is usually given as Callovian
Oxfordian (e.g. Silva Nieto et al. 2002), but recent UPb
radioisotopic age determinations (Cabaleri et al. 2010) and
palynological research (Volkheimer et al. 2008) indicates
that it is probably considerably older, with dates ranging
from 171 ± 5 to 167 ± 4 Ma (AalenianEarly Bathonian;
Salani 2007; Cabaleri et al. 2010).
Diagnosis Small heterodontosaurid (estimated body length
of approximately 5060 cm) with the following autapo-
morphies: jugal with strongly developed, dorsally placed
lateral boss; dorsal part of the postorbital process of the
jugal very slender and flexes abruptly posteriorly at the
beginning of the articular facet for the postorbital; forebrain
facet on the ventral surface of the frontal enlarged and
with significantly raised margins; posterior teeth with
asymmetric arrangement of denticles and with a mesial
concavity in which the distal margin of the preceding
tooth is lodged; posteriormost dentary tooth hand-
shaped, with only one or two mesial denticles, the most
anterior of which diverges mesially from the mesial
margin of the crown; presence of small crenulations
along the cutting margin of each denticle.
The holotype has preserved most elements of the skull and
lower jaws, most of the precaudal axial skeleton, including
cervical, dorsal and sacral vertebrae, the left scapula and
coracoid, and almost complete pelvic girdles (Fig. 1). Most
of the elements of the skull roof are preserved, with the
exception of the premaxillae, lacrimals, prefrontals and
parietals, which could not be identified with confidence.
Furthermore, the braincase is almost completely preserved,
some fragments of the palate are present, and the mandible
is only missing the predentary (cand din Fig. 2), making
the skull of Manidens one of the most complete hetero-
dontosaurid skulls known. Skull elements were found
mainly disarticulated, although some were found in
articulation (most notably the almost complete right lower
jaw and the left temporal region) or retained a close
association (Figs. 1and 2).
Despite the disarticulation of the skull, a few aspects of
general skull shape and morphology can be evaluated. The
length of the right mandible is 63 mm without the
predentary, which might account for another 510 mm
(based on Heterodontosaurus, in which the predentary
accounts for approx. 10% of the length of the mandible).
Because mandible length is similar to skull length in basal
ornithischians, the skull of Manidens was most probably no
more than 75 mm long and thus closely comparable in size
to that of Fruitadens, one of the smallest known ornithis-
chian dinosaurs, for which Butler et al. (2010: Fig. 3e)
reconstructed a skull length of approximately 70 mm. The
preserved jugal and postorbital demonstrate that the orbit
was round and very large (Fig. 2), as in most basal
ornithischians, and, together with the rather small maxilla,
that the preorbital region of the skull was probably rather
short. The lower temporal fenestra was much narrower than
the orbit ventrally, but rapidly increased in anteroposterior
length dorsally, as indicated by the very long posterior
process of the postorbital and anterior branch of the
squamosal (Fig. 2).
The maxilla has a posterodorsally sloping anterior
margin, without a large anterior embayment for the
reception of the enlarged dentary tooth, as it is present in
all other known heterodontosaurids for which this element
is known (Tianyulong: Zheng et al. 2009;Fruitadens:
Butler et al. 2010;Abrictosaurus: Thulborn 1974;Lyco-
2004a), although the preservation of this area does not rule
out the possibility of a considerably smaller embayment.
The presence of such an embayment in Echinodon is
uncertain (Norman and Barrett 2002). A well-developed
buccal emargination is present and is separated from the
large antorbital fossa by a horizontal ridge, which becomes
more conspicuous posteriorly. This emargination seems to
be more strongly developed than in Echinodon (Norman
and Barrett 2002), Tianyulong (Zheng et al. 2009) and
Fig. 1 Preserved elements of M. condorensis gen. et sp. nov. Outline
reconstruction of the skeleton, indicating preserved elements, with
photographs of selected skeletal elements of the type specimen (MPEF
PV 3211). aPelvic girdle, lateral. bSchematic drawing of pelvic
girdle. cDorsal vertebrae, lateral. dCervical vertebrae, lateral. e
Quadrate, anterior. fTemporal (lateral) and occipital (posterior) skull
elements. fSchematic drawing of temporal and occipital region. il
illium, is ischia, jjugal, or occipital region of the braincase, pb pubis,
po postorbital, pod postorbital depression, pp preacetabular process,
sq lateral shelf of the squamosal. Dashed areas represent broken
surfaces and dotted areas represent sediment. Scale bars indicate
10 mm (a,b,f,g), 2 mm (c,d) and 1 mm (e)
Fruitadens (Butler et al. 2010), but similar to the condition
in Lycorhinus (Gow 1975)andHeterodontosaurus (SAM
K337). The antorbital fenestra was very small and placed in
the posterodorsal margin of the antorbial fossa of the
maxilla, as in Lesothosaurus (Sereno 1991), Heterodonto-
saurus (Norman et al. 2004a) and other basal ornithischians
(Norman et al. 2004a,b; Barrett et al. 2005). The anterior
ramus of the jugal is slender and formed most of the ventral
margin of the orbit (Fig. 2). At the junction with the
postorbital ramus, a pronounced lateral boss is present, as in
Heterodontosaurus (Norman et al. 2004a) and, probably,
Abrictosaurus (Thulborn 1974). However, in contrast to the
former taxon, in which the boss is ventrally placed, it is
found at the dorsal margin of the bone in Manidens (aand
bin Fig. 2). A jugal boss seems to be absent in Tianyulong,
although the posterior part of the jugal is missing in this
Fig. 2 Anatomical details of the craniomandibular and dental remains
of M. condorensis gen. et sp. nov. aPhotographs of preserved cranial
and mandibular elements of the holotype (MPEF-PV 3211) super-
imposed on a skull reconstruction in lateral view. bReconstruction of
the skull and mandible in lateral view. cPhotograph of right lower jaw
and associated elements of the holotype (MPEF-PV 3211). d
Interpretative drawing of right lower jaw in lateral view (right maxilla,
left lower jaw and other bones shaded in grey); dashed areas represent
broken surfaces and dotted areas represent sediment. ehSEM images
of posterior mandibular tooth in mesial (e) and bucal (fi) views
corresponding to MPEF-PV 3810 (e), MPEF-PV 3811 (f)and
holotype MPEF-PV 3211 (gi). ad anteriormost denticle mesially
offset, afo antorbital fossa, an angular, at anterior teeth of left dentary,
ca caniniform, cr crenulations, ddentary, dc denticles, dv dorsal
vertebra, ffrontal, gglenoid fossa, jb jugal boss, mmaxilla, mc mesial
cavity, nnasal, po postorbital qquadrate, qj quadratojugal, sq
squamosal, sa surangular, saf anterior surangular foramen. Scale bars
indicate 10 mm (ad), 1 mm (eg), 0.5 mm (h) and 0.1 mm (i)
taxon (Zheng et al. 2009). The postorbital process of the
jugal flexes abruptly posteriorly at the beginning of the
articular facet for the postorbital (Fig. 1). The posterior
process of the jugal is short, much higher than the anterior
process, and bifurcates posteriorly, forming a wide angle
between the two processes (aand bin Fig. 2), also
resembling the condition in Heterodontosaurus (Norman
et al. 2004a). Although a bifurcated posterior end of the
jugal is also present in other basal ornithischians (Barrett
and Han 2009) and saurischians (e.g. Sereno and Novas
1993), the two processes usually form a narrower angle and
both contact the quadratojugal, whereas only the dorsal
process contacts the quadratojugal in Heterodontosaurus
and Manidens. The postorbital is triradiate and has a very
long posterior and very short anterior process. A well-
developed lateral boss is present at the posterodorsal margin
of the orbit just below the junction between the anterior and
ventral rami of the postorbital, as in Lesothosaurus (Sereno
1991) and many saurischians (e.g. Sereno and Novas
1993). Posterior to this boss, the postorbital of Manidens
has a depression, resembling the condition of Heterodonto-
saurus tucki (SAM K337). The posterior end of a stout,
rod-like palpebral is preserved above the anterior process of
the left postorbital, indicating that this bone was very long
and probably transversed the whole length of the orbit, in
contrast to the situation in Heterodontosaurus, but as in
some other ornithischians, such as Agilisaurus (Peng 1992;
Barrett et al. 2005). The squamosal has a long, straight
lateral shelf dorsally above its ventral process, considerably
more developed than a similar structure in Heterodonto-
saurus (Norman et al. 2004a). Anterior to this shelf, the
long anterior process of the squamosal flexes notably
ventrally to meet the posterior process of the postorbital,
indicating that the main body of the squamosal was
considerably tilted, as in Heterodontosaurus (Norman et
al. 2004a), Lesothosaurus (Sereno 1991) and Hypsilopho-
don (Galton 1974). The left and right nasals and frontals are
fused at their midline sutures without any visible suture, but
apparently not with each other. The nasals are flat and
gradually widen posteriorly. Their lateral margins are
slightly thickened, as is the case in Heterodontosaurus
(Butler et al. 2008b). The frontal has a considerably
widened, strongly rimmed ventral facet for the forebrain.
The quadrate is slender and only slightly flexed posteriorly.
The quadrate foramen is developed as a large embayment in
the lateral flange of the bone, as in Hypsilophodon (Galton
1974) and iguanodontians. The lateral condyle for the
articulation with the lower jaw is much larger than the medial
condyle, as in other heterodontosaurids and ceratopsians
(Butler et al. 2010).
In the braincase, the foramen magnum has been
dorsoventrally flattened by deformation, but it was
originally larger than the stout, semicircular occipital
condyle (Fig. 1). The paroccipital processes are dorso-
ventrally high, relatively short and have rounded lateral
margins. The post-temporal fenestra is developed as a
large foramen within the paroccipital process, well
separated from the exoccipitalsquamosal suture, as in
Heterodontosaurus (Norman et al. 2004a)andGaspar-
inisaura (Coria and Salgado 1996). The basal tubera are
separated by a wide notch below the condyle. The
basisphenoid is wide and short, with a well-developed
ventral basisphenoid recess, resembling the condition in
some basal theropods (Raath 1985; Rauhut 2003b).
No external mandibular fenestra is present in the lower
jaw (Fig. 2), unlike the situation in Heterodontosaurus and
Tianyulong (Norman et al. 2004a; Zheng et al. 2009) and
most other basal ornithischians (e.g. Haubold 1990; Sereno
1991; Butler et al. 2007), but similar to Abrictosaurus
(Thulborn 1974), Scelidosaurus (Owen 1863) and more
derived cerapodans. The dentary is robust and dorsoven-
trally high, in contrast to the more slender dentaries in other
heterodontosaurids (Thulborn 1974; Norman and Barrett
2002; Norman et al. 2004a; Zheng et al. 2009; Butler et al.
2010). It has a strongly enlarged, caniniform first dentary
tooth typical of many heterodontosaurids (Norman et al.
2004a; Zheng et al. 2009; Butler et al. 2010). The dorsal
part of its posterior end extends posterodorsally to form the
anterior margin of the coronoid process, as in all ornithi-
schians. The latter is a well-developed, triangular eminence
that rises to about 160% of the height of the dentary at the
tooth row, which is less than in Tianyulong (Zheng et al.
2009) and Abrictosaurus (Thulborn 1974), although this is
mainly due to the unusual robustness of the dentary. The
surangular forms the entire posterior part of the process in
lateral view, and there is an enlarged anterior surangular
foramen near its dorsal margin, just posterior to the apex of
the coronoid process (Fig. 2). Posteriorly, the surangular
becomes rapidly lower towards the jaw articulation, which
is located considerably ventral to the level of the tooth row
as in Heterodontosaurus and derived ornithopods (Weish-
ampel 1984). The glenoid facet is developed as an elongate
concavity, which is considerably longer anteroposteriorly
than the distal quadrate head and is delimited anteriorly by
a well-developed, triangular dorsal projection of the
surangular. The retroarticular process is a stout, poster-
oventrally directed process with a median ridge along its
posterodorsal surface resembling the condition of some
ornithopods, such as Thescelosaurus (Galton 1997). As in
most ornithischians, this process is shorter than the
mandibular glenoid articulation.
The dentition is strongly heterodont. The exact tooth
count cannot be established due to overlap and incomplete-
ness of some of the elements. However, the lower dentition
is composed of at least 11 teeth, including the hypertro-
phied anterior caniniform of the dentary (cand din Fig. 2)
This number is slightly lower than in Heterodontosaurus
and Abrictosaurus, which have 13 dentary teeth (Norman et
al. 2004a), but higher than in Tianyulong (nine dentary
teeth; Zheng et al. 2009) and comparable to Fruitadens
(911 dentary teeth; Butler et al. 2010). The caniniform is a
stout, recurved pointed tooth that seems to lack marginal
denticles, as in Fruitadens (Butler et al. 2010), but in
contrast to the situation in Heterodontosaurus,Lycorhinus
and Abrictosaurus (Charig and Crompton 1974; Hopson
1975). The first three post-caniniform teeth are very small
and well spaced from each other (but poorly preserved in
MPEF-PV 3211; din Fig. 2). The subsequent dentary teeth
rapidly increase in size posteriorly and become mesiodis-
tally expanded, but the distal-most two teeth slightly
decrease in size so that the highest tooth crowns are
situated at the mid-length of the posterior region of the
tooth row (cand din Fig. 2), similar to the situation in
Fruitadens (Butler et al. 2010) and Abrictosaurus (Thul-
born 1974). In contrast, although there is also an increase in
tooth size from the first to the third post-canine tooth in
Tianyulong and Heterodontosaurus, the decrease in at least
the mesiodistal size of the posteriormost teeth in these taxa
is much less marked (Hopson 1980; Norman et al. 2004a;
Zheng et al. 2009). The crowns of posterior teeth are
asymmetrical, unlike the much more symmetrical dentary
teeth of other heterodontosaurids (Thulborn 1974; Charig
and Crompton 1974; Hopson 1975; Norman and Barrett
2002; Zheng et al. 2009; Butler et al. 2010). They are leaf-
shaped, lateromedially compressed and have a weakly
developed central ridge on the lingual and labial surfaces
(fand gin Fig. 2), more marked than in Fruitadens (Butler
et al. 2010), but apparently less conspicuous than in
Heterodontosaurus (Hopson 1980). Unlike the situation in
Echinodon (Norman and Barrett 2002), Tianyulong (Zheng
et al. 2009) and Fruitadens (Butler et al. 2010), the tooth
crowns are considerably higher than wide, comparable to
the situation in Lycorhinus (Hopson 1975) and Hetero-
dontosaurus (Hopson 1980; Norman et al. 2004a). The
margins of the crowns bear well-developed denticles,
usually one or two mesial to the apex and four or five
distal to the apex, creating the aforementioned asymmetry
in the tooth crown (fand gin Fig. 2). The margin of each
denticle bears small crenulations, which are likely formed
exclusively by ridges on the enamel (giin Fig. 2), and
have not been reported in any other heterodontosaurid so
far, although subdivided denticles are present in some other
ornithischians (Bakker et al. 1990; Rauhut 2002). All
crowns have a gentle distal curvature that is more
conspicuous in the apical region (fhin Fig. 2). Both the
number of denticles and the apical curvature of the crown
vary along the tooth row. The posteriormost dentary tooth
has a distinct hand-likeappearance, with the anteriormost
denticle being offset mesially from the mesial margin (fin
Fig. 2). The posteriormost six asymmetric teeth are higher
and tightly appressed against each other, unlike the more
widely spaced teeth in Tianyulong (Zheng et al. 2009) and
Fruitadens (Butler et al. 2010), but similar to the situation
in Lycorhinus (Hopson 1975)andHeterodontosaurus
(Hopson 1980; Norman et al. 2004a,b). Each crown bears
a mesial groove, delimited by two ridges (ein Fig. 2),
which houses the distal margin of the preceding tooth, as in
the closely packed dental batteries of more derived
The cervical vertebrae are shorter than the dorsal
vertebrae and have short and stout diapophyses and para-
pophyses. Strongly elongate hypertrophied epipophyses are
present in the preserved anterior cervicals, as in Hetero-
dontosaurus (Santa Luca 1980). Cervical and dorsal neural
spines are anteroposteriorly elongate and low. There are six
sacral vertebrae, the neural spines of which form a
continuous sheet of bone over the ilium. An anterior caudal
vertebra has a low elongate centrum with well-developed
chevron facets.
Only the left coracoid and proximal portion of the
scapula are preserved. The coracoid has a well-developed,
hook-like posteroventral process that is separated from the
glenoid cavity by a wide notch. The pelvic girdle is
complete, with the exception of the distal ends of the
pubes and ischia (Fig. 1). The ilium is low and elongate,
with a preacetabular process that accounts for approximate-
ly 50% of the total length of the bone. A longitudinal ridge
extends along the lateral surface of the preacetabular
process, but is less well-developed than in Heterodonto-
saurus (Santa Luca 1980). Unlike the latter taxon and other
basal ornithischians, in which the pubic peduncle is longer
than the ischial peduncle, the former is subequal in length
or even slightly shorter than the latter in Manidens.Asin
all ornithischians, the pubis is opisthopubic with a very
slender posteroventral shaft (Fig. 1). The prepubic process
is short, only little extending beyond the pubic peduncle of
the ilium anteriorly, and robust. A small obturator foramen
is present below the acetabulum. The ischium is more
robust than the pubis and has an extensive medial suture
along its shafts, which are rectangular in cross-section. Not
enough of the shaft is preserved to establish the presence or
absence of an obturator process.
To test the phylogenetic relationships of the new taxon, we
included it in a slightly modified version of the data matrix
of Butler et al. (2010), which focuses on the interrelation-
ships of basal ornithischian clades and includes the most
extensive taxon sampling of heterodontosaurids published
to date. The final data matrix included 51 taxa and 230
characters (see ESM) and was analysed using equally
weighted parsimony in TNT, version 1.1 (Goloboff et al.
2008a,b). We performed a traditional heuristic search with
1,000 replicates with random addition sequences followed
by tree bissectionreconnection (TBR) branch swapping,
followed by a second round of TBR.
The analysis resulted in 216 MPTs with a length of 551
steps, the strict consensus of which (Fig. 3) is well resolved
for basal ornithischians. In particular, the results show
phylogenetic relationships for heterodontosaurids that have
both evolutionary and biogeographic implications for the
group. M. condorensis was found to be a heterodontosaurid
more closely related to Early Jurassic southern African
forms than to the later northern representatives of the clade.
The position of Manidens within Heterodontosauridae is
supported by the presence of three of the six unambiguous
synapomorphies of this clade [lateral condyle of quadrate
larger than medial (character 63.2), coronoid process well-
developed (character 101.1), enlarged caniniform anterior
dentary tooth (character 124.1)]. The clade of Manidens
and the Early Jurassic taxa from South Africa clusters all
heterodontosaurids from Gondwana (node 2 in Fig. 3) and
is supported by two unambiguous synapomorphies [lack of
alveolar foramina (character 126.1) and apicobasally high
mid-dentary and maxillary tooth crowns (character 228.0)]
and one ambiguous synapomorphy [angular occupying
more than half the depth of the mandible at the level of
the coronoid process (character 230.1)]. However, Man-
idens is placed as the sister taxon of the South African clade
(node 1 in Fig. 3) since it lacks the unambiguous
synapomorphy of this group [systematic development of
wear facets along the entire tooth row (character 222.1)].
See ESM for a full list of synapomorphic characters of each
clade. The discovery of Manidens in the Middle Jurassic of
Patagonia and the phylogenetic hypothesis presented here
have important implications for understanding several
evolutionary aspects of heterodontosaurids, including the
pace and mode of their radiation and biogeographic history,
the evolution of body size and the evolution of their
adaptations to herbivory.
Radiation and distribution of Heterodontosauridae
Given the wide geographic range of other EarlyMiddle
Jurassic dinosaurs, such as basal theropods and sauropodo-
morphs (Weishampel et al. 2004; Smith et al. 2007), the
Pisanosaurus mertii
Echinodon becklessi
Tianyulong confuciusi
Fruitadens haagarorum
Manidens condoriensis
Abrictosaurus consors
Heterodontosaurus tucki
Lycorhinus angustidens
Eocursor parvus
Lesothosaurus diagnosticus
Stormbergia dangershoeki
Agilisaurus louderbacki
Hexinlusaurus multidens
Orodromeus makelai
Scutellosaurus lawleri
Emausaurus ernstii
Scelidosaurus harrisonii
Fig. 3 Results of the phylogenetic analysis showing the proposed
interrelationships of M. condorensis within ornithischians. The
phylogenetic tree is plotted against geological time to calibrate the
phylogeny and highlight the extensive ghost lineages in basal
heterodontosaurids (grey lines). Derived clades of Ornithischia have
been collapsed into single taxonomic units for clarity. For details of
phylogenetic analysis, see text and ESM
apparent restriction of derived heterodontosaurids to southern
Gondwana is somewhat surprising. Furthermore, the fact that
the two most basal heterodontosaurids, Fruitadens and
Tianyulong, are currently only known from the Northern
Hemisphere (though in much higher stratigraphic levels)
seems to contradict the hypothesis that the early ornithischi-
an radiation took place in southern Gondwana (Rauhut and
Lopez-Arbarello 2008). However, the phylogenetic uncer-
tainty on the position of some forms, such as Echinodon
from the Middle Purbeck Beds (Berriasian) of southern
England (see Sereno 1997; Norman and Barrett 2002),
fragmentary remains from the Late Triassic of southern
Patagonia (Báez and Marsicano 2001) and the undescribed
remains from the Kayenta Formation (Attridge et al. 1985;
Sues et al. 1994;Sereno1997), precludes the assessment of a
robust biogeographic scenario for heterodontosaurids. Fur-
thermore, the minute size of some heterodontosaurids (see
below) and the generally poor Early and Middle Jurassic
fossil record may explain their disparate distribution. Thus,
future finds may change our view of both heterodontosaurid
and basal ornithischian evolution and biogeography.
However, based on the currently available information, the
phylogenetic analysis indicates that there was an early
radiation of heterodontosaurids at least in the Early Jurassic
and probably in the Late Triassic (as suggested by the remains
from this time found in southern Patagonia; Báez and
Marsicano 2001). The phylogenetic position of Early
Jurassic forms indicates that several lineages must have been
generated in this initial radiation of Heterodontosauridae,
including the lineages leading towards Tianyulong and
Fruitadens and the derived and probably endemic clade
from southern Gondwana (node 2 in Fig. 3). The occurrence
of Manidens in the Middle Jurassic of central Patagonia
demonstrates that this clade still persisted at least into the
Middle Jurassic. The initial radiation of heterodontosaurids
(and the phylogenetic positions of Tianyulong and Fruita-
dens, and probably Echinodon) implies at least two other
long-lived lineages of heterodontosaurids (Fig. 3). These
mark a major mismatch between the phylogenetic topology
obtained for heterodontosaurids and the order of appearance
of taxa in the fossil record (see ESM), which further
underlines the extremely poor fossil record of this clade.
The undescribed form from the Kayenta Formation indicates
that the group might have achieved a Pangean distribution by
the Early Jurassic. Thus, it is expected that future discoveries
will show an even higher diversity and wider geographic
distribution of heterodontosaurids in the Early Jurassic (and
possibly also in the Late Triassic).
Ontogenetic stage and body size
One of the aspects of the evolution of Heterodontosauridae that
was recently emphasized is that post-Early Jurassic forms
represent some of the smallest ornithischian dinosaurs,
including the smallest known adult ornithischian to date (i.e.
Fruitadens;Butleretal.2010). This is confirmed by the find
of Manidens: Based on the closely comparable size of the
cranial remains, this taxon was probably in the same size
range as Fruitadens, for which Butler et al. (2010) estimated a
total body length of 6575 cm and a mass of <1 kg. One
important question, of course, is whether the type of
Manidens represents a juvenile or an adult or subadult
individual. Butler et al. (2008b) demonstrated that ontogenetic
changes in Heterodontosaurus included a relative lengthening
of the snout, an increase of the number of teeth and the fusion
of several sutures in the skull, such as the nasalnasal suture.
Although the relatively large orbits, short snout and low
number of teeth in Manidens (in comparison with adult
Heterodontosaurus) might thus be taken as indications that
the type specimen represents a juvenile, there are several
aspects that argue against this interpretation. First, the number
of teeth in the dentary of Manidens (11) is lower than that of
large individuals of Heterodontosaurus (13; Norman et al.
2004a), but it is comparable to or even higher than that in the
basal heterodontosaurids Tianyulong (9) and Fruitadens
(911), which are of comparable size (Zheng et al. 2009;
Butler et al. 2010). Second, the interfrontal and internasal
contacts in the type specimen of Manidens are fused without
any visible suture, which, according to Butler et al. (2008b),
would indicate that it is not a juvenile. Finally, the neural
arches of the presacral vertebrae in the type specimen are also
fused to their respective centra without any visible suture.
Butler (2010: 676) discussed the timing of neurocentral fusion
in ornithischians and came to the conclusion that neuro-
central fusion may only have occurred in the very oldest
individuals of basal ornithischian species.Thus, the type
specimen might not only represent a sexually mature, but
even an old individual (see also Brochu 1996; Irmis 2007).
Given that other basal ornithischians, such as Pisanosaurus
(Bonaparte 1976), Eocursor (Butler 2010), Lesothosaurus
(Sereno 1991;Knoll2002)andScutellosaurus (Colbert
1981) are slightly larger animals, there seems to have been
a tendency towards miniaturization in basal heterodontosaur-
ids. The juvenilecharacters of small heterodontosaurids,
such as the low number of teeth and the large orbit and short
snout, might thus be explained as a result of heterochrony,
which seems to have played a role in miniaturization in other
reptiles as well, such as lepidosaurs (Rieppel 1984). The
same process might have played a role in the evolution of
maniraptoran theropods, as well, in which small forms also
display large orbits (e.g. Turner et al. 2007).
Evolution of herbivory in Heterodontosauridae
The discovery of Manidens and the phylogenetic hypothesis
presented here indicate a trend towards greater sophistication
in the adaptations to herbivory within the phylogeny of
Heterodontosauridae. As Butler et al. (2010)noted,three
adaptations to herbivory are present in Heterodontosaurus,
including closely packed teeth, high tooth crowns, and
extensive wear facets on the maxillary and dentary teeth.
Basal heterodontosaurids, such as Tianyulong and Fruita-
dens, lack these adaptations and bear lower crowns that are
more widely spaced and lack extensive wear facets. The new
taxon fills the gap between the basal forms and the derived
South African clade of Heterodontosaurus in having high
and closely appressed crowns but lacking extensive wear
facets. Thus, the pattern of character acquisition in hetero-
dontosaurids indicates that an increase in tooth crown height
preceded the development of extensive wear facets in this
clade (Fig. 3). This is in marked contrast to the evolutionary
pattern observed in other groups of ornithischian dinosaurs in
which the evolution of sophisticated chewing mechanisms
(involving intensive wear on the teeth) predated the increase
in relative crown height and the appearance of high tooth
batteries in iguanodontians (Weishampel 1984) and ceratop-
sians (You and Dodson 2004;Xuetal.2006). The evolution
of herbivory in these other groups of dinosaurs resembles the
pattern of character acquisition present in other groups of
vertebrates (e.g. Cenozoic herbivorous mammals; Pascual
1996), placing the evolution of herbivory in heterodonto-
saurids as a distinct case among amniotes. It is noteworthy
that this increased sophistication of the dietary adaptations in
the southern African heterodontosaurids, which might
account for their relative diversity in the Elliot Formation,
does not contradict the idea that the more generalized
dentition of basal heterodontosaurids favoured their longev-
ity as evolutionary lineages (Butler et al. 2010).
The discovery of a heterodontosaurid in the Middle
Jurassic of Patagonia underlines the recently recognized
diversity of the clade, increases the recently extended
geographical and temporal range of this clade, and shows
that heterodontosaurids remained a component of herbivo-
rous dinosaurian faunas of Gondwana at least until the
Middle Jurassic. Given the general rarity of small terrestrial
vertebrates in many Jurassic localities, the absence or rarity
of heterodontosaurids might represent an artefact of the
fossil record. The relative diversity and abundance of these
animals in comparison to that of large-bodied dinosaurs
was probably higher than previously suspected and will
likely be further appreciated in light of future discoveries.
Acknowledgements We thank Guillermo Rougier for collecting the
specimen described here. Fieldwork was only possible with the
friendly support of the Farias family, the Subsecretaría de Cultura of
the Chubut province and the School number 31 at Cerro Cóndor.
Leandro Canessa carried out the very delicate preparation of the type
specimen and Pablo Puerta and Leandro Canessa prepared the isolated
teeth. Fieldwork was supported by the project Paleontological
Exploration of Patagonia(Fundación Antorchas and University of
Louisville) and NSF DEB-0946430 for the study of Mesozoic
mammals from South America (to Guillermo Rougier). This research
was conducted with the support of ANPCYT (grant PICT 1756) and
international collaboration grant CONICET-Chinese Academy of
Sciences to DP, and DFG (grant RA 1012/9-1) to OR. Access to
SEM lab was possible thanks to ALUAR Aluminio Argentino, and the
technical help of Mr. Jaime Groizard is deeply appreciated. R. Butler
is deeply thanked for providing constructive comments and discussion
about this specimen. Line drawings of 2 have been conducted by Mr.
Jorge Gonzalez. Ms. Sheena Kaal is thanked for access to comparative
specimens of Heterodontosaurus at the Iziko-South African Museum
to DP. Mr. Zheng Xiao-Ting is thanked for access to comparative
specimens of Tianyulong at the Shandong Tianyu Museum of Nature
to DP. Ms. Zhang Xiaomei is also thanked for her help, and Dr. Xu
Xing is thanked for providing access to other relevant comparative
material. Critical comments by Richard Butler and four anonymous
reviewers have considerably helped to improve the manuscript.
Aberhan M, Bussert R, Heinrich W-D, Schrank E, Schultka S, Sames
B, Kriwet J, Kapilima S (2002) Palaeoecology and depositional
environments of the Tendaguru Beds (Late Jurassic to Early
Cretaceous, Tanzania). Mitt Mus Naturk Berlin, Geowissensch
Reihe 5:1944
Attridge J, Crompton AW, Jenkins FA Jr (1985) The southern African
Liassic prosauropod Massospondylus discovered in North America.
J Vertebr Paleontol 5:128132
Báez AM, Marsicano CA (2001) A heterodontosaurid ornithischian
dinosaur from the Upper Triassic of Patagonia. Ameghiniana
Báez AM, Nicoli L (2008) A new species of Notobatrachus
(Amphibia, Salientia) from the Middle Jurassic of northwestern
Patagonia. J Paleontol 82:372376
Bakker RT, Galton P, Siegwarth J, Filla J (1990) A new latest Jurassic
vertebrate fauna, from the highest levels of the Morrison
Formation at Como Bluff, Wyoming. Part IV. The dinosaurs: a
new Othnielia-like hypsilophodontid. Hunteria 2:819
Barrett PM, Han F-L (2009) Cranial anatomy of Jeholosaurus
shangyuanensis (Dinosauria: Ornithischia) from the Early Creta-
ceous of China. Zootaxa 2072:3155
Barrett PM, Butler RJ, Knoll F (2005) Small-bodied ornithischian
dinosaurs from the Middle Jurassic of Sichuan, China. J Vertebr
Paleontol 25:823834
Barrett PM, Butler RJ, Novas FE, Moore-Fay SC, Moody JM, Clark
JM, Sánchez-Villagra MR (2008) Dinosaur remains from the La
Quinta Formation (Lower or Middle Jurassic) of the Venezuelan
Andes. Paläontol Z 82:163177
Bonaparte JF (1976) Pisanosaurus mertii, Casamiquela and the origin
of the Ornithischia. J Paleontol 50:808820
Bonaparte JF (1979) Dinosaurs: a Jurassic assemblage from Patago-
nia. Science 205:13771379
Bonaparte JF (1986) Les Dinosaures (Carnosaures, Allosauridés,
Sauropodes, Cétiosauridés) du Jurassique moyen de Cerro
Cóndor (Chubut, Argentine). Ann Paleontol 72:326386
Brochu CA (1996) Closure of neurocentral sutures during crocodilian
ontogeny: implications for maturity assessment in fossil arch-
osaurs. J Vertebr Paleontol 16:4962
Butler RJ (2010) The anatomy of the basal ornithischian dinosaur
Eocursor parvus from the lower Elliot Formation (Late Triassic)
of South Africa. Zool J Linn Soc 160:648684
Butler RJ, Porro LB, Heckert AB (2006) A supposed heterodonto-
saurid tooth from the Rhaetian of Switzerland and a reassessment
of the European Late Triassic record of Ornithischia (Dinosau-
ria). N Jb Geol Paläontol Mh 2006:613633
Butler RJ, Smith RMH, Norman DB (2007) A primitive ornithischian
dinosaur from the Late Triassic of South Africa, and the early
evolution and diversification of Ornithischia. Proc R Soc B
274:20412046. doi:10.1098/rspb.2007.0367
Butler RJ, Upchurch P, Norman DB (2008a) The phylogeny of the
ornithischian dinosaurs. J Syst Palaeontol 6:140. doi:10.1017/
Butler RJ, Porro LB, Norman DB (2008b) A juvenile skull of the
heterodontosaurid dinosaur Heterodontosaurus tucki from the
Stormbergof southern Africa. J Vert Paleont 28:702711
Butler RJ, Galton PM, Porro LB, Chiappe LM, Henderson DM,
Erickson GM (2010) Lower limits of ornithischian dinosaur body
size inferred from a new Upper Jurassic heterodontosaurid from
North America. Proc R Soc B 277:375381. doi:10.1098/
Cabaleri N, Volkheimer W, Silva Nieto D, Armella C, Cagnoni M,
Hauser N, Matteini M, Pimentel MM (2010) UPb ages in
zircons from Las Chacritas and Puesto Almada members of the
Jurassic Cañadón Asfalto Formation, Chubut province, Argen-
tina. VII South American Symposium on Isotope Geology, pp
Casamiquela RM (1967) Un nuevo dinosaurio ornitisquio triásico
(Pisanosaurus mertii; Ornithopoda) de la Formación Ischigua-
lasto, Argentina. Ameghiniana 5:4764
Charig AJ, Crompton AW (1974) The alleged synonymy of
Lycorhinus and Heterodontosaurus. Ann S Afr Mus 64:167189
Colbert EH (1981) A primitive ornithischian dinosaur from the
Kayenta Formation of Arizona. Mus N Arizona Bull 53:161
Cordoniú L, Rauhut OWM, Pol D (2010) Osteological features of
Middle Jurassic pterosaurs from Patagonia (Argentina). Acta
Geosci Sinica 31:1213
Coria RA, Salgado L (1996) A basal iguanodontian (Ornithischia:
Ornithopoda) from the Late Cretaceous of South America. J Vert
Paleont 16:445457
Escapa IH, Sterli J, Pol D, Nicoli L (2008) Jurassic tetrapods and flora
of Cañadon Asfalto Formation in Cerro Condor area, Chubut
Province. Rev Asoc Geol Arg 63:613624
Galton PM (1974) The ornithischian dinosaur Hypsilophodon from
the Wealden of the Isle of Wight. Bull Nat Hist Mus Lond (Geol)
Galton PM (1997) Cranial anatomy of the basal hypsilophodontid
dinosaur Thescelosaurus neglectus Gilmore (Ornithischia: Orni-
thopoda) from Upper Cretaceous of North America. Rev
Paléobiol 16:231258
Goloboff PA, Farris JS, Nixon KC (2008a) TNT, a free program for
phylogenetic analysis. Cladistics 24:113
Goloboff PA, Farris JS, Nixon KC (2008b) TNT (Tree analysis using
new technology) ver. 1.1.Published by the authors, Tucumán,
Gow CE (1975) A new heterodontosaurid from the Redbeds of South
Africa showing clear evidence of tooth replacement. Zool J Linn
Soc 57:333339
Haubold H (1990) Ein neuer Dinosaurier (Ornithischia, Thyreophora)
aus dem Unteren Jura des Nördlichen Mitteleuropa. Rev
Paléobiol 9:149177
Hopson JA (1975) On the generic separation of the ornithischian
dinosaurs Lycorhinus and Heterodontosaurus from the Storm-
berg Series (Upper Triassic) of South Africa. S Afr J Sci 71:302
Hopson JA (1980) Tooth function and replacement in early Mesozoic
ornithischian dinosaurs: implications for aestivation. Lethaia
Irmis RB (2007) Axial skeleton ontogeny in the Parasuchia (Arch-
osauria: Pseudosuchia) and its implications for ontogenetic
determination in Archosaurs. J Vertebr Paleontol 27:350361.
Irmis RB, Knoll F (2008) New ornithischian dinosaur material from
the Lower Jurassic Lufeng Formation of China. N Jb Geol
Paläont Abh 247:117128
Irmis RB, Parker WG, Nesbitt SJ, Liu J (2007) Early ornithischian
dinosaurs: the Triassic record. Hist Biol 19:322
Knoll F (2002) New skull of Lesothosaurus (Dinosauria: Ornithischia)
from the Upper Elliot Formation (Lower Jurassic) of southern
Africa. Geobios 35:595603
Knoll F (2005) The tetrapod fauna of the Upper Elliot and Clarens
formations in the main Karoo Basin (South Africa and Lesotho).
Bull Soc Geol France 176:8191. doi:10.2113/176.1.81
Kuhn O (1966) Die Reptilien, System und Stammesgeschichte.
Krailling bei München, Oeben
Maier G (2003) African dinosaurs unearthed: the Tendaguru expedi-
tions. Indiana University Press, Indiana, 512 pp
Martin T, Rauhut OWM (2005) Mandible and dentition of Asfalto-
mylos patagonicus (Australosphenida, Mammalia) and the
evolution of tribosphenic teeth. J Vertebr Paleontol 25:414425
Moreno K, Blanco N, Tomlinson A (2004) New dinosaur footprints
from the Upper Jurassic of northern Chile. Ameghiniana 41:535
Norman DB, Barrett PM (2002) Ornithischian dinosaurs from the
Lower Cretaceous (Berriasian) of England. Spec Pap Palaeontol
Norman DB, Sues H-D, Witmer LM, Coria RA (2004a) Basal
Ornithopoda. In: Weishampel DB, Dodson P, Osmólska H (eds)
The Dinosauria, 2nd edn. University of California Press,
Berkeley, pp 393412
Norman DB, Witmer LM, Weishampel DB (2004b) Basal Ornithi-
schia. In: Weishampel DB, Dodson P, Osmólska H (eds) The
Dinosauria, 2nd edn. University of California Press, Berkeley, pp
Owen R (1842) Report on British fossil reptiles. Part II. Rep British
Assoc Adv Sci 1841:60204
Owen R (1863) A monograph of the fossil Reptilia of the Liassic
Formations. II. Scelidosaurus harrisonii. Continued. Palaeontogr
Soc Monogr 14:126
Pascual R (1996) Late CretaceousRecent land-mammals: an ap-
proach to South American geobiotic evolution. Mastozool Neo-
trop 3:133152
Peng G (1992) Jurassic ornithopod Agilisaurus louderbacki (Ornitho-
poda: Fabrosauridae) from Zigong, Sichuan, China. Vert PalA-
siatica 30:3953
Raath MA (1985) The theropod Syntarsus and its bearing on the
origin of birds. In: Hecht MK, Ostrom JH, Viohl G, Wellnhofer P
(eds) The beginnings of birds. Freunde des Jura-Museums
Eichstätt, Willibaldsburg, pp 219227
Rauhut OWM (2002) Dinosaur teeth from the Barremian of Uña
(Province of Cuenca, Spain). Cret Res 23:255263
Rauhut OWM (2003a) A dentary of Patagosaurus (Sauropoda)
from the Middle Jurassic of Patagonia. Ameghiniana 40:425
Rauhut OWM (2003b) The interrelationships and evolution of basal
theropod dinosaurs. Spec Pap Palaeontol 69:1213
Rauhut OWM (2005) Osteology and relationships of a new theropod
dinosaur from the Middle Jurassic of Patagonia. Palaeontology
Rauhut OWM, Lopez-Arbarello A (2008) Archosaur evolution during
the Jurassic: a southern perspective. Rev Asoc Geol Arg 63:557
Rauhut OWM, Lopez-Arbarello A, Puerta P, Martín T (2001) Jurassic
vertebrates from Patagonia. J Vertebr Paleontol 21:91A
Rauhut OWM, Martin T, Ortiz-Jaureguizar E, Puerta P (2002) A
Jurassic mammal from South America. Nature 416:165168
Rieppel O (1984) Miniaturization of the lizard skull: its functional
and evolutionary implications. Symp Zool Soc London
Rougier GW, Martinelli AG, Forasiepi AM, Novacek MJ (2007a)
New Jurassic mammals from Patagonia, Argentina: a reappraisal
of australosphenidan morphology and interrelationships. Am
Mus Novit 3566:154
Rougier GW, Garrido A, Gaetano L, Puerta P, Corbitt C, Novacek MJ
(2007b) A new triconodont from South America. Am Mus Novit
Salani FM (2007) Aporte a la edad de la Formación Cañadón Asfalto,
Chubut, Argentina. Resúmenes 30 Simposio Argentino del
Jurásico, p 71
Santa Luca AP (1980) The postcranial skeleton of Heterodontosaurus
tucki (Reptilia, Ornithischia) from the Stormberg of South Africa.
Ann South Afr Mus 79:159211
Seeley HG (1887) On the classification of the fossil animals
commonly named Dinosauria. Proc Roy Soc Lond 43:165171
Sereno PC (1986) Phylogeny of the bird-hipped dinosaurs (Order
Ornithischia). Natl Geogr Res 2:234256
Sereno PC (1991) Lesothosaurus,Fabrosaurids,and the early
evolution of Ornithischia. J Vertebr Paleontol 11:168197
Sereno PC (1997) The origin and evolution of dinosaurs. Ann Rev
Earth Planet Science 25:435489
Sereno PC (1999) The evolution of dinosaurs. Science 284:2137
2147. doi:10.1126/science.284.5423.2137
Sereno PC, Novas FE (1993) The skull and neck of the basal
theropod Herrerasaurus ischigualastensis. J Vertebr Paleontol
Silva Nieto DG, Cabaleri NG, Salani FM, Gonzales Díaz E, Coluccia
A (2002) Hoja Geológica 4368-27 Cerro Cóndor, provincia de
Chubut. Instituto de Geología y Recursos Minerales, Servicio
Geológico Minero Argentino, Buenos Aires, Argentina, 68 pp
Smith ND, Makovicky PJ, Pol D, Hammer WR, Currie PJ (2007) The
dinosaurs of the Early Jurassic Hanson Formation of the central
Transantarctic Mountains: phylogenetic review and synthesis. U.
S. Geological Survey and the National Academies, Short
Research Paper 003, p 5. doi:10.3133/of20071047.srp003
Sterli J (2008) A new, nearly complete stem turtle from the Jurassic of
South America with implications for turtle evolution. Biol Lett
Sues H-D, Clark JM, Jenkins FA (1994) A review of the Early
Jurassic tetrapods from the Glen Canyon Group of the American
Southwest. In: Fraser NC, Sues H-D (eds) In the shadow of the
dinosaurs: early Mesozoic tetrapods. Cambridge University
Press, Cambridge, pp 284294
Thulborn RA (1974) A new heterodontosaurid dinosaur (Reptilia:
Ornithischia) from the Upper Triassic Red Beds of Lesotho. Zool
J Linn Soc 55:151175
Turner AH, Pol D, Clarke JA, Erickson GM, Norell MA (2007) A
basal dromaeosaurid and size evolution preceding avian flight.
Science 317:13781381
Volkheimer W, Quattrocchio M, Cabaleri NG, García V (2008)
Palynology and paleoenvironment of the Jurassic lacustrine
Cañadón Asfalto Formation at Cañadón Lahuincó locality,
Chubut Province, Central Patagonia, Argentina. Rev Española
Microplaeont 40:7796
Weishampel DB (1984) Evolution of jaw mechanisms in ornithopod
dinosaurs. Adv Anat Embryol Cell Biol 87:1110
Weishampel DB, Witmer LM (1990) Heterodontosauridae. In:
Weishampel DB, Dodson P, Osmólska H (eds) The Dinosau-
ria, 1st edn. University of California Press, Berkeley, pp 486
Weishampel DB, Barrett PM, Coria RA, Le Loeuff J, Xu X, Zhao X,
Sahni A, Gomani EMP, Noto CR (2004) Dinosaur distribution. In:
Weishampel DB, Dodson P, Osmólska H (eds) The Dinosauria, 2nd
edn. University of California Press, Berkeley, pp 517606
Xu X, Forster CA, Clark JM, Mo J (2006) A basal ceratopsian with
transitional features from the Late Jurassic of northwestern China.
ProcRSocB273:21352140. doi:10.1098/rspb.2006.3566
You H-L, Dodson P (2004) Basal Ceratopsia. In: Weishampel DB,
Dodson P, Osmólska H (eds) The Dinosauria, 2nd edn.
University of California Press, Berkeley, pp 478493
Zheng X-T, You H-L, Xu X, Dong Z-M (2009) An Early Cretaceous
heterodontosaurid dinosaur with integumentary structures. Nature
458:333336. doi:10.1038/nature07856
... Manidens is unexpectedly recovered as a carnivore by the biomechanical model. This is likely the result of analyzing isolated teeth in a species that had evolved a dental battery composed of closely packed, high crowned teeth as an adaptation to herbivory (48,49). Because of its unique dental morphology, the isolated teeth of Manidens experience high stresses, as in extant carnivores. ...
... Despite such omnivory in the earliest ornithischians, a highly efficient craniodental apparatus, including dental batteries, evolved in Early Jurassic clades such as heterodontosaurids (55,64), indicating a shift to herbivory in some early ornithischian lineages. Among heterodontosaurids, Manidens has been described as having intermediate craniodental traits (41,48), with an incipient dental battery compared to Heterodontosaurus (64) but with an efficient jaw apparatus to process plant material (65). Our prediction based on tooth morphology is in line with this evidence, although Manidens is here classified as a carnivore based on tooth mechanics. ...
Full-text available
Dinosaurs evolved a remarkable diversity of dietary adaptations throughout the Mesozoic, but the origins of different feeding modes are uncertain, especially the multiple origins of herbivory. Feeding habits of early dinosaurs have mostly been inferred from qualitative comparisons of dental morphology with extant analogs. Here, we use biomechanical and morphometric methods to investigate the dental morphofunctional diversity of early dinosaurs in comparison with extant squamates and crocodylians and predict their diets using machine learning classification models. Early saurischians/theropods are consistently classified as carnivores. Sauropodomorphs underwent a dietary shift from faunivory to herbivory, experimenting with diverse diets during the Triassic and Early Jurassic, and early ornithischians were likely omnivores. Obligate herbivory was a late evolutionary innovation in both clades. Carnivory is the most plausible ancestral diet of dinosaurs, but omnivory is equally likely under certain phylogenetic scenarios. This early dietary diversity was fundamental in the rise of dinosaurs to ecological dominance.
... However, at the end of the Norian, six of 17 genera of sauropodomorphs disappeared (35%), but eight new genera were recorded at the beginning of the Rhaetian (Figs. 1 and 14). The ornithischian record of the Upper Triassic is scarce and restricted to a small geographical area in southern Gondwana (Thulborn, 1970;Brusatte et al., 2010;Butler, 2010;Pol et al., 2011) (Fig. 10) and they were less significant in terrestrial ecosystems than the anomodonts, traversodont cynodonts, rhynchosaurs, and sauropodomorphs. However, Barrett (2000) suggested that early ornithischians may have been facultatively omnivorous, rather than strictly herbivorous. ...
Full-text available
The Early Jurassic Jenkyns Event (~183 Ma) was characterized in terrestrial environments by global warming, perturbation of the carbon cycle, enhanced weathering and wildfires. Heating and acid rain on land caused a loss of forests and affected diversity and composition of land plant assemblages and the rest of the trophic web. We suggest that the Jenkyns Event, triggered by the activity of the Karoo-Ferrar Large Igneous Province, was pivotal in remodelling terrestrial ecosystems, including plants and dinosaurs. Macroplant assemblages and palynological data show reductions in diversity and richness of conifers, cycadophytes, ginkgophytes, bennetitaleans, and ferns, and continuation of seasonally dry and warm conditions. Major changes occurred to sauropodomorph dinosaurs, with extinction of diverse basal families formerly called ‘prosauropods’ as well as some basal sauropods, and diversification of the derived Eusauropoda in the Toarcian in South America, Africa, and Asia, and wider diversification of new families, including Mamenchisauridae, Cetiosauridae and Neosauropoda (Dicraeosauridae and Macronaria) in the Middle Jurassic, showing massive increase in size and diversification of feeding modes. Ornithischian dinosaurs show patchy records; some heterodontosaurids and scelidosaurids disappeared, and major new clades (Stegosauridae, Ankylosauridae, Nodosauridae) emerged soon after the Jenkyns Event, in the Bajocian and Bathonian worldwide. Among theropod dinosaurs, Coelophysidae and Dilophosauridae died out during the Jenkyns Event and a diversification of theropods (Megalosauroidea, Allosauroidea, Tyrannosauroidea) occurred after this event with substantial increases in size. We suggest then that the Jenkyns Event terrestrial crisis was marked especially by floral changes and origins of major new sauropodomorph and theropod clades, characterized by increasing body size. Comparison with the end Triassic Mass Extinction helps to understand the incidence of climatic changes driven by activity of large igneous provinces on land ecosystems and their great impacts on early dinosaur evolution.
... Second, the ornithischians have been subject to extensive phylogenetic research (Boyd 2015;Han et al. 2018;Dieudonné et al. 2020), allowing phylogenetic information to be used in diversification rate estimation. Third, the ornithischians have a fossil record of adequate but not exceptional quality, marked by global episodes of poor sampling, patchy local records, and a substantial proportion of singletons (taxa known from a single stratigraphically unique occurrence) (Pol et al. 2011;Tennant et al. 2018). In terms of size and completeness, ornithischian phylogenetic and occurrence data are thus typical of the data sets widely in use by vertebrate paleontologists, whose broad availability may lead them to be repurposed for diversification rate estimation as methods like Fossil BAMM and PyRate grow in popularity. ...
Full-text available
Changes in speciation and extinction rates are key to the dynamics of clade diversification, but attempts to infer them from phylogenies of extant species face challenges. Methods capable of synthesizing information from extant and fossil species have yielded novel insights into diversification rate variation through time, but little is known about their behavior when analyzing entirely extinct clades. Here, we use empirical and simulated data to assess how two popular methods, PyRate and Fossil BAMM, perform in this setting. We inferred the first tip-dated trees for ornithischian dinosaurs, and combined them with fossil occurrence data to test whether the clade underwent an end-Cretaceous decline. We then simulated phylogenies and fossil records under empirical constraints to determine whether macroevolutionary and preservation rates can be teased apart under paleobiologically realistic conditions. We obtained discordant inferences about ornithischian macroevolution including a long-term speciation rate decline (BAMM), mostly flat rates with a steep diversification drop (PyRate) or without one (BAMM), and episodes of implausibly accelerated speciation and extinction (PyRate). Simulations revealed little to no conflation between speciation and preservation, but yielded spuriously correlated speciation and extinction estimates while time-smearing tree-wide shifts (BAMM) or overestimating their number (PyRate). Our results indicate that the small phylogenetic datasets available to vertebrate paleontologists and the assumptions made by current model-based methods combine to yield potentially unreliable inferences about the diversification of extinct clades. We provide guidelines for interpreting the results of the existing approaches in light of their limitations, and suggest how the latter may be mitigated.
... The surface of the jugal in all examined Haya specimens is smooth, with no trace of the jugal rugosities seen in some Jeholosaurus and Changchunsaurus specimens (Barrett and Han, 2009;Jin et al., 2010). It further lacks the jugal bosses present in Heterodontosaurus, Manidens, Zephyrosaurus, and Orodromeus (Sues, 1980;Scheetz, 1999;Norman et al., 2011;Pol et al., 2011). ...
Full-text available
Haya griva is an early-diverging neornithischian (“hypsilophodontid”) dinosaur known from several well-preserved skulls and articulated postcranial skeletons, in addition to dozens of partial or isolated finds from the Upper Cretaceous Khugenetslavkant and Zos Canyon localities (Javkhlant Formation and equivalent beds) in the Gobi Desert of Mongolia. Collectively, nearly the entire skeletal anatomy of Haya is known, including partial growth series of skulls and femora. Detailed description and comparisons with other ornithischians, including novel anatomical information about the palate and braincase gleaned through high-resolution x-ray microcomputed tomography, reveals a wealth of osteological data for understanding the growth and relationships of this key taxon. Though the Haya specimens span a wide size range, bone histology reveals that all are likely perinatal to subadult individuals, with specimens of intermediate age the most common, and skel- etally mature specimens absent. Phylogenetic analyses place Haya as one of the few Asian members of Thescelosauridae, an important noncerapodan neornithischian group of the Late Cretaceous.
Full-text available
The origin and evolutionary relationships of ornithischian dinosaurs are topics that have undergone a series of substantial revisions. At present there are several competing hypotheses concerning the relationship between Ornithischia and the other principal clades of Dinosauria. Some hypotheses have posited a tree topology within Dinosauria that imply a ‘ghost-lineage’ for Ornithischia (whose representatives make their first unambiguous appearance in the Hettangian) that extends through a substantial portion of Triassic time. In contrast, other hypotheses have placed conventionally Triassic dinosauromorph (stem-lineage Dinosauria) taxa within the clade Ornithischia. Recently, a large-scale phylogenetic analysis recovered an array of taxa, known as ‘silesaurids’, as a paraphyletic assemblage of taxa (referred to in this article using the informal terms silesaurs or silesaurians) on the branch leading to the clade Ornithischia. This latter hypothesis of relationships would account for the apparent absence of Triassic ornithischians, because stem-lineage ornithischians (silesaurs in this article) are exclusively Triassic. However, the analysis that produced this novel topology used a dataset that, in its original form, did not include all early representatives of Ornithischia (sensu lato), and did not incorporate all the anatomical characters that have been suggested to unite Ornithischia with other dinosaurian clades (Theropoda and Sauropodomorpha). Nor did the initial study go on to expand upon some important taxonomic, palaeobiological and evolutionary implications of a topology that links a paraphyletic array of silesaurs to the clade Ornithischia. The present article addresses these latter issues by expansion and re-analysis of the original dataset. The results find further support for the hypothesis that silesaurs comprise a paraphyletic grouping of taxa on the stem of Ornithischia and that successive silesaur taxa acquire anatomical characters anagenetically in a process that culminates in the assembly of what may be described as a ‘traditional’ ornithischian. The overall topology of the consensus tree remains but little changed from the original analysis, despite the addition of new taxa and characters. To provide stability to this area of the tree and to preserve the most important of the relevant taxonomic names, we suggest a revised taxonomic framework for ornithischians that is consistent with this new topology. We retain the name Ornithischia for the total-group (traditional Ornithischia and its stem-lineage), while we resuscitate a name originally proposed by Richard Owen, Prionodontia (= ‘coarse edged teeth’) for the clade containing only the so-called traditional ornithischian (= ‘bird-hipped’) dinosaurs. We also erect Parapredentata as a more exclusive subclade in Ornithischia. This novel taxonomic framework is intended to provide phylogenetic clarity and a degree of stability in Ornithischia and Dinosauria as further analyses and new data continue to refine and re-shape the tree. The data presented in this study represent a stage in our attempt to establish an early dinosaur dataset in which character definitions and character scores are agreed upon and used consistently.
Full-text available
The extinct herpetofauna of the Chubut Province is one of the most diverse, temporally and spatially extensive, and well-known extinct faunas in Argentina and South America. These fossils help understanding the evolution of the herpetofauna during more than 180 million years, not only in the Patagonian region, but also in a worldwide scale due to the importance of some of them. Since its establishment in 1990, the Museo Paleontológico Egidio Feruglio (MPEF) plays a key role in the discovery, protection, study, and display of the important fossils of the Province. The paleoherpetological study at MPEF went through three different stages: the Initial, the Intermediate, and the Current stages. At present, the paleoherpetological collection contains approximately 960 specimens of amphibians and reptiles-including turtles, lepidosaurs, plesiosaurs, crocodiles, pterosaurs, dinosaurs, and birds-found in sedimentary formations that span from the Early Jurassic to the late Miocene. Based on this material, at least 32 new species were named, and more than 200 studies were published in less than three decades. © 2022 Asociacion Paleontologica Argentina. All rights reserved.
The South American fossil record of Mesozoic mammals and close relatives is one of the best for Gondwana. Early mammals and relatives are found in about a dozen localities in Argentina, Brazil, Bolivia, Chile, and presumably Peru, including a broad sample of non-mammaliaform cynodonts of the Triassic age. Mesozoic mammals span from the latest Early Jurassic to the latest Cretaceous, furthermore some of those archaic lineages unexpectedly survived the end of the Cretaceous period, remaining as minority elements in the Paleocene–Miocene faunal associations. The fossiliferous localities bearing these fossils are presented in this chapter, highlighting the geological setting, age, and their faunal associations.
A stegosaurian humerus from the Oxfordian–Tithonian(?) Cañadón Calcáreo Formation of Chubut, Argentina, extends the fossil record of this clade of thyreophoran ornithischian dinosaurs to the Upper Jurassic of South America. The element shares the derived character of an oblique ridge extending from the deltopectoral crest towards the medial distal condyle with taxa such as Kentrosaurus and Stegosaurus and thus represents a derived representative of the clade. The presence of stegosaurs in the Cañadón Calcáreo Formation underlines the similarities of its dinosaur fauna with other Late Jurassic dinosaur faunas, such as the Morrison Formation of North America or the Tendaguru Formation of Tanzania, in at least broad systematic terms.
The Middle Jurassic Kota Formation of the Pranhita-Godavari Valley in peninsular India is well known for its vertebrate fauna comprising fishes, sphenodontians, iguanian lizards, cryptodire turtle, crocodilians, pterosaurs, sauropod dinosaurs and early mammals. However, no theropod and undoubted ornithischian dinosaur remains have been reported from the Jurassic of India until now. Here we describe the first theropod dinosaur teeth representing five morphotypes of Dromaeosauridae, one Richardoestesia-like form, and one Theropoda indet. The ornithischian dinosaur teeth are described under five morphotypes of Ornithischia indet. The new dinosaur fauna improves the diversity of the Jurassic vertebrate fauna of India significantly. It also improves the impoversished Jurassic record of dromaeosaurid and primitive ornithischian dinosaurs of the Gondwana. At higher taxonomic levels, the Kota fauna demonstrates close compositional similarities with Laurasian Jurassic faunas, such as the Middle Jurassic fauna of England, and limited Gondwanan affinities, which may suggest closer connection with the Laurasian continents and existence of some biogeographic partitioning within the Gondwana in the Jurassic.
Full-text available
Skull material of the prosauropod dinosaur Massospondylus, previously known only from Africa, has been found in the Kayenta Formation (Glen Canyon Group) of northeastern Arizona. A reconstruction of the skull, corrected for distortion, is compared with that of Plateosaurus. The dentition provides evidence for an herbivorous diet in prosauropods; the presence of small palatal teeth is reported for the first time in any dinosaur. The associated fauna is related to faunas from the Elliot and Clarens sandstone formations in southern Africa, and an Early Jurassic (rather than Late Triassic) age is accepted for these formations as well as for the Kayenta Formation.
Full-text available
The Late Jurassic to Early Cretaceous Tendaguru Beds (Tanzania, East Africa) have been well known for nearly a century for their diverse dinosaur assemblages. Here, we present sedimentological and palaeontological data collected by the German-Tanzanian Tendaguru Expedition 2000 in an attempt to reconstruct the palaeo-ecosystems of the Tendaguru Beds at their type locality. Our reconstructions are based on sedimentological data and on a palaeoecological analysis of macroinvertebrates, microvertebrates, plant fossils and microfossils (ostracods, foraminifera, charophytes, palynomorphs). In addition, we included data from previous expeditions, particularly those on the dinosaur assemblages. The environmental model of the Tendaguru Beds presented herein comprises three broad palaeoenvironmental units in a marginal marine setting: (1) Lagoon-like, shallow marine environments above fair weather wave base and with evidence of tides and storms. These formed behind barriers such as ooid bar and siliciclastic sand bar complexes and were generally subject to minor salinity fluctuations. (2) Extended tidal flats and low-relief coastal plains. These include low-energy, brackish coastal lakes and ponds as well as pools and small fluvial channels of coastal plains in which the large dinosaurs were buried. Since these environments apparently were, at best, poorly vegetated, the main feeding grounds of giant sauropods must have been elsewhere. Presumably, tidal flats and coastal plains were visited by dinosaurs primarily during periods of drought. (3) Vegetated hinterland. Vegetation of this environment can only be inferred indirectly from plant material transported into the other depositional environments. Vegetation was dominated by a diverse conifer flora, which apparently formed part of the food source of large herbivorous sauropods. Evidence from various sources suggests a subtropical to tropical palaeoclimate, characterised by seasonal rainfall alternating with a pronounced dry season during the Late Jurassic. In Early Cretaceous times, sedimentological and palaeontological proxies suggest a climatic shift towards more humid conditions. Die Tendaguru-Schichten von Tansania in Ostafrika (Oberjura bis Unterkreide) sind als Lagerstätte oberjurassischer Dinosaurier seit nahezu einem Jahrhundert weltweit bekannt. Anhand von sedimentologischen und paläontologischen Daten, die während der Deutsch-Tansanischen Tendaguru Expedition 2000 im Typus-Gebiet der Tendaguru-Schichten gewonnen wurden, werden Paläo-Ökosysteme rekonstruiert. Grundlage der Rekonstruktionen sind die Auswertung sedimentologischer Daten sowie die paläo-ökologische Analyse von Makroinvertebraten, Mikrovertebraten, pflanzlichen Fossilien und Mikrofossilien (Ostrakoden, Foraminiferen, Charophyten, Palynomorphen). Darüber hinaus werden Informationen über Dinosaurier berücksichtigt, die bei früheren Expeditionen gewonnen wurden. Das hier vorgestellte Ablagerungsmodell der Tendaguru-Schichten umfaßt drei Teilbereiche eines randlich marinen Sedimentationsraumes, die wie folgt gekennzeichnet werden können: (1) Lagunen-artige, marine Flachwasserbereiche, die oberhalb der Schönwetter-Wellenbasis lagen und unter deutlichem Einfluß von Gezeiten und Stürmen standen. Sie waren vom offenen Meer durch Barrieren, wie Ooidbarren und siliziklastischen Sandbarrenkomplexen, getrennt und wiesen einen leicht schwankenden Salzgehalt auf. (2) Ausgedehnte Wattgebiete und flache Küstenebenen. Dort befanden sich niedrig-energetische, brackische Strandseen und Teiche sowie Tümpel und kleinere Flußrinnen, in denen die großen Dinosaurier eingebettet wurden. Da diese Lebensräume bestenfalls dürftig bewachsen waren, müssen die Nahrungsquellen und der eigentliche Lebensraum der riesigen Sauropoden anderswo gelegen haben. Vermutlich wurden die Wattgebiete und Flachküsten von Dinosauriern vorrangig in den Trockenzeiten aufgesucht. (3) Bewachsenes Hinterland. Die Vegetation dieses Lebensraumes kann nur indirekt aus Pflanzenresten erschlossen werden, die in die anderen Ablagerungsraume transportiert wurden. Die Vegetation wurde von einer diversen Koniferenflora dominiert, die zumindest teilweise die Nahrungsgrundlage der großen, herbivoren Sauropoden bildete. Sedimentologische und paläontologische Indikatoren sprechen für ein subtropisches bis tropisches Klima wahrend der späten Jurazeit mit einem jahreszeitlichen Wechsel von Regenfällen und ausgeprägten Trockenzeiten. In der frühen Kreidezeit deutet sich ein Wechsel zu starker humiden Bedingungen an. doi:10.1002/mmng.20020050103
Full-text available
Fragmentary remains of a new heterodontosaurid species, comparable to Heterodontosaurus Crompton and Charig, were discovered in concretions in the Laguna Colorada Formation, a Late Triassic continental sequence in Santa Cruz Province, Argentina. The material consists of a weathered, left posterior maxillary fragment with dentition, and, tentatively, an isolated caniniform with anterior and posterior serrations. The preserved three maxillary teeth bear flat wear facets, and are columnar and closely packed. The anterior and posterior surfaces of the crowns are in contact, a feature considered a synapomorphy of Heterodontosaurus and Lycorhinus from the Early Jurassic upper Stormberg Group of southern Africa. As in Heterodontosaurus tucki Crompton and Charig, the maxillary teeth lack a cingulum or a constriction separating crown and root, and the wear facets of adjoining teeth form a single, continuous surface. However, the posterior maxillary teeth bear more. numerous and narrower ridges on their labial surfaces than those of H. tucki. This new record of a heterodontosaurid extends the temporal range of this group of small ornithischians and, considering the phylogeny of ornithischians as now understood, indicates an extensive phyletic diversification of these dinosaurs in the Late Triassic.
Full-text available
Many recent studies of theropod relationships have been focused on the phylogeny of coelurosaurs and the question of the origin of birds, but the interrelationships and evolution of basal theropods are still poorly understood. Thus, this paper presents a phylogenetic analysis of all theropods, but focuses on the basal members of this clade. The result supports the inclusion of Eoraptor and herrerasaurids in the Theropoda, but differs from other recent studies in two main aspects: (1) The taxa usually grouped as ceratosaurs form two monophyletic clades that represent successively closer outgroups to tetanurans. The more basal of these clades, the Coelophysoidea, comprise the majority of Late Triassic and Early Jurassic theropods. The other clade of basal theropods that are usually included in the Ceratosauria comprises Ceratosaurus, Elaphrosaurus, and abelisaurids. (2) Two monophyletic groups of basal tetanurans are recognized: the Spinosauroidea and the Allosauroidea. In contrast to other recent phylogenetic hypotheses, both clades are united in a monophyletic Carnosauria. The branching pattern of the present cladogram is in general accordance with the stratigraphic occurrence of theropod taxa. Despite the differences in recent analyses, there is a significant level of consensus in theropod phylogeny. At least four different radiations of non-avian theropods can be recognized. These radiations show different patterns in Laurasia and Gondwana, and there are increasing differences between the theropod faunas of the two hemispheres from the Triassic to the Cretaceous.
A detailed description of the skull and mandible of the Chinese cerapodan ornithischian dinosaur Jeholosaurus shangyuanensis (Lower Cretaceous, Yixian Formation) is presented for the first time and this information is used to reassess its phylogenetic position. Jeholosaurus can be distinguished from all other cerapodans on the basis of one autapomorphy (a row of small foramina on the nasal) and a character combination that is unique among ornithischians. Previously undescribed specimens add considerably to our knowledge of Jeholosaurus, providing new insights into its anatomy and ontogeny. Revised character scores increase the resolution of phylogenetic hypotheses and provide additional support for placement of Jeholosaurus within Ornithopoda.