A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone

Abstract

The South American Late Triassic offers the most comprehensive window to the early radiation of dinosaurs. This is enhanced by the discovery of Sacisaurus agudoensis, a new dinosauriform from the Caturrita Formation of Brazil. Various morphological features suggest its close phylogenetic affinity to Silesaurus, and both may be basal ornithischian dinosaurs. Sacisaurus has a pair of elements forming the tip of its lower jaw, hypothesized to be equivalent to the ornithischian predentary. This suggests that during an initial stage of their evolution, those dinosaurs had a paired predentary, which later fused into a single structure. As an originally paired bone, the predentary is comparable to elements that more often form the vertebrate mandible, such as the mentomeckelian bone. Although synapomorphic for ornithischians, the predentary does not seem neomorphic for the group, but primarily homologous to parts of the symphyseal region of the lower jaw of other vertebrates.

Full text

A Late Triassic dinosauriform from south Brazil and the origin
of the ornithischian predentary bone
JORGE FERIGOLO
1,†
& MAX C. LANGER
2
1
Museu de Cie
ˆncias Naturais, Fundac¸a˜o Zoobota
ˆnica do Rio Grande do Sul, Rua Dr Salvador Franc¸a 1427, Porto Alegre
90690-000, Brazil, and
2
Faculdade de Filosofia Cie
ˆncias e Letras de Ribera˜o Preto, Universidade de Sa˜o Paulo-USP,
Av. Bandeirantes 3900, Ribeira˜o Preto 14040-901, Brazil
Abstract
The South American Late Triassic offers the most comprehensive window to the early radiation of dinosaurs. This is enhanced
by the discovery of Sacisaur us agudoensis, a new dinosauriform from the Caturrita Formation of Brazil. Various morphological
features suggest its close phylogenetic affinity to Silesaurus, and both may be basal ornithischian dinosaurs. Sacisaurus has a
pair of elements forming the tip of its lower jaw, hypothesized to be equivalent to the ornithischian predentary. This suggests
that during an initial stage of their evolution, those dinosaurs had a paired predentary, which later fused into a single structure.
As an originally paired bone, the predentary is comparable to elements that more often form the vertebrate mandible, such as
the mentomeckelian bone. Although synapomorphic for ornithischians, the predentary does not seem neomorphic for the
group, but primarily homologous to parts of the symphyseal region of the lower jaw of other vertebrates.
Keywords: Sacisaurus, Late Triassic, ornithischia, predentary, Brazil, Caturrita Formation
Introduction
The presence of a separate ossification at the tip of the
lower jaw, the predentary bone, is as typical of
ornithischian dinosaurs as their opistopubic pelvis.
Some consider the junior synonym Predentata Marsh
1894, to more “properly” designate the taxon, given
that various maniraptorans are obviously “bird-
hipped” (Ostrom 1976; Barsbold 1979; Hutchinson
and Chiappe 1998), but no other major dinosaur
group possesses a predentary. Despite its ambiguous
presence in the putative basal-most member of the
group, Pisanosaurus mertii from the Late Triassic of
Argentina (Casamiquela 1967; Bonaparte 1976;
Sereno 1991), the predentary is often considered
synapomorphic for Ornithischia as a whole (Norman
1984; Sereno 1984, 1986; Maryanska and Osmo
´lska
1985; Cooper 1985; Norman et al. 2004). Otherwise,
a homonymous bone has only been referred to some
teleosts and fossil birds (Regan 1909; Gregory and
Conrad 1937; Bardack and Sprinkle 1969; Martin
1987, 1991; Brito 1997). The origin of the
ornithischian predentary is not comprehensively
known, but new material from southern Brazil
provides information that can help to understand the
acquisition of this unique element.
The new taxon described here comes from a bone
accumulation horizon within the Caturrita Formation,
Rio Grande do Sul, Brazil (Figure 1). This stratigraphic
unit is of Late Triassic age (Rubert and Schultz 2004;
Langer 2005a), suggesting that the new form is one of
the oldest known putative ornithischians. The first
members of the Ornithischia are of Ischigualastian age
(early-mid Carnian), including Pisanosaurus and
possible isolated remains from the North American
Atlantic coast (Galton 1983; Hunt and Lucas 1994;
Weishampel and Young 1996) and Morocco (Galton
1985a; Gauffre 1993; but see Jalil and Knoll 2002).
ISSN 0891-2963 print/ISSN 1029-2381 online q2006 Taylor & Francis
DOI: 10.1080/08912960600845767
†
E-mail: jorge.ferigolo@fzb.rs.gov.br
Correspondence: M. C. Langer, Faculdade de Filosofia Cie
ˆncias e Letras de Ribera
˜o Preto, Universidade de Sa
˜o Paulo-USP, Av. Bandeirantes
3900, Ribeira
˜o Preto 14040-901, Brazil. E-mail: mclanger@ffclrp.usp.br
Historical Biology, 2006; 1–11, iFirst article

Other alleged Triassic ornithischians include an hetero-
dontosaurid from Patagonia (Baez and Marsicano
2001), an undescribed basal neornithischian from
southern Africa (Butler 2005), and fragmentary
material from Western USA (Chatterjee 1984; Hunt
and Lucas 1994; Heckert 2004; Irmis et al. 2006),
Europe (Godefroit and Cuny 1997; Cuny et al. 2000),
and India (Weishampel et al. 2005). The ornithischian
affinity of most of these remains was based on often
criticized (Sereno 1991; Knoll 2002) characters of tooth
morphology. More recently, Parker et al. (2005; see also
Irmis et al. 2006) demonstrated that the putative
ornithischian Revueltosaur us callenderi represents a
pseudosuchian archosaur with herbivorously-adapted
teeth, showing that several of the alleged ornithischian
dental apomorphies are not unique to that dinosaur
group among Late Triassic archosaurs. Following this
conservative approach, it is the mainly South American
Late Triassic records that are referable to Ornithischia
(Casamiquela 1967; Baez and Marsicano 2001),
emphasizing that, as with saurischians (Langer 2004),
this continent played a pivotal role in the origin and early
radiation of those dinosaurs (Parker et al. 2005).
Systematic palaeontology
Archosauria Cope, 1869
Ornithosuchia Gauthier, 1986
Dinosauriformes Novas, 1992
cf. Dinosauria Owen, 1842
cf. Ornithischia Seeley, 1887
Sacisaurus agudoensis,gen.andsp.nov.(Figures2–4)
Derivation of name
The genus name is formed from the Portuguese
derivation of the indigenous—Tupi–name Saci (¼a
fabled entity of Brazilian lore that possesses a single leg)
and the Greek word sauros (¼lizard), in an anecdotal
allusion to the fact that only right femora of the new
taxon have been found. The species name refers to
Agudo, the town where the material was found.
Locality and horizon
All specimens referred to Sacisaurus agudoensis were
collected in a single locality (Figure 1) inside the urban
area of Agudo, Rio Grande do Sul, Brazil (1984301200 S;
4784500400 W). The type stratum is composed of fine
grained sandstones full of mudstone rip-up clasts and
isolated fossil remains within the “highstand systems
tract” of the Santa Maria 2 sequence (Zerfass et al.
2003). This corresponds to the top of the Alemoa
Member (Santa Maria Formation) and to the Caturrita
Formation (Andreis et al. 1980), from the base of which
the new material was excavated. In biostratigraphic
terms, isolated teeth of stem-mammals (Bonaparte et al.
2003, 2005), the tritheletondid Riograndia (Bonaparte
et al. 2001), and a large traversodontid, possibly
Exaeretodon (Abdala et al. 2002), suggest a correlation
to the “Ictidosaur Assemblage Zone” (Rubert and
Schultz 2004), which is typically considered post-
Ischigualastian and can be given a late Carnian to early
Norian age (Langer 2005a,b).
Holotype (Figures 2C, 3B)
Partial left mandible (MCN PV10041) housed at the
Museu de Cie
ˆncias Naturais (MCN), Fundac¸a
˜o
Zoobota
ˆnica do Rio Grande do Sul, Porto Alegre,
Brazil; this includes most of the dentary, with three
preserved herbivorously-adapted teeth, and an eden-
tulous rostral portion that might represent a separate
paired ossification.
Diagnosis
Dinosauriform differing from other known basal
members of the group, except Silesaurus opolensis and
ornithischians, for the presence of an edentulous rostral
portion of the mandible. This jaw segment differs from
that of S. opolensis (Dzik 2003) because its front tip is
not dorsally curved, and from that of ornithischians
because it does not form a single (unpaired) predentary,
but articulates to its counterpart in the midline.
Referred material (Figures 2–4)
Most of the partial lower-jaws collected in the type-
locality (MCN PV10042, PV10043, PV10044,
PV10061) share with the holotype of Sacisaurus
agudoensis a similar edentulous rostral portion, and are
clearly referable to that taxon. A mandible fragment
lacking the rostral part (MCN PV10048), as well as
the single recovered maxilla (MCN PV10050), bear
similar ornithischian-like dentition, and are also
tentatively assigned to S. agudoensis. This is also the
Figure 1. Sketch map of Rio Grande do Sul showing the outcrop
areas of the Santa Maria sequence (shaded) and approximate
location of the type-locality of Sacisaurus agudoensis gen. et sp. nov.
(arrowed). Scale bar represents 200 km.
J. Ferigolo & M. C. Langer2

case of numerous isolated teeth, whereas no other kind
of archosaur teeth has been recorded in the bone-bed.
Other isolated remains are also tentatively assigned to
S. agudoensis, namely: postorbital (MCN PV10051);
ectopterygoid (MCN PV10049), vertebrae (MCN
PV10028, PV10029, PV10032, PV10090, PV10097),
scapula (MCN PV10033), ilium (MCN PV10100),
pubes (MCN PV10023, PV10024), ischium (MCN
PV10025), femora (MCN PV10009, PV10010,
PV10011, PV10013, PV10014, PV10015, PV10016,
PV10018, PV10019, PV10063, PV10075), tibia
(MCN PV10020), and phalanges. These are of similar
relative sizes and have the morphology expected for a
basal dinosauriform. Two femora (MCN PV10007,
PV10008) and one ilium (MCN PV10026) from
the type-locality do not seem to be referable to
S. agudoensis. These differ in morphology from the
ilium and femora attributed to that taxon and
apparently represent a much larger basal dinosaur.
Comparative description
The ascending process of the maxilla of Sacisaur us
(Figures 2B, 3A) extends from the rostral margin of
the bone, and is not caudally inset as in basal
eusaurischians (Langer 2004). The internal and
external antorbital fenestrae are more extensive than
usual for basal ornithischians (Sereno 1991; Haubold
1991), defining a narrow antorbital fossa. Sacisaurus
also differs from those dinosaurs because it possesses a
thinner caudal maxillary ramus, the outer surface
of which lacks large nutrient foramina and has an
oblique dorsal margin. The referred postorbital
(MCN PV10051) is triradiate, forming a slightly
convex dorsocaudal orbital margin, as typical of basal
dinosaurs in general (Sereno 1991; Langer 2004;
Haubold 1991; Tykoski and Rowe 2004), while the
ectopterygoid (MCN PV10049) is composed of a
caudally curved lateral ramus and a ventrally
excavated medial body. The front portion of the
mandible (Figure 3B–I) includes an edentulous
rostral tip and a broad tooth bearing section. Except
for its nearly straight dorsal margin, the tip of the
lower jaw is remarkably similar to that of Silesaurus
opolensis (Dzik 2003). It is laterally striated and
depressed in relation to the rest of the mandible
(Figure 3B–C, E–G), implying that a typical
ornithischian corneous beak (Norman et al. 2004)
was present. Its neural and vascular supply was
provided through a mental foramen (Figure 3B),
hypothesized to be equivalent to the “anterior dentary
foramen” that pierces the jaw at the caudal margin of
the depressed area and leads cranially to a bifurcating
furrow, as seen in the predentary of Lesothosaurus
(Sereno 1991). In two specimens (Figure 3C–F), it is
possible to recognize that the depressed mandibular
rostral portion is formed by a subtriangular separate
ossification, the caudal margin of which extends
obliquely below and above the mental foramen. This
demarcation is not visible in other mandibles
(Figure 3B, G, I), in which the bone is apparently
fused to the dentary. This ossification is considered
homologous to the predentary bone of ornithischians
and its implications are discussed below. The rest of
the lateral surface of the mandible is formed by the
dentary, which bears an irregular row of nutrient
Figure 2. (A), skeletal reconstruction of Sacisaur us agudoensis gen. et sp. nov., with preserved bones on black outline based on Lesothosaurus
diagnisticus. Scale bar ¼20 mm. Individual bones referred to S. agudoensis in lateral (G –G, J– K) and cranial (I) aspects: (B), right maxilla
(MCN PV10050, reversed); (C), partial left hemi-mandible (MCN PV10041, holotype); (D), right scapula (MCN PV10033, reversed); (E),
left ilium (MCN PV10100); (F), left pubes (MCN PV10023); (G), mid-caudal vertebra (MCN PV10 097); (H), distal caudal vertebra (MCN
PV10029); (I), right femur (MCN PV10019); (J), right tibia (MCN PV10020, reversed); (K), indeterminate ungual phalanx (MCN
PV10096). Scale bars ¼10 mm. Abbreviations: afo, antorbital fossa; ct, cranial trochanter; dp, descending process; op, obturator process; pd,
predentary; prz, prezygapophisis.
A Late Triassic dinosauriform from Brazil 3

foramina (Figure 3B – C, E –G). Medially, the meck-
elian groove leads cranially to a sharp ridge, that forms
part of the striated symphysial area of the jaw
(Figure 3I).
The maxilla and most complete dentaries (MCN
PV-10043, PV-10061) referred to Sacisaurus have
about ten and 15 tooth positions, respectively. This
count is smaller than that of most basal dinosaurs
(Colbert 1989; Sereno and Novas 1993; Sereno et al.
1993; Benton et al. 2000), including most
ornithischians (Colbert 1981; Sereno 1991; Haubold
1991; Peng 1992), and closer to the condition of
Pisanosaurus (Casamiquela 1967; Bonaparte 1976)
and Silesaurus (Dzik 2003). Also unlike ornithischians,
the teeth of Sacisaurus are not markedly inset from the
lateral margin of the bearing bones, and the upper
series does not reach the caudal end of the maxilla
(Figure 3A). On the other hand, elements from
Figure 3. Jaw/dental elements referred to Sacisaurus agudoensis gen. et sp. nov. in lateral (A– C, E –G), ventral (D), medial (H – I), and
distal/mesial (J) aspects. (A), right maxilla (MCN PV10050); (B– I), partial left (B, G– H) and right (C– E, G), mandibles, and rostral portion
of partial right mandible (F); (B), MCN PV10041(holotype); (C – D), MCN PV10040; (E– F), MCN PV10061; (G), MCN PV10042; (H),
MCN PV10048 (rostral part not preserved); (I), MCN PV10043; (J), isolated cheek tooth (MCN PV10060). Scale bars: (A– E, G –
I) ¼10 mm, (F), (J) ¼5 mm. Abbreviation: mf, mental foramen; mg, meckelian groove; ms, mandible symphyseal area.
J. Ferigolo & M. C. Langer4

the central to caudocentral part of the series are the
largest (Figure 3A, H – I), a condition regarded as
typical for those dinosaurs (Sereno 1991, 1999; but
see Yates 2003). Maxillary and dentary teeth are
similar in most aspects; no crown has the longitudinal
striations present in Silesaurus (Dzik 2003), but some
bear a rounded eminence extending apically along the
centre of its labial surface (Figure 3H) that is common
to ornithischians (Colbert 1981; Norman et al. 2004).
This is continuous with the cingulum (Figure 3J) that
occurs at the base of the lingual surface (MCN
PV10048, PV10060; Figure 3J), in the position where
a semi-lunar pit might develop due to wear (MCN
PV10053). The tooth crowns are mesiodistally
expanded, so that the distal margin of each element
laterally overlaps the mesial portion of the one behind
(Figure 3H). This gives the impression that the crowns
are constricted by a neck, separating them from the
long (twice the crown length) subcylindrical root, a
condition often considered to diagnose Ornithischia
(Heckert 2004; but see Parker et al. 2005). Teeth on
the rostral part of both maxilla and dentar y are more
slender, and have fainter denticles (possibly due to
wearing) forming oblique angles to the long axis of the
tooth (Figure 3A – I). Their mesial margin is evenly
convex, whereas the distal margin is convex at the
base and concave apically. As a result, their acute (less
than 458) apex is slightly curved caudally. More caudal
teeth are stouter, with prominent cinguli. Their mesial
and distal margins are more expanded at the base and
straight apically, so that the apex forms an angle of
about 908. The denticles are more apparent, and
subparallel to the long axis of the tooth (Figure 3A – I).
From the vertebral column were recovered an
atlantal intercentrum (MCN PV10032) and various
caudal vertebrae (Figure 2G–H). Proximal tail
vertebrae (MCN PV10028) have broad centra as
long as high, with a concave ventral margin in lateral
aspect. The transverse processes are elongated, each
bearing a deep ventral pit along its base, while the
postzygapophyses are raised on the neural spine, as in
various ornithischians (Janensch 1955; He and Cai
1984). Mid-tail vertebrae (MCN PV10097) are
lateromedially compressed, with an axially elongated
fossa below each transverse process, as seen in
ornithischians in general (Galton 1974; Santa Luca
1980). The most remarkable feature of the distal tail
vertebrae (MCN PV10029, PV10090) are their
prezygapophyses, which extend over one third of the
proximally adjacent centrum. The scapular blade
Figure 4. Right femora (A –D) and tibia (E –H) referred to Sacisaurus agudoensis gen. et sp. nov. (A– B, D), MCN PV10019 in (A), cranial;
(B), proximal; and (D), craniolateral (proximal portion) aspects; (C), MCN PV10018 in proximal aspect; (E– G), MCN PV10020 in (E),
lateral; (F), proximal; (G), craniolateral (distal portion), and (H), distal aspects. Scale bars: (A, E) ¼20 mm; (B– C) ¼5 mm; (D, F–
H) ¼10 mm. Arrow in (B –C) points cranially. Abbreviations: aa, articulation of astragalar ascending process; cc, cnemial crest; cf, fibular
crest; ct, cranial trochanter; dlt, dorsolateral trochanter; dp, descending process, fc, fibular condyle; mc, medial condyle.
A Late Triassic dinosauriform from Brazil 5

(Figure 2D) broadens gradually towards its rim, and
forms an angle of more than 908to the acromion. The
more robust ventrocaudal portion of the bone
supports the glenoid, which forms an angle of 458to
the long axis of the blade.
If the pelvic bones assembled from the type-locality
(Figure 2) belong to Sacisaurus, the new taxon
represents one of the three putatively propubic
ornithischians, the others being Pisanosaurus (Sereno
1991) and Silesaurus (Dzik 2003). Its acetabulum is
almost fully closed, with the iliac inner wall forming a
convex ventral margin as in Silesaurus and other basal
dinosauriforms (Novas 1996). The ilium (Figure 2E)
is incomplete, but approaches the morphology of
Silesaurus (Dzik 2003), “Caseosaurus”(Long
and Murry 1995), and poposaurid pseudosuchians
(Galton 1985b; Galton and Walker 1996). It bears a
short preacetabular ala buttressed by a robust ridge
that extends towards the acetabulum. The acetabular
craniodorsal margin is laterally expanded to form a
well-developed crest. The postacetabular ala is much
longer, accounting for nearly half the length of the
bone, and expands distally. The pubis (Figure 2F)
bears well-developed obturator plate and ambiens
process, and the shaft is laminar medially and thicker
at the lateral margin. The ischium (MCN PV10025)
meets its pair for most of the plate-like shaft and its
proximal portion is not ventrally concave as in basal
ornithischians (Sereno 1991; Norman et al. 2004).
Two femoral types with size disparity were excavated
in the type-locality: the larger one is known from two
(left and right) nearly complete bones (MCN
PV10007, PV10008) about 150mm long, whereas 15
right femora of the smaller kind were recovered, nine of
which are almost complete (see referred material).
These morphotypes are believed to represent different
taxa, and the smaller ones are tentatively assigned to
Sacisaurus, based on their matching size to other
skeletal parts. They range from 88 to 103 mm long, and
are typical of basal dinosauriforms (Figures 2I, 4A– D),
as given by their sigmoid shape and head not well set
from the shaft, the long axis of which forms an angle of
about 408to the intercondylar line. The flat proximal
surface of the head has a subtriangular outline, with
nearly straight cranial, craniolateral, and caudomedial
surfaces, and bears a longitudinal groove. This
morphology approaches that of forms such as in
Pseudolagosuchus (Novas 1996), Silesaurus (Dzik 2003),
and Eucoelophysis (Sullivan and Lucas 1999). Some
femora (Figure 4C) have a prominent medial tubero-
sity, as in some basal dinosauriforms and dinosaurs
(Padian 1986; Novas 1996), whereas this structure is
lacking in other specimens (Figure 4B). The ridge-like
dorsolateral ( ¼“greater”) trochanter overhangs
slightly cranially, as seen in basal saurischians (Langer
and Benton 2006), and ornithischians (Sereno 1991).
The small “spike-like” cranial trochanter is separated
from the shaft by a cleft, and a “trochanteric shelf” is
lacking, whereas the small fourth trochanter is
symmetrical and non-pendant. This set of features
resembles the most those seen in the femora of
Guaibasaurus (Bonaparte et al. 1999) and basal
theropods (Welles 1984; Rauhut 2003).
The straight tibia (Figures 2J, 4E–H) has a
subtriangular proximal articulation, with fibular and
medial condyles nearly aligned at the caudal margin.
This is seen in Lagerpeton,Silesaurus,Pisanosaurus,and
other basal dinosaurs (Langer 2004), but not in
Marasuchus (Sereno and Arcucci 1994) or Lesothosaurus
(Thulborn 1972). The cnemial crest is not well-
developed and proximally projected as in most
dinosauriforms (Novas 1996), but resembles those of
basal ornithischians (Thulborn 1972; Bonaparte
1976). A well-developed fibular crest is also present
proximally on the tibia, as seen in Silesaurus (Dzik 2003)
and basal theropods (Padian 1986; Rauhut 2003). The
distal articulation of the tibia has a typically dinosaurian
descending process, as described by Novas (1996), but
also seen in Silesaurus (Dzik 2003). In addition, that
process expands laterally to partially overlap the distal
portion of the fibula, as seen in various theropods
(Welles 1984; Raath 1990), but more markedly in
ornithischians, in which it forms the “outer malleolus”
(Thulborn 1972; Colbert 1981). All recovered ungual
phalanges are non-trenchant (Figure 2K).
Discussion
Phylogenetic relationships of sacisaurus agudoensis
Previous phylogenetic studies (Norman 1984; Sereno
1984, 1986, 1999; Maryanska and Osmo
´lska 1985;
Cooper 1985; Norman et al. 2004) established the
presence of a predentary bone as one of the most
conspicuous syampomorphic features of Ornithischia.
Although dissimilar to the unpaired element of those
dinosaurs, we hypothesize that the pair of bones that
form the mandibular tip of Sacisaur us is its homo-
logue. This suggests the nesting of the new taxon
within the stem of “all dinosaurs closer to Iguanodon
than to Cetiosaurus” (Norman et al. 2004). Addition-
ally, the “anterior dentary foramen” leading cranially
to a bifurcated furrow is otherwise known in
Lesothosaurus (Sereno 1991) and might be another
basis for referring Sacisaurus to Ornithischia.
Ornithischian dental synapomorphies are harder to
define (Gauffre 1993; Heckert 2004), but typical traits
are seen in Sacisaurus. These include: 1—larger teeth
on the caudocentral part of the series (Sereno 1986;
Gauffre 1993); 2—low triangular crowns in lateral
profile (Sereno 1986; Hunt and Lucas 1994); 3—
basal cingulum more expanded lingually, so that the
tooth is asymmetrical in mesial and distal views (Hunt
and Lucas 1994; Norman et al. 2004); 4—carinae
composed of large denticles (Sereno 1986; Hunt and
Lucas 1994). More recently, Parker et al. (2005)
J. Ferigolo & M. C. Langer6

showed that most of the putative ornithischian
synapomorphies based on tooth morphology are not
unique to those dinosaurs among Late Triassic
archosaurs. Of these, only the basal cingulum might
be diagnostic for the group (Parker et al. 2005), a trait
seen in most specimens of Sacisaurus. Other features
reminiscent of the ornithischian condition are seen in
the tibia of Sacisaurus. It shares with Lesothosaurus and
Pisanosaurus a non-proximally expanded cnemial
crest, and an “other malleolus” that projects laterally
and distally to cover most of the caudal margin of the
fibula. The latter feature is seen in most members of
the group (Galton 1974; Colbert 1981), as well as, but
to a lesser degree, in basal theropods and some
sauropodomorphs (Novas 1989; Langer and Benton
2006).
If Sacisaurus is an ornithischian, its basal position is
clear based on various plesiomorphic traits otherwise
unknown in typical members of that dinosaur group,
namely: large antorbital fenestrae, narrow caudal
ramus of maxilla with oblique dorsal margin, small
number of teeth, propubic pelvis, closed acetabulum,
short preacetabular ala of ilium, medially laminated
pubic shaft, knob-like cranial trochanter, and non-
pendant fourth trochanter. The ischium attributed to
Sacisaurus also lacks a typically saurischian rod-like
shaft (Langer 2003, 2004), but other referred material
posses theropod features such as a ventrally excavated
ectopterygoid with a strongly curved jugal process,
long prezygapophises on the distal caudal vertebrae,
and a well-developed fibular flange in the tibia (Sereno
1999; Rauhut 2003). However, a theropod-like
ectopterygoid was described for the sauropodomorph
Thecodontosaurus (Yates 2003), and a fibular crest is
also seen in Silesaurus (Dzik 2003). Indeed, the
distribution of these characters casts doubts upon
their validity as theropod synapomorphies, alluding to
a broader distribution among basal dinosaurs. Alter-
natively, the mosaic of characters seen in Sacisaurus
might point against the association of its skeletal
remains as seen in Figure 2. Accordingly, its inclusion
as such into a numerical phylogenetic analysis is
potentially misleading and was not attempted here.
Regardless of their phylogenetic position, the
resemblance and probable affinity of Sacisaur us and
Silesaurus is clear. This is based on morphological
similarities of not only the front portion of the
mandible and teeth, but also the pelvic and hind limb
bones. The peculiar edentulous and depressed
mandibular tip of both taxa is remarkably similar,
and its equivalence to the predentary may support
their ornithischian affinity, as hinted in the original
description of Silesaurus (Dzik 2003). The mor-
phology of that structure might unite those two taxa
into a clade, but could also represent a preliminary
step towards the acquisition of a typical predentary,
shared as a plesiomorphy by very basal members of the
ornithischian lineage. Other features that could
suggest the affinity of both Sacisaurus and Silesaurus
with the Ornithischia include a large mental foramen
in the rostral portion of the dentary (possibly related
to neural and vascular supply for the corneous beak),
and a well developed “outer malleolus” in the tibia.
Yet, the distal tibia of Silesaurus is more rounded,
whereas those of Sacisaurus and basal ornithischians
more axially compressed (Langer and Benton 2006).
Likewise, in the evolutionary context of dinosauri-
forms with herbivorously-adapted teeth, those of
Sacisaurus seem more coarsely denticulated, and
closer to the ornithischian condition than those of
Silesaurus. The femur of Sacisaurus lacks a “trochan-
teric shelf” but otherwise resembles that of Silesaurus
(Dzik 2003) for its proximally flat and subtriangular
head, which is not well set from the shaft. This is also
seen in Pseudolagosuchus (Novas 1996), implying a
non-dinosaur affinity. The ilia of Sacisaurus and
Silesaurus are also atypical for dinosaurs, but resemble
those of poposaurid rauisuchians (Galton and Walker
1996). Although their ornithosuchian affinity is not
in question, the iliac anatomy might also be a hint
to the basal phylogenetic position of Sacisaurus and
Silesaurus (Langer and Benton 1996) among
dinosauriforms.
Origins of the predentary bone
The predentary is usually considered a neomorphic
feature of ornithischians; i.e. a structure with no
evident equivalence to ordinary organismal traits from
which it could have arisen. In fact, because the bone
was never homologized with skeletal parts of the
outgroups to Ornithischia, its presence has been
regarded as synapomorphic for the group. A homo-
nymous bone was, however, reported to some fossil
birds (Martin 1987, 1991) and both fossil and extant
teleosts—e.g., aspidorhynchids (Brito 1997), ichthyo-
dectids (Bardack and Sprinkle 1969), and istiophorid
sailfishes (Regan 1909; Gregory and Conrad 1937).
Albeit non-homologous in phylogenetic terms, it is
plausible that these bones have a similar ontogenetic
origin, representing the expression of developmental
patterns common to these groups, and therefore to
most vertebrates.
The most peculiar attribute of the predentary is its
unpaired condition. This is very unusual for lower jaw
bones, which are as a rule directly or indirectly
connected to the development of the pair of Meckel’s
cartilages (De Beer 1937). Indeed, if the predentary
origin is linked to the mandibular arch, it almost
certainly derives from the fusion of formerly paired
ossification centres. At least for ornithischians, the
recognition of a paired bone in the rostral tip of some
mandibles attributed to Sacisaurus strengthens that
hypothesis. It is noteworthy that this taxon lived
during the time interval of the early radiation of
dinosaurs and has a suite of plesiomorphic features
A Late Triassic dinosauriform from Brazil 7

indicating its basal phylogenetic position. Hence, it is
possible to envisage an initial stage of ornithischian
evolution in which the predentary was a paired bone.
In this scenario, the single predentary of derived
ornithischians was acquired latter, by the fusion of
those two ossifications. In Sacisaur us, the predentaries
tended to coossify caudally, rather than to its
counterpart at the midline. Of the recovered partial
mandibles, the larger (MNC PV10041) has the
predentary fused to the dentary, but this varies within
the smaller specimens. On the contrary, the single
predentary of ornithischians is never caudally fused,
even in juveniles (Carpenter 1994; Horner and Currie
1994; Hill et al. 2003) and this seems important for the
bone to act as a lower jaw stabilizer during occlusion
(Crompton and Attridge 1986). It is possible, there-
fore, to recognize a paedomorphic component in the
early evolution of ornithischians (Figure 5), regarding
the caudal fusion of the predentary. This would be
characterized by its retention as a separate rostral
mandibular ossification along the life of more derived
forms. Sacisaur us, and perhaps Silesaur us, would
represent an intermediary stage of this paedomorpho-
cline, in which that ossification was separate in
juvenile forms, but eventually fused to the rest of the
jaw in adult individuals.
Various vertebrate groups posses a paired ossifica-
tion at the rostral tip of the mandible. This is termed
the mental, mentomandibular, or more often mento-
meckelian bone, and is better known in some jawed
fishes (Schultze 1993; Grande and Bemis 1998;
Adriaens and Verraes 1998) and lissamphibians
(Trueb 1993; Sheil 1999; Yeh 2002). Less commonly,
a similar element is found in the lower jaws of extant
lizards (De Beer 1937; Jollie 1973) and birds (Baumel
and Witmer 1993). This bone frequently fuses to its
pair and/or to the dentary at the simphyseal area
(Romanoff 1960; Trueb 1993), and is normally
considered to be an ossification of the tip of Meckel’s
cartilage (De Beer 1937; Schultze 1993), although a
different embryologic origin has been proposed for
anurans (Trueb 1993). Mammals lack a mentomeck-
elian bone, but small bilateral ossification centres
referred to as ossicula mentalia are involved in the
formation of their mental-symphyseal region (Testut
and Latarjet 1899; Spalteholz 1965; Radlanski et al.
2003), but rarely remain isolated from the rest of the
jaw (Meckel 1832). These are currently believed to
result from the ossification of either the rostral tip of
Meckel’s cartilage (Rodrı
´guez-Va
´squez et al. 1997) or
other possibly secondary cartilages (Goret-Nicaise
et al. 1984; Hinrichsen 1990; Bareggi et al. 1994).
As acknowledged by Presley (1993) “for any
neomorphic feature some consideration of the
developmental processes by which it could have arisen
is obligatory before using the feature as a phylogenetic
discriminant”. In this context, the recognition of the
ornithischian predentary as derived from the fusion of
originally paired structures allows its comparison to
similar rostral elements in the lower jaw of other
vertebrates. This is particularly the case of the
mentomeckelian, which fits to the topographic criteria
for the definition of homology (Jardine 1969). Indeed,
following the homology concept advocated by
Panchen (1994), the lower jaw symphyseal bones of
various vertebrate groups might represent equivalent
evolutionary units, given that they share a common
developmental origin; even if they are not present as
separate elements in immediate sister taxa of those
groups. Therefore, although synapomorphic for
ornithischians the predentary does not seem to
represent a neomorphic structure of these dinosaurs.
Instead, its homology to the mentomeckelian bone,
and possibly also to parts of the rostral portion of most
vertebrate mandibles, is proposed here. In this case, it
does not correspond to a dermal bone as most of the
lower jaw, but to an ossification preceded by cartilage.
Acknowledgements
The material of Sacisaurus agudoensis was collected by
the crew of FZB/RS during field trips funded by
“Projeto Pro
´-Guaiba”. We thank Ana Maria Ribeiro
for her curatorial assistance, and Adam Yates,
Paul Barrett, Randall Irmis, and Sterling Nesbitt, for
critically reviewing the MS. We are particularly
indebted to R. Irmis and S. Nesbitt for discussing
ideas and providing essential information that deeply
Figure 5. Graphic representation of the two-phase
paedomorphocline suggested for the early evolution of
ornithischians. Lower jaw reconstructions (in oclusal aspect) based
on Galton (1984) for Plateosaurus,Sereno(1991)forLesothosaurus,
Dzik (2003) for Silesaurus, and MCN PV10044 for Sacisaurus.
J. Ferigolo & M. C. Langer8

improved this paper. MCL acknowledges the financial
support granted by the Brazilian agency FAPESP. We
also thank colleague Marcelo Trotta, who shared with
us his insightful idea for the generic name.
References
Abdala F, Barberena MC, Dornelles JF. 2002. A new species of the
traversodontid cynodont Exaeretodon from the Santa Maria
Formation, Middle/Late Triassic) of southern Brazil. J
Vertebrate Paleontol 22:313 –325.
Adriaens D, Verraes W. 1998. Ontogeny of the osteocranium in the
African catfish, Clarias gariepinus (Burchell, 1822) (Siluriformes:
Clariidae): ossification sequence as a response to functional
demands. J Morphol 235:183–237.
Andreis RR, Bossi GE, Montardo DK. 1980. O Grupo Rosa
´rio do
Sul, Tria
´ssico) no Rio Grande do Sul. XXXI Congresso
Brasileiro de Geologia (Camboriu
´). Anais 2:659–673.
Baez AM, Marsicano C. 2001. A heterodontosaurid ornithischian
dinosaur from the Upper Triassic of Patagonia. Ameghiniana
38:271– 279.
Bardack D, Sprinkle G. 1969. Morphology and relationships of
saurocephalid fishes. Fieldiana Geol 16:297–340.
Bareggi R, Narducci P, Grill V, Sandrucci MA, Bratina F. 1994.
On the presence of a secondary cartilage in the mental
symphyseal region of human embryos and fetuses. Surg Radiol
Anat 16:379– 384.
Barsbold R. 1979. Opisthopubic pelvis in the carnivorous dinosaurs.
Nature 279:792– 793.
Baumel JJ, Witmer LM. 1993. Osteologia. In: Baumel JJ, editor.
Handbook of Avian Anatomy: Nomina Anatomica Avium.
Cambridge: Publications of the Nuttall Ornithological Club.
p 45–132.
Benton MJ, Juul L, Storrs GW, Galton PM. 2000. Anatomy and
systematics of the prosauropod dinosaur Thecodontosaur us
antiquus from the upper Triassic of southern England. J
Vertebrate Paleontol 20:77 –108.
Bonaparte JF. 1976. Pisanosaurus mertii Casamiquela and the origin
of the Ornithischia. J Paleontol 50:808–820.
Bonaparte JF, Ferigolo J, Ribeiro AM. 1999. A new Early Late
Triassic saurischian dinosaur from Rio Grande do Sul State,
Brazil. National Sci Museum Monogr 15:89 –109.
Bonaparte JF, Ferigolo J, Ribeiro AM. 2001. A primitive Late
Triassic ‘ictidosaur’ from Rio Grande do Sul, Brazil. Palaeonto-
logy 44:623– 635.
Bonaparte JF, Martinelli AG, Schultz CL, Rubert R. 2003. The sister
group of mammals: small cynodonts from the Late Triassic of
Southern Brazil. Revista Brasileira de Paleontologia 5:5–27.
Bonaparte JF, Martinelli AG, Schultz CL. 2005. New information
on Brasilodon and Brasilitherium (Cynodontia, Probainogathia)
from the Late Triassic, southern Brazil. Revista Brasileira de
Paleontologia 8:25– 46.
Brito PM. 1997. Re
´vision des Aspidorhynchidae (Pisces Actino-
pterygii) du Me
´sozoı¨que: oste
´ologie, relations phyloge
´ne
´tiques,
donne
´s environnementales et bioge
´pgraphiques. Geodiversitas
19:681– 772.
Butler RJ. 2005. The ‘fabrosaurid’ ornithischian dinosaurs of the
upper Elliot Formation (Lower Jurassic) of South Africa and
Lesotho. Zoo J Linn Soc 145:175– 218.
Carpenter K. 1994. Baby Dryosaurus from the Upper
Jurassic Morrison Formation of Dinosaur National Monument.
In: Carpenter K, Hirsch KF, Horner JR, editors. Dinosaur eggs
and babies. Cambridge: Cambridge University Press. p
288– 297.
Casamiquela RM. 1967. Un nuevo dinosaurio ornitisquio Tria
´sico
(Pisanisaurus mertii; Ornithopoda) de la Formacio
´n Ischigual-
asto, Argentina. Ameghiniana 4:47– 64.
Chatterjee S. 1984. A new ornithischian dinosaur from the Triassic
of North America. Naturwissenschaften 71:630 –631.
Colbert EH. 1981. A primitive ornithischian dinosaur from the
Kayenta Formation of Arizona. Bull Museum of Northern
Arizona 53:1–61.
Colbert EH. 1989. The Triassic dinosaur Coelophysis. Bull Museum
of Northern Arizona 57:1 – 160.
Cooper MR. 1985. A revision of the ornithischian dinosaur
Kangnasaurus coetzeei Haughton, with a classification of the
Ornithischia. Ann South African Museum 95:281 – 317.
Cope ED. 1869. Synopsis of the extinct Batrachia, Reptilia, and
Aves of North America. Trans Am Philos Soc 14:1 –252.
Crompton AW, Attridge J. 1986. Masticatory apparatus of the larger
herbivores during Late Triassic and Early Jurassic times. In:
Padian K, editor. The beginning of the age of dinosaurs.
Cambridge: Cambridge University Press. p 223–236.
Cuny G, Hunt A, Mazin J-M, Rauscher R. 2000. Teeth of enigmatic
neoselachian sharks and an ornithischian dinosaur from the
uppermost Triassic of Lons-le-Saunier (Jura, France). Pala¨onto-
logische Zeitschrift 74:171–185.
De Beer GR. 1937. The development of the vertebrate skull.
Oxford: Oxford University Press.
Dzik J. 2003. A beaked herbivorous archosaur with dinosaur
affinities from the Early Late Triassic of Poland. J Vertebrate
Paleontol 23:556– 574.
Galton PM. 1974. The ornithischian dinosaur Hypsilophodon from
the Wealden of the Isle of Wight. Bull Br Museum Nat Hist
(Geol) 25:1–152.
Galton PM. 1983. The oldest ornithischian dinosaur in
NorthAmericafromtheLateTriassicofNovaScotia,
North Carolina and Pennsylvania. Geol Soc Am, Abstr
Programs 15:122.
Galton PM. 1984. Cranial anatomy of the prosauropod dinosaur
Plateosaurus from the Knollenmergel (Middle Keuper, Upper
Triassic) of Germany. I. Two complete skulls from Trossingen/
wu
¨rtt. with comments on the diet. Geologica et Palaeontologica
18:139– 171.
Galton PM. 1985a. Diet of prosauropod dinosaurs from the Late
Triassic and Early Jurassic. Lethaia 18:105– 123.
Galton PM. 1985b. The poposaurid thecodontian Teratosaurus
suevicus v. Meyer, plus referred specimens mostly based
on prosauropod dinosaurs, from the Middle Stubensandstein
(Upper Triassic) of Nordwu
¨rttemberg. Stuttgarter Beitra¨ge
zur Naturkunde (series B—Geologie und Pala¨ ontologie)
116:1–29.
Galton PM, Walker AD. 1996. Bromsgroveia from the
Middle Triassic of England, the earliest record of a poposaurid
thecodontian reptile (Archosauria: Rauisuchia). Neues
Jahrbuch fu
¨rGeologieundPala¨ontologie, Abhandlung
201:303–325.
Gauffre F-X. 1993. The prosauropod dinosaur Azendohsaurus
laaroussi from the Upper Triassic of Marocco. Palaeontology
36:897– 908.
Gauthier J. 1986. Saurischian monophyly and the origin of birds.
Memoirs of the Californian Academy of Sciences 8:1 – 55.
Godefroit P, Cuny G. 1997. Archosauriform teeth from the Upper
Triassic of Saint-Nicolas-de-Port (Northeastern France).
Palaeovertebrata 26:1– 34.
Goret-Nicaise M, Lengele B, Dhem A. 1984. The function of
Meckel’s and secondary cartilages in the histomorphogenesis of
the cat mandibular symphysis. Archives D’Anatomie Micro-
scopique et de Morphologie Experimentale 73:291 –303.
Grande L, Bemis WE. 1998. A comprehensive phylogenetic study of
amiid fishes (Amiidae) based on comparative skeletal anatomy.
An empirical search for interconnected patterns of natural
history. Soc Vertebrate Paleontol Mem 4:1–690.
Gregory WK, Conrad GM. 1937. The comparative osteology of the
swordfish (Xiphias) and the sailfish (Istiophorus). Am Museum
Novitates 952:1– 25.
A Late Triassic dinosauriform from Brazil 9

Haubold H. 1991. Ein neuer Dinosauria (Ornithischia, Thyreo-
phora) aus dem unteren jura des no¨ rdlichen Mitteleuropa.
Revue de Pale
´obiologie 9:149–177.
He X, Cai K. 1984. The Middle Jurassic Dinosaurian Fauna from
Dashanpu,Ziogong,Sichuan.Vol.1.TheOrnithipod
Dinosaurs. Sichuan Scientific and Technological Publishing
House.
Heckert AB. 2004. Late Triassic microvertebrates from the lower
Chinle Group (Otischalkian– Adamanian:Carnian), south-
western U.S.A. New Mexico Museum Nat Hist, Bull 27:1–170.
Hill RV, Witmer LM, Norell MA. 2003. A new specimen of
Pinacosaurus grangeri (Dinosauria: Ornithischia) from the Late
Cretaceous of Mongolia: ontogeny and phylogeny of Ankylo-
saurs. Am Museum Novitates 3395:1– 29.
Hinrichsen KV. 1990. Humanembryologie. Berlin: Springer.
Horner JR, Currie PJ. 1994. Embryonic and neonatal morphology
and ontogeny of a new species of Hypacrosaurus (Ornithischia,
Lambeosauridae) from Montana and Alberta. In: Carpenter K,
Hirsch KF, Horner JR, editors. Dinosaur eggs and babies.
Cambridge: Cambridge University Press. p 312–336.
Hunt AP, Lucas SG. 1994. Ornithischian dinosaurs from the Upper
Triassic of the UnitedStates. In: Fraser NC, Sues H-D, editors. In
the shadow of the dinosaurs. Cambridge: Cambridge University
Press. p 227–241.
Hutchinson J, Chiappe LM. 1998. The first alvarezsaurid
(Theropoda: Aves) from North America. J Vertebrate Paleontol
18:447– 450.
Irmis RB, Parker WG, Nesbitt SJ, Liu J. 2006. Early ornithischian
dinosaurs: the Triassic record. Historical Biol (this volume).
Jalil N-E, Knoll F. 2002. Is Azendohsaurus laaroussii (Carnian,
Morocco) a dinosaur? J Vertebrate Paleontol 22(suppl. to
number 3): 70A.
Janensch W. 1955. Der Ornithopode Dysalotosaurus der Tenda-
guruschichten. Palaeontographica (suppl. 7) 1:105–176.
Jardine N. 1969. The observational components of homology:
a study based on the morphology of the dermal skull-roofs of
rhipidistan fishes. Biol J Linn Soc 1:327– 361.
Jollie M. 1973. Chordate morphology. New York: Robert Krieger
Publishing Company Inc.
Knoll F. 2002. A nearly complete skull of Lesothosaurus (Dinosauria:
Ornitischia) from the Upper Ellitot Formation (Lower Jurassic)
of Lesotho. J Vertebrate Paleontol 22:238– 243.
Langer MC. 2003. The sacral and pelvic anatomy of the stem-
sauropodomorph Saturnalia tupiniquim (Late Triassic, Brazil).
Paleobios 23:1– 40.
Langer MC. 2004. Basal Saurischians. In: Weishampel DB, Dodson
P, Osmo
´lska H, editors. The Dinosauria (second edition).
Berkeley: University of California Press. p 25 – 46.
Langer MC. 2005a. Studies on continental Late Triassic tetrapod
biochronology. I. The type locality of Saturnalia tupiniquim and
the faunal succession in south Brazil. J South Am Earth Sci
19:205– 218.
Langer MC. 2005b. Studies on continental Late Triassic tetrapod
biochronology. II. The Ischigualastian and a Carnian global
correlation. J South Am Earth Sci 19:219 – 239.
Langer MC, Benton MJ. 2006. Early dinosaurs: a phylogeneti study.
J Syst Palaeontol, in press.
Long JA, Murry PA. 1995. Late Triassic (Carnian and Norian)
tetrapods from the Southwestern United States. Bull New
Mexico Museum Nat Hist Sci 4:1–254.
Marsh OC. 1894. The typical Ornithopoda of the American
Jurassic. Am J Sci, series 3, 48:85 –90.
Martin L. 1987. The beginnings of the modern avian radiation.
In: Mourer-Chauvire C, editor. L’evolution des oiseaux d’apre
`s
le te
´moignage des fossils. Lion: Universite
´Claude-Bernard.
p 177– 183.
Martin L. 1991. Mesozoic birds and the origin of birds. In: Schultze
H-P, Trued L, editors. Origins of the higher groups of Tetrapods.
Comstock: Cornell University Press. p 485 –540.
Maryanska T, Osmo
´lska H. 1985. On ornithischian phylogeny. Acta
Palaeontologica Polonica 30:137– 150.
Meckel JF. 1832. Manual of general, descriptive and pathological
anatomy. Philadelphia: Carey and Lea.
Norman DB. 1984. A systematic reappraisal of the reptile order
Ornithischia. III Symp Mesozoic Terrestrial Ecosystems, Short
Papers 1:157– 162.
Norman DB, Witmer LM, Weishampel DB. 2004. Basal
Ornithischia. In: Weishampel DB, Dodson P, Osmo
´lska H,
editors. The Dinosauria (second edition). Berkeley: University
of California Press. p 325–334.
Novas FE. 1989. The tibia and tarsus in Herrerasauridae
(Dinosauria, incertae sedis) and the origin and evolution of the
dinosaurian tarsus. J Paleontol 63:677–690.
Novas FE. 1992. Phylogenetic relationships of the basal dinosaurs,
the Herrerasauridae. Palaeontology 35:51–62.
Novas FE. 1996. Dinosaur monophyly. J Ver tebrate Paleontol
16:723– 741.
Ostrom JH. 1976. Archaeopteryx and the origin of birds. Biol J Linn
Soc 8:91–182.
Owen R. 1842. Report on British fossil reptiles. Part II. Reports of the
British Association for the Advancement of Science 11:60 – 204.
Padian K. 1986. On the type material of Coelophysis Cope
(Saurischia: Theropoda) and a new specimen from the Petrified
Forest of Arizona (Late Triassic: Chinle Formation). In: Padian
K, editor. The beginning of the age of dinosaurs. Cambridge:
Cambridge University Press. p 45–60.
Panchen AL. 1994. Richard Owen and the concept of homology. In:
Hall BK, editor. Homology, the hierarchical basis of comparative
biology. San Diego: Academic Press. p 21 –62.
Parker WG, Irmis RB, Nesbitt SJ, Martz JW, Browne LS. 2005. The
Late Triassic pseudosuchian Revueltosaurus callenderi and its
implications for the diversity of early ornithischian dinosaurs.
Proc R Soc B 272:963–969.
Peng G. 1992. Jurassic ornithopod Agilisaurus louderbacki (Ornitho-
poda: Fabrosauridae) from Zigong, Sichuan, China. Vertebrata
PalAsiatica 30:39– 53.
Presley R. 1993. Preconception of adult structural pattern in the
analysis of the developing skull. In: Hanken J, Hall BK, editors.
The skull, volume 1: development. Chicago: Chicago University
Press. p 347– 377.
Raath M. 1990. Morphological variation in small theropods and its
meaning in systematics: evidence from Syntarsus rhodesiensis.
In: Carpenter K, Currie PJ, editors. Dinosaur systematics.
Approaches and perspectives. Cambridge: Cambridge University
Press. p 91– 105.
Radlanski RJ, Renz H, Klarkowski MC. 2003. Prenatal develop-
ment of the human mandible; 3D reconstructions, morphometry
and bone remodelling patter n, sizes 12 – 117 mm CRL. Anat
Embryol 207:221 –232.
Rauhut OWM. 2003. The interrelationships and evolution of basal
theropod dinosaurs. Special Pap Palaeontol 69:1– 213.
Regan CT. 1909. On the anatomy and classification of the
scombroid fishes. Ann Mag Nat Hist 8(III):66– 75.
Rodrı
´guez-Va
´squez JF, Me
´rida-Velasco JR, Me
´rida-Velasco JA,
Sa
´nchez-Montesinos I, Espı
´n-Ferra J, Jime
´nez-Collado J. 1997.
Development of Meckel’s cartilage in the symphyseal region in
man. Anat Rec 249:249–254.
Romanoff AL. 1960. The avian embryo. New York: MacMillan
and Co.
Rubert RR, Schultz CL. 2004. Um novo horizonte decorrelac¸a
˜o para
o Tria
´ssico Superior do Rio Grande do Sul. Pesquisas 31:71– 88.
Santa Luca AP. 1980. The postcranial skeleton of Heterodontosaurus
tucki (Reptilia, Ornithischia) from the Stormberg of South
Africa. Ann South African Museum 79:15 – 211.
Schultze H-P. 1993. Patterns of diversity in the skulls of Jawed
fishes. In: Hanken J, Hall BK, editors. The skull, volume 1:
patterns of structural and systematic diversity. Chicago: Chicago
University Press. p 189–254.
J. Ferigolo & M. C. Langer10

Seeley HG. 1887. On the classification of the fossil animals
commonly named Dinosauria. Proc R Soc Lond 43:165 –171.
Sereno PC. 1984. The phylogeny of the Ornithischia: A reappraisal.
III Symposium on Mesozoic Terrestrial Ecosystems Short
Papers 1:219– 226.
Sereno PC. 1986. Phylogeny of the bird-hipped dinosaurs (order
Ornithischia). National Geographic Res 2:234 –256.
Sereno PC. 1991. Lesothosaurus, “fabrosaurids”, and the early
evolution of Ornithischia. J Vertebrate Paleontol 11:168–197.
Sereno PC. 1999. The evolution of dinosaurs. Science
284:2137– 2147.
Sereno PC, Arcucci AB. 1994. Dinosaurian precursors from
the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov.
J Vertebrate Paleontol 14:53 –73.
Sereno PC, Novas FE. 1993. The skull and neck of the basal
theropod Herrerasaurus ischigualastensis. J Vertebrate Paleontol
13:451– 476.
Sereno PC, Forster CA, Rogers RR, Monetta AM. 1993. Primitive
dinosaur skeleton from Argentina and the early evolution of the
Dinosauria. Nature 361:64–66.
Sheil CA. 1999. Osteology and skeletal development of Pyxicephalus
adspersus (Anura: Ranidae: Ranidae). J Morphol 240:49 –75.
Spalteholz W. 1965. Atlas de Anatomia Humana. Vol. 1. Barcelona:
Editorial Labor.
Sullivan RM, Lucas SG. 1999. Eucoelophysis baldwini, a new theropod
dinosaur from the Upper Triassicof New Mexico, and thestatus of
the original types of Coelophysis. J Vertebrate Paleontol 19:81– 90.
Testut L, Latarjet A. 1899. Traite
´d’Anatomie Humaine. Paris:
Mason.
Thulborn RA. 1972. The post-cranial skeleton of the Triassic
ornithischian dinosaur Fabrosaurus australis. Palaeontology
15:29–60.
Trueb L. 1993. Patterns of diversity in the Lissamphibian skull. In:
Hanken J, Hall BK, editors. The skull, volume 1: patterns of
structural and systematic diversity. Chicago: Chicago University
Press. p 255– 343.
Tykoski RS, Rowe T. 2004. Ceratosauria. In: Weishampel DB,
Dodson P, Osmo
´lska H, editors. The Dinosauria (second
edition). Berkeley: University of California Press. p 517 – 606.
Yates AM. 2003. A new species of the primitive dinosaur
Thecodontosaurus (Saurischia: Sauropodomorpha) and its implica-
tions for the systematics of earlydinosaurs. J SystPaleontol 1:1– 42.
Yeh J. 2002. The evolution of development: two portraits of skull
ossification in pipoid frogs. Evolution 56:2484– 2498.
Weishampel DB, Young L. 1996. Dinosaurs of the East Coast.
Baltimore: Johns Hopkins University Press.
Weishampel DB, Barrett PM, Coria RA, Le Loeuff J, Xu X, Zhao X,
Shani A, Gomani EMP, Noto CR. 2004. Dinosaur distribution.
In: Weishampel DB, Dodson P, Osmo
´lska H, editors.
The Dinosauria (second edition). Berkeley: University of
California Press. p 517–606.
Welles SP. 1984. Dilophosaurus wetherilli (Dinosauria, Theropoda).
Osteology and comparisons. Palaeontographica 185:85– 180.
Zerfass H, Lavina EL, Schultz CL, Garcia AGV, Faccini UF,
Chemale F Jr. 2003. Sequence stratigraphy of continental
Triassic strata of southernmost Brazil: a contribution to
Southwestern Gondwana palaeogeography and palaeoclimate.
Sediment Geol 161:85–105.
A Late Triassic dinosauriform from Brazil 11