A NEW TRAVERSODONTID CYNODONT
(THERAPSIDA, EUCYNODONTIA) FROM THE
MIDDLE TRIASSIC SANTA MARIA FORMATION OF
RIO GRANDE DO SUL, BRAZIL
by MIRIAM REICHEL* , CESAR LEANDRO SCHULTZ� and
MARINA BENTO SOARES�*Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 1K7, Canada; e-mail: [email protected]
�Instituto de Geociencias – UFRGS, Universidade Federal do Rio Grande do Sul, Avenida Bento Goncalves, 9500. CEP 91509-900, Porto Alegre, RS, Brazil;
e-mail: [email protected]
�Instituto de Geociencias – UFRGS, Universidade Federal do Rio Grande do Sul, Avenida Bento Goncalves, 9500. CEP 91509-900, Porto Alegre, RS, Brazil;
e-mail: [email protected]
Typescript received 9 May 2008; accepted in revised form 17 September 2008
Abstract: Remains of a peculiar traversodontid cynodont,
Protuberum cabralensis gen. et sp. nov., are described herein.
The material was collected from two outcrops representing
the Therapsid Cenozone (Middle Triassic) of the Santa
Maria Formation, and consists of a cranium with most of
its dentition preserved and an associated postcranial skele-
ton. The upper postcanines have two sharp cusps that are
connected by a medial crest on unworn postcanines. The
specimens possess several autapomorphies, including: (1)
presence of thickened bone on the dorsal surface of the
skull; (2) thick dorsal ribs, with remarkable processes situ-
ated on their dorsal borders that decrease in size distally;
and (3) an iliac blade with a series of rugosities along its
dorsal border. The lumbar ribs bear overlapping costal
plates and have distally projecting rib shafts that differ from
the pattern observed in Thrinaxodon, Pascualgnathus and
Cynognathus.
Key words: traversodontid, protuberances, Santa Maria
Formation, Therapsid Cenozone, Middle Triassic, Brazil.
The family Traversodontidae (Therapsida, Eucynodon-
tia) was established by von Huene (1936) and is one of
the best known and most widespread families of non-
mammalian cynodonts. Members of this family occur in
rocks of Middle to Upper Triassic age from Africa
(Crompton 1972a; Kemp 1980; Gow and Hancox 1993;
Flynn et al. 2000), Asia (Chatterjee 1982), South America
(Bonaparte 1962; Romer 1967; Barberena 1981a, b;
Abdala et al. 2002; Abdala and Ribeiro 2002, 2003), North
America (Hopson 1984; Sues and Olsen 1990; Sues et al.
1992, 1994, 1999) and Europe (Tatarinov 1973; Hahn
et al. 1988; Godefroit and Battail 1997). The broad geo-
graphical and temporal distribution of this clade suggests
that it represents a successful adaptive radiation that may
have been facilitated by the development of many special-
ized features (e.g. precise dental occlusion).
The traversodontids were diverse herbivores that can be
characterized by their specialized dental morphology. The
postcanines are transversely enlarged in occlusal view,
providing the upper ones with a rectangular outline and
the lower ones with a square outline. This structure
allowed precise dental occlusion that resembles the pat-
tern observed in most mammals in some respects. The
external crest functioned to shear food items, while the
internal basin facilitated crushing. This dental configura-
tion of traversodontids represents an important evolu-
tionary step, representing a great improvement in terms
of food processing (Hopson 1984). Although travers-
odontids possess many derived (and mammal-like) fea-
tures, details of their teeth indicate that this family is not
close to mammalian origins (Hopson and Kitching 2001;
Rowe 1988; Luo 1994; Luo and Wible 2005).
There are no specific postcranial characteristics that
diagnose traversodontids that are not known in other
non-mammalian cynodonts, but this may reflect the poor
fossil record of their rather conservative postcranial skele-
tons. Rib specializations are known in some cynodonts
(Brink 1955; Jenkins 1971) and some mammaliaforms
(Ji et al. 2006), but these specialized features are not diag-
nostic of traversodontids and are also present in widely
variable forms in galesaurids, cynognathids and dia-
demodontids (Jenkins 1970). The presence of a series of
[Palaeontology, Vol. 52, Part 1, 2009, pp. 229–250]
ª The Palaeontological Association doi: 10.1111/j.1475-4983.2008.00824.x 229
processes along the ribs represents a remarkable feature of
the new cynodont taxon described herein: much needed
anatomical data on other parts of the cynodont postcrani-
um are also provided by this new taxon.
MATERIALS
The new taxon is based on specimens collected by Father
Daniel Cargnin at two outcrops in the state of Rio
Grande do Sul, southern Brazil (Text-fig. 1). Some pecu-
liar ribs and vertebrae were found in the Municipality of
Paraıso do Sul in 1977, in a taphocoenosis comprising
specimens of several taxa, including cynodonts (Masseto-
gnathus ochagaviae and Probelesodon kitchingii) and dic-
ynodonts (Dinodontosaurus sp.). In 1989, Father Cargnin
collected part of an articulated skeleton with the associ-
ated skull from an outcrop located in the Municipality of
Novo Cabrais. This specimen is housed at the Guido
Borgomanero Museum in Mata (Rio Grande do Sul).
The specimen from Novo Cabrais includes articulated
vertebrae and ribs. A skull and some additional thoracic
ribs were associated with the specimen. The vertebrae are
poorly preserved, but their general features can be
described. The cranium is also poorly preserved, with the
exception of the dentition. The specimen from Paraıso do
Sul is better preserved but, consists of only a few isolated
elements.
GEOLOGICAL SETTING
The holotype of Protuberum cabralensis (MGB 368 ⁄ 100)
was collected from the ‘Sıtio Cortado’ outcrop (S
29�44¢54.4¢¢ W 53�01¢49.4¢¢: Text-fig. 1), located in the
municipal district of Novo Cabrais. The paratypes were
collected from the ‘Rincao do Pinhal’ outcrop (S
29�43¢14.8¢¢ W 53�13¢46.8¢¢; Text-fig. 1) in the municipal
district of Paraıso do Sul. Both outcrops are composed of
thin layers (each only a few centimetres thick) of red
massive mudstones that alternate with amalgamated len-
ticular bodies of fine sandstones. Two layers of carbonate
concretions were described by Da Rosa et al. (2004) in
the former outcrop. These lithologies are typical of the
Alemoa Member of the Santa Maria Formation (Schultz
et al. 2000).
The tetrapod fauna of the Santa Maria Formation has
been divided into four biostratigraphic units (Text-fig. 2).
The lowermost, which includes the two outcrops yeilding
Protuberum material, represents the Ladinian aged Therap-
sid Cenozone (Rubert and Schultz 2004), and is dominated
by the herbivorous dicynodont Dinodontosaurus, with
TEXT -F IG . 1 . Map showing location
of the outcrops. Key to localities: 1, Sıtio
Cortado. 2, Rincao do Pinhal.
230 P A L A E O N T O L O G Y , V O L U M E 5 2
some occurrences of the cynodonts Massetognathus and
Probelesodon.
Institutional abbreviations. MCP, Museu de Ciencias e Tecnolo-
gia da Pontifıcia Universidade Catolica, Porto Alegre; MGB,
Museu Guido Borgomanero, Mata; UFRGS, Universidade Fed-
eral do Rio Grande do Sul, Porto Alegre.
SYSTEMATIC PALAEONTOLOGY
THERAPSIDA Broom, 1905
CYNODONTIA Owen, 1861
EUCYNODONTIA Kemp, 1982
TRAVERSODONTIDAE von Huene, 1936
Genus PROTUBERUM gen. nov.
Etymology. The generic name refers to the numerous protuber-
ances present on the ribs and ilia.
Diagnosis. As for the type and only species.
Protuberum cabralensis sp. nov.
Etymology. In reference to the Municipality of Novo Cabrais
where the holotype was collected.
Holotype. MGB 368 ⁄ 100, a skull with most of its dentition but
lacking the lower jaw and an articulated series of 19 vertebrae
(two cervicals?, nine thoracics, five lumbar and three sacral)
including four articulated thoracics, 10 lumbar ribs (five from
each side) and four sacral ribs (two from each side), a fragment
of the left ilium and seven isolated thoracic ribs.
Paratypes. The paratypes are represented by (1) UFRGS PV
0981T, a proximal fragment of a right cervical rib; (2) UFRGS
PV 0983T, an isolated vertebra; (3) UFRGS PV 0985T, an isolated
vertebra; (4) UFRGS PV 0986T, an isolated vertebra; (5) UFRGS
PV 1009T, a left cervical rib; (6) UFRGS PV 1010T, a left tho-
racic rib; and (7) UFRGS PV 1011T, a fragment of a thoracic rib.
Diagnosis. Protuberum is a large traversodontid in which
the upper postcanines have two main cusps (one labial
and one lingual) that are connected by a sharp transverse
crest. As in Luangwa, Pascualgnathus, Scalenodon, Andes-
cynodon and Traversodon, the postcanines of Protuberum
lack the shouldering pattern (in which the mesial of one
tooth ‘shoulders’ into the proper area of the preceeding
tooth) observed in Massetognathus and Exaeretodon. The
paracanine fossae are anteroposteriorly elongated and pos-
teriorly placed in relation to the upper canine. This fea-
ture is also present in Exaeretodon and Scalenodontoides.
The parietal crest is short, as in Scalenodontoides
macrodontes (Gow and Hancox 1993). Protuberum has
well-developed masseteric processes of the jugals, as in
Exaeretodon. The paraoccipital process is bifurcated in
Protuberum, as in tritylodontids, brasilodontids (Bona-
parte et al. 2005) and some early mammals (Kermack
et al. 1981; Crompton and Luo 1993), in contrast to the
unbifurcated condition present in other traversodontids.
Autapomorphies observed in the skull include: (1) incisive
foramina totally enclosed by the maxillae; and (2) a bony
thickening that forms wide crests on the dorsal surface
of the skull. The postcranium of Protuberum is robust and
the contacts between lumbar vertebrae, as well as between
the lumbar vertebrae and ribs, are very strong. The lum-
bar ribs of Protuberum have costal plates that differ from
those in Thrinaxodon, Pascualgnathus and Cynognathus, as
rib shafts are situated distal to all of the costal plates in
the new taxon. Other postcranial autapomorphies are: (1)
all ribs show very pronounced processes on their dorsal
border, the most proximal of these is generally the largest
and the others become smaller distally; and (2) the iliac
blade has a series of rugosities along its dorsal border.
Description
Cranium
The type specimen, MGB 368 ⁄ 100, includes an almost complete
cranium (Text-figs 3–10), with the right quadrate and
TEXT -F IG . 2 . Stratigraphic correlations between Brazil and
Argentina for the Middle–Upper Triassic. Modified from Rubert
and Schultz (2004), and Schultz and Soares (2006).
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 231
A
B
232 P A L A E O N T O L O G Y , V O L U M E 5 2
quadratojugal preserved in their original positions and with
most of the upper dentition present; the right postorbital bar
and the lower jaws were not preserved. The cranium is some-
what distorted, especially in its dorsal portion. The total cranial
length (from the anterior border of the premaxilla to the con-
dyles) is approximately 200 mm, while the parietal crest mea-
sures about 15 mm, representing only 7.5 per cent of the
length of the cranium.
The cranium is heavily built, with thick bones in the preor-
bital region and in the lambdoid crests. The short parietal crest
is high and the temporal openings are wide. The occiput is
exposed in dorsal view with posteriorly projecting occipital con-
dyles. The internarial process of the premaxilla is not present, so
that the external naris is a single and confluent opening.
The canines are reduced in size, when compared to the pro-
portions observed in Exaeretodon. The incisors (which are of
similar size to the canines) and postcanines are slightly procum-
bent. In palatal view, the postcanine rows diverge posteriorly.
Facial region. The rostrum is short and wide. The anterodorsal
surfaces of the premaxillae are very similar to those of Exaereto-
don (Bonaparte 1962) as an ossified internarial process is absent
in both taxa. In Protuberum, however, there is no relict of a
conic appendix, in contrast to the condition in Exaeretodon
(Bonaparte 1962). The anterior margin of the premaxillae is
broad and the opening of the external naris is wide (Text-fig. 5).
The maxillary process of the premaxilla (Text-fig. 6A) is reduced
(it does not reach the nasals), as also occurs in Massetognathus
(Romer 1967) and Exaeretodon.
The margins of the maxillae are unclear, especially on the dor-
sal part of the cranium. In lateral view (Text-fig. 6), a depression
can be observed adjacent to the dorsal border of the maxilla.
A wide foramen is present near the anterior margin of the
maxilla, above the canine. The septomaxillary foramen, which
should be immediately dorsal to this foramen, is not preserved.
Another maxillary foramen opens lateral to the third postcanine.
The facial process of the septomaxilla (Text-fig. 6A) is well
TEXT -F IG . 3 . The skull of Protuberum cabralensis (MGB 368 ⁄ 100). A, dorsal, and B, palatal views. Scale bar represents 50 mm.
A
B
TEXT -F IG . 4 . The skull of Protuberum
cabralensis (MGB 368 ⁄ 100). A, lateral,
and B, occipital views. Scale bar
represents 50 mm.
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 233
developed in Protuberum. Its subtriangular shape is similar to
that of Exaeretodon (Bonaparte 1962). The premaxillae partici-
pate in the formation of the posterior and ventral borders of the
narial opening.
The margins of the nasals are not clear. Their middle portion
is constricted at the level of the paracanine fossae, forming a
bony thickening that is developed as an anteriorly directed ‘V’
shaped crest (Text-fig. 5). This crest continues posterolaterally
along the prefrontals and postorbitals, and connects with the dor-
sal margin of the orbit. The crest is symmetrical and well-defined
and is unlikely to be the result of post-mortem deformation.
Palate. Each premaxilla contains three incisors. The canine is
placed near the anterior border of the maxilla and only a small
space is present between the canine and the posteriormost inci-
sor, as also occurs in Exaeretodon (Bonaparte 1962), Massetogna-
thus (Romer 1967) and Probainognathus (Romer 1970). The
premaxillae participate in the borders of the incisive foramina
(Text-fig. 7), which are placed near the anteromedial border of
the maxillae and are totally enclosed by them. This feature has
not been observed in other traversodontids, but is present in
Diademodon (Brink 1955). The paracanine fossae (Text-fig. 7)
are positioned posterior to the canines (a feature observed in
only two other traversodontids: Exaeretodon and Scalenodon-
toides; see Abdala and Ribeiro 2003) and are deep and antero-
posteriorly elongate.
A marked ridge separates the dorsal depression of the maxillae
from their ventral surface. This ridge corresponds to the upper
limit of the area described as a maxillary bulge by von Huene
(1935–1942). This maxillary bulge is quite well developed in Pro-
tuberum, as in other traversodontids, with an accentuated lateral
ridge on the maxillae.
The posterior border of each maxilla reaches the subtemporal
fossa, by means of a narrow process that intervenes between the
anterior border of the jugal and the pterygoid, as in Exaeretodon.
The process of the jugal that extends between the posterior bor-
der of the maxilla and the pterygoid in Exaeretodon (Bonaparte
1962) could not be observed in Protuberum. The jugal does,
however, have a small medial process that is inclined towards
the pterygoid (Text-fig. 7), but which does not contact it.
TEXT -F IG . 5 . Reconstruction of the
skull of Protuberum cabralensis in dorsal
view. Scale bar represents 20 mm.
234 P A L A E O N T O L O G Y , V O L U M E 5 2
The ventral contact between the maxillae and the palatines
begins at the posterior border of the third postcanine along a
serrated suture and extends backwards, medial to the postcanine
tooth row, until reaching the pterygoids posteriorly. The pala-
tines extend for a considerably distance posteriorly, reaching the
level of the masseteric processes of the jugals (Text-fig. 7). No
palatal foramina could be observed.
A crest along the medial contact between the maxillae starts at
a point level with the anterior border of the paracanine fossae
and continues along the medial contact of the palatines to the
posterior terminus of the secondary palate (Text-fig. 7). This
crest is continuous with an ossified septum within the nasal cav-
ity. This septum is probably formed from the fused vomers and
is also observed in Traversodon (MR, pers. obs.) and Exaeretodon
(Bonaparte 1962). The opening of the internal choanae is tall, as
in Exaeretodon (Bonaparte 1962), and wide, as in Massetognathus
(Romer 1967).
The pterygoids of Protuberum form long descending processes
(Text-figs 5–7), resembling those in Exaeretodon (Bonaparte
1962), but they are more vertically directed and are proportion-
ally wider than in the latter taxon. Posterolaterally, the pteryg-
oids contact the epipterygoids.
Ventrally, the cultriform process of the parasphenoid (Text-
fig. 7) extends between the posterior ends of the pterygoids.
At this level, the pterygoids form a pronounced crest continu-
ous with the parasphenoid and the basipterygoid process of
the basisphenoid (Text-fig. 7). These features are similar to
those in Exaeretodon, but are not present in Massetognathus
(MR, pers. obs. UFRGS PV 0968T). Protuberum lacks an
interpterygoid vacuity (a feature that is variably present in
Massetognathus: Romer 1967; Reichel and Schultz 2004). Ante-
rolaterally, the pterygoids contact the maxillae, participating in
the anterior border of the subtemporal fossa. In contrast to
the condition in Massetognathus (Romer 1967) and Travers-
odon (Barberena 1981a), the pterygoids do not reach the jugals
laterally.
Orbital region and zygomatic arch. The lacrimal forms most of
the anterior border of the orbit and the anterior wall within the
orbit (Text-fig. 6). The limits of this bone inside the orbits are
not visible, but a clear serrated suture is present at the contact
with the maxilla. This suture has a semicircular outline. The lac-
rimal foramen is not preserved. A foramen located in the inter-
nal wall of the orbit is probably the posterior opening of the
infraorbital canal.
The limits of prefrontals and frontals are not clear (Text-
fig. 5). The region occupied by the frontals is quite depressed
because of the thickening of the lateral border of the prefrontal,
which forms the dorsomedial rim of the orbit. The postorbital
bar is preserved only on the left side of the skull. The dorsal
portion of the postorbital process is divided by an ascending
cuneiform projection of the jugal, as in Exaeretodon (Bonaparte
1962). However, the resulting ‘V’-shaped contact in Protuberum
is observed on the anterior and posterior faces of the postorbital
bar, differing from Exaeretodon, in which this contact is devel-
oped on the lateral and medial faces. In lateral view, the post-
A
B
TEXT -F IG . 6 . Reconstruction of the
skull of Protuberum cabralensis in lateral
view. A, complete, and B, without the
zygomatic arch. Scale bar represents
20 mm.
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 235
TEXT -F IG . 7 . Reconstruction of the
skull of Protuberum cabralensis in palatal
view. Scale bar represents 20 mm.
TEXT -F IG . 8 . Reconstruction of the
skull of Protuberum cabralensis in
occipital view. Scale bar represents
20 mm.
236 P A L A E O N T O L O G Y , V O L U M E 5 2
orbitals extend posteriorly covering most of the anterolateral
portion of the reduced parietal.
The parietals are fused dorsally to form the parietal crest
(Text-fig. 5), which is remarkably short in Protuberum. The pari-
etal foramen (Text-fig. 5) opens dorsally and slightly anteriorly.
It is located at the level of the posterior margin of the postorbi-
tals, which cover the anterior ends of the parietals.
The masseteric process of the jugal (Text-figs 6–7) can be
observed on the anteroventral portion of the zygomatic arch.
This process has also been described in Exaeretodon (Bonaparte
1962), Luangwa (Kemp 1980), Traversodon (Barberena 1981a),
Pascualgnathus (Bonaparte 1966) and Santacruzodon (Abdala
and Ribeiro 2002). In Protuberum it is ventrally directed, as in
Exaeretodon. The lateral view of the zygomatic arch resembles
that in Exaeretodon, although the dorsal prolongation of the
jugals does not project as far posteriorly as in the latter taxon.
The squamosals extend for a considerable distance anteriorly,
forming a cuneiform process that divides the posterior portion
of the jugals, and almost reaches the level of the postorbital bar,
as in Exaeretodon (Bonaparte 1962) and Massetognathus (Romer
1967).
Lateral wall of the braincase. In dorsal view, the posterior por-
tion of the squamosals resembles the condition in Exaeretodon.
The groove that separates the neurocranium and the zygomatic
arch is very deep (Text-fig. 5) and this contact is narrow, resem-
bling that of Massetognathus (Romer 1967). In lateral view, the
posterodorsal border of the portions of the squamosals that
form the lambdoid crests is rectangular (in contrast to that in
Massetognathus, in which this border is rounded) and extends
ventrally, outlining the external auditory meatus (Text-fig. 6A),
as occurs in Exaeretodon and Massetognathus.
The posteroventral articulation of the epipterygoid with the
prootic is preserved on the right side of the braincase. On this
border, a foramen is present for the exit of the maxillary (V2)
and mandibular (V3) branches of the trigeminal nerve (Text-
fig. 6B).
The pterygoparoccipital foramen appears to open laterally, but
this region is not well preserved. A similar condition is observed
in tritylodontids, in the tritheledontid cynodonts Riograndia
guaibensis and Pachygenelus (Luo 1994), and in the early mam-
mals Sinoconodon and Morganucodon (Wible and Hopson 1993),
but not in other traversodontids, in which the pterygoparoccipi-
tal foramen is enclosed by the squamosal. For most eucynodonts
(including other traversodontids), the laterally open pterygopa-
roccipital foramen is a derived feature (Luo 1994; Luo et al.
2002), but in mammaliaforms, this feature is variable and homo-
plastic. It is open in Sinoconodon and all morganucodontians
A BTEXT -F IG . 9 . Reconstruction of the
quadrate and quadratojugal of
Protuberum cabralensis (top) and
Massetognathus pascuali (bottom),
modified from Luo and Crompton
(1994). A, posteroventral, and B,
anterior views. Scale bar represents
10 mm.
A B
TEXT -F IG . 10 . The last left postcanine (unworn) of
Protuberum cabralensis. A, posterolateral view. B, occlusal view.
Scale bar represents 20 mm.
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 237
(Wible and Hopson 1993; Luo 1994) but closed in Adelobasileus
(Lucas and Luo 1993) and Hadrocodium (Luo et al. 2001).
The limits of the prootics are unclear (especially ventrally).
Laterally the sutures with the parietal and epipterygoid indicate
that this bone forms much of the sidewall of the braincase and
that it extends further dorsally than in Exaeretodon (Bonaparte
1962). In lateral view, the anteroventral limits of the prootic and
the epipterygoid are very clear, especially at the level of the tri-
geminal foramen. Posteroventrally, the prootic delimitates the
pterygoparoccipital foramen and posterodorsally the posttempo-
ral fossa (Text-fig. 6B). Both openings communicate through a
deep groove, in which only the portion closest to the posttem-
poral fossa (Brink 1955) is enclosed in a canal. A similar feature
is present in Massetognathus: in the latter taxon this short canal
was described as a lateral flange vascular canal by Rougier et al.
(1992). Conversely, in Exaeretodon the pterygoparoccipital fora-
men and the post-temporal fossa communicate through a closed
canal (Bonaparte 1962).
Basicranium. In ventral view, the squamosal bears a groove for
the external auditory meatus that rapidly decreases in diameter
medially and curves anteromedially (Text-fig. 7), terminating
behind the quadrate and the quadratojugal. The quadrate and
quadratojugal articulate with grooves in the squamosal. These
elements are tightly fused, as in Massetognathus (Luo and
Crompton 1994). Medial to the groove for the quadrate, a crest
of the squamosal encloses the quadrate into the concavity. The
squamosal does not make contact with the quadrate ramus of
the epipterygoid (Text-fig. 7). The dorsal plate of the quadrate
(Text-fig. 9) of Protuberum is similar to that of Massetognathus,
but it possesses a quadrangular anterior outline. The surface of
the dorsal plate is slightly concave and the dorsal angle is par-
tially covered by the squamosal, as in Massetognathus.
On the ventral area of both prootics, the cavum epiptericum
(Text-fig. 7) is open, as in most non-mammalian cynodonts
(Wible and Hopson 1993; Luo and Crompton 1994). In ventral
view, the paraoccipital process (Text-fig. 7) is better preserved
on the left side of the cranium. The process is bifurcated, with
an anterior and a posterior region, which is not observed in
other traversodontids. This is a derived feature, present in trityl-
odontids, brasilodontids (Bonaparte et al. 2005) and in early
mammals such as Morganucodon (Kermack et al. 1981) and
Sinoconodon (Crompton and Luo 1993). The posterior paraoc-
cipital crest (Text-fig. 7) is very clear and more strongly devel-
oped in Protuberum than in Brasilodon (Bonaparte et al. 2005)
and extends from the contact with the squamosal to the border
of the jugular foramen.
Although the preservation of the fenestra ovalis is not good
on either side of the braincase, their borders appear to have been
formed by a thickened ring of bone, which is a primitive feature
that is also observed in other traversodontids (Kemp 1980) and
non-mammalian cynodonts with the exception of Brasilitherium
(Bonaparte et al. 2003, 2005). This is otherwise a derived condi-
tion present in mammaliaforms (Luo et al. 1995). The jugular
foramina are better preserved and each is clearly confluent with
the fenestra rotunda.
The margins of the parasphenoid and basisphenoid are not
clear. In ventral view, the crest formed by the cultriform process
of the parasphenoid is very high, as observed in Exaeretodon
(MR, pers. obs., UFRGS PV0715T). Its anterior portion (extend-
ing between the pterygoids) is much shorter than in Massetogna-
thus (Romer 1967) and is more similar to that of Exaeretodon
(Bonaparte 1962). Posteriorly, the basisphenoid contacts the
basioccipital along a clear serrated suture (Text-fig. 7). Laterally,
the basisphenoid wing extends towards the fenestra ovalis (con-
tributing to its medial margin), but its contact with the prootic
is indistinguishable. Anteriorly, the basipterygoid process of the
basisphenoid forms the anterior margin of the ventral opening
of the cavum epiptericum. The foramina for the internal carotid
are absent in the basisphenoid, as also occurs in other travers-
odontids, Cynognathus and trytilodontids (Hopson and Barghu-
sen 1986).
It is not possible to determine if the basioccipital extends pos-
teriorly between the occipital condyles (Text-fig. 7), as it does in
Massetognathus (Romer 1967). No hypoglossal foramina are evi-
dent in the specimen, so they were probably confluent with the
jugular foramina (Text-fig. 7) as in most non-mammalian cyno-
donts, including traversodontids (Luo 1994; Luo et al. 2002). As
in most non-mammalian cynodonts, the occipital condyles of
Protuberum are mostly composed of the exoccipitals. The exocci-
pitals contact each other medially, but their articulation with the
basioccipital is not clear. The odontoid notch could not be
observed. The condyles project posteriorly, so that in ventral
view they are aligned with the posterior border of the lambdoid
crests, in contrast to the condition in Exaeretodon (Bonaparte
1962) and Massetognathus (Romer 1967). The condyles are pos-
teriorly placed in relation to the quadrates, as also occurs in
Massetognathus. The ventral parts of the condyles are very close
to each other, to a greater extent than occurs in Exaeretodon
frenguellii (Bonaparte 1962), but similar to their position in Exa-
eretodon riograndensis (Abdala et al. 2002). They are not as verti-
cally inclined as in the former and their form is bulbous, which
is the most primitive form among non-mammalian cynodonts,
including traversodontids (Lucas and Luo 1993).
Upper dentition
The dental formula of Protuberum consists of three incisors, one
canine and seven postcanines. Only the second and third incisors
are preserved on the left side and the second incisor on the right
side. They are slightly procumbent, but not as much as in Exa-
eretodon (Bonaparte 1962). Each incisor is similar in size, but
the second has a spatulate tip. It is possible to observe enamel
layers only on the labial face of incisors, which is also the case
in Exaeretodon (Chatterjee 1982; Abdala et al. 2002) and
Luangwa (Kemp 1980).
The right canine is small and approximately the same size as
the incisors: the canine is vertically oriented. As with the inci-
sors, the enamel layer can only be observed on the labial surface.
The paracanine fossa is placed in a posteromedial position in
relation to the upper canine, as is also observed in Exaeretodon
and Scalenodontoides. This fossa is very deep and anteroposteri-
orly elongate so that it almost fills the diastema that is present
between the canine and postcanines. The size of the lower canine
238 P A L A E O N T O L O G Y , V O L U M E 5 2
is unknown, but the anteroposterior length of the paracanine
fossa suggests that movement of the lower jaw occurred in a
posterior direction.
The postcanine rows diverge somewhat in their posterior half.
The first four teeth are implanted at right angles to the medial
plane. The posteriormost postcanines begin to diverge markedly,
reaching an angle of 50 degrees relative to the medial plane.
They increase in size posteriorly and are extremely worn, with
the exception of the posteriormost one (Text-fig. 10), which
shows no wear. The third and fourth left postcanines are free
from their alveoli. One of these became attached to the palate
during fossilization, while the other became associated with the
right paracanine fossa. A single root is visible on the former and
does not show any sign of division. Its length is the same as the
width of the crown of the tooth, so that the root shows the
shape of an inverted triangle in distal view. The empty alveoli
corroborate this observation.
The unworn teeth (Text-fig. 10) are similar in morphology to
the postcanines of Pascualgnathus. Two cusps can be observed,
one lingual and one labial. The lingual cusp is slightly higher
than the labial and a low transverse crest (that can be observed
only on the left unworn tooth) connects the cusps. There is no
cingulum. Wear increases from the back to the front along the
tooth row, as also observed in Luangwa (Kemp 1980), Masseto-
gnathus pascuali (Romer 1967) and other traversodontids. On
the fifth postcanine the transverse crest has been worn off, pro-
ducing two well-marked crests: a low one at the anterior border
of the tooth and a high one at the posterior border. These crests
enclose a deep concavity, so that the crown surface forms an
oval concave area that lacks internal features. The original differ-
ence in size between the lingual and labial cusps is accentuated
in comparison to the most anterior postcanines.
On the first four postcanines wear has produced a flat occlusal
surface, that is continuous anteroposteriorly. The lingual and
labial crests tend to decrease in size and no longer differ in size
from each other. The general morphology of the worn postca-
nines resembles that in Luangwa but is much simpler. The
shouldering of postcanines (an advanced feature for travers-
odontids, which is observed in Exaeretodon and Massetognathus,
for example) is absent in Protuberum, a characteristic it shares
with Luangwa, Pascualgnathus, Scalenodon, Andescynodon and
Traversodon. In occlusal view, the teeth are subrectangular in
outline and are nearly twice as broad as they are long anteropos-
teriorly, as also occurs in Massetognathus pascuali.
Axial skeleton
The axial skeleton of Protuberum (Text-figs 11–14) is peculiar
due to the presence of numerous processes on the ribs and neu-
ral spines with expanded distal ends that are similar to those
observed by Sues (1985) in the thoracolumbar vertebrae of Kay-
entatherium. The axial skeleton of Protuberum also resembles
that of Pascualgnathus (Bonaparte 1966), Thrinaxodon, Cynogna-
thus and Diademodon (Jenkins 1971), in its development of
costal plates.
In some non-mammalian cynodonts (e.g. Thrinaxodon, Cyno-
gnathus and Diademodon), posterior ribs with costal plates deli-
mit the intergirdle portion of the vertebral column into thoracic
and lumbar regions (Brink 1955; Jenkins 1971). In other cyno-
donts costal plates are absent and it is not possible to recognise
this division (e.g. Exaeretodon; Bonaparte 1963). There is also
another pattern, which may be represented by Massetognathus
(Jenkins 1970), in which specialized lumbar ribs occur; these are
not in the form of costal plates but appear to be reduced ver-
sions of these plates, lending a ‘Y’-shape to the distal end of ribs.
In Protuberum, the transition between the last thoracic and the
first lumbar rib is based on the presence ⁄ absence of overlapping
costal plates. On the lumbar ribs, the costal plates overlap with
adjacent ribs anteriorly and posteriorly, with each posterior plate
overlapping the anterior plate of the following rib.
The criteria proposed by Jenkins (1971) to distinguish
between thoracic and lumbar regions in non-mammalian cyno-
donts were (1) thoracic ribs possess a rib shaft that extends dis-
tal to the costal plates and (2) the first lumbar rib can be
defined as the first rib that bears a costal plate that contacts
adjacent costal plates. In the case of Protuberum, all of the ribs
possess a shaft distal to the costal plates. Therefore, the second
criterion applies better in Protuberum, but in this taxon the defi-
nition is modified slightly so that the first lumbar rib is identi-
fied as that which bears a costal plate that contacts adjacent
costal plates both anteriorly and posteriorly.
Vertebral column
There are 19 vertebrae in the holotype of Protuberum, consisting
of two cervicals, nine thoracics, five lumbars and three sacral
vertebrae. All of the vertebrae are amphicoelous and robust with
posteriorly inclined neural spines. Each neural spine bears pos-
terolateral expansions at its dorsal end, so that in dorsal view
the spines have a triangular outline. These expansions are more
robust than those observed in Kayentatherium (Sues 1985).
The transverse processes of the cervical and the first thoracic
vertebrae project posterolaterally, but from the third to the
eighth thoracic vertebra these processes extend laterally. From
the ninth thoracic (the last) to the third lumbar the transverse
processes project anterolaterally, but on the two last lumbars
(fourth and fifth), these processes project laterally again, as do
those of the sacral vertebrae. Cervical and anterior thoracic cen-
tra are anteroposteriorly short, while the centra of the posterior
thoracics, lumbars and sacral vertebrae increase in length and
become more spool shaped. This trend is especially marked in
the lumbar region where the centra have expanded anterior and
posterior borders.
Cervical series. The two first vertebrae (Text-figs 11, 12A) of the
holotype are considered to be cervicals, because they differ from
the next vertebrae (here considered to be thoracic) in several
aspects. The expansions at the extremity of the neural spine are
much smaller in the cervicals than in the first thoracic, even
though the expansions seen in the second cervical are larger than
those present on the first cervical. In addition, the cervical neu-
ral arches are much narrower than those on the thoracic verte-
brae and they lack the anterior lamina that is present in the
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 239
A
B
240 P A L A E O N T O L O G Y , V O L U M E 5 2
thoracics (see description, below). Moreover, the proportions of
the neural spines and vertebral centra are quite different, so that
the neural arches of the cervicals are proportionately much
higher than those of the thoracics, although the total height of
the cervical and anterior thoracic vertebrae remains almost the
same.
The cervical centra do not differ significantly from those of
the first thoracics. They are short anteroposteriorly and bear a
small laterally compressed ventral ridge. Cervical zygapophyses
resemble those of the thoracic vertebrae: the prezygapophyses
project beyond the anterior border of the vertebral centrum,
while the postzygapophyses terminate above the posterior border
of the centrum. A shallow anterior concavity is present on the
dorsal border of the centrum, ventral to the prezygapophyses,
which appears to act as an articular surface for a small tuberos-
ity that extends posteriorly from the preceding centrum (Text-
fig. 12A–B). This feature creates a very precise intervertebral
articulation.
Thoracic series. The largest neural spines expansions are present
in thoracic vertebrae 1–6 (Text-fig. 11), which might indicate
that they were subjected to some kind of additional mechanical
stress. The thoracic vertebrae (Text-fig. 12B) have anteroposteri-
orly elongated neural spines with an anterior lamina that pro-
jects into the posterior border of the anteceding vertebra. The
proportions of the neural arches and centra differ from those
observed in Exaeretodon (Bonaparte 1963) and Diademodon
(Jenkins 1971): however, the thoracic neural spines of Protube-
rum are generally low and resemble the pattern observed in Mas-
setognathus pascuali (Jenkins 1970). There are no clear sutures
between the neural arches and centra (in contrast to Exaereto-
don, in which those elements were not fused).
The anterior centra are anteroposteriorly short and com-
pressed laterally, so that a low ventral ridge is present. These
proportions change along the column and the posteriormost
vertebrae have centra are at least 50 per cent longer. The length
of the centra ranges from 18–30 mm. There is no evidence of
intercentra. The zygapophyses have the same pattern as
described above for the cervical vertebrae. Although it is hard to
observe the articular surfaces of the pre- and postzygapophyses
in the articulated vertebrae, it seems that these are almost verti-
cal on the anterior thoracic vertebrae but are oriented more hor-
izontally in the posterior vertebrae. The parapophyses are well
developed on the dorsolateral aspect of centrum, adjacent to the
articular surface. In Protuberum the facets for the thoracic rib
heads are situated intervertebrally, as in Thrinaxodon and
A B C D
TEXT -F IG . 12 . Reconstruction of the vertebrae of Protuberum cabralensis in lateral (top) and posterior (bottom) views. A, cervical,
B, thoracic, C, lumbar, and D, sacral vertebrae. Scale bar represents 20 mm.
TEXT -F IG . 11 . The articulated postcranium of Protuberum cabralensis (MGB 368 ⁄ 100). A, dorsal view, and B, ventral view. Striped
area represents sediment. Scale bar represents 40 mm.
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 241
Cynognathus (Jenkins 1971) and in the anterior dorsal vertebrae
of Massetognathus (Jenkins 1970). There are no indications of
anapophyses in MGB 368 ⁄ 100, although poor preservation and
the fact that most of the vertebrae are articulated in this speci-
men (with some matrix filling the spaces between them) could
have obscured this feature. In the isolated vertebra UFRGS
PV0985T (probably a thoracic), well-preserved anapophyses are
present.
Lumbar series. The lumbar vertebrae (Text-fig. 12C) have short,
robust and anteroposteriorly broad neural spines. No space is
present between adjacent neural spines, due to poor preserva-
tion. The expansions at the distal extremities of the neural spines
tend to decrease in size posteriorly.
The vertebral centra of the lumbar vertebrae are spool-shaped
in ventral view and their lengths range from 27–37 mm. The ante-
rior and posterior borders of the centra are expanded so that the
contact area between centra of adjacent vertebrae is enlarged. The
strength of their union can be confirmed by a postmortem incli-
nation of the posterior part of the column that caused the break-
age of the third, fourth and fifth lumbar vertebrae through the
middle portion of their centra, but did not disarticulate them. The
parapophyses are intervertebral, as in Massetognathus (Jenkins
1970). In Thrinaxodon, the last lumbar vertebrae have parapophy-
ses located on the centra (Jenkins 1971). From the third lumbar
vertebra and continuing posteriorly, synapophyses (fused parap-
ophyses and diapophyses) occur in an intervertebral position in
Protuberum, as also seen in the lumbars of Luangwa (Kemp 1980)
and Thrinaxodon and the sacrals of Massetognathus. Articulations
between lumbar pre- and postzygapophyses are unclear. The
transverse processes are robust and anteroposteriorly broad.
Sacrum. The sacral vertebrae (Text-fig. 12D) are identified on
the basis of contact between the ribs and the internal surface of
the iliac blade. The solid construction of the posterior part of
the vertebral column continues in this region. The first three
A
B
C
TEXT -F IG . 13 . Ribs of Protuberum cabralensis. A, cervical rib (UFRGS PV 1009T) in posterior view, B, thoracic rib (UFRGS PV
1010T) in anterior view, and C, thoracic rib (UFRGS PV 1010T) in posterior view. Striped area represents sediment. Scale bar
represents 20 mm.
TEXT -F IG . 14 . The sacral region of Protuberum cabralensis (MGB 368 ⁄ 100). A, lateral view of the articulated sequence of the
postcranial skeleton. B, detail of the fragment of the iliac blade, and C, reconstruction of the pelvis of Protuberum cabralensis.
242 P A L A E O N T O L O G Y , V O L U M E 5 2
A
B
C
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 243
sacral vertebrae are preserved in the type specimen (Text-
fig. 11), but the sacral region of Protuberum probably contained
more vertebrae, as Thrinaxodon has five sacrals (Jenkins 1971),
while Exaeretodon has seven (Bonaparte 1963).
The only preserved neural spine is that of the first sacral ver-
tebra. It is shorter than those of the lumbar vertebrae and is less
robust. The expansions at the distal extremity of the neural
spine are smaller than those on the lumbar vertebrae. Sacral
centra are spool-shaped (as in the lumbar vertebrae). The length
of the first sacral vertebra is about 32 mm, the second has a
severe fracture and dislocation of the centrum, making its mea-
surement difficult, but the third is approximately 24 mm long,
indicating a tendency towards shortening of the posterior sacral
vertebrae. The breakage of the second sacral vertebra occurs in a
similar way to that described for the third, fourth and fifth lum-
bar vertebrae (see above), with an intact intervertebral articula-
tion indicating strong fusion between the sacrals as well as the
lumbars.
Synapophyses are developed on the sacral vertebrae, but they
are placed on the anterior border of each vertebra (instead of
intervertebrally, in contrast to the lumbars). It is impossible to
distinguish the pre- and postzygapophyses, due to the poor pres-
ervation and the strong intervertebral attachment. The transverse
processes are anteroposteriorly narrower than those of the lum-
bar vertebrae.
Ribs
The presacral ribs of Protuberum (Text-figs 11, 13) are unique
among traversodontids, for having a series of distinctive knob-
like processes along their dorsal borders. These processes
decrease in size distally on each rib, so that the proximal pro-
cesses (close to the tuberculum) are generally the largest. On
some of thse processes, a dorsolateral concavity develops. The
middle thoracic ribs are the longest and bear up to eight pro-
cesses. The number of processes decreases in shorter ribs (i.e.
the posterior thoracic, lumbar and cervical ribs), but the pro-
cesses themselves do not change significantly in size wherever
they are found along the column. Regular spacing separates
each process and they form rows that are parasagittally
aligned. Similar processes occur on the dorsal margin of the
illium, with these processes in alignment with those on the
ribs (see below). This condition is comparable to Thrinaxodon
(Jenkins 1971), in which tubercles are present on the dorso-
medial edge of costal plates and also form parasagittally
aligned rows.
The surface of each process is smooth and they are composed
primarily of compact (probably pachyostotic) bone, suggesting
that they were not covered by cartilaginous tissue. All of the pre-
sacral ribs (including the cervical ribs) exhibit modest curvature
in transverse section, so the trunk of Protuberum was probably
wide and flat. The rib-vertebra contact is very strong on the pos-
terior thoracic and lumbar regions, making it hard to distinguish
the limits between the rib heads and their respective apophyses
on the vertebrae. All of the ribs on the left side are fractured
and somewhat displaced between the tuberculum and the first
protuberance (this fracture has affected all of the ribs from the
thoracic to sacral region) but their heads remain articulated with
the vertebrae. Conversely, the anterior portion of the trunk in
MGB 368 ⁄ 100 does not preserve any articulated ribs, indicating
a weaker articulation of the ribs on the vertebrae in this region.
The ventral and dorsal borders of ribs are convex to produce an
ellipsoid transverse cross-section. A dichocephalous condition
(Romer 1956, p. 277) is observed in most ribs, except for the
last lumbar and sacrals, where the tuberculum and capitulum
are fused.
Cervical ribs. Cervical ribs are rarely preserved in non-mamma-
lian cynodonts, so few specimens are available for comparison.
However, comparisons with Exaeretodon suggest that two ribs
referred to Protuberum represent the cervical region and that
they are probably from posterior cervicals. One of these ribs is
well preserved (UFRGS PV 1009T; Text-fig. 13A) and lacks only
the distal tip, while the other is represented by its proximal end
only (UFRGS PV 0981T).
UFRGS-PV1009T has three processes on its dorsal margin,
which decrease in size distally. These protuberances occur only on
the proximal half of the rib. The first protuberance has a distinct
morphology, being twice as elongate proximodistally as the other
two. The rib has a small ridge on the posterior surface, which
begins at the capitulum and ends 15 mm beneath the tuberculum.
In the same region, but on the anterior surface of the rib, a shal-
low groove is present. The capitulum is very broad in UFRGS PV
1009T and presents a slightly convex, almost flat articular facet.
UFRGS PV 0981T (a right proximal fragment) has a small capitu-
lum, that is approximately the same size as the tuberculum. The
larger size of the capitulum in the former is probably a conse-
quence of preservational distortion, so it is most likely that the
tuberculum and capitulum had similar sizes originally.
The curvature observed in UFRGS PV 1009T is not particu-
larly strong: this contrast with the morphology of the first cervi-
cal ribs of Exaeretodon, which have a ‘horseshoe form’
(Bonaparte 1963, page 20).
Thoracic ribs. No anterior thoracic ribs are preserved, so it is
not possible to observe the transition between the cervical and
thoracic ribs. The processes of the thoracic ribs are characterized
by a globular shape. The most proximal process sometimes dis-
plays a concavity dorsolaterally and is generally the largest and
anteroposteriorly longest process on each rib, although the sec-
ond process reaches a similar size in some ribs (e.g. in the last
left thoracic rib the second process is longer than the first one).
The number of processes present varies from eight (as seen on
the seventh thoracic rib) to five (on the ninth thoracic rib).
An anterior crest arises in the proximal region of some tho-
racic ribs (Text-fig. 13B), also occurs in Massetognathus (Jenkins
1970) and Cynognathus (Jenkins 1971). This crest begins below
the most proximal dorsal process. From the eighth thoracic rib
onward, another crest on the posterior margin of the ribs can be
observed. These crests do not overlap adjacent ribs. Both crests
become slightly larger on the ninth (last) thoracic, so that the
posterior crest of this rib overlaps the anterior costal plate of the
first lumbar rib. The crests abruptly enlarge in the lumbar region
(and are termed costal plates hereafter), whereas in Luangwa
(Kemp 1980), Cynognathus and Diademodon (Jenkins 1971),
244 P A L A E O N T O L O G Y , V O L U M E 5 2
these crests gradually increase in size along the thoracic and
lumbar series. The posterior surface of the shaft is marked by a
shallow groove (Text-fig. 13C), which is also observed on ribs
bearing a posterior crest and lies directly beneath this structure.
According to Jenkins (1971), this groove probably represents an
intercostal neurovascular sulcus.
The heads on the middle thoracic ribs consist of a short
tuberculum and an elongate and robust capitulum, as occurs in
some thoracic ribs of Exaeretodon (Bonaparte 1963). A small
ridge is present between the tuberculum and capitulum of
each thoracic rib. The heads of the posterior thoracic ribs are
comparable to those of many non-mammalian cynodonts (e.g.
Cynognathus, Diademodon, Luangwa, Massetognathus and Exaere-
todon), with an enlargement of the tuberculum and a shortening
of the capitulum; consequently, these structures converge in the
posterior region of the axial skeleton. The distal portion of each
thoracic rib decreases in size gradually, but the tips terminate
abruptly, presenting a peg-like morphology: in contrasts with
Exaeretodon in which the distal ends of ribs taper gradually.
Lumbar ribs. All ten lumbar ribs are articulated with the five
lumbar vertebrae in MGB 368 ⁄ 100 (Text-fig. 11). The costal
plates of the lumbar ribs are lanceolate in shape, and lack the
subrectangular outline described in Thrinaxodon, Diademodon
and Cynognathus (Jenkins 1971) and Pascualgnathus (Bonaparte
1966). An anteriorly directed process arises from the anterior
border of the last costal plate in ventral view.
The general morphology of the costal plates in Protuberum dif-
fers significantly from that of other non-mammalian cynodonts,
in which the costal plates of the lumbar ribs are characterized by a
reduction of the distal portion of the shaft of the ribs, so that just
the plate remains. In Protuberum the shafts of the ribs do not exhi-
bit such severe reduction, and a portion of the shaft continues dis-
tal to the costal plates. The dorsal processes of the lumbar ribs are
similar to these observed on the thoracic ribs. They differ in num-
ber, however, with four on each lumbar rib, except for the last rib,
which is short and bears only one process.
The lumbar ribs are fused to the vertebrae. The capitular pro-
cesses become progressively shorter toward the sacrum and shift
dorsally to be in closer proximity to the tuberculi. All capituli
articulate intervertebrally. Starting from the third lumbar rib,
the capitular and tubercular facets are essentially confluent. The
last lumbar rib has a fused capitulum and tuberculum.
The last lumbar rib shows a marked decrease in length. Its
posterior border has a broad contact with the anterior portion
of the iliac blade, which is facilitated by the lateral curvature of
the anterior portion of the iliac blade. The distal ends of the
lumbar ribs terminate abruptly, with a sub-quadrangular outline
in anterior view, and a small process is placed just dorsal to the
distal tip of the rib.
Sacral ribs. Only two pairs of sacral ribs are preserved in the
type specimen (Text-fig. 11). They are poorly preserved, but
some of their features can still be described. The sacral ribs lack
dorsal processes. Their general morphology resembles that of the
sixth and seventh sacral ribs of Exaeretodon (Bonaparte 1963).
The first sacral rib is the most robust, especially distally where it
contacts the iliac blade. The second rib has a smaller distal
expansion and a distal fragment of the third left sacral rib, which
is still attached to the iliac blade, is even more slender.
As in Thrinaxodon (Jenkins 1971) and the last lumbar rib of
Protuberum, the capituli and tuberculi are fused. The shaft is
short and posterolaterally oriented and the distal ends are
expanded anteroposteriorly and strongly fused to the iliac blade.
Ilium
A fragmentary left ilium (Text-figs 11, 14) is present in the type
specimen, but its acetabular and ventral portions are not pre-
served. It has a robust and elongate blade, with a lanceolate
anterior edge, which possesses rounded processes along its
dorsal border that are similar to those of the presacral ribs.
These processes are aligned with those on the ribs and form part
of the same parasagittal series (see above). The blade is laterally
concave, especially in its anterior half, where it curves laterally:
the anterior part of the ilium extends parallel to the last lumbar
rib at an angle of approximately 80 degrees to vertebral column.
DISCUSSION
Craniodental features
One of the most striking features of Protuberum is the
short parietal crest, which represents only 7.5 per cent of
skull length. In Exaeretodon (Bonaparte 1962), the parietal
crest represents about 30 per cent of skull length, while in
Luangwa sudamericana this figure is 28 per cent (Abdala
and Teixeira 2004: MCP 3284) and is 24 per cent in Mas-
setognathus (UFRGS PV 0968T). The thickened skull roof
is quite remarkable: its function is unknown, but it is
possible that it was associated with defense or burrowing.
The incisors of Protuberum have differential thicknesses
of enamel on their labial and lingual surfaces. Kemp
(1980) described a similar condition in Luangwa and
observed that this feature ensured that the ridges on the
teeth remained sharp throughout life. This self-sharpening
tooth could have been employed in gripping, cutting and
tearing off food. Moreover, the wide concave areas
formed on the crowns could be employed for plant crush-
ing. The postcanines of Protuberum are deeply worn
(except for the posteriormost teeth) as also occurs in
other traversodontids, such as Massetognathus (Crompton
1972a), Dadadon (Goswami et al. 2005) and Luangwa
(Kemp 1980). The latter possesses a pattern of tooth wear
that seems applicable to Protuberum (Text-fig. 15). The
mechanism proposed for the formation of the broad but
poorly matching concave wear facets present on the upper
and lower postcanines of Luangwa was a form of food-to-
tooth contact analogous with mammalian puncture-
crushing (Crompton and Hiiemae 1969), rather than
abrasion caused by occlusion. The wear pattern observed
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in these traversodontids supports the hypothesis of a pos-
terodorsally directed power stroke of the mandible
(Crompton 1972a), which is reinforced in Protuberum by
the presence of anteroposteriorly elongate paracanine fos-
sae and the probable mobility of the quadrate.
Luo and Crompton (1994) and Crompton (1972b) also
interpreted proposed a posteriorly directed movement of
the lower jaw of power stroke in Massetognathus, based
on the morphology of the quadrate. The quadrate troch-
lea in Protuberum is not as well pronounced as in Mas-
setognathus, but its orientation is similar and consistent
with the same type of movement. An anteroposterior
movement was also suggested for the quadrate of Dia-
demodon (Brink 1955), which is closely related to travers-
odontids (Abdala and Ribeiro 2003). The quadrate in
Protuberum is not rigidly attached to the squamosal and
may, therefore, have had some freedom of movement as
also suggested for Exaeretodon (Allin 1975).
Postcranial features
Limited morphological diversity is apparent in the post-
cranial skeletons of Triassic non-mammalian cynodonts.
However, rib morphology does appear to be useful for
distinguishing traversodontid taxa. Pascualgnathus polan-
skii, the earliest traversodontid (Puesto Viejo Formation,
Late Olenekian–Early Anisian; Bonaparte 1966) for which
ribs are known, has a costal morphology similar to that
of Diademodon (Scythian–early Anisian; Kitching 1995),
Luangwa (Anisian; Brink 1963) and Cynognathus (Scyth-
ian–early Anisian; Kitching 1995). Massetognathus pascuali
(Chanares Formation, Ladinian; Jenkins 1970), which is
temporally intermediate between P. polanskii and Exaere-
todon, has rib specializations that are restricted to the
lumbar region, while Exaeretodon (Ischigualasto Forma-
tion, Carnian; Bonaparte 1963) lacks rib specializations.
This reversal to a non-specialized condition was inter-
preted as a derived feature by Jenkins (1970). Protuberum
(Ladinian), however, shows unique and distinctive rib
morphology: while other traversodontids, such as Exaere-
todon, tended to simplify rib structure, Protuberum deve-
loped more elaborate ribs.
The presence of costal plates of Protuberum allows rec-
ognition of separate thoracic and lumbar regions, as in
Diademodon, Thrinaxodon and Cynognathus (Jenkins
1971). This distinction points to a possible division into
thoracic and abdominal cavities, as suggested by Brink
(1955). In the case of Protuberum, the presence of both
dorsal processes and costal plates gives the lumbar region
an exceptionally robust appearence. This, in combination
with the simple curvature of the ribs, indicates that Pro-
tuberum had a distinctive trunk morphology. It is possible
that this robust and specialized postcranial structure may
have provided protection against predators, a conclusion
supported by some other features of the skeleton, such as
the thickened skull roof (see above).
The accentuated curvature of the anterior portion of
the iliac blade provided a wide surface for muscle inser-
tion in that region. Therefore, the hindlimb and associ-
ated musculature may have been very strong, especially
the m. iliofemoralis and m. iliotibialis, both of which origi-
nate on the iliac blade. Indeed, strong, robust limbs
would have been necessary to support the robust axial
skeleton, and could have been employed in burrowing or
digging for food.
Systematics
A phylogenetic analysis to investigate the relationships of
Protuberum to other cynodonts was conducted using the
28 craniodental characters proposed by Abdala and Ribe-
iro (2003). Our data matrix incorporates 16 taxa, includ-
ing Diademodon, Trirachodon and 14 traversodontids.
Analyses were performed using the beta version of PAUP
4.0 (Swofford 1998) with Diademodon as the outgroup.
The branch-and-bound search method was applied and
produced a single most parsimonious tree (tree
length = 58, Consistency Index = 0.569, Rescaled Consis-
tency Index = 0.418).
It is important to be cautious with the resulting clado-
gram (Text-fig. 16), because the data matrix used by
Abdala and Ribeiro (2003) focused on dental characters
(21 characters, with the remaining seven relating to the
rest of the cranium and mandible) and excluded
TEXT -F IG . 15 . Dental wear in postcanines of Luangwa (Kemp 1980). A, occlusion of postcanines in sagital section. B, mechanism
of development of the transversely concave wear facet of the upper postcanine by occlusion with a narrower lower postcanine.
Modified from Kemp (1980).
246 P A L A E O N T O L O G Y , V O L U M E 5 2
postcranial information. In addition, as the mandible of
Protuberum is currently unknown, our analysis is missing
data for eight lower dentition ⁄ mandibular characters.
However, this preliminary analysis places Protuberum in a
clade with Gomphodontosuchus, Exaeretodon, Scalenodon-
toides hirschsoni and Menadon. This clade shares charac-
ters such as large incisors (acquired convergently in S.
hirschsoni), the presence of three upper incisors (acquired
convergently in S. hirschsoni and Pascualgnathus), paraca-
nine fossae positioned posterior to the upper canine,
absence of the internarial bar and the presence of a well
developed posterior extension of the jugal above the squa-
mosal in the zygomatic arch (this condition is unknown
in Gomphodontosuchus).
CONCLUSIONS
Protuberum cabralensis is a new traversodontid cynodont
that can be diagnosed on the basis of several distinctive
features, particularly the presence of prominent processes
on the cervical, thoracic and lumbar ribs, similar protu-
berances on the anterodorsal margin of the ilium and in
its unique dental morphology. Protuberum possesses a
combination of characters thought to be derived (e.g. the
lack of the internarial process of the premaxilla, bifurca-
tion of the paroccipital process and the lateral opening of
the pterygoparoccipital foramen) and primitive (e.g. mor-
phology of the iliac blade and presence of rib specializa-
tions) among traversodontids: more work is needed to
establish the phylogenetic position of this taxon within an
expanded analysis of traversodontid relationships.
Acknowledgements. We would like to thank C. Salla Bortolaz
(technician at MGB) for completion of the arduous and skillful
preparation of the type specimen and for assistance on begin-
ning this work. Additional thanks to A. Battaglin Cafaro (Secre-
tary of Tourism and Culture in the Municipality of Mata) for
lending us the type specimen. Special thanks to J. F. Bonaparte,
E. Snively, R. C. Fox, T. Kemp and Z.-X. Luo for valuable com-
ments on earlier versions of the manuscript. D. Larson helped
with the phylogenetic analysis. L. Morato and T. Veiga de Olive-
ira also contributed important ideas. Conselho Nacional de
Desenvolvimento Cientıfico e Tecnologico (CNPq) provided
financial support.
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APPENDIX
Character list
Morphological characters used in this paper are as follows. Char-
acters are derived from Abdala and Ribeiro (2003). ‘0’ represents
the primitive state.
1. Number of upper incisors: four (0); three (1).
2. Incisor size: small (0), large (1).
3. Diastema between upper incisors and canine: present (0),
absent (1).
4. Upper canine size: large (0), reduced (1).
5. Lower canine size: large (0), reduced (1).
6. Position of paracanine fossae in relation to the upper canine:
anteromedial (0), medial (1), posteromedial (2).
R E I C H E L E T A L . : N E W T R A V E R S O D O N T I D C Y N O D O N T F R O M S A N T A M A R I A F O R M A T I O N 249
7. Overall morphology of the upper postcanines: ovoid-ellipsoid
(0), rectangular-trapezoidal (1).
8. Shouldering in upper postcanines: absent (0), present (1).
9. Posteromedial inclination of the last upper postcanines:
absent or small (0), oblique (1).
10. Transverse crest of upper postcanines: central (0), anterior
(1), posterior (2).
11. Number of cusps in the transverse crest of upper postca-
nines: two (0), three (1).
12. Central cusp of upper transverse crest: midway between buc-
cal and lingual cusps (0), closer to the lingual cusp (1).
13. Posterior cingulum in upper postcanines: present (0), absent
(1).
14. External cingulum in the anterior portion of the upper post-
canines: absent (0), present (1).
15. Anterolingual cusp in upper postcanines: absent (0), present
(1).
16. Number of cusps in the sectorial border of the upper post-
canines: three (0), one (1), two (2).
17. Overall morphology of the lower postcanines: ovoid-ellip-
soid (0), quadrangular (1).
18. Transverse crest in lower postcanines: central (0), anterior
(1).
19. Number of cusps in the transverse crest of the lower postca-
nines: two (0), three (1).
20. Size of the anterior cusps in the lower postcanines: labial
lower than lingual (0), labial higher than lingual (1).
21. Cingulum in front of the transverse crest in the lower post-
canines: absent (0), present (1).
22. Internarial bar: present (0), absent (1).
23. Maxillary labial platform: absent (0), present (1).
24. Parietal foramen in adults: present (0), absent (1).
25. Zygomatic process of the jugal: conspicuously projected (0),
little projected (1), a ball-like process (2), absent (3).
26. Posterior extension of the jugal above the squamosal in the
zygoma: absent or with a small extension (0), well-developed
(1).
27. Coronoid process of the mandible: cover the last postcanine
(0), does not cover (1).
28. Dentary angle: not or weakly projected posteriorly (0), well
projected posteriorly (1).
Data matrix
12345 67891
0
11111
12345
11112
67890
22222
12345
222
678
Diademodon 00000 00000 000?? 0000? ?0000 000
Trirachodon 00000 00000 100?? 1001? ?0100 010
Andescynodon 00000 01001 0?001 11101 10113 0?0
Massetognathus 00111 11112 11100 01100 00111 000
Exaeretodon 11101 21112 0?101 01101 01110 101
Luangwa 00000 01002 11011 21100 10101 000
Scalenodon
angustifrons
00000 01000 11010 11100 1010? ?0?
Scalenodon
hirschsoni
1111? 010?2 11001 21100 101?? ???
Traversodon 00000 01012 11000 01100 00101 ?0?
Gomphodontosuchus 01111 11112 ??10? ?1101 001?? ?0?
Pascualgnathus 10000 01000 0?0?1 111?? ??111 000
Scalenodontoides 111?? 211?2 0?10? 01101 0111? 101
Menadon 11111 ?1112 0?101 2???? ?11?3 101
Dadadon 000?? 01112 11111 2???? ?01?2 ???
Santacruzodon 000?? 01112 11101 01101 001?2 ?00
Protuberum 1111? 21000 ??100 2???? ?1100 1??
Abbreviations in text-figures
An., anapophysis; Ant. Lam., anterior lamina; B. Th., bone thick-
ening; Bas. Pro. Bas., basipterygoid process of basisphenoid; Bas-
iocc., basioccipital; C., canine; Cap., capitulum; Cav. Ep., cavum
epiptericum; Cho., choana; Cont. F., contact facet; Cr., crest;
Cult. Proc. Parasph., cultriform process of parasphenoid; Desc.
Proc. Pt., descending process of pterygoid; Dor. Ang., dorsal
angle; Dor. Pl., dorsal plate; Epipt., epipterygoid; Ext. A. Meat.,
external auditory meatus; Fen. Ov., fenestra ovalis; For. Mag.,
foramen magnum; Fr., frontal; Gr., groove; I.c., posterior open-
ing of infraorbital canal; Inc. For., incisive foramen; Int., interpa-
rietal; Jug., jugal; Jug. For., jugular foramen; L., lacrimal; Lab.
Cusp, labial cusp; Lam. Cr., lambdoid crest; Lat. M., lateral mar-
gin; Lat. Tr. C., lateral trochlear condyle; Ling. Cusp, lingual
cusp; Mas. Proc. Jug., masseteric processes of jugal; Med. M.,
medial margin; Med. Proc. Jug., medial process of the jugal; Mx.,
maxilla; Mx. B., maxillary bulge; Mx. Proc. Prmx., maxillary pro-
cess of the premaxilla; N., nasal; Occ. Cond., occipital condyle; P.
Temp. Fos., post-temporal fossa; Pal. palatine; Par., parietal;
Para., parapophysis; Par. Cr., parietal crest; Paro. Cr., posterior
paraoccipital crest; Par. For., parietal foramen; Par. Fos., paraca-
nine fossa; Par. Proc., paraoccipital process; Po., postorbital; Prf.,
prefrontal; Prm., premaxilla; Pro., prootic; Pt., pterygoid; Ptp.
For., pterygoparoccipital foramen; Q. Ram. Ep., quadrate ramus
of the epipterygoids; Qj., quadratojugal; Qu., quadrate; R., ridge;
Sm., septomaxilla; Sph. Op., sphenorbital opening; So., supraoc-
cipital; Sq., squamosal; Syn., synapophysis; Tab., tabular; Tr.
For., trigeminal foramen; Trans. Crest, transverse crest; Tro. Tr.,
trochlear trough; Tuber., tuberosity; Tub., tuberculum.
250 P A L A E O N T O L O G Y , V O L U M E 5 2
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