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Home , Adelobasileus, Brasilitherium, Hadrocodium, Massetognathus, Pachygenelus, Probainognathia

ISSN (impreso) 0326-1778 / ISSN (on-line) 1853-6581

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30

DISCOVERIES IN THE LATE OF IMPROVE KNOWLEDGE ON THE ORIGIN OF Descubrimientos en el Triásico tardío de Brasil perfeccionan nuestro conocimiento sobre el origen de los mamíferos

José F. Bonaparte1, 2, Marina B. Soares3, and Agustín G. Martinelli4

1Museo Municipal de Ciencias Naturales “Carlos Ameghino”, Calle 26 512 (6600), Mercedes, Buenos Aires, Argentina. 2Departamento de Ciencias Naturales y Antropología, Fundación de Historia Natural Félix de Azara, Universidad Maimónides, Hidalgo 775 piso 7 (C1405BDB), Ciudad Autónoma de Buenos Aires, República Argentina. [email protected] 3Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do , Av. Bento Gonçalves 9500, Caixa Postal (15.001, 91501-970), Porto Alegre, RS, Brasil. 4Centro de Pesquisas Paleontológicas L. I. Price, Complexo Cultural e Científico Petrópolis (CCCP/UFTM), BR-262, Km 784, Bairro Peirópolis, 755, Uberaba, Minas Gerais, Brazil.

5 Bonaparte J. F., Soares M. B. and Martinelli a. g.

Abstract. A new specimen of riograndensis, which includes complete , lower jaws, dentition and some postcranial bones, is described, along with a redescription of the skull, lower jaws and dentition of Minicynodon maieri, both derived eucynodonts from the of Southern Brazil. The anatomical comparison confirms the close relationships of both genera with the Morganucodonta and suggest that the is the of the Brasilodontidae. Some comments after the anatomical information from the brasilodontids are developed on the following subjects: the sister group of mammals, the interpterygoid vacuity, and on , and Microconodon.

Key words. Brasilodontidae, Brasilitherium, Minicynodon, Triassic, Brazil.

Resumen. Un nuevo especimen de Brasilitherium riograndensis, el cual incluye un cráneo completo, mandíbulas, dentición y algunos huesos postcraneanos, conjuntamente con la descripción del crá- neo, mandíbulas y dentición de Minicynodon maieri son descriptos. Ambos son eucinodontes deri- vados del Triásico Tardío del sur de Brasil. La comparación anatómica confirma la cercana relación filogenética de estos géneros con los Morganucodonta y sugiere que los Trithelodontidae serían el grupo hermano de Brasilodontidae. Luego de la revisión de la información anatómica brindada por los brasilodóntidos se realizan comentarios sobre los siguientes aspectos: el grupo hermano de los mamíferos, la vacuidad interpterigoidea, y sobre los géneros Adelobasileus, Hadrocodium y Microco- nodon.

Palabras clave. Brasilodontidae, Brasilitherium, Minicynodon, Triásico, Brasil.

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INTRODUCTION promoted discussions of correlated prob- lems of such complex anatomical change. Starting in the late nineteenth and ear- Two notably well preserved and ly twentieth century, the problem of the lower jaws were discovered in 2005 thanks origin of mammals attracted the attention to a grant from National Geographic Soci- of numerous paleontologists and com- ety to J.F. Bonaparte. One of the specimens parative anatomists, most notably Robert represents a new and of the Broom (1912), who in 1914 first outlined non-mammalian eucynodonts, Minicy- the principal stages of the transition from nodon maieri (Bonaparte et al., 2010), and non-mammalian to mammals the second specimen correspons to Brasi- based primarily on Permo-Triassic litherium riograndensis (Bonaparte et al., from the Karroo of South Africa. Richard 2003, 2005). During a three months visit Owen (1861) had first noted the similari- to the Tübingen University of Germany, ties between certain Karroo therapsids and both specimens were carefully analized in mammals. Broom and others established cooperation with Prof. Dr. W. Maier, who that one group, the Cynodontia, included was particularly interested to study in full the precursors of mammals, but extensive detail the Brasilitherium skull, UFRGS-PV- parallel evolution among the known cyno- 1043-T. So, he has in preparation a paper on dont taxa made it difficult to identify the both external and internal anatomy of these closest sister-group of mammals. specimens through a set of tomographies. Based primarily on postcranial features, The description of these specimens pre- Kemp (2005) considered the highly de- sented here is a brief, traditional descrip- rived, rodent-like as the tion of some characters of these species not sister-group of mammals, an interpretation well known before. followed, as well as objected, by several pa- leontologists (e.g., Rowe, 1988, 1993; Luo, 1994; Sues and Jenkins, 2006). Hopson and DESCRIPTION Barghusen (1986) hypothesized the still incompletely known Tritheledontidae as Brasilitherium riograndensis Bonaparte, the sister-group of mammals, an interpre- Martinelli, Schultz and Rubert, 2003 tation most recently followed by Kielan- Jaworowska et al. (2004). The scarcity of General aspects of the skull relevant evidence, especially from The skull of Brasilitherium measures 38 the Middle and Late Triassic, has rendered mm in total length, it is elongate and nar- testing of these hypotheses difficult. row, with little lateral bowing of the zy- Recent discoveries of remarkably well- gomatic arches, and a long, narrow snout preserved specimens of derived non- with prominent expansion around the ca- mammalian from the Early Late nine alveoli and a narrow premaxilary re- Triassic of southern Brazil (Bonaparte and gion (Figure 1; see also reconstruction in Barberena, 1975, 2001; Bonaparte et al., figures 8 and 9). Its outline resembles that 2003, 2005, 2010; Martinelli and Bonaparte, of , but differs from the 2011; Bonaparte, 2012) revealed a substan- and other more de- tial amount of new anatomical information rived cynodonts in which the zygomatic on the cynodont- transition and arches are often considerably bowed out

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 7 Bonaparte J. F., Soares M. B. and Martinelli a. g. and the snout is rather short and wide. The In the dorsal view (Figure 1), it is notice- orbitotemporal openning is 3/5 the length able the wide braincase (see also Figure of the skull, larger than in Morganucodon 2), wider than in any other known non- (Kermarck et al., 1981). mammalian cynodonts. The snout shows

Figure 1- Brasilitherium riograndensis (UFRGS-PV-1043-T). Palatal, dorsal and right lateral views of the specimen as preserved. Abbreviations: al, alisphenoid; bs, basisphenoid; cav, cavum epiptericum; ci, carotid internal foramina; ex, exoccipital; fc, paracanine fossa; fv, fenestra vestibuli; fp, perilymphatic foramen; fdm, diploetic artery foramen; fr, frontal; gl, incipient glenoid; grsa, groove for stapedial artery; jf, jugular foramen; j, jugal; lf, lacrimal foramen; mx, ; mr, medial ridge; n, nasal; oc, occipital condyle; op, opistotic; osf, orbitosphenoid; prm, promontorium; pl, palatine; pr, prootic; psf, parasphenoid; pt, pterygoid; ptf, postemporal foramen; ptr, pterygoid ridge; ptt, pterygoid trough; ptv, pterygoid vacuity; ptw, pterygoid wing; ptf, postemporal foramen; px, premaxilla; qpt, quadrate ramus of pterygoid; q, quadrate; sq, squamosal; st, stapedial recess; vr, ventral ridge.

8 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 Origin of the mammals

a marked constriction behind the canines, jection, which is the reverse of the condition which appears to be confluent with the in Morganucodon (Luo and Crompton, 1994), buccal margin of the diastema. The dorso- in which the lateral projection is anterolat- lateral compression of the skull affected the eral. The stapedial process cannot be identi- width of both palate and interpterygoid va- fied in the adult UFRGS-PV-1043-T, but the cuities. However, the skull clearly was rath- process is well preserved in UFRGS-PV- er low and elongate, with the highest point 0929-T (Bonaparte et al., 2005), and closely marked by the frontal on the anteromedial resembles that of Morganucodon (Luo, pers. rim of the orbit. Posterior to it, the reduced com., 2004). parietal crest extends almost horizontally Orbito-temporal region. The parietal crest is to its end whereas the dorsal profile of the low, decreasing its height anteriorly. The frontals snout turns down anteriorly. underlay the parietals. Anteriorly the frontals of Brasilitherium become wider and contact the na- The zygomatic arch sals along an interdigitate suture as in Morganu- The slender jugal lacks a postorbital codon. Observations on this area of the skull process and it is laterally convex in trans- of (Bonaparte and Barberena, verse section. The jugal extends back to the 1975), (Bonaparte and Barber- level of the pterygo-paraoccipital foramen ena, 2001), and the tritheledontid where it contacts a short anterior process of (Soares, 2004; Soares et al., 2011), suggest the squamosal. Anteriorly, the jugal over- that the anterolateral portion of the frontal lies the posterior process of the maxilla and may represent a prefrontal that became in- it is overlain by the lacrimal. distinguishably fused to the frontal. The squamosal is incompletely known in Dorsally the frontal have a slightly de- UFRGS-PV-1043-T. The posterior surface of pressed median area. A weak dorsal ridge it, where the quadrate is attached, is dors- marks the extent of the temporalis muscula- oventrally low and bears a shallow groove ture. A supraorbital foramen of unknown that presumably formed the external au- function is present on the dorsolateral as- ditory meatus. The ventral side of the left pect of the frontal, near the contact with incomplete squamosal is anteroposteriorly the nasal. Interestingly, a similar foramen wide just lateral to the quadrate, showing on the same position was recorded in the a glenoid-like depression delimited by primitive tritheledontid Riograndia (Soares, a distinct border. The zygomatic arch of 2004; Soares et al., 2011). Brasilitherium, resembles that of the earliest mammals. The left quadrate is inserted in the squa- mosal and firmly attached below the paraoc- cipital process; it has been slightly displaced from its original position. In ventral view, the quadrate trochlea is rather large, with its anteroposterior axis longer than in Mor- ganucodon. The posterior border of the tro- chlea is slightly concave whereas the ante- Figure 2 - Brasilitherium riograndensis (UFRGS-PV- rior margin is convex. The lateral trochlear 1043-T). Tomographic transverse section of the posterior condyle has a dorsal and posterolateral pro- braincase area to show the wide cranial cavity.

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 9 Bonaparte J. F., Soares M. B. and Martinelli a. g.

In dorsal view (Figure 1), the wide brain- and the earliest mammals. In lateral view case and the region of the olfatory bulbs the epipterygoid contacts the dorsomedial of Brasilitherium become narrower at the aspect of the quadrate ramus of the ptery- level of the anterior portion of the parietals. goid and is exposed in ventral view par- From this point backwards, the braincase ticipating in the contact between pterygoid increases in width to a lesser degree than and basisphenoid. This character is another in Morganucodon (Kermack et al., 1981), but one plesiomorphic feature compared with from that point forward the width of the the condition in and Morganu- olfatory bulbs increases more than in Mor- codon. A similar feature has been figured ganucodon. In Brasilitherium the braincase is for (Kemp, 1979) and Thri- proportionally smaller than in Minicynodon naxodon (Fourie, 1974), but has not been (this paper) as well as in Morganucodon. In reported in , Sinoconodon and Minicynodon the braincase is proportionally Morganucodon. It may be homologous with wider and shorter, more comparable in its the “ventral prong of the epipterygoid proportions to that of Morganucodon. bone´s basal plate” recorded in The good preservation of the floor of the (Lillegraven and Krusat, 1991). orbit and lateral side of the braincase merits The quadrate ramus of the epiptery- further discussion. The orbital floor is com- goid extends posterolaterally close to the posed of ventral processes of the frontal as pterygoparaoccipital foramen, far from the well as a large lacrimal component. More quadrate and ventral to the prootic. There medially the palatine is superimposed on is a distinct foramen on the left epiptery- the pterygoid. The palatine may contrib- goid, located anterior from the V3 nerve ute to the orbital floor but the evidence is exit of the prootic. The anterior border of ambiguous in this specimen as well as in the epipterygoid is thick and rounded, sug- UFRGS-PV-0804-T. gesting that it may have been extended in There is a large interorbital vacuity, with cartilage. only a small piece of bone located medial Both prootics are the first complete proot- to the anterodorsal border of the epiptery- ics known for Brasilitherium. They show goid (alisphenoid), possibly representing clear sutures with epipterygoid, pterygoid, a partially ossified orbitosphenoid (Figure squamosal and parietal, as well, in ventral 1). There is tomographic evidence of an view, with the opisthotic and basioccipital. anteriorly displaced orbitoesfenoides me- The surface structure shows that the pos- dially to the orbital process of the frontal. terodorsal region is medially twisted, con- The UFRGS-PV-1043-T specimen preserves tributing to the vault of the braincase; the complete epipterygoid. It is longer antero- posteroventral area projects posterolater- posteriorly than tall dorsoventrally, not dif- ally, contacting the squamosal and closing ferent from Thrinaxodon, but broader than the pterygo-paraoccipital foramen. Here in (Rougier et al., 1992), the lateral side of the prootic forms a ro- Pachygenelus (Wible and Hopson, 1993), bust, rod-like structure dorsoventrally di- Sinoconodon (Lucas and Luo, 1993), and rected, bordering the groove for the proxi- Morganucodon (Kermack et al., 1981). Possi- mal stapedial artery (Rougier et al., 1992). bly the plesiomorphic state is a broad epip- This structure, possibly representing an au- terygoid which shows progressive reduc- tapomorphic character for Brasilitherium, is tion in derived non-mammalian cynodonts sharply defined anteriorly by a pronounced

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step in the surface of the prootic, forming a to the trough on the prootic. This feature, bridge for a large, posterodorsally directed not known in other non-mammalian cyno- foramen, confluent with the afore men- donts or earliest mammals may be an auto- tioned groove. It may correspond to the pomorphy for Brasilitherium. passage of the lateral head vein in Thrinax- The promontorium is well developed in odon (Rougier et al., 1992). In Morganucodon, Brasilitherium (Bonaparte et al., 2005), but a comparable foramen is present anterior less globular than in Minicynodon maieri to the groove for the stapedial artery (Wible (Bonaparte et al., 2010), possibly due to dor- and Hopson, 1993). soventral compression. On the left prom- Posterodorsally, the prootic contacts the ontorium of Brasilitherium (Figure 3), the squamosal, contributing to the cover of the more anterior portion of the structure, near foramen for the large diploetic artery pass- its contact with the basisphenoid, is broken, ing to the post-temporal foramen. revealing the internal chamber, which also

Two foramina for the maxillary (V2) and extends anteriorly to that contact. The glob-

mandibular (V3) branches of the trigeminal ular portion of the pars cochlearis (prom- nerve are present on the anterior lamina of ontorium) that extends ventromedially and

the prootic. The more ventral one for the V3 laterally, as seen through the broken area,

is larger than that for the V2, representing is a derived character that Brasilitherium a derived condition (Wible and Hopson, shares with Sinoconodon and more derived 1993; Luo et al. , 2002), shared with Ade- mammaliforms such as Morganucodon and lobasileus, Sinoconodon and Morganucodon. (Luo et al., 2002). The prom- ontorium is composed of the prootic and Ventral view of the skull is bordered by the basioccipital medially In ventral view the prootic has a well de- and the basisphenoid anteromedially. It is fined exposure medial to the pterygoparaoc- unclear whether the basioccipital overlaps cipital foramen, forming the lateral trough the medial side of the promontorium. The and the promontorium, and contacting the opisthotic and prootic form the crista in- opisthotic and exoccipital posteriorly (Fig- terfenestralis. On the opisthotic this crest ures 1,3). Sutures are not clearly defined in is well defined, distinct, directed to the this region. The anterior extension of the posterior region of the paraoccipital pro- trough is more developed than in Pachy- cess, representing another autopomorphy genelus (Wible and Hopson, 1993), more of Brasilitherium. Lateral and anterior to similar to Sinoconodon (Crompton and Sun, this crest is the “stapedial recess” (Figure 1985), but less developed than in Morganu- 3) into which the fenestra vestibuli opens codon (Kermack et al., 1981; Wible and Hop- posterolaterally, towards the place occu- son, 1993). The small opening of the prootic pied by the quadrate. The groove of the sinus is lateral to the fenestra vestibuli and stapedial artery is well marked on the roof anterior to the groove of the stapedial ar- of the “stapedial recess”. Medial to the lat- tery. The foramen for the facial nerve (VII) ter, the perilymphatic foramen is confluent opens anteromedially to the latter. Between with the jugular foramen (Figure 3) in the the openings of the facial nerve and the specimen UFRGS-PV-1043-T, but separated prootic sinus, and bordering anteriorly the by bone in Minicynodon UFRGS-PV-1030-T. fenestra vestibuli, a crest extends up from The cavum epiptericum is rather large. the lateral border of the promontorium The ventral surface of the basioccipital is

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 11 Bonaparte J. F., Soares M. B. and Martinelli a. g. concave anteroposteriorly and transversely In general terms it appears more derived except for the posterior region between the than in Probainognathus and Pachygenelus. perilymphatic recesses and near the occipi- The sutures between the basisphenoid, tal condyles where it is flat transversely. basioccipital and prootic are not evident, Possibly the median portion of the perilym- suggesting that these bones might be fused phatic recess is formed by the basioccipital; to each other. The lateral margins of the ba- it bears three small, possibly vascular fo- sisphenoid form continuous, narrow crests, ramina. The sutures of the basioccipital are “basisphenoid wings” (Crompton, 1964), not visible, but that of the exoccipital and which meet to the parasphenoid and form opisthotic is evident. The condylar foramen a pronounced ventral process, probably for is quite near the jugular foramen but on a attachment ofM. longus capitis. This ventral more ventral position. process is not present in other derived cy- nodonts and basal mammals, and may rep- resent an autopomorphy for Brasilitherium. The carotid foramina are located near the basisphenoid wing, at some distance be- hind the parasphenoid. Two distinct ru- gosities of unknown function (muscular attachment?) are present just behind the carotid foramina. The lateral ends of the basipterygoid pro- cesses are slightly concave, bordering the cavum epiptericum, and contact the ptery- goid at almost right angles to the sagittal plane. This contact shows noticeable sepa- ration in UFRGS-PV-1043-T suggesting a no rigid union (Figure 4), permiting some kind of movement between pterygoids and basisphenoid. If so, the line of flexure ap- pears to continue laterodorsally through the interorbital unosified area to the loose contact frontoparietal in which the former Figure 3 - Brasilitherium riograndensis (UFRGS- is overlain by parietal. The parasphenoid PV-1043-T). Ventral view of the left braincase area. Abbreviations as in previous figures and: cf, condylar rostrum is not well preserved in either foramen; qal, quadrate ramus of epipterygoid/aliesphenoid; Brasilitherium or Minicynodon specimens sc, sinus canal; sta, stapedial fossa; uoa, unossified area; described here. VII, foramen for nerve VII. In lateral view (Figure 4), the pterygoid forms a large, lateral, posteroventrally pro- Based on UFRGS-PV-1043-T the struc- jecting flange and an anterior process that ture of the basicranium of Brasilitherium contacts the maxilla and palatine. The pos- can now be interpreted. It resembles those terolateral border of the pterygoid flange is of Adelobasileus (Lucas and Luo, 1993) and crescentic, as in Sinoconodon (Crompton and Morganucodon but differs in the confluence Luo, 1993), bordering a wide, concave and of the perilymphatic and jugular foramina. posteriorly facing area which is confluent

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with the ventral surface of the wide ptery- pterygoid was possibly for insertion of the goid along the margins of the interptery- velum palatinum muscles (Maier, pers. com., goid vacuity. It possibly served as the area 2006). Except for this process, the pattern of origin for part of the pterygoid muscula- of crests and troughs is almost identical to ture (Kielan-Jaworowska et al., 2004). The that of Morganucodon (Kermack et al., 1981), distal end of the pterygoid flange is turned Sinoconodon (Crompton and Luo, 1993), medially. The ventral face of the pterygoid Riograndia (Soares et al., 2011), and Pachy- is transversely wide, with the medial bor- genelus (Hopson, pers. com., 2001), but dif- der turned ventrally. Near the anterior end ferent from that in Probainognathus (Romer, of the interpterygoid opening, the median 1970) where the medial trough is wider border of the pterygoids forms a distinct anteriorly, shorter posteriorly, ending in ventral step and the ventromedial process, a ventromedian keel formed by the paras- which is large and well defined in the spec- phenoid and pterygoids. imen UFRGS-PV-1043-T. This process rep- There is not distinct ectopterygoid. Here resents the posterior end of the nasopha- the pterygoid forms a broad contact with ryngeal crest, laterally delimiting a deep the medial and posterior side of the max- nasopharyngeal passage. It slightly diverg- illa, participating in the border of the sub- es from the internal nares with the pres- orbital opening. Behind the internal nares, ence of a low median keel extending into the “primary palate” (the interpterygoid re- the internal nares. Lateral to this trough is gion) does not exhibit any sutures between the less deep concavity for the Eustachian the palatines, pterygoids and vomer. tube (Hopson and Barghusen, 1986), later- The secondary bony palate extends back ally bordered by the pterygoid flange, and to the level of the last postcanine in all spec- extending to the lateral margin of the inter- imens of Brasilitherium. The anterior border nal nares. The ventromedial process of the of the palatine is indicated by a short ex-

Figure 4 - Brasilitherium riograndensis (UFRGS-PV-1043-T). Lateral view of the left pterygoid wing and its contact with epipterygoid and basicraneal bones. Abbreviations as in previous figures and: arpt, anterior ramus of pterygoid; bs, basisphenoid; lbs-pt, contact basisphenoid-pterygoid; pcpt, posterior cavity of pterygoid; vpt, posterior ventral process of pterygoid.

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 13 Bonaparte J. F., Soares M. B. and Martinelli a. g. tent of suture at the level of the fourth post- Lower jaw canine, indicating a rather long palatine, Both lower jaws with complete dentitions longer than in Probainognathus (Romer, and without the postdentary bones are pres- 1970) and Sinoconodon (Crompton and Luo, ent in the UFRGS-PV-1043-T. 1993), but shorter than Pachygenelus (Hop- The dentary has a long, low horizontal ra- son, pers. com., 2001) and Morganucodon mus, with a dorsally elevated symphyseal (Kermack et al., 1981). portion (Figure 5). The posteriorly inclined ascending process is larger than the horizon- Preorbital region tal ramus and bears a large lateral depression The structure of the bones on the lateral for the masseter muscles. The articular pro- side of the antorbital region shows no dif- cess forms the posteriormost point of the jaw ferences from previously reported mate- and is separated from the tip of the coronoid rial of Brasilitherium (Bonaparte et al., 2003, process by a crescentic posterior edge. The 2005). The paracanine fossae on the maxilla, dentary condyle is incipiently developed. located anteromedially to the canines, are The groove for the postdentary bones is large anteroposteriorly. The short internar- large and continued anteriorly by the Meck- ial process of the small premaxilla contacts elian groove, which extends close to the ven- the long anterior process of the nasal. tral border. The proportions of the horizon- The length of the -bearing portion of tal ramus of the dentary show differences the maxilla and premaxilla is less than half between Brasilitherium and the Minicynodon the total length of the skull in the specimen specimens. In the former, the length of the UFRGS-PV-1043-T (43%), but is almost half horizontal ramus (measured from the poste- (48%) in Minicynodon. The corresponding rior border of the last postcanine to the an- ratio is 38-41% in Probainognathus, 52% in terior tip of the ) is less than half the Pachygenelus, 50% in Sinoconodon, and 54% length of the dentary. The ascending process in Morganucodon. is proportionally larger in Brasilitherium. The The limited ventral exposure of the pre- anterior border of the coronoid process is maxilla (Figure 1) suggests it was smaller rather thick. On the medial side of the den- than in Pachygenelus (Hopson, pers. com., tary, a short distance behind the last postca- 2001) and Sinoconodon (Crompton and Luo, nine, there is a triangular medially directed 1993) but more similar to Morganucodon. process, possibly a coronoid boss.

Figure 5 - Brasilitherium riograndensis (UFRGS- PV-1043-T). Left lower jaw without postdentary bones. Note that the cusp “a” is more mesially displaced than the center of the postcanines.

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Dentition ed ventrally in life. The third is sep- A complete, associated upper and lower arated from the canine by a long diastem dentition has not been previously available formed by the laterally expanded paraca- for Brasilitherium. However, basic informa- nine fossa. tion was derived from several incomplete specimens (Bonaparte et al., 2003, 2005; Fig- Lower incisors ure 7). In the two skulls reported here both The specimen has three lower incisors. set of teeth are complete, although they are The first is more procumbent than the only adequately prepared and exposed in third, a condition shared with Riograndia the Brasilitherium specimen. (Soares, 2004; Soares et al., 2011) and Pachy- genelus (Hopson, pers. com., 2001). There is Upper incisors not evidence of incisors replacement. The specimen UFRGS-PV-1043-T bears three incisors. The third is thicker but Canines shorter than the first. The incisors are bent The cross-section near the base of the back due to crushing but probably project- crown is almost circular in the upper ca-

Figure 6 - Brasilitherium riograndensis (UFRGS-PV-1043-T). Left upper and lower postcanines as preserved in the specimen. A, buccal view and B, occlusal view of the uppers; C, occlusal view and D, buccal view of the lowers. Abbreviations: bcc, buccal cingular cusps, and those corresponding to the upper and lower cusps.

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 15 Bonaparte J. F., Soares M. B. and Martinelli a. g. nines, and transversely narrow in the lower provides additional information. On pre- ones. As shown in specimens UFRGS-PV- viously described lower postcanines, the 0594-T and UFRGS-PV-0929-T, the relative principal cusp “a” is slightly displaced size of the canines resembles that of Morga- mesially; a smaller cusp “b”, two small pos- nucodon but they are larger in the UFRGS- terior cusps “c” and “d”, and two lingual PV-1043-T specimen, similar to those in cusps “e” and “g” are also present (Figure Sinoconodon (Kielan-Jaworowska et al., 6). There are not any evidence of “premo- 2004). The position of the upper canines far lars” or “molars”. behind the anterior margin of the premaxil- la in all specimens of Brasilitherium, is com- Tooth replacement parable to that in the earliest mammals, and The Brasilitherium specimen shows anky- different from that in Probainognathus and losis of the left postcanines 2, 4 and 7, and Chiniquodontidae, where the canine is situ- the right postcanine 7 on the maxilla. The ated more anteriorly. Pachygenelus appears remaining postcanines show slight separa- to show an intermediate position (Hopson, tion from the alveolar margins. In the den- pers. com., 2001). tary, only the left tooth row is exposed; the postcanines 1, 4 and 5 are also ankylosed Postcanines to the alveoli, indicating that tooth replace- In Brasilitherium, the diastema between ment worked in a rather primitive sequence canine and the first postcanine is propor- (see Martinelli and Bonaparte, 2011). As tionally longer in the dentary than in the noted earlier, tooth replacement in Brasilith- maxilla. The UFRGS-PV-1043-T skull has erium was more frequent than in the closely nine postcanines in the maxilla and six or related Brasilodon, and apparently similar to seven in the dentary (Figures 1, 6). the condition in the basal eucynodont Thri- The structure of the postcanines of Brasi- naxodon (Osborn and Crompton, 1973). In litherium has previously been described the primitive mammal Sinoconodon (Kielan- (Bonaparte et al., 2003; 2005); the new ma- Jaworowska et al., 2004) the tooth replace- terial (Figure 6) confirms that account but ment was frequent but in a different way.

Figure 7 - Brasilitherium riograndensis (UFRGS-PV-0759-T). A, right maxila in buccal view; B, left dentary in lin- gual view. Taken from Bonaparte et al. (2003).

16 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 Origin of the mammals

Figure 8 - Brasilitherium riograndensis. Reconstruction of the skull based on specimen UFRGS-PV-1043-T, in dorsal and palatal views. Total skull length 33 mm.

Figure 9 - Brasilitherium riograndensis. Reconstruction of the occipital view of the skull based on specimen UFRGS- PV-1043-T. Abbreviations as in previous figures.

Postcranial bones (Figure 10). The humerus (Figure 10A) re- A few appendicular bones of specimen sembles that of Morganucodon (Jenkins and UFRGS-PV-1043-T are complete, without Parrington, 1976) but the deltoid crest is apparent distortion: a left humerus, ulna more developed distally. The humeral head and radius; and a right femur and tibia is spherical, projected dorsally and separat-

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 17 Bonaparte J. F., Soares M. B. and Martinelli a. g.

Figure 10 - Brasilitherium riograndensis (UFRGS-PV-1043-T). A, left humerus in dorsal and ventral views; B, left ulna in lateral view; C, left radius in posterior view; D, right femur in ventral and medial views; E, right tibia in lateral view. Scale bar 5mm.

ed from both greater and lesser tuberosities with the ectepicondyle. This is somewhat by deep groves. The former is smaller and larger proximodistally and the shaft of the more proximally placed than the latter. A humerus shorter than in Morganucodon. pronounced dorsal, rounded ridge runs In ventral view the lesser tuberosity is distally through a great portion of the hu- larger than the greater tuberosity. The bi- merous length becoming distally confluent cipital groove is deep, distinct up to the end

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of the deltoid crest. The latter appears less Minicynodon maieri Bonaparte, Schultz, developed medially than in Morganucodon Soares and Martinelli, 2010 (Jenkins and Parrington, 1976: Figure 5C). On the medial side at level with the distal This species was briefly studied in a pa- end of the deltopectoral crest, there is a pro- per on the whole records from the nounced process for muscular attachment, Late Triassic beds of the Caturrita Forma- resembling that of Irajatherium (Martinelli et tion (Andreis et al., 1980), corresponding al., 2004; Oliveira et al., 2011), larger than in to the top of the Sequence Santa Maria 2 Morganucodon. The shaft of the humerus ap- (Zerfass et al., 2003), exposed near Faxi- pears better defined and longer in Morganu- nal do Soturno, Rio Grande do Sul, Brazil codon in ventral view. Both radial and ulnar (Bonaparte et al., 2010). It was collected condyles are well exposed in ventral view, from the same levels that yielded Brasilodon the former larger and more deeply separat- quadrangularis and Brasilitherium riogran- ed than the latter. In dorsal view the ulnar densis (Bonaparte et al., 2003), Riograndia condyle is larger than the radial. The humer- guaibensis (Bonaparte et al., 2001), and Ira- us length is 15,7 mm, the length of ulna: 15,8 jatherium hernandezi (Martinelli et al., 2005). mm, the length of radius: 12,7 mm. Originally, the senior author considered the The complete right femur is exposed in tiny skull and lower jaws of the Brasilith- ventral view. The Brasilitherium femur is erium riograndensis type specimen (UFRGS- different from other non-mamalian cyno- PV-1030-T) as a juvenile, but after long dis- donts as Thrinaxodon, , Ex- cussions and restudy of the specimen with aeretodon and Therioherpeton because the the Prof. Wolfgang Maier, he persuaded me is in a higher position, the that the specimen is actually an adult crea- major trochanter is separated from the fem- ture bearing several anatomical characters oral head by a groove, and the head of the of its adult condition. Such experience of femur is sub-spherical, with a pronounced working together with a so trained mam- medial scar for capital ligaments. The femo- malogist proved to be of important help. ral head is deflected more medially than in Morganucodon. The major trochanter is no- General aspect of the skull ticeable larger than the lesser trochanter. The small size of the skull with jaws in The intertrochanteric fossa is pronounced, articulation, the fine preservation, the com- deeper towards the lesser trochanter and plete upper dentition exposed on one side separated from the fossa of the adduc- and only some small deformation make of tor muscles (Jenkins, 1971), by a rounded it an exceptional specimen of a non-mama- ridge connecting both trochanters. Distally, lian cynodont. However, important fails of the lateral condyle is larger than the medial good preservation are seen in the palatal condyle. The posterior projection of them view because from the internal nares back- suggests an important angle was between wards only the right basicraneal area is femur and tibia–fibula. The total length of preserved. It has not expanded zygomatic the femur is 16,5 mm and the length of tibia arches, the snout is rather elongate, slender, is 15,2 mm. and the braincase transversally expanded. Detail description of these postcranial The parietal crest is much reduced. The elements will be presented in a future con- temporal region is axially shorter than the tribution. orbito–rostral portion of the skull. In gen-

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 19 Bonaparte J. F., Soares M. B. and Martinelli a. g. eral terms it is very similar with the Brasi- the contact between the parietal and frontal litherium riograndensis skull. bones is different. In Minicynodon the pari- etals bear an extensive facet dorsally for the The zygomatic arch overlying posterior border of the frontals. The zigomatic arch is very slender as in In Brasilitherium the parietals overlie the other brasilodontids, with small contribu- frontals. tion of the squamosal located only in the The posterior area of nasals and the an- posterior section of the arch. An overlying terior of frontals are very intimately fused, and long contact is seen between squa- a character not observed in Brasilodon or mosal and jugal. Because the right lower Brasilitherium (Bonaparte et al., 2003, 2005). jaw and the quadrate are forwardly dis- The foramen supraorbital recorded in placed it is not possible to observe the Brasilitherium is present on both frontals, ventral side of the squamosal. It is inferred as it is also present in Riograndia (Soares, that an incipient glenoid fossa was pres- 2004; Soares et al., 2011), suggesting some ent because the dentary condyle is clearly kind of relationships between them. seen in the right lower jaw (Figure 11A). In the orbit the ventral process of the frontal and the dorsal process of palatine Orbito temporal region are present contacting between them. On The parietal crest is reduced in a simi- the floor of the orbit only small fragments lar condition as in Brasilitherium. However, of palatine and lacrimal are preserved.

Figure 11 - Minicynodon maieri (UFRGS-PV-1030-T). A, Right lateral and B, left lateral views of the skull and lower jaws of the specimen. C, reconstruction of the skull in dorsal view. Abbreviations as in previous figures.

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The braincase is proportionally wider than in Brasilitherium, but shorter, more sim- ilar to that of Morganucodon (Kermack et al., 1981; Kielan-Jaworowska et al., 2004). Unfor- tunately only the right side of the braincase is preserved. It shows the large epipterygoid and a large area without ossification in the interorbital vacuity. The prootic seems simi- lar to that of Brasilitherium but not details of it can be observed.

Ventral area of the braincase The promontorium is well preserved and its volume is proportionally larger than in Brasilitherium. Opistotic and prootic appear to be fused. The jugular foramen is separated from the perilymphatic foramen by bone, different to the condition in Brasilitherium, in which they are confluent. The posterior area of the prom- ontorium is connected to the interfenestralis crest, not separated as it is in Brasilitherium. Figure 12 - Minicynodon maieri (UFRGS-PV-1030-T). A, right mandibular-skull articulation, as preserved, Lower jaw in lateral view; B, the same articular area with the The lower jaws are in with the bones in their anatomical position. Abbreviations as in uppers. The left ramus lacks the postdentary previous figures. bones, but the right one, which is anteriorly displaced, has the postdentary bones in the Dentition corresponding dentary groove and the ar- Because the lower jaws are in tight occlu- ticular is closely articulated to the quadrate sion, many small details are not possible to (Figure 12). observe. Some small but possibly signifi- The dentary is low and elongate, and the cant differences can be seen between Mini- coronoid process rather low and posteriorly cynodon and Brasilitherium dentition. inclined. In the right lower jaw there is a dis- tinct, incipient condyle seen in lateral view Upper incisors (Figure 12A) because the jaw is a bit anteri- Minicynodon has not a diastema between orly displaced. It was not observed in Brasi- canines and incisiform. It has five incisi- litherium but possibly it was present because form teeth, three in the premaxilla and two an incipient glenoid groove was observed or possibly three in the maxilla. They are (Figure 1). Possibly an incipient glenoid rather cylindrical and ventrally directed. was also present in Minicynodon. The proportion between the horizontal Lower incisors branch of dentary and the total length of it It has four lower incisors. The fourth is is larger than in Brasilitherium. thicker than the more procumbent first in-

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 21 Bonaparte J. F., Soares M. B. and Martinelli a. g. cisor. There is not a diastema between the steps between cynodonts and mammals are lower incisors and the canine. safely established. Actually, the anatomy of the brasilodontids suggests that there are too Canines much to learn on this fascinating subject on Upper and lower canines are proportion- the origin of mammals. On this respect it is ally smaller than those of Brasilitherium. interesting to cite an opinion by Tom Kemp included in his recent book on The Origin Postcanines and (2005:78): “For Upper and lower postcanines are sepa- the moment, this mosaic of ancestral and rated from the canines by a very small derived mammalian characters seen among diastema. There are seven postcanines in the most progressive eucynodont groups, the maxilla, similar with those of Brasilith- tritylodontids, tritheledontids, therioher- erium, and seven or eight in the dentary. petids, juvenile probainognathids, and pre- The lower postcanines show some differ- sumably also dromatherians and their like, ences with those of Brasilitherium, because reveals the possibility that several lineages they have the main cusp “a” on the center of eucynodonts were inde- of the crown, not mesially displaced as in pendently evolving reduced body size with Brasilitherium. a concomitant convergence of several basic characters associated with small body size, Tooth replacement but superimposed upon divergent charac- The last postcanine of the left dentary was ters associated with differing diets, etc. It is in process of eruption. Not other indication perhaps significant, as described in a later of tooth replacement was observed. chapter, members of the taxon mammalian almost at their first appearance consisted of at least four distinct groups”. This state- ment demonstrates that the information and DISCUSSION knowledge of these transitional stages was far from complete. Transition eucynodonts-mammals The specializations in the transitional stages between derived eucynodonts and It seems clear that the discovery and the earliest mammals presented by Kemp studies on the brasilodontids have opened (2005) seem to us that are more in accordance new opportunities to improve knowledge with the state of this fascinating subject. The on the eucynodonts–mammals transition evolutionary significance of the brasilodon- (Bonaparte, 2012a). New interpretations af- tids demonstrates that some traditional and ter new evidences improve the knowledge recent ideas (Kielan-Jaworowska et al., 2004; although usually giving room for new inter- Kemp, 2005) have to be improved and up- pretative problems. date. After the magnificent chapter on the ori- gin of mammals in Kielan-Jaworowska et al., (2004), with very much anatomical infor- The sister group of mammals mation especially, on the transformation of characters, we have the false impression that For many years it was considered that most of the knowledge on the transitional Tritylodontidae (e.g., Kemp, 1982) and

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then the Tritheledontidae (e.g., Hopson litherium (Bonaparte et al., 2003, 2005) from and Barghusen, 1986) were the sister group the Late Triassic of Southern Brazil, was of mammals, ideas that are still supported confirmed the interpretation by Bonaparte by several authors (Kielan-Jaworowska et et al., (2003) that the brasilodontids rep- al., 2004; Kemp, 2005; among others). Now, resent the sister group of mammals (Luo, after the discoveries of Brasilodon and Brasi- 2007). The characters supporting this inter-

Figure 13 - The four Brasilodontidae genera. A, Protheriodon (Middle Triassic); B, Brasilodon (Upper Triassic); C, Brasilitherium (Upper Triassic); D, Minicynodon (Upper Triassic).

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 23 Bonaparte J. F., Soares M. B. and Martinelli a. g. pretation are from almost complete skulls, discussion on the subject were published, lower jaws, dentitions and a few appen- notably, by Martinelli and Rougier (2007) dicular bones (this paper), from three spe- who postulate that the dissapear and reap- cies from the Late Triassic () and one pearance of the character by the most di- from the Middle Triassic (Bonaparte et al., verse and hypothetical processes, includ- 2006) from Southern Brazil (Figure 13). ing heterochronic factors. Althoug brasilodontids clearly resemble However, the brasilodontids clearly show the Morganucodonta (Kielan-Jaworowska et that the interpterygoid vacuities were a per- al., 2004) a few autopomorphies of Brasilith- sistent primitive character inherited from erium may discard an ancestor-descendant the procynosuchids, present in all the four hypothesis after the known species (McK- genera of Brasilodontidae and in the sister enna and Bell, 1997). group, the Thritheledontidae. However, Brasilodontidae was made, In the earliest mammals as Sinoconodon probably, not only by the few genera and (Crompton and Sun, 1985) and Morganu- species recorded from a small region of codon (Kermack et al., 1981) the wide ptery- Southern Brazil, and possibly they were goid is present on its original place but the present on other latitudes of the huge Pangea vacuities are covered by medial growing of , as recently demonstrated the lateral branch of the pterygoid, preserv- (Bonaparte, 2012b) by the presence of Panch- ing the width space of the primary palate. etocynodon in India (Das and Gupta 2012). At The process of closing the vacuities was present, the hypotesis that Brasilodontidae different in Thrinaxodontidae, Probainog- originated the Morganucodonta appears nathidae, Chiniquodontidae, - reasonable because not reversal of charac- tidae and Tritylodontidae to that of Brasilo- ters is required for such interpretation. dontids and mammals, because the ptery- goid moved medially and become firmly appressed to the parasphenoid, making The interpterygoid vacuities the characteristic ventromedial keel that connects the anterior with the posterior The comparative anatomy of brasilo- regions of the skull. Finally, the presence dontid genera and the inferred plyloge- of the pterygoid vacuities in the Trithele- netic relationships with procynosuchids dontidae is explained because they are the (Bonaparte et al., 2011) have shed some sister group of Brasilodontidae, retaining light on the presence or absence of the in- such primitive character. terpterygoid vacuities. The evolutionay The functional aspect of the vacuities is history of the vacuities was greatly con- not discussed here, although the interpre- fused because most of the Early and Mid- tations by Barghusen (1986) appear well dle Triassic cynodonts do not present such founded (see also Martinelli and Rougier, openings and thereafter the character reap- 2007). pear in some Late Triassic and Early Juras- sic derived cynodonts as the Tritheledon- tidae (Crompton, 1958; Bonaparte, 1980; Adelobasileus, Hadrocodium, and Hopson and Barghusen, 1986). Such dual Microconodon. information have stimulated hypothesis to understand the problem. Detailed and long The knowledge of the Late Triassic Brasi-

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lodontidae gives opportunity to discuss and figured forBrasilitherium (Bonaparte something more on the species Adelobasile- et al., 2003, 2005). us cromptoni Lucas and Hunt, 1990, Micro- c) “an ossified floor to the cavum epip- conodon tenuirostris Osborn, 1886, and on tericum for the trigeminal ganglion”. Hadrocodium wui Luo, Crompton and Sun, However, in the reconstruction of the 2001. Adelobasileus is from the Late Triassic basicranium of Adelobasileus presented Tecovas Formation of , USA, of Late in Kielan-Jaworowska et al., (2004, Fig- age. The only known specimen is ure 4. 11C), the cavum is not totally os- the holotype, a very incomplete skull pre- sified. In Brasilitherium the cavum epip- serving only a partial braincase and some tericum is similarly unossified as in the details of the basicranium. Several mam- type specimen of Adelobasileus shown in malian characters were observed by Luo the cited figure of Kielan-Jaworowska et (1994), Lucas and Luo (1993), Luo et al. al. (2004). (2001) and Kielan-Jaworowska et al. (2004), d) “full enclosure of the pterygo-paraoc- but they were not enough to be sure of its cipital foramen (for the stapedial artery) actual relationships because the absence by bone and partial enclosure of the of critical diagnostic characters from the ascending channel for the orbitotempo- dentition, lower jaw, and zygomatic arch. ral…”. In the specimen of Brasilitherium However its mammalian affinities were UFRGS-PV-1043-T is the same situation, emphasized by the authors that described but in the holotype of Brasilodon and one and discussed it. Kielan-Jaworowska et specimen of Brasilitherium the pterygo- al. (2004) include Adelobasileus, tentatively paraoccipital foramen is not totally within the “Earliest Stem Mammals”, other closed. The state of this character and authors as Rougier et al. (1996) and Luo et that of the channel for the diploetica ar- al. (2001, 2002) have interpreted Adelobasile- tery appear to be variable on this level of us as intermediate between Sinoconodon derivation toward the mammalian con- and other stem mammals. dition. So, both of these characters may It is interesting to point out that most of be of doubtful value. characters indicated by Kielan-Jaworows- e) “separation of the cochlear foramen from ka et al. (2004, p. 185), to support, even the jugular foramen and separation of tentatively, the mammalian condition of the hypoglosal (condylar) foramen from Adelobasileus have been recorded in the the jugular foramen”. In Brasilitherium non-mammalian cynodonts brasilodontids specimen UFRGS-PV-1043-T the cochle- (Bonaparte et al., 2003, 2005, 2006, 2010). ar and jugular foramina are confluent, They are the following: but in the type specimen of Minicynodon a) “incipient promontorium”. (Promon- UFRGS-PV-1030-T they are separated by torium well developed are present in bone. The condylar foramen is separated specimens of Brasilitherium UFRGS-PV- from the jugular foramen in Brasilodon, 1043-T and of Minicynodon UFRGS-PV- Brasilitherium and Minicynodon available 1030-T). specimens. b) “an enlarged anterior lamina of the pet- It seems clear that these five significant rosal for the lateral wall of the braincase characters are not enough to assume that encircling the foramina…”. The same or Adelobasileus may be considered a stem very similar are the characters observed mammal, as cited by Kielan-Jaworowska

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 25 Bonaparte J. F., Soares M. B. and Martinelli a. g. et al. (2004). The presence of a small ptery- Hadrocodium wui (Luo, Crompton and goid vacuity (Lucas and Luo, 1993: 320), Sun, 2001) is represented only by the holo- and the presence of the median pterygoid type skull, a quite small specimen, 12 mm crest (Lucas and Luo, 1993: fig.9; Kielan- long, which includes complete dentition Jaworowska et al., 2004, Figure 4. 11A and and lower jaws in natural connection with C) suggests a more plesiomorphic level of the skull. organization than both in Sinoconodon and Preservation of the palatine and basicra- Morganucodon, that is more in accordance neal regions is not the best, and some defor- with the anatomical characters present mation is also present. In 2004, the former in the Late Triassic brasilodontids. So, it author had the opportunity, thanks to Dr. seems reasonable to interpret Adelobasileus Z.-X. Luo, to observe the specimen that was as a member of the Family Brasilodontidae temporarily at the Carnegie Museum of Nat- or of some other taxon of non-mammalian ural History. In 2005 Bonaparte et al. (2005) cynodonts. published some observations on the well

Figure 14 - Tentative cladogram of the Epicyno- dontia discussed in this paper. Abbreviations: 1, Epicynodontia. 2, Gomphodontia. 3, Galesauria. 4, Brasilodontia. Modified from Bonaparte (2012b).

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developed pterygoid wing present in Had- forms previous to the earliest known mam- rocodium. Originally, Luo et al. (2001: 336) mal. So, the ideas of Kemp (2005, p.78) indicated: “The small hamulus of pterygoid that indicate: “… may be the “reptilian- is similar to the condition in Haldanodon, mammalian” boundary was crossed sev- Ornithorhynchus and multituberculates but eral times, if such a cladistically incorrect more reduced than the homologous trans- statement may be forgiven”, seems to have verse flange of cynodonts…”. The well de- a real conceptual value. veloped pterygoid wing observed in the type specimen of Hadrocodium (Bonaparte et al., 2005) is, without doubt, a functional CONCLUSIONS character related to the masticatory func- tion, indicating a level of primitive organi- The anatomical description and com- zation of some muscles controlling occlusal parisons of the new specimen of Brasilith- movements of the lower jaws. So, probably erium riograndensis (UFRGS-PV-1043-T) the unreduced pterygoid wings of Hadroco- and of the holotype of Minicynodon maieri dium may shed doubts on the mammalian (UFRGS-PV- 1030-T) (Bonaparte et al., 2003, condition of this small Chinese genus. 2005, 2010) confirms the very close rela- At present times, after the anatomical in- tionships of them to Morganucodon watsoni formation on Late Triassic Brasilodontidae (Kermack et al., 1981). Both genera of Brasi- we suggest that Hadrocodium may be in an lodontidae show a great similar morpholo- intermediate evolutionary position be- gy suggesting that the possibility of ances- tween Brasilitherium and Morganucodon. tor-descendent appears to be quite clear at Microconodon tenuirostris Osborn 1886 is the family level. A few autopomorphies in known by a large number of specimens. both genera make uncertain closer relation- The numerous species supposedly related ships. It is confirmed that the Brasilodon- to it from North America and Europe were tidae (Bonaparte et al., 2005) is composed extensively and carefully analized by Sues by the genera Protheriodon (Bonaparte et al., (2001). Tricuspes (Huene, 1933), Pseudotri- 2006) from the Middle Triassic, and Brasi- conodont (Hahn et al., 1984), Lepagia (Hahn lodon (Bonaparte et al., 2003), Brasilitherium et al., 1987), Gaumia (Hahn et al., 1987), (Bonaparte et al; 2003), and Minicynodon “Pseudotriconodont” (Lucas and Hoakes, (Bonaparte et al., 2010) from the Late Tri- 1988), Therioherpeton (Bonaparte and Bar- assic (Norian) of Southern Brazil. Very re- berena, 1975), and Prozostrodon (Bonaparte cently Bonaparte (2012b) considered that and Barberena, 2001), although of uncer- the Early Triassic Panchetocynodon from tain systematic interpretations, because of the Panchet Formation of India (Das and incomplete material, they obviously are Gupta, 2012) is a primitive Brasilodontidae enough to demonstrate that the variety of although represented by an incomplete left derived non-mammalian cynodonts taxa lower jaw. The tentative cladogram in Fig- was very significant and of great geograph- ure 14 shows the possible phylogenetic po- ical distribution on Pangea. These incom- sition of the Early Triassic Panchetocynodon, pletely known taxa along with Brasilodon, as presented in Bonaparte (2012b). Brasilitherium and Minicynodon (Bonaparte The synonymy of Brasilitherium with et al., 2003, 2005, 2006, 2010) show the ex- Brasilodon proposed by Liu and Olsen istence of a rich evolutionary scenario of (2010) is the result of quick and superficial

HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 HISTORIA NATURAL Tercera Serie Volumen 2 (2) 2012/5-30 27 Bonaparte J. F., Soares M. B. and Martinelli a. g. observations ignoring evolving characters no Rio Grande do Sul. Anais 31° Congresso of advanced eucynodonts. Brasileiro de Geologia 2: 659-673. It is considered that the Tritheledontidae Barghusen H. 1986. On the evolutionary origin of the therian tensor veli palatini and tensor is the sister group of Brasilodontidae, both tympani muscles. In: Hotton, N., MacLean, constituting a subclade closely related to P.D., Roth, J.J. y Roth, E.C. (Eds.) The Ecol- Morganucodontidae and quite separated ogy and Biology of Mammal-like . from the remaining eucynodonts (Kemp, Smithsonian Institution Press, Washington 1982). The small size of these taxa suggests DC, 253-262 pp. Bonaparte, J.F. 1980. El primer ictidosaurio insectivorous habits and the retention of ple- (Reptilia-Therapsida) de América del Sur, siomorphic characters along with derived Chaliminia musteloides, del Triásico Supe- ones connected with mastication, hearing, rior de La Rioja, República Argentina. Actas olfaction and an improved nervous system del 2° Congreso Argentino de Paleontología y as indicated by the larger braincase. On the Bioestratigrafía, y 1° Congreso Latinoamericano de Paleontología, 1: 123-133. other hand, Thrinaxodontidae, Cynognathi- Bonaparte, J.F. 2012a. Miniaturisation and the dae, Chiniquodontidae and Probainognathi- origin of Mammals. Historical Biology, 24: dae developed several adaptive characters 43-48. for a carnivorous habit. Bonaparte, J.F. 2012b. Evolution of the Brasilo- According with Bonaparte (2012b), the dontidae (Cynodontia-Eycynodontia). His- subclade Brasilodontia, so different to the torical Biology, iFirst, 2012: 1-11. Bonaparte, J.F. y Barberena, M.C. 1975. A pos- well know Triassic eucynodonts, opens sible mammalian ancestor from the Middle doors for new interpretations on the origin Triassic of Brazil (Therapsida-Cynodontia). of mammals. Journal of Paleontology, 49: 931-936. Bonaparte, J.F. y Barberena, M.C. 2001. On two carnivorous cynodonts from the Late Trias- sic of southern Brazil. Bulletin of the Museum ACKNOWLEDGEMENTS of Comparative Zoology, 156: 59-80. Bonaparte, J.F., Martinelli, A.G., Schultz, C.L. The Senior author acknowledges contin- y Rubert R. 2003. The sister group of mam- ued support from the National Geographic mals: small cynodonts from the Late Trias- Society for field Works; to the Humboldt sic of southern Brazil. Revista Brasileira de Paleontologia, 5: 5-27. Stiftung for stays in Germany; to Professor Bonaparte, J.F., Martinelli, A.G. y Schultz C.L. W. Maier (Tübingen) for long and fruitful 2005. New information on Brasilodon and discussions; to the Ligabue Foundation Brasilitherium (Cynodontia, Probainog- (Venice) for support and estimulate; to the nathia) from the Late Triassic of southern Federal University of Rio Grande do Sul Brazil. Revista Brasileira de Paleontologia, 8: 25-46. for many scientific opportunities in Porto Bonaparte, J.F., Bento Soares, M. y Schultz, C.L. Alegre; and to the Fundación de Historia 2006. A new non-mammalian cynodont Natural “Félix de Azara” for help and en- from the Middle Triassic of sourthern Brazil couraging. and its implications for the ancestry of mam- mals. Bulletin of the New Mexico Museum of Natural History and Science, 37: 599-607 Bonaparte, J.F., Schultz, C.L., Bento Soares, M. BIBLIOGRAPHY y Martinelli, A.G. 2010. La fauna local de Faxinal do Soturno, Triásico Tardío, Rio Andreis, R.R., Bossi, G.E. y Montardo, D.K. Grande do Sul, Brazil. Revista Brasileira de 1980. O Grupo Rosario do Sul (Triássico) Paleontologia, 13: 233-246.

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