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Home , Chiniquodon, Exaeretodon, Santa Maria Formation, Therioherpeton

A new therioherpetid from the (middle Late ), southern

Fernando ABDALA Museu de Ciências e Tecnologia, Pontifícia Universidade Católica de , Avenida Ipiranga 6681, 90619-900 Porto Alegre, RS (Brazil) [email protected]

Ana Maria RIBEIRO Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Rua Dr Salvador França, 1427, 90690-000 Porto Alegre, RS (Brazil) [email protected]

Abdala F. & Ribeiro A. M. 2000. — A new therioherpetid cynodont from the Santa Maria Formation (middle ), southern Brazil. Geodiversitas 22 (4) : 589-596.

ABSTRACT A new cynodont with sectorial postcanines, from the Santa Maria Formation of southern Brazil, is described. Charruodon tetracuspidatus n. gen. n. sp., KEY WORDS represented by a fragmentary lower jaw, shows a postcanine morphology close Cynodontia, to that of cargnini, thereby justifying a tentative inclusion of Therioherpetidae, the new species within the family Therioherpetidae. Comparisons among middle Late Triassic, Brazil, with sectorial teeth are suggestive of a sequence of morphological sectorial tooth. changes in the sectorial postcanines of advanced cynodonts.

RÉSUMÉ Un nouveau cynodonte thérioherpétidé de la Formation Santa Maria (Trias supé- rieur) du Sud du Brésil. Un nouveau cynodonte aux dents postcanines sectoriales, provenant de la Formation Santa Maria au Sud du Brésil, est décrit. La morphologie des dents postcanines de Charruodon tetracuspidatus n. gen. n. sp., représentée par un MOTS CLÉS fragment de mandibule, est proche de celle observée chez Therioherpeton car- Cynodontia, gnini, ce qui par conséquent l’inclut dans la famille des Therioherpetidae. Des Therioherpetidae, comparaisons avec d’autres cynodontes ayant une dentition sectoriale vien- Trias supérieur, Brésil, nent suggérer une série de modifications morphologiques qui affectent les dent sectoriale. postcanines sectoriales chez les cynodontes évolués.

GEODIVERSITAS • 2000 • 22 (4) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.mnhn.fr/publication/ 589 Abdala F. & Ribeiro A. M.

INTRODUCTION crown morphology resembling that seen in Therioherpeton. The purpose of this paper is to The Santa Maria Formation in southern Brazil is provide a description of this new cynodont mate- well-known for its abundant Triassic continental rial and compare it with that of other sectorial- fauna (Barberena et al. 1985; Schultz 1995). toothed cynodonts. Ranging from ? to , this form- ation preserves a heterogeneous sample of the ABBREVIATIONS vertebrates of the epoch (see Barberena et al. MCP PV Paleontological collection of the Museu de 1985 for a list of taxa). Ciências e Tecnologia of the Pontifícia Important components of the Santa Maria fauna Universidade Católica de Rio Grande do are non-mammalian cynodonts, a paraphyletic Sul; PVL Paleontologia de Vertebrados Lillo collec- assemblage that includes the closest relatives of tion, Universidad Nacional de Tucumán; the early (i.e. in The cusp terminology follows that used by Hopson & Rowe 1988). The transition to mammals is one Crompton (1969: 23) to describe the molars of of the best documented evolutionary events in (= ). the record, allowing detailed examination of the successive changes leading to the origin of a major group (Kemp 1982; Hopson & SYSTEMATIC Barghusen 1986; Sidor & Hopson 1998). Non-mammalian cynodonts are represented in Order THERAPSIDA Broom, 1905 Brazil by the numerically dominant traversodont- Suborder CYNODONTIA Owen, 1861 ids, characterized by transversely broad postca- Family THERIOHERPETIDAE nines (Barberena 1974), and by the medium- Bonaparte & Barberena, 1975 to-large-sized chiniquodontids, distinguished by sectorial postcanine teeth (Romer 1969; Teixeira Charruodon n. gen. 1982; Abdala 1996). In addition, there are smal- TYPE SPECIES BY ORIGINAL DESIGNATION.— ler forms such as brasiliensis Charruodon tetracuspidatus n. sp. Barberena, Bonaparte & Teixeira, 1987, which ETYMOLOGY. — In honor to the Charruas, a native features cingular cusps along the base of the South American tribe that lived in southern Brazil, crown of postcanine teeth, and Therioherpeton and from the Greek odon which means tooth. cargnini Bonaparte & Barberena, 1975, which DIAGNOSIS. — As for the species, by monotypy. has fully sectorial postcanines. The latter species, represented only by the holotype, comes from Santa Maria city and was proposed as a probable Charruodon tetracuspidatus n. sp. ancestor by Bonaparte & Barberena (Figs 2; 3; Tables 1; 2) (1975). HOLOTYPE. — Fragment of the left dentary horizontal In the paleontological collection of the Museu de ramus, with alveoli for three incisors, roots of the Ciências e Tecnologia, Pontifícia Universidade canine and three postcanines, and a fifth tooth with a Católica de Rio Grande do Sul, a fragment of the well-preserved crown (Figs 2; 3) (MCP-3934 PV). left lower jaw of a small cynodont was found bear- ETYMOLOGY.— tetracuspidatus, in reference to the ing a sectorial tooth. The specimen comes from four-cusped crown morphology. the same locality (Fig. 1) in which the traverso- LOCALITY. — 29°42’07.44’’S, 52°51’43.95’’W, dontid cynodont Cabrera, 1943 and approximately 8 km West of the city of in the State of Rio Grande do Sul, southern Brazil. the basal Proterochampsa nodosa Barberena, 1982 were discovered. HORIZON. — Santa Maria Formation. The presence of Exaeretodon and Proterochampsa here is strongly Close inspection of the jaw fragment revealed the suggestive of a age for this stratum of the for- presence of a replacement tooth with a sectorial mation (Rogers et al. 1993).

590 GEODIVERSITAS • 2000 • 22 (4) A new cynodont from the Brazilian middle Late Triassic

Rio Pardo

Rio Jacui VENÂNCIO SANTA AIRES MARIA CANDELÁRIA

BR 287

ARGENTINA N RIO GRANDE DO SUL

30°

CACHOEIRA BR BRAZIL DO SUL 471

URUGUAY BR 290 PANTANO GRANDE 120 km 25 km 54° 53°

FIG. 1. — Map showing the location of the fossil outcrop.

DIAGNOSIS. — Lower jaw with a high horizontal pear relatively small compared with the anterior ramus when compared with the postcanine size, height of the jaw. Originally, the region preserved approximately 0.31 with respect to the anteroposterior length of the crown of the fifth postcanine; four well- extended as far posteriorly as the fifth alveolus, developed cusps on the crown of the postcanine; sec- which contained a replacing tooth that preserved a ond cusp “a” is the largest, followed closely in size by complete crown. This tooth was isolated and pre- the third (“c”); the three posterior cusps (“a”, “c” and pared in order to examine its crown morphology “d”) are directed posteriorly; a sharp constriction dis- tinguishes the crown from the root; roots undivided. (Fig. 3). Four aligned cusps are present and there is no indication of a cingulum. The main cusp “a” is slightly larger than the first posterior accessory DESCRIPTION cusp “c” from which it is separated by a notch. The dentary fragment extends from an open and Both of these cusps are slightly recurved posterior- high symphysis to the level of the third postcanine ly. The second posterior accessory cusp “d” is (Fig. 2A, B). There are three alveoli for the inci- the lowest. It is posteriorly directed and well- sors. The root of the canine is larger than those of separated from cusp “c” by a notch. The anterior the incisors and postcanines, but has undergone accessory cusp “b” is relatively small and closely some transverse compression during fossilization. united with the main cusp by a high crest. In oc- The mental foramen is located at the level of the clusal view, the crown is bulbous, with convex la- second postcanine, and closer to the symphysis are bial and lingual sides, the latter being particulary some nutritive foramina (Fig. 2B). Three postca- rounded. The root is undivided and distinguished nines are represented only by their roots. All ap- from the crown by a prominent constriction.

GEODIVERSITAS • 2000 • 22 (4) 591 Abdala F. & Ribeiro A. M.

A

B

FIG. 2. — Stereo pair and line drawing of the mandibular ramus of Charruodon tetracuspidatus n. sp. (MCP-3934 PV); A, labial view; B, lingual view. Scale bar: 10 mm.

TABLE 1. — Charruodon tetracuspidatus n. sp., holotype. DISCUSSION AND CONCLUSION Measurements of the specimen MCP-3934 PV (mm). Several new Late Triassic European cynodonts Total length of specimen 23.5 Height at the level of the first postcanine 15.2 have been described over the past two decades Anteroposterior length of the root of the canine 5.0 mainly on the basis of isolated teeth (Hahn et al. Anteroposterior length of the root of postcanine 1 2.8 1984, 1988, 1994; Sigogneau-Russell & Hahn Anteroposterior length of the root of postcanine 2 3.0 1994; Godefroit 1997; Godefroit & Battail Anteroposterior length of the root of postcanine 3 3.0 1997). As outcome of these findings, different systematic proposals for cynodont taxonomy have emerged to incorporate the new evidence. TABLE 2. — Charruodon tetracuspidatus n. sp., holotype. Measurements of the fifth postcanine (mm). Battail (1991) recognized Dromatheriidae, Chiniquodontidae and Therioherpetidae, among Crown length 4.8 others, as valid cynodont families, all character- Crown height 3.0 ized by the presence of sectorial postcanines bea- Crown width 1.8 ring a faint cingulum or lacking one entirely.

592 GEODIVERSITAS • 2000 • 22 (4) A new cynodont from the Brazilian middle Late Triassic

A B C

A, B

FIG. 3. — Fifth tooth of Charruodon tetracuspidatus n. sp. (MCP-3934 PV); A, labial view; B, lingual view; C, crown view. Scale bars: 10 mm.

Chiniquodontids are Middle to Late Triassic morphologies (see in Godefroit & Battail 1997). cynodonts that are restricted to Some diagnostic features of dromatheriids, such (sensu Abdala 1996, but see Battail 1991; as the low dentary ramus and symphysis and the Hopson & Barghusen 1986; Hopson 1991). The narrower crowns (Battail 1991; Godefroit & postcanines of chiniquodontids lack cingula and Battail 1997) contrast with the new material des- have undivided roots (Abdala 1996). The crowns cribed herein. Nevertheless, the crown morpho- of the posterior postcanines possess four cusps logy of Charruodon tetracuspidatus is mostly with the anterior accessory cusp being faintly coincident (e.g., in the development and curvatu- defined (Fig. 4A). The anterior postcanines are re of its cusps) to that of Meurthodon gallicus less complex, with only a central cusp and a pos- Sigogneau-Russell & Hahn, 1994, from Saint- terior accessory cusp. The main cusp is notably Nicolas-du-Port, France (Fig. 4D), originally more developed than the others and curved sharp- represented by an isolated tooth described by ly backwards in chiniquodontids (Abdala 1996), Russell et al. (1976). The presence of a double a clearly different morphology from that develo- root in the latter species precludes assignment of ped in Charruodon tetracuspidatus. the otherwise similar Santa Maria cynodont to Dromatheriids, from the Late Triassic of United Meurthodon. It is difficult to envisage the overall States and Europe, are represented by scarce morphology of the dromatheriids (sensu material comprising an incomplete lower jaw and Godefroit & Battail 1997), considering the isolated teeth (Lucas & Oakes 1988; Battail conspicuous variations in tooth crown morpholo- 1991). They were considered Cynodontia incer- gy, and especially taking into account the presen- tae sedis by Hopson & Kitching (1972), but they ce of taxa with and without divided roots. are better represented with the discovery of new Therioherpetidae is Battail’s (1991) emendation European material (Godefroit & Battail 1997). of Bonaparte & Barberena’s (1975) nomen The- The group, as currently defined, is noticeably rioherpetontidae. The validity of the family has heterogeneous, showing different kinds of crown been alternately denied and supported by

GEODIVERSITAS • 2000 • 22 (4) 593 Abdala F. & Ribeiro A. M.

AB C D

FIG. 4. — Lower postcanines in lateral (above) and crown (below) views; A, theotonicus (sensu Abdala, 1996, PVL 4444); B, Charruodon tetracuspidatus n. sp.; C, Therioherpeton cargnini (from Bonaparte & Barberena 1975, Museu Histórico e Cultural Vicente Palloti, Santa Maria, Rio Grande do Sul, Brazil); D, Meurthodon gallicus (from Russell et al. 1976). Scale bars: 10 mm. various authors. Hahn et al. (1984, 1994) and and the relative development of the cusps. Godefroit & Battail (1997) assigned Therioher- Nevertheless, the latter species differs from the peton cargnini Bonaparte & Barberena, 1975 to former in that the cusps do not seem to be the Dromatheriidae, whereas Sigogneau-Russell recurved, and each root exhibits a longitudinal & Hahn (1994) recognized a Therioherpetidae furrow, a feature that has been interpreted as an that included Therioherpeton and Meurthodon “incipient bifurcation of the root” (Bonaparte & gallicus. The holotype of Therioherpeton cargnini Barberena 1975). (uncatalogued specimen in the Museu Histórico In addition to the above-mentioned cynodonts, e Cultural Vicente Palloti, Santa Maria, Rio strictly sectorial postcanines are known also in Grande do Sul, Brazil) preserves a series of bro- cynognathids and galesaurids. However, the dif- ken upper postcanines, except the fifth tooth ferences are even more conspicuous in terms of that retains some vestiges of the crown. Further- crown pattern between these cynodonts and more, there is a portion of the crown of the fifth Charruodon tetracuspidatus, and the late appear- lower postcanine (Fig. 4C). Upper and lower ance of the Santa Maria form makes assignment postcanines both possess four aligned cusps and to either family highly doubtful. lack a cingulum (although the lower postcanine The new material presents, as it is clearly evident crown is missing its base). The “a” and “c” cusps from the above comparisons, a number of simila- are the larger cusps, whereas the “b” and “d” are rities and differences with members of all groups almost the same size (Bonaparte & Barberena of advanced cynodonts. We propose the provisio- 1975). Thus, it is noteworthy that the crown nal inclusion of Charruodon tetracuspidatus morphology of Charruodon tetracuspidatus is within Therioherpetidae, pending further evi- similar to that of T. cargnini in both the number dence for an alternative assignment.

594 GEODIVERSITAS • 2000 • 22 (4) A new cynodont from the Brazilian middle Late Triassic

A review of the phylogenetic interrelationships of Maria, Rio Grande do Sul, Brazil) kindly let us advanced cynodonts is beyond the scope of our examine specimens in their care. For comments paper. Instead, we would like to propose a and advice, we thank J. Ferigolo, M. Langer and sequence of morphological changes in the secto- L. Maciel, who also made suggestions for the rial postcanines of some advanced cynodonts name of the species. We particularly thank the (Fig. 4). At first, the chiniquodontid postcanines reviewers, B. Battail (Laboratoire de Paléon- show the prominence of the central cusp sharply tologie, MNHN, Paris) and P. Godefroit posteriorly directed. The condition in Charruo- (Institut des Sciences naturelles de Belgique), don is similar, but the accessory cusps are more whose comments and suggestions greatly im- developed and even retain some posterior curva- proved the final version of the paper. S. Modesto ture. In Therioherpeton, the morphology of the revised our English. Preparation of the material teeth is mostly similar to that of Charruodon, but was performed by M. Isasi, then at the Museo the cusps are not directed posteriorly and the root Argentino de Ciencias Naturales Bernardino features a prominent groove. Finally, the postca- Rivadavia in Buenos Aires. This research was nine morphology of Meurthodon is similar to that made possible by financial support from the of Charruodon, and possibly Therioherpeton, but Conselho Nacional de Desenvolvimento the crown is narrower and the roots are complete- Cientifico e Tecnológico (CNPq) of Brazil, the ly divided (Russell et al. 1976; Sigogneau-Russell Museu de Ciências e Tecnologia, Pontifícia & Hahn 1994). The latter feature suggests a Universidade Católica de Rio Grande do Sul, mammaliaforme evolutionary level for Meur- Brazil and the Museu de Ciências Naturais da thodon, judging from the recent phylogenetic Fundação Zoobotânica de Rio Grande do Sul. proposals of Hopson & Barghusen (1986), Rowe (1988), Wible (1991), Crompton & Luo (1993) and Luo (1994). REFERENCES The new sectorial-toothed cynodont Charruodon Abdala F. 1996. — Los Chiniquodontoideos (Synapsida, tetracuspidatus from the Santa Maria Formation Cynodontia) sudamericanos. Tesis Doctoral, confirms the high diversity of the Brazilian Facultad de Ciencias Naturales, Universidad Triassic fauna. The association of cynodonts with Nacional de Tucumán, Tucumán, Argentina, sectorial teeth, the traversodontid Exaeretodon, 398 p. Barberena M. C. 1974. — Contribução ao conhecimen- and the basal archosaur Proterochampsa is record- to dos cinodontes gonfodontes (Cynodontia- ed also from the Carnian age Ischigualasto Tritylodontoidea) do Brasil. Ministério de Educação Formation of Argentina (Rogers et al. 1993; e Cultura, Universida Federal do Rio Grande do Sul, 194 p. Martinez et al. 1996), which suggests that the Barberena M. C. 1982. — Uma nova espécie de stratum in the Santa Maria Formation yielding Proterochampsa (P. nodosa sp. nov.) do Triássico do Charruodon tetracuspidatus is approximately Brasil. Anais da Academia Brasileira de Ciências 54: 228 my. old. 127-141. Barberena M. C., Araújo D. C. B., Lavina E. L. & Azevedo S. A. 1985. — O estado atual do conheci- Acknowledgements mento sobre os tetrápodes permianos e triássicos do We are especially grateful to D. Cargnin who Brasil meridional, in Campos D. A. & Gimenez- showed us the locality of provenance. J. Bertoletti Armesto R. C. (eds), Coletânea de Trabalhos paleon- tológicos. MME-DNPM, série Geologia, No. 27, and M. Richter (Laboratório de Paleontologia, Paleontologia/Estratigrafia 2: 21-28, Brasília, DF. Museu de Ciências e Tecnologia, Pontifícia Barberena M. C., Bonaparte J. F. & Teixeira A. M. S. Universidade Católica de Rio Grande do Sul, 1987. — Thrinaxodon brasiliensis sp. nov., a Brazil), J. Powell (Colección Paleontología de primeira ocorrência de cinodontes Galessauros para o Triássico do Rio Grande do Sul. 1: 67-74, in Vertebrados Lillo, Universidad Nacional de Anais do Xe Congresso Brasileiro de Paleontologia, Rio Tucumán, Argentina) and A. Brutti (Museu de Janeiro 1987. Sociedade Brasileira de Histórico e Cultural Vicente Palloti, Santa Paleontologia, Rio de Janeiro.

GEODIVERSITAS • 2000 • 22 (4) 595 Abdala F. & Ribeiro A. M.

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Submitted on 17 August 1999; accepted on 23 March 2000.

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