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A Traversodontid Cynodont of African Affinity in the South American Triassic

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A Traversodontid Cynodont of African Affinity in the South American Triassic A traversodontid cynodont of African affinity in the South American Triassic F. Abdala1* & A.M. Sa-Teixeira2 1Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa 2Rua São Luis 600, 90.620-170, Porto Alegre, RS, Brazil Received 1 June 2003. Accepted 20 February 2004 The Traversodontidae represent one of the most diverse and abundant families of non-mammaliaform cynodonts, particularly in Gondwanan faunas of Middle to Late Triassic age. Although a great diversity of traversodontids is known for South American (approximately nine species) and African (six to seven species) Triassic faunas, the record of the group in these continents does not show similarities beyond the family level. Here we describe a new traversodontid, Luangwa sudamericana, from the Santa Maria Formation of southern Brazil, which is most similar to the Anisian traversodontids Luangwa drysdalli from the upper portion of the Ntawere Formation in Zambia, and Scalenodon angustifrons from the Manda Formation in Tanzania. Features in common with these African taxa are oval-outlined upper postcanines presenting an anterior labial cingulum. The new species is similar to L. drysdalli in a number of features, including the presence of a posterior cingulum in the upper postcanines, anterior cingulum in front of the transverse crest in the lower postcanines, short snout, enormous orbits and short temporal region. Differences with L. drysdalli are the less developed posterior cingulum behind the upper transverse crest that does not extend along the entire posterior border of the tooth, and the presence of a well-defined posterior accessory cusp on the sectorial crest of the upper postcanines. The comparison of the quadrate, preserved in situ in the squamosal notch of the new taxon, and that from other traversodontids, suggests that the quadratojugal is involved in the formation of the lateral condyle of the traversodontid suspensorium. Luangwa represents the first genus of traversodontid, and the second of non-mammaliaform cynodont shared by South American and African faunas. A significant biochronological implication of this finding is that part of the Santa Maria Formation may now be considered Anisian in age, and thus older than generally recognized for the unit. Keywords: Traversodontidae, Middle Triassic, Brazil, Zambia, Cynodontia, Luangwa. INTRODUCTION America and Africa, the faunas of these continents do not The southern Brazilian Santa Maria Formation is well show similarities beyond the family level, with the known for its record of an important continental Triassic carnivorous Cynognathus being the only genus evidencing vertebrate fauna. Pioneering studies in this unit were faunal commonality between these continents. This taxon performed by Friedrich von Huene, a German palaeon- has been recorded in the fauna biostratigraphically tologist who in 1928 conducted a six-month field trip to known as the Cynognathus Assemblage Zone, from strata various localities in the Rio Grande do Sul State, southern of the Burgersdorp Formation, Karoo Basin, South Africa Brazil. Huene discovered and published many species of (Kitching 1995; Hancox 2000), and in the Puesto Viejo tetrapods, including Gomphodontosuchus brasiliensis, the Formation, Argentina (Bonaparte 1969; Abdala 1996). first traversodontid cynodont ever described (Huene In this report, we describe Luangwa sudamericana sp. nov. 1928; Hopson 1985). He later identified other species of from the Santa Maria Formation of southern Brazil. One of the Traversodontidae in his seminal work on the Brazilian the specimens included in the new species (UFRGS 267PV) Triassic reptile fauna (Huene 1936). Barberena (1974, was previously described as Luangwa sp. by Teixeira 1981a,b) reinterpreted some of the traversodontid materials (1995). The new species is most similar to Luangwa drysdalli previously studied by Huene (1936) and, based on new from the upper beds of the Ntawere Formation, Zambia, discoveries, described new species of this group (Barberena and to Scalenodon angustifrons from the Manda Formation, 1981a). Tanzania, in eastern central Africa (Crompton 1955, 1972; Many traversodontid species have been described from Brink 1963; Kemp 1980), and thus demonstrate Triassic faunas from Brazil and Argentina (Bonaparte traversodontids of African affinity in the South American 1982; Abdala et al. 2002) and genera such as Massetognathus Middle Triassic. This finding also has important chrono- (Romer 1967; Barberena 1981a; Abdala & Giannini 2000) logical implications, because both the Manda Formation and Exaeretodon (Bonaparte 1962; Abdala et al. 2002) were and the upper portion of the Ntawere Formation are recognized from Ladinian and Carnian faunas of both considered Anisian in age (Cox 1991; Battail 1993), and, as countries. This family is also well diversified in Triassic a consequence, some of the outcrops of the Santa Maria deposits of Africa (including Madagascar), where it is Formation in southern Brazil could be older than the represented by six to seven species (Crompton 1955; Brink Ladinian age usually recognized for its oldest fauna. 1963; Kemp 1980; Gow & Hancox 1993; Flynn et al. 2000). Institutional abbreviations. BP: Bernard Price Institute Despite this relatively high diversity of the group in South for Palaeontological Research, University of the *E-mail: [email protected] Witwatersrand, Johannesburg; MCP: Museo de Ciências e ISSN 0078-8554 Palaeont. afr. (December 2004) 40: 11–22 11 Figure 1. Luangwa sudamericana, holotype (MCP 3167PV); a, lateral view of snout; b, stereopair of upper dental series; c, lateral view of mandible; d, stereopair of lower dental series. Scale bars = 20 mm. Tecnología, Pontifícia Universidade Católica do Rio Grande Referred material. UFRGS 267PV,a well-preserved partial do Sul, Porto Alegre; MCZ: Museum of Comparative skull and a fragment of the left lower jaw with three Zoology, Harvard University, Cambridge, Massachussets; postcanines (Figs 2 & 3). NMQR: National Museum, Bloemfontein; OUMNH: Horizon and locality. Santa Maria Formation, Middle to Oxford University Museum of Natural History; SAM: Upper Triassic. Specimen MCP 3167PV is from an un- South African Museum, Cape Town; UFRGS: Instituto de known locality; specimen UFRGS 267PV comes from an Geociências, Universidade Federal do Rio Grande do Sul, unknown outcrop located on the border between the dis- Porto Alegre; UMZC, University Museum of Zoology, tricts of Candelaria and Vera Cruz, Rio Grande do Sul Cambridge. State, Brazil. Many outcrops are present in this area, and recent field trips to the various outcrops yielded only frag- SYSTEMATIC PALAEONTOLOGY mentary remains. Thus, the exact locality remains uncer- tain. Therapsida Broom 1905 Comparative material. BP/1/3731, skull with articulated Eucynodontia Kemp 1982 mandible and some postcranial bones, probably of the Traversodontidae von Huene 1936 manus, attached to the snout; holotype of Luangwa Luangwa Brink 1963 drysdalli (Brink 1963; Fig. 6); BP/1/3733, poorly preserved anterior portion of the skull with dentition. Specimen Luangwa sudamericana sp. nov., Figs 1–5 smaller than the type, most likely a juvenile of the same Etymology. Sudamericana refers to the first record for species; OUMNH TSK121, partial skull with mandible South America of a genus of Traversodontidae previously (Fig. 7) and postcranial elements assigned to Luangwa known only in east Africa. drysdalli by Kemp (1980). These specimens come from out- Holotype. MCP 3167PV, a well-preserved partial skull and crops of the upper beds of the Ntawere Formation in the mandible. The skull includes the rostrum and rim of the Luangwa Valley,Zambia (Drysdall & Kitching 1963; Kemp right orbit, with complete dentition, and an isolated por- 1975). tion of the basicranium, and the most posterior portion of UMZC T.907, partial skull with lower jaw, holotype of the zygoma, including the quadrate in situ (Figs 1, 4 & 5). Scalenodon angustifrons (Parrington 1946; Crompton 1955; 12 ISSN 0078-8554 Palaeont. afr. (December 2004) 40: 11–22 Figure 2. Luangwa sudamericana, UFRGS 267PV; a, dorsal, b, ventral and c, left lateral views of skull; d, stereopair of the upper postcanines; e, stereopair of lower postcanines. Scale bars = 20 mm (a, b, c, d) and 10 mm (e). Fig. 8a,b); UMCZ T.908; T.909; T.910; T.911; T.912; T.913; tiny cuspules in front of the anterior transverse crest of the T.914; T.915; T.916; T.917; T.918. All these specimens are lower postcanines forming an incipient cingulum. Other skull and/or lower jaw fragments, with UMCZ T.910 similarities with L. drysdalli include a short snout and showing the best-preserved upper and lower postcanines temporal region, large orbits and angle of the dentary (Fig. 8c,d). They come from the locality B 29 of Stockley slightly projected posteriorly. Differentiating L. sudamericana (1932), between Gingama and Tschikonge, Ruhuhu from L. drysdalli and S. angustifrons is a well-defined poste- Valley, Tanzania and were described by Crompton (1955) rior accessory cusp on the labial crest of the upper as S. angustifrons. postcanines. The presence of one anterior accessory cusp on the labial (sectorial) crest of the upper postcanines is a Diagnosis difference with the holotype of L. drysdalli (BP/1/3731), but A traversodontid most similar to Luangwa drysdalli Brink not with OUMNH TSK 121. 1963 and Scalenodon angustifrons (Parrington 1946). As in these species
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