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A NEW CYNODONT from the SANTA MARIA FORMATION, SOUTH BRAZIL, IMPROVES LATE TRIASSIC PROBAINOGNATHIAN DIVERSITY by AGUSTIN G

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A NEW CYNODONT from the SANTA MARIA FORMATION, SOUTH BRAZIL, IMPROVES LATE TRIASSIC PROBAINOGNATHIAN DIVERSITY by AGUST�IN G [Papers in Palaeontology, 2017, pp. 1–23] A NEW CYNODONT FROM THE SANTA MARIA FORMATION, SOUTH BRAZIL, IMPROVES LATE TRIASSIC PROBAINOGNATHIAN DIVERSITY by AGUSTIN G. MARTINELLI1 , ESTEVAN ELTINK2, ATILAA.S.DA-ROSA 3 and MAX C. LANGER4 1Laboratorio de Paleontologia de Vertebrados, Departamento de Paleontologia e Estratigrafia, Instituto de Geoci^encias, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Goncßalves 9500, Agronomia, 91540–000, Porto Alegre, RS Brazil; [email protected] 2Colegiado de Ecologia, Universidade Federal do Vale do S~ao Francisco, Av. Tomaz Guimar~aes S/N, Bairro Santos Dumont, 48970000, Senhor do Bonfim, BA Brazil; [email protected] 3Laboratorio de Estratigrafia e Paleobiologia, Departamento de Geoci^encias, Universidade Federal de Santa Maria, Av. Roraima, 1000, predio 17, sala 1131B, 97105-900, Santa Maria, RS Brazil; [email protected] 4Laboratorio de Paleontologia de Ribeir~ao Preto, FFCLRP, Universidade de S~ao Paulo, Av. Bandeirantes 3900, 14040-901, Ribeir~ao Preto, S~ao Paulo Brazil; [email protected] Typescript received 30 January 2017; accepted in revised form 10 April 2017 Abstract: The fossil record of non-mammaliaform based on a left lower jaw with almost complete dentition probainognathian cynodonts is outstanding in the Late Tri- that exhibits a combination of features not seen in any other assic rocks of Brazil and Argentina. Approximately 15 genera known probainognathian. Its slender lower jaw, anterodor- are known, providing unique insights in the study of the sally bent process of the dentary, high number of lower inci- major skeletal transformations prior to the mammalian con- sors, reduced canine, triconodont-like postcanine teeth with dition. Globally, the diversity of probainognathians is possi- mesiolingual and distolingual cingular cusps are all features bly under-represented, as the discovery of small- to very that support the inclusion of A. huebneri as a member of the small-sized taxa based on relatively well-preserved specimens Prozostrodontia clade. This new find highlights the conspic- is rare. Several species, for example much of the Laurasian uous probainognathian cynodont fossil record in southern record, are based on isolated teeth and jaw fragments. Here, Brazil, with a plethora of forms near the mammalian origin. we describe a new probainognathian from the Late Carnian Hyperodapedon Assemblage Zone of the Santa Maria Forma- Key words: Cynodontia, Prozostrodontia, South America, tion, south Brazil. Alemoatherium huebneri gen. et sp. nov. is Santa Maria Supersequence. C YNODONT therapsids are abundant components of & Barberena 2001; Bonaparte et al. 2003, 2005, 2012; most Middle to Late Triassic tetrapod assemblages in Martinelli et al. 2005, 2016; Oliveira et al. 2010). The southern Brazil and western Argentina (Abdala & fossil record of these groups comes from the San Rafael Ribeiro 2010; Martinelli & Soares 2016). There are Block, Cuyana, Ischigualasto-Villa Union, and Marayes- about 30 documented species of gomphodontids, cynog- El Carrizal basins in Argentina (e.g. Romer 1973a; nathids, traversodontids and probainognathians, within Martınez et al. 2013, 2015; Bonaparte & Migale 2015) a time span ranging from the Anisian–Ladinian to the and from the Santa Maria Supersequence (Parana Basin) Norian (e.g. Abdala 1996; Bonaparte & Barberena 2001; in southern Brazil (Langer et al. 2007; Oliveira et al. Abdala & Giannini 2002; Bonaparte et al. 2005; Marti- 2010; Soares et al. 2011; Martinelli & Soares 2016; Mar- nelli et al. 2005, 2009; Abdala & Ribeiro 2010; Oliveira tinelli et al. 2016). et al. 2010; Soares et al. 2011, 2014; Martınez et al. The Probainognathia clade (sensu Hopson & Kitching 2013; Martinelli & Soares 2016; Martinelli et al. 2016). 2001; Liu & Olsen 2010) which includes the Mammalia The most diverse and well-documented groups are the crown-group (e.g. Rowe 1988; Kielan-Jaworowska et al. herbivorous/omnivorous traversodontid gomphodonts 2004) originated at least during the early Middle Triassic, (e.g. Abdala & Giannini 2000; Abdala & Ribeiro 2003; exhibiting its greatest diversity during the late Middle–Late Liu & Abdala 2014; Melo et al. 2015) and the faunivo- Triassic, and represents quite disparate groups regarding rous non-mammaliaform probainognathians (Bonaparte size and diet. Main non-mammaliaform representatives © The Palaeontological Association doi: 10.1002/spp2.1081 1 2 PAPERS IN PALAEONTOLOGY include ecteniniids, chiniquodontids, probainognathids, expedition by the Laboratorio de Paleontologia, Universi- therioherpetids/dromatheriids, ‘brasilodontids’, ictidosaurs dade S~ao Paulo (USP, Ribeir~ao Preto), and Laboratorio (Martınez & Forster 1996; Hopson & Kitching 2001; Bona- de Estratigrafia e Paleobiologia, Universidade Federal de parte & Barberena 2001; Sues, 2001; Abdala & Giannini Santa Maria (UFSM, Santa Maria), in the outskirts of 2002; Martinelli & Rougier 2007; Oliveira et al. 2010) and Santa Maria, Rio Grande do Sul, south Brazil (Fig. 1). possibly tritylodontids (this group has a dual position as UFSM 11579b was included in the data matrix pub- Gomphodontia, e.g. Sues 1985; Hopson & Kitching 2001; lished by Liu & Olsen (2010) and modified by Martinelli or as Probainognathia, e.g. Kemp 1982, 1983; Abdala 2007; et al. (2016). In addition, Therioherpeton cargnini was re- Liu & Olsen 2010; see also Luo 1994). Among probaino- scored for some character-states (see Martinelli et al. gnathians, decrease in size is evident especially in forms clo- 2017). Three extremely fragmentary taxa, which are com- sely related to mammaliaforms (Rowe 1988; Ruta et al. parable with Alemoatherium, were also included: San- 2013; see also Bonaparte 2012), but this seems not to be tacruzgnathus abdalai (based on UFRGS-PV-1121-T and unidirectional in the clade. The diversity of cynodonts, Martinelli et al. 2016), Microconodon tenuirostris (based especially probainognathians, is possibly under-repre- on Simpson 1926 and Sues 2001) and Charruodon tetra- sented, as the discovery of small- to very small-sized taxa cuspidatus (based on MCP-3934 PV and Abdala & Ribeiro based on relatively well-preserved specimens is rare. The 2000). Due to the incompleteness of the taxa, we per- description of several species, for example much of the formed three different analyses: the first only including Laurasian probainognathian record (e.g. Lucas & Oakes Alemoatherium huebneri, the second also including San- 1988; Hahn et al. 1984, 1987, 1994; Godefroit & Battail tacruzgnathus abdalai and Microconodon tenuirostris, and 1997; Sues 2001) are based on isolated specimens (mainly the third also including Charruodon tetracuspidatus. The teeth and few fragmentary jaws). In this context, the fossil modified data matrix was analysed under equally- record of small-sized probainognathians is outstanding in weighted parsimony using TNT 1.5 (Goloboff & Catalano the Late Triassic rocks of Brazil (e.g. Bonaparte & Barber- 2016). An heuristic search of 500 replications of Wagner ena 2001; Bonaparte et al. 2003, 2005, 2012; Martinelli trees, followed by TBR branch-swapping algorithm (hold- et al. 2005, 2016; Oliveira et al. 2011; Soares et al. 2011, ing 10 trees per replication) was performed. All characters 2014; Martinelli & Soares 2016) and Argentina (Romer were treated as non-additive. Bremer support (= decay 1970, 1973b; Bonaparte 1980; Bonaparte & Crompton indices; Bremer 1994) and a bootstrap resampling analysis 1994; Martınez & Forster 1996; Martınez et al. 1996; Marti- (Felsenstein 1985) were conducted. The character list, the nelli & Rougier 2007) providing unique insights in the modified data matrix, changes included for T. cargnini, study of the major skeletal transformations prior to the and complete strict consensus trees are presented in Mar- mammalian condition (e.g. Luo 1994, 2007; Bonaparte tinelli et al. (2017). et al. 2003, 2005, 2012; Kielan-Jaworowska et al. 2004; Several eucynodont specimens were examined first Martinelli & Rougier 2007; Rodrigues et al. 2013, 2014; hand by AGM for comparison. The institutions in which Ruta et al. 2013; Ruf et al. 2014). these specimens are deposited are detailed in the text In this contribution, we describe a new probaino- below. Otherwise, bibliographical sources were used and gnathian cynodont from the late Carnian Hyperodapedon these are cited in the text. Assemblage Zone (AZ) of southern Brazil based on a tiny isolated lower jaw with well-preserved dentition, which can be unambiguously differentiated from all other GEOLOGICAL SETTING known cynodonts. The finding of such small specimen provides positive evidence on the hidden diversity of The specimen UFSM 11579b comes from deposits of the small-sized forms within Triassic faunal associations. Alemoa Member of the Santa Maria Formation at the site Moreover, comments on two other cynodonts from the known as Cerro da Alemoa or Waldsanga (Fig. 1; Langer Hyperodapedon AZ (Charruodon tetracuspidatus and The- et al. 2007; Da Rosa 2004; Da-Rosa 2015) which have also rioherpeton cargnini) are drawn based on the re-study of yielded the type specimens of the dinosaur Saturnalia the published specimens. tupiniquim (Langer et al. 1999). Accordingly to recent sequence stratigraphy studies (Horn et al. 2014) these strata belong to the Candelaria Sequence, Santa Maria MATERIAL AND METHOD Supersequence (Santa Maria 2 Sequence of Zerfass et al. 2003) which congregates the upper part of the Santa The specimen studied here, UFSM 11579b, was found Maria Formation (Gordon
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