New rhynchocephalian specimen in the Late Triassic of southern Brazil and comments on the palatine bone of Brazilian rhynchocephalians

Triassic rhynchocephalians from South America are relatively sparse, based on one taxon from the Norian of Argentina (i.e., Sphenotitan leyesi) and three records from the Late Carnian (i.e., indet. taxon) and Norian (i.e., Clevosaurus brasiliensis and indet. taxon) of Brazil. We described here a new occurrence of rhynchocephalians from a new Late Carnian locality of southern Brazil, based on an isolated palatine with teeth, referred to that group due to the morphological similarity whit the palatines of the other taxa of the same group. The specimen comes from the municipality of Vale do Sol, collected within a layer with abundant material of Hyperodapedon sp. (Rhynchosauria), which is referred to the Hyperodapedon Assemblage Zone (Late Carnian) of the Candelária Sequence, Santa Maria Supersequence. The isolated palatine here described cannot be referred to any hitherto known species, but it provides an additional record for the few putative ones of Carnian age in South America. Moreover, we figure and describe the palatine anatomy of Clevosaurus brasiliensis, based on two specimens, which have relevant data poorly addressed in previous contributions.Fil: Romo de Vivar Martínez, Paulo Rodrigo. Universidade Federal do Rio Grande do Sul; BrasilFil: Martinelli, Agustín Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Paes Neto, Voltaire D.. Universidade Federal do Rio Grande do Sul; BrasilFil: Scartezini, Camila A.. Universidade Federal do Rio Grande do Sul; BrasilFil: Lacerda, Marcel B.. Universidade Federal do Paraná; BrasilFil: Rodrigues, Carlos N.. Museu Municipal Aristides Carlos Rodrigues; BrasilFil: Soares, Marina Bento. Universidade Federal do Rio Grande do Sul; Brasi

The African cynodont Aleodon (Cynodontia, Probainognathia) in the Triassic of southern Brazil and its biostratigraphic significance.

In this contribution we report the first occurrence of the enigmatic African probainognathian genus Aleodon in the Middle-early Late Triassic of several localities from the state of Rio Grande do Sul in southern Brazil. Aleodon is unusual among early probainognathians in having transversely-expanded postcanine teeth, similar to those of gomphodont cynognathians. This genus was previously known from the Manda Beds of Tanzania and the upper Omingonde Formation of Namibia. The Brazilian record of this genus is based upon multiple specimens representing different ontogenetic stages, including three that were previously referred to the sectorial-toothed probainognathian Chiniquodon theotonicus. We propose a new species of Aleodon (A. cromptoni sp. nov.) based on the specimens from Brazil. Additionally, we tentatively refer one specimen from the upper Omingonde Formation of Namibia to this new taxon, strengthening biostratigraphic correlations between these strata. Inclusion of A. cromptoni in a phylogenetic analysis of eucynodonts recovers it as the sister-taxon of A. brachyrhamphus within the family Chiniquodontidae. The discovery of numerous specimens of Aleodon among the supposedly monospecific Chiniquodon samples of Brazil raises concerns about chiniquodontid alpha taxonomy, particularly given the extremely broad geographic distribution of Chiniquodon. The discovery of Brazilian Aleodon and new records of the traversodontid Luangwa supports the hypothesis that at least two subzones can be recognized in the Dinodontosaurus Assemblage Zone

Biostratigraphy of the <i>Dinodontosaurus</i> and <i>Santacruzodon</i> AZs.

<p>Tetrapod fossil comparisons and shared taxa with the Chañares Formation of western Argentina. The ages of the column follow Gradstein et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177948#pone.0177948.ref036" target="_blank">36</a>]. The radiometric dating of 236.1, 231.4 and 225.9 Ma on the Ischigualasto-Villa Unión Basin column correspond to the first half of the Chañares Formation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177948#pone.0177948.ref045" target="_blank">45</a>], the base of the Ischigualasto Formation, and the base of Los Colorados Formation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177948#pone.0177948.ref105" target="_blank">105</a>], respectively, and the one in the <i>Santacruzodon</i> AZ follows Philipp et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177948#pone.0177948.ref043" target="_blank">43</a>].</p

<i>Aleodon cromptoni</i> from southern Brazil.

<p>Specimen UFRGS-PV-0274-T in dorsal (A) and ventral (B) views, and detail of the snout in ventral view (C) with interpretative drawing of the right postcanine tooth row and detail of left PC6. Scale bar equals 50mm. Abbreviations: aPC, alveolus; PC, upper postcanine.</p

<i>Aleodon cromptoni</i> sp. nov. from southern Brazil.

<p>Specimen UFRGS-PV-0146-T, detail of left upper postcanine row (A) and left lower postcanine row, with accompanying line drawings. Scale bar equals 10mm. Abbreviations: C, upper canine; Ca, upper canine alveolus; enl, enamel layer; lpl, lingual platform; PC/pc, upper, lower postcanine.</p

Dendrogram of main localities of the state of Rio Grande do Sul yielding fossil tetrapods of the <i>Dinodontosaurus</i> AZ (see data matrix in S1 File).

<p>Cophenetic correlation coefficient = 0.8474. (W), and (C), and (E) refers to the West, Central, and East portions, respectively, of the state of Rio Grande do Sul.</p

<i>Chiniquodon</i> from South America.

<p>Skull of specimen MCP-PV-1600-T (holotype of <i>Probelesodon kitchingi</i>) in lateral view (A). Skull and articulated jaws of specimen UFRGS-PV-1331-T (ex UFRGS-PV-0066-Tg) in lateral (B) and dorsal (C) views, and of specimen PVL 4444 in lateral view (D). Detail of posterior upper left postcanines of PVL 4674 in labial (E) and ventrolingual (F) views. Details of posterior lower left postcanines of PVL 4444 in labial (G) and lingual (H) views. Note the absence of a lingual platform. The arrow points to the mesial side. The dotted lines indicate the shape of the dorsal profile of the skull. Scale bar equals 20mm in A-D and 5mm in E-H.</p

Biostratigraphy of selected Gondwanan Triassic units.

<p>Relevant therapsid content considering radiometric data and problematic implications among Gondwanan Triassic units, and accompanying paleomap (modified from Abdala and Smith [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177948#pone.0177948.ref013" target="_blank">13</a>]) during the Middle Triassic with the location of <i>Aleodon cromptoni</i> in southern Brazil and Namibia and <i>A</i>. <i>brachyramphus</i> in Tanzania. Abbreviations: AF, Africa; Ind., Induan; Madag., Madagascar; Ole, Olenekian; SA, South America.</p

Localities with <i>Aleodon cromptoni</i> sp. nov.

<p>Map of the main Middle to early Upper Triassic outcrops in the state of Rio Grande do Sul, southern Brazil, highlighting the occurrence of <i>Aleodon</i> (A) and its skeletal reconstruction with available bones (in yellow) based on all known specimens (made by VDPN).</p

Occurrence of taxa and main localities of the <i>Dinodontosaurus</i> AZ in the state of Rio Grande do Sul, southern Brazil (see Suppl. Info. for references of each occurrence).

<p>Occurrence of taxa and main localities of the <i>Dinodontosaurus</i> AZ in the state of Rio Grande do Sul, southern Brazil (see Suppl. Info. for references of each occurrence).</p