Taxonomic reappraisal of the sphagesaurid crocodyliform Sphagesaurus montealtensis from the Late Cretaceous Adamantina Formation of São Paulo State, Brazil

Abstract

Sphagesaurus montealtensis is a sphagesaurid whose original description was based on a comparison with Sphagesaurus huenei, the only species of the clade described to that date. Better preparation of the holotype and the discovery of a new specimen have allowed the review of some characteristics and the identification of several synapomorphies of S. montealtensis with the genus Caipirasuchus: presence of antorbital fenestra; external nares bordered only by the premaxillae; premaxilla with four teeth and one diastema (between the 3rd–4th teeth); one diastema between the 4th premaxillary tooth and the 1st maxillary tooth; dentary with ten teeth and two diastemata (between the 4th–5th and 5th – 6th teeth); nasal with a groove parallel to the suture with the frontal bone; nasal long, with an acute anterior margin touching anterolaterally the premaxilla, jugal is a straight bar in the lateral view; frontal is longer than wide; a dorsoventrally expanded and vertically oriented quadrate with a groove separating the medial and lateral condyles; the frontal has a discrete sagittal crest; dentary with six posterior sphagesauriform teeth and four anterior conical teeth, the first three are the smallest of the series and the fourth is slightly laterally compressed. The referral of S. montealtensis to the genus Caipirasuchus, as Caipirasuchus montealtensis comb. nov. is proposed here, based on the new taxonomic observations and the results of a phylogenetic analysis.

A New Notosuchian from the Late Cretaceous of Brazil and the Phylogeny of Advanced Notosuchians

“…A third genus of Sphagesauridae, Caipirasuchus , was erected [11] for the new species C. paulistanus , based on an almost complete skull and mandible that include a complete toothrow (although several details of its dentition are not well preserved). The holotype of Caipirasuchus paulistanus is remarkably similar to that of Sphagesaurus montealtensis and, although the two taxa can be distinguished based on a few characters (see below), their similarities have led Iori et al [12] to consider them cogeneric (erecting the new combination Caipirasuchus montealtensis , which is adopted here). A fourth genus, Caryonosuchus , was also recently erected [13] based on a rostrum and symphyseal mandibular region that differs from other sphagesaurids by the presence of notorious protuberances and other ornamentations on the dorsal surface of the rostrum.…”

“…The second described sphagesaurid ( Caipirasuchus montealtensis ) was depicted as the sister group of Sphagesaurus huenei [10]. However, subsequent phylogenetic studies that included newly discovered sphagesaurids (e.g., Armadillosuchus , Adamantinasuchus , Yacarerani , Caipirasuchus paulistanus ) rejected the monophyly of a clade clustering all the taxa referred to Sphagesauridae [11], [12], [15], [18], [19]. In these studies, some of these taxa (e.g., Adamantinasuchus , Yacarerani , Armadillosuchus ) were depicted as more closely related to baurusuchids [18] or to other notosuchians (e.g., Mariliasuchus ; [11], [12], [15], [19]) than to Sphagesaurus .…”

Revisão da família Baurusuchidae e seu posicionamento filogenético dentro do clado Mesoeucrocodylia

“…Uma dentição semelhante à esfagessáuria também foi reportada em Yacarerani, do Cretáceo da Bolívia (Novas et al, 2009). Nas análises recentes, Yacarerani e Adamantinasuchus formam um clado monofilético, mas não em conjunto com o gênero Sphagesaurus (Novas et al, 2009;Iori & Carvalho, 2011;Iori et al, 2013), dando a entender que a morfologia peculiar dos "esfagessáurios" pode ter evoluído em paralelo em duas linhagens. No entanto, esfagessauros sempre aparecem na irradiação cretácica notossúquia.…”

“…Na análise filogenética de Pol & Powell (2011), Cynodontosuchus não seria um Baurusuchidae, formando uma politomia com Baurusuchidae e Sebecidae. Alguns trabalhos posteriores incluíram mais gêneros descritos posteriormente, como Pol et al (2012), Montefeltro et al (2011Montefeltro et al ( , 2013 e Iori et al (2013).…”

“…Nas análises de Pol et al (2012) e Iori et al (2013), baurussuquídeos não formam um clado monofilético, sendo um conjunto de táxons sucessivamente irmãos de Sebecidae, este sim, monofilético. No primeiro artigo, apenas Stratiotosuchus e Pabwehshi formam um clado, sendo os demais unidos em uma grande politomia com Sebecidae.…”