A new notosuchian from the Late Cretaceous of Brazil and the phylogeny of advanced notosuchians.

Diego Pol,Claudio Riccomini,Paulo M Nascimento,Ricardo A Pires-Domingues,Hussam Zaher,Alberto B Carvalho,Leon Claessens

doi:10.1371/journal.pone.0093105

Abstract

A new notosuchian crocodyliform from the Late Cretaceous Bauru Group found in the southeastern State of São Paulo (Brazil) is described here. The new taxon, Caipirasuchus stenognathus, is referred as a new species of the recently erected genus Caipirasuchus within the clade Sphagesauridae based on a phylogenetic analysis of basal mesoeucrocodylians. Caipirasuchus stenognathus is represented by an almost complete skull and lower jaw that has autapomorphic characters that distinguish it from other species of Sphagesauridae. These autapomorphies include: maxilla forming part of the orbital margin (absence of lacrimal-jugal contact), nasal with smooth depressions on the posterior region close to the contact with the maxilla and lacrimal, postorbital with posterior palpebral facet that extends posteriorly underneath the ear-flap groove, and a distinct anterior process of the medial flange of the retroarticular process. Additionally, the new taxon lacks autapomorphic features described in other sphagesaurids. The phylogenetic analysis results in a monophyletic genus Caipirasuchus, that is the sister group of a clade fomed by Sphagesaurus huenei, Caryonosuchus pricei, and Armadillosuchus arrudai. Sphagesaurids also include a basal clade formed by Adamantinasuchus navae and Yacarerani boliviensis. Other notosuchian taxa, such as Mariliasuchus amarali, Labidiosuchus amicum, Notosuchus terrestris, and Morrinhosuchus luziae are successive sister taxa of Sphagesauridae, forming a clade of advanced notosuchians that are restricted to the Late Cretaceous of South America. These results contrast with most previous phylogenetic hypotheses of the group that depicted some members of Sphagesauridae as more closely related to baurusuchids, or found Asian (e.g., Chimaerasuchus) or African (Malawisuchus, Pakasuchus) forms nested within advanced notosuchians that are, according to our analysis, endemic of the Late Cretaceous of South America.

Highlights

Notosuchian crocodyliforms were extremely diverse in the Cretaceous of Gondwana and are abundant in some Late Cretaceous deposits of South America [1]
All other notosuchians are grouped together in a large and diverse clade, which has its basal forms recorded in Cretaceous beds of Africa and South America (e.g., Candidodon, Libycosuchus, Malawisuchus, Pakasuchus) and two major derived clades: Sebecosuchia (i.e., Baurusuchidae and Sebecidae) and a derived clade of advanced notosuchians
Our results show this clade of derived notosuchians as exclusively found in the Late Cretaceous of South America, and composed by Morrinhosuchus, Notosuchus, Coringasuchus, Mariliasuchus, Labidiosuchus, and a monophyletic Sphagesauridae

Summary

Introduction

Notosuchian crocodyliforms were extremely diverse in the Cretaceous of Gondwana and are abundant in some Late Cretaceous deposits of South America [1]. Members of this group have been interpreted as terrestrial organisms, given the absence of widely recognized adaptations to the aquatic environment present in other crocodyliforms [2,3]. A set of unique apomorphic features characterizes sphagesaurid dentition, including the presence of posterior teeth that are obliquely oriented ( present in Notosuchus) that bear strongly developed and well spaced apicobasal ridges, a wrinkled enamel surface, and a distal (maxillary) or mesial (dentary) keel with large tuberous denticles [6,7]

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Conclusion