A new prozostrodontian cynodont (Therapsida) from the Late Triassic Riograndia Assemblage Zone (Santa Maria Supersequence) of Southern Brazil.

Marina B Soares,Téo V De Oliveira,Agustín G Martinelli

doi:10.1590/0001-3765201420140455

Abstract

We report here on a new prozostrodontian cynodont, Botucaraitherium belarminoi gen. et sp. nov., from the Late Triassic Riograndia Assemblage Zone (AZ) of the Candelária Sequence (Santa Maria Supersequence), collected in the Botucaraí Hill Site, Candelária Municipality, state of Rio Grande do Sul, Brazil. The new taxon is based on a single specimen (holotype MMACR-PV-003-T) which includes the left lower jaw, without postdentary bones, bearing the root of the last incisor, canine and four postcanines plus one partial crown inside the dentary, not erupted, and two maxillary fragments, one with a broken canine and another with one postcanine. The features of the lower jaw and lower/upper postcanines resemble those of the prozostrodontians Prozostrodon brasiliensis from the older Hyperodapedon AZ and Brasilodon quadrangularis and Brasilitherium riograndensis from the same Riograndia AZ. The inclusion of Botucaraitherium within a broad phylogenetic analysis, positioned it as a more derived taxon than tritylodontids, being the sister-taxon of Brasilodon, Brasilitherium plus Mammaliaformes. Although the new taxon is based on few cranial elements, it represents a additional faunal component of the Triassic Riograndia AZ of southern Brazil, in which small-sized derived non-mammaliaform cynodonts, closely related to the origin of mammaliaforms, were ecologically well succeed and taxonomically diverse.

Highlights

The rich fossil tetrapod content from the MiddleUpper Triassic of southern Brazil is recorded in beds related to the Santa Maria Supersequence, in which four recognized faunal tetrapod associations succeed in time: Dinodontosaurus, Santacruzodon, Hyperodapedon and Riograndia Assemblage Zones (AZ) (Soares et al 2011) (Fig. 1)
There are no recorded specimens of Brasilodon and Brasilitherium in the Botucaraí Hill Site
Within the Botucaraí region there is a record of Brasilitherium-like teeth in Sesmaria do Pinhal 3 Site, located about 1000 meters away from the Botucaraí Hill Site (Soares et al 2011, Bittencourt et al 2013)

Summary

INTRODUCTION

The dentary has a large diastema between canine and postcanines and the canine base and alveolar level of the incisor is positioned slightly dorsal to the alveolar level of the postcanine series (Fig. 4A) This condition is similar to that observed in Prozostrodon, Brasilodon, Brasilitherium (Bonaparte and Barberena 2001, Bonaparte et al 2003, 2005) and other possibly related forms such as Microconodon and Dromatherium (Hahn et al 1994, Sues 2001). In the lingual side of the postcanines there is a well-developed cingulum with a small mesial cusp e (better observed in pc2), followed by a series of tiny cuspules that reach the distal margin of the crown, forming a cingular shelf (Fig. 4B, C). It should be emphasized that the sequence of postcanine eruption and the number of replacement per locus at the non-mammaliaform prozostrodontians-mammaliaforms boundary is a matter still poorly understood

DISCUSSION

A NEW CYNODONT FROM THE LATE TRIASSIC OF BRAZIL