Cristian Pereira Pacheco

A new Permian temnospondyl with Russian affinities from South America, the new family Konzhukoviidae, and the phylogenetic status of Archegosauroidea

A new Permian temnospondyl from South America is described and considered to represent a new species – Konzhukovia sangabrielensis sp. nov. – of the genus Konzhukovia previously recorded exclusively from Russia. It consists of the anterior half and partial right side of the skull roof and palate. A comprehensive phylogenetic analysis was performed with several archegosauroids and other well-supported groups of temnospondyls in order to access the affinities of the new Brazilian species and test the monophyly of Archegosauroidea. Archegosauroidea was not recovered as a monophyletic group, comprising successive paraphyletic taxa. The only monophyletic group of ‘archegosauroids’ is the ‘Tryphosuchinae’ (in a sister-group relationship with Stereospondyli), composed of Tryphosuchus paucidens, Konzhukovia vetusta, K. tarda and K. sangabrielensis. As the diagnosis of T. paucidens is unclear and based on incomplete material, nested among three species of Konzhukovia, we consider this taxon to be a nomen dubium and purge it from the strict consensus tree. An alternative solution would be to erect a new taxonomic combination for T. paucidens. In order to solve these taxonomic problems, it is necessary to discover more complete material with a clear set of diagnostic characters, to either revalidate this taxon or provide a new combination for it. The phylogenetic results support the erection of a new family – Konzhukoviidae – to replace ‘Tryphosuchinae’ and accommodate Konzhukovia vetusta, K. tarda and K. sangabrielensis, the new Brazilian species basal to the Russian forms. An early diverging konzhukoviid in Gondwana leads to interesting insights regarding the evolution of the new family, stereospondyl origins, their early diversification and their palaeobiogeographical patterns of distribution. http://zoobank.org/urn:lsid:zoobank.org:pub:4772DC7E-C427-4F5F-89FD-9E68E3B0BFD5

Prozostrodon brasiliensis, a probainognathian cynodont from the Late Triassic of Brazil: second record and improvements on its dental anatomy

Abstract Probainognathian cynodonts are conspicuous elements of the Assemblage Zones of the Triassic Santa Maria Supersequence in southern Brazil. Within this group, the derived clade Prozostrodontia, in which the crown group Mammalia is included, is taxonomic diverse in the Hyperodapedon and Riograndia AZs. We describe here the second known specimen (CAPPA/UFSM 0123) of Prozostrodon brasiliensis, until now only represented by its holotype. CAPPA/UFSM 0123 includes a right dentary with dentition. As in the holotype of P. brasiliensis, it has four lower incisors, pc4 with conspicuous cusp a, and small cusps b, c, and d, pc5-pc6 of ‘triconodont’ type with cusps a > c > b > d, with continuous lingual cingulum bearing up to six small discrete cusps, length of the lower tooth row more than half the length of the dentary, and relatively deep horizontal ramus of the dentary. The new specimen is about 25% smaller than the holotype and there is not a diastema between the canine and postcanine teeth, indicating its juvenile condition. Based on both known specimens of P. brasiliensis, a discussion on tooth replacement is presented, showing that the adult individual has more postcanine tooth morphotypes than the juvenile one.

The role of ontogeny on character polarization in early dinosaurs: a new specimen from the Late Triassic of southern Brazil and its implications

Abstract Only recently, new ontogenetic series of early dinosaurs and related groups have been described. Here, we present an isolated immature dinosauriform femur from the Late Triassic of southern Brazil and investigate its influence on character polarization. Because the specimen shares a number of synapomorphies with Pampadromaeus barberenai, herein we postulate that it corresponds to a juvenile individual of that taxon. Accordingly, we investigate the morphological variation between juvenile and mature individuals of P. barberenai. Scoring these character states into a published phylogenetic data-set of Dinosauromorpha reveals that morphological variation is higher than that observed among closely-related taxa. Ontogenetic variation thus exerts influence on character polarization. In addition, modification of the scores affected by ontogeny produces different topologies, as noted by the reduction in both the number of most parsimonious trees and number of steps, and increased inclusivity of some clades and reduction of polytomies as well. Our study, together with other recent contributions, sheds light on the morphologic pathways seen during dinosauromorph ontogenetic development, which is crucial to more reliably assess phylogenetic reconstructions and macroevolutionary patterns of this widespread and successful group.