Anatomy, cranial ontogeny and phylogenetic relationships of the pareiasaurDeltavjatia rossicusfrom the Late Permian of central Russia

Abstract

ABSTRACTNew material of the pareiasaurDeltavjatia rossicusfrom the Kotel'nich locality, Kirov Province, Russia, is described in detail. The taxon is characterised by a distinctive pattern of dermal sculpture and the exaggerated embayment of the posterior skull roof, resulting in the dorsal exposure of the braincase. Postcranially,Deltavjatiashares some aspects of its morphology with basal pareiasaurs, including the osteoderm pattern. Features such as the forward-slanting and pointed iliac blade are shared with stratigraphically younger, more derived forms. Well-preserved material of the taxon spans a wide size-range, allowing an assessment of ontogenetic trends. A geometric morphometric analysis of the skull roof ofDeltavjatiareveals an allometric increase in snout length and postorbital area, a result that can serve as a basis for examining morphological trends within pareiasaurs. A reassessment of pareiasauromorph relationships, using both parsimony and Bayesian methods of phylogenetic inference, recovers similar topologies in both cases. Four Bayesian analyses were completed, with and without a gamma-shaped parameter and with and without the inclusion of autapomorphies. Despite differing taxon and outgroup selection, the recovered topologies are similar to previous phylogenies of pareiasaurian relationships, withDeltavjatiaappearing as a relatively basal taxon.