Primeira ocorrência de dicynodontoides em Moçambique: anatomia, taxonomia e implicações filogenéticas

Abstract

The Karoo of Mozambique is rich in vertebrate fossils, particularly dicynodonts. Dicynodontia is a group of therapsids with a common ancestor to mammals, which belong to the class Synapsida. Dicynodonts are herbivorous and insectivorous animals characterized by the presence of two canine fangs and a pair of temporal fenestrae. These animals predominated from the middle Permian to the Triassic, in a period in which the continents were united forming Pangea. The present work aims to describe a new dicynodont skull collected in fine sandstones of the K6 Formation member K6a2 in the Metangula graben, specimen cataloged as PPM2019-38Z. This specimen was initially subjected to mechanical and chemical preparation techniques in order to remove excess rock matrix and fully expose the bone. After preparation, PPM2019-38Z was described based on comparison with other dicynodonts known from the Metangula graben as well as from contemporary Karoo basins. The anatomical description led to the identification of several characters that allowed the identification of PPM2019-38Z as a Dicynodontoides sp., such as the premaxilla in an inverted V shape anteriorly, elongated pineal foramen, crest-shaped parietal in the intertemporal region, median vomer plate with a circular depression immediately anterior to the premaxilla, present and well-developed interpterygoid vacuity. The classification of PPM2019-38Z as Dicynodontoides sp. is also supported by phylogenetic analysis, and the specimen has specific affinity with another Dicynodontoides from the Metangula graben, specimen PPM2019-106R. The following characters define the affinity between the two skulls: both have the same angulation of the occiput in relation to the palate, which is measured in the ratio between the dorsal and basal length of the skull, and both are characterized by the absence of a depression or groove in the middle ventral plate of the vomer. Dicyndontoides is a genus with a wide temporal distribution, occupying strata from Endothiodon to Daptocephalus Assemblage Zone. Thus, the presence of this taxon in member K6a2 allows this member to be correlated with the range covered by the various biozones. On the other hand, the occurrence of Dicynodontoides in the Metangula graben increases the knowledge of paleontology in Mozambique(TRADUÇÃO NOSSA)