A parareptile from the lower Permian of the Parnaíba Basin, northeastern Brazil

Abstract

The aquatic mesosaurids, from theParaná and Karoo basins in southern Gondwana, have long been the onlyparareptiles (and amniotes in general) known from the lower Permian of thesouthern hemisphere. Recent fieldwork in the Pedra de Fogo Formation (PdF), inthe Parnaíba Basin of northeastern Brazil, has revealed a new tetrapod faunadominated by temnospondyls, with amniotes represented by a single captorhinid.Collecting efforts in 2016 in the vicinity of Teresina, Piauí State, produced asecond amniote from the PdF. The specimen, comprising a disarticulated cranium(~4 cm long) and a partially articulated postcranium, exhibits a number offeatures characteristic of the Parareptilia. These include an ornamented skulland jaw, a premaxilla bearing a thin arched dorsal process, a maxilla raisedanterodorsally, and vertebrae possessing swollen neural arches. The maxillabears an enlarged anteriormost foramen, another synapomorphy of Parareptilia. Abone that borders the orbit, tentatively identified as the postorbital, bears aprominent tubercle. Circumorbital tubercles are characteristic of someparareptiles such as nycteroleters, lanthanosuchids and pareiasaurs. Somemaxillary teeth bear weak striations, a feature known in parareptiles such as Macroleter,lanthanosuchids and millerettids. A preliminary phylogenetic analysis suggestsa sister group relationship with the genus Colobomycter from Oklahoma,USA, within the subclade Lanthanosuchoidea. Unlike all other PdF tetrapodsfound in the area, which were preserved in massive, silicified siltstones of lacustrine origin, the newparareptile was collected from an erosive-based fine-grained sandstone thatsuggests a fluvial flux bringing terrestrial material into the lake. The close affinities of the Piauífossil with the Oklahoma parareptiles (which comprise the majority of known lanthanosuchoids)corroborates previous findings of PdF tetrapods (dvinosaurs, captorhinids)which are also close relatives to counterparts in the southwestern USA.Overall, this supports a model in which the characteristic Cisuraliancontinental fauna of North America was part of a biogeographic province thatextended into the Gondwanan tropics.