A new extreme longirostrine temnospondyl from the Triassic of Madagascar: phylogenetic and palaeobiogeographical implications for trematosaurids

摘要

Trematosaurids form a very large and remarkable clade of Triassic tetrapods (Temnospondyli: Stereospondyli) with a worldwide geographical distribution. Compared with specimens from Europe, Australia or North America, they remain relatively scarce in African rocks, where they are mainly known in the Early Triassic of Madagascar and South Africa. Longirostrine trematosaurids were only known from Madagascar, represented by the genus Wantzosaurus. However, we describe herein a new species of the longirostrine trematosaurid Aphaneramma, Aphaneramma gavialimimus sp. nov., from the Olenekian (Lower Triassic) of Madagascar. This genus was previously known from the Early Triassic of Europe and Asia. Based on a new nearly complete skull, the new species is characterized by a premaxilla-nasal suture anteriorly directed, not contacting the nostrils; choanae completely included within the palatines; the ventral opening of the orbits in the anterior part of the interpterygoid vacuities; a very elongated nasal covering more than 50% of the prenarial length; and an anteriorly widened cultriform process. Aphaneramma gavialimimus sp. nov., with a skull length of about 40 cm, may be one of the largest known trematosaurids. Its inclusion in a new phylogenetic analysis confirms its close affinities with the North American genus Cosgriffius, and clarifies the relationships of trematosaurids in general and lonchorhynchines in particular. The new species also increases the palaeobiodiversity of marine trematosaurs in Gondwana and allows discussing their apparently rapid cosmopolitanism just after the great Permian-Triassic mass extinction.