A new hupehsuchian (Reptilia: Ichthyosauromorpha) from the Lower Triassic of South China with implications for the evolution of polydactyly

Abstract

Hupehsuchia, an enigmatic group of marine reptiles from the Lower Triassic of South China, is characterized by a suite of features including polydactyly in either or both fore and hind limbs. Particularly, one parahupehsuchine specimen shows seven-digited forelimbs and a six-digited hind limb. However, questions remain as to what sequence manus configuration evolved in hupehsuchians. Here, we describe a new hupehsuchian with seven manual digits associated with extra carpals and digits. Our new phylogeny revealed the evolutionary sequence of extra carpals, metacarpals, and phalanges in hupehsuchians through preaxial and central polydactyly and suggested that the polydactyly of the manus evolved stepwise in hupehsuchians.