Acerosodontosaurus

Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Late Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in deposits of the Lower Sakamena Formation. Based on skeletal characteristics, it has been suggested that Acerosodontosaurus individuals were at least partially aquatic.

Acerosodontosaurus has generally been considered a "younginiform", part of a paraphyletic grade of Permian diapsids which linked the most basal ("primitive") diapsids (araeoscelidians such as Petrolacosaurus) to more derived ("advanced") diapsids, including the earliest ancestors of modern reptiles such as crocodilians and lizards (Sauria). However, its position within the grade is controversial. Initially considered a specimen of the contemporaneous Tangasaurus, Acerosodontosaurus was later described as a younginid in 1980 and a tangasaurid in 2009. More recent studies have even supported the hypothesis that it was not a "younginiform" at all, but rather that it was an early member of Pantestudines, the reptile lineage that would lead to modern turtles. However, this theory is still controversial, and other studies have continued to support the "younginiform" interpretation.