Hovasaurus

Hovasaurus is an extinct genus of diapsid reptile belonging to the order Eosuchia. It lived in what is now Madagascar during the Late Permian and Early Triassic, being a survivor of the Permian–Triassic extinction event and the paleontologically youngest member of the Tangasauridae. Fossils have been found in the Permian Lower and Triassic Middle Sakamena Formations of the Sakamena Group.
Description.
"Hovasaurus" resembled a slender lizard, and was around long, of which two thirds was taken up by its long tail. It was well adapted to an aquatic life, with the tail being laterally flattened like that of a sea snake. Some stones have been found in the abdomen of fossil "Hovasaurus", indicating the creatures swallowed these for ballast, preventing them from floating to the surface when hunting fish.