Hovasaurus boulei, an aquatic eosuchian from the Upper Permian of Madagascar

Currie, P. J.
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Bernard Price Institute for Palaeontological Research
Hovasaurus is the most specialized of four known genera of tangasaurid eosuchians, and is the most common vertebrate recovered from the Lower Sakamena Formation (Upper Permian, Dzulfian Standard Stage) of Madagascar. The tail is more than double the snout-vent length, and would have been used as a powerful swimming appendage. Ribs are pachyostotic in large animals. The pectoral girdle is low, but massively developed ventrally. The front limb would have been used for swimming and for direction control when swimming. Copious amounts of pebbles were swallowed for ballast. The hind limbs would have been efficient for terrestrial locomotion at maturity. The presence of long growth series for Hovasaurus and the more terrestrial tangasaurid Thadeosaurus presents a unique opportunity to study differences in growth strategies in two closely related Permian genera. At birth , the limbs were relatively much shorter in Hovasaurus, but because of differences in growth rates, the limbs of Thadeosaurus are relatively shorter at maturity. It is suggested that immature specimens of Hovasaurus spent most of their time in the water, whereas adults spent more time on land for mating, laying eggs and/or range dispersal. Specilizations in the vertebrae and carpus indicate close relationship between Youngina and the tangasaurids, but eliminate tangasaurids from consideration as ancestors of other aquatic eosuchians, archosaurs or sauropterygians.
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eosuchian; Permian; Madagascar;