mesosaurids

Mesosaurids were a group of small, extinct aquatic reptiles that lived during the Early Permian period. They are the only known group of reptiles that exclusively inhabited freshwater environments, with fossil evidence found in both South America and Africa. This distribution is significant as it was long before the supercontinent Pangaea began to break apart, suggesting that these reptiles were present when the continents were joined.

These animals were adapted for a marine or possibly brackish water lifestyle, possessing long, slender bodies and paddle-like limbs. Their skulls were elongated and filled with numerous small, pointed teeth, indicating a diet of small aquatic prey such as crustaceans and fish. The mesosaurid skull also featured a unique nostril position, located far back on the skull, which may have aided in breathing while keeping the rest of the body submerged.

Mesosaurids are considered important in understanding continental drift. The discovery of their fossils on widely separated continents like Brazil and South Africa provided early evidence for the theory of plate tectonics. The restricted temporal and geographical range of mesosaurids makes them a key index fossil for correlating rock layers from the Early Permian period across these continents. Despite their specialized adaptations, mesosaurids had a relatively short existence, disappearing by the late Early Permian.