Plaster caste of Mesosaurus tenuidens
Mesosaurus is an extinct reptile which lived approximately 300 million years ago during the Early Permian Period. Mesosaurus is one of the first reptiles to return to an aquatic lifestyle. The nostrils are on top of the skull and the legs are suited more for aquatic movement than that on land. The tail may have sported a fin similar to the earlier tetrapod amphibians, and the feet were webbed. As an early reptile is possible that Mesosaurus would have had to return to the land to lay its eggs. When on land it might of had to push itself with its legs as opposed to lift its body and actually walk. A further development is the pachyostosis of the bones. This is where the bones become thickened and more solid resulting in a denser bone structure. This may helped to deal with buoyancy issues allowing Mesosaurus to have greater agility in the water.
Mesosaurus was approximately 3 feet long and weighed around 20 pounds. That made it the size of a yardstick and about the weight of a Dachshund dog. It was an anapsid reptile – which means it didn’t have the openings in the sides of its skull that therapsids and pelycosaurs had. The teeth of Mesosaurus are very fine and were originally interpreted to have formed a comb like structure for filtering food out of the water. However, further specimens have cast doubt upon this method of feeding as the teeth are always too few to form such a structure. With this in mind it is more likely that Mesosaurus hunted small fish and invertebrates. It is generally considered that Mesosaurus dwelt in freshwater. When the theory of continental drift was still being debated amongst the scientific community, the fossils of Mesosaurus recovered from both sides of the Atlantic ocean were taken as evidence to support the theory. One of the most fascinating facts about Mesosaurus, however, is the fact that it was instrumental in proving continental drift theory. It lived in both eastern South America and southern Africa. However, since it only swam in fresh water, it is highly unlikely it could have swum the Atlantic Ocean to get from South America to Africa. This most likely means that these two areas were connected at one point in time and over time, spread apart. A theory that is known as continental drift.