Mesosaurus - The Facts

Mesosaurus represents an extinct group of water going reptiles from well before the time that the dinosaurs dominated the earth. These creatures lived in the period of time called the Permian, between 320 - 280 million years ago. They are not to be confused with mosasaurs, which were much larger and lived far later in history. Also, mosasaurs belonged to a different family of reptiles to these creatures, known as the euryapsid reptiles.

Mesosaurs were the first reptiles (that we know of) that returned to the water to live. In form they look like crocodiles or alligators, as the image to the right shows. The color scheme is personal choice. They have been shown to range in size from 40 cm to 2 meters in length, though the majority of specimens are on the small side.

Range

Fossils of Mesosaurus and very related species have been found in South Africa and South America. In fact, these creatures helped develop the theory of continental drift as their location on these two landmasses could not otherwise be explained. These creatures were thought to live in fresh water and so could not have crossed the vast oceans that now separate the two continents.

Definitely Anapsids

The scientists who analyze fossil skeletons have shown that the mesosaurs belong to the anapsid group of reptiles, one of the three ancient lineages. Exactly where it fits in as far as other anapsids are concerned has not yet been determined.

Convergent Evolution In Anapsids

This adaptation to the aquatic environment makes a couple of important points.

Firstly this reinforces the idea that certain environments force animals to take on similar shapes, regardless of their origins. Here we have an anapsid reptile taking on the familiar crocodile form, yet it is not even remotely related to modern crocodiles. This has been seen elsewhere; the Phytosaurs of ancient times were virtually identical to crocodiles, and even today there is the Crocodile fish that has taken on crocodile characteristics due to its lifestyle.

Secondly it helps to further show the strength and diversity of the anapsid reptile group; not only had they successfully spread out on land, they had also ventured back into the water before any other reptiles we know of. The idea of anapsid reptiles as sorry losers from a bygone age is rightfully disappearing.

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