Cienciaes.com: Simiosaurs in the Tethys Sea

2010-09-16 15:48:38

Since the end of the 1970s, the remains of three species of reptiles adapted to arboreal life that lived during the Triassic period, between 250 and 200 million years ago, have been discovered in northern Italy, when the region was a coastal area dotted with tropical, forest-covered islands. These reptiles, which have received the names Drepanosaurus (“sickle-reptile”), Megalancosaurus (“long-armed reptile”) and Vallesaurus (“Valley reptile”), form a group that is difficult to classify, the simiosaurs or drepanosaurids. Although the fossils found in Italy are the most complete, simiosaur remains have also been found in England and the United States.

Simiosaurs are small quadrupedal reptiles, between 15 and 50 centimeters in length, slender and light, with large eyes located on the sides of a triangular head, wide behind and ending in a long and narrow snout, bristling with small teeth. triangular, adapted to crush the shell of the insects on which they feed. The neck is long and flexible. The neck and arm muscles are very powerful, forming a hump over the shoulders. The legs are long and graceful, with prehensile toes ending in long, narrow, sharp nails. The tail, flattened laterally, is relatively rigid in its middle part, although the end is prehensile and serves to hold on to the branches of trees, as chameleons do; in some species the tail ends in a sharp downward-curving claw, which is formed by the union of the last vertebrae and serves to improve grip. At least in Megalancosaurus, the best-known species, the first toe lacks a nail and is opposable in one sex; it is used to hold the partner during copulation, which also takes place in the trees.

Over the years, various theories have been put forward about the position of apes on the reptile evolutionary tree. Its head is similar to that of primitive birds, while the anatomy of the neck and shoulders is more similar to that of pterosaurs and the rest of the body relates them to other groups of more primitive reptiles. Today, the hypothesis that the apes were the ancestors of birds seems to be ruled out, although a consensus on their relationship with other groups of reptiles has not yet been reached.