Prehistoric Animals


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People often think that Dimetrodon was a dinosaur when in fact this creature was part of a species of prehistoric reptiles known as the pelycosaurs that lived during the Permian period, tens of millions of years before the first dinosaurs began to appear. Pelycosaurs were more closely related to the therapsids - "mammalian reptiles" - than to the archosaurs that later evolved into dinosaurs, which means that Dimetrodon was closer to mammals than to dinosaurs.

The name Dimetrodon, awarded by the famous American fossil hunter Edward Drinker Cope, comes not from its sail that resembles that of Spinosaurus but rather from the fact that its jaw had two different types of teeth. The arsenal of this dinosaur included large, pointed canines on the front of its snout - a bit like the Smilodon but much less prominent - and shear teeth in the back to crush the rigid muscles and bones. Although impressive, the dentition of this reptile would have been no match against that of predatory dinosaurs who lived tens of millions of years later.

As is the case for many prehistoric animals discovered during the 19th century, the fossil record of this reptile is extremely complicated. For this reason, Dimetrodon has been known by many names. For example, before appointing Dimetrodon, Edward Drinker Cope assigned the name Clepsydrops to another fossil specimen digged up in Texas and also erected the genera Theropleura and Embolophorus. Two decades later, another paleontologist erected the now discarded genus Bathyglyptus.

Dimetrodon had a huge sail like that of Spinosaurus

Dimetrodon sail
Dimetrodon sail

The hallmark of this pelycosaur is the enormous sail mounted on its back by long dorsal spines reminiscent of the gigantic African dinosaur of the Middle Cretaceous Spinosaurus. Probably a cold-blooded animal, the sail had to act as a regulator to allow it to control the temperature of its body: it absorbed light rays during the day and dissipated excess heat during the night.

Sailing was probably also a feature of sexual selection. Since the fossils of Dimetrodon are quite common, paleontologists have been able to hypothesize that males had an anatomy considerably different from that of females: they were much wider - about 15 feet long for a weight of 500 pounds in most large specimens - had thicker bones and a much more prominent sail. This fact tends to support the theory that the sail of Dimetrodon had a partial sexual connotation; males with larger sails were more attractive to females during the mating season.

Dimetrodon walked with legs apart

One of the main features that distinguishes the first true dinosaurs from the archosaurs, pelycosaurs and therapsids that preceded them is the straight and upright orientation of the limbs. This is one of the reasons, among others, that allows us to be certain that Dimetrodon was not a dinosaur: this reptile had a posture and gait very similar to that of crocodiles rather than the straight and vertical one that we find in quadruped dinosaurs of comparable size that evolved tens of millions of years later.

Dimetrodon lived with giant amphibians

At the time Dimetrodon lived, reptiles and lizards were not yet dominant over their immediate evolutionary predecessors, the giant amphibians of the early Paleozoic era. In the American southwest, for example, Dimetrodon shared its environment with the amphibian Eryops, who size was similar to that of a mature man, as well as with others with more puny stature. It was only during the Mesozoic that amphibians (as well as small mammals and other types of reptiles) were set aside by their descending giant dinosaurs.

There are more than a dozen species of Dimetrodon

Dimetrodon fossil
Dimetrodon fossil

There are at least 15 species of Dimetrodon, most of which have been found in North America in parts of Texas. Only one species has resurfaced from Western Europe, which was once directly connected to America. A vast majority of these species have been named by the fossil hunter Edward Drinker Cope which helps to understand why Dimetrodon is so often confused as being a dinosaur rather than a pelycosaur.

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