Pelycosaur

Pelycosaurs (meaning "basin lizards") were the earliest synapsids. They were not dinosaurs or reptiles. They are an informal group which were once called the "mammal-like reptiles". The term is only used informally, if at all, in the modern scientific literature.

Pelycosaurs Temporal range: Upper Carboniferous – Upper Permian
Dimetrodon grandis skeleton at the National Museum of Natural History
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Tetrapoda
Class:	Synapsida
Order:	Pelycosauria * Cope, 1878
Suborders
Sphenacodontia †Caseasauria

These tetrapods appeared during the Pennsylvanian and went extinct at the end of the Permian period. They were the dominant land animals for some 40 million years, and were almost wiped out by the P/Tr extinction event. A few survived until the lower Triassic to form the therapsids. The therapsids led to the mammals.

Because the term "Pelycosaur" does not include their descendants, it is not used much now.

The most notable of these land animals was Dimetrodon, the top predator of its time.

Characteristics

Pelycosaur fossils have been found mainly in Europe and North America, although some small, late-surviving forms are known from Russia and South Africa.

At least two pelycosaur clades independently evolved a tall sail of elongated vertebral spines. In life, this would have been covered by skin, and possibly was a thermoregulatory device and/or a mating display. Unlike lepidosaurian reptiles, pelycosaurs lacked epidermal scales.

In 1940 the group was reviewed in detail and every species known at the time described (and many illustrated) in an important monograph. Well-known pelycosaurs include the genera Dimetrodon, Sphenacodon, Edaphosaurus, and Ophiacodon.

Classification

Pelycosauria	Sphenacodontia Sphenacodontoidea Ophiacodontidae Varanopidae Caseasauria Caseidae Eothyrididae Paleohatteriidae