This lifeform has been extinct for over 20,000 years.

Dimetrodon is a well-known species of sail reptile. Some students of this genus believe that the sail was useful for capturing heat in the morning and releasing it during the day. This would have permitted Dimetrodon to maintain a uniform body temperature.

Pelycosauridae were a family of ancient reptiles that are related to modern mammals. Most Pelycosaurids were less than ten feet long, and included both plant and meat-eating species. This family became extinct before the Triassic Period.

Mammal-Like Reptiles (Synapia) lived in the Paleozoic and Mesozoic (Triassic-Jurassic-Cretaceous) time periods. Their skulls indicate that these reptiles could have contained the ancestors to the mammals that live today. Technically, these animals are not called Dinosaurs.

Reptiles (Class Reptilia) are an ancient group of scaled  chordates. These scales may be permanently joined, as in the  turtles, or flexible, as in the snakes. Reptiles are land-based. Their eggs are laid on land and the young are air breathing.

Backboned Animals (Phylum Chordata) are the most advanced group of animals on earth. These animals are characterized by having a spinal cord or backbone. Most members have a clearly defined brain that controls the organism through a spinal cord. Fish, amphibians, reptiles, birds, and mammals are in this phylum.

Currently, some taxonomists believe that the fish should be divided into two groups (sharks and regular fishes) and that there are some other primitive groups in the phylum such as hagfish or lampreys.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.