Euparkeria had a light, lean body, long tail, and a small skull with tiny, needle-like teeth. Euparkeria had small bony plates that ran along the center of its back and tail, and its hindlegs were one-third longer than its forelimbs; longer than any other reptile of similar size during its time. This has led some paleontologists, such as Carroll, (1988) to suggest that Euparkeria may have been "facultatively bipedal", in that it may have been able to run bipedally for short periods of time. It most likely fed on insects and any other small animals that it could find on the forest floor, and would periodically shed its teeth in order to keep them sharp.
Like other archosaurs, Euparkeria had an opening in the skull between its eyes and nasal breach (the antorbital opening) and two additional apertures in the skull behind one eye (the upper and lower temporal openings). Its teeth were set in sockets, rather than being attached to the side of the jawbone or perched atop it. These teeth were long, sharp, and recurved, which attested to the carnivorous habit that seems to have been common among the first archosaurs. Euparkeria also possessed teeth on its palate, which was also common among earlier reptiles and amphibians.
However, Welman (1995) contends that, based on braincase characters, Euparkeria is closer to birds than to crocodyliforms or dinosaurs. This is highly controversial, however, and runs counter to other archosaur phylogenies. However, Dr. David Gower and ornithologist Erich Weber were able to show that Welman's purported cases of homology between Euparkeria and birds was incorrect or mistaken, and in fact the data supported the following conclusions:
- 1. The division of archosaurs into a crocodile branch and a bird branch
- 2. The nesting of birds within ornithodirans
- 3. The exclusion of Euparkeria from the crocodile-bird crown group.
Euparkeria was one of the smaller reptiles of its time, with the adults reaching the size of a large lizard (55 cm or 22 in). It lived in a world with many predators, so it had to be quick on its feet. It walked on four legs for most of the time, but if a quick getaway was needed, it could rise on to its hind legs and run at a very high speed. Euparkeria had relatively long hind legs, and may have been semi-bipedal, able to move using only its hind legs when running quickly (Carroll, 1988). This tendency towards bipedal locomotion makes Euparkeria one of the earliest reptiles to walk on two legs, a feature that would be retained in some dinosaurs and early Crurotarsi. Another means of defence that Euparkeria possessed was a sharp claw on its thumb, which could have been used as a weapon in close combat.