Segisaurus (meaning "Segi canyon lizard") is a genus of small coelophysid theropod dinosaur, that measured approximately 1 metre (3.3 feet) in length.

[4] Segisaurus was described in 1936 by the paleontologist Charles Lewis Camp, based on specimen UCMP 32101, a fragmentary fossil skeleton which consisted of portions of the limbs, pelvis, and vertebrae.

When the specimen was examined during this period, all who viewed it commented on the supposed presence of clavicles and the apparently "solid" bones that the dinosaur had.

In 2005, a re-examination of the Segisaurus holotype revealed that contrary to reports it did in fact have hollow bones and that the clavicles were instead fragmented furculae.

The specimen was found in calcareous sandstone, which was deposited during the Pliensbachian - Toarcian stages of the Jurassic, approximately 190 to 174 million years ago.

When the specimen of Segisaurus was discovered, Camp likened its posture to that of a "sitting hen", due to the position the dinosaur's remains were in.

Geological features of the Navajo Sandstone Formation suggest that this genus lived in an environment resembling modern sand dunes.