Segisaurus, meaning “Segi canyon lizard,” is a genus of coelophysoid theropod dinosaur from the Early Jurassic Period (183 million years ago). It was discovered by a Navajo Indian — Max Littlesalt — in 1933 in Tsegi Canyon, Arizona, for which it was named. Segisaurus is the only dinosaur ever to be excavated from that area. Although it was described in 1936 by paleontologist Charles Lewis Camp, the specimen went relatively ignored for the next half century.

When the specimen was discovered, Camp likened it to that of a “sitting hen,” due to the position the dinosaur’s remains were found in. Other theropods used this position to sleep or to stay sheltered during sand or ash storms. Segisaurus was indeed found in sandstone, suggesting that the dinosaur had been submerged in a layer of sand and died. This of course is only a hypothesis, as no nest or den materials were found along with the Segisaurus specimen.

In 2005, the Journal of Vertebrate Paleontology published a report which re-examined the remains of the Segisaurus holotype. They concluded, that although very unusual, it was firmly a coelophysoid. They also suggested it Segisaurus was a relative of Procompsognathus.

The specimen excavated consisted of portions of the limbs, pelvis, and vertebrae. There was no skull material found. Segisaurus seems to be closely related to the better-known Coelophysis. Although, the bones of Segisaurus were solid, whereas those of Coelophysis were hollow. Later studies of the specimen showed that Segisaurus did in fact have hollow bones, rather than solid bones.

Segisaurus was a primitive bipedal theropod, It was roughly 3.25 feet in length, 1.5 feet tall and weighed 9 to 15 pounds. It was a nimble insectivore, although it may have scavenged for meat as well. It had a birdlike structure, with a flexible, elongated neck and stout body. It was three-toed and had powerful legs that were long compared to its body length. Segisaurus also had a long tail and long forearms. Its collar bone was similar to that of a bird, strengthening arguments that dinosaurs were related to avians.

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