Dystrophaeus

Dystrophaeus is an extinct genus of sauropod dinosaur. Its type and only species is Dystrophaeus viaemalae, named by Edward Drinker Cope in 1877. Its fossils were found in the Tidwell Member of the Morrison Formation of Utah. Due to the fragmentary condition of its only known specimen, the affinities of Dystrophaeus are uncertain, although excavations carried out at the discovery site since 1989 have uncovered more of the original specimen and hold the potential for an improved understanding of the taxon.

Dystrophaeus viaemalae is known from a single fragmentary specimen, the holotype USNM 2364. The specimen initially consisted of a partial dorsal vertebra, a partial scapula, a nearly complete ulna, a partial radius, and three metacarpals. More recent excavations have discovered additional parts of the same specimen, including a phalanx, teeth, and additional vertebrae from the back and tail. The specimen was found in the Tidwell Member of the Morrison Formation and is approximately 158 million years old, making it the oldest species of sauropod from the Morrison Formation by several million years.