Perhaps the first dinosaur to be discovered in North America, Anchisaurus was rather longer than a human's height. It was among the smallest and most primitive of all prosauropods - plant-eating cousins of the mighty sauropods

The earliest discovery of  fragmentary remains of Anchisaurus was made in 1818. These, were not confidently identified as reptilian until 1855. In 1912 Richard Swan Lull was reviewing the fossils found in the Connecticut Valley, and he referred that material to the prosauropod dinosaur Anchisaurus.

Between the time of the first discovery and its final identification, other material was discovered in adjoining areas of the Connecticut Valley. Edward Hitchcock reported bones which were named Megadactylus polyzelus by his son E. Hitchcock Junior and subsequently renamed Amphisaurus by Marsh in 1882 (because the name Megadactylus was preoccupied), and then again in 1885 renamed Anchisaurus polyzelus by Marsh because the name Amphisaurus was already preoccupied! The most productive site in the Connecticut Valley proved to be a quarry near Manchester, Connecticut, this produced three well-preserved prosauropod skeletons and a few other fragments. These skeletons were described in some detail by O. C. Marsh in ther early 1880s as Anchisaurus major, A. colurus and A. solus, A. major was renamed Ammosaurus major and A. colurus became Yaleosaurus colurus.