Thespesius

Thespesius (meaning "wondrous one") is a dubious genus of extinct hadrosaurid dinosaur based on two caudal vertebrae and a phalanx from the late Maastrichtian-age Upper Cretaceous Lance Formation of South Dakota (although at first thought to be from the Miocene). Like Trachodon, another duckbill genus named by Joseph Leidy, it is an historically-important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists.

Two other species of duckbill started out as species of Thespesius: T. saskatchewanensis, now thought to be a species of Edmontosaurus; and T. edmontoni, now considered to be the same as Edmontosaurus annectens. Both of them were included in Anatosaurus for many years.