fossil beds as Claosaurus annectens, and that therefore the older name (T. occidentalis) should be used for the Lance-aged "trachodonts." Many later researchers, including L.S. Russell and Charles M. Sternberg, continued to use the names Thespesius occidentalis or Thespesius annectens for the Lance hadrosaurids through the 1920s and 1930s. However, as early as 1913, paleontologist Lawrence Lambe regarded the type fossils of Thespesius occidentalis as inadequate and that any inferences based on them were too conjectural, as was the case for Trachodon. In an influential 1942 paper on hadrosaurids by Richard S. Lull and Nelda E. Wright, the authors classified most specimens of Thespesius annectens in the new genus Anatosaurus, and referred Cope's giant "duck-billed" specimens to Anatosaurus copei. Though they noted that T. occidentalis could possibly be distinguished from Anatosaurus based on its shorter tail vertebrae, they ultimately agreed with Lambe that, despite its historical importance, Thespesius occidentalis was too incomplete for good comparison. It has been generally ignored as a nomen dubium ever since. A referred species of Thespesius, T. saskatchewanensis, was named by Sternberg in 1926, but Nicolás Campione and David Evans found that it was a synonym of Edmontosaurus annectens in a 2011 study of edmontosaur diversity. Campione and Evans also found Thespesius edmontoni, named by Gilmore in 1924, to be a synonym of Edmontosaurus regalis. See also Timeline of hadrosaur research References Late Cretaceous dinosaurs of North America Saurolophines Nomina dubia Fossil taxa described in 1856 Taxa named by Joseph Leidy Paleontology in South Dakota Maastrichtian genus first appearances Maastrichtian genus extinctions Ornithischian genera