IN CELEBRATION OF 100 YEARS OF TYRANNOSAURUS REX: MANOSPONDYLUS GIGAS, ORNITHOMIMUS GRANDIS, AND DYNAMOSAURUS IMPERIOSUS, THE EARLIEST DISCOVERIES OF TYRANNOSAURUS REX IN THE WEST

One hundred years ago (1905), H. F. Osborn created the name for the largest, most fearsome predatory dinosaur of North America: Tyrannosaurus rex. Perhaps best known from Montana specimens, T. rex fossils were first found in Colorado, South Dakota, and Wyoming. The earliest documented discovery of T. rex was made in 1874 by A. Lakes from the Denver Fm. near Golden, Colorado. This specimen of a "Fossil Saurian Tooth" was sent to O. C. Marsh at Yale University. In the early 1890s, J. B. Hatcher, working for Marsh, collected a number of large theropod postcranial elements in the "Laramie Beds" (now Lance Fm.) of eastern Wyoming. Marsh never described the Colorado material and only identified the Wyoming specimens as a new, large species of Ornithomimus (O. grandis) in 1896. At approximately the same time and not far away, E. D. Cope discovered some large "agathaumid ceratopsian" vertebral fragments from the Cretaceous units of western South Dakota. He named them Manospondylus gigas in 1892. These postcranial remains of O. grandis and M. gigas would later be shown to represent some of the earliest records of T. rex.

The importance of T. rex fossils was not recognized until the discovery of various partial skeletons in the early 1900s. The first was made by B.Brown and crew in 1900 in eastern Wyoming, where they found a partial skeleton of a large theropod. This specimen (AMNH Field #12) consisted of lower jaws and teeth, various post cranial elements, and numerous dermal plates. H. F. Osborn named this 13% complete skeleton Dynamosaurus imperiosus in 1905, in particular because of the osteoderms (later identified as ankylosaurian). Osborn also named Tyrannosaurus rex in this same paper, based on a very preliminary description of a partial skeleton found in the Hell Creek Fm. of Montana by Brown in 1902. Osborn rushed to publish his paper on Cretaceous carnivorous dinosaurs prior to complete collection and preparation of the Montana T. rex specimen, as O. A. Peterson of the Carnegie Museum was also working on a skeleton of a large theropod found in the Lance Fm. of Wyoming in 1902. In 1906, Osborn would synonymize D. imperiosus with T. rex and Brown would uncover an even more complete skeleton of T. rex in Montana. Eventually, the type specimen of T. rex was sold to the Carnegie Museum in 1941 and the skeleton of D. imperiosus was sent to London in 1960.