The first described
fossil specimen was a bone obtained secondhand by
Ferdinand Vandeveer Hayden in 1869 (original discoverer unknown). It came from Middle Park, near
Granby, Colorado, probably from Morrison Formation rocks. Hayden reported that several similar fossils had been identified as petrified
horse hooves. Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra, and tentatively assigned it to the European dinosaur genus
Poekilopleuron as
Poicilopleuron [sic]
valens, based on the shared presence of a large medullary cavity. He identified the presence of
trabeculae in
P.
valens as a distinguishing character from
P.
bucklandii but also noted that should better remains show more characters that could sufficiently distinguish the two taxa, it might be named
Antrodemus. with a replica skull in the 1950s of what was then considered
Antrodemus In 1920,
Charles W. Gilmore concluded that the tail vertebra named
Antrodemus by Leidy was indistinguishable from those of
Allosaurus and that
Antrodemus should be the preferred name because, as the older name, it had priority.
Antrodemus became the accepted name for this familiar genus for over fifty years until
James Madsen published on the Cleveland-Lloyd specimens of
Allosaurus in 1976 and concluded that the
Allosaurus name should be used because
Antrodemus was based on material with poor, if any, diagnostic features and locality information (for example, the
geological formation that the single bone of
Antrodemus came from is unknown). Subsequent authors have agreed with this assessment and have considered
Antrodemus a
nomen dubium. The paleontological site that still in the present day presents the highest concentration of fossilised individuals of
Allosaurus fragilis is the Cleveland-Lloyd Dinosaur Quarry, now part of the
Jurassic National Monument in
Utah. The first skeletal mount obtained out of the Quarry was extracted in the late 1930s/early 1940s and finally mounted in 1961 in Guyot Hall,
Princeton University,
Princeton,
New Jersey, where it remained on display until 2024. For years, that skeletal mount was presented to the visitors under the taxonomic name
Antrodemus, before the specimens from the Cleveland-Lloyd Quarry were attributed to
Allosaurus. ==References==