''Antrodemus'' ("chamber bodied") is a

dubious Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty, ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Kimmeridgian In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxfordian ...

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...

age

Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Morrison Formation The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...

of Middle Park,

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

. It contains one species, ''Antrodemus valens'', first described and named as a species of ''

Poekilopleuron ''Poekilopleuron'' (meaning "varied ribs") is a genus of tetanuran dinosaur, which lived during the middle Bathonian of the Jurassic, about 168 to 166 million years ago. The genus has been used under many different spelling variants, although on ...

'' by

Joseph Leidy Joseph Mellick Leidy (September 9, 1823 – April 30, 1891) was an American paleontologist, parasitologist and anatomist. Leidy was professor of anatomy at the University of Pennsylvania, later was a professor of natural history at Swarthmore ...

in 1870. The first described

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

specimen was a bone obtained secondhand by

Ferdinand Vandeveer Hayden Ferdinand Vandeveer Hayden (September 7, 1829 – December 22, 1887) was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union Ar ...

in 1869 (original discoverer unknown). It came from Middle Park, near

Granby, Colorado The Town of Granby is the Statutory Town that is the most populous municipality in Grand County, Colorado, United States. The town population was 2,079 at the 2020 United States Census. Granby is situated along U.S. Highway 40 in the Middle P ...

, probably from Morrison Formation rocks. The locals had identified such bones as petrified

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

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 ''

'' as ''Poicilopleuron'' ic''valens''. He later decided it deserved its own genus, ''Antrodemus''. In 1920,

Charles W. Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...

came to the conclusion that the tail vertebra named ''Antrodemus'' by Leidy was indistinguishable from those of ''

Allosaurus ''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...

'', 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'' 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 A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

that the single bone of ''Antrodemus'' came from is unknown). Subsequent authors have agreed with this assessment and have considered ''Antrodemus'' a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

''.

References

{{Taxonbar, from=Q772822 Late Jurassic dinosaurs of North America Allosaurids Nomina dubia Fossil taxa described in 1873 Taxa named by Joseph Leidy Paleontology in Colorado