''Ischyrotherium'' is an extinct genus named by Joseph Leidy in 1856 for fossils from the

lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

deposits in Nebraska. Originally considered an herbivorous

cetacean Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

, Leidy then reassigned it to Sirenia as a relative of manatees, before

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...

reclassified it as a non-mammalian, suggesting the new name ''Ischyrosaurus'' to better identify its reptilian origins, as he considered it a sauropterygian. ''Ischyrotherium'' was found alongside material from the hadrosaur ''

Thespesius ''Thespesius'' (meaning "wondrous one") is a dubious genus of hadrosaurid dinosaur from the late Maastrichtian-age Upper Cretaceous Lance Formation of South Dakota. History In 1855 geologist Ferdinand Vandeveer Hayden sent a number of fossils ...

'' and turtles ''

Compsemys ''Compsemys '' is an extinct genus of prehistoric turtles from the Late Cretaceous and Paleocene of North America and possibly Europe. The type species ''C. victa'', first described by Joseph Leidy from the Hell Creek Formation in Montana in 1856 ...

'' and '' Emys'', and the fish '' Mylognathus''. The name ''Ischyrosaurus'' was also used by John Whitaker Hulke for the sauropod now known as '' Ornithopsis manseli'', as he was unaware it was preoccupied by Cope.

References

{{Taxonbar, from1=Q119484945 Cretaceous reptiles of North America Cretaceous reptiles Prehistoric reptile genera