''Osteopygis'' is a

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 ...

of extinct

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

. ''Osteopygis'', as traditionally seen, is a chimera: the postcrania (including the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

) belong to a non-marine stem-cryptodire, whilst the crania belong to sea turtles. In 2005 the referred material was split between two taxa: the postcrania remained in ''Osteopygis'', while the crania were reassigned to '' Euclastes wielandi''.A reassessment of the referral of sea turtle skulls to the genus Osteopygis (Late Cretaceous, New Jersey, USA)
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References

Macrobaenidae Nomina dubia Fossil taxa described in 1868 Taxa named by Edward Drinker Cope Extinct turtles {{turtle-stub