''Plastomenus'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

that inhabited western North America during the early

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

period.

Evolution

''Plastomenus'' belongs to the clade Pantrionychidae, represented by softshell turtles in modern times. It is the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

of the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Plastomeninae Plastomeninae is an Extinction, extinct subfamily of Trionychidae, softshell turtles that inhabited most of North America from the Cretaceous to the Eocene. Members of this subfamily are also known as plastomenines. Taxonomy and evolution The ...

(also treated as the family Plastomenidae), a group of extinct turtles that lived from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

to the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

. The type species, ''P. thomasii'', was first described by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

in 1872. The following species are known: * †''P. joycei'' Lyson, Petermann & Miller, 2021 -

Early Paleocene The Danian is the oldest age (geology), age or lowest stage (stratigraphy), stage of the Paleocene Epoch or series (stratigraphy), Series, of the Paleogene Period or system (stratigraphy), System, and of the Cenozoic Era or Erathem. The beginnin ...

of Colorado, USA (

Denver Formation The Denver Formation is a geological Formation (geology), formation that is present within the central part of the Denver Basin that underlies the Denver, Colorado, area. It ranges in age from Late Cretaceous, latest Cretaceous (Maastrichtian) to ...

) * †''P. thomasii'' (

Cope A cope ( ("rain coat") or ("cape")) is a liturgical long mantle or cloak, open at the front and fastened at the breast with a band or clasp. It may be of any liturgical colour. A cope may be worn by any rank of the Catholic or Anglican clerg ...

, 1872) - Early to Middle

(

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...

) of Wyoming, USA ( Bridger Formation) * †''P. vegetus'' ( Gilmore, 1919) - Early Paleocene of New Mexico, USA ( Nacimiento Formation) Many other species formerly placed in this genus, from both North America and Asia, have been reclassified into other genera, synonymized with one of the extinct species, or are now considered '' nomina dubia''.

Phylogeny

Based on Joyce & Lyson (2017):Alternatively, ''Plastomenus'' may be most closely related to ''Gilmoremys''.

Description

''Plastomenus'' turtles are distinguished by their low, rounded shells and elongated skulls, which set them apart from other contemporary softshell turtles.

References

{{Taxonbar, from=Q20072377 Trionychidae Prehistoric turtle genera Danian first appearances Ypresian genera Lutetian genus extinctions Fossils of the United States Paleocene turtles Eocene turtles Paleocene reptiles of North America Eocene reptiles of North America Fossil taxa described in 1873 Taxa named by Edward Drinker Cope