Plastomeninae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 ...

of softshell turtles that inhabited most of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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 ...

. Members of this subfamily are also known as plastomenines.

Taxonomy and evolution

They are thought to have originated in North America during or shortly before the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

from basal trionychids that dispersed from

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. They reached their peak diversity from the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

through the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

, having survived the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...

. However, they went entirely extinct by the

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 ...

. The last surviving member of this subfamily is thought to have been ''

Plastomenus thomasii ''Plastomenus'' is an extinct genus of turtle that inhabited western North America during the early Paleogene period. Evolution ''Plastomenus'' belongs to the clade Pantrionychidae, represented by softshell turtles in modern times. It is the ...

'', which is the only known member of the subfamily to have survived past the Paleocene into the Eocene. Morphological analysis supports them being the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to the flapshell turtles (subfamily Cyclanorbinae), which still survive to the present day in parts of tropical

and

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

, in contrast to the exclusively North American plastomenines.

Genera

These extinct genera are known: * Subfamily Plastomeninae ** †''

Aspideretoides ''Aspideretoides'' is an extinct genus of soft-shelled turtle from the Late Cretaceous of North America. Naming and description The genus was named in 1995 by James D. Gardner and colleagues to unite multiple species that had at times been ref ...

'' ** †'' Atoposemys'' ** †''

Gilmoremys ''Gilmoremys'' is an extinct genus of softshell turtle which lived during the late Cretaceous (Maastrichtian stage) of North Dakota, Montana and Wyoming, United States. Remains ''Gilmoremys'' is known from five skulls, a mandible and an incomp ...

'' ** Tribe Plastomenini *** †''

Hutchemys ''Hutchemys'' is an extinct genus of softshell turtles from the late Cretaceous (Maastrichtian stage) to the late Paleocene of New Mexico, Montana, Wyoming, Utah, and North Dakota, United States. It was first named by Walter G. Joyce, Ariel Reva ...

'' *** †'' Helopanoplia'' *** †''

Plastomenus ''Plastomenus'' is an extinct genus of turtle that inhabited western North America during the early Paleogene period. Evolution ''Plastomenus'' belongs to the clade Pantrionychidae, represented by softshell turtles in modern times. It is the ...

References

{{Taxonbar, from=Q16937458 Plastomeninae Prehistoric animal subfamilies Taxa named by Oliver Perry Hay