Hutchemys

Hutchemys Temporal range: Late Cretaceous to Late Paleocene, 70.6–55.8 Ma PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Cryptodira
Family:	Trionychidae
Subfamily:	†Plastomeninae
Genus:	†Hutchemys Joyce et al., 2009
Species
†H. arctochelys Joyce et al., 2009 †H. rememdium Joyce et al., 2009 (type) †H. tetanetron Joyce & Lyson, 2011 (Hutchison, 2009) †H. sterea Joyce & Lyson, 2011 (Hutchison, 2009) †H. acupictus Joyce & Lyson, 2011 (Hay, 1907) †H. sp
Synonyms
Plastomenoides Hutchison, 2009 Derrisemys Hutchison, 2009 Plastomenus acupictus Hay, 1907 Aspideretes? nassau Paleotrionyx? nassau Trionyx nassau “Plastomenine” type A

Hutchemys (Hutchison's turtle) is an extinct genus of softshell turtles from the late Cretaceous (Maastrichtian stage) to the late Paleocene of New Mexico, Montana, Wyoming and Utah, USA. It was first named by Walter G. Joyce, Ariel Revan, Tyler R. Lyson and Igor G. Danilov in 2009, and the type species is Hutchemys rememdium. H. rememdium is known from the holotype YPM PU 16795, which consists of a nearly complete postcranial skeleton, and from the referred specimen YPM PU 16781, found in the Ekalaka Member of the Fort Union Formation, Montana. Another referred specimen, YPM PU 14985, was found in the Cedar Point Quarry, Wyoming. The second species, H. arctochelys, is known from the holotype YPM PU 16319, a nearly complete carapace, and from the paratypes YPM PU 16320, YPM PU 16321, YPM PU 16322, YPM PU 16238. All specimens of H. arctochelys were recovered from the same quarry of the Tongue River Member, Fort Union Formation, near Burns Mine of Montana. A possible third species is represented by the unnamed specimen UCMP 130000 from the Paleocene Tullock Formation of Montana. Aspideretes? nassau (YPM PU 11566) from the Fort Union Formation, Duffy’s Ranch of Sweet Grass County, Montana was also assigned to Hutchemys sp.^[1]

The generic name honors John Howard Hutchison, a turtle paleontologist. Hutchison himself named later in 2009 two new genera of extinct softshell turtles from New Mexico, Montana, Wyoming and Utah: Plastomenoides (two new species: P. lamberti (type) and P. tetanetron) and Derrisemys (new species: D. sterea (type) and new combination D. acupictus [originally Plastomenus]).^[2] In 2011, Joyce and Lyson noted that P. lamberti and Hutchemys rememdium are based on the same type specimen (YPM PU 16795) and therefore P. lamberti and Plastomenoides are objective junior synonyms of H. rememdium and Hutchemys. P. tetanetron Hutchison, 2009 is also cogeneric with H. rememdium. They also found that D. sterea is the closest relative of P. tetanetron and therefore both D. sterea and D. acupictus were reassigned to Hutchemys.^[3]

Phylogeny

Cladogram after Joyce, Revan, Lyson and Danilov, 2009:^[1]

Trionychidae	Cyclanorbinae Cyclanorbis Cycloderma Lissemys †Plastomeninae Hutchemys Plastomenus Trionychinae Trionyx Chitra Pelochelys Apalone Rafetus Amyda Aspideretes Nilssonia Dogania Palea Pelodiscus

Cladogram after Joyce and Lyson, 2011:^[3]

Trionychidae	Trionychinae Cyclanorbinae †Plastomeninae Gilmoremys Plastomenus Hutchemys H. rememdium H. arctochelys H. tetanetron H. sterea

References

1. Walter G. Joyce, Ariel Revan, Tyler R. Lyson and Igor G. Danilov (2009). "Two New Plastomenine Softshell Turtles from the Paleocene of Montana and Wyoming" (PDF). Bulletin of the Peabody Museum of Natural History 50 (2): 307–325. doi:10.3374/014.050.0202.
2. John Howard Hutchison (2009). "New soft-shelled turtles (Plastomeninae, Trionychidae, Testudines) from the Late Cretaceous and Paleocene of North America". PaleoBios 29 (2): 36–47.
3. Walter G. Joyce and Tyler R. Lyson (2011). "New Material of Gilmoremys lancensis nov. comb. (Testudines: Trionychidae) from the Hell Creek Formation and the Diagnosis of Plastomenid Turtles". Journal of Paleontology 85 (3): 442–459. doi:10.1666/10-127.1.