Sinemydidae is an extinct family of turtles from Cretaceous to Paleocene deposits in Asia and North America. Their exact position is engimatic, they have alternatively been considered stem-group

cryptodires The Cryptodira ('' el, hidden neck'') are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-necked turtles) in that they lower their necks and pull the heads straight back into the ...

, but also "crownward stem-turtles" alongside

Macrobaenidae Macrobaenidae is an extinct family of turtles, known from the Early Cretaceous to Paleogene of Laurasia. Their relationships to other turtles and whether or not they form a monophlyletic group are controversial. They are typically interpreted a ...

, Paracryptodira, Xinjiangchelyidae, Thalassochelydia and Sandownidae outside of crown Testudines.

Genera

*'' Dracochelys'' Lianmugin Formation, China, Early Cretaceous (Aptian-Albian) *'' Hongkongochelys'' Upper Shaximiao Formation, China, Middle-Late Jurassic *''

Jeholochelys ''Jeholochelys'' is an extinct genus of sinemydid turtle that lived during the Early Cretaceous of what is now China. The holotype specimen was discovered in the Jiufotang Formation of Sihedang in Lingyuan, western Liaoning. In 2018, the Chi ...

'' Jiufotang Formation, China, Early Cretaceous (Aptian) *''

Liaochelys ''Liaochelys'' is an extinct genus of macrobaenid turtle which existed in western Liaoning, China during the early Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the thi ...

'' Jiufotang Formation, China, Early Cretaceous (Aptian) *'' Manchurochelys'' Yixian Formation, China, Early Cretaceous (Aptian) *''

Ordosemys ''Ordosemys'' is an extinct genus of sea turtle from the Cretaceous period The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the ...

'' **''O''. ''leios''

Luohandong Formation The Luohandong Formation is an Early Cretaceous geologic formation of the Ordos Basin in Inner Mongolia, China. The formation was initially dated to the earliest Cretaceous; Valanginian to Barremian, but later dating established an Aptian to Alb ...

, China, Early Cretaceous **''O''. ''liaoxiensis''

Chengzihe Formation Chengzihe () is a district of Jixi, Heilongjiang, People's Republic of China. Administrative divisions There are five subdistricts, one township, and one ethnic township in the district: Subdistricts: * Chengzihe Subdistrict (), Chengxi Su ...

, China, Early Cretaceous (Aptian) **''O''. ''brinkmania'' Lianmugin Formation, China, Early Cretaceous (Aptian-Albian) **''O''. ''perforata'' Khulsangol Formation, Mongolia, Early Cretaceous (Albian) **''O''. ''donghai''

, China, Early Cretaceous (Aptian-Albian) *'' Sinemys'' **†''Sinemys brevispinus'' Tong and Brinkman 2012 Laohongdong Formation, China, Early Cretaceous **†''Sinemys chabuensis'' Ji and Chen 2018

Jingchuan Formation The Jingchuan Formation is a Barremian geologic formation in China. Various dinosaur fossils and tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. Vertebrate paleofauna * ''Wuerhosaur ...

, China, Early Cretaceous ( Barremian) **†''Sinemys gamera'' Brinkman and Peng 1993

, China, Early Cretaceous ( Valanginian- Hauterivian) **†''Sinemys lens'' Wiman 1930 Mengyin Formation, China, Early Cretaceous ( Berriasian-Valanginian) *'' Wuguia'' **†''Wuguia efremovi'' Khozatsky 1996 Hutubei Formation, China, Hauterivian/Barremian Lianmuxin Formation, China, Early Cretaceous (Aptian-Albian) **†''Wuguia hutubeiensis'' Matzke et al. 2004 Hutubei Formation, China, Hauterivian/Barremian *'' Xiaochelys'' Lianmugin Formation, China, Early Cretaceous (Aptian-Albian) *'' Yumenemys'' Hui-Hui-P'u, China, Late Cretaceous

References

Cryptodira Extinct turtles Prehistoric reptile families {{paleo-turtle-stub