Sinemydidae is an extinct family of

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 t ...

s from Cretaceous to Paleocene deposits in Asia and North America. Their exact position is engimatic, they have alternatively been considered stem-group cryptodires, 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 as ...

Paracryptodira __NOTOC__ Paracryptodira is an extinct group of reptiles in the clade Testudinata (which contains modern turtles and their extinct relatives), known from the Jurassic to Paleogene of North America and Europe. Initially treated as a suborder sis ...

, Xinjiangchelyidae,

Thalassochelydia Thalassochelydia is a clade of extinct marine turtles from the Late Jurassic and earliest Cretaceous of Europe and South America. The group is defined as including '' Eurysternum'', ''Plesiochelys'' and '' Thalassemys'' to the exclusion of '' Pe ...

and

Sandownidae Sandownidae is a family of extinct marine turtles from the Cretaceous and Paleogene distributed around the Atlantic Ocean and adjacent areas. The family is defined as all taxa closer to the type genus '' Sandownia'' than to '' Pelomedusa'', '' T ...

outside of crown Testudines.

Genera

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

Shaximiao Formation The Shaximiao Formation () is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around the ...

, China, Middle-Late Jurassic *'' Jeholochelys''

Jiufotang Formation The Jiufotang Formation (Chinese: 九佛堂组, pinyin: ''jiǔfótáng zǔ'') is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see ...

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

Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its exq ...

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

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma ( million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preced ...

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

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the ...

) **†''Sinemys lens'' Wiman 1930 Mengyin Formation, China, Early Cretaceous (

Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ag ...

-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