Sandownidae is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

marine

turtles Turtles are an order (biology), order of reptiles known as 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) an ...

from the

Cretaceous 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 longest. At around 79 million years, it is the longest geological period of th ...

and

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

distributed around the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and adjacent areas. The family is defined as all taxa closer to the type genus '' Sandownia'' than to ''

Pelomedusa The African helmeted turtle (''Pelomedusa subrufa''), also known commonly as the marsh terrapin, the crocodile turtle, or in the pet trade as the African side-necked turtle, is a species of omnivorous side-necked terrapin in the family Pelomedus ...

'', '' Testudo'', ''

Solnhofia ''Solnhofia'' is a genus of extinct thalassochelydian turtle from the Late Jurassic of Germany. The type species is ''Solnhofia parsonsi'', named by Gaffney in 1975 for a partial skull and jaw from the early Tithonian of the Solnhofen Formation ...

'', ''

Eurysternum ''Eurysternum'' is an extinct genus of thalassochelydian turtle. Its type species is ''Eurysternum wagleri'', the holotype of which has since been lost and only survives in illustrations. Formerly assigned species ''Eurysternum ignoratum'' Bra ...

'', ''

Plesiochelys ''Plesiochelys'' is a genus of late Jurassic European and Asian turtle. The type species is ''Plesiochelys etalloni''. Fossil records have discovered ''Plesiochelys bigleri'' and ''Plesiochelys etalloni'' from the Kimmeridge Clay of England and ...

'', ''

Thalassemys ''Thalassemys'' is a genus of extinct thalassochelydian turtle from the Late Jurassic of western and central Europe. While the genus was originally named by Rütimeyer in 1859 for a large carapace and other associated fragments from the late Kim ...

'' or '' Protostega'', a definition that encompasses the previous concept of the clade while also excluding it from being synonymous with other clades of modern or extinct marine turtles. Sandownidae may be within the larger clade

Angolachelonia Angolachelonia is a clade of extinct turtles from the Late Jurassic to Paleogene of Eurasia. The group is defined as all taxa derived from the ancestor of the type genus ''Angolachelys'' and '' Solnhofia'', a definition that could potentially e ...

, defined as inclusive of ''Angolachelys'' and ''Solnhofia'', sister to the entirely

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

marine group

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 ''Pelome ...

, although the concepts of the clades may shift with further phylogenetic analysis.

Genera

* '' Sandownia'' Meylan et al. 2000

Atherfield Clay Formation The Atherfield Clay Formation is a Geological formation in Southern England. Part of the Lower Greensand Group it dates to the Aptian age of the Early Cretaceous. The deposit is of marine origin largely consisting of massive yellowish brown to ...

, England, Early Cretaceous (

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

) * '' Brachyopsemys'' Tong and Meylan 2013

Ouled Abdoun Basin The Oulad Abdoun Basin (also known as the Ouled Abdoun Basin or Khouribga Basin) is a phosphate sedimentary basin located in Morocco, near the city of Khouribga. It is the largest in Morocco, comprising 44% of Morocco's phosphate reserves, and a ...

, Morocco,

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), E ...

(

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretaceous� ...

) * ''

Angolachelys ''Angolachelys'' is an extinct genus of African eucryptodiran turtle which existed in Angola during the Turonian stage of the Late Cretaceous. The type species is ''Angolachelys mbaxi''. The type MGUAN-PA includes skull, jaw, and postcranial frag ...

'' Mateus et al. 2009

Itombe Formation The Itombe Formation is a geological formation of the Kwanza Basin in Angola dated to the Coniacian stage of the Late Cretaceous. The environment of deposition is shallow marine. Reptile fossils have been recovered from the Tadi beds locality wi ...

, Angola, Late Cretaceous (

Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by t ...

) * ''

Leyvachelys ''Leyvachelys'' is an extinct genus of turtles in the family Sandownidae from the Early Cretaceous ( Late Aptian to Early Albian) of the present-day Altiplano Cundiboyacense, Eastern Ranges, Colombian Andes. The genus is known only from its type ...

'' Cadena 2015

Paja Formation Paja may refer to: * Paja, Iran, a village in Sari County * Paja (given name), a Serbian masculine name * Paja (surname) * Paja Formation, geologic formation in Colombia * Paja Brava :''Paja Brava is also used in Spanish speaking countries to ...

, Colombia, 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 preceded ...

)

Glen Rose Formation The Glen Rose Formation is a shallow marine to shoreline geological formation from the lower Cretaceous period exposed over a large area from South Central to North Central Texas. The formation is most widely known for the dinosaur footprints ...

, Texas, Early Cretaceous, (

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

)

Phylogeny

After Evers and Benson, 2018:

References

Cretaceous turtles Paleogene turtles Cryptodira Turtle families Prehistoric reptile families {{paleo-turtle-stub