The Cryptodira are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira in that they lower their necks and pull the heads straight back into the shells, instead of folding their necks sideways along the body under the shells' marginals. They include among their species freshwater turtles, snapping turtles, tortoises, softshell turtles, and sea turtles.
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 Kimmeridgian of the Reuchenette Formation of Switzerland, although the taxon was not validly named until 1873 when Rütimeyer designated the type species T. hugii. Rütimeyer also named T. gresslyi from the Reunchenette Formation in the same paper as T. hugii, but it cannot be differentiated from the type material of T. hugii and is therefore a junior synonym. A large assemblage of shell and postcranial material from the Reunchenette was named as a species of Eurysternum, E. ignoratum, by Bräm in 1965. While originally distinguished based on the presence of fontanelles on the plastron, the feature was later identified on T. hugii and E. ignoratum was designated a junior synonym. Additional material from the Kimmeridgian of the United Kingdom has also been referred to T. hugii.
Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles). Though it was first coined as the group containing turtles by Jacob Theodor Klein in 1760, it was first defined in the modern sense by Joyce and colleagues in 2004. Testudinata does not include the primitive stem-turtle Odontochelys, which only had the bottom half of a shell. A recent phylogenetic tree of Testudinata included Angolachelonia and Testudines as sister-taxa and subgroups of Testudinata.
Hispaniachelys is an extinct genus of paracryptodire or basal testudines turtle known from the Lorente Formation of southern Spain. Reinterpretation of the original material shows that the taxon lacks diagnostic characteristics and is thus a nomen dubium.
Palaeomedusa testa is an extinct species of sea turtle from the Tithonian of the Late Jurassic. It was first described by the German palaeontologist Christian Erich Hermann von Meyer in 1860. It is the only species classified under the genus Palaeomedusa.
The Plesiochelyidae are an extinct family of turtles in the clade Thalassochelydia originally classified within the Cryptodira suborder, mostly belonging from the Jurassic period. An alternate study placed the clade Thalassochelydia in the Angolachelonia and outside the Testudines.
Eurysternidae is an extinct family of turtles in the clade Thalassochelydia of the order Cryptodira. It consists of several genera of marine turtles from marine deposits in Europe, including Achelonia, Chelonides, Eurysternum. Hydropelta, Chelonides, Idiochelys, Palaeomedusa, Parachelys. and Solnhofia.
Achelonia is an extinct genus of sea turtle belong to Eurysternidae. Its type species is Achelonia formosa.
Cyrtura is a dubious genus of extinct Testudinata from the Late Jurassic of the Solnhofen Formation of Bavaria, Germany. Cyrtura was originally described as a temnospondyl amphibian by Otto Jaekel in 1904 on the basis of MNB 1890, the distal portion of a tail with 14 caudal vertebrae. Most authors overlooked the genus, although those who mentioned Cyrtura dismissed it as either undiagnostic or referable to Testudines rather than Temnospondyli. Warren and Hutchinson (1983) rejected the temnospodyl classification of the genus based on examination of a cast of the holotype, and subsequent studies showed that Cyrtura is actually a marine turtle, although the lack of diagnostic characters renders it a nomen dubium.
Parachelys is a genus of late Jurassic turtle from marine deposits in Bavaria, southern Germany.
Hydropelta is a genus of late Jurassic turtle from marine deposits in the Jura Mountains of eastern France.
Chelonides is a genus of late Jurassic turtle from marine deposits in Lower Saxony, Germany.
Idiochelys is a genus of late Jurassic turtle from marine deposits in the Jura Mountains of eastern France and Bavaria, Germany.
Thalassochelydia is a clade of extinct turtles from the Late Jurassic and potentially Early Cretaceous of Europe. The group is defined as including Eurysternum, Plesiochelys and Thalassemys to the exclusion of Pelomedusa, Testudo and Protostega. While a clade uniting the families Eurysternidae, Plesiochelyidae and Thalassemydidae had been supported by phylogenetic evidence, a name was not given for the clade until 2017, when Jérémy Anquetin and colleagues coined Thalassochelydia. While inner relationships of the clade are so uncertain as to make the monophyly of the families questionable, the significant diversity of thalassochelydians makes using the potentially invalid terms useful to describe the different morphologies. The monophyly of Thalassochelydia was further supported by a later analysis by Serjocha Evers and Roger Benson in 2019, where the group, represented by Solnhofia and Plesiochelyidae was sister taxon to Sandownidae within the clade Angolachelonia, which, unlike as found by Anquetin et al. earlier, was outside Cryptodira and Testudines. The phylogeny below of Thalassochelydian inter-relationships follows the results of Anquetin and colleagues in 2017.
Solnhofia is a genus of extinct thalassochelydian turtle from the Late Jurassic of Germany. The type species is Solnhofia parsoni, named by Gaffney in 1975 for a partial skull and jaw from the early Tithonian of the Solnhofen Formation in Bavaria. Additional material including a complete skeleton is known from the late Kimmeridgian of Switzerland and the Kimmeridgian/Tithonian of other deposits within Bavaria, and potentially also unprepared material from the Late Jurassic of France. The genus was referred to the family Eurysternidae by Anquetin and colleagues in 2017, which may represent an artificial clade of early thalassochelydians. In 2020 a new species Solnhofia brachyrhyncha was described from the Kimmeridigan aged Reuchenette Formation of Switzerland.
Enaliochelys is a genus of extinct thalassochelydian turtle from the Late Jurassic of the United Kingdom. The type and only species is Enaliochelys chelonia, named by Harry Govier Seeley in 1869 for a partial disarticulated skeleton from the early Kimmeridgian of the Kimmeridge Clay in Cambridgeshire, and additional material from the Kimmeridge Clay has also been referred to the taxon. While it has long been considered a synonym of Thalassemys hugii, Enaliochelys would have priority due to it being named first, although it has multiple distinguishing features, including its large carapace over 60 cm (24 in) long. The genus lacks the features diagnostic to its parent clade Thalassochelydia, but shared features of the scapula and shell suggest it may be closely related to Thalassemydidae.
Euryaspis is a dubious genus of extinct thalassochelydian turtle from the Late Jurassic of Germany. The type and only species is Euryaspis radians, originally proposed by Wagner in 1859 before being validly described and illustrated in 1861. The only specimen was a partial carapace probably from the Tithonian, although the original locality is unknown. The genus is referred to Thalassochelydia and has been considered a synonym of Eurysternum or Acichelys before, but casts that remain of the lost holotype show that it bears no features that can clarify its validity making it a nomen dubium.
Owadowia is a genus of extinct thalassochelydian turtle from the Late Jurassic of Poland. The type and only species is Owadowia borsukbialynickae, named by Szczygielski and colleagues in 2017 for a partial lower jaw, coracoid, ilium and femur from the early Tithonian Kcynia Formation. The limited material means that it is difficult to compare Owadowia to its relatives, and it may not be a unique taxon. The genus lacks the features diagnostic to its parent clade Thalassochelydia, has similarities to Solnhofia and Portlandemys as well as being a Late Jurassic marine turtle like the remainder of the group.
Pelobatochelys is a genus of extinct thalassochelydian turtle from the Late Jurassic of the United Kingdom. The type and only species is Pelobatochelys blakii, named by Harry Govier Seeley in 1875 for a central carapace fragment along with five additional specimens from the remainder of the shell from the early Kimmeridgian of the Kimmeridge Clay in Dorset, and additional material from the Kimmeridge Clay has also been referred to the taxon. The material was considered to be related to various turtles throughout time, including being reassigned to Tropidemys as T. blakii based on limited evidence. A large shell also from Weymouth, Dorset may represent further material of Pelobatochelys, but could also be from Tropidemys langii which was also present in the deposits.
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 encompass a clade of entirely marine turtles. Angolachelonia was originally inclusive of only Solnhofia, Angolachelys and Sandownia when originally concevied by Octavio Mateus and colleagues in 2009, but later phylogenetic analyses by Serjocha Evers and Roger Benson in 2018 unites the family Sandownidae, including Angolachelys and Sandownia among other taxa, with the entirely Late Jurassic clade Thalassochelydia, where Solnhofia may be a basal member. While the placement of Solnhofia is weak and the clade that Angolachelonia represents may change with further analysis, the clade of Sandownidae and Thalassochelydia is well-supported, and does not collapse despite the uncertain evolutionary history of the group. Three alternative potential origins of Angolachelonia sensu Evers and Benson are shown below.
