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 and Cryptodira, which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, including land-dwelling tortoises and freshwater terrapins. They are found on most continents, some islands and, in the case of sea turtles, much of the ocean. Like other amniotes they breathe air and do not lay eggs underwater, although many species live in or around water.
Dinocephalosaurus is a genus of long necked, aquatic protorosaur that inhabited the Triassic seas of China. The genus contains the type and only known species, D. orientalis, which was named by Li in 2003. Unlike other long-necked protorosaurs, Dinocephalosaurus convergently evolved a long neck not through elongation of individual neck vertebrae, but through the addition of neck vertebrae that each had a moderate length. As indicated by phylogenetic analyses, it belonged in a separate lineage that also included at least its closest relative Pectodens, which was named the Dinocephalosauridae in 2021. Like tanystropheids, however, Dinocephalosaurus probably used its long neck to hunt, utilizing the fang-like teeth of its jaws to ensnare prey; proposals that it employed suction feeding have not been universally accepted. It was probably a marine animal by necessity, as suggested by the poorly-ossified and paddle-like limbs which would have prevented it from going ashore.
Proganochelys is an extinct, primitive stem-turtle that has been hypothesized to be the sister taxon to all other turtles creating a monophyletic group, the Casichelydia. Proganochelys was named by Georg Baur in 1887 as the oldest turtle in existence at the time. The name Proganochelys comes from the Greek word ganos meaning 'brightness', combined with prefix pro, 'before', and Greek base chelys meaning 'turtle'. Proganochelys is believed to have been around 1 meter in size and herbivorous in nature. Proganochelys was known as the most primitive stem-turtle for over a century, until the novel discovery of Odontochelys in 2008. Odontochelys and Proganochelys share unique primitive features that are not found in Casichelydia, such as teeth on the pterygoid and vomer and a plate-like coracoid.
Claudiosaurus is an extinct genus of diapsid reptiles from the Permian Sakamena Formation of the Morondava Basin, Madagascar. The pattern of the vertebrate, girle, and limbs indicates that Claudiosaurus and Thadeosaurus share a common ancestor.
Thalattosauria is an extinct order of prehistoric marine reptiles that lived in the middle to late Triassic period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and Thalattosauroidea. Askeptosauroids were endemic to the Tethys Ocean, their fossils have been found in Europe and China, and they were likely semiaquatic fish eaters with straight snouts and decent terrestrial abilities. Thalattosauroids were more specialized for aquatic life and most had unusual downturned snouts and crushing dentition. Thalattosauroids lived along the coasts of both Panthalassa and the Tethys Ocean, and were most diverse in China and western North America. The largest species of thalattosaurs grew to over 4 meters (13 feet) in length, including a long, flattened tail utilized in underwater propulsion. Although thalattosaurs bore a superficial resemblance to lizards, their exact relationships are unresolved. They are widely accepted as diapsids, but experts have variously placed them on the reptile family tree among Lepidosauromorpha, Archosauromorpha, ichthyosaurs, and/or other marine reptiles.
Desmatochelys is an extinct genus of sea turtles belonging to the family Protostegidae. This genus contains two known species, D. lowii and D. padillai. D. lowii was first discovered in 1895, followed by D. padillai in 2015. Having been estimated at over 120 million years old, D. padillai is currently the oldest known species of sea turtle.
The turtle shell is a shield for the ventral and dorsal parts of turtles, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell likely evolved by including dermal armor into the rib cage.
Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Upper Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in marine deposits of the Lower Sakamena Formation. In conjunction with several skeletal characteristics, this may indicate that Acerosodontosaurus individuals were at least partially aquatic.
Eunotosaurus is an extinct genus of amniote, possibly a close relative of turtles. Eunotosaurus lived in the late Middle Permian and fossils can be found in the Karoo Supergroup of South Africa. Eunotosaurus resided in the swamps of southern Africa. Its ribs were wide and flat, forming broad plates similar to a primitive turtle shell, and the vertebrae were nearly identical to those of some turtles. Accordingly, it is often considered as a possible transitional fossil between turtles and their prehistoric ancestors. However, it is possible that these turtle-like features evolved independently of the same features in turtles, since other anatomical studies and phylogenetic analyses suggest that Eunotosaurus may instead have been a parareptile, an early-diverging neodiapsid unrelated to turtles, or a synapsid.
Henodus is an extinct placodont of the Late Triassic period during the early Carnian age. Fossils of Henodus chelyops were found in the Estherienschichten Member of the Grabfeld Formation, near Tübingen, Germany. It was around 1 metre (3.3 ft) in length. The single species within the genus is H. chelyops.
Psephosauriscus is an extinct genus of placodont reptile from the Middle Triassic of Israel and Egypt. It is known from bony armor plates that have been found from Makhtesh Ramon in Israel's Negev desert and Araif en Naqua on Egypt's Sinai Peninsula. The genus was erected in 2002 as a replacement name for several species of the genus Psephosaurus, which was named in 1957. It includes the species P. mosis, P. ramonensis, P. sinaiticus, and a possible fourth species, P. rhombifer. All species, with the exception of P. ramonensis, were once assigned to the genus Psephosaurus. Remains of P. mosis and P. ramonensis were found in Makhtesh Ramon, while P. sinaiticus and P. rhombifer were found in Araif en Naqua.
Diandongosuchus is an extinct genus of archosauriform reptile, possibly a member of the Phytosauria, known from the Middle Triassic of China. The type species Diandongosuchus fuyuanensis was named in 2012 from the Zhuganpo Formation of Yunnan Province. It is a marine species that shows similarities with another Chinese Triassic species called Qianosuchus mixtus, although it has fewer adaptations toward marine life. It was originally classified as the basal-most member of the pseudosuchian clade Poposauroidea. However, a subsequent study conducted by Stocker et al. indicated it to be the basalmost known phytosaur instead.
Chinlechelys is an extinct genus of stem-turtle belonging to Testudinata. It lived in the Norian age of the Late Triassic and is the oldest turtle known from North America. Among turtles it is unique, mostly because of its very thin shell. The type and only species, C. tenertesta, was named and described with the genus by Walter G. Joyce et al. in 2009. It was probably terrestrial, and was found by Joyce et al. to be closely related to Proganochelys, another terrestrial testudinatan.
Pantestudines or Pan-Testudines is the group of all reptiles more closely related to turtles than to any other living animal. It includes both modern turtles and all of their extinct relatives.
Eohupehsuchus is a genus of extinct aquatic diapsid from the Upper Spathian of Hubei Province, located in Central China. The genus is monotypic and belongs to the order Hupehsuchia, whose members are characterized by toothless beak-like snouts, a row of dermal plates along their backs, and aquatic adaptations including paddle-shaped limbs and fusiform bodies with pachyostotic ribs.
Pappochelys is an extinct genus of diapsid reptile possibly related to turtles. The genus contains only one species, Pappochelys rosinae, from the Middle Triassic of Germany, which was named by paleontologists Rainer Schoch and Hans-Dieter Sues in 2015. The discovery of Pappochelys provides strong support for the placement of turtles within Diapsida, a hypothesis that has long been suggested by molecular data, but never previously by the fossil record. It is morphologically intermediate between the definite stem-turtle Odontochelys from the Late Triassic of China and Eunotosaurus, a reptile from the Middle Permian of South Africa.
Basilemys is a large, terrestrial trionychoid turtle from the Upper Cretaceous. In Greek, the word "Basil" means royal or kingly and the word "Emys" means turtle. Therefore, Basilemys means King Turtle. Basilemys has been found in rocks dating to the Campanian and Maastrichtian subdivisions of the Late Cretaceous and is considered to be the largest terrestrial turtle of its time. Basilemys has solely been found in North America. The family Nanhsiungchelyidae, which is the family Basilemys belongs to, made its first appearance in the Lower Cretaceous, in what we now call Asia. Because of Basilemys, we know that this family appeared in North America in the Upper Cretaceous. It is possible that Basilemys and other nanhsiungchelyids are immigrants from Asia. They might have arrived in North America by passing through what we now call the Bering Strait somewhere during the Cretaceous. In an analysis made by Sukhanov et al. on a new Nansiunghelyid turtle from the Upper Cretaceous of Mongolia, it was demonstrated that Asian nanhsiungchelyids gave rise to the North American nanhsiungchelyids. Basilemys shares some traits with another member of nanhsiungchelyidae, Zangerlia, which is similar to Basilemys in, for example, skull proportions. However, Basilemys has a more complex triturating surface that includes well-defined pockets on the dentary, and it also has tooth-like projections on the triturating surface of the maxilla.
Litorosuchus is a genus of armored, semiaquatic archosauriform reptile from the Middle Triassic of China, closely related to the morphologically similar Vancleavea. It contains one species, L. somnii.
Eorhynchochelys is an extinct genus of stem-turtle from the Late Triassic Xiaowa Formation of southwestern China.
Drazinderetes is a large bodied genus of soft shell turtle from the Middle Eocene Drazinda Formation of Pakistan. Its presence in the shallow marine deposits of the Drazinda Formation suggests that Drazinderetes may have been a partially or fully marine animal. Indetermined trionychine remains from the same formation may suggest that Drazinderetes could have been among the largest known turtles, with one entoplastron indicating a potential length of 1.5 to 2.1 meters. Drazinderetes currently consists of only a single species: Drazinderetes tethyensis.
