Proterocheris is another ancient fossil turtle that lived at the same time as Proganochelys. The Anapsida is thought to have been ancestral to the Diapsida-a lineage of reptiles whose skull was characterized by two temporal fenestrae and would subsequently include all archosaurs as well as lizards and tuataras. A third hypothesis suggests that turtles arose as anapsids-a lineage whose skull contained no openings (temporal fenestrae) in the side of the head.
A second hypothesis posits that turtles were more closely related to lizards and tuataras. The DNA hypothesis suggests that turtles were a sister group to the archosaurs (the group that contains the dinosaurs and their relatives, including crocodiles and their ancestors and modern birds and their ancestors). One hypothesis relies heavily on DNA analysis, whereas the others are based on morphological studies of fossils. There are three main hypotheses concerning their origins, and existing evidence is such that there is a lack of overwhelming support for any one of them. What do you call a walking vegetarian turtle that isn’t fond of water?Īlthough Odontochelys, Proganochelys, and Eunotosaurus offer insight into early anatomy, the origin of turtles remains a strongly debated issue. In contrast to Odontochelys, the shell of Proganochelys possessed most of the features of modern turtles, and it completely encased the shoulder and pelvic girdles. Teeth were still present in turtles at this time, appearing in both the upper and lower jaws of Odontochelys.Ī slightly younger fossil species, Proganochelys quenstedi, also had teeth, but the teeth were located on the roof of the mouth, not on the upper or lower jaw. This evidence also suggests that the carapace of later turtles arose from neural plates that hardened over time to become flat sections of bone (osteoderms) supported by wide dorsal ribs. Authorities contend that this species is evidence that the carapace evolved after the plastron.
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Odontochelys semitestacea, a species dating from about 220 million years ago, during the Late Triassic, is the oldest species to possess a complete plastron, broad dorsal ribs, and a series of neural plates, though it lacked a fully developed carapace. (Similar structures also appear in Pappochelys, a younger, toothed species dating from about 240 million ago during the Middle Triassic Epoch.) These broad-ribbed structures likely evolved to provide these early forms with more stability and leverage for burrowing. Collectively, these modified bones may have served as a type of intermediate shell structure from which the carapace and plastron evolved. Eunotosaurus was toothed, and its midsection contained nine elongated trunk vertebrae, nine pairs of broad T-shaped dorsal ribs, and five pairs of gastralia (ventrally located abdominal ribs). However, early turtles did possess precursors to these structures.Įunotosaurus africanus, the earliest known turtle, lived 260 million years ago. Many of the oldest and most primitive forms not only lacked a shell but also lacked a plastron and a carapace. Whereas living turtles are toothless, many ancestral forms possessed teeth. The earliest turtles known date to the Late Permian Epoch (the Permian Period lasted from 298.9 million to about 251.9 million years ago). SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.
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