Palatal dentition refers toteeth that naturally grow on the bones of the roof of the mouth in some fish andtetrapods (as opposed to the "marginal dentition" that grows at the edge of the mouth), either in rows or as a stippled covering referred to as a "shagreen". While ancestrally present in tetrapods, in many living tetrapod groups, including mammals, birds, turtles, and crocodilians, these teeth have been lost, though they are still retained in livinglepidosaur reptiles andlissamphibians.
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In tetrapods, palatine teeth can occur on thevomer,palatine,pterygoid (including the pterygoid flange),ectopterygoid, andparasphenoid. These teeth can either be placed in rows, similar to the marginal dentition on the edge of the mouth, or as a stippled covering referred to as a "shagreen". These teeth vary considerably in size and in some cases can exceed the size of the marginal teeth.[1]
Palatal teeth are both present inActinopterygii (ray-finned fish)[2] andSarcopterygii, and were inherited as anancestral trait by the last commontetrapod ancestor. Palatal dentition is widespread amongst early tetrapods, though in many lineages ofAmniota the palatal dentition became reduced and in some cases entirely lost, the latter includingcynodonts (the ancestor of mammals), the ancestors of living turtles (though it is retained in very early stem turtles likeProganochelys), as well as the vast majority ofarchosaurs (which includescrocodilians,dinosaurs and their bird descendants), though a handful of archosaurs are known to retain a pterygoid tooth row, including the primitive dinosaursEodromaeus andEoraptor, and the primitive pterosaurEudimorphodon. Loss was not entirely uniform, and some lineages appear to have regained regions of palatal teeth that had been previously ancestrally lost.Lepidosaurian reptiles, includingsquamates (lizards and snakes) and thetuatara as well as livinglissamphibians retain palatal teeth. Some lizard groups have lost palatal teeth, includinggeckoes,agamids andchameleons.[1] Numerous lineages offrogs have also lost palatal teeth (often alongside the marginal teeth), while they are retained in allsalamanders andcaecilians.[3]
Palatal dentition is widely thought to help manipulate food in the mouth in combination with the tongue, including by increasing grip, in some cases likely helping to restrain prey. In some lineages their function was modified. InSphenodontidae (including the tuatara), the tooth row on the palatine bone is enlarged and orientated parallel to the upper marginal tooth row, with the lower marginal tooth row slotting between them, allowing for a shearing bite. InPlacodontia, they became plate-like and served tocrush prey.[1] In livinglungfish, marginal teeth are entirely lost in adults, and the palatal teeth modified into crushing tooth plates.[4] In manysnakes, the palatal tooth rows are used in combination with the marginal teeth (or alone in the case ofelapids andviperids) to envelop the prey in the mouth and then moved viacranial kinesis to push prey further into the throat (the so-called "pterygoid walk").[5]