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Diadectidae
Diadectidae is an extinct family of early tetrapods that lived in what is now North America and Europe during the Late Carboniferous and Early Permian, and in Asia during the Late Permian. They were the first herbivorous tetrapods, and also the first fully terrestrial animals to attain large sizes. Footprints indicate that diadectids walked with an erect posture. They were the first to exploit plant material in terrestrial food chains, making their appearance an important stage in both vertebrate evolution and the development of terrestrial ecosystems.
The best known and largest representative of the family is ''Diadectes'', a heavily built animal that attained a maximum length of several metres. Several other genera and various fragmentary fossil remains are also known. Although well known genera like ''Diadectes'' first appear in the Late Pennsylvanian, fragmentary remains of possible diadectids are known from much earlier deposits, including a piece of lower jaw found in Mississippian strata from Tennessee.
==Description==
Diadectids have large bodies with relatively short limbs. The rib cage is barrel-shaped to accommodate a large digestive tract necessary for the digestion of cellulose in plants. The skulls of diadectids are wide and deep with blunt snouts. The internal nares (holes for the nostrils) are also short. Paleontologist E.C. Case compared diadectids to turtles in 1907, noting their large pectoral girdles, short, strong limbs, and robust skulls. Case described them as "lowly, sluggish, inoffensive herbivorous reptiles, clad in an armor of plate to protect them from the fiercely carnivorous pelycosaurs."
Diadectids have a hederodont dentition, meaning that their teeth vary in shape along the length of the jaws. The teeth are wide and bear many cusps or projections, an indication that diadectids ate tough plants. Some teeth are leaf-shaped and laterally compressed, another indication that diadectids were able to shred plant material. The procumbent front teeth of the lower jaw project forward. Diadectids likely had strong jaw muscles for processing plant material; the placement of the jaw joints above or below the level of the occlusal plane (the plane at which the teeth come together) would have given diadectid jaws mechanical advantage. The joints themselves give the jaws a complex range of movement suitable for consuming plants. Large holes and cavities in the skull called adductor chambers and temporal openings would have provided room for large jaw-closing muscles.〔 A ridge on the dentary bone of the lower jaw may have provided a surface for chewing or even supported a beak.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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