Transitional Vertebrate FossilsTransition from amphibians to amniotes (first reptiles)The major functional difference between the ancient, large amphibians and the first little reptiles is the amniotic egg. Additional differences include stronger legs and girdles, different vertebrae, and stronger jaw muscles. For more info, see Carroll (1988) and Gauthier et al. (in Benton, 1988) •Proterogyrinusor another early anthracosaur (late Mississippian) -- Classic labyrinthodont-amphibian skull and teeth, but with reptilian vertebrae, pelvis, humerus, and digits. Still has fish skull hinge. Amphibian ankle. 5-toed hand and a 2-3-4-5-3 (almost reptilian) phalangeal count.•Limnoscelis, Tseajaia(late Carboniferous) -- Amphibians apparently derived from the early anthracosaurs, but with additional reptilian features: structure of braincase, reptilian jaw muscle, expanded neural arches.•Solenodonsaurus(mid-Pennsylvanian) -- An incomplete fossil, apparently between the anthracosaurs and the cotylosaurs. Loss of palatal fangs, loss of lateral line on head, etc.
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Synapsid, additional reptilian features, stronger jaw muscles, fish skull hinge