Two new specimens of Glyphoderma kangi (Placodontia, Sauropterygia, Reptilia) from the Middle Triassic of South China

Résumé fourni par la source

Glyphoderma kangi from the Ladinian of the Middle Triassic is the oldest record of cyamodontoid placodonts known in South China, but several aspects of the anatomy of its skull and dorsal shell remained unknown, due to the preservation of the holotype specimen in dorsal view. Two new mostly complete and well-preserved skeletons are described here to reveal new anatomical information on the skull, pectoral girdle, pelvic girdle, transverse processes, ribs, and gastralia. In addition to the unique osteoderms with radiating grooves and ridges that form the carapace, six other types of osteoderms are found covering the skull and the mandible, composing the lateral wall, and forming an incomplete inner layer of the carapace. The inferred inner layer, formed by osteoderms located beneath the surface osteoderms near the peripheral margin of the carapace, probably helped to reinforce the carapace margins together with the dorsal ribs. Features including relative limb length indicate that Glyphoderma kangi has reached the marine adaptation step of at least M4, indicating minimized terrestrial travel and loss of terrestrial feeding. Considering its morphology and ecology, Glyphoderma kangi probably pursued a bottom-dwelling lifestyle where danger mainly came from above.

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