B19
The caudal part of right mandibular ramus of Capitosauroidea
the oldest terrestrial tetrapod from Japan

The oldest terrestrial terapod emerged during the Late Devonian, but the oldest terrestrial terapod from Japan described here is much younger, about 250 million years ago, found from the Hiraiso Formation, Inai Group of Karashima, Miyagi prefecture. This specimen belongs to Stereospondyli (Temnospondyli), which is basal amphibian that ranges from the Carboniferous to the Cretaceous. Triassic forms had large skull with flatten body shape that can reach length of six meters and occupied the niche similar to modern crocodilian. The specimen preserves the glenoid fossa and the area posterior to it. Morphological characters, such as the relative size of the glenoid fossa, dorsally strongly projected caudal process of the glenoid fossa and relatively large size of the area posterior to the glenoid fossa indicate this specimen belongs to Capitosauroidea. The Inai Group belongs to the South Kitakami Terrane (SKT), which exposes the longest continuous strata in Japan from the Silurian to Cretaceous. Recently, zilcons in sandstones of SKT were analyzed to reveal where these zilcons came from. From the Permian to the Early Jurassic, zilcons of SKT were not originated from continental blocks that indicates existence of a sea between SKT and continents. The finding of capitosaurid, which dwelled in flesh-water and could not cross oceans, from the Early Triassic indicates SKT was located not far from either north or south China continental block before the end of the Early Triassic. (Tai Kubo)

References

Nakajima, Y. & Schoch, R. R. (2011) The first temnospondyl amphibian from Japan. Journal of Vertebrate Paleontology 31: 1154–1157.