A new Wuttagoonaspid (Placodermi, Arthrodira) from the Lower Devonian of Yunnan (South China): Origin, dispersal, and paleobiogeographic significance

摘要

Wuttagoonaspida is a very peculiar group of Arthrodira, hitherto known only in the Early-Middle Devonian deposits of Australia. The new genus and species Yiminaspis shenme described here is known from an incomplete skull roof from the Pragian of Zhaotong (Yunnan, South China). Despite sharing some features with the Petalichthyida (e.g. two pairs of posterior pitlines), it presents many features of the genus Wuttagoonaspis (e.g. long preorbital plates not separated by the pineal plate, pineal plate placed further anteriorly from the orbits). Some thoracic armor material, also from Zhaotong, is referred to this taxon on the basis of the ornamentation. The occurrence of such a basal arthrodire from the Lower Devonian of China, added to the ante-Emsian geographic isolation of the South China block (evidenced by its vertebrate endemism rate), suggests a Chinese origin for the Wuttagoonaspididae, and a migration episode into the northeastern margin of Gondwana dated at the end of the Pragian (E'Em bioevent).