The morphology of Yujiangolepis liujingensis (Placodermi, Arthrodira) from the Pragian of Guangxi (south China) and its phylogenetic significance

The morphology of the arthrodire placoderm Yujiangolepis liujingensis Wang, Pan & Wang, 1998, from the Lower Devonian of Guangxi is redescribed, and compared to that of the basal arthrodires Antarctaspis White, 1968 from Antarctica, Toombalepis Young & Goujet, 2003 and Wuttagoonaspis Ritchie, 1973 from Australia, and Yiminaspis Dupret, 2008 from south China. A very small plate of the skull roof at the junction of the nuchal, marginal, postorbital, and paranuchal plates is considered as the vestigial homologue of the anterior paranuchal plate in the Petalichthyida and Acanthothoraci. Yujiangolepis is attributed to the family ‘Antarctaspididae’ White, 1968, together with the genera Antarctaspis and Toombalepis. A computerized phylogenetic analysis resolved Yujiangolepis as the most basal arthrodire, and the family ‘Antarctaspididae’ appears paraphyletic, Yujiangolepis being possibly the most basal. The family Wuttagoonaspididae contains the genera Wuttagoonaspis and Yiminaspis, and remains monophyletic. A Chinese origin of the ‘Antarctaspididae’ is proposed, together with a southward dispersal into Gondwana during the Early Emsian.