Postcranial disparity of galeaspids and the evolution of swimming speeds in stem-gnathostomes

Galeaspids are extinct jawless relatives of living jawed vertebrates whose contribution to understanding the evolutionary assembly of the gnathostome bodyplan has been limited by absence of postcranial remains. Here, we describe Foxaspis novemura gen. et sp. nov., based on complete articulated remains from a newly discovered Konservat-Lagerstatte in the Early Devonian (Pragian, similar to 410 Ma) of Guangxi, South China. F. novemura had a broad, circular dorso-ventrally compressed headshield, slender trunk and strongly asymmetrical hypochordal tail fin comprised of nine ray-like scale-covered digitations. This tail morphology contrasts with the symmetrical hypochordal tail fin of Tujiaaspis vividus, evidencing disparity in galeaspid postcranial anatomy. Analysis of swimming speed reveals galeaspids as moderately fast swimmers, capable of achieving greater cruising swimming speeds than their more derived jawless and jawed relatives. Our analyses reject the hypothesis of a driven trend towards increasingly active food acquisition which has been invoked to characterize early vertebrate evolution. Zhikun Gai and colleagues describe the extinct jawless fish Foxaspis novemura, only the second galeaspid known from complete remains. Their analysis of swimming speeds based on tail morphology reveals that relatives of the ancestral jawed vertebrate were ecologically diverse, rejecting the hypothesis of a trend to increasingly active food acquisition.

Automated summary

Based on well-preserved fossils from the early Devonian of Guangxi, South China, the complete and articulated remains of Foxaspis novemura provide insights into the swimming speed and tail morphology of galeaspids, indicating disparate postcranial anatomies. These findings reject the hypothesis of a driven trend towards increasingly active food acquisition in early vertebrate evolution.