The oldest complete jawed vertebrates from the early Silurian of China
DOI: 10.1038/s41586-022-05136-8
Article: https://www.nature.com/articles/s41586-022-05136-8
Abstract source: https://www.ebi.ac.uk/europepmc/webservices/rest/search?query=DOI%3A10.1038%2Fs41586-022-05136-8&format=json&resultType=core&pageSize=1

AUTHOR ABSTRACT

Molecular studies suggest that the origin of jawed vertebrates was no later than the Late Ordovician period (around 450 million years ago (Ma)) 1,2 . Together with disarticulated micro-remains of putative chondrichthyans from the Ordovician and early Silurian period 3-8 , these analyses suggest an evolutionary proliferation of jawed vertebrates before, and immediately after, the end-Ordovician mass extinction. However, until now, the earliest complete fossils of jawed fishes for which a detailed reconstruction of their morphology was possible came from late Silurian assemblages (about 425 Ma) 9-13 . The dearth of articulated, whole-body fossils from before the late Silurian has long rendered the earliest history of jawed vertebrates obscure. Here we report a newly discovered Konservat-Lagerstätte, which is marked by the presence of diverse, well-preserved jawed fishes with complete bodies, from the early Silurian (Telychian age, around 436 Ma) of Chongqing, South China. The dominant species, a 'placoderm' or jawed stem gnathostome, which we name Xiushanosteus mirabilis gen. et sp. nov., combines characters from major placoderm subgroups 14-17 and foreshadows the transformation of the skull roof pattern from the placoderm to the osteichthyan condition 10 . The chondrichthyan Shenacanthus vermiformis gen. et sp. nov. exhibits extensive thoracic armour plates that were previously unknown in this lineage, and include a large median dorsal plate as in placoderms 14-16 , combined with a conventional chondrichthyan bauplan 18,19 . Together, these species reveal a previously unseen diversification of jawed vertebrates in the early Silurian, and provide detailed insights into the whole-body morphology of the jawed vertebrates of this period.