Specifically, this is the first stem gnathostome with dermal marginal jaw bones. "Guiyu" had spine-bearing pectoral girdle, a feature which can be found in primitive gnathostome vertebrates. The very first gnathostome (jawed fish) appeared in the Late Ordovician epoch. For this reason, "Acanthodes" has become an indispensable component in early gnathostome phylogenies. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates.