The early evolution of the jawed vertebrates (gnathostomes) is a hot topic in palaeontology. Brazeau and colleagues use computed tomography scanning to take a new look at a 415-million-year-old braincase and skull roof from the Early Devonian of Siberia, originally described in 1992 by Hans-Peter Schultze as coming from an early osteichthyan (bony fish). They find that the underlying braincase is a mix of features seen separately in osteichthyans, chondrichthyans or in neither. Phylogenetic analysis places the fish at base of the gnathostomes and suggests that the enigmatic acanthodians - an extinct group of fossil fishes - were relatives of cartilaginous fishes.
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