A researcher from the University of Uppsala has described the skull and jaws of a fish that lived more than 400 million years ago, giving us valuable insight into the early evolution of jawed vertebrates.
Publishing the results of his research in a recent issue of the journal Nature, Martin Brazeau describes the first-known braincase of Ptomacanthus anglicus, an early jawed fish belonging to a group known as the Acanthodii that lived during the early Devonian period (418"412 million years ago).
The acanthodians are a group of fishes characterized by a shark-like appearance and the presence of numerous spines, whose relationships to modern jawed vertebrates are still poorly understood. This is partly due to the fact that knowledge of their internal head skeleton is so scanty.
Prior to this study, the only acanthodian whose braincase has been studied is the genus Acanthodes, which is a group that appears late in acanthodian history, Brazeau explained.
The braincase of Acanthodes resembles those of early bony vertebrates, a lineage that includes humans and other land vertebrates (for this reason, acanthodians are thought to be more closely related to bony fishes than to sharks).
Ptomacanthus is about 100 million years older than Acanthodes and Brazeau's study has shown that its braincase shares little in common with those of bony vertebrates and is more similar to those of early shark-like fishes.
As a consequence, the results indicate that Ptomacanthus was either a very early relative of sharks, or close to the common ancestry of all modern jawed vertebrates, says Brazeau.
For more information, see the paper: Brazeau, M (2009) The braincase and jaws of a Devonian ~acanthodian and modern gnathostome origins. Nature 457, pp. 305"308.