by Greg Mayer
In a paper in press in Nature, Min Zhu and colleagues describe a new species of placoderm from the Silurian period of China. Placoderms are an extinct group of (usually) heavily armored jawed fishes that lived in the Silurian and Devonian. The new species is based on a beautifully preserved 3-D specimen, and is interesting, but it is being widely misreported in the press.
To understand why this new species is interesting requires some background information. First, we need to know that while most modern vertebrates (backboned animals such as ourselves) have jaws, and are called gnathostomes (“jaw mouths”), not having jaws is the primitive condition (jawless vertebrates, represented today only by hagfish and lampreys, are called agnathans). The origin of jaws is thus a key episode in the vertebrate story.
Second, we need to know that there are four great groups pf gnathostomes, the
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