Dunkleosteus and the armoured placoderms

Placoderms were the most diverse jawed fish of the Silurian and Devonian, with heads and shoulders armoured in bony plates. Entelognathus primordialis, a 423-million-year-old fish from Yunnan, China, described in 2013 by Zhu Min and colleagues, shows a placoderm body with the cheek and jaw bones of a bony fish, which hints that placoderms sit near the root of all jawed vertebrates. The group peaked in the Late Devonian, about 370 million years ago, and vanished near the end of the Devonian.

Dunkleosteus terrelli, from the Cleveland Shale of Ohio and relatives in Morocco and Poland, was the top predator of its day. It had no true teeth. Its jaws carried sharp-edged bony plates that sharpened themselves as they wore. Calculations by Philip Anderson and Mark Westneat in 2007 suggest a bite of several thousand newtons, among the strongest of any fish, and a jaw that opened in about a fiftieth of a second to suck prey in. Recent estimates of length are about 3.4 metres, well below older guesses of 6 metres or more. The fish was named in 1956 for David Dunkle, a paleontologist at the Cleveland Museum of Natural History.