Ancient Armored Fish Had First Bad Bite

Sculpture of placoderm Dunkleosteus; image courtesy of Esben Horn, 10tons; supervised by Martin Rücklin, John Long and Philippe Janvier

The ancient ocean was a frightening place. But the emergence of the armored placoderm fish would have made it even more terrifying. These fish were no great whites—some weren’t much bigger than a goldfish. But they were some of the first vertebrates to have jaws, and new research shows that they were probably the first to brandish teeth as well.

The emergence of pearly whites has been a bit of an evolutionary mystery, with some pointing to these early armored fish, which lived some 430 million to 360 million years ago, and others suggesting that teeth didn’t emerge until later groups of vertebrates.

New analysis of fossil Compagopiscis croucheri placoderm specimens reveals that these ancient jawed fish did indeed already have teeth to gnash. The findings were published online October 17 in Nature (Scientific American is part of Nature Publishing Group). With individual teeth present in these basal vertebrates, it suggests a very early origin of these assets for the rest of us—rather than them developing multiple times in different lineages.

Model of the front of a toothy placoderm; CT scan courtesy of Phil Anderson, University of Massachusetts Amherst; Michael Ryan and Eric Snively, Cleveland Museum of Natural History; model and images Martin Rücklin, University of Bristol.

“This is solid evidence for the presence of teeth in these first jawed vertebrates,” study co-author Philip Donoghue of the University of Bristol’s Department of Earth Sciences, said in a prepared statement.

The placoderms examined for this study likely had teeth that developed shallowly in the jaw, like many of today’s boney fish. These toothy fish, however, hadn’t perfected all of the options of modern dentition. For example, they don’t appear to have been able to replace choppers when they wore out.

The researchers used x-ray tomographic microscopy and computational algorithms to generate detailed 3-D models of the ancient fossils. “This technique allows us to obtain a perfect digital model and very detailed insight views of the old fossil without destroying it,” Marco Stampanoni, of the Paul Scherrer Institute in Switzerland and study co-author, said in a prepared statement.

Indeed, much of the reason the origins of teeth has remained so obscured is that few studies have been able to dig into these important fossils. “These wonderfully preserved fossils from Australia yield many secrets of our evolutionary ancestry but research has been held back waiting for the kind of nondestructive technology that we used in this study,” study co-author Zerina Johanson, of London’s Natural History Museum, said in a prepared statement. “Without the collaborations between paleontologists and physicists, our evolutionary history would remain hidden in the rocks.”

Drake Farrah Fawcett