410-Million-Year-Old Fish Fossil Hints At Origins Of Teeth

[edd]

photo credit: Color scheme, from gold to purple, represents the sequence of tooth addition. (a) Dental plate. ( Transverse and © longitudinal virtual sections showing addition of teeth and basal layer. (d) Detail of ©. Rücklin & Donoghue/Biol. Lett. 2015

The fossil of a small, toothy fish who lived in the Arctic 410 million years ago suggests that teeth originated much further back than we thought. But they weren’t individual pearly whites like we see today: They were pointy bumps on a jagged, bony plate that expanded as the fish gained additional teeth on the edges of this so-called toothplate. The findings were published in Biology Letters this week.

Most studies on the origins of teeth usually focus on cartilaginous fish with jaws, like sharks. They were thought to reflect some primitive condition. But extinct armored fish called placoderms show a greater diversity and complexity of dentitions. Romundina stellina, for instance, who swam the arctic seas off Prince of Wales Island in Canada during the Early Devonian, is among the earliest-known jawed vertebrates. So Martin Rücklin, from the Naturalis Biodiversity Center, and University of Bristol’s Philip Donoghue used X-rays from a synchrotron to study the internal structures and growth of Romundina’s upper toothplate.

The toothplates, they discovered, were made up of teeth with multiple cusps, and each tooth had a hard enameloid cap and a core of dentine (much like modern teeth). These teeth grew on the toothplate sequentially, around the pioneer tooth. As Romundina grew, new toothy structures appeared in nearby tissue, Science explains, and then merged onto the edge of the expanding toothplate. In the images above, the color scheme – from gold to purple – represents the sequence of tooth addition. The result is a tool for crushing and shredding prey.

What’s especially interesting is that the teeth and jaws developed independently. This means that the intimate integration that we see nowadays was something that evolved later. Furthermore, "our data show that teeth and scales of Romundina are made of the same tissues, and these are also found in our teeth," Rücklin tells ABC Science. This fits with the idea that scales evolved first and teeth were derived from them.

Edited August 29, 2015 by edd