Washington DC [US], May 25 : New research from the University of Chicago shows that dentine, the inner layer of teeth that transmits sensory information to nerves inside the pulp, first evolved as sensory tissue in the armoured exoskeletons of ancient fish.
Paleontologists have long believed that teeth evolved from the bumpy structures on this armour, but their purpose wasn't clear.
The new study, published this week in Nature, confirms that these structures in an early vertebrate fish from the Ordovician period, about 465 million years ago, contained dentine and likely helped the creature sense conditions in the water around it.
The research also showed that structures considered to be teeth in fossils from the Cambrian period (485-540 million years ago) were similar to features in the armor of fossil invertebrates, as well as the sensory organs in the shells of modern arthropods like crabs and shrimp.
These similarities imply that sensory organs in the armor of diverse animals evolved separately in both vertebrates and invertebrates to help them sense the larger world around them.
"When you think about an early animal like this, swimming around with armour on it, it needs to sense the world. This was a pretty intense predatory environment, and being able to sense the properties of the water around them would have been very important," said Neil Shubin, PhD, Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy at UChicago and senior author of the new study.
"So, here we see that invertebrates with armour like horseshoe crabs need to sense the world too, and it just so happens they hit on the same solution," added Neil Shubin.
While they didn't pin down the earliest vertebrate fish, Shubin said this discovery was more than worth the effort.
"For some of these fossils that were putative early vertebrates, we showed that they're not. But that was a bit of misdirection," Shubin said.
"We didn't find the earliest one, but in some ways, we found something way cooler," Shubin added.
The study, "The Origin of Vertebrate Teeth and Evolution of Sensory Exoskeletons," was supported by the National Science Foundation, the US Department of Energy, and the Brinson Family Foundation.
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