Our Teeth May Descend From Sensitive Bumps on Prehistoric Fish Armor, New Research Finds
Hundreds of millions of years ago, fish had sensory features on their exoskeletons that contained dentine, the material that makes our teeth sensitive today
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Paleontologists have long suspected that our teeth evolved from bumpy structures called odontodes on the exoskeletons of prehistoric fish—but they didn’t understand exactly what these bumps were used for.
New research, however, bolsters evidence that the odontodes of 465-million-year-old fish had dentine: the same material that makes up the layer between your teeth’s hard outer enamel and the soft dental pulp inside. Dentine is responsible for transporting sensory information, so their work suggests these precursors to teeth once helped long-extinct fish sense their surroundings.
“Covered in these sensitive tissues, maybe when it bumped against something it could sense that pressure, or maybe it could sense when the water got too cold and it needed to swim elsewhere,” Yara Haridy, a vertebrate paleontologist at the University of Chicago, tells CNN’s Ashley Strickland.
Haridy and her colleagues’ study, published Wednesday in the journal Nature, originally had a completely different aim: identifying the earliest known vertebrate. As such, Haridy began CT-scanning fossils from the Cambrian period (485 million to 539 million years ago) in the hope of identifying vertebrate features, such as the presence of dentine within odontodes.
One promising example came from a fossil animal called Anatolepis, which had pores filled with material that seemed like dentine. The team thought this might represent the first tooth-like structure in a Cambrian vertebrate, dating to millions of years earlier than any known vertebrate fossil. “We were high fiving each other, like ‘oh my god, we finally did it,’” Haridy says in a statement.
However, when they compared Anatolepis to a confirmed fossil arthropod—an invertebrate like the insects, spiders and crustaceans of today—they concluded that they’d been mistaken. The structures they had thought were dentine-filled odontodes actually appeared more similar to sensilla: external sensory organs found in invertebrates. In other words, Anatolepis was not a vertebrate at all, but a long-extinct invertebrate arthropod.
On the other hand, the researchers discovered that odontodes on a vertebrate fish called Eriptychius—dating to the Ordovician period between 444 million to 485 million years ago—did have dentine. This makes the Eriptychius—and not Anatolepis—the oldest known “toothed” animal, as reported by New Scientist’s Michael Marshall.
Today, some fish still have odontodes, while animals like catfish, sharks and skates have small, tooth-like structures on their skin called denticles, which give them a texture like sandpaper. The team “performed experiments on modern fish that confirmed the presence of nerves” in these denticles, Haridy tells Bénédicte Rey of the Agence France-Presse (AFP). This indicates that “tooth tissues of odontodes outside the mouth can be sensitive—and perhaps the very first odontodes were as well.”
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Given the similarities between odontodes in vertebrates and sensilla in invertebrates, scientists say the organs likely developed independently to perform the same sensory function in different animals—a process called convergent evolution.
“Dentine is likely a vertebrate novelty, yet the sensory capabilities of a hardened external surface were present much earlier in invertebrates,” says Gareth Fraser, a biologist at the University of Florida who wasn’t involved in the study, to New Scientist.
While arthropods today still have sensilla, odontodes seem to have largely evolved into teeth. At some point “it became advantageous to have pointy structures” near the mouth, Haridy explains to the AFP. “Little by little, some fish with jaws had pointy odontodes at the edge of the mouth, and then eventually, some were directly in the mouth.”
Although the team didn’t identify the earliest known vertebrate, “in some ways, we found something way cooler,” Neil Shubin, a biologist at the University of Chicago and co-author of the study, says in the statement.
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