The University of Chicago has released new research shedding light on the evolutionary origins of sensitive teeth. According to the study, published in Nature, dentine—an inner layer of teeth responsible for transmitting sensory information—first evolved as sensory tissue in the armored exoskeletons of ancient fish.
Paleontologists have long theorized that teeth originated from bumpy structures on these exoskeletons. The purpose of these structures was not well understood until now. The research reveals that an early vertebrate fish from the Ordovician period, around 465 million years ago, contained dentine within its armor, which likely helped it sense environmental conditions.
The study also compared fossils from the Cambrian period (approximately 485-540 million years ago) with modern arthropods like crabs and shrimp. It found similarities suggesting that sensory organs evolved independently in both vertebrates and invertebrates.
Neil Shubin, senior author and a professor at UChicago, stated: "When you think about an early animal like this, swimming around with armor on it, it needs to sense the world."
Yara Haridy, who led the study as a postdoctoral researcher in Shubin’s lab, initially sought to identify the earliest vertebrate fossil record by examining Cambrian specimens through CT scans at Argonne National Laboratory's Advanced Photon Source. She noted: “It was a night at the particle accelerator—that was fun.”
During their analysis, they discovered that what appeared to be vertebrate features in Anatolepis were actually more similar to sensory organs found in modern arthropods. This indicated that Anatolepis is an ancient invertebrate arthropod rather than a vertebrate.
Haridy remarked: “This shows us that ‘teeth’ can also be sensory even when they're not in the mouth.”
The findings contribute to ongoing debates about how tooth-like structures evolved. The "outside-in" hypothesis posits that sensitive structures first developed on exoskeletons before evolving into teeth.
While identifying the earliest vertebrate fish remains elusive, Shubin expressed satisfaction with their findings: “We didn’t find the earliest one, but in some ways we found something way cooler.”
The research received support from various institutions including the National Science Foundation and involved contributions from multiple universities such as Harvard University and Missouri State University.