In a groundbreaking study reshaping our understanding of vertebrate evolution, researchers from the University of Chicago have uncovered remarkable insights into the origins of teeth, revealing that the sensitive tissues within teeth evolved initially not in mouths, but as sensory structures embedded in the armored exoskeletons of ancient fish. This discovery not only challenges long-held assumptions about the evolutionary trajectory of dental tissues but also highlights the complex interplay between form and function in early vertebrates dating back nearly half a billion years.
For generations, paleontologists have debated the evolutionary roots of teeth. Conventional wisdom held that teeth gradually emerged from external bumps on the protective armor of ancient fish, eventually migrating into mouths to become specialized tools for feeding. The new research, however, provides compelling evidence that these external bumpy structures, known as odontodes, originally functioned as sensory organs. These odontodes contained dentine—the mineralized tissue inside modern teeth responsible for transmitting sensory information—which would have allowed early fish to detect environmental stimuli through their armored bodies.
Using high-resolution computed tomography (CT) scanning techniques, the team led by postdoctoral researcher Dr. Yara Haridy conducted an extensive examination of fossil specimens originating from the Cambrian and Ordovician periods, a span covering approximately 485 to 465 million years ago. The scans, performed at Argonne National Laboratory’s Advanced Photon Source, allowed the researchers to visualize microscopic internal structures in unprecedented detail. Among the specimens studied was Anatolepis, a Cambrian fossil previously believed to represent one of the earliest vertebrate fishes. Initial analysis suggested this fossil contained dentine, indicating vertebrate affinity and potentially extending the vertebrate fossil record further back in time than previously verified.
However, subsequent analyses that compared Anatolepis to a broad array of fossilized and modern arthropod samples revealed a surprising truth: the structures that resembled dentine-lined tubules in Anatolepis more closely matched sensory organs called sensilla found on the shells of crabs and other arthropods. This unexpected finding effectively reclassified Anatolepis as an ancient invertebrate, thereby clarifying a persistent confusion in the fossil record about early vertebrate presence. The research thus delineates a clearer boundary between vertebrate and invertebrate sensory adaptations, emphasizing convergent evolutionary solutions to environmental sensing.
The structure of dentine-bearing odontodes in Ordovician fish such as Eriptychius further bolsters this evolutionary narrative. These tubules contained dentine and a vascular network capable of transmitting sensory signals, illustrating that the armored exoskeleton of these early vertebrates was a vital sensory apparatus. Such adaptations would have offered these armored animals a critical survival advantage in the fiercely competitive and predator-rich waters of the Paleozoic era, enabling them to detect pressure, temperature changes, and potentially even pain via their armor’s sensitive tubules.
This study also situates its findings within the broader context of sensory organ evolution across diverse taxa. The resemblance between the dentine structures in vertebrate odontodes and the sensilla of modern arthropods strengthens the case for independent evolutionary pathways toward similar sensory solutions in both groups. It appears that nature repeatedly converged on mineralized sensory structures atop soft tissues to reconcile the conflicting demands of protection and environmental awareness, a testament to the flexible power of evolutionary innovation.
Intriguingly, the research team’s experiments extended beyond fossil analysis to include studies on living animals such as miniature suckermouth catfish. These modern teleosts possess skin denticles—tiny, tooth-like scales composed of dentine and enamel—that not only protect their bodies but also connect to nerve fibers, allowing the catfish to sense mechanical stimuli through their skin. This functional parallelism between ancient odontodes and modern denticles underscores the deep evolutionary roots of sensory integration within dermal structures, blurring the lines between defensive armor and sensory organ.
The debate about the evolutionary origin of teeth itself encompasses two main hypotheses: the “inside-out” and the “outside-in” models. The inside-out hypothesis posits that teeth first arose within the mouth’s internal structures and later adapted for protective roles on body surfaces. Conversely, the outside-in hypothesis, now gaining traction thanks to this study, argues that sensitive armored structures external to the mouth predated teeth, with later genetic and developmental co-options internalizing these features to form teeth. The University of Chicago researchers’ findings strongly support this outside-in thesis, emphasizing the primacy of sensory armor in dental evolution.
“The presence of sensory dentine beyond the oral cavity fundamentally challenges our understanding of what teeth originally were,” explained Neil Shubin, senior author and a distinguished biology professor at UChicago. “It shows that what we think of as teeth started not as tools for feeding, but as sensory extensions of the body’s armor—allowing early vertebrates to engage with their environment in remarkably sophisticated ways.” This insight opens new vistas for studying the evolutionary interplay between defensive and sensory traits across deep time.
Furthermore, these revelations highlight the sometimes-misleading nature of the fossil record, where convergent morphologies can obscure true evolutionary relationships. Earlier claims that certain Cambrian fossils represented the earliest vertebrates are now reconsidered in light of better morphological and chemical evidence, thus refining the timeline and narrative of vertebrate evolution. Such improvements exemplify the potency of modern imaging technologies combined with comparative biology to unravel ancient biological mysteries.
The study’s implications extend beyond paleontology into evolutionary developmental biology and sensory neuroscience, as it offers a rare glimpse of how mineralized tissues interact with nerve systems to confer environmental awareness. The vascularized tubules within odontodes indicate an early coupling of mineralized structural protection with a neural sensory network—a dual function that presumably afforded these animals the ability to detect and respond rapidly to mechanical and possibly chemical stimuli, a necessity for survival in dynamic aquatic ecosystems.
In essence, this research redefines teeth as evolutionary innovations birthed from a dual need for protection and sensory perception rather than strictly for feeding. The mineralized, dentine-filled tubules embedded in the exoskeleton’s surface did not simply serve as rudimentary armor but also as sensory organs interacting closely with the nervous system. Such a fusion of sensory and protective roles may have set the stage for the complex teeth and advanced sensory systems observed in later vertebrate lineages.
By leveraging the power of advanced imaging at cutting-edge facilities and integrating a broad spectrum of fossil and modern biological data, the research team has opened new avenues for exploring how sensory systems evolved hand in hand with external body armor. This interdisciplinary approach showcases the transformative impact of convergent technological and analytical innovations on our understanding of life’s deep history.
As the evolutionary story unfolds, the oldest vertebrate fossils may yet be reshuffled, but the insight gained from the interplay of ancient armored sensory systems with nervous tissue marks a compelling chapter in the saga of vertebrate origins. This alliance between sensory relevance and structural innovation reveals how some of the earliest vertebrates perceived their watery worlds—not just as armored fish but as creatures keenly attuned to the subtle currents and pressures around them.
Subject of Research: Animal tissue samples
Article Title: The origin of vertebrate teeth and evolution of sensory exoskeletons
News Publication Date: 21-May-2025
Web References: http://dx.doi.org/10.1038/s41586-025-08944-w
Image Credits: Yara Haridy
Keywords: vertebrate evolution, dentine, odontodes, sensory exoskeleton, paleontology, CT scanning, Cambrian fossils, Ordovician period, evolutionary biology, sensory organs, denticles, outside-in hypothesis
