These findings not only provide an interesting new glimpse into the early evolutionary history of teeth. It connects these changes to the ancient evolutionary innovations of fish ancestors, occurring over 500 million years ago. Yara Haridy, chief researcher, explores how these structures, called odontodes—literally tooth-like structures—first appeared on the outside armor of ancient fish. This change might have played a huge role in the fate of these wonderful old creatures. Published in the journal Nature, these new findings give insight into how these structures formed over time.
The research team, which included senior author and University of Chicago paleontologist Neil Shubin, was exploring why odontodes had emerged. Haridy’s investigation started by looking at where teeth came from. His work culminated in the groundbreaking finding that early vertebrates are more closely related to other vertebrates’ alternative forms like cephalopods than previously thought. The research shows that even such early animals had to avoid a “really gnarly predatory ecosystem,” requiring them to evolve unique features to stay alive.
Origins of Odontodes
Odontodes, which are bony structures in the skin, are thought to be the evolutionary precursors of vertebrate teeth. The published research proposes a few theories about their original emergence. Other researchers suggest that odontodes shielded early vertebrates from attack by larger animals. Other paleobiologists contend these structures aided locomotion in water or functioned as storage for minerals.
Haridy’s research was centered on Anatolepis, a Cambrian fossil. Researchers used to think that it was the secret to understanding the origins of teeth. As she started to compare Anatolepis to the other specimens, she started to make an exciting discovery. The tubules matched sensory structures known as sensilla from arthropods. This finding triggered a major reevaluation of Anatolepis’s classification. Consequently, it was finally reclassified as an invertebrate due to its peculiar features.
“Arthropods and early vertebrates independently evolved similar sensory solutions to the same biological and ecological problem” – Yara Haridy
During the expedition, the research team found remarkable similarities between structures seen in Anatolepis and in vertebrate jawless fish over 465 million years ago. This evolutionary gaze provides the evolutionary context for why odontodes are evolutionarily important and how they ultimately led to the development of true teeth in vertebrates.
Sensory Adaptations in Early Fish
Fiorito and coauthors’ study highlights the possibility that primitive fish needed advanced sensory functions to move around their surroundings with proficiency. Neil Shubin stated, “Being able to sense the properties of the water around them would have been very important.” Such an aptitude would be key for life in a fiercely predatory environment.
As fish branched out to occupy new ecological roles, jaws began to evolve within fish, which created a clear advantage for having pointed structures around their mouths. Haridy noted, “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.” This step-by-step evolution shows how simple odontodes evolved into more complex structures that eventually became true teeth.
“A toothache is actually an ancient sensory feature that may have helped our fishy ancestors survive!” – Yara Haridy
Their presence beyond the mouth suggests that these structures were not only somatic but possibly sensitive odontodes as well. Haridy mentioned that “tooth tissues of odontodes outside the [mouth] can be sensitive—and perhaps the very first odontodes were as well.” This sensitivity would have been crucial to how primitive fish first navigated their environments.
Modern-Day Implications
Even still, modern-day descendants of these prehistoric fish retain characteristics that harken back to their evolutionary history. Sharks, stingrays, and catfish all have skin that’s almost entirely covered in tiny, microscopic teeth. This special adaptation provides their skin with a coarse, abrasive texture, akin to sandpaper. This adaptation is multifunctional to protect and increase their strike rate when capturing prey.
F untHaridy’s analysis required examining hundreds of vertebrate specimens with a CT scanner. Other specimens were small enough to perch on the end of a toothpick. To us this is just more evidence for the staggering diversity and complexity of the anatomy of early fishes.
Odontodes provide a window into the evolutionary origins of teeth. It broadens our sense of evolutionary biology and sensory adaptations within ancient aquatic environments.