Uncovering the Origins of the Classic ‘Tooth Hurty’ Joke: How Ancient Armored Fish Inspire Humorous Wordplay

Whenever Yara Haridy, a paleontologist at the University of Chicago, talks about her fossils, people often feel let down. Unlike the grand bones of dinosaurs, her fossils look more like "fish flakes," tiny remnants that can get overlooked easily. These fragments are so small they can’t be found on-site. Instead, scientists extract rock layers and dissolve them in acid to reveal these delicate bits. They found these flakes hidden in Cambrian rocks, a key period in Earth’s history.

The first vertebrates were slightly squishy and worm-like, lacking any hard features. Then, after a big gap of around 20 million years, the record shows armored creatures that swim like tiny tanks. Haridy believes that these fish flakes may offer clues about a type of vertebrate that fits between these ancient squishy beings and more evolved fish.

In her research with Neil Shubin, known for the discovery of Tiktaalik, Haridy is focused on transitions—specifically from squishy bodies to skeletons. While many ancient creatures like jellyfish thrived without skeletons, she questions why that is. Why develop a skeleton at all?

Initially, she set out to find the earliest fish but instead discovered that Anatolepis, long thought to be the oldest vertebrate, was actually an invertebrate. Her recent findings, published in Nature, clarify the role of teeth, tracing their origins back to sensory structures in ancient armored fish.

Gareth J. Fraser, an evolutionary biologist, commented on her work, noting its excitement in understanding the initial functions of teeth, whether internal or external. Haridy’s journey started by examining early Cambrian fossils and seeking insights from experts like Karma Nanglu. As they sifted through various specimens, they narrowed it down to a few vital fossils that displayed hardened parts.

Anatolepis, which existed around 500 million years ago, had tiny bumps called odontodes, made of dentin, the same material in our teeth. Under closer inspection, these bumps appeared remarkably tooth-like.

To study these tiny fossils in detail, Haridy utilized advanced imaging at Argonne National Laboratory. This facility offers powerful X-ray technology, revealing intricate details of the samples. The research unveiled how similar sensory structures evolved independently among ancient and modern species.

Despite discovering Anatolepis was an ancestor of modern arthropods like crabs and spiders, not vertebrates, Haridy sees value in this confusion. It highlights the often-overlooked complexity of invertebrates. She points out that while vertebrates are often thought of as the pinnacle of evolution, invertebrates have their own unique complexities.

This led her to ponder why these ancient structures resemble teeth so closely. Javier Ortega-Hernández identified Anatolepis as a type of marine arthropod, showing that these bumps served sensory purposes. Modern crabs have similar structures today that help them feel their environment.

The origins of teeth stem from two main theories. The "outside-in" model suggests that bumps from the ancient exoskeletons became teeth, while the "inside-out" theory argues they originated within the fish itself. Current evidence leans toward the outside-in theory, although supporters of both theories continue to research.

Haridy’s findings shed light on the evolution of teeth, emphasizing their deep-rooted history. While she has yet to uncover the earliest vertebrate, her work bridges the gap in our understanding of these ancient creatures and the evolution of complex structures like teeth, connecting it all back to life’s ongoing story.

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