Spider Teeth: Urokodia aequalis

Publication Info:

Transcript:

Y. Liu et al. Urokodia sheds light on the origin of chelicerae and book gills of Chelicerata. Nature, published online July 1, 2026; doi: 10.1038/s41586-026-10713-2

Meet Urokodia aequalis, this species may not be new, but the insights paleontologists are getting from it sure are, and are pushing the origins of arachnid chelicerae back to over half a billion years, in our planet's Cambrian oceans.

Episode 304

Notes:

Hey, so do you know how old spiders are, or at least their teeth are? Here's your most recent paleontology news almost daily or whenever I get around to it. So, first of all, spiders don't actually have teeth. What you think of as teeth or what sometimes get called teeth or fangs are actually chelicerae. They're modified mouth parts, which I know by definition sounds a lot like teeth, but they aren't. And the terminology does matter because the chelicerae are actually what their entire group is named after. And I don't just mean arachnids like spiders and scorpions, I mean chelicerates, which includes the arachnids like spiders, scorpions, ticks, mites, but also animals like horseshoe crabs because they all have that one unifying feature, which is their chelicerae, which can look very different in different groups. After all, spiders have almost like hypodermic needles, while scorpions have pretty much another set of small pinchers halfway inside their mouths, which if you haven't looked at a scorpion face close up, enjoy that. And while yeah, superficially they look pretty different, structurally and developmentally they are the same thing. And luckily that one defining feature for chelicerates goes all the way back in their evolution and is getting pushed back even a little further. Meet Urokodia aequalis, a 518-million-year-old arthropod from Cambrian China. There's already evidence for chelicerates dating back over half a billion years, like the very arachnid brain that was found in a fossil of Mollisonia last year. But some brand new research has discovered structures that look a whole lot like pincher-like chelicerae in this 518-million-year-old animal using x-ray tomography along with structures that look a lot like book gills on the limbs. And Urokodia looks like it could represent a transitional period between segmented limbs and actual chelicerae in the oldest spider ancestors before they even thought of moving on land. As usual, if you want more information, here's the source.