Ankylosaurs are common features on documentaries or animated films about dinosaurs. Their armored body and club-like tail make them easy to identify. But how did that tail actually evolve? Evolutionary biologists show us the “first draft” of a popular dinosaur.

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We see a lot of the familiar ankylosaur, and we know it by the knob at the end of its tail. In popular depictions, it uses its tail like a club, which paleontologists agree is how the original dinosaurs probably used it. What we rarely notice, or see in early depictions, is the fact that the “tail” has changed in more ways than one. It’s not a swinging rope with a club at the end—it’s more of a hammer with a stiff handle. The vertebrae have been fused together.

Victoria Arbour, a researcher at North Carolina State University, has rounded up fossils of ankylosaurus and found that the “handle” came first, and the head of the hammer came second. The fused vertebrae came first, so at one point, early “drafts” of the ankylosaur just had weird, stiff tails.

Before that, the dinosaur was just a roly-poly armored tank with a regular curling tail. Below, we have a timeline of ankylosaur evolution.

Just as a note—I have seen a lot of press releases announcing new discoveries, but none of them had a title this good. They put it out under the heading, “Tail as Old as Time.” Well done, guys.

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[Source: Ankylosaurid dinosaur tail clubs evolved through stepwise acquisition of key features]