How Armored Dinosaur Got Its Bone-Bashing Tail

Armored, squat, and built like a tank, ankylosaurs were a type of dinosaur known for their bony, protective exterior and distinct, sledgehammer-shaped tails. Now, scientists have pieced together how the animals’ rear-end weapons evolved, finding that the hammer’s “handle” came first.

Ankylosaurs were a group of bulky, tanklike dinosaurs with bony plates covering much of their bodies. Some of these animals — a subgroup known as ankylosaurids — also came equipped with a weaponized tail club as well.

“Ankylosaur tail clubs are made of two parts of the body,” said study lead author Victoria Arbour, a postdoctoral researcher in the Department of Biological Sciences at North Carolina State University and the North Carolina Museum of Natural Sciences. “They’re made of the bones of the tail — the vertebrae — that change so that they’re stiff and lock together in a really characteristic way. We call that the handle, like the handle of an ax. And the other part of the tail is the knob.” [Paleo-Art: Dinos Come to Life in Stunning Illustrations]