Gargoyleosaurus

An early armoured dinosaur

Gargoyleosaurus was a small, low-slung plant-eater covered in bony armour. It was described in 1998 from a skeleton with a nearly complete skull found at Bone Cabin Quarry in Wyoming, in the Morrison Formation, and lived about 154 million years ago.

It belongs to the ankylosaurs, the group of armoured dinosaurs that later produced Ankylosaurus itself. Because it is so early, Gargoyleosaurus helps scientists understand how this group began.

Built like a tank

Its back was covered with rows of bony plates called osteoderms set into the skin, with larger spikes along the sides. The skull was armoured too, giving it the knobbly appearance that inspired its name. Unlike later ankylosaurs it had no bony club at the end of its tail.

It probably fed close to the ground on ferns and other low plants, relying on its armour rather than speed to survive predators like Allosaurus.

Not to be confused with Ankylosaurus

Ankylosaurus, the famous club-tailed armoured dinosaur, lived at the very end of the Cretaceous, about 68 to 66 million years ago, more than 80 million years after Gargoyleosaurus. Jurassic armoured dinosaurs were smaller and simpler, and none had tail clubs.

Which branch of the armoured family?

Ankylosaurs are usually split into two main groups: the ankylosaurids, which later developed tail clubs, and the nodosaurids, which never did and often had large shoulder spikes. Some researchers add a third group, the polacanthids, for early forms with a shield of fused armour over the hips.

Where Gargoyleosaurus fits is debated. A 2005 redescription placed it among the polacanthids, while other analyses put it near the base of the ankylosaurids. Either way, it is one of the oldest ankylosaurs known from good fossils, and it shows that the group already had heavy armour before it spread across the world in the Cretaceous.

Bone Cabin Quarry and its neighbours

Bone Cabin Quarry, where Gargoyleosaurus was found, is a historic site. It got its name because a shepherd had built a cabin out of dinosaur bones lying on the surface, and from 1898 the American Museum of Natural History dug tonnes of fossils there, including Allosaurus and sauropods.

Gargoyleosaurus was not the only armoured dinosaur of the Morrison Formation. Mymoorapelta, described in 1994 from western Colorado, is another small Late Jurassic ankylosaur. Both were much smaller than Stegosaurus, the most common armoured dinosaur in the same rocks, and they probably fed on different plants.