A New Ankylosaur from Chile

In December 2021, a [study] was published describing a new, mostly complete ankylosaur from Chile. Complete skeletons are very rare in the fossil record, so this discovery is exciting for many reasons.

The new fossil is an ankylosaur, one of my favorite types of dinosaurs! I always used to say “an-KLEE-o-saur” when I was a kid, but I eventually learned that its “an-KY-lo-saur.” Ankylosaurs are spectacular. They’ve got armored backs and tails and heads and even eyelids (in some). They were basically walking, herbivorous tanks. And the lived all over the world.

Some of the global ankylosaur diversity. Image by paleontologist Dr. Victoria Arbour.

There are 2 general types of ankylosaurs: Nodosaurids (that do not sport a tail club) and Ankylosaurines (that have a tail weapon). The new ankylosaur, Stegouros (“roof tail”) elengassen (after an armored mythical creature of the local Aónik’enk people), had a unique tail weapon. It was a frond of flat plates coming off horizontally on each side, instead of a ball-like club. A big weapon for an animal only 2.5 meters long.

An image of Stegouros by Lucas Jaymez.

After a phylogenetic analysis, it seems this new ankylosaur did not belong to Ankylosaurinae or Nodosauridae, but rather to a third clade (group). The analysis joined Stegouros with Antarctopelta (from Antarctica) and Kunbarrasaurus (from Australia). These three dinosaurs, all from the southern hemisphere, had combinations of traits that look more like stegosaurs than ankylosaurs, and more ankylosaur-like traits. Stegosaurs are the sister taxon to ankylosaurs (the most closely related group), so it makes sense that these early ankylosaurs look a little more general.

We’ve learned a lot about ankylosaurs in the last decade and it’s exciting to see more material for this group.

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