> Armored dinosaurs like Stegosaurus and Ankylosaurus were mostly big, bulky animals that walked on four legs, but paleontologists have now discovered a bizarre relative the size of a dog that strutted around on two legs.

> The team says this makes it a member of an ancient basal thyreophoran lineage that survived well into the Cretaceous – long after relatives like Stegosaurus evolved and died out. And being the first of its kind to be found in South America shows that this group was more widespread than previously thought.

That’s new!

It does make sense, because the ancestors of all dinosaurs were all facultative bipeds, able to go about on either two legs or four. Following that, the ancestors of both the ornithischian and saurischian dinosaurs were facultative bipeds. From there they could go down either the two legged or four legged route.

So this new fossil suggests that the ankylosaurs branched off the tree early, retaining that ability to go either way.

But not necessarily. We have other instances of quadrupeds evolving into bipeds. Not often, but occasionally. Humans are one example. Kangaroos another. And the pangolin is an armoured creature that can run on two legs.

Checking the web. This is an interesting website “:Know your ankylosaurs”:https://pseudoplocephalus.com/2015/08/23/know-your-ankylosaurs-everybodys-in-this-together-edition/ The earliest true ankylosaur was in the Ordovician at the start of the upper Jurassic, so quite late. Hold on, this new fossil is a thyreophoran, so not a true ankylosaur.

I see that our Minmi is the earliest separate branch of true ankylosaurs.

Lesothosaurus was a biped.

Scelidosaurus was armoured and it is sometimes drawn as running on four legs and sometimes drawn as running on two. This is one of the thyreophora, lower Jurassic. So closest on the above chart to this new fossil.

Opposing images of scelidosaurus. On four legs or two.

On four legs.

On two legs.

Huangosaurus is usually drawn on four legs.

But is sometimes drawn with shorter front legs suggesting that it could run on two.

Australia’s minmi was about the size of a dog.

This is mymorapelta.

OK, so it all fits together. The ancestral thyreophoran was probably a facultative biped. The ankylosaurs later tended to walk about on four.