Ankylosaurus: The Cretaceous dinosaur that armed itself to the teeth

Ankylosaurus was the tank of the dinosaurs: from neck to tail it wore a thick coat of bony armour, looking almost unbreachable. It was the largest and the last of the ankylosaurs, and it shared Late Cretaceous North America with Tyrannosaurus rex. Let's meet this fully armoured plant-eater.

Its body

The back and head of Ankylosaurus were paved with rows of bony plates that locked together like a puzzle, with spikes set between them. From above, the whole animal looked like a single shield. The only soft spot was its belly, so when threatened it probably crouched low to tuck that soft underside away.

Its most fearsome weapon was the club at the end of its tail, made of several large, fused bony knobs. Computer simulations of a full swing suggest it could shatter bone — enough to make even a predator like Tyrannosaurus think twice. Its beak-like mouth snipped low plants, and it had a very roomy gut that processed huge volumes of ferns and shrub leaves.

Where it lived and what it ate

Ankylosaurus was a plant-eater, cropping ferns and shrubs close to the ground. Heavy and sturdy on four thick legs, it did not run fast, but its armour was enough to protect it. It probably lived alone, crouching low and swinging its tail club when danger appeared.

Where its fossils were found

Its fossils come from western North America, especially the United States and Canada. It lived at the very end of the Late Cretaceous and was one of the last ankylosaurs.

What the fossils tell us — and what they do not

Fossils reveal the arrangement of the plates and the rough shape of the tail club, but the colour of the horny layer, exactly how the club was swung and how it walked have to be reconstructed. The "bone-shattering" result comes from computer simulations, not direct fossil evidence. So the colours and pose on the stage are evidence-informed interpretations.

A note for grown-ups

You could talk with a child about "where the shield is and where the weak spot is": Ankylosaurus is armoured almost everywhere except its soft belly. Realising that every kind of defence has a cost is a lovely way to understand how animals survive.