WWD: Ankylosaurus magniventris

One of the most heavily-fortified animals to have ever lived, this was probably the largest of the thyreophorans, with size estimates ranging between 7-11 tonnes and up to 9 metres in length. Even its eyelids were augmented into bony shutters, and of course its tail ended in a heavy, bony club which could be more than two feet wide. The tendons in the back half of the tail were ossified and the caudal vertebrae were fused, rendering it inflexible as a pole, strengthening its power when swung as a weapon. If a human were ever struck by that thing, it would be like getting shot by a cannonball, you would be splattered into ground beef. Of course, no weapon was overkill when one lives alongside one of the most fearsome carnivores to ever walk the Earth.

Ankylosaurs seemed to have evolved tail clubs in conjunction with the rise of tyrannosaurids, as only more derived Asian and North American ankylosaurids of the Late Cretaceous are known to have had them (although the parankylosaurians of the southern hemisphere had a roughly analogous structure). The powerful jaws of T. rex would have been strong enough to pierce its bony armour, so it needed a more proactive defence. They were the perfect weapon for bashing the thin and delicate shins and ankles of these predators; for a multi-ton biped, an injury like that is almost guaranteed to be a death sentence. The side-to-side movement was good, but up and down much less so, so the Ankylosaurus clubbing the Tyrannosaurus mother in the upper chest is unlikely, the knee at best.

The series' portrayal of Ankylosaurus has pretty wonky anatomy, but it's hard to blame them when their armour arrangement was very complex and, Ankylosaurus, poorly known. Much of the skeleton is unknown and the armour plates and spikes are found scattered, so their positions in life are largely speculative (Ankylosaurus did not have rows of spikes along their sides, that are shown in many portrayals, like in the Jurassic Park movies). WWD uses a very old reconstruction (done by Barnum Brown in 1908) which shows the osteoderms being tightly packed and largely uniform, but newer reconstructions depict it as being much more complicated and widely spaced apart (note that smaller osteoderms would be present between the larger ones and on the thighs, but are here depicted as being subdermal). The back was also much flatter and its body much wider than shown. Also its horns should be much bigger and its mouth would have been wider (ankylosaurids were thought to be non-selective feeders as a result). Something rarely depicted (due to most skeletal diagrams being from sideview) was so incredibly wide ankylosaurs were; Ankylosaurus' hips could've been about two metres in width and nearly as long, hence its massive thighs. Also, it's another dinosaur in the series plagued with elephant foot syndrome, but I've already gone into that enough. And its tail club looks like lumpy poop for some reason.

One mildly intriguing fact about ankylosaurs is that they have very large and complex sinus chambers. I didn't get into them in this revision because the purpose of these is still unknown, although their use as resonating chambers has been speculatively suggested. Just this year, an ankylosaurid was described with a preserved syrinx, the structure birds use to produce birdsong, indicating that they could potentially produce similar vocalizations. Previously, such structures were unknown in non-avian dinosaurs, and ankylosaurs are not closely related to birds at all, so perhaps it was actually widespread and we just haven't been finding them.