Swimming capabilities of Ankylosauria

[Killekor]

Crocodilians don't tend to attack animals many times their own size. All but the smallest ankylosaurs could likely have fended off most crocodiles with kicking alone if one was foolish enough to bother them.

The very large animals like Deinosuchus and Sarcosuchus, in addition to being rare, were heavily focused on attacking aquatic prey.

Thanks for the explanation!

Killekor

[Flaffy]

Found this: John Conway depicting a pair of Pinacosaurus.

[stargatedalek]

They were probably quite great swimmers, but likely not much of divers. We think of them as heavy animals because of their armor but they are also just very broadly built animals in general which tends to make for strong swimmers that float relatively comfortably. They are also known almost exclusively from water rich habitats, everything from swamps to salt marshes but none of that dry land in between. More of a water buffalo than a hippopotamus.

Saichania is believed to have lived in a dessert environment. There is also a strong preservation bias for aquatic environments so I'm not sure that means Ankylosaurs were an aquatic oriented group. Unless there are strong anatomical indicators of an semi aquatic lifestyle across the family I'd say it's more likely they were generalists.

A desert with large areas of permanent above ground water that was already well on its way to literally turning into a giant wetland. Think more scrub-land and less Sahara. Early Nemegt was a desert due mostly to soil composition, not dryness per-se.

[Newt]

It is a rare terrestrial animal that cannot swim at least a little bit. That said, nothing in ankylosaur anatomy shows adaptation to swimming or even wading. Their toes are quite short, which makes them less useful as paddles for swimming or as "snow-shoes" for walking on soft substrates. Their tails are ill-designed for sculling. They might well have been quite buoyant, but this would only make them good flotsam, not good swimmers. The closest living analogues to ankylosaurs are probably testudinine tortoises and other terrestrially-adapted turtles, which are miserable swimmers. I've rescued more than one box turtle I found drifting in rivers and creeks; once the water gets high enough for them to start floating, they just close their shells and hope for the best. Often they end up in an eddy they cannot escape, or lodged in a branch - like this fellow (I don't have any pre-rescue photos of him; he'd probably been trapped in the branch where I found him, well above the river's surface, since a flood several days earlier).





As for why ankylosaurs end up in wetland and marine deposits so often, I have a few thoughts: first, as Neosodon already pointed out, those are the kinds of depositional environments that preserve most terrestrial vertebrate remains, so there may not be much signal there.


Assuming there really is a bias, that still may not indicate aquatic habits on the part of these animals. All else being equal, the armored hide of anyklosaurs may have made their carcasses hold together longer and so be more likely to be washed far from their actual death site. I'm thinking here of gars and armadillos, whose semi-intact carcasses often can be found along riverbanks, held together and protected from scavengers by their tough armor, where less well-armored critters would have disintegrated or been devoured.








Another possibility is that their bodies so often ended up in watery habitats precisely because they were so ill-adapted to them. This may seem counter-intuitive, but think of it this way: every fossil comes from an animal that died. Ankylosaurs ended up fossilized in these watering holes because they couldn't get out of them.


So why wouldn't ankylosaurs just avoid these dangerous places? Thirst is one obvious answer; everybody's got to drink, danger or no. Just think of all those nervous ungulates dipping their snouts into the crocodile-infested rivers of the Serengeti. Another potential draw more specific to ankylosaurs is calcium. All that bony armor takes tremendous quantities of calcium to grow. Foliage can provide some, but probably not enough. Ankylosaurs would need some other source, just as today's tortoises do. Calcium-rich soils are one possibility. Terrestrial carcasses are another, but these are relatively sparsely distributed in space and time. But a reliable source of calcium can be found along the banks of lakes, streams and seas: shells! No doubt other littoral debris such as cuttlebone, crustacean exuvia, and fish and other vertebrate remains would also be hoovered up by calcium-hungry ankylosaurs (thus the fish scales). But accessing these rich calcium sources was risky for our armored friends, and some never returned from their forays to the beach. This is just my pet theory, backed up by no evidence whatsoever, so take it how you will.

[SidB]

The analogy with box turtles makes a lot of sense, in particular to their categorization as "miserable swimmers. But I'd have a question to add/ask: what about Ankylosaurus tails as potential propulsion units? Did these not have good side-to-side capabilities that could have been employed for this purpose? How about the Nodosaurs without a heavy tail chub to impede movement?

[Newt]

If an ankylosaur did end up in the water, it probably would be able to propel itself a bit with its tail. But if you look at animals that habitually use their tails for sculling, like crocodilians, seasnakes, salamanders, and the more aquatic lizards, you'll find their tails to be tall, narrow (at least towards the distal end), and flexible, because that's what makes a tail a good oar. Ankylosaurid tails are low, fat, and stiff - good for clubbing, bad for sculling. Nodosaurid tails are less ill-suited to swimming than their cousins', but still not what you would expect from an aquatic animal.

[SidB]

If an ankylosaur did end up in the water, it probably would be able to propel itself a bit with its tail. But if you look at animals that habitually use their tails for sculling, like crocodilians, seasnakes, salamanders, and the more aquatic lizards, you'll find their tails to be tall, narrow (at least towards the distal end), and flexible, because that's what makes a tail a good oar. Ankylosaurid tails are low, fat, and stiff - good for clubbing, bad for sculling. Nodosaurid tails are less ill-suited to swimming than their cousins', but still not what you would expect from an aquatic animal.

Agreed. It's hardly an aquatic, but maybe a Nodosaur could cope with an accidental plunge, so as to be able to extricate itself, or perhaps habitually cross small rivers (if the current was relatively slow) so as to extend its foraging range. It certainly won't be becoming the new Spinosaurus!

[Brocc21]

I wanna say thanks Newt for such a long reply. And I really like the idea of Ankylosaurs crunching down on the shells of invertebrates. This behavior has been seen before in Hadrosaurs (for those that don't know some Hadrosaur coprolites have been discovered with the remains of crabs shells contained in them.) so there's no doubt an Ankylosaur would do the same. Many herbivores consume meat or some other part of an animal as a supplement. I would post a video of this behavior, but I doubt y'all would want to see it, as cows have been seen eating chicks who
we're to far away from the protection of mom.