Ankylosaurus magniventris

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Ankylosaurus magniventris
“The great-bellied fused reptile”

Specimen Name: Rosalynn (female)
Specimen Height: 1.70 m
Specimen Length: 8.43 m
Specimen Weight: 4.45 tonnes

Ankylosaurus was among one of the last thyreophoran dinosaurs to ever exist, persisting through the Maastrichtian to witness the Cretaceous-Paleogene extinction event (also known as the smashy space rock event). Had this species survived, it’s likely they would’ve gone on to become the United States of America’s mascot over the bald eagle — simply by virtue of being literal walking tanks. 3-5 rows (depending on where on the body and who you ask) of bony osteoderm nodes covered the animal’s back.

The business end of an Ankylosaurus led to a large tail club, which was likely used for smashing inconveniences such as territorial rivals or tyrannosaurs. If that wasn’t enough, the final third (or so) of the caudal vertebrae were interlocking and reinforced, meaning the animal wielded the biological equivalent of a blunt handheld mace (only, y’know, on its tail).

This is Borealopelta. Like other nodosaurs (a branch of ankylosaurs), they lacked Ankylosaurus‘s clubbed tail. Image by Davide Bonadonna, courtesy of National Geographic.

In situations where both the armor and club tail didn’t do the animal any favors, ankylosaurs employed the use of a specific kind of camouflage called countershading, where the top of the animal was much darker in coloration than the underside. This helps break up the animal’s outline in certain environments (it’s particularly popular with fish). Our understanding of dinosaur coloration has exploded in recent years; a dinosaur related to Ankylosaurus known as Borealopelta was found to have traces of pigmentary structures left behind that indicate a counter-shaded pattern. This means that armor wasn’t enough to defend these dinosaurs.

Kinda makes you glad whatever was stalking these things is long gone too, yeah?

Ankylosaurus, despite being the largest and arguably the most famous of its taxonomic clade (unless you know a six-year-old who will tell you of EuoplocephalusNodosaurusPolacanthus, and other “armored bois”) is quite different from its cousins (Arbor and Mallon 2017):

  • Their teeth are comparatively tiny; they don’t follow an otherwise very well-fit linear model correlating ankylosaur teeth to overall body size
  • Their nostrils (“nares” if you’re a fancy science person) faced outwards instead of forward
  • Their armor is configured…uniquely
  • A comparatively narrower tail club and shorter tail length compared to other ankylosaurs

Arbour and Mallon present some interesting thoughts on ankylosaurus’s ecology. These animals might’ve been diggers, not unlike modern boars and such, that churn up the ground after roots and invertebrates. Extrapolated muscle anatomy could also be in line to support this hypothesis. This makes perfect sense when you consider the orientation of their nares and their very wide mouth; these things were not particularly picky with what they were eating. Maybe they were also nest raiders? Not even the most dedicated hadrosaur mother could stop a hungry anky snacking on her new clutch. It makes for an interesting mental image, doesn’t it?

Artist Notes:

This is the first Ankylosaurus (and thyreophoran, period) in a very long time. My last rendition is from December 2016.

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It definitely feels dated.

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My new Ankylosaurus incorporates overall better rendering, body proportions, and musculature. The armor arrangement is again based on the work of Arbour and Mallon (2017). I’ve had a few correspondences with Ms. Arbour via Twitter over the multi-month process to create this tanky beast. Not that it took all that time to draw one. I just kept getting busy. The underlying skeletal structure that functions as the base for this restoration is by “getawaytrike” on Twitter and DeviantArt.

I’ve taken inspiration from members of testudines, who may or may not be archosaurs. They can have some pretty funky patterns on their shells. I decided to not go totally all-out on the anky (since, remember, they might’ve had some cryptic colorations in accordance to new science), but it could be something to look at for males.