Monday, September 21, 2015

Ankylosaurus: Beast of the Week

This week let's check out an extremely famous, yet not so well known, dinosaur.  Enter Ankylosaurus magniventris!

Ankylosaurus was a plant-eating dinosaur that lived in what is now the western United States during the very end of the Cretaceous Period, between 68 and 66 million years ago.  It was a member of the family, ankylosauridae, which is named after it.  Ankylosaurids are characterized by having thick, bony pieces of armor, called osteoderms, in their skin.  Osteoderms are found in other animals, too, but the ankylosaurids had the most and the toughest!  Some parts of ankylosaurid armor were fused together, like on the head or the giant plate over the hips, called the sacral shield.  In fact, the name, "Ankylosaurus" translates to "fused lizard/reptile" because parts of its skeleton were reinforced in this manner.  Ankylosaurus was one of the largest members of this family, with adults estimated to have measured about twenty feet long from beak to tail.  Some paleontologists, however, have estimated even larger sizes, closer to thirty feet.  (No complete skeleton has been found so its true full size is uncertain.)

Ankylosaurus magniventris takes a midday nap.  Reconstruction by Christopher DiPiazza.

Ankylosaurus, although by far the most popular of the ankylosaurids, is not the most well-known.  In fact, we still don't know what the entire skeleton looks like exactly, including the sacral shield.  (We assume it had one based on other, related ankylosaurids.)  More often than not, especially when it comes to pop culture and plastic toys (cheaper ones at least) when you see a dinosaur labelled "Ankylosaurus" the creature you are looking at is mostly based on Euoplocephalus, a closely related, more completely known kind of ankylosaurid.

This toy, labelled "Ankylosaurus", although beautifully mostly modeled after other ankylosaurids, mainly Euoplocephalus.  Actual Ankylosaurus would have a different club and different armor.

Ankylosaurus had an interesting-shaped skull.  It's snout, which was tipped with a broad beak, sloped downwards and the armor above it was so wide that its nostrils would have been very narrow and faced sideways, under it.  It had two shallow, triangular horns facing backwards on both sides of the back of its skull, and two downwards and sideways facing horns attached to its jugals ("cheek bones")  The overall skull was wider than it was long.  In the back of its mouth, Ankylosaurus possessed a series of small, leaf-shaped teeth, which would have been ideal for shredding plant material.  Like its relative, Euoplocephalus, it is likely Ankylosaurus was not a picky eater, and just scarfed down any vegetation that was in front of it.  We assume this based on the fact that its beak was broad, rather than narrow.

Side and dorsal view of the skull of Ankylosaurus, which is now on display at the American Museum of Natural History in New York.

The armor of Ankylosaurus was simple, but would have been effective in protecting it against predators, and possibly rivals of its own species.  Unlike relatives, like Euoplocephalus, which had some pointed, spike-like osteoderms, most of Ankylosaurus' armor consisted of smooth, flat osteoderms.  They varied in size greatly and to be honest, paleontologists don't know exactly how they were arranged on the dinosaur's body, but they have a pretty good idea based on related ankylosaurids that fossilized better.  This armor was actually not as heavy as it looked, but would have still been extremely strong in life.  Under a microscope, one would find that these osteoderms looked like a network of bony fibers with hollow spaces between.  This allowed the armor of Ankylosaurus to remain strong, but also be light.

Ankylosaurus tail club on display at the American Museum of Natural History in New York.

 Of course, we need to talk about Ankylosaurus' signature tail.  This dinosaur's tail was thick and muscular at the base, and became stiff more towards the tip, thanks to ossified tendons running along the vertebrae, which had a mass of solid bone at the end of it.  This tail club could have been swung from side to side with devastating force and may have been used as a defense weapon against potential predators, like Tyrannosaurus.  I should also note that when I say "solid bone" the tail still varied in density.  The outermost layer of the club was dense and heavier, but the inside of it was made of lighter, spongier bone.  This would have allowed the tail to have been light enough to carry, but still dangerous.

That is all for this week!  As always feel free to comment below or on our facebook page!  Also special thanks to Dr. Victoria Arbour for her consultant work as I made the life painting and info on this page.


Arbour, Victoria Megan. "Estimating Impact Forces of Tail Club Strikes by Ankylosaurid Dinosaurs." PLoS ONE 4.8 (2009): n. pag. Web.

Arbour, V. M.; Currie, P. J. (2015). "Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs". Journal of Systematic Palaeontology.

Carpenter, K. (2004). "Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America". Canadian Journal of Earth Sciences 41: 961–86.

Scheyer, T. M.; Sander, P. M. (2004). "Histology of ankylosaur osteoderms: implications for systematics and function". Journal of Vertebrate Paleontology 24 (4): 874–93. 

Vickaryous, M. K., Maryanska, T.; Weishampel, D. B. (2004). "Ankylosauria". In Weishampel, D. B.; Dodson, P.; Osmólska, H. The Dinosauria. University of California Press. pp. 363–92.

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