Euoplocephalus: Prehistoric Animal of the Week

Sorry for the delay.  (Not really though because I had no choice in the matter.)  This week we will be looking at a well studied, but until recently not so well understood armored dinosaur.  Check out Euoplocephalus tutus!

Euolpocephalus tutus life reconstruction by Christopher DiPiazza.

Euoplocephalus was a heavily-armored, plant-eating dinosaur that lived in what is now Canada, during the late Cretaceous period, about 77 to 75 million years ago.  It belonged to the ankylosaurid family, which also includes the larger, "more famous", Ankylosaurus.  (I say "more famous" because many depictions in pop culture or in toy form that are labelled as Ankylosaurus are usually based on Euoplocephalus because it is more completely known.)  The genus name, Euoplocephalus, translates to "well-armed head" and the species name, tutus, translates to "safely protected" because this dinosaur had a LOT of armor.  It was twenty feet long from snout to tail and would have co-existed with many other dinosaurs like Chasmosaurus, Styracosaurus, Parasaurolophus, and Corythosaurus. 

Euoplocephalus mount on display at the Senkenberg Museum of Natural History in Germany.

Euoplocephalus' body had a series of bone chunks embedded in the skin, separate from its actual skeleton, called osteoderms.  Osteoderms have been discovered in a number of other kinds of dinosaurs like the titanosaurs, and stegosaurs.  They can also be observed in modern animals, like crocodilians.  Ankylosaurs, however, were the most heavily armored.  This armor most likely would have protected the animal from predators or possibly from rivals of the same species if they ever did engage in such behaviors over dominance, territory, and/or mating rights.  Some of the armor on Euoplocephalus took the form of small osteoderms, along the back and sides, but other osteoderms were keeled, and almost blade-like, higher up on the back.  Euoplocephalus also had two rings of keeled osteoderms on its neck, called cervical rings, and a flat, wide sheet of bone covering the entire dorsal portion of its extremely wide pelvis, called a sacral shield.  Euoplocephalus's head was armored, too, including the eyelids, and it had horns on the back of its skull and its jugal bones (under the eyes).  Although armor from the tail was never found, it is likely that Euoplocephalus had rows of osteoderms down there, as well, since they are known from a related ankylosaur from Asia, called Pinacosaurus.  As if all that armor wasn't enough, Euoplocephalus was armed with a mass of solid bone on the tip of its tail that it could have swung around as a serious weapon against other dinosaurs.  The tail just in front of this bony club was stiffened and fortified to support it and absorb shock when it smashed into things like wimpy theropod legs.  The base of the tail was not stiffened to give the weapon some range, and would have been supported by large muscles.

Euoplocephalus possessed a wide, flat beak which was a good adaptation for grasping low vegetation.  Because of the broadness of the beak, it wasn't likely a picky eater and probably acted like a giant, reptilian lawnmower, just sucking up any plants it walked in front of.  The plants would then be shredded by its small teeth, located farther back on the jaws.

Euoplocephalus skull on display at the American Museum of Natural History in New York.

 Inside the skull, Euoplocephalus had a series of long passages running through its skull which were attached to it's nostrils.  It was first believed that these had something to do with a heightened sense of smell.  It was later found out that Euoplocephalus had an inner ear that was capable of picking up extremely low-frequency noises.  Because of this, it is also possible that Euoplocephalus used these hollow passages inside its skull to make ultra-low sounds to communicate with members of its own species.  This behavior can be observed in animals alive today, like Elephants.  Euoplocephalus also had tiny eye sockets, but this doesn't mean it would have had poor vision.  In fact, it is likely it could see pretty darn good.  Remember, all of those spikes, horns, and armor were likely just as much for display within the species, as they were defense against predators, so being able to see them on a rival/potential mate was important to Euoplocephalus.

Another Euoplocephalus skull.  This one is from the University of Alberta.  Photo was taken and provided by Victoria Arbour for her latest paper on ankylosaur taxonomy.  (more on that soon!)

That is all for this week!  Special thanks to Dr. Larry Witmer and Victoria Arbour for providing their expertise for the information and life reconstruction in this post.  Feel free to comment below or on our facebook page!  

References

Arbour V.M. and Currie P.J. (2013). "Euoplocephalus tutus and the Diversity of Ankylosaurid Dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA". PLoS ONE 8 (5): e62421. doi:10.1371/journal.pone.0062421.

Arbour, V. M. (2009). "Estimating Impact Forces of Tail Club Strikes by Ankylosaurid Dinosaurs". PLoS ONE 4 (8): e6738. doi:10.1371/journal.pone.0006738. PMC 2726940. PMID 19707581..

Coombs W. (1972). "The Bony Eyelid of Euoplocephalus (Reptilia, Ornithischia)". Journal of Paleontology 46 (5): 637–50. JSTOR 1303019..

Coombs W. (1979). "Osteology and myology of the hindlimb in the Ankylosauria (Reptilia, Ornithischia)". Journal of Paleontology 53: 666–84. JSTOR 1304004.

K Carpenter (1982). "Skeletal and dermal armor reconstruction of Euoplocephalus tutus (Ornithischia: Ankylosauridae) from the Late Cretaceous Oldman Formation of Alberta". Canadian Journal of Earth Sciences 19 (4): 689–97. doi:10.1139/e82-058.

Miyashita T, Arbour VM, Witmer LM, Currie PJ, (2011). "The internal cranial morphology of an armoured dinosaur Euoplocephalus corroborated by X-ray computed tomographic reconstruction". Journal of Anatomy 219 (6): 661–75. doi:10.1111/j.1469-7580.2011.01427.x.

M. K. Vickaryous, A. P. Russell (2003). "A redescription of the skull of Euoplocephalus tutus (Archosauria: Ornithischia): a foundation for comparative and systematic studies of ankylosaurian dinosaurs". Zoological Journal of the Linnean Society 137 (1):