Most dinosaur groups are stereotyped by the first found or the largest. Stegosaurus is the only stegosaur in the mass media, Tyrannosaurus the only tyrannosaur, Brontosaurus the only sauropod, etc. I’m sure Ankylosaurus is the only armored dinosaur known to most people-it’s the last, it’s the largest, it’s the first to be found, and it was a neighbor to Tyrannosaurus rex. However, ankylosaurs had existed for almost 100 million years before Tyrannosaurus. In fact, we’re going to look at two genera dating back to the time of Brontosaurus in the late Jurassic period, and lived alongside the giant sauropods and Stegosaurs. They are the first ankylosaurs-the smallest and most primitive known, but already well-armored and distinctively ankylosaurs.
These animals are Gargoyleosaurus parkpinorum and Mymoorapelta maysi. Mymoorapelta was first discovered in 1994 and Gargoyleosaurus in 1998- I first remember going the Denver museum and finding the skeleton being prepared for mounting that year. It still stands underneath the DMNS’ giant Diplodocus, a contrast of Jurassic herbivores. Yes, these are both Morrison animals, much rarer than any other herbivore but some primitive ornithiscians like Othnielosaurus and Drinker. In a fauna dominated by sauropods, they shuffled in the shadows of the giants, and found their own niche.
They were both found by Utah paleontologists and Ankylosaur experts Kenneth Carpenter and James Kirkland, albeit in different sites. Mymoorapelta was found in the Myatt-Moore quarry (hence the name) on Colorado’s border in Utah, in rocks belonging to the Brushy Basin member. Meanwhile, Gargoyelosaurus was discovered in Bone Cabin Quarry (first found by Walter Granger in 1897) in Wyoming. Geologically, it was in the Salt Wash member, a million years before the Brushy Basin and with a subtly different fauna. There’s no reason to assume they never coexisted, but they seem to be connected to different environments.
They’re both connected to the family Polacanthinae, and we’ll return to that family at a later date. They are the earliest, most basal family of ankylosaurs, dating from these two genera to the middle Cretaceous where they are completely replaced by nodosaurs and ankylosaurs. They’re characterized in having spiky armor, especially on the neck and shoulders. While Allosaurus was far larger than these potential prey, it would have significant difficulty trying to pierce bony armor that could hurt the attacker in the meantime.
They’re each about 10 feet long, a very common size for ankylosaurs until the middle Cretaceous Peloroplites and Sauropelta. Why did Ankylosaurs grow so small? For one thing, most predators couldn’t harm them through the armor. It wasn’t until early Tyrannosaurs and large dromaeosaurs evolved that large sizes became necessary to counter their powerful weapons. For another, instead of sheer size for digestion, ankylosaurs were very wide for extra gut for digestion. Indeed, looking at an ankylosaur head on, they’re downright tubby.
In addition to the armor and the body shape, both Mymoorapelta and Gargoyleosaurus had many other ankylosaurian characteristics-triangular, slightly domed heads (longer in nodosaurs, and wide and horned for ankylosaurs), lateral lines of armor shaped like spikes or blades, wideset, crouched legs, and tiny herbivore teeth. These characteristics would be shared for the next hundred million years until the extinction of the entire line at the Creteaceous-Paleogene extinction.
Now, they are clearly not the same animals. Indeed, when Kirkland and Carpenter and their team discovered Gargoyelosaurus, they compared it to Mymoorapelta. Luckily, both animals were represented by good partial skeletons so they could be compared. Gargoyleosaurus is not only an earlier animal, but less derived as well. There’s subtle differences in the shape of the vertebrae, scutes, pelvis, metacarpals, caudal ribs, and skull, and the chevrons of the spine are not fused. They also show different similarities to the other ankylosaurs. Gargoyelosaurus resembles more the true Ankylosaurs, while Mymoorapelta has more in common with Nodosaurs. It’s possible they were ancestors of the clades, or of the lines of Polacanthids that later became each group. Ankylosaur evolution is still a puzzle and at the base are these two species.
Because they’re early, small, and rare, neither species gets much view in the public eye, being literally overshadowed by Brontosaurus, Stegosaurus, and the rest. You can see their specimens, however. Gargoyleosaurus is mounted underneath the Diplodocus in the Denver Museum of Nature and Science. Mymoorapelta can be found on the other side of Colorado, in the Dinosaur Journey Museum in Fruita. Fortunately, casts of both have been made and can be seen in touring museums of dinosaur casts. Their relative complete specimens make them less obscure than some other dinosaurs but they are quite obscure. And, of course, it’s their obscurity that makes me want to promote them.
So anyway, Hollywood, give them a break. Museums, keep them on display. Toy companies, here’s a new fresh face. Authors, think about the crap you’re writing and how this genus could perk up the place. And remember, shop Mymoorapelta and Gargoyleosaurus where you work or play!
I would like to thank James Kirkland for his help with the papers for this entry. I actually wasn’t going to cover them, but I asked him a question on these and he was gracious enough to let me read his papers on the taxa.