It's hard to read anything about dinosaurs without bringing along preconceived notions of what the creatures might have looked or acted like. Most people either read books as children or watched television or movies that depicted dinosaurs as massive, monstrous creatures, seeking to destroy or devour anything in their path. Some of those animals, like Tyrannosaurus, were huge predators. But not all dinosaurs fit that bill. Enter the Ankylosaur.
A Plant-eating Tank of a Dinosaur
While this four-legged dino was certainly big – the largest Ankylosaurus ever found was 20.5 feet (6.25 meters) long and weighed around 4 tons (3.6 metric tons) – Ankylosaurus was an herbivore, a plant-eating tank of an animal. And we do mean tank. The Ankylosaurus was covered with thick, bony plates – a defense that came in handy for this hefty herbivore and lent it its name. Ankylosaurus means "fused lizard" in Greek – the bony plates were fused to the dinosaur's skull and other body parts making it extremely sturdy.
Dr. Hans Sues is the senior research geologist and curator of fossil vertebrates in the department of paleobiology at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., and has published widely on many species of dinosaurs, including a 2020 article on the skull of one species from the ankylosaur group in the journal Biological Communications.
"The first line of defense was their outer armor composed of bony plates," Sues says via email. "In fact, ankylosaurs were so heavily armored that even their upper eyelid was protected by a bony plate. One group of ankylosaurs, Ankylosauridae, had massive clubs of bone at the end of their tails, and they could swing their tails to inflict massive damage on the legs of an attacking predator."
The Ankylosaurus' body was thick and squat, its legs sturdy. It had a broad, triangular shaped skull. But it was the armor that made the difference – hard plates covered with bony spikes jutting from its flanks and bony knobs called osteoderms or scutes protruding from its back. Horned protuberances stood out above each eye and on the sides of the face. Not all ankylosaurs had the same armor patterning but all had armor to protect them from predators, most notably Tyrannosaurus, Tarbosaurus and Deinonychus.
And ankylosaurs needed that protection because they spent most of the day eating massive amounts of food – stripping leaves from low-lying plants.
"They have small teeth similar to those of present-day plant-eating lizards," Sues says. "An amazing discovery of a nearly perfect ankylosaur skeleton from Alberta [British Columbia, Canada] preserved gut contents that confirmed that ankylosaurs ate plants." However, Sues shared a startling discovery. "One small-bodied ankylosaur recently discovered in northern China apparently went into lakes and even ate small fish," he says.
Though the first ankylosaur fossil was discovered by Barnum Brown in the Hell Creek Formation in Montana in 1906, Sues says ankylosaurs have been found in many places throughout the world including Europe, Antarctica, Asia, Australia and North and South America.
"In fact, one of the first dinosaurs ever to be discovered was an ankylosaur, Hylaeosaurus from southern England, discovered in 1831," he says.
Ankylosaur Could Smell Prey and Predators
Ankylosaurs had a complex nasal system which included a large cavity volume for the region of the brain that handles the olfactory sense (sense of smell). A 2011 study in the Journal of Anatomy suggested that ankylosaurs may have had a highly developed sense of smell in order to find food and to avoid predators.
We do not know whether or not ankylosaurs were social as adults, whether they moved in herds. According to Sues there's simply no evidence one way or the other, though he said that a group of very young ankylosaurs were discovered in the Gobi Desert.
And though Ankylosaurus armor and body type might bring to mind thoughts of alligators and crocodiles, Sues says they are not related. "The closing living relatives of dinosaurs are birds," he adds.
Interestingly, Ankylosaurus was estimated to have lived between 65.5 million to 66.8 million years ago in North America during the Late Cretaceous period which means ankylosaurs were among the last dinosaurs roaming the earth. According to the U.S. Geological Survey (USGS) dinosaurs went extinct about 65 million years ago at the end of the Cretaceous period. In addition to fossil sites in Montana, Ankylosaurus tracks have been found in the western U.S. in Arches National Park in Utah and in the Patuxent Formation, where the Little and Big Patuxent Rivers meet in Maryland.