Ankylosaurus: A Tank-like Herbivore With a Killer Club Tail

While these armored dinosaurs were certainly big — the largest Ankylosaurus specimen ever found was 20.5 feet (6.25 meters) long and weighed around 4 tons (3.6 metric tons) — the species was herbivorous, meaning meaty prey could rest (relatively) easy around this plant eater.

What Did Ankylosaurus Eat?

Fossils indicate that ankylosaurus grazed on low-growing plant matter along the ground. The heavily armored dinosaur came equipped with leaf-shaped teeth teeth which were perfect for grinding up thick shrubbery but not suited for combat with other species. These grinding teeth sat behind a beak-like formation in the ankylosaurus skull.

Dr. Hans Sues is the senior research geologist and curator of vertebrate paleontology 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 complete 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 tail clubs to inflict massive damage on the legs of an attacking predator."

The Ankylosaurus' body was thick and squat, its hind limbs 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 limb bones and armored knobs called osteoderms or scutes protruded from its back.

Horned protuberances stood out above each eye and on the sides of the face. Not all ankylosaurid dinosaurs had the same armor patterning but all had armor to protect them from predators, most notably Tyrannosaurus, Tarbosaurus and Deinonychus.

And ankylosaurus needed that protection because it 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. It's possible that some species were evolving in order to consume animal matter.

Though the first known ankylosaurus remains were discovered by Barnum Brown in the Hell Creek Formation in Montana in 1906, Sues says ankylosaurid dinosaurs 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.

Ankylosaurs had a complex nasal system which included a large cavity volume for the olfactory region of the brain that handles 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 other dinosaurs.

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, research shows Ankylosaurus lived between 65.5 million to 66 million years ago in what is now the western United States during the Late Cretaceous period. This means ankylosaurs were among the last dinosaurs roaming Earth.

According to the U.S. Geological Survey (USGS) dinosaurs went extinct about 65 million years ago at the end of the upper 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.

The largest known ankylosaurus skull (designated CMN 880) was discovered by American paleontologist Charles Sternberg in 1947, along with a jawbone and pieces of armor.

This skull suggests a full specimen significantly larger than other ankylosaurs discovered around the world, but it is also damaged in places. Getting the full picture of ankylosaurus biology is difficult because a full skeleton has never been recovered.