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Famous for its clubbed tail, Ankylosaurus roamed North America some 70 million to 66 million years ago in the late Cretaceous period.

Stocktrek Images/Nat Geo Image Collection
ScienceExplainer

Here's what made Ankylosaurus the armored tank of dinosaurs

From its clubbed tail to spike-studded body, find out how this impressive herbivore defended itself against the predators of the late Cretaceous period.

Ankylosaurus magniventris was the prehistoric tank of the late Cretaceous period, some 70 million to 66 million years ago. This enormous four-legged dinosaur had a squat body covered with bony plates that were studded with spikes. At its tail, the plates fused together to form a thick club that the dinosaur could swing to fend off threats.

This impressive defense offered Ankylosaurus protection from large land predators such as Tyrannosaurus rex, which also roamed North America around this time. Would-be predators would have had to flip this armored dinosaur over to reach its broad underbelly—its only weak spot.

Relatives

Ankylosaurus magniventris is an ankylosaur—a suborder of four-legged, armored, and mostly herbivorous dinosaurs—but not all ankylosaurs were Ankylosaurus. This dinosaur is the namesake of its suborder, which included both ankylosaurids and the more primitive nodosaurids. Ankylosaurus magniventris was the last and largest species of ankylosaurid. The dinosaur grew up to 33 feet long and probably weighed about four tons. Its size—combined with its small teeth and oddly placed nostrils—make this species one of the more unusual ankylosaurs.

While nodosaurs share the armor and tank-like build of Ankylosaurus, they did not have the dinosaur’s clubbed tail. In 2011, the unearthing of a remarkably well-preserved nodosaur fossil—one of the best ever found—offered new insight into the nodosaur’s pigmentation, which may have served as camouflage, as well as the size and shape of its armor. The discovery of a fossilized ball of digested plant matter in this animal’s stomach also confirmed what researchers had suspected about armored dinosaurs: They preferred to graze on ferns and other low-growing plants.

Ankylosaurus had a narrow beak at the end of its skull to help it strip leaves from plants. It also had small, leaf-shaped teeth, which may have been useful for gnashing small fruits or invertebrates, and a large gut for digesting the large quantities of plant matter necessary to sustain its formidable body.

Evolving fossil knowledge

Though Ankylosaurus is among the most famous dinosaurs, it is also one of the most puzzling. Unlike its nodosaur relatives, scientists have only unearthed a handful of Ankylosaurus fossil fragments, and with each new discovery, our understanding of the species grows. Paleontologists have rearranged the available fossils time and again, with the most recent proposed body shape suggesting it may have been longer and thinner than previously thought, and equipped with a denser coat of spikes.

In 2017, a team of paleontologists redefined Ankylosaurus once again, revealing its large body size, small teeth, and nostrils that were placed to the side of its head rather than in the front of its snout. Its displaced nostrils might signal an evolutionary change in its diet or sense of smell. But it will take more research—and the discovery of more specimens—to better understand this iconic dinosaur.

Dinosaurs 101 Over a thousand dinosaur species once roamed the Earth. Learn which ones were the largest and the smallest, what dinosaurs ate and how they behaved, as well as surprising facts about their extinction.