Ankylosaurs | Armored Herbivores With a Wicked Tail Club

Ankylosaurs were a group of herbivorous dinosaurs known for their heavily armored bodies and unique tail clubs. These creatures roamed the Earth millions of years ago, from the Middle Jurassic to the Late Cretaceous. Their name, which means ‘fused lizard’ in Greek, aptly describes their most characteristic feature of fused bony plates covering their backs and sides to provide protection from predators. Built like giant moving tanks, these dinosaurs give a fascinating silhouette to contrast their less-armored peers.

The Fossil Record of Ankylosaurs

Among the original three dinosaurs named by Richard Owen in 1842, Hylaeosaurus was the first Ankylosaur discovered and named. It was found in 1832 in the United Kingdom by Gideon Mantell. Later in 1877, renowned paleontologist Othniel Charles Marsh placed all Ankylosaurs within the Stegosaur group as the ‘armored dinosaurs’.

This group still exists today as Thyreophora, but Ankylosaurs were split off from Stegosaurs in 1923 by Henry Fairfield Osborn due to their differences in armor modifications. For this new group he chose the name Ankylosauria, meaning ‘fused lizards’ in Greek, to represent the hard, fused osteoderms that formed their armor. 

Skeleton of Ankylosaurus, showcasing its sturdy frame with characteristic bony armor and clubbed tail, displayed in a museum. This Late Cretaceous herbivorous dinosaur is known for its defensive adaptations against predators.
Gary Todd from Xinzheng, China, CC0, via Wikimedia Commons

The earliest Ankylosaur was recently found in the Middle Jurassic of Africa but is still not well understood. Most of the early evolution of Ankylosaurs took place in the Late Jurassic of China. These dinosaurs survived until the mass extinction of dinosaurs in the Late Cretaceous, by which time they had spread all over the globe.

Unfortunately, the early records of Ankylosaurs are not well-known due to a lack of fossils. The few fossils that have been found are poorly preserved or only fragments of skeletons. This makes it difficult to determine how they evolved and from what group, but paleontologists believe their close relationship with Stegosaurs may hold clues to a shared ancestry. 

Paleontologists began truly studying Ankylosaur fossils in the 1800s. However, long before that, Native Americans had been uncovering, transporting, and using fossils from Ankylosaurs and other dinosaurs for years. These fossils were used for anything from magical rituals to toothache medicine. Moreover, Native Americans would later help American paleontologists find the fossil sites of these bones to study them.

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Evolutionary Relationships

Dinosaurs are split into two main groups—Saurischians (lizard-hipped) and Ornithischians (bird-hipped). Ankylosaurs are Ornithischians, meaning their pubic bones are oriented backwards like modern birds. Other Ornithischian relatives include Ceratopsians, Pachycephalosaurs, and the Ankylosaur cousins—Stegosaurs. 

Ankylosaurs and Stegosaurs can be grouped together into Thyreophora, a name from Greek that means ‘shield bearers’ and reflects their unique armor adaptations. This armor comes in the form of spikes, plates, clubs, and thick osteoderms or scutes covering the body. Stegosaurs modified this armor into protrusions like plates and spikes to ward off predators whereas Ankylosaurs fused this armor into a shield-like covering and clubbed tails.

Illustration of Ankylosaurus magniventris, a heavily armored herbivorous dinosaur, walking through a forest. Known for its large, bony plates and clubbed tail, this Late Cretaceous species used its physical defenses to protect against predators.
LadyofHats, Public domain, via Wikimedia Commons

There is another split within Ankylosaurs between Ankylosaurids and Nodosaurids. The main difference between these two groups are their characteristic tails. Ankylosaurids have the typical tail modifications and clubs we expect an Ankylosaur to have, but Nodosaurids retain a flexible tail tip and lack any clubs. So far, Ankylosaurids are restricted entirely to the North Hemisphere and all southern Ankylosaurs are Nodosaurids. Nodosaurids are the older, more primitive forms of Ankylosaurs and the more evolved species belong to the Ankylosaurids.

Ankylosaur Anatomy in Detail

Whether Nodosaurid or Ankylosaurid, all Ankylosaurs are heavily built, quadrupedal animals that stay low to the ground and graze or browse on low-lying vegetation. Their teeth are leaf-shaped to help them process tough vegetation. It is also possible that, like modern ruminants, they had some sort of extra fermentation or longer digestion process in their gut. This would have given them an advantage over contemporary herbivores by allowing them to eat lower-quality and tougher vegetation that competitors would have had to skip over. 

Scale comparison showing the size of Ankylosaurus magniventris next to a human. Ankylosaurus, a Late Cretaceous herbivore, measured about 6 meters in length and was heavily armored with bony plates and a clubbed tail for defense.
Matthew Martyniuk, CC BY-SA 4.0, via Wikimedia Commons

These armored dinosaurs are often described as tanks. They were medium-to-large dinosaurs that would have been heavy for their size due to their armor modifications. They were covered in hardened scales on the dorsal side of their body with especially tough protection around their necks.

This made them slow-moving, lumbering creatures in comparison to other herbivores of the same size. The largest Ankylosaur was Ankylosaurus, with a length of 20.0-26.0 feet long and a weight of 5.3-8.8 tons. The smallest Ankylosaur, Liaoningosaurus, is also one of the oldest Ankylosaur fossils. However, it is only known from juvenile specimens that may belong to a larger species such as Chuanqilong.

The potential adult size of these juveniles specimens is difficult to interpret. However, the current largest juvenile is only approximately 1.5 feet long. Furthermore, it is possible that these tiny Ankylosaurs had become turtle-like piscivores. This is based on one specimen being found associated with fish fossils near its stomach.

Illustration of Ankylosaurus magniventris, a heavily armored herbivorous dinosaur from the Late Cretaceous period. The Ankylosaurus is depicted with its characteristic bony plates and spikes, as well as its distinctive clubbed tail used for defense.
Ankylosaurus artwork by Melody Thomas, copyright ©

Flails for Tails

While the earliest Ankylosaurs were all armored, they did not all have the distinctive tail club we have come to associate with this group. The earliest Ankylosaurs from the Jurassic had flexible tails, which had become stiff and fused by the Early Cretaceous. These fused tail tips form the handle of the club.

By the Late Cretaceous, special osteoderms on the tips of the tail had formed and fused to form the different clubs used as weapons by Ankylosaurs. Other dinosaurs, such as the Sauropod Shunosaurus, formed tail clubs but even non-dinosaurs like glyptodonts or some turtles had them.

The obvious use for these heavy clubs is as weapons, like flails or maces. One study found that Ankylosaurs were capable of swinging their tails with enough force to break bones on impact. However, it is also possible that the clubs were used for intraspecies competition for mates where males competed with each other for females.

Ankylosaurus Games

If you want to test your knowledge about the species Ankylosaurus, here is a fun quiz you can play. Don’t worry if you don’t get all questions right, it is a learning opportunity! Have fun!

Don’t forget to try our other games as well!

Interesting Points about Ankylosaurs

Where did they live?

Ankylosaurs have an excellent fossil record in the northern hemisphere. However, very few fossils have been found on southern continents. The first Antarctic Ankylosaur, Antarctopelta, was found in 1986. Moreover, it was the first dinosaur to be found in Antarctica at all. Australian Ankylosaurs were all grouped into the genus Minmi until 2015 separated them into two genera—Minmi and Kunbarrasaurus. The first and only Ankylosaur from South America was Stegouros, found in 2015 in Chile. It has its own unique, flat tail modifications. Africa also has only one Ankylosaur, Spicomellus, which was found very recently in 2021 in Morocco. It is the earliest known Ankylosaur and one of the ancestral species of the group.


What does the name mean?

The name comes from the Greek words ‘ankylos’ and ‘sauros’ and means ‘fused lizard’.

Where have these fossils been found?

They have been found on every continent. However, they are very rare to find in Africa, Antarctica, Australia, and South America.

What did they eat?

Ankylosaurs had small, leaf-shaped teeth for browsing on low-growing plants.

What did they use their tails for?

Their clubbed tails were used for defense and may have been part of mating rituals or other social displays.

Did all ankylosaurs have a clubbed tail?

No, only Ankylosaurids have clubbed tails. Nodosaurids relied only on body armor and spikes for defense and had flexible tails.


Article last fact checked:Joey Arboleda, 06-09-2023

Featured Image Credit: Emily Willoughby, CC BY-SA 3.0, via Wikimedia Commons