Dinosaurs A to Z
Ankylosauridae

Ankylosaurus magniventris ang-KIE-loh-SOR-us

"Fused lizard"

Ankylosaurus silhouette
You 1.8 m (5.9 ft) tall
Ankylosaurus 7 m (23 ft) long
as long as 4 people standing fingertip to fingertip
silhouette · Itai Fein (CC0) via PhyloPic
Length
7 m (23 ft) — About 7 m long, ~4 tonnes — a living tank with a club-tipped tail.
Period
Late Cretaceous (68–66 Mya)
Place
North America · Western United States · Alberta, Canada
Food
Herbivore — Low-growing tough plants — the wide gut housed bacteria that broke down fibrous material.
Clade
Ankylosauridae Dinosauria Ornithischia Thyreophora Ankylosauria Club-tailed armored herbivores.

An armored, broad-bodied browser with a bony tail club, among the last non-avian dinosaurs.

Ankylosaurus was a heavily armored herbivore that lived alongside Tyrannosaurus rex right up until the asteroid impact. Bony plates covered its body from the eyes to the tip of the tail, and the tail ended in a huge bony club that could swing with enough force to break the leg of a T. rex.

More about Ankylosaurus

Discovery

Named by Barnum Brown · 1908 · Hell Creek Formation, near Gilbert Creek, Montana

An American Museum of Natural History expedition led by Barnum Brown found the type specimen (AMNH 5895) in 1906, with collector Peter Kaisen locating the remains. Brown scientifically described the animal in 1908 from a partial skull, teeth, vertebrae, ribs, and more than thirty armor plates.

The genus name comes from Greek and means "fused", "bent", or "crooked" lizard, referring to the medical term ankylosis (the stiffness produced by bones fusing in the skull and body). The species name, magniventris, means "great belly", referring to the animal's wide body.

Portrait of Barnum Brown
Barnum Brown American paleontologist who discovered and named Ankylosaurus, and made it the type genus of a new family, Ankylosauridae.
What was the tail club actually for?
The tail club is thought to have been used in defense against predators or in intraspecific combat (fights between members of the same species). The text presents both as possibilities rather than a settled answer.
Why did Ankylosaurus have sinuses and nasal chambers in its snout?
The function of the snout's sinuses and nasal chambers is uncertain. They may have helped with heat and water balance, or they may have played a role in vocalization.

What we know

  • Body almost completely covered by armor — even the eyelids were bony.
  • Tail ended in a fused mass of bone — a club weighing around 30 kg.
  • Lived alongside T. rex, Triceratops, and Edmontosaurus in the final million years of the Cretaceous.
  • Wide barrel-shaped body to house a long fermenting digestive tract.

What we guess

  • Tail club swing speed and force — biomechanical models suggest enough to fracture bone.
  • Whether it could outright defeat a T. rex or just discourage attack.
  • Whether it lived in herds or solo, since most specimens are isolated.