Ankylosauridae

Ankylosauridae is a family of armored dinosaurs that evolved 125 million years ago (along with another family of ankylosaurs, the Nodosauridae) and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event. Ankylosaurids have been found in western North America, Europe and East Asia, though good specimens are rare; most are known only from bone fragments.

Features
The heavy armour, forming a veritable shell on the backs of ankylosaurids and their clubbed tails, makes them look superficially similar to the mammalian glyptodonts (and to a lesser degree to the giant meiolaniid turtles of Australia).

Their heavily armoured heads formed a toothless beak at the front (comparable to modern birds), though the sides of the mouth and the lower jaw did bear small teeth, deeply inset from the jaw.

Armour
Ankylosaurids usually had a thick armour plating of fused bone, often interspersed with a variety of spikes and lumps. Ankylosaurids were so heavily armored that some advanced species even had armoured eyelids.

Tail
Many ankylosaurids also had an enlarged mass of bone forming a "club" on the end of their tails, made of two enlarged bone lumps. This tail club has traditionally been used to separate ankylosaurids from their close relatives the nodosaurids, although the most primitive ankylosaurids (polocanthines) also lacked tail clubs.

Taxonomy
Two subfamilies are generally recognised. In one paper, Ken Carpenter raised Polacanthinae to family status, which is not recognised by other paleontologists.

The Polacanthinae are late Jurassic to early Cretaceous in age and Kirkland observed they appeared to become extinct about the same time a land bridge opened between Asia and North America.

Definitions (after Sereno, 2005) :
 * Ankylosauridae : The most inclusive clade containing Ankylosaurus magniventris but not Panoplosaurus mirus.
 * Ankylosaurinae : The most inclusive clade containing Ankylosaurus magniventris but not Gargoyleosaurus parkpinorum, Minmi paravertebra, or Shamosaurus scutatus.

The following uses the ranks from Benton 2004:
 * Infraorder Ankylosauria
 * Family Ankylosauridae
 * Aletopelta
 * Cedarpelta
 * Gobisaurus
 * Minotaurasaurus
 * Shamosaurus
 * Subfamily Ankylosaurinae
 * Ankylosaurus
 * Euoplocephalus
 * Nodocephalosaurus
 * Pinacosaurus
 * Saichania
 * Shanxia
 * Talarurus
 * Tarchia
 * Tianzhenosaurus
 * Tsagantegia
 * Subfamily Polacanthinae
 * Gargoyleosaurus
 * Gastonia
 * Hoplitosaurus
 * Hylaeosaurus
 * Mymoorapelta
 * Polacanthus