Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.

They possess accessory ossifications on cranial bones that cover some skull openings and form wedge-shaped, horn-like structures.

[1] Nodosauridae and Ankylosauridae also share the unique attribute of abundant structural fibres in both primary and secondary bone.

[6] The "handle" of the tail club involves the vertebrae, and requires elongated prezygapophyses to overlap at least half of the preceding vertebral centrum length.

[6] Derived ankylosaurids possess a fusion of posterior dorsal, sacral, and sometimes anterior caudal vertebrae, which forms a singular structure called a "synsacrum complex".

[7] In 2017, Victoria M. Arbour and David C. Evans described a new genus of ankylosaurine that preserved extensive soft tissues along the body.

[8] Barnum Brown and Peter Kaisen discovered the first ankylosaurid genus, Ankylosaurus, in 1906 in the Hell Creek Beds in Montana.

[4] The fossil material they found was a portion of the skull, two teeth, some vertebrae, a distorted scapula, ribs and more than thirty osteoderms.

[4] Reconstruction of the specimen was initially met with skepticism by those who believed it to be at least very close to, or completely a part of the genus Stegopelta, and Brown himself placed it within the suborder Stegosauria.

However, a sexual dimorphism theory would predict roughly equal numbers of individuals with two distinct sizes of tail clubs.

[12] Daniel Madzia and colleagues in 2021 formally defined Ankylosauridae in the PhyloCode as "the largest clade containing Ankylosaurus magniventris, but not Nodosaurus textilis".

[13] The basal subfamily Shamosaurinae is formally defined as "the largest clade containing Gobisaurus domoculus and Shamosaurus scutatus, but not Ankylosaurus magniventris".

[15] They based their resulting phylogeny on characters representing cranial, post-cranial, and osteodermal anatomy, and details of synapomorphies for each recovered clade.

[15] Huayangosaurus taibaii Stegosaurus armatus Nodosauridae Minmi paravertebra Liaoningosaurus paradoxus Cedarpelta bilbeyhallorum Gobisaurus domoculus Shamosaurus scutatus Zhongyuansaurus luoyangensis Tsagantegia longicranialis Shanxia tianzhensis "Crichtonsaurus" benxiensis Dyoplosaurus acutosquameus Pinacosaurus mephistocephalus Ankylosaurus magniventris Euoplocephalus tutus Minotaurasaurus ramachandrani Pinacosaurus grangeri Nodocephalosaurus kirtlandensis Talarurus plicatospineus Tianzhenosaurus youngi Saichania chulsanensis Tarchia gigantea In 2016, Arbour and Currie have presented a phylogenetic analysis of Ankylosauridae consisting of Gastonia, Cedarpelta, Chuanqilong, other basal ankylosaurids, and a number of derived ankylosaurids.

[16] Lesothosaurus Scelidosaurus Stegosauria Minmi paravertebra Gargoyleosaurus More derived nodosaurids Gastonia Ahshislepelta Aletopelta Liaoningosaurus Cedarpelta Chuanqilong Gobisaurus Shamosaurus Crichtonpelta Tsagantegia "Zhejiangosaurus" Pinacosaurus grangeri Pinacosaurus mephistocephalus Saichania Tarchia Zaraapelta Dyoplosaurus Talarurus Nodocephalosaurus Ankylosaurus Anodontosaurus Euoplocephalus Scolosaurus Ziapelta Ankylosaurids were likely very slow-moving animals.

[17] Ankylosaurids tend to have horizontal rather than an obliquely vertical orientation of zygapophyseal articulations in the free caudal vertebrae of the tail.