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Ankylosauridae (/ ˌ æ ŋ k ɪ l oʊ ˈ s ɔː r ɪ d iː /) is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event . [ 1 ]
Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name. Ankylosaurus is a member of the family Ankylosauridae, and its closest relatives appear to be Anodontosaurus and Euoplocephalus.
The two main families of ankylosaurians, Nodosauridae and Ankylosauridae are primarily known from the Northern Hemisphere (North America, Europe and Asia), but the more basal Parankylosauria are known from southern Gondwana (South America, Australia and Antarctica) during the Cretaceous.
The type and only species, Akainacephalus johnsoni, is known from the most complete ankylosaur specimen ever discovered from southern Laramidia, including a complete skull, tail club, a number of osteoderms, limb elements and part of its pelvis, among other remains.
The skull measures about 38 cm (380 mm) in length, with a near width of 25 cm (9.8 in), missing the lower jaws. Unlike other Asian ankylosaurs, in Tsagantegia the caputegulae ( cranial ornamentation) are not subdivided into a mosaic of polygons but are amorphous and flattened; they show some degree of symmetry.
The largest known skull, that of specimen AMNH 5403, has a length of 411 millimetres and a width of 478 millimetres. Most skull elements are completely fused and two skull openings normally present with dinosaurs, the antorbital fenestra and the upper temporal fenestra, have closed. The skull has nineteen to twenty-four teeth in each upper jaw.
The 2007 specimen skulls have brought new insights into the neurocranial capacities and dietary habits of Talarurus, specifically the specimen MPC-D 100/1354, which is a well-preserved, almost complete cranium. MPC-D 100/1354 was described in extensive detail along with a very complete skull of Tarchia by Paulina
Saichania skull cast mounted on the skeleton of cf. Pinacosaurus in Mongolia. The skull had very complex air passages. The main entrance of each external nostril consisted of a roomy "nasal vestibule". In each vestibule again two smaller entrances were present, vertically arranged.