Ankylosauridae

'' tail reconstruction, showing terms used for parts of ankylosaurid tails Ankylosaurids are stout, solidly built, armoured dinosaurs. They possess accessory ossifications on cranial bones that cover some skull openings and form wedge-shaped, horn-like structures. Along the ankylosaurid torso are scute rows, which are filled in with smaller ossicles to create a fused shield of armour. Ankylosaurids also have an S-shaped narial passage. The "handle" of the tail club involves the vertebrae, and requires elongated prezygapophyses to overlap at least half of the preceding vertebral centrum length. In 2017, Victoria M. Arbour and David C. Evans described a new genus of ankylosaurine that preserved extensive soft tissues along the body. This animal, named Zuul after its resemblance to the Ghostbusters monster, is also the first ankylosaur from the Judith River Formation. == History of study ==

'' Barnum Brown and Peter Kaisen discovered the first ankylosaurid genus, Ankylosaurus, in 1906 in the Hell Creek Beds in Montana. ==Phylogeny==

349 In 1978, W.P. Coombs, Jr. classified almost all valid species of Ankylosauria within either Nodosauridae or Ankylosauridae. This was a pivotal study and described many characters of ankylosaurs in the earliest phylogenetic analyses of the group. Later in 1998, Paul Sereno formally defined Ankylosauridae as all ankylosaurs more closely related to Ankylosaurus than to Panoplosaurus. Ankylosaurs not known to possess a tail club were included in Kenneth Carpenter's 2001 phylogeny of Ankylosauridae. Daniel Madzia and colleagues in 2021 formally defined Ankylosauridae in the PhyloCode as "the largest clade containing Ankylosaurus magniventris, but not Nodosaurus textilis". The basal subfamily Shamosaurinae is formally defined as "the largest clade containing Gobisaurus domoculus and Shamosaurus scutatus, but not Ankylosaurus magniventris". In 2012, Thompson et al. undertook an analysis of almost all known valid ankylosaurs and outgroup taxa at the time. They based their resulting phylogeny on characters representing cranial, post-cranial, and osteodermal anatomy, and details of synapomorphies for each recovered clade. This study placed Gargoyleosaurus and Gastonia within basal Nodosauridae, and put Cedarpelta and Liaoningosaurus as basal ankylosaurids. }} == Paleobiology ==

Posture and locomotion Ankylosaurids were likely very slow-moving animals. In all Ankylosauria, the fibula is more slender than the tibia, suggesting that the tibia carried most of the weight of the animal, while the fibula served as an area of muscular attachment. Hindlimb muscles of Euoplocephalus have been restored and the placement of several muscles inserting on the femur have very short moment arms. Muscles inserting on the tibia and fibula have longer moment arms. This pattern of retractor muscles points to an elephantine locomotion, consistent with columnar posture. The most well developed muscles in the pectoral region had more of a weight-bearing function than a rotational one. It has also been postulated that the carpals and metacarpals bear resemblance to those of tetrapods with fossorial (burrowing) habits. It appears that in the mid-Cretaceous, Asian nodosaurids were replaced by ankylosaurine ankylosaurids. Euoplocephalus tutus possess ridges and grooves on their teeth that have no relation to their marginal cusps. while Liaoningosaurus has been proposed to be a piscivore. Either would be exceptional evidence of carnivory among ornithischians. There are a few prevailing theories for ankylosaurid tail club function. The first is agonistic behaviour within a species. In most vertebrates, including dinosaurs, this behaviour is accompanied by structures for display or combat. Some researchers believe this phenomenon would have been implausible considering there is no modern tetrapod analogue that uses the tail for this purpose. These paleontologists instead propose that ankylosaurids made use of their broad, flat skull for head-butting between individuals. The second theory for tail club function is for defense against predators. It has been postulated that the club would be most effective against the metatarsals of an attacking theropod. The bones that form cranial ornamentation have physiological costs, and so would be inefficient to produce merely for protection against predation. The theory has therefore been posed that these wedge-shaped osteoderms could support a partly sexually selected interpretation. ==Timeline of genera==

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