Ankylosauridae (/ˌæŋkɪloʊˈsɔːrɪdiː/) are a family of the armored dinosaurs within Ankylosauria, and sister group to Nodosauridae. Ankylosaurids appeared 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.
Ankylosauridae is exclusively known from the northern hemisphere, with specimens found in western North America, Europe, and East Asia. The first discoveries within this family were of the genus Ankylosaurus, by Peter Kaiser and Barnum Brown in Montana in 1906. Brown went on to name Ankylosauridae and the subfamily Ankylosaurinae in 1908.
|Mounted skeleton of Scolosaurus thronus, Royal Tyrrell Museum of Palaeontology|
Syrmosauridae Maleev, 1952
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. Only two collars of armour plates can be found on the neck, as opposed to the sister group, nodosaurids, which have three. Nodosauridae and Ankylosauridae also share the unique attribute of abundant structural fibres in both primary and secondary bone. Ankylosaurids also have an S-shaped narial passage.
The most distinguishing feature of ankylosaurids is the presence of a tail club. It is made out of modified interlocking distal caudal vertebrae and enlarged, bulbous osteoderms. The “handle” of the tail club involves the vertebrae, and requires elongated prezygapophyses to overlap at least half of the preceding vertebral centrum length. These distal caudal vertebrae also lack transverse processes and neural spines, and therefore tend to be longer than they are wide; the reverse is true for proximal caudal vertebrae. Derived ankylosaurids possess a fusion of posterior dorsal, sacral, and sometimes anterior caudal vertebrae, which forms a singular structure called a “synsacrum complex”. There is a complete fusion between centra, neural arches, zygapophyses, and sometimes neural spines.
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.
Barnum Brown and Peter Kaiser discovered the first ankylosaurid genus, Ankylosaurus, in 1906 in the Hell Creek Beds in Montana. The fossil material they found was a portion of the skull, two teeth, some vertebrae, a distorted scapula, ribs and more than thirty osteoderms. 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.
It has previously been interpreted that variation in ankylosaurid tail club shape is due to sexual dimorphism, which assumes that tail club morphology has a sex-linked intraspecific function. This is possible if the tail club was used for agonistic behaviour. However, a sexual dimorphism theory would predict roughly equal numbers of individuals with two distinct sizes of tail clubs. Obvious sexual dimorphism has not been documented, but if the clubs of one sex are much larger, then there would be a bias for preservation and discovery towards that sex.
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 Panaplosaurus. Ankylosaurs not known to possess a tail club were included in Kenneth Carpenter’s 2001 phylogeny of Ankylosauridae.
In a study done in 2004 by Vickaryous et al., Gargoyleosaurus, Gastonia, and Minmi were recorded as basal ankylosaurids, with the rest of the ankylosaurids filled out with Gobisaurus, Shamosaurus, and ankylosaurines from China, Mongolia, and North America.
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.
Most recently, Arbour and Currie have presented a phylogenetic analysis of Ankylosauridae consisting of Gastonia, Cedarpelta, Chuanqilong, other basal ankylosaurids, and a number of derived ankylosaurids. Their phylogeny includes some uncertain phylogenetic relationships, between Ankylosaurus, Anodontosaurus, Scolosaurus, and Ziapelta.
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.
Restoration of Euoplocephalus forelimbs demonstrate similarities to crocodilian forelimb musculature. 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.
Several muscles in the posterior of ankylosaurids (dorsalis caudae, ilio-caudalis, coccygeo-femoralis brevis, coccygeo-femoralis longus, ilio-tibialis, and ischio caudalis) were used for motion of the tail and tail club. Ankylosaurids tend to have horizontal rather than an obliquely vertical orientation of zygapophyseal articulations in the free caudal vertebrae of the tail. This arrangement is most effective for side-to-side rather than vertical mobility. The absence of musculature to elevate the tail, and this orientation of zygapophyses suggest that the tail and its club swept parallel to and slightly above the ground.
It is difficult to establish the geographical origin of Ankylosauridae at present. There is a mix of basal ankylosaurids from both North America and Asia, which carries on through accepted cladistic analyses. It appears that in the mid-Cretaceous, Asian nodosaurids were replaced by ankylosaurine ankylosaurids. Some researchers postulate that Ankylosaurines migrated into North America from Asia between the Albian and Campanian, where they diversified into a clade of ankylosaurines characterized by arched snouts and flat cranial bone plates (caputegulae). There is no evidence for ankylosaurids in Gondwana.
Within Ankylosauridae there is much individual and interspecific variation in expression of armour. However, the most researched aspect of ankylosaurid armour is the tail club. There has been substantial ontogenetic and individual variability found in the morphology of this feature. There have been at least 16 caudal vertebrae included in the handle of the tail club of Pinacosaurus grangeri, and Euoplocephalus has an estimated 9 – 11 coossified caudals.
Variations in tail knob shape, thickness, and length are attributed to individual variation, taxonomy, or representation of different growth phases. There are difficulties with this last aspect, however, in that known clubs do not conform to a single growth series, yet some differences must be ontogenetic and allometric.
Most ankylosaurid teeth were leaf-shaped, implying a mainly herbivorous diet. Their teeth could be smooth or fluted, or may differ on labial and lingual surfaces. Euoplocephalus tutus possess ridges and grooves on their teeth that have no relation to their marginal cusps. With their downward-facing neck and head, it is plausible for ankylosaurids to feed in a grazing pattern.
Non-herbivorous habits have been implicated for some species, however. Pinacosaurus has been speculated as being an ant-eater-like long tongued insectivore, 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 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.
Ahshislepelta is a genus of herbivorous
ankylosaurine ankylosaurid dinosaur from Late Cretaceous (late Campanian stage) deposits of San Juan Basin, New Mexico, USA.
Ahshislepelta is known from the holotype SMP VP-1930, a closely associated and incomplete postcranial skeleton of an adult individual consisting of the shoulder girdle, a partial left forelimb, vertebrae and osteoderms. It was discovered in 2005 and collected between 2005 and 2009 from the Hunter Wash Member of the Kirtland Formation at the Ah-shi-sle-pah Wash locality. Ahshislepelta was first named by Michael E. Burns and Robert M. Sullivan in 2011 and the type species is Ahshislepelta minor. The generic name comes from the Ah-shi-sle-pah Wash locality, where the fossils were found, and pelta, "shield" in Greek. The specific name is derived from minor, "small" in Latin, in reference to its smaller adult size relative to other ankylosaurids from North America. Humerus length is thirty-one centimetres.Ahshislepelta was assigned to the Ankylosauridae and more precisely to the Ankylosaurinae.Ankylosauria
Ankylosauria is a group of mainly herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the early Jurassic Period, and persisted until the end of the Cretaceous Period. They have been found on every continent. The first dinosaur ever discovered in Antarctica was the ankylosaurian Antarctopelta, fossils of which were recovered from Ross Island in 1986.
Ankylosauria was first named by Henry Fairfield Osborn in 1923. In the Linnaean classification system, the group is usually considered either a suborder or an infraorder. It is contained within the group Thyreophora, which also includes the stegosaurs, armored dinosaurs known for their combination of plates and spikes.Ankylosaurinae
Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as Ankylosaurus, Pinacosaurus, Euoplocephalus, and Saichania.Ankylosaurus
Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; the only species in the genus is A. magniventris. The genus name means "fused lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
Possibly the largest-known ankylosaurid, Ankylosaurus is estimated to have been between 6 and 8 metres (20 and 26 ft) long and to have weighed between 4.8 and 8 tonnes (4.7 and 7.9 long tons). It was quadrupedal, with a broad, robust body. It had a wide, low skull, with two horns pointing backward from the back of the head, and two horns below these that pointed backward and down. Unlike other ankylosaurs, its nostrils faced sideways rather than towards the front. The front part of the jaws was covered in a beak, with rows of small, leaf-shaped teeth farther behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. 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. Ankylosaurus is thought to have been a slow-moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or may have played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. Ankylosaurus has been found in the Hell Creek, Lance, Scollard, Frenchman, and Ferris formations, but appears to have been rare in its environment. Although it lived alongside a nodosaurid ankylosaur, their ranges and ecological niches do not appear to have overlapped, and Ankylosaurus may have inhabited upland areas. Ankylosaurus also lived alongside dinosaurs such as Tyrannosaurus, Triceratops, and Edmontosaurus.Crichtonpelta
Crichtonpelta is a genus of extinct herbivorous ankylosaurid dinosaur from the Cretaceous of China.In 2007, Lü Junchang, Ji Qiang, Gao Yubo and Li Zhixin named and described a second species of Crichtonsaurus: Crichtonsaurus benxiensis. The specific name refers to the Benxi Geological Museum.The holotype, BXGMV0012, is a skull found near Beipiao in a layer of the Sunjiawan Formation probably dating from the Albian. Specimen BXGMV0012-1, a skeleton lacking the skull, discovered in the same quarry as the holotype, was referred to the species. Furthermore, a skeleton with skull, displayed by the Sihetun Fossil Museum as a Crichtonsaurus bohlini specimen, was in 2014 referred to Crichtonpelta. In 2017, a fourth specimen was described, from the same quarry as the holotype, G20090034, consisting of a skull lacking the front snout.In 2014, Victoria Arbour concluded that Crichtonsaurus were a nomen dubium. Therefore, she named a separate genus for its second species: Crichtonpelta. The generic name combines a reference to Michael Crichton, the author of Jurassic Park, with a Greek πέλτη, peltè, "small shield". At the time this was an invalid nomen ex dissertatione. However, in 2015, Crichtonpelta was validly named by Arbour and Philip John Currie. The type species is Crichtonsaurus benxiensis; the combinatio nova is Crichtonpelta benxiensis. There was a possibility that, though Crichtonsaurus bohlini was a nomen dubium, its fossil material in fact belonged to Crichtonpelta. Arbour however, noted clear differences in the scapula and humerus between BXGMV0012-1 and LPM 101, a specimen previously referred to Crichtonsaurus bohlini: the scapula of the former has a tab-like acromion and its humerus a much longer deltopectoral crest.Arbour established several distinguishing traits. One of these was an autapomorphy, unique derived trait: the apex of the (quadrato)jugal, or cheek, horn, is pointing upwards. Also a unique combination of in themselves not unique traits is present. The upper snout armour forms an amorphous mass, not clearly separated into distinctive tiles. The jugal bone is deeper than that of Pinacosaurus. The skull roof is not notched at the lacrimal bone as in Pinacosaurus grangeri. The squamosal horns are shorter than those of Pinacosaurus mephistocephalus. However, these horns are longer and more pointed than those of Gobisaurus or Shamosaurus. The point of the cheek horn is located on the rear edge. The transverse crest on the top of the rear skull has two points.The holotype of Crichtonpelta is somewhat larger than Crichtonsaurus, itself about three to four metres long. It is uncertain whether Crichtonpelta already possessed a tail club.Crichtonpelta was, within the Ankylosauridae, placed in the Ankylosaurinae, in a basal position. If correct, this makes it the oldest known ankylosaurine.Emausaurus
Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Germany. The type and only species, Emausaurus ernsti, was formalized by Harmut Haubold in 1990. The generic name is composed of an acronym of Ernst Moritz Arndt University of Greifswald and Greek sauros/σαυρος (lizard). The specific name is derived from the name of geologist Werner Ernst, who found the fossil, holotype SGWG 85, in the summer of 1963 at a loampit near Grimmen, in strata dating from the Toarcian.Gobisaurus
Gobisaurus is an extinct genus of herbivorous basal ankylosaurid ankylosaur from the Upper Cretaceous of China (Nei Mongol Zizhiqu). The genus is monotypic, containing only the species Gobisaurus domoculus.Invictarx
Invictarx is a genus of herbivorous nodosaurid dinosaur from New Mexico dating from the early Campanian epoch of the Late Cretaceous.Jinyunpelta
Jinyunpelta ("Jinyun shield") is a genus of herbivorous ankylosaurine thyreophoran dinosaur from the Cretaceous Liangtoutang Formation of Jinyun County, Zhejiang, China; it has one species, the type species J. sinensis. This species is the basalmost ankylosaur known to have had a proper tail club.Minmi paravertebra
Minmi is a genus of small herbivorous ankylosaurian dinosaur that lived during the early Cretaceous Period of Australia, about 119 to 113 million years ago.Nodosaurus
Nodosaurus (meaning "knobbed lizard") is a genus of herbivorous ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found in North America.Saichania
Saichania (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China.
The first fossils of Saichania were found in the early 1970s in Mongolia. In 1977 the type species Saichania chulsanensis was named. The description of this species has been based on limited fossil material; especially the rear of the animal is not well known.
Saichania was over five metres long and weighed over two tonnes. It was more robustly built than other members of the Ankylosauridae. Neck vertebrae, shoulder girdle, ribs and breast bones were fused or firmly connected. Its body was flat and low-slung, standing on four short legs. The forelimbs were very powerful. The head was protected by bulbous armour tiles. It could defend itself against predators like Tarbosaurus with a tail-club. On the torso keeled osteoderms were present. Saichania bit off plants in its desert habitat with a horny beak and processed them in its wide hindgut.Shamosaurus
Shamosaurus is an extinct genus of herbivorous basal ankylosaurid ankylosaur from Early Cretaceous (Aptian to Albian stage) deposits of Höövör, Mongolia.Shanxia
Shanxia is a genus of ankylosaurid dinosaur that lived during the upper Cretaceous Period. Its fossils were recovered and named after the Shanxi Province of China, and it is known only from scrappy remains found in river deposits. Based on the relative lengths of the femur and other leg bones, it probably reached a length of around 3.6 metres (12 ft).
Barrett et al. (1998) distinguished Shanxia from other ankylosaurs in having long and flattened triangle-shaped horns that project backward from the squamosal bones on either side of the rear portion of its skull at an angle of 145 degrees. However, Sullivan (1999) considered Shanxia a nomen dubium, possibly synonymous with the related ankylosaurid Tianzhenosaurus, arguing that the unique shape of the squamosal horns could be a product of individual variation, but Upchurch and Barrett (2000) reaffirmed the validity of Shanxia. In their systematic review of ankylosaurids, Arbour and Currie (2015) treated Shanxia as a junior synonym of Saichania.Silvisaurus
Silvisaurus, from the Latin silva "woodland" and Greek sauros "lizard", is a nodosaurid ankylosaur from the middle Cretaceous period.Tatankacephalus
Tatankacephalus is a basal genus of nodosaurid dinosaur that lived during the Early Cretaceous.
Its fossil has been collected from the Cloverly Formation (Aptian-Albian) of central Montana, USA, during 1996, 1997 and 1998, in the region of the Middle Dome in Wheatland County. The type species is T. cooneyorum, described by William L. Parsons and Kirsten Parsons in 2009. The genus name is derived from Oglala tatanka, "bison" and Greek kephale, "head", in reference to the rounded head form. The specific name honours the family of John Patrick Cooney. The holotype is MOR 1073, a partial skull with an estimated total undamaged length of 32 centimetres, lacking the lower jaws. Also some ribs, osteoderms and a tooth have been recovered. The front of the snout is missing. The specimen is that of an adult individual.According to the authors the fossil has not been deformed by compression, allowing to distinguish it from Sauropelta edwardsorum, another akylosaurian found in the same formation. The head is domed and the eye-sockets are round. A large bone ridge runs transversely across the back of the head. The fossil skull itself no longer had any teeth in it but a single tooth was found, lacking the cingulum. Two osteoderms were found; one was intact. It has a length of 137 and a width of 115 millimetres. It is hollow and conical.A cladistic analysis showed that Tatankacephalus was a basal member of the Ankylosauridae and relatively closely related to Gastonia. Basal traits include the retention of premaxillary teeth in the front of the upper jaws and a skull opening, the lateral temporal fenestra, that was not covered by the skull armour. A new cladistic analysis performed by Thompson et al., 2011 suggests that Tatankacephalus is a basal nodosaurid.Tatisaurus
Tatisaurus is a genus of ornithischian dinosaur from the Early Jurassic from the Lower Lufeng Formation in Yunnan Province in China. Little is known as the remains are fragmentary.Tsagantegia
Tsagantegia (; meaning "of Tsagan-Teg"; Tumanova, 1993) is a genus of medium-sized ankylosaurid dinosaur from the Upper Cretaceous Mongolia, during the Cenomanian stage.
The holotype specimen (GI SPS N 700/17), a complete skull, was recovered from the Bayan Shireh Formation (Cenomanian-Santonian), at the Tsagan-Teg ("White Mountain") locality, Dzun-Bayan, in the southeastern Gobi Desert, Mongolia. The genus is monotypic, including only the type species, T. longicranialis.Zaraapelta
Zaraapelta is an extinct genus of herbivorous ankylosaurid thyreophoran dinosaur from the Late Cretaceous of Mongolia. The type species is Zaraapelta nomadis, named and described by Arbour et alii in 2014. Zaraapelta is known from a single skull from the Barun Goyot Formation. It was found to be closest to Tarchia in the phylogenetic analysis within its description.