Ankylosaurus

Ankylosaurus Temporal range: Late Cretaceous
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Thyreophora
Infraorder:	Ankylosauria
Family:	Ankylosauridae
Genus:	Ankylosaurus Brown, 1908

Ankylosaurus (pronounced /æŋˈkɪl.əˌsɔː.ɹəs/ or ang-KI-lo-SAWR-us; "stiffened lizard") is a genus of ankylosaurid ankylosaurian dinosaur, containing only a single species, A. magniventris, from the latest Cretaceous of western North America. This was the last, largest and most famous of the armored dinosaurs, known for its heavily-armored body and for its tail club.

Discovery and species

Ankylosaurus was named by American paleontologist Barnum Brown, in 1908. The generic name is derived from the Greek words αγκυλος (ankylos; "barbed" or "hooked") and σαυρος (sauros; "lizard"). Brown intended this name to refer to the fusion of many bones in the skull and body, so the name's meaning is actually "stiffened lizard" or "fused lizard," used in the same sense as the medical term ankylosis, which really comes from the other meaning of the Ancient Greek word (i.e. bent or crooked). The type species is named A. magniventris, from the Latin words magnus ("great") and venter ("belly"), referring to the great width of the animal's body.

The holotype or original specimen of A. magniventris was found in the U.S. state of Montana, in 1906. This consisted of the top of the skull and a partial skeleton. However, remains of Ankylosaurus had been found as early as 1900, when armor plates were found in a Wyoming quarry and mistakenly assigned to Dynamosaurus (now known as Tyrannosaurus), which had been discovered in the same quarry. The tail club was unknown until the 1910 discovery of a partial skeleton in Alberta, Canada, which also included the most completely known skull. All three of the above specimens were collected by Barnum Brown and are now housed at the American Museum of Natural History in New York City. The largest known skull of this animal was collected in Alberta by Charles M. Sternberg, in 1947 and is now housed at the Canadian Museum of Nature. Many other isolated bones, armor plates, and teeth have been found throughout the years.

Ankylosaurus species

• A. magniventris

Classification

Ankylosaurus is the type genus of both the family Ankylosauridae and the larger taxon Ankylosauria, which also contains the nodosaurids. Within the ankylosaurids, Ankylosaurus and Euoplocephalus are often thought to be sister taxa. Other analyses have found these genera in different positions.

Paleobiology

A full-grown Ankylosaurus was a very large animal, compared to the majority of modern land animals. The largest known specimen has an estimated total body length of 6.25 meters (20 ft.), a maximum width of 1.5 meters (5 ft.) and a height of about 1.7 meters (67 in.) at the hip. Other estimates range up to 9 meters (30 ft.) in length. Overall, the body shape was low-slung and very wide. Ankylosaurus was quadrupedal, with short and powerful legs. The rear legs were longer than the forelegs. Although the feet have not been completely preserved in any known specimen, comparisons with other ankylosaurs suggest this animal probably had five toes on each foot. Like other ankylosaurs, Ankylosaurus was herbivorous. Skull bones were extremely thick, leaving only a small brain cavity. The skull was relatively low, and triangular in shape. The known fossil skulls are wider than they are long, with the largest 64.5 centimeters (25 in.) long but 74.5 centmeters (29 in.) wide at the back end.

Armor

The most obvious feature of Ankylosaurus would have been its armor, consisting of massive knobs and plates of bone, known as osteoderms, embedded in the skin. Osteoderms are also found in the skin of crocodiles, armadillos, and some lizards. The bone was probably overlain by a tough, thorny layer of keratin. These osteoderms range greatly in size, from wide, flat plates to small, round nodules. The plates were aligned in regular horizontal rows down the animal's neck, back and tail, with the many smaller nodules protecting the areas between the large plates. Compared to the closely related but older Euoplocephalus, the plates of Ankylosaurus were much smoother and did not show the high keels found on the armor of Edmontonia, a more distant relative which lived in the same time band and region. Tough, rounded scales protected the top of the skull, while four large pyramidal horns projected outwards from the rear corners of the skull.

Tail club

The famous tail club was also composed of several large plates, which were fused to the last few tail vertebrae. It seems to have been used as a more active defensive weapon. It was very heavy and supported by the last seven tail vertebrae, which interlock to form a stiff rod at the base of the club. Thick tendons have been preserved, which attach to these vertebrae. These tendons were partially ossified (or bony) and were not very elastic, allowing great force to be transmitted to the end of the tail when it was swung. Such a weapon would have a devastating impact and might have broken the bones of an assailant.

Other proposed uses for the club have been largely discredited, such as acting as a decoy for the head.

Environment

Ankylosaurus existed from 68 to 65 million years ago, in the latest Maastrichtian stage of the Late Cretaceous Period, and was one of the last dinosaurs before the Cretaceous-Tertiary extinction event. The holotype is from the Hell Creek Formation of Montana, while other specimens have been found in the Lance Formation in the United States and the Scollard Formation in Canada, all of which belong to the very end of the Cretaceous.

The Hell Creek in particular is composed largely of mudstone, indicating a floodplain environment. Fossils of Ankylosaurus are very rare in these sediments, especially compared to the super-abundant Triceratops and Edmontosaurus, which make up most of the large herbivore fauna.

Another ankylosaur, the nodosaurid Edmontonia, is also found in the same formations. However, the two species seemed to be separated both geographically and ecologically. Ankylosaurus seems to be limited to the upland regions, away from the coast of the ancient Western Interior Seaway and has a wide muzzle, which may have been well-suited for non-selective grazing. Edmontonia seems to have lived in the lowlands, closer to the coast and had a narrower muzzle, which may have been better suited to a more selective diet.

In popular culture

The monster Anguirus, as seen in Godzilla vs. Gigan from 1972

File:Ecran ankylosaurus.jpg

A reconstruction of Ankylosaurus as shown on the BBC television program Walking with Dinosaurs.

Due to its easily recognizable appearance and the intense public interest in dinosaurs, Ankylosaurus has been a feature of worldwide popular culture for many years. For instance, a life-sized reconstruction of Ankylosaurus was featured at the 1964 World's Fair in New York City.

Several motion picture series have featured ankylosaurs. Starting with Godzilla Raids Again in 1955, several films in the Japanese Godzilla series featured Anguirus, a creature similar to a gigantic Ankylosaurus, at first an enemy but later a loyal ally to Godzilla. Beginning in 1988, Ankylosaurus also has brief cameos in several movies in the Land Before Time series, though never a large part. Ankylosaurus can also be seen grazing alongside several other species in the 2001 film Jurassic Park III.

This dinosaur has also made its way onto television. The sixth and final episode of Walking With Dinosaurs, a 1999 miniseries produced by the BBC, featured an Ankylosaurus, which hammered a Tyrannosaurus with its tail club, killing the larger predator. Ankylosaurus appears in The Truth About Killer Dinosaurs, winning an animated fight with a Velociraptor.