Fossil range: Late Cretaceous
|An Ankylosaurus skull, profile view. This specimen is from the Edmonton Formation of Alberta.|
Ankylosaurus (pronounced /ˌæŋkɨlɵˈsɔrəs/, which means "fused lizard") is a genus of ankylosaurid dinosaur, containing one species, A. magniventris. Fossils of Ankylosaurus are found in geologic formations dating to the very end of the Cretaceous Period in western North America.
Although a complete skeleton has not been discovered and several other dinosaurs are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal armored dinosaur. Other ankylosaurids shared its well-known features, like the heavily-armored body and massive bony tail club, but Ankylosaurus was the largest member of its family.
In comparison with modern land animals the adult Ankylosaurus was very large. Some scientists have estimated a length of 9 meters (30 ft). Another reconstruction suggests a significantly smaller size, at 6.25 m (20.5 ft) long, up to 1.5 m (5 ft) wide and about 1.7 m (5.5 ft) high at the hip. Ankylosaurus may have weighed over 6,000 kilograms (13,000 lb). The body shape was low-slung and quite wide. Ankylosaurus was quadrupedal, with the hind limbs longer than the forelimbs. Although its feet are still unknown, comparisons with other ankylosaurids suggest Ankylosaurus probably had five toes on each foot. The skull was low and triangular in shape, wider than it was long. The largest known skull measures 64.5 centimeters (25 in) long and 74.5 cm (29 in) wide. Like other ankylosaurs, Ankylosaurus was herbivorous, with small, leaf-shaped teeth suitable for cropping vegetation. These teeth were smaller, relative to the body size, than in any other ankylosaurid species. Ankylosaurus did not share the grinding tooth batteries of the contemporaneous ceratopsid and hadrosaurid dinosaurs, indicating that very little chewing occurred. Bones in the skull and other parts of the body were fused to increase their strength.
The most obvious feature of Ankylosaurus is its armor, consisting of massive knobs and plates of bone, known as osteoderms or scutes, 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, horny layer of keratin. These osteoderms ranged 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 hips, with the many smaller nodules protecting the areas between the large plates. Smaller plates may have been arranged on the limbs and tail. Compared to the slightly more ancient ankylosaurid Euoplocephalus, the plates of Ankylosaurus were smooth in texture, without the high keels found on the armor of the contemporaneous nodosaurid Edmontonia. A row of flat, triangular spikes may have protruded laterally along each side of the tail. Tough, rounded scales protected the top of the skull, while four large pyramidal horns projected outwards from its rear corners.
The famous tail club of Ankylosaurus was also composed of several large osteoderms, which were fused to the last few tail vertebrae. It was heavy and supported by the last seven tail vertebrae, which interlocked to form a stiff rod at the base of the club. Thick tendons have been preserved, which attached 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. It seems to have been an active defensive weapon, capable of producing enough of a devastating impact to break the bones of an assailant. A 2009 study showed that large tail knobs could generate sufficient force to break bone during impacts, but average and small knobs could not, and that tail swinging behavior is feasible in ankylosaurids, but it remains unknown whether the tail was used for interspecific defense, intraspecific combat, or both. It has also been proposed that the tail club acted as a decoy for the head, although this idea is now largely discredited.
Ankylosaurus magniventris existed between 68 to 65.5 million years ago, in the final Maastrichtian stage of the Late Cretaceous Period, and was one of the dinosaurs to survive until the Cretaceous-Tertiary extinction event. The type specimen is from the Hell Creek Formation of Montana, while other specimens have been found in the Lance Formation of Wyoming and the Scollard Formation in Alberta, Canada, all of which date to the end of the Cretaceous.
The Lance, Hell Creek and Scollard Formations represent different sections of the western shore of the shallow sea that divided western and eastern North America during the Cretaceous. They represent a broad coastal plain, extending westward from the seaway to the newly formed Rocky Mountains. These formations are composed largely of sandstone and mudstone, which have been attributed to floodplain environments. The Hell Creek is the best studied of these ancient environments. At the time, this region was subtropical, with a warm and humid climate. Many plant species were supported, primarily angiosperms, with less common conifers, ferns and cycads. An abundance of fossil leaves found at dozens of different sites indicates that the area was largely forested by small trees.
Fossils of Ankylosaurus are considerably rare in these sediments, compared to Edmontosaurus and the super-abundant Triceratops, which make up most of the large herbivore fauna. Another ankylosaur, Edmontonia, is also found in the same formations. However, Ankylosaurus and Edmontonia seem to have been separated both geographically and ecologically. Ankylosaurus had a wide muzzle, perhaps used for non-selective grazing and may have been limited to the upland regions, away from the coast, while Edmontonia had a narrower muzzle, indicating a more selective diet, and seems to have lived at lower elevations, closer to the coast.
Ankylosaurus was named as the type genus of the family Ankylosauridae. Ankylosaurids are members of the larger taxon Ankylosauria, which also contains the nodosaurids. Ankylosaur phylogeny is a contentious topic, with several mutually exclusive analyses presented in recent years, so the exact position of Ankylosaurus within Ankylosauridae is unknown. Ankylosaurus and Euoplocephalus are often thought to be sister taxa. However, other analyses have found these genera in different positions. Further discoveries or research may clarify the situation.
Ankylosaurus was named by American paleontologist Barnum Brown, in 1908. The generic name is derived from the Greek words αγκυλος/ankulos ('curved') and σαυρος/sauros ('lizard'). Brown intended this name in the same sense as the medical term ankylosis, to refer to the stiffness produced by the fusion of many bones in the skull and body, so the name is often translated as 'stiffened lizard.' The type species is A. magniventris, from the Latin magnus ('great') and venter ('belly'), referring to the great width of the animal's body.
A team led by Brown discovered the type specimen of A. magniventris (AMNH 5895) in the Hell Creek Formation of Montana, in 1906. This consisted of the top of the skull, as well as vertebrae, ribs, part of the shoulder girdle and armor. Six years earlier, Brown found the skeleton of a large theropod dinosaur (AMNH 5866) in the Lance Formation of Wyoming. This specimen was named Dynamosaurus imperiosus in 1905 but is now thought to belong to Tyrannosaurus rex. Associated with AMNH 5866 were more than 75 osteoderms of various sizes, which were attributed to Dynamosaurus. However, these osteoderms are nearly identical in form to those of A. magniventris and most probably belong to this species. In 1910, while on an expedition to Alberta, Barnum Brown recovered his third specimen of A. magniventris (AMNH 5214), from the Scollard Formation. AMNH 5214 includes a complete skull and the first known tail club, as well as ribs, limb bones and armor. All three of the above specimens are now housed at the American Museum of Natural History in New York City. The largest known skull of this animal (NMC 8880) 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 over the years.
Since its description in 1908, Ankylosaurus has been publicized as the archetypal armored dinosaur, and 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. A life-sized reconstruction of Ankylosaurus featured at the 1964 World's Fair in New York City greatly contributed to its popularity. Ankylosaurus has also been featured on several television documentary miniseries, including Walking with Dinosaurs (1999) and The Truth About Killer Dinosaurs (2005).
Ankylosaurus means 'fused lizard' in Greek. It is one of largest members of a group of armoured dinosaurs.
Ankylosaurus was heavily armoured. Its back was covered in thick plates. Also, there were two rows of spikes along its back and its tail ended in a big bony club. These features were used as a defence against bigger dinosaurs like Tyrannosaurus. However the belly was unprotected, but because Ankylosaurus had a row of spikes on each side, and was very heavy, it was hard to flip it over.
Ankylosaurus was a herbivore. This means it only ate plants.
Ankylosaurus lived between 68 to 65.5 million years ago, during the late Cretaceous Period, and was one of the dinosaurs to survive until the K-T mass extinction.
Ankylosaurus lived in woodland with lots of open spaces and clearings, where lots of plant-life could be found. They lived in North America but close relatives lived in Asia.
Ankylosaurus fossils have been found in the continent of North America. They were named in 1908 by a famous fossil-hunter named Barnum Brown. Ankylosaurus footprints have been found in Bolivia, South America.
Species: A. magniventris
Ankylosaurus Brown, 1908
Fossil range: Late Cretaceous
| Ankylosaurus magniventris|
The Ankylosaurus (Ankylosaurus magniventris) was a type of dinosaur.
Its back was covered in spikes and bits of bone to protect itself from predators. The ankylosaurus's whole body was covered with bony plates and spikes. Even the ankylosaurus's eyelids had bony shutters. Underneath its back was not covered in anything but normal skin, so other dinosaurs, like the tyrannosaurus rex, would try to attack it there. It would defend itself by using its clubbed tail.
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