Ankylosaurus

*Ankylosaurus magniventris*

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***Ankylosaurus*** was a late Cretaceous ankylosaur that lived about 68 to 66 million years ago in North America. It was the size of an elephant. It lived alongside carnivores such as *Tyrannosaurus rex* but like all ankylosaurs was not in any danger from them due to its armored back - which no carnivore would be able to bite through - and tail club, which could mortally injure a *T. rex*.

## Description

Compared 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 much 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), making it one of the heaviest armored dinosaurs yet discovered. The body shape was low-slung and quite wide. It 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. Their teeth were weaker than ceratopsid and hadrosaurid dinosaurs of the time, so they probably chewed very little.

### Armor

The armor of *Ankylosaurus* was made of huge 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 may have been covered by a tough, horny layer of keratin. These osteoderms ranged in size, from wide, flat plates to small, round nodules. The plates were lined up 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 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 nodosaurid *Edmontonia*. A row of flat, triangular spikes may have stuck out sideways along each side of the tail. Tough, rounded scales protected the top of the skull, while four horns were behind the eyes and the ends of the mouth.

### Tail club

Classification
*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 heated topic, with several mutually exclusive studies given 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 studies have found these genera in different positions. Further discoveries or research may clear up the situation.

## History

*Ankylosaurus* was named by American paleontologist Barnum Brown, in 1908. The name comes 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 from 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.

## Paleobiology

*Ankylosaurus magniventris* lived between 66.5 to 65.5 million years ago, in the final Maastrichtian stage of the Late Cretaceous Period, and was one of the last dinosaur species that appeared before 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 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. *Ankylosaurus* shared its environment with dinosaurs including the ceratopsids *Triceratops* and *Torosaurus*, hypsilophodont *Thescelosaurus*, hadrosaurid *Edmontosaurus*, nodosaurid *Denversaurus*, pachycephalosaurian *Pachycephalosaurus*, and the theropods *Ornithomimus* and *Tyrannosaurus*.

Fossils of *Ankylosaurus* are quite rare in these grounds, compared to *Edmontosaurus* and the superabundant *Triceratops*, which make up most of the large herbivore fauna. Another ankylosaur, *Denversaurus*, is also found in the same formations. However, *Ankylosaurus* and *Denversaurus* seem to have been separated both geographically and ecologically. *Ankylosaurus* had a wide muzzle, perhaps used for non-selective grazing and thus may have been limited to the upland regions, away from the coast, while *Denversaurus* had a narrower muzzle, indicating a more selective diet, and seems to have lived at lower elevations, closer to the coast.

## JPInstitute.com Description

Ankylosaurus was like a tank, with lots of thick, bony armor on its body. It also had a nasty weapon, a heavy club on the end of its tail, which it could swing around and smash into an attacking dinosaur. There probably weren't many creatures, even a big T. rex, who would want to mess with this guy.

As a defensive creature, Ankylosaurus was one of nature's most perfect designs. It was almost impervious to being bitten from above and its long, strong tail muscles would have been able to swing its club with great force.

There is very little fossil material from this dinosaur - it was apparently the last and largest of this family of armored dinosaurs. It walked fairly upright on all four legs, carrying its tail off the ground and it is theorized that it would drop to the ground when attacked to use its armor as a shield to cover its legs and under belly.

## Dinosaur Field Guide Description

Ankylosaurus ("fused lizard") is the name-bearer for the group of dinosaurs known as the Ankylosauria, or "tank dinosaurs." They're called "tanks" because the upper parts of their bodies are covered with various types of armor that are fused together. The armor of ankylosaurs can be either solid or hollow. It is found on top of their bodies and tails, and also all around the skull--imagine putting on a football helmet and having your skin grow over it! This extreme level of defense was necessary because no ankylosaur could outrun a theropod, or meat-eating dinosaur. In 1998, another new species of ankylosaur was named. It was called Animantarx ("living fortress"). In Ankylosaurus, the last half of the tail has been modified into a giant war club, with the last tail bones fused together. When this club was swung from side to side, it was at the same level as the knees of theropods like Tyrannosaurus. How's that for strategically placed weaponry!

### Fun Facts

Ankylosaurus had eight sinus cavities, as compared to only four in nodosaurs (and also in humans).

### Trivia

Ankylosaurus was the last of the Thyreophore ("shield-bearers, " a group that includes the ankylosaurs and stegosaurs). The earliest was Scelidosaurus.

## Links

http://web.archive.org/web/20040214172748fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_ankyl.html

## References

1. ↑ 1.0 1.1 1.2 Vickaryous, M.K., Maryanska, T., & Weishampel, D.B. 2004. Ankylosauria. In: Weishampel, D.B., Dodson, P., & Osmólska, H. (Eds.). *The Dinosauria* (2nd edition). Berkeley: University of California Press. Pp. 363-392.
2. ↑ 2.0 2.1 2.2 Carpenter, K. 2004. Redescription of *Ankylosaurus magniventris* Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. *Canadian Journal of Earth Sciences* 41: 961–986.
3. ↑ Coombs, Walter P. (December 1978). "Theoretical Aspects of Cursorial Adaptations in Dinosaurs". The Quarterly Review of Biology 53 (4): 393–418. doi:10.1086/410790.
4. ↑ Carpenter, K. 2004. Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. Canadian Journal of Earth Sciences 41: 961–986
5. ↑ Carpenter K. 2004. Redescription of *Ankylosaurus magniventris* Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. *Canadian Journal of Earth Sciences*, **41**: 961–986.
6. ↑ 6.0 6.1 Brown, B. 1908. The Ankylosauridae, a new family of armored dinosaurs from the Upper Cretaceous. *Bulletin of the American Museum of Natural History* 24: 187–201.
7. ↑ Carpenter, K. 2001. Phylogenetic analysis of the Ankylosauria. In: Carpenter, K. (Ed.). *The Armored Dinosaurs*. Bloomington: Indiana University Press. Pp. 454–483.
8. ↑ Hill, R.V., Witmer, L.M., & Norell, M.A. 2003. A new specimen of *Pinacosaurus grangeri* (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: ontogeny and phylogeny of ankylosaurs. *American Museum Novitates* 3395: 1-29.
9. ↑ Lofgren, D.F. 1997. Hell Creek Formation. In: Currie, P.J. & Padian, K. (Eds.). *The Encyclopedia of Dinosaurs*. San Diego: Academic Press. Pp. 302-303.
10. ↑ Breithaupt, B.H. 1997. Lance Formation. In: Currie, P.J. & Padian, K. (Eds.). *The Encyclopedia of Dinosaurs*. San Diego: Academic Press. Pp. 394-395.
11. ↑ Eberth, D.A. 1997. Edmonton Group. In: Currie, P.J. & Padian, K. (Eds.). *The Encyclopedia of Dinosaurs*. San Diego: Academic Press. Pp. 199-204.
12. ↑ Johnson, K.R. 1997. Hell Creek Flora. In: Currie, P.J. & Padian, K. (Eds.). *The Encyclopedia of Dinosaurs*. San Diego: Academic Press. Pp. 300-302.
13. ↑ Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution". *The Dinosauria* (2nd). 517–606.
14. ↑ Template:Cite web