Triceratops

Triceratops is a genus of ceratopsian dinosaur from the Late Cretaceous Period of North America. It is one of the most well known of all dinosaurs.

Description
Triceratops was one of the largest ceratopsians, measuring up to 9 meters in length and perhaps 6 to 12 tonnes in weight. Its most distinctive feature was its skull, which was adorned with three horns and a frill. One horn was positioned above the nostrils, and the other two (which could reach lengths of a meter or more ) sat above the eyes. The frill of Triceratops was relatively short compared to other ceratopsians, and was also completely solid.

It was initially believed that the front limbs of Triceratops sprawled at an angle in order to bear the weight of its large head. However, recently discovered ceratopsian trackways and digital reconstructions of the animal show that all its legs were held upright with only slight flexion in the elbow region, which is a similar position to that of modern rhinoceroses.

An as-yet undescribed specimen of Triceratops shows that its skin may have been covered in bristle-like structures, similar to its earlier relative Psittacosaurus.

Classification
Many early researchers classified Triceratops as a centrosaurine ceratopsian, but several analyses since then have found it is better understood as a chasmosaurine. Two valid species are known, T. horridus and T. prorsus, although many others have been named.

The below cladogram by Scott Sampson and colleagues in 2010 shows the position of Torosaurus among the ceratopsians:

History
A pair of brow horns belonging to Triceratops was discovered near Denver, Colorado in 1887. The paleontologist Othniel Charles Marsh believed that the horns were of Pliocene age, and classified the specimen as a bison, which he named Bison alticornis. He found similar fossils the next year, describing them as part of the dinosaur genus Ceratops, but still interpreted the original pair of brow horns to be from a bison. It was not until a more complete skull was found that Marsh recognized all the specimens to be of the same genus, which he named Triceratops in 1889.

John Scannella and Jack Horner proposed in 2010 that the closely related genus Torosaurus was actually the adult form of Triceratops. Their conclusions have not been universally accepted, however (see the corresponding section in the Torosaurus article).

Social behavior
Triceratops is often portrayed as a herding animal, although there is little direct evidence to support this. In fact, only one bonebed of the genus has been found, containing only three juveniles.

Diet
Triceratops was herbivorous, and like other ceratopsians it had a large beak. It had especially large batteries of teeth, and at any time a single animal may have had up to 800 teeth in its mouth (although only a small fraction was in use at any given time due to tooth replacement). Due to the position and structure of its skull and teeth, Triceratops likely ate low-growing, fibrous plants.

Horns and frill function
The horns and frill of Triceratops were traditionally thought to have been used in self-defense. Although this is a feasible use for these structures (and one perhaps supported by fossil evidence), more recent studies have shown that their primary use was likely for display. Modern animals with similar structures use them for this purpose, and the wide range of ceratopsian adornments make each species highly distinctive from each other.

In popular culture
Triceratops is one of the most famous dinosaurs due to its distinctive appearance, and is often depicted in combat with Tyrannosaurus, which was a contemporary predator in the area. It has appeared in a multitude of books, movies, television shows, and other media. Triceratops is also the state fossil of South Dakota and the state dinosaur of Wyoming.