Wednesday, December 7, 2016

Triceratops in the forest by Swordlord3d

Triceratops is a genus of herbivorous ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the late Cretaceous period, about 68 million years ago (mya) in what is now North America. It is one of the last known non-avian dinosaur genera, and became extinct in the Cretaceous–Paleogene extinction event 66 million years ago. The term Triceratops, which literally means “three-horned face”, is derived from the Greek τρί- (tri-) meaning “three”, κέρας (kéras) meaning “horn”, and ὤψ (ops) meaning “face”.

Size of T. prorsus (orange) and T. horridus (green) compared to a human. Author: Matthew Martyniuk

Triceratops is one of the best known of all dinosaurs and was the largest of the ceratopsians. Its massive head bore a short frill of solid bone along with the three large horns for which it is named-one above each eye and a smaller one on the snout. Traces of blood vessels found in the frill and horn have suggested to some paleontologists that the frill may have served as a means of regulating the animal’s body temperature. As with other ceratopsians, the frill would have been covered with skin and may also have been used during courtship display.

The first named specimen now attributed to Triceratops is a pair of brow horns attached to a skull roof, found near Denver, Colorado in the spring of 1887. This specimen was sent to Othniel Charles Marsh, who believed that the formation from which it came dated from the Pliocene, and that the bones belonged to a particularly large and unusual bison, which he named Bison alticornis. He realized that there were horned dinosaurs by the next year, which saw his publication of the genus Ceratops from fragmentary remains, but he still believed B. alticornis to be a Pliocene mammal. It took a third and much more complete skull to change his mind. The specimen, collected in 1888 by John Bell Hatcher from the Lance Formation of Wyoming, was initially described as another species of Ceratops. After reflection, Marsh changed his mind and gave it the generic name Triceratops, accepting his Bison alticornis as another species of Ceratops (it would later be added to Triceratops). The sturdy nature of the animal’s skull has ensured that many examples have been preserved as fossils, allowing variations between species and individuals to be studied. Triceratops remains have subsequently been found in the American states of Montana and South Dakota (in addition to Colorado and Wyoming), and in the provinces of Saskatchewan and Alberta, Canada.

An earlier specimen, also recovered from the Lance Formation, was named Agathaumas sylvestris by Edward Drinker Cope in 1872. Originally identified as a hadrosaur, this specimen consists only of post-cranial remains and is only provisionally considered an example of Triceratops.

T.rex vs Triceratops by Swordlord3d

Triceratops is the best known genus of the Ceratopsidae, a family of large North American horned dinosaurs. The exact location of Triceratops among the ceratopsians has been debated over the years. Confusion stemmed mainly from the combination of short, solid frills (similar to that of Centrosaurinae), and the long brow horns (more akin to Ceratopsinae, also known as Chasmosaurinae). In the first overview of horned dinosaurs, R. S. Lull hypothesized two lineages, one of Monoclonius and Centrosaurus leading to Triceratops, the other with Ceratops and Torosaurus, making Triceratops a centrosaurine as the group is understood today. Later revisions supported this view, formally describing the first, short-frilled group as Centrosaurinae (including Triceratops), and the second, long-frilled group as Chasmosaurinae.

Skull growth series: A display of Triceratops horridus skulls, from baby to adult, at the Museum of the Rockies in Bozeman, Montana. Dinosaurs are classified into four growth stages: baby, juvenile, subadult, and adult. The skull to the far right is a baby, collected in Garfield County, Montana. (This is a cast.) The second and third skulls from the right are juveniles, one larger than the other. (The one second from the right was found in Garfield County, Montana. The one third from the right was found in McCone County, Montana.) Note the triangular frill nodules (not yet fused with the frill), the backward-curving horns, the longer snouts, and the lack of holes in the frill. The fourth from the right is a subadult (teenager). Although the horns still curve backward, the frill nodules are fusing with the frill and the snout is showing large “excavation” (areas of no bone). The final skull on the far left is an adult. All of these skulls were collected in Montana. Author: Tim Evanson

In 1949, C. M. Sternberg was the first to question this and favoured instead that Triceratops was more closely related to Arrhinoceratops and Chasmosaurus based on skull and horn features, making Triceratops a ceratopsine (chasmosaurine of his usage) genus. He was largely ignored, with John Ostrom, and later David Norman both placing Triceratops within Centrosaurinae.

Subsequent discoveries and analyses upheld Sternberg’s view on the position of Triceratops, with Lehman defining both subfamilies in 1990 and diagnosing Triceratops as ceratopsine (chasmosaurine of his usage) on the basis of several morphological features. In fact, it fits well into the ceratopsine subfamily, apart from its one feature of a shortened frill. Further research by Peter Dodson, including a 1990 cladistic analysis and a 1993 study using RFTRA (resistant-fit theta-rho analysis), a morphometric technique which systematically measures similarities in skull shape, reinforces Triceratops’ placement in the ceratopsine subfamily.

Reconstruction of a Triceratops skeleton in the Senckenberg Museum in Frankfurt am Main, assembled from fragments of different skeletons

Valid species

  • T. horridus (Marsh, 1889) (originally Ceratops) (type species)

  • T. prorsus (Marsh, 1890)

Synonyms and doubtful species

The following species are considered nomina dubia (“dubious names”), and are based on remains that are too poor or incomplete to be distinguished from pre-existing Triceratops species.

  • T. albertensis (C. M. Sternberg, 1949)

  • T. alticornis (Marsh, 1887 [originally Bison])

  • T. brevicornus (Hatcher, 1905) (=T. prorsus)

  • T. calicornis (Marsh, 1898) (=T. horridus)

  • T. elatus (Marsh, 1891) (=T. horridus)

  • T. eurycephalus (Schlaikjer, 1935)

  • T. flabellatus (Marsh, 1889) (=T. horridus)

  • T. galeus (Marsh, 1889)

  • T. hatcheri (Lull, 1907) (contentious; see Nedoceratops below)

  • T. ingens (Lull, 1915)

  • T. maximus (Brown, 1933)

  • T. mortuarius (Cope, 1874) (nomen dubium; originally Polyonax mortuarius)

  • T. obtusus (Marsh, 1898) (=T. horridus)

  • T. serratus (Marsh, 1890) (=T. horridus)

  • T. sulcatus (Marsh, 1890)

  • T. sylvestris (Cope, 1872) (nomen dubium; originally Agathaumas sylvestris)

The skull (AMNH 5116) of this T. horridus composite specimen was formerly assigned to T. elatus. Author: Michael Gray

Triceratops were herbivorous, and because of their low head, their primary food was probably low growth, although they may have been able to knock down taller plants with their horns, beak, and bulk. The jaws were tipped with a deep, narrow beak, believed to have been better at grasping and plucking than biting.

Triceratops teeth were arranged in groups called batteries, of 36 to 40 tooth columns, in each side of each jaw with 3 to 5 stacked teeth per column, depending on the size of the animal. This gives a range of 432 to 800 teeth, of which only a fraction were in use at any given time (tooth replacement was continuous and occurred throughout the life of the animal). They functioned by shearing in a vertical to near-vertical orientation. The great size and numerous teeth of Triceratops suggests that they ate large volumes of fibrous plant material, with some suggesting palms and cycads, and others suggesting ferns, which then grew in prairies.