Fossilguy Topics:
Information about Ceratopsidians
By Jayson & Amy
Figure 1: An image of the model of a Triceratops at the Field Museum of Natural History in Chicago. Notice the mammal like posture of this model.
Triceratops originates from a long and diverse family tree. Although it is hard to believe, Triceratops belongs to the bird-hipped dinosaurs, the Ornithischian order. This means they had a hip structure similar to birds. However, this does not mean they evolved into birds. Their sub-order is the Marginocephalias, or fringed-headed dinosaurs. From this sub-order, Triceratops belongs to the Ceratopsia infraorder. This infraorder is further subdivided into micro-orders, the Psittacosaurus and the Neoceratopsia. Pssittacosaurus is a primitive micro-order. It means "parrot lizard." Dinosaurs in this micro-order are small, have very short snouts, and have high nasal openings, and may have been able to stand on two legs. However, Triceratops belongs to the Neoceratopsia micro-order. This micro-order contains both small and large bodied dinosaurs with large brow horns and frills. They also had large beaks, and large heads in relation to their bodies. Finally, Triceratops belongs to the Ceratopsidae family. (Fastovsky 175-179).
Figure 2: An image of the Triceratops skeleton on display at the Field Museum of Natural History in Chicago. Notice the reptilian like posture of this skeleton, which is unlike the model on display.
The Ceratopsidae family is known from characteristically long horns and broad neck frills. They are found only in western North America, from Alberta to New Mexico (Farlow 324). Some of the characteristics of this family included their very large nasal openings and large bodies. The bodies of the various members of the family were similar in that they had long hind limbs, and thick, heavy leg bones, which eludes to an animal with great power but not so great speed. A skeleton of a Triceratops can be seen in the above figure. The quadrupedal Ceratopsidians' average walking speed is thought to be 2-4 km/hr. Notice the structural variations in the forelimbs in figures 1 and 2. In figure 1, the model has a mammal like posture, which meant the animal was capable of running. However, in figure 2, the specimen has a reptile-like posture, which means the beast could not have run. There is simply not enough evidence to prove which posture is correct for Ceratopsians. This controversy is being waged by paleontologists on an ongoing basis. However, due to the animals' large skull size, and fused neck vertebrae, if it had a mammal like posture, it still could not have run very fast. If the animal could have run, its maximum running speed is thought to have been only 30-35 km/hr (Fastovksy 185). Good thing they were herbivores.
Ceratopsian skulls differed in ornamentation (i.e. length, type, location, etc. of horns and frills). Their skulls alone could reach lengths greater than 6 feet, which are the biggest of any land animal to ever walk the earth (Farlow 324). Their skulls had a narrow, deep, beak-like snout and widely flared cheeks, and were essentially triangular in shape (Farlow 376). In addition, they had a secondary "roofing" over their braincases, likely to protect from injuries (Farlow 325). Triceratops' brain size is equivalent to a that of a modern day crocodile (Fastovsky 188). A bone unique to this infraorder is called the rostral bone, which forms the dinosaurs' upper beak. The texture of the rostral is pitted, signaling the area was covered by a beak. This bone is found nowhere else in dinosaurs (Fastovsky 175).
The Ceratopsidians had double rooted teeth (see figure 3), and with this grouping came the evolution of the dental battery, a unique tooth set-up where adjacent teeth were locked together in longitudinal rows and in vertical columns. With at least 3 teeth in each column, 1 was functional and 2 were "replacements." The teeth, which were continually replaced throughout dinosaurs' lives, were positioned so vertically and were so sharp (self-sharpening in fact) that they could shear like scissors. During chewing, these dinosaurs' teeth really did not touch at all like humans' do; instead they slide past each other, in a slicing motion (Fastovsky 183). Because of these razor sharp teeth and very strong jaw muscles, they are often referred to as "Nature's first Cuisinarts!!" (or food processors for those of you who are kitchenetically challenged). (Farlow 85).
Figure 3: This sketch done by a starving artist depicts the double rooted tooth.
Scientists are somewhat unsure of their exact diet. They suspect, due to their relatively low browsing height, that they may have eaten such plants as angiosperms, ferns, and small conifers growing at that height. Due to their large and heavy skulls, they could not rise up on their hind legs, but these lawnmowers of the west may have been able to knock over trees in order to gain access to the leaves (Fastovsky 183).
Of course, one of the most distinguishing characteristics of the Ceratopsidians were their horns and neck frills. Each subdivision has its own pattern of horns, spikes, and frills. Most of the Ceratopsidians had huge frills, etc, with the exceptions of Diceratops and Triceratops, whose frills were comparatively reduced in size (Fastovsky 180). In bone beds found across North America, remains were found which display significant variation in horn and frill morphology. At first, their variations were thought to be pathological or from different species; however today the conclusion is that this variation occurred within the same species, but at different stages of development. Simply stated, horns and frills were not fully developed until adulthood (Farlow 327). Increases in frill size during life directly affected jaw muscle strength (the larger the frill, the larger/stronger the jaw muscle) (Fastovsky 186).
Frills and horns were used for dominance, defense, and display. Like living antelopes, chameleon, and deer, Ceratopsidians may have used their horns within their own species for territorialism and mating rights. Puncture wounds have been commonly found in skulls and frills from intraspecies combat (Farlow 327). It is also hypothesized that their elaborate frills were used in sexual dimorphism and selection (Fastovsky 186). Additionally, their horns may have been used for defense to ward off predators. For example, they may have been used during the interspecies "face-off" between Triceratops and Tyrannosaurus (Fastovsky 185). Typically, these animals are thought to have traveled in herds, consistent with the fact that horn usage is more prevalent in herding animals, such as deer, gazelle, and buffalo.
Ceratopsidians were one of the last groups of dinosaurs on earth. They arose in the early Cretaceous and lasted through the decline of the dinosaurs toward the end of the Cretaceous. Finally, Triceratops became extinct, along with the remaining dinosaurs, at the end of the Cretaceous around 65 million years ago.
Farlow, O. James, Brett-Surman, M.K., Editors (1997). The Complete Dinosaur. IN: Indiana University Press.
Fastovsky, E. David, Weishampel, B. David (1996). The Evolution And Extinction Of The Dinosaurs. NY: Cambridge University Press.
Back to Montana Dig Article
Back to additional images and information in the MOntana Dig Article
Back to Topics
