Larger The Frill example essay topic

Ceratopsians and Pachycephalosaurs Around 144 million years ago, began the emergence of the Ornithischian dinosaurs during the cretaceous period and diversified into North America and Asia. Ornithischians were classified as having a hip structure similar to that of birds, although they are not the descendants of birds. Marginocephalians, meaning 'fringed heads' are a group of Ornithischians that have a distinctive skull structure, consisting of a slight shelf or bony frill on the back of the skull, a unique palate, and a short hip structure. These herbivores include two major groups: the Ceratopsians and the Pachcephalosaurians. These plant-eaters include the Ceratopsians, horned dinosaurs such as the Triceratops, Styrachosaurus, Pentaceratops, and the Protoceratops. Pachycephalosaurians, thick-skilled dinosaurs like such as the Stegoceras and the Pachycephalosaurus.

(1) Ceratopsians and Pachycephalosaurs are closely related in their characteristics. Ceratopsians processed a saddle-shaped bone frill that extended from the skull to the neck and typically had horns over the nose and eyes. The most popular was the triceratops, which could reach over 26 feet and weigh in excess of twelve metric tons. Their frills served as two major functions. It protected the vulnerable neck from being harmed. The second major function that the frill provided was due to the fact that the frill contained a network of blood vessels on its underside, which were used as a means to get rid of excess heat.

The Pachycephalosaurs were considered to be bipedal. They were also found to have thick skulls, flattened bodies, and tail that were covered in an array of body rods. Pachycephalosaurs were thought to have been more than fifteen feet long and processed a skull that was surrounded by a rounded dome of solid bone. It was thought that they used their heads in combat or mating contests, but that was disproved fairly recently, which I will discuss later in the paper.

Both Ceratopsians and Pachycephalosaurs were "bird-hipped" and both of these suborders contained a backwards pubic bone. Both were Marginocephilia, or "fringed heads", which is one of three class under the Orinthiscia order. They were also herbivore dinosaurs that inherited their fringe at the back of the skull from earlier ancestors. (2) Their classification is as follows. The Pachycephalosaurs were of the kingdom animali a; the phylum chordate, the class Archosauria, the subclass Orintodira, and the order Orinthiscia. The Ceratopsians were of the kingdom Animalia, the phylum Chordate, the class Archosauria, the order Orinthiscia, and the suborder Ceratopia.

The Ceratopsians are broken down into three different families: the Ceratopsidae, the Psittacosauridae, and the Protoceratopsidae. The most primitive group is the Psittacosauridae. There is only one member in this family and that is the Psittacosaurus, found in the lower cretaceous on the continent of Asia. It is considered to be a smaller form of the Ceratopsians, measuring around two meters in length. Psittacosaurus contain possess only an overhanging shelf, as apposed to the larger and more advanced Ceratopsians that possess and actual frill. There is a major difference found in the teeth of the Psittacosaurus from the earlier and more primitive Ornithischians in that "the enamel is thicker on one side of each tooth".

The thickened side of the upper teeth can be found on the outside, whereas the thickened side of the lower teeth can be found on the inside of the tooth. This thickening provides the dinosaur with a "self-sharpening" edge that assists with the ability to chew threw vegetation in a more efficient way. "Psittacosaurus was probably bipedal since the fore limb is about one-half the length of the hind limb. However, the hand is broad and could have supported a portion of the body weight. Ossified tendons lay along the back from the thorax to the middle of the tail.

The tibia is longer than the femur, suggesting that Psittacosaurus was fairly agile". (3) The next two families are classified into the group called Neoceratopsia, consisting of the Protceratopsidae and the Ceratopsidae. The Neoceratopsia set themselves apart from the Psittacosaurus in the following ways: "The head and frill are much larger in the, the beak of Neoceratopsians is more compressed and was probably used to pluck rather than slice plants, Neoceratopsians have horns on the nasal bones and above the orbits, the first three cervical vertebrae in Neoceratopsians are fused, and the shaft of the ischium is curved forward in Neoceratopsians". (3) The smallest of the Neoceratopsians is the Protoceratopsids, measuring around two to five meters long. A number of Protoceratops skeletons from various growth stages have been recovered in Mongolia, making them the main source of knowledge about the Protoceratopsids. Many studies on these skeletons have revealed various significant shape changes that took place during the growth of these dinosaurs.

Males and females were found to have skulls that were shaped differently. Nests with eggs have been found along with Protoceratops fossils, giving concrete evidence as to how dinosaurs reproduced, which I will discuss later. They have upward arching nasals, although some had only a small horn found on the nasal. The teeth were arranged in a fashion that was very suitable for the chewing of the teeth. When the jaw was closed they met at an angle which facilitated this. "The rest of the skeleton of Protoceratopsids is similar to the larger Ceratopsids, but less robust.

One major exception is the existence of ossified clavicles in Protoceratops, but not in the Ceratopsids". (3) The final family is the Ceratopsidae, which are found in the Upper Cretaceous but are only found in North America, not Asia. These dinosaurs possessed noticeably larger skulls measured around four to eight meters long. They possessed frills that were a lot greater in size than the previous two families, which explains the reason for the uniquely larger head. These frills were found to have horns or spikes. "The Ceratopsidae is divided into two subfamilies: the Centrosaurinae and the Chasmosaurinae.

The two subfamilies can be distinguished by the size and shape of their frills. Centrosaurines have a relatively shorter frill, greater ornamentation along the edge of the frill in the form of spikes and hooks, and a nasal horn larger than the orbital horns. Centrosaurines also tend to be slightly smaller animals. Examples of Centrosaurines are Styracosaurus with long spikes on the frill, Centrosaurus with forward curved hooks on the frill, and Pachyrhinosaurus with a huge and blunt process in place of the nasal horn.

Chasmosaurines have a much larger frill, larger orbital horns than nasal horns, and extra ossifications along the edge of the frill called Epoccipitals". (3) The most common Chasmosaurines are the Triceratops and the Chasmosaurus. The Ceratopsids possessed more advanced teeth than the Protoceratopsids. They were more advanced in that they possessed a greater number of teeth that covered a greater surface area.

The main difference was found in the angle of the teeth; they were no longer at an angle, but were very close to being vertical. "For many years it has been accepted that the frill of all Ceratopsians evolved as a site for larger jaw muscles. The larger the frill, the more powerful the jaw muscles. These muscles presumably ran from the lower jaw through the supra temporal fenestra and onto the dorsal side of the frill. However, only the have large temporal fenestra e.

In the, the fenestra e are much smaller". Dr. Rias z goes on to say, "There is abundant evidence that the shapes of frills with their spikes and ornaments are specific to a species. There was probably also sexual dimorphism in frill shape, but this has been shown only for Protoceratops. The frill could serve as an effective visual signal for the identification of other members of a species and potential mates. The often huge horns of are usually compared with a rhino's horn. The argument then would be that the horns were used against predators.

However, as with the frills, horns are not all the same shape. In many cases, the shape of the horns is species specific. The horns may actually have been used in a more ritualized combat between males". (3) He goes on to discuss how the frill plays a greater role, and that is for thermo regulation. Grooves can be found on the frill to indicate blood vessels. This presence of numerous blood vessels gives evidence that the dinosaur would be able to self regulate its body temperature in order to release or absorb heat.

This evidence is very persuasive and I have found many different sources that would agree that the function of the numerous blood vessels would have been for the regulation of the body temperature. At least that is the most feasible explanation as to their existence. The two main families of Pachycephalosaurs are the and the Stegosaurs. The Pachycephalosaurus was considered a dome-headed dinosaur, consisting of an enormously thick skull, measuring up to ten inches thick. They were said to have been about fifteen feet long, weighing up to 950 pounds. Consisting of bumpy knobs on its snout and also located at the back of the skull.

The main characteristic of this dinosaur, other than its head, were its short arms and thick tail. These dinosaurs were thought to have used their very thick head as a ramming devise to fight rivals over mating, or in as a last line of defense. Paleontologist Mark Goodwin of the University of California at Berkeley made a remarkable discovery that changed the way we view the purpose of the thick skull found in the Pachycephalosaurus. After viewing many skulls, he was not able to find any scars that would have suggested use of the skull. He also realized that the thick bone was very porous and fragile, as apposed to the earlier notion that it was very rigid and solid. Goodwin says, "It's time to kill the myth...

It certainly wouldn't be in their own best interests to ram heads in a fight", said Goodwin "They would have killed each other, and a couple of bowling balls would hardly make good targets. It is more likely that Pachycephalosaurus butted other animals sides (flank-butting), rather than their heads. This would inflict damage on the other animal and not injure the Pachycephalosaurus". (4) The second family of Pachycephalosaurs is the Stegosaurus. These dinosaurs have seventeen plates on its neck, back, and tail, along with spikes found at the tip of the tail. It was originally thought that these plates were used as a means of protection, but upon further investigation, scientists found grooves all over the plates.

These groves suggested that there were blood vessels covering the plates. They were most likely used as a means of self regulation of the body temperature. They were able to absorb or release heat as necessary. Another hypothesis that surrounded the Stegosaurus was that it contained two brains. Paleontologists thought this because their brain was so small that it was hard to comprehend that such a small brain would be able to control such a large animal. This myth was later disproved and it is now accepted that they only possessed one brain.

There is another mystery involving the front legs. "As a baby fossil, the front legs are straight up and down. As an adult fossil, however, they are splayed out to the side. Which is correct? We " re not sure, since they seem to fit both ways".

(5) Their massive tail was used as the main line of defense for this dinosaur, although it was previously viewed that the plates were also a form of defense. Both Ceratopsians and Pachycephalosaurs were Ornithischians but more specifically they were from one of the three main class called Marginocephilia. Both are herbivores that inherited their fringe at the back of the skull from earlier ancestors. The Pachycephalosaurs evolved from Hypsilophodon, a small, agile bipedal herbivore. The Ceratopsians appeared at beginning of cretaceous period from the family Ornithopoda. Pachycephalosaurs contained a ten inch thick skull, which was actually fairly fragile, and their first line of self defense would be to run away.

Ceratopsians, which mean horned face, are large beasts with horns that can defend themselves pretty well. Both were very similar, but contained distinct differences.

Bibliography

1) Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. W.H. Freeman and Company, New York. 2) web) Dr. Robert Ries z, University of Toronto, "Ceratopsia and Ornithopoda" web and ornithopod a. html 4) Enchanted Learning; "Pachycephalosaurus" web) American Museum of Natural History web fossil / Fossils/Specimens / stegosaurus. html.