The Dinosaurs: History, Physiology, Behavior (Report Sample)
Warm-Bloodedness, Ecology, Countship Behavior
The paper reports on the fact that dinosaurs were huge terrestrial reptiles that lived on the Earth long before humans. Giant dinosaur bones had been found in the land where people lived in the ancient times. For example, in ancient Greece, they were regarded as the remains of the heroes of the Trojan War era, while in the Middle Ages, they were believed to be the remains of giants. Besides, they were mentioned in the Bible together with animals that died during the Flood.
The paper examines the various aspects of the dinosaurs’ life such as their physiologic peculiarities, countship behavior, environment and background. One of the key concepts reflected in the paper is the history of the dinosaurs’ development and the functions they performed in their society. Furthermore, the paper deals with the dinosaurs’ behavior patterns and their relations between each other.
The History of the Dinosaurs’ Development
Over time, dinosaurs were referred to as a polyphyletic group, consisting of different subgroups that were unrelated and developed in parallel; however, the uniformity (monophyly) has been proven by a great number of studies. Dinosaurs originated about 230-235 million years ago, while 20 million years after at the border of the Permian and Triassic periods, the mass extinction occurred as the ground and marine biota extinction. The first group of dinosaurs of the Triassic period occupied a niche group of extinct archosaurs and therapsid. Assumptions about the long-term ‘competition’ with other groups of reptiles were not proved as the dinosaurs did not show a steady increase in diversity (Brusatte et al., 2015). Apparently, the dinosaurs occupied the empty niches. Post-Triassic development of the dinosaur fauna is synchronous with the changes in the flora and paleogeographic situation.
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In the late Triassic and early Jurassic periods, the continents were connected into a single super-continent named Pangaea, and dinosaurs were represented mainly by theropods and herbivorous prosauropods that had spread universally. It is possible that the main source of food was gymnosperms (conifers in particular), which were widespread and diverse in the late Triassic period.
The homogeneous nature of the dinosaurian fauna was maintained in the middle and late Jurassic period, but Asian dinosaurs were somewhat different from the American, European and African ones. Pangea split, and acquired quite a high degree of endemism (Preston, 2014). Significant changes took place in the mid-Cretaceous, when they began to rapidly spread angiosperms. Some groups of dinosaurs, such as ceratopsians and hadrosaurs, developed complex types of masticatory system in the form of dental battery recycling plant food. In the late Cretaceous dinosaur fauna, there were three types of dinosaurs, one of which had a range that covered the west of North America and Asia; in the majority of cases, the theropods were tyrannosaurs and many types of small theropods and herbivorous dinosaurs prevailed among the hadrosaurs, ceratopsians, ankylosaurs and pachycephalosauria. Therefore, the current paper is aimed at investigating the peculiarities of dinosaurs’ background, physiology and countship behavior within their environment.
Dinosaurs: The Background
The scientific discovery of the dinosaurs took place in the first half of the 19th century, when scientists worked on the study of the remains of dinosaurs and restored their entire appearance. Basically, the bones from dinosaurs were preserved. Finding a complete skeleton and skull with teeth was an extremely rare occurence. More often than not paleontologists had to work with bone fragments and individual teeth.
Of great value are the footprints, because they can be used to learn about the lifestyle, the speed of movement and weight of the animal. Hence, the National Park “Valley of the Dinosaurs,” located near the town of Glen Rose, Texas (USA), was known throughout the world due to a variety of dinosaur footprints located on the banks of the river PAICEX. 110-113 million years ago, these places were the sea shore where the footprints of the dinosaurs were imprinted. Then the giant reptile paw prints were discovered.
The first dinosaurs appeared 230 million years ago, and for a long time, they gradually spread and became full owners of the land. At the end of the Cretaceous period – 65 million years ago – the dinosaurs completely died out. Among dinosaurs were giants that reached tens of meters in length and small creatures the size of a dog. All dinosaurs are usually divided into two major groups: Saurischia and Ornithischia, and in each of the groups two main squads can be distinguished.
The Dinosaurs’ Physioilogy
The physiology of the heart and lungs of the dinosaurs, and especially in the giant sauropods with their long necks, remains unknown due to the complete disappearance of these animals, so that it is impossible to study them in their ‘alive’ condition (Weishampel, 1984). What was the pressure of an animal that was 12 meters high, if they took out the air to breathe through the 9-meter long trachea? All new discoveries forced scientists to investigate these issues (Moen & Morlon, 2014). For this purpose, a comparative study on living species had been conducted, which explains the evolutionary relationships, and applies new methods of assessment, computer modeling, as well as new information about the Mesozoic of the Earth’s atmosphere.
The pumping of blood along the vertical column of 8 m above the heart would be required in case the arterial blood pressure was 600 mm and a value for the heart’s size and its functions has led to the proposal of several alternative cardiopulmonary theories. In recent years, it has become increasingly popular to think that many juvenile dinosaurs were warm-blooded and active metabolically, but the metabolism slowed down when they approached an adult body size. There is an assumption that the dinosaurs were four-hearted (Weishampel, 1984). Some paleontologists believe that birds evolved from dinosaurs and the air sacs of the respiratory system such as avian, inherited from their predecessors, were more effective than the respiratory system of mammals. Dinosaurs and mammals throughout their co-existence did not compete (Moen & Morlon, 2014). They occupied parallel ecological niches and were very rare. The competition between them arose only in the middle of the Cretaceous period, when there were large carnivorous mammals of the size of a badger that could eat the cubs of dinosaurs. An example is Repenomamus robustus from the Yixian Formation (north-east China), in whose stomach the remains of a young Psittacosaurus were found. The appearance of carnivorous mammals became a serious negative factor, which significantly reduced the probability of reaching the reproductive age for the majority of the dinosaurs.
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The identification of nutrition and diet of dinosaurs is fundamental for the study of Paleobiology of these animals and their role in Mesozoic terrestrial ecosystems. Hadrosaurs had a unique mechanism of continuous tooth replacement, as the chewing surface of the tooth batteries were quickly wearing out because of the roughage, as well as due to a large number of mineral particles contained in the food. Beak hadrosaurs resemble the modern duck beaks (Weishampel, 1984). In the past, it was a filter device, while at the hadrosaurs jaw apparatus was the specialized body that performed cut-and-cutting and ground movements. Such a device has arisen for processing crude vegetable food.
The duck-like beaks and powerful battery toothbrushes suggest that dinosaurs dug in the swamps and lakes, then filtered sludge, and after that crushed them all by the jaws into the organic residues of both vegetable and animal origin (Moen & Morlon, 2014). Horny ramfoteka that covered beak was used for cutting terrestrial plants close to the soil surface.
Recently, the research of the jaw mechanics, diet and trophic niche of hadrosaur Edmontosaurus had been undertaken. It states that the dinosaurs had powerful jaws, a large body, a small front and strong hind legs, as well as a thick tail. It is possible to find quite a large number of entire skeletons, the length of which is about 13 m (Moen & Morlon, 2014). Such lizard holds the record for the number of teeth (over a thousand); its battery molars were the largest and most impressive of all known hadrosaurs (Weishampel, 1984). The edges of them, covered with hard enamel, stood out from the soft dentin and formed a sharp cutting edge, like pruners or shears. Roth ended with wide beak, which was folded down.
The analysis of teeth produced strong arguments to test the hypothesis regarding hadrosaurs’ eating habits. Orientation of the micro-scratches studied the teeth, and found direct evidence of the relative movement of the jaws in capturing the food.
As it is known, microscopic scratches are formed on the teeth during feeding as a result of interaction of opposing dentition and the interaction of the teeth in capturing food. Statistical research shows that the teeth of Edmontosaurus retain four clearly expressed complex scratches moving in different directions (Moen & Morlon, 2014). Following the laws of the jaw mechanics, it can be assumed that they were almost vertical producing a powerful blow at the time of feeding and almost vertical opening movement of the jaw faced backwards (Benton, Forth, & Langer, 2014). Chewing surface could move relative to each other in all three directions, and hinged upper jaw chewing food made slightly different chewing movements than in other animals – at the closing the upper jaw protruded, and the tooth surfaces slid relative to each other, rubbing food. Based on the straightness and parallelism of scratches, it can be concluded that the closure of the jaw was tight. The food of the dinosaurs, according to the scratch, contained gravel particles (characteristic of animals, plucking and chewing low plants) or silica (found in herbs, but more common in the horsetails, which were ubiquitous and could easily enter the hadrosaurs’ diet). The dominance of micro-scratches on dentin indicates that the Edmontosaurus, apparently, was a grazing animal, not a leaf-eater.
Countship of Dinosaurs
In order to understand the countship behavior of the dinosaurs, it is necessary to investigate their reproductive function. One of the most famous Maiasaura formation of Two Medicine (Montana, USA) had been well-studied at all stages of growth including hadrosaurs and
Hypacrosaurus formation of Horseshoe Canyon (Alberta, Canada). Findings presented mayazavrov skeletons of animals of almost all age groups, as well as clutches of eggs. There are burials of thousands of skeletons of these dinosaurs reaching 8-9 meters in length.
The first discovery was the skeleton of an adult animal with a socket-shaped hill, with petrified whole eggs, egg fragments and 15 young dinosaurs about 1 m in length. Perhaps young hadrosaurs had time to grow up, as their teeth had already been erased. Perhaps they were in a nest under the care of the parents (or parent) which is still quite a long time after the end of the incubation. The scholars opened colonial nesting of Maiasaura in sediment formation Two Medicine. It was the first solid proof of parental care of the young hadrosaurs. Animals built nests in dry upland locations. They dug the earth which formed a crater, surrounded by a wall nesting platform about 3 meters in diameter and 1.5 m high. The nest was renewed year after year, when the adult species came to their old nesting sites annually.
They were at a distance of about 7 m from each other, in case other animal accidentally stepped on them, and were zealously guarded from predators (close to the remains of theropod Troodon, and even his balls were found, which means that most likely small predators moved following migrating herds of herbivores and ate if possible, their eggs and young species). Eggs (about 20, each 20 cm in diameter) were deposited on a circle, while the layers were previously lined on the bottom of the socket plants, each layer hidden with ground to preserve heat (Benton et al., 2014). Newly hatched baby was about 30 cm long and weighed less than 1.5 kg. Its bones were still rather weak, which is the evidence that for some time the kids were helpless and in need of caring parents. As the adults were nearly 9 meters in length and weighing about 3 tons, scientists have suggested that they were too big to hatch the eggs in the nests. Instead, eggs were kept warm in the nest as the dinosaurs brought the plants that were starting to decompose and ferment, like compost. Modern crocodiles incubated eggs in the same way (Amiot et al., 2015). The nest was found to consist of the plant material, which may have been the remnants of food or the material for insulation. Breeding period is the warm season, when food was available and young dinosaurs were growing up in a very short period of time and then migrated along with the whole herd to the place of feeding. Perhaps the development of mechanisms of rapid growth and maturation of young species took place in response to predation.
For example, the species, Nipakrosaurus stebingeri grew 3-5 times faster than the predators tyrannosaurid Albertosaurus, its gigantic relative Tyrannosaurus rex, as well as small Velociraptor, like Troodon, reaching sexual maturity at the age of 2-3 years old (Benton et al., 2014). They were completely formed at the age of 12 years, while their predators weighed 20-30 kg. It is possible that it was beneficial for growth check juveniles. Bone study showed that hadrosaurs of this place reached adult size at the age of 3-5 years old (Brusatte et al., 2015). Most likely, going to the larger size class, the dinosaurs migrated to the central part of the basin, where abundant pastures could be found around the lake and rivers, where the dinosaurs could find refuge from predators. However, the large sized herbivorous dinosaurs were some kind of insurance against the attacks of tyrannosaurs and crocodiles, just as in the African savannah lions and crocodiles attack beware of elephants.
The Ecology and Environment of Dinosaurs
The peaceful nature of hadrosaurs can be analyzed on the basis of their herbivorous lifestyle. The bodies of these dinosaurs could reach a weight of about 8 times larger than the largest modern land mammals. Factors responsible for the achievement of the maximum size include the quantity and quality of resources, recycled food consumption, and the rate of vertebral energy. Of the two species, with the same flow of energy, appearance, the rate of spending maximum energy is lower. So, a much larger mass of marine mammals reflects the abundance of resources in the marine environments. Presumably, the low cost of energy allowed Mesozoic dinosaur community to support the biomass which was 5 times greater than that of modern herbivorous mammals of Africa. Estimated biomass of dinosaurs was calculated for the Campanian-Maastrichtian localities of Western Canada reaching about 2 tons per 1 ha (Amiot et al., 2015).
Herbivorous dinosaurs of the Mesozoic period were undeniable resource for the existence and development of predators. Some bones of hadrosaurs clearly prove the cases of the predator attacks. For example, it is known that the tail of Edmontosaurus regalis in case it was bitten by dinosaur rex, was healed by itself. Another example is the famous Amur Olorotitan arharensis of Kundur. It has repeatedly been subjected to attacks by predators and consequently had a damaged spine and limb girdle.
Injuries also occur on the lower jaw and the distal caudal vertebrae of the spine. Apparently, during the lifetime this dinosaur had several tumors crustaceans and probably limped on one leg, as the collision and the calcaneus firmly fused with the big and small tibia. The words “struggle for existence” for Olorotitan arharensis were clearly relevant. The deposits ofAguja Formation (Campanian, Upper Cretaceous) in northern part of the state of Coahuila (Mexico) as well as numerous fossils of vertebrates have been discovered, including duckbilled dinosaurs. There were found the remains of young species that were 2 m long, and adults up to 11 m (Benton et al., 2014).
The presence of species of different ages can be described as a group behavior of these animals and the possible presence of dinosaur’s “kindergarten” in these surroundings. One of the caudal vertebrae hadrosaur’s length was 8.5 cm, which is the evidence of predation of the giant crocodile Deinosuchus riograndensis on these animals. Bite traces thereon were 8 mm in diameter and 6 mm in depth (Amiot et al., 2015). Pit being divided in half is indicative of a crocodile teeth, and noticeable force on the bone.
Apparently, deinosuchus attacked hadrosaur from the side of the water, but the latter managed to escape. Since the edges of the wound were covered with calluses, platypus dinosaur most likely died several days later from loss of blood or infection.
Examples of eating carnivorous dinosaurs are multiple, and theropods bones are found relatively frequent, while many large dinosaurs’ bones were damaged by predators or scavengers (Brusatte et al., 2015). The tyrannosaurid teeth were ideally suited for crushing and cracking of bones, so traces of bone damage by predators or scavengers could be frequently observed (Moen & Morlon, 2014). Epiphyseal were deprived of nearly half of the limbs (at least in the Russian Amur locations). Modern crocodiles, alligators and gavials actively digest bone and hostile environment of the stomach allows almost completely dissolving the bone material. However, in most localities of the remnants of the young dinosaurs, which could be killed by the theropods, the dinosaurs preferred to hunt and eat the young species and teenagers of herbivorous reptiles. Regarding the above-mentioned formation Two Medicine, it is also known for numerous findings of dinosaur coprolites with snail shells. Snails association with dinosaur dung demonstrates that gastropods (7 different genera, both terrestrial and aquatic) and dinosaurs occupied the same habitat and trophic that were linked (Benton et al., 2014). Snails used dinosaur dung that is large, moist and rich in microbes, which supplied them with food, and also served as a breeding ground.
Evidence of the lack of migration of the hadrosaurs was obtained by studying and comparing stable isotopes contained in the localities of Campanian age. Dinosaur formations Two Medicine, Dinosaur Park, Judith River, Kaiparowits and Fruitland migrated from north to south of the North American continent to the very distant territories. To do this, we measured the ratio of isotopes of oxygen and carbon but the carbonate contained the enamel and dentin hadrosaurids samples from five different locations in which the age difference was not more than 2 million years (within the statistical margin of error) (Amiot et al., 2015). In total, teeth of 13 species of hadrosaurs were examined. According to information received, the hadrosaurs of these different locations ate plants and drank water with different ratios of isotopes. One of the conclusions regarding these differences is that late Cretaceous hadrosaurs in the western part of the present North America did not migrate over long distances, so the differences in isotopes have not been established.
The difference may also be due to very different physiological characteristics of each species of hadrosaurs, even though their patterns of eating and drinking were the same. However, this version does not correspond to reality, if to compare hadrosaurs and modern ungulates in which the difference in isotope ratio is not more than 2%, even for quite different animals, but residing in the same area. It is also interesting that the isotope ratio of hadrosaurs in low-lying coastal areas was quite different compared to that of animals of the interior of the continent and mountainous regions, indicating that the environmental conditions affected these differences. Indirect proof of the absence of migration is provided by the findings from the mountains, which were the breeding areas of hadrosaurs, while the coastal plains were the breeding regions of other species.