Introduction
Multiple researches suggest that dinosaurs are among the most successful groups of animals to have ever lived on earth. Their body physique and adaptability enhanced their survival thereby extending their life longevity. In the course of time, these species evolved into diverse shapes and sizes. As a result, the different types of evolved organisms embraced various modes of living. According to Xu (2006), nearly 150 years after the discovery of the first fossils of the dinosaur, this species was believed be a reptile. In fact, when Richard Owen found the first remains of this organism, the paleontologists used the word “dinosaur” that is Greek for “terrible lizard” to describe its displeasing nature (Prum, 2008). Nonetheless, the perception of this species gradually began to change during the dinosaur renaissance. Between the late 1960 and the early 1990s, a lot of evidence emerged linking the dinosaurs to birds. This information led the paleontologists into believing that birds are direct descendants of the theropod group of dinosaurs. As such, it is rational to conclude that the modern birds are fathered dinosaurs.
The oviraptor is considered to be the most bird like dinosaur that existed millions of years ago. This organism belongs to a genus of a small section of the Mongolian dinosaurs. It lived in the late Cretaceous period in the Campanian stage that is approximately 75 million years ago. These theropods are believed to have been covered in feathers on most parts of their body. In fact, they were avian, had the ability to fly. This paper evaluates the origin of feathers in dinosaurs. Through the utilization of the oviraptor as an example of a feathered dinosaur, it seeks to explain the reasons for these physical changes during the renaissance period. It provides a rationale for the controversial researches based on feather like dinosaurs in the cretaceous period. To enhance the credibility of the information presented, multiple paleontological researches will be used to supplement the claims presented. For a fact, the modern species of birds evolved from the feathered dinosaurs that existed in the Campanian stage approximately 75 million years ago.
Evolution of feather in dinosaurs
Many paleontologists believe that the integumentary structures that sparked the development of feathers of the birds and the legendary dinosaurs can be seen in the modern species of fish and birds. According to the theory of evolution through natural selection Zhang and Zhou (2000), organisms change over time because of the alterations in their heritable behavioral and physical traits. With this in mind, it is worth acknowledging the fact that dinosaurs might have experienced a similar process during the renaissance period. Through these changes, the development of feathers commenced giving rise to feathered dinosaurs. The evolution of the complex coats of the dinosaurian family is thought to have proceeded from the simple growth of hollow filaments through compound stages of development. In fact, the Geological Journal argues that the feather follicle originated from the cylindrical epidermal depression on the feather papilla base (Fucheng, Zhoghe & Dyke, 2006). This initial development led to undifferentiated tubular development of the collar that resulted in the visibility of these structures. In the course of time, newly conceived dinosaurs grew feathers.
During the second stage of the feather development, the basilar follicle collar grew into a longitudinal barb of ridges. These structures had non-branched keratin filaments to enhance the strength of the middle layer. According to Xu, Zheng and You (2010), the structure of the primitive feather was somewhat larger that what is visible in the modern birds. It is believed that since the most of the dinosaurs were non-avian, the feather structures became vestigial as opposed to other body parts since they were mostly used for insulation. As such, they grew smaller during the evolution period with the emergence of the modern day birds. In the final stage of the feather development, the dinosaurs grew pennaceous feathers that enhanced their survival mechanisms. During this period, bipinnate plimilaceous feathers, asymmetrical flight feathers and filoplumes evolved to mature structures. Few of the theropod dinosaurs with the ability to fly utilized these structures to their advantage by flying and keeping warm. However, dinosaurs with a larger form of complex skin did not develop these structures. Instead, they had a dry and scale like outer cover that resembles that of the modern day Gonocephalus and iguanas.
Reasons for their development
The development of feathers among the dinosaurs during their period of evolution was accredited to multiple reasons. According to Norell & Xu (2005), there were different types of feathers linked to specific dinosaurs in accordance with their size, feeding mechanism and sex. As such, one is justified to claim that the development of feathers served three functions. Precisely, support thermoregulation through insulation, enhance attractiveness thereby favoring reproduction and to enhance locomotion for predators looking for prey. However, determining the primary reason for their development is somewhat challenging. Lingham-Soliar (2003) argues that some of the abovementioned functions were co-opted to supplement the survival of the dinosaurian family. For instance, if the oviraptor theropod developed feathers to enhance its attractiveness to the organisms of the opposite sex, this provision can be considered as the function for the feather development. Nonetheless, if these structures aid in insulation of body heat during the cold season, or enhance the movement of the organism during hunting, one is justified to claim that these functions are co-opted to augment the survival chances of the specie in question.
Multiple researches have presented evidence that supposes that the early feathers had different colors and this adaptation enhanced their reproductive success. The evidences presented to support this claim suggest that coloration was the original adaptation of the feathers during the renaissance period and the later functions such as flight and thermoregulation were co-opted. According to Norell et al. (2002), this hypothesis has largely been supported through the discovery of pigmented feathers belonging to different types of dinosaur species. In fact, paleontologists have established that the coloration feature of the feathers was a defining characteristic of the herbivore dinosaurs during the evolution period thereby dispensing their locomotive function among the predator dinosaurs. Additionally, Fucheng, Zhonghe and Dyke (2006) argue that some discovered feathers have been found to have iredescent display features. This characteristic affirms the fact that the primary reason for the development of these feathers was to provide higher attractiveness to the mates thereby enhancing reproduction. Many current researches have validated the fact that the extinct theropods had commendable levels of visual acuity to discern the level of attractiveness created by the colored feathers.
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Aside from the flight function the evolved feathers in the theropod dinosaurs, some research sources claim that these structures served an insulation purpose in the organisms. In fact, a lot of evidence suggests that this was among the primary reason for their development. For starters, the preserved patches of the skin in large tyrannosauroids reveal the presence of scutes while those in smaller and more primitive dinosaurs show feathers. Scutes are bony external scales located on the skins of reptiles such as crocodiles and on the feet of birds (Xu, 2006). When these structures are located on the skin, their primary function is to preserve the heat generated from the bodies of the animals. As such, they serve an insulation purpose. On the other hand, the smaller organisms developed feathers for the same reason since the surface area that needed insulation was relatively lesser than that of the tyrannosauroids. Since the tyrannosauroids were very large organisms with a comparable weight to that of a modern day African elephant, they needed to radiate their body heat efficiently as they were endotherms. The development of feathers would have altered with their body metabolisms. Consequently, they never developed feathers as they had an efficient way of regulating their body temperatures through scutes.
Controversial research on topic
Some researchers claim that the development of feathers was common in most species of the dinosaurs in the renaissance period. In fact, the Geological Journal (2006) claims that the ancestors of the dinosaurian family had feathers. These researchers believe that the development of these structures took place in the same period and was maintained throughout multiple generations until the extinction of he dinosaurian family. To establish the validity of this claim, these researchers believe that the presence of scutes in the larger tyrannosauroids and other gargantuan dinosaurs was replaced with feathers through continuous evolution. However, substantial research to affirm this hypothesis is quite lacking. Owing to the fact that the nature of feathers is quite delicate, these structures are vulnerable to decay in the presence of favorable factors. As such, exemplary preservation mechanisms have to be employed to ensure these structures survive for a considerable amount of time. Additionally, these groups of researchers have not established a proper rationale for the development of feathers in non-avian species.
Multiple sources claim that the primary reason for the development of feathers among the dinosaurs was for flight. As such, this claim establishes a hypothesis leading one to conclude that only the avian dinosaurs had feathers to enhance their movement. This notion therefore dispenses the possibility of non-avian dinosaur species having feathers. Instead, it proposes the presence of scutes in these organisms regardless of size and body physique. According to Prum (2003), the comparisons established between the modern day birds and the dinosaurian family has revealed that both skeletons had a strengthened section in their skeletal system to accommodate flight. These sections include the shoulder bone, the breastbone, clavicle and the pubis. Researchers have since concluded that the shared features in the dinosaur and bird biology show close association between the two species. As such, birds must have evolved from specific types of dinosaurian species. On the other hand, the non-avian dinosaurs lacking feathers evolved into other organisms. In spite of the credibility of the arguments presented by these researchers, it is worth mentioning that substantial evidence about the presence of feathers in non-avian dinosaurs has been found.
A section of paleontologist believe that the oviraptor’s outer body covering was feathers and scales while others dispute this notion in support of scutes. According to Xu (2006), the oviraptor is believed to be the most birdlike organism among all other dinosaurs. In fact, he claims that his theropod had a to chicken like wattle and a sharp, toothless beak. These pieces of evidence suggest that the organism was an exclusive herbivore due to the absence of teeth. Those in favor of feathers as an outer body cover believe that they aided in the incubation period since this organism was a monotreme. As such, the presence of scutes would have minimized the incubation chances for the organism. On the other hand, those in favor of scutes covering believe that the oviraptor was a flightless dinosaur and it therefore lacked feathers. Norell et al. (2002) argue that the organism maintained its body temperature through this structure, as it was easier to radiate excessive heat during the hot season this way. As such, the possibilities of developing feathers through evolution for this genus of dinosaurs were minimal. These differences in evidence presentation have, therefore, sparked a lot of controversies on the body covering of the oviraptor during the Cretaceous period.
Current research hypotheses
Despite the controversies about the presence of feathers in all dinosaurs, recent research has proven that there were multiple species of the theropod dinosaurs lacking this covering. In fact, the Geological Journal reports that feathered dinosaurs were less prevalent than it has been anticipated in the past. Owing to the fact that the development of these covering took place due to evolution, the earlier species must have been covered in a different membrane before the renaissance period. According to Fucheng, Zhonghe & Dyke (2006), an erroneous assumption about dinosaurs living in the same time frame has led many paleontologists into making inaccurate conclusions. Lingham-Soliar (2003) reports that scientists examined the fossil records of a selected dinosaur skin and combined it with an evolutionary tree to anticipate the possibility of feathers appearing in different groups of dinosaurs. The results of this analysis affirmed that the majority of the non-avian dinosaurs like the tyrannosauruses were more likely to have scales than to show signs of developing feather-like structures. Consequently, drawing conclusions about the presence of feathers in all the dinosaurs is a flawed notion.
The presence of feathers in the evolved dinosaurs served diverse functions. As mentioned earlier, multiple researches suggest that the dinosaurs developed these structures to enhance their body thermoregulation. However, some of the feather fossils that have been collected over the years have revealed that these structures had different features. As such, one is justified to claim that they were used to enhance their appeal to the species of the opposite sex. This provision enhanced the levels of reproduction among the species. Additionally, the presence of feathers in small dinosaurs served an influential purpose in thermoregulation. According to Prum (2003), the smaller theropods produced less body heat than the larger tyrannosauroids. Consequently, there was a need to retain the minimal heat evolved by the body to enhance the body functions. Consequently, feathers served a co-opted value of regulating the body temperature. Finally, these structures were influential to the flying predators. In fact, Lingham-Soliar (2003) argues that the avian dinosaurs had a locomotive advantage over their preys thus enhancing their survival. As such, the development of feathers in the dinosaurs was a continuous process and it was influential in more than one way to the organisms.
Feathers covered a large section of the oviraptor’s body while a small section had scales. According to Norell and Xu (2005), people commonly assume that the oviraptor was an avian dinosaur and therefore it was purely covered in feathers. This assumption leads one into drawing inaccurate conclusions due to the limited amount of information. Owing to the fact that the dinosaurian family did not live in the same time frame, continuous evolution occurred among the species. As such, the first oviraptor was purely covered in sclaes before the development of feathers. Scientists at the Natural History Museum have determined that the area of the oviraptor covered in feathers increased after centuries due to continuous evolution. Similarly, other types of theropods went through similar evolution depending on their lifestyle and genetic composition. Several recent discoveries have determined that there might have been a filament-like feather among the dinosaurs that had a similar ancestry. These studies have determined that the meat eating dinosaurs were mostly covered in feathers with an exception of a few species. Oviraptors fall in this category and it should not be assumed that their bodies were purely covered in scales or feathers.
Conclusion
In conclusion, the origin of feathers in the dinosaurian family was a gradual process through evolution. Nearly 75 million years ago during the renaissance period, the theropods began developing feather like structures due to multiple reasons. Thermoregulation is believed to be the most rational explanation to this adaptation. Specifically, the dinosaurian family adapted to the changing environment by growing feathers to retain their body temperature. Since smaller theropods could not generate enough heat through their body processes, there was a need to retain the little amount created with the healp of these structures. On the other hand, large tyrannosauroids could not develop feathers, as it would have had a negative impact on their heat radiation. However, other researchers believe that the development of feathers during this period was mainly because of locomotive abilities. Precisely, predators needed the wings to fly so that they could get their prey relatively easier than it would have been while on the ground. Finally, the diversity in the color and types of feathers discovered over the years created the possibility of the dinosaurs developing feathers for elegance. Specifically, this feature enhanced the appeal of these organisms making it lesser challenging to attract dinosaurs of the opposite sex.
References
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