Origin and Evolution of Birds Paper - Assignment Example

?Chul lee Blake Animal Biology 102 November 28, Origin and Evolution of Birds Birds are a truly unique set of animals in the world. For millions of generations, birds have constantly been living on earth. As the evolution theory came to being and many scientists came forth to prove it, the evolution of birds was not left behind. Birds are animals that evolved millions of years ago due to a number of factors in order to resemble the modern day birds (Heilmann 2). As more research is put forth on the origin and the evolution of birds, many results seems to be emanating day by day as new discoveries are made. In the recent years, with enhancement in scientific development, much has been able to be got related to the origin and evolution of birds (Miller, Vandome & McBrewster 20). With the help of techniques like computerized carbon dating and the rest, the origin of birds could be able to be pinpointed and much of the changes that took place in evolution place in a certain time (Heilmann 5). Since every species ought to survive in a given environment, a number of adaptation changes are adopted. Often, some of these adaptations result into serious and minor changes in the physical nature of the given species resulting in evolution. Evolution essentially is the gradual change of a species from the original to a different version. Birds too were not left behind in the evolution process (Heilmann 34). Survivals always a key feature in the maintenance of a given species. For any species to survive, means they had first to acquire the basic want like food and security. Birds for instance migrate to distance lands in search of food and a reproduction place. In terms of security, birds that were preyed on by land animals might have found a way to fly to escape such predators. Often evolutions come as a means to overcome daily challenges in life. Over millions of years back, it has been researched that birds were the ancestors of dinosaurs called theropods. One of the most efficient survival strategies was migration. Migration was a complex task, yet most species created their own migration strategies for survival. Some species would migrate for a short distance and some would take long distances seeking for suitable environment (Feduccia 2). Thus, for species which needed long distance migration had their own specialized strategies. From this concept, we can think about the evolutionary origin of birds and their similarities to reptiles. For survival, reptiles had to go to a higher place in search for food, so they had the power to fly. Therefore, birds developed their wings, and later on they developed feathers. Birds have move power at flying than reptiles now. Bird flight origin is an immense issue in avian biology plus in the overall evolutionary theory. Often, many scientists have pointed to the fossilized Archaeopteryx specimens as evidence to the existence of a transitional vertebrate which developed during the evolution of birds from reptilian dinosaurs (Feduccia 18). Often, most birds do fly, therefore distinguishing them from the other vertebrate classes. Hence, flight is the chief means of locomotion in many bird species and can be for feeding, breeding, feeding, and escape plus predator avoidance. Birds have many adaptations for flight. These include having a lightweight skeleton, the pectorals (which accounts for 15% of the total mass of the bird), two large flight muscles, and the supracoracoideus. Often, the wing size and shape determine a given bird’s species flight type (Feduccia 26). Often, many bird’s combine power and the flapping of their wings to fly, and once on air, flap less extensively to save on energy. It is estimated that about 60 bird species that are extant are flightless as were the case of many extinct birds (Miller, Vandome & McBrewster 234). Flight is hence seen as a very serious adaptation process in the evolution of birds that have enabled them to survive time. It has been found out that flightlessness sometimes arises in birds located in isolated islands, probably because of limited resources plus the absence of predators. Penguins which are flightless use similar musculature plus movements to “fly” in water the same way dippers, shearwaters and auks do. In accordance to some researches on birds, it was found out that the histo-chemistry and anatomy of flight muscles often exists in wing-propelled diving bird too (Feduccia 33). Furthermore, wings have provided a crucial aspect for birds to use in flying for ages since evolution process started taking place. There are four types of wings that have been identified so far (Miller, Vandome & McBrewster 44). Elliptical wings have a low aspect ratio and are slotted between the primary feathers.  These wings prevent stalling during sharp turns with low speed flight, and frequent landing and takeoff.   High aspect ratio wings can sweep back and taper to a slender tip, lacking wing-tip slotting characteristics of elliptical wings.  These types of wings are essential for high-speed flight though cannot keep easily a bird in the air at low speeds (Feduccia 45).  Fastest birds, such as sandpipers, clocked at 175 km per hour, belong to this group. Dynamic soaring wings are adapted for dynamic soaring.  Species containing dynamic soaring can be only done over sea with strong, reliable, winds, and exploits different wind speeds near the ocean surface and well above the surface.  High-lift wings are broad wing and wing slots (Feduccia 50). For example, soaring birds as the pelican and the eagle have wide and elastic tail, while diving and gliding birds, such as the gull and the albatross, wings are long and narrow. Another example, hoverers and darters like the hummingbird and swallow their wings like a narrow and the main especially long to help a rapid, unpredictable flight. Based on biological and fossil and evidence, most scientists have come to accept that birds originated and hence are a specialized subgroup of dinosaurs called theropod (Feduccia 65). In addition, it has been found out that Dinosaurs and descendants of birds were more specifically members of maniraptora. With time, as scientists discovered more theropods of the nonavian type that were closely related to birds, clear distinction between birds and non birds became more blurred (Heilmann 67). Some recent discoveries in North East China, Liaoning Province of northeast China, demonstrated that many small theropod dinosaurs possessed feathers, contributing to this ambiguity. Scientists hence view Archaeopteryx that lived approximately 150 million years back, as the earliest known member of modern bird’s lineage, though it retained some features of the small dinosaurs (Miller, Vandome & McBrewster 5). The small, two-legged dinosaurs named theropods scurried something like what resembles today's roadrunners (Feduccia 76). Some characteristics which typify birds were present in some theropods before even birds evolved, including a wish bone, hollow bones, a backward-pointing pelvis, plus a three-toed foot. As the theropod evolution continued, the hands and forelimbs became progressively longer. In addition, in some theropods, wrist bones took shape to allow sideways flexibility at the joints (Miller, Vandome & McBrewster 83). The purpose of that evolution was to allow the given animals to whip the long hands the possessed forward in motion that was swift snatching in order for other to catch prey (Miller, Vandome & McBrewster 115). Furthermore, the theropods’ wishbone served mostly to anchor specific muscles that pulled forward the forelimb in a grabbing movement. A motion analysis of that movement proved to be somehow identical to modern birds’ flight stroke (Feduccia 89). The agreement in contemporary paleontology show that the avialans or birds were close relatives to the deinonychosaurs, and that included the troodontids, dromaeosaurids and archaeopterygids (Heilmann 77). An Archaeopteryx-like theropod from China and the origin of Avialae Together, the three formed the group called Paraves. In addition, some basal members of the paraves group, such as and Archaeopteryx and Microraptor , have features that enabled them to fly or glide (Miller, Vandome & McBrewster 67). Deinonychosaurs, the most basal of them were very small. From this evidence, the possibility of the paravians’ ancestors was raised as being arboreal, and may have been capable of gliding or flying or both (Heilmann 68). Unlike the Archaeopteryx and some feathered dinosaurs, which primarily ate meat, some recent studies have shown that the first birds may have been herbivores (Feduccia 90). The Archaeopteryx in the late Jurassic is known as the first found transitional fossils, plus it supported the evolution theory in the 19th century. The first fossil to be displayed to have both reptilian and modern bird features was the Archaeopteryx. It had clawed fingers, teeth, and lizard-like tail, plus wings that had flight feathers similar to those seen in modern birds. Anyway, some people do not consider it a direct ancestor to modern birds, however there might be a possibility of some relation to the real ancestor (Feduccia 134). Despite the evolution of birds picture becoming more clearer from theropod dinosaurs, few scientists still remain unconvinced. To date, no alternative hypothesis has been brought to explain the many similarities between theropods and birds. However, there is still scant evidence to evidence that there was the link of any kind between the two despite the many similarities mentioned above. Meanwhile, some evidence connecting theropods and birds continues to accumulate (Feduccia 150). Furthermore, for a very long time, feathers have been regarded as a very unique avian feature. Anyway, recent fossil evidence has revealed that feathers, too, may have evolved earlier in theropods before birds. The reason why they evolved for is still not known and what exists are just speculations and theories (Snow 50). For a small, light bipedal predator that leaped into the air when it needed to catch insect prey, some primitive feathers might have been of importance in giving it a lift. In addition, larger feathers might have lifted the bird so as to stay airborne during short distances. Hence, the evolution of feathers that were asymmetrical in shape, like of Archaeopteryx, more so enhanced the early birds flight capabilities (Feduccia 160). The fossil records after Archaeopteryx suggested that birds diversified rapidly in the evolution process. For example, the Cretaceous early birds might have looked weird to us since they possessed clawed fingers and toothed beaks. Therefore, our knowledge of evolution of birds during this period is increasing rapidly. Ever since 1990, there have been more than 3 time bird fossils that have been dated from the Cretaceous and had been discovered in the past two centuries. Anyway, while some of the bird lineages which arose in the Cretaceous might have died out, it is documented that some of them might have survived and given rise to the many diversity of birds that we see today (Feduccia 189). For a long time, birds have developed unique body characteristics for flying. Since birds want toward the long and safe flight, they have to reduce their body weight in various ways. Therefore the bones are honeycombed with air spaces and strengthened by crisscrossing structures. Due to the fusion of the combination of bird’s bones, the skeleton is strong enough for flight, even though those bones have extremely lightweight (Feduccia 200). The hollow with criss-cross structures form rigid girders and platforms, and allowing for mobility (Heilmann 110). They hence formed a strong plate that rested on the thigh bones plus supported the birds as it walked on the ground (Snow 83). Furthermore, birds do possess more cervical vertebrae compared to other animals; most of which are highly flexible and consist of 13-25 vertebrae (Feduccia 234). Therefore, birds remain to date as the only vertebrates that possesses a fused collarbone called the furculaor wishbone or breastbone or keeled sternum. Usually, the keeled sternum serves the function of muscular attachment site for muscles used to enhance flight motion (Snow 35). In addition, flightless birds like ostriches, did not develop pectoral muscles and hence lacked a pronounced keeled sternum. It has been noted that some swimming birds possess a wide sternum, while some walking birds possessed a long or high sternum. In contrast, flying birds had height of keeled sternum and width being equal to those of swimming birds (Feduccia 278). Bird’s skeleton system have five main bones which are the frontal bones where tip head, parietal bone where of head, premaxillary and nasal bon where top beak and ate the bottom beak which is called mandible. Birds possess ribs that have uncinate processes. These are hence hooked extensions from the rib bones that help in strengthening of the rib cage through overlapping the rib behind them (Feduccia 290). Furthermore, they also possessed greatly elongated tetradiate pelvis like that seen in some reptiles. Usually, the hind limb had an intra-tarsal joint like that seen in some reptiles. In the evolution process, there have been extensive fusions of the vertebrae trunk as well as the pectoral girdle. The birds also had a disposed skull like other reptiles with similar pre-lachrymal fosse (Heilmann 204). In addition, the skull possesses a single condyle on the occipital. Furthermore, the shoulder comprised of the shoulder blade, the scapula, humerus and coracoid at the upper arm.The metarcarpus and carpus formed the wing of the birds. More so, the hips consisted of the pelvis, and comprised of three major bones; ischium, ileum, and a pubis (Feduccia 299). The 3 bones worked in unison to form a bony structure called the innominate bone. The mentioned bony structure played a significant role in reproduction as it was an important site for laying of eggs. When compared to their ancestors and modern birds, it has been found out that some bones became modifies with time. A good example comprises the modification of the three-fingered manus, the long tail, the toothed jawbones (Feduccia 302). Anatomically, birds also have own unique respiratory system toward flight. Because of their high metabolic rate that they use while flying, birds often have high oxygen demand (Snow 60). The development of a very efficient respiratory system might also have been an important feature in the evolution of birds that enabled them to fly. Birds often ventilate their lungs through having air sacs (Feduccia 322). Air sacs serve as the basic component of their lungs. Birds take in the air via their nostril and passes through their wind pipe to the gaseous exchange center. There are 3 distinct organs that perform respiration and are the lungs, the anterior sacs and posterior sacs. Often, the anterior and posterior air sacs are 9 and usually expand during inhalation. Usually, air enters via the trachea (Snow 68). Then, half of the air that enters goes through the posterior air sacs and the other half goes through lungs into anterior air sacs. Therefore, air coming from the anterior air sacs is directed into the trachea out of the bird's nares or mouth. Furthermore, the posterior air sacs direct their air to the lungs. Other taxonomic groups like the Passeriformes have 7 air sacs, because the clavicular air sacs might have been fused with the some or all of the cranial thoracic air sacs (Feduccia 345). Usually, as air flows through their lungs and air sac system, mixing of the oxygenated air and the carbon dioxide is limited in birds. Therefore, the oxygen partial pressure in the bird’s lungs often remains the same like the environment and hence birds possess a more efficient gaseous exchange system than most mammals (Snow 58). Furthermore, air usually passes via the lungs in both inspiration and exhalation, with the air sacs serving the function of being air reservoir. The avian lungs often do not have alveoli like the mammalian lungs and so instead contain millions of parabronchi (tiny passages) connected at either ends (Feduccia 350). As air flow through the parabronchi honeycombed walls of the parabronchi named atria. The atria often give rise to small air capillaries, where carbon dioxide and oxygen are exchanged by diffusion. In addition, birds also do not have diaphragms. Often, the entire body cavity of birds tries to acts as bellows to assist in moving air through the lungs (Snow 234). During the active respiration phase in birds, exhalation often require a lot of muscular contraction is exhalation. In birds, the syrinx is an organ that produces sound when air flows past it. In some birds, the syrinx may produce complex vocals and some may even mimick human speech like in parrots. The syrinx in some songbirds, produce more sounds at a time (Feduccia 361). Like the human being, birds respiratory system also delivery oxygen into tissues and remove carbon dioxide from their body. Moreover, birds’ respiratory systems play an important role for maintaining normal body temperature. Different from other vertebrate, birds possess small lungs with nine air sacs, which are located in pairs in the thoraxes, and abdomen an even extended by thin tubes into the center of the long bones (Heilmann 234). In summary, we realize that birds also underwent evolution to reach where they are now. From the research, it is evident that birds may bear some ancestral origin to the theropod dinosaurs that lived many years ago. Flight as a feature in birds also underwent evolution among other features (Feduccia 422). It is documented that dinosaur like birds existed in coelurosaurian and birds might have evolved from them. After Archaeopteryx, bird evolution might have focussed on improving their flight apparatus. Furthermore, secondary flightlessness birds might have evolved due to their lifestyles (Heilmann 334). The Tertiary bird may have been very different from the Mesozoic one, leading us to the possibility of a massive extinction to have occurred (Feduccia 425). All in all, a lot about the evolution of birds is known and more is still being discovered as more research is directed towards that field. As new fossils become discovered, more is brought onto the table concerning the birds, their origin and evolution (Feduccia 2). Works Cited Feduccia, Alan. The origin and evolution of birds. Emerald: Yale University Press, 1999. Print. Frederic Miller, Agnes Vandome, John McBrewster. The Origin of birds. London: VDM Publishing House Ltd, 2010. Print. Heilmann, Gerhard. The Origin of birds. Michigan: Dover Publications, 2003. Print. Snow, Philip. The Design and Origin of Birds. New York: Day One Publications, 2009. Print. Read More