Evaluating The Evolution Of Flight Among The Various Vertebrate Groups Essay Example

1. Introduction
Understanding the evolution of animals and their traits in fact provides clues to the adaptation of animals in the changing environmental conditions. Different hypothesis and assumptions are associated with the evolution of flight in vertebrate groups and still there appear no solid proof that points out to a single line of evolution with regard to the flight in vertebrates. But evolutionary biologists clearly find some form of association between the morphological and physiological adaptation of dinosaurs with that of the present day structures that assist flight in vertebrates and details of the evolution and its related aspects are discussed.
2. Definition of flight
According to Rayner (2008, 269) flight is defined as the “ability to produce useful aerodynamic forces by flapping the wings”, which is considered as remarkable feature in the evolution of vertebrates. Based on the similarities with regard to the morphological and anatomical features of theropod dinosaurs and birds they are considered to have closest ancestral associations with birds. Based on the American Museum of Natural History (AMNH) record, “flying reptiles called pterosaurs” are considered as the “first flying vertebrates” (AMNH records 2).
3. Evolution of flight in vertebrates
There appear different school of thoughts regarding the evolution of flight and several researchers considered flight to have evolved from the arboreal behaviour of the ancestors. While others argue that the “running and leaping” behaviour of ancient dinosaurs might have paved the way towards the evolution of flight (Rayner 2008, 274). Though there are no major evidences for substantiating these claims, both these claims seem to have logical significance in the evolution. Lack of clarity in the evolution of flight is possibly associated with the discrepancies in the definitions, absence of consensus in the interpretation of paleontological evidences and difficulty in connecting the discontinuous fossil based evidences at morphological and functional levels.
The recent identification of “large pernaceous feathers” in the hind limbs of “non avian dinosaurs” in fact provides some important insights on the evolution of flight in birds (Zheng et al 2013, 1309). Presence of metatarsal feathers with similar structural arrangements and “characteristics like the presence of stiff vanes and curved rachises”, which is believed to be “aerodynamic in function, providing lift, creating drag, and enhancing manoeuvrability” might probably have some evolutionary significance, particularly associated with flight in birds (Zheng et al 2013, 1310). According to Xu et al (2009) despite the morphological differences in the hind limb feathers of ancient animals belonging to different taxa, the presence of these metatarsal feathers in Pedopenna, Anchiornis, Microraptor, etc strongly suggests about the existence of four winged creatures, which could probably have ancestral linkages to birds. In agreement with these views, Wang, McGowan and Dyke (2011) claims that though there appear morphological differences in the flight assisting structures like the wing elements, bones, etc the adaptation occurred from the Mesozoic birds could surely be pointers to the evolutionary linkages to these groups. “Miniaturization of the bones” of the dinosaurs might also have strong connections with the evolution of flight in vertebrates (Russell, Hertz and McMillan 2011, 216).
4. Nature of the structures used in flight
The main structures that assist flight in birds are the wings which are the adapted forelimbs having atypical “articulating surfaces” that facilitates the movements that are essential for flight (Russell, Hertz and McMillan 2011, 196). Though the “basic skeletal structures of the forelimb of birds and bat was inherited from their common ancestor, the theropod vertebrate” that lived millions of years ago; it is well documented that the “flat surfaces of the wings and the flying behaviour are homoplastic” and not homologous (Russell, Hertz and McMillan 2011, 196). In birds, flight is also assisted by feathers that cover the wings and this seems to be different in bats and pterosaurs. So it can be confirmed that some of the structures like the bones of the wings that assist flight are homologous while some structures like the flat surfaces and feathers of the wings are homoplastic.
5. Conclusion
Evaluations on the evolution of flight in vertebrates revealed that though evolutionary biologists have found some evidences that suggest evolution of flight, yet there is no possibility for making substantiations in this regard. But the recent investigation results like the identification of feathers in the hind limbs of non avian dinosaurs and other similar discoveries point towards uncovering more truth regarding evolutionary links.
6. References
AMNH Records. 2012. Hall of fame. http://www.amnh.org/exhibitions/permanent-exhibitions/fossil-halls/hall-of-vertebrate-origins
Rayner, M.V. Jeremy. 2008. “The evolution of vertebrate flight”. Biological Journal of Linnaean Society, 34 (3): 269 – 287. http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8312.1988.tb01963.x/abstract
Russell, Peter J., Hertz, Paul, E. and McMillan, Beverly. 2011. Biology: The Dynamic Science. Belmont: Cengage Learning.
Wang, X., McGowan, A. J. and Dyke, G. J. 2011. “Avian Wing Proportions and Flight Styles: First Step towards Predicting the Flight Modes of Mesozoic Birds”. PLoS ONE, 6 (12). http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028672
Xu, X. et al, 2009a. A new feathered maniraptoran dinosaur fossil that fills morphological gap in avian origin. Chin. Sci. Bull. 54: 430 – 435.
Zheng, Xioating. et al, 2013. Hind Wings in Basal Birds and the Evolution of Leg Feathers. Science, 339: 1309 – 1312.