Bird Dinosaurs Debate and their species origin

Issues pertaining to the origin of any species of animals have always been contentious. This may have resulted from the varied explanations of the origins of human beings and other animal species, each of which comes with supporting “evidence”, as well as flaws that raise doubts as to the authenticity of the explanations. Needless to say, evolution has been one of the most widely accepted theories. Indeed, human beings are said to have evolved from monkeys and apes, a theory that has raised immense debates and controversy (Zhang 35). However, recent times have seen increased interest in the origin of birds. This is especially with regard to the supposed link between birds and dinosaurs. Indeed, the notion or theory that birds evolved from theropod dinosaurs has almost certainly been touted as the most widely accepted fact pertaining to evolution (Longand Peter 45). Scholars have noted that a large number of evolutionary researchers had moved from asking the “if” question and started asking “how”. This theory was crafted by Thomas Huxley, one of the most famous supporters of the Darwinian theory of evolution, through his publications on the same between 1868 and 1870 (Shealy and Michael 16). Huxley was building up on Sir Richard Owen’s observations that dinosaurs, which were fearfully great reptiles, were a unique group of reptiles that were quite different from current day’s lizards. In addition, Owen had noted that dinosaurs were reptiles that not only walked upright but also had a posture that resembled that of rhinos and elephants. Huxley, in propagating this theory noted that a large number of dinosaurs had a short torso, long hind limbs, long and mobile neck, massively braced hips, as well as bird-like ankle joints that were considerably typical of the anatomy of birds  (Longand Peter 49). Of course, other types of evidence were crafted as more researchers studied dinosaurs and compared their anatomy with that of birds. However, increased research has also unearthed evidence to the contrary and poked holes on the fabric of the theory that links birds to dinosaurs.

Evidence that birds evolved from dinosaurs

Varied forms of evidence have been crafted in support of the link between birds and dinosaurs.

First, researchers have found birdlike eggs inside the fossils of a female dinosaur. The dinosaur called theropod had the capacity to produces two eggs simultaneously. This capacity, researchers have noted, lies somewhere between the capacity of birds and that of primitive reptiles, which suggests that there is a link between the two animals (Shealy and Michael 17). Indeed, theropods have been considered as some of the closes dinosaur ancestors of present-day birds. It is worth noting that reptiles have the capacity to lay a clutch of eggs at the same time while birds lay a single egg at a time. In essence, scientists have explained this phenomenon and stated that birds have the capacity to produce only one egg at a time as a way of lightening their load for flight.

In addition, scientists have drawn similarities between the behaviour of male-meet eating dinosaurs such as the Troodon to guard nests and even brood developing eggs in a manner considerably similar to present-day birds. The aspect of male animals guarding eggs is typical among large flightless birds such as rheas and emus. Indeed, scientists note that males, in over 90% of the living bird species take part in the parental care of their young ones (Shealy and Michael 19). Scientists noted that the dino-nest-guarding dads were likely freeing up the moms to forage for more meaty meals that would enable them to lay more and bigger eggs thereby increasing their chances of survival. Researchers also noted that there was a high possibility that the dinosaurs’ nests incorporated eggs from a number of females, a trait that is common with ostriches.

Moreover, an examination of dinosaurs has shown the evolution of the breathing system of birds. An 85-million-year-old carnivorous dinosaur that was unearthed in Argentina came with a breathing system that had air sacs of bellows that allowed for the pumping of air through its lungs. Scientists have noted that only birds can breathe in such a manner today (Chiappe and Lawrence 64). They underlined the fact that the bones of the dinosaur called Aerosteon riocoloradensis came with telltale pockets, as well as a sponge-like texture referred to as pneumatization, that allowed air sacs from the lungs to invade the bones. As much as Aerosteon possibly had feathers, it is highly unlikely that it could fly (Dingus and Timothy 59). The researchers underlined the fact that instead, it was highly likely that the birdlike breathing system evolved to assist in keeping the tipsy two-legged runner considerably more balanced, or even as a cooling mechanism (Shealy and Michael 28). Complementing this argument further is the evidence derived from meat-eating dinosaurs such as the velociprator, which had breathing structures known as uncinate processes. Researchers have underlined the fact that the breathing structures are also seen in birds (Dingus and Timothy 64). Uncinate processes refer to small bones that function as levers in moving the sternum and ribs in the course of breathing. Researchers from the University of Manchester noted that the long uncinate processes present in meat-eating dinosaurs had similarities to those present in diving birds like cormorants or even pelicans.

On the same note, scientists have examined the features of the earliest known bird called Archaeopteryx. They note that the bird had dinosaur-type feet as shown by the analysis of well-reserved fossils (Dingus and Timothy 67). This may be contrasted with the modern day birds which have a backward-pointing hind toe that assists them in clinging to power lines and branches. The Archaeopteryx fossil, on the other hand, showed a first toe that extended from one side of its foot as is the case for a human thumb. This configuration bears considerable similarity to that of dinosaurs such as the velociraptos, which is said to have been extremely fasts and would ran on two feet. This similarity renders credibility to the argument that birds evolved from dinosaurs.

Lastly, scientists have examined pieces of ancient gunk and opined that it confirms the link between dinosaurs and birds. Soft tissue that is found in a 68-million years old Tyrannosaurus rex leg bone that was discovered in Montana offered extremely compelling evidence pertaining to the possibility modern birds descended from dinosaurs (Chiappe and Lawrence 49). The gunk or soft tissue incorporates collagen proteins (Dyke and Gary 64). Researchers have decoded these proteins and tried to draw comparisons with proteins from soft tissues of 21 living organisms. The comparison revealed that the dinosaur proteins bore close resemblance with birds such as chicken and ostrich than with those of any other creature such as lizards and alligators.

 

Evidence that birds did not evolve from dinosaurs

While there may be immense evidence showing that birds emerged from dinosaurs, scientists have been working to eliminate any supposed link between the two. Indeed, they have drawn up evidence showing that such a link may not even exist.

First, they have underlined the importance of determining whether feathers are symmetric or asymmetric when assessing fossils that have feathers. They note that all flying birds come with flight feathers or asymmetric wings, in which case it would be reasonable to assume that every other fossil that had asymmetric feathers belongs to a flying creature. Symmetric feathers, on the other hand, are found on wings of flightless birds (Feduccia 79). Scientists have contested the suggestion that some Chinese fossils incorporated some proto-feathers. They studied the supposed evidence on the fossil birds and the manner in which the skin of reptiles decomposes and compared it with fossils of other animals that incorporated dino-fuzz. From these studies, the scientists concluded that there existed no proper evidence showing that fossilized structures that had been discovered in china were rudimentary feathers, rather the fossilized patterns appeared like bits of decomposed skin, as well as supporting tissues that only bore some resemblance with feathers to an entirely modest degree.

In addition, scientists examined the femur of birds and compared it with that of dinosaur. Indeed, research on the connection between the two animals is hinged on the upper leg bone (femur) of birds. Scholars have noted that a bird’s femur, unlike that of other waking creatures does not move significantly (Feduccia 59). Instead, birds, articulate the lower part of the leg in order to run or walk. The surprising discovery made by these scientists was that the knee running anatomy that has nearly fixed musculature and femur bones is extremely important in the prevention of the collapse of a bird’s air-sac lung every time the bird is taking a breath (Dyke and Gary 97). This has been cited as extremely fundamental to the physiology of birds. The location of the muscles and the thigh bone is extremely critical to the functioning of the lung, which in turn provides them with sufficient lung capacity to enable flight (Martyniuk 34). Of particular note is the fact that this fixed femur is deficient in dinosaurs, including the theropod dinosaurs from which proponents of the bird-dinosaur link say the birds evolved. Indeed, the scientists noted that the theropod dinosaurs incorporated a moving femur, in which case, it could not have incorporated a lung that functioned in that manner in birds. In fact, their abdominal air sac would essentially have collapsed if they had one, that is. This evidence undermines the critical or important piece of supporting evidence pertaining to the link between dinosaurs and birds.

Moreover, scientists examined the respiratory physiology to refute any ideas pertaining to the relationship between birds and dinosaurs. There exists immense evidence that lungs of birds do not resemble those of dinosaurs in a lot of crucial ways. Scientists undertook a comparison of the present day mammals and those of crocodiles and mammals with those derived from fossils of theropod dinosaurs and early birds (Martyniuk 69). Like mammals, crocodiles come with diaphragms that assist in their respiration although their piston-style diaphragms id significantly different from that of mammalian structures. Of particular note is that the theropod fossils seem to exhibit a similar separation pertaining to the visceral activity, not to mention fundamental skeletal features that resemble those of crocodiles. This, in essence, shows that most likely had diaphragms that looked like those of crocodiles (Paul 27). Indeed, the fossilized and bird-like dinosaur called Sinosauropteryx also exhibited traces of a soft tissue separation in the body cavity. Birds, by contrast, come with no diaphragms partitioning or dividing their body cavities. In fact, they utilize the movements pertaining to the movement of their chests and pelvises to breath, not to mention that they come with lungs of varying types (Kaiser 30). Fossils of early bird called Archaeopteryx exhibited a skeletal structure that was consistent with being a bird. It is impossible that birds that do not have diaphragms evolved from dinosaurs that have diaphragms as such a condition is likely to result in breathing problems.

Lastly, there existed considerable morphological variations between birds and dinosaurs. As much as the Archaeopteryx had feathers, its skeleton was uniquely non-bird-like with a particularly long bony tail, claws on its wings, as well as teeth rather than a beak (Kaiser 47). On the same note, the Archaeopteryx’s skeleton comes with too many bird-like characteristics for it to be considered coelurosaur. The Archaeopteryx, for instance, came with a wishbone or furcular, as well as bird-like feet, which negates any insinuations pertaining to its being merely a feathered dinosaur. On the same note, dinosaurs came with serrated teeth, while birds come with peg-like teeth. In addition, dinosaurs come with a characteristic join in the lower jaws used in grasping prey (Paul 34). Such features are alien to birds, in which case it is quite impossible that they were the ancestors of birds.

 

 

 

 

 

 

 

References

Kaiser, Gary W. The Inner Bird: Anatomy and Evolution. Vancouver: UBC Press, 2007. Print.

Martyniuk, Matthew P. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, N.J: Pan Aves, 2012. Print.

Feduccia, Alan. The Origin and Evolution of Birds. New Haven [u.a.: Yale Univ. Press, 1996. Print.

Paul, Gregory S. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore, Md. [u.a.: Johns Hopkins Univ. Press, 2002. Print.

Dyke, Gareth, and Gary W. Kaiser. Living Dinosaurs: The Evolutionary History of Modern Birds. Chichester, West Sussex: Wiley-Blackwell, 2011. Internet resource

Dingus, Lowell, and Timothy Rowe. The Mistaken Extinction: Dinosaur Evolution and the Origin of Birds. New York: W.H. Freeman, 1998. Print.

Chiappe, Luis M, and Lawrence M. Witmer. Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley, Calif: University of California Press, 2002. Print.

Shealy, Dennis R, and Michael W. Skrepnick. Dinosaurs Alive!: The Dinosaur-Bird Connection. New York: Random House, 2001. Print.

Zhang, Miman. The Jehol Biota: The Emergence of Feathered Dinosaurs, Beaked Birds and Flowering Plants. Shanghai: Shanghai Scientific & Technical Publishers, 2003. Print.

Long, John A, and Peter Schouten. Feathered Dinosaurs: The Origin of Birds. Oxford: Oxford University Press, 2008. Print.


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