I will try to investigate and hopefully prove the relationship between birds and dinosaurs in a 2 part series of posts involving my research into finding the kinship between the two.
The word ‘fossil’ typically forms a picture of a dinosaur in one’s mind, this is because they are renowned for their osseous matter. A dinosaur called the Archaeopteryx which lived between the Tithonian and Barremian periods (approximately 150.8 million years ago and 125.45 million years ago) during the Mesozoic epoch, was commonly thought to have been a bird due to its abundance of feathers and its comparable appearance. However, after its first fossil was unearthed by Christian Erich Hermann von Meyer on the 30th of September 1861 , and for 158 years, Vertebrate Palaeontologists around the world, have investigated its anatomical features and drew the conclusion that it was not a bird. This is because the Archaeopteryx was found to possess the same wing shape as a modern-day bird, however the glenoid fossa of scapula (shoulder socket of birds) of the Archaeopteryx was distinctive from the modern-day bird. This implies that Archaeopteryx could not carry out a proper flight stroke. This also suggests that this particular dinosaur could have been a ground dweller. The theory that ground dwelling maniraptorans increased their velocity to gain enough speed to propel themselves upward and possibly into flight, is called the ‘ground up hypothesis’. Following this theory, a modern-day bird called the chukar is able to run up a surface of high incline and gain velocity by flapping its wings. This theory is called Wing Assisted Incline Running (WAIR). I think that the Archaeopteryx could have used this technique to escape from predators or to reach higher branches to prey on insects. By repeating this technique over many generations, the Archaeopteryx would have been able to evolve to it’s ecological niche, by developing larger feathers, longer forelimbs and stronger wing and arm muscles, resulting in the inevitable birth of flight. In addition to this, it is shown that modern day birds possess the breastbone called the sternum. The sternum is ‘the main site of attachment for the pectoralis muscle which pulls the wing down during flight strokes’ . The sternum is not present in any Archaeopteryx specimen, further emphasising the fact that it was unable to fly. However, this discovery does open a door towards gliding, which is highly likely, due to the application of the technique of Wing Assisted Incline Running and the ground up hypothesis, possibly leading to the development of proper flapping strokes, allowing Archaeopteryx to fly. It is said that when two organisms are ‘not closely related’ but appear indistinguishable, they emerge with comparable traits as a result of adapting to the same or similar ecological niches. This theory is called Convergent Evolution. An example of it, involves the non-bird maniraptorans Oviraptorosaurs, Troodontids and Dromaeosaurids. They were endowed with a body overlaid with convoluted and small feathers . This therefore implies that their physical appearance matched that of a modern-day bird. This example of Convergent Evolution helps us to determine that the following Maniraptorans were not related to modern day birds. This implies that Birds may not be similar with certain dinosaurs, but may have evolved from another species of dinosaur. Another anatomical feature possessed by birds is the gizzard (also known as the ventriculus). This organ is a part of the digestive system and allows the organism to digest harder food items due to it’s roughened structure. It uses stones or rocks called gastroliths that are in the organisms stomach to grind hard pieces of matter, enabling ease of digestion for the animal. The gizzards of birds are lined with a carbohydrate – protein substance called koilin, which preserves the muscles in the gizzard from damage. The gizzard is likewise also found in dinosaurs such as Seismosaurus, Barosaurus, Apatosaurus and Sellosaurus. The wishbone, is considered as the breastbone in birds. Palaeontologists around the world have also discovered wishbones in several Theropod dinosaurian specimens. In addition to this, it is a known fact, that this breastbone is unique to birds, and we have now discovered that it is unique to birds and dinosaurs too. The wishbone supports the body of a bird during flight, providing a significant balance of weight. The fact that this bone was possessed by dinosaurs too, suggests that they would have evolved to their specific niches to obtain it. They may have needed it to support their bodies too during strenuous activity, maybe for flight? This illustrates their evolution, opening a door into the evolution into birds through flight, like the Archaeopteryx. This therefore implies that birds may have evolved from Theropod dinosaurian.
Be sure to wait for the Second Part of 'What the HPQ??!!'