Evolution of Birds Unravelled

Scientists have arrived at momentous juncture wherein they have completely sequenced whole genome of 45 different existing bird species to answer the little known origins of the Birds. Children who are unassumingly attracted by the veracity of the dinosaurs, perished when an asteroid stuck the earth 66 million years ago. This catastrophe eventually facilitated the evolution of mammals which dominated various niches of earth left vacant by the extinction of the gigantic dinosaurs. Studies of the fossils and the genome sequencing indicated that nearly 10,000 species birds might have descended from theropods, the two-legged dinosaurs which include Tryannosaurus rex that survived the extinction. Over 200 scientists from 20 different countries have collaborated to create evolutionary tree that reveals the exquisite features of the birds like the colourful plumage, loss of teeth and their ability to croon songs. Genetic codes were used to understand a wide range of issues- related to brain functioning, learning concepts, reconstruction of ancient ancestor of birds and if had evolved from dinosaurs.

Overwhelming fossil evidences suggested that birds evolved from small predatory dinosaurs. Scientific theories undergo constant change. The fluctuating nature of science is attributed largely to knowledge which is being constantly upgraded in the face of new evidence and with availability of new technology. Members of the project, Avian Phylogenomics Consortium who developed the Avian family tree published a series of 8 papers  in the latest edition of Science magazine and in more than 20 different scientific journals. To begin with scientists started extracting DNA from finger nail sized pieces of frozen flesh of 45 different species gathered from different museums of the World. The DNA was then subjected to the painstaking genome sequencing. Tonnes of the sequence information was fed to 9 super computers (the equivalent time of 400 years of processor time) to compare all the genomes and align them into a comprehensive family tree. The construction of the bird family tree is a spectacular achievement and it was produced by amalgamating the new information with the previously published sequences of Zebra Finches, domestic turkeys and chickens. Rapid decline of cost of genome sequencing after 2007 and tremendous computing power of beefy super computers which sifted through the tonnes of the genomic sequences made the large scale genomic analysis possible. It indicated that NeoAves the order that contains nearly 95% of the modern birds arose spectacularly and paved way for evolutionary opportunity just few million years after the asteroid collision.

Genomic analysis has indicated that distinctive bird characteristics like the feathers, flight, endothermic physiology, unique strategies for reproduction and growth and novel pulmonary system might have evolved from the Mesozoic terrestrial dinosaurs. Studies in developmental biology and other disciplines also complemented the crucial evidence about the origin and development of various bird characteristics. Modern extant bird orders during the major part might have undergone a gradual and step wise transition with occasional bursts of morphological novelty. In addition to birds three orders of nearest ancestors of crocodiles were studied to logistically understand the origins and evolution of birds. While birds evolved at similar rate as mammals bird genomes are one-third the size. They are similar to mammals in their capacity for vocal learning. The genes identified for vocal learning in birds could provide a clue in rectifying the problems of stuttering or Parkinson’s disease in human beings as well. While water birds had lowest number of genes linked to feather colouration domesticated and agricultural birds had eight times as many genes. Common ancestor of all living birds lost teeth 100 million years ago. The most primitive chromosome pattern revealed that domestic chicken is the closest relative to a living dinosaur. The research threw light on penguin’s (Emperor and Adelie) ability to adapt to frigid conditions. The gene DSG1 that causes thick skin on feet and hands in humans is present all over the body in penguins. They evolved 60 million years ago, lost the ability to fly but their wings have become adaptable to underwater acrobatics.

These genome wide studies unravelled some important titbits in the evolutionary cycle. Birds evolved rapidly than their close crocodilian ancestors which remained largely unchanged over 100 million years. Studies indicated that “archosaurs” which lived 240 million years ago was common ancestor of reptiles, birds and dinosaurs. Evolutionary rates greatly help palaeontologists to estimate the generation time or how soon an animal can reproduce. Slower evolutionary rates go hand in hand with longer generation times. Scientists were able to reconstruct about half of the archosaur genome based on the reptile and bird genome analysis. Though the DNA of archosaur was lost to history they were able to reconstruct genome code and generation time. This first ever comprehensive whole genome analysis of birds resolved lots of fundamental questions and the genome information helped to re-evaluate which species are related.