A study has shown the effect of the earth’s history on the evolution of modern day avians.
The evolution of modern day birds was shaped by the geographical contingencies and climatic changes that took place during the history of the planet.
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As the DNA study, published in the journal Science Advances, showed so clearly, most of the bird population of the world had their cradle of birth in South America. This occurred about 90 million years ago.
This event mainly took place around the Cretaceous-Paleogene extinction when all the dinosaurs that were not birds died. The birds were left behind and they migrated to all the other land masses from the focal point that was South America.
The birds took the common routes via several land bridges and also underwent proliferation during cool periods in history. Modern day birds are a rich and diversified group of creatures.
They are distributed throughout the world and scientists still do not fully understand the mystery of their huge dissemination throughout history. The main glitch is the missing links in the fossil record. As far as the phylogeny of birds is concerned this study is the first one of its kind.
DNA sequences from some 130 fossils of birds were examined for evidence. This way a novel evolutionary tree of sorts was built. Fossils of avians have been found only after the Cretaceous-Paleogene extinction.
Most scientists think that birds didn’t start their diversification process until after this event. That is because their main rivals in the animal kingdom were for all purposes extinct. However, the new study shows that the diversification had begun long before the K-Pg extinction. After this extinction, most birds employed two routes to spread throughout the globe. One was to North America and the Old World. Then there was a route taken to Australia and New Zealand across Antarctica. These regions were warmer in those times.
Bird diversification increased during periods of global cooling. This was naturally to be expected. The moment the planet undergoes cooling and drought, the disintegration of rainforests takes place.
Thus the avian populations are isolated. While the chances of these populations undergoing extinction are there, it also happens that sometimes they undergo a burgeoning into different species.
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A biotic expansion occurs when the warming resumes. Furthermore, avian expansion also depends upon shifts in plate tectonics and environmental shocks. The birds we see today have thus been through a lot.