Sixty-six million years in the past, an asteroid slammed into the Gulf of Mexico. The disaster led to the extinction of as many as three-quarters of all species on Earth, together with dinosaurs like Tyrannosaurus rex. However some flying feathered dinosaurs survived, and finally developed into the greater than 10,000 species of birds dwelling right this moment, together with hummingbirds, condors, parrots and owls.
Primarily based on the fossil report, paleontologists have lengthy argued that the asteroid’s impression was adopted by a giant pulse of hen evolution. The mass extinction of different animals might have eradicated plenty of competitors for the birds, giving them the possibility to evolve into the exceptional variety of species that fly round us right this moment.
However a new examine on the DNA of 124 hen species challenges that concept. A global workforce of scientists discovered that birds started diversifying tens of hundreds of thousands of years earlier than the fateful collision, suggesting that the asteroid had no main impact on hen evolution.
“I think about this may ruffle a couple of feathers,” stated Scott Edwards, an evolutionary biologist at Harvard and one of many examine’s authors. The analysis was printed on Monday within the Proceedings of the Nationwide Academy of Sciences.
Dinosaurs developed primitive feathers not less than 200 million years in the past, not for flight however most probably for insulation or a mating show. In a single lineage of small bipedal dinosaurs, these feathers turned extra advanced after which in the end took the creatures into the air as birds. How feathers was wings for flight continues to be debated. However as soon as birds developed, they diversified into a wide range of varieties, lots of which turned extinct when the asteroid plunged the Earth right into a yearslong winter.
When looking for fossils of the most important teams of birds alive right this moment, scientists have discovered virtually none that shaped earlier than the asteroid hit. That placing absence has led to a idea that the mass extinctions cleared the evolutionary enviornment for birds, permitting them to blow up into many new varieties.
However the brand new examine got here to a really totally different conclusion.
“We discovered that this disaster didn’t have impression on trendy birds,” stated Shaoyuan Wu, an evolutionary biologist at Jiangsu Regular College in Xuzhou, China.
Dr. Wu and his colleagues used the birds’ DNA to reconstruct a household tree that confirmed how the most important teams had been associated. The oldest break up created two lineages, one that features right this moment’s ostriches and emus, and the opposite with the remainder of all dwelling birds.
The scientists then estimated when the branches break up into new lineages by evaluating the mutations that collected alongside the branches. The older the break up between two branches, the extra mutations every lineage constructed up.
The workforce included paleontologists who helped to fine-tune the genetic estimates by inspecting the age of 19 fossils of birds. If a department seemed to be newer than a fossil that belonged to it, they adjusted the pc mannequin that estimated the tempo of hen evolution.
Michael Pittman, a paleontologist on the Chinese language College of Hong Kong who was not concerned within the new examine, stated that it was notably noteworthy due to the fossil evaluation. “That they had a dream workforce of paleontologists,” he stated.
The examine discovered that dwelling birds shared a typical ancestor that lived 130 million years in the past. New branches of its household tree steadily break up off all through the Cretaceous Interval and afterward at a reasonably regular tempo, each earlier than and after the asteroid impression. Dr. Wu stated that this regular development might need been fueled by the rising variety of flowering vegetation and bugs throughout the identical interval.
Jacob Berv, an evolutionary biologist on the College of Michigan who was not concerned within the examine, stated that it illustrated state-of-the-art strategies for crunching big quantities of genetic information to reconstruct evolutionary historical past. However he didn’t agree with its conclusion.
If the brand new examine was proper, there ought to be fossils of all main teams of dwelling birds from properly earlier than the asteroid impression. However virtually none have been discovered.
“The sign from the fossil report isn’t ambiguous,” Dr. Berv stated.
Dr. Berv suspects that the right story comes from the fossils, and that the majority main teams of birds emerged after the asteroid impression. The issue with the brand new examine, he stated, is that it assumes that the hen DNA collected mutations at a gentle charge from one technology to the following.
However the devastation of the asteroid’s impression — inflicting forests to break down and creating shortages of prey — might need led to the deaths of larger birds, whereas smaller birds survived. Small birds take much less time to breed, and they might produce many extra generations — and lots of extra mutations — than birds did earlier than the impression. If scientists ignore this type of mutational overdrive, they may get the timing of evolution fallacious.
Nonetheless, Dr. Berv acknowledged that scientists are simply beginning to develop strategies to that might permit them to raised estimate the speed of evolution and combine it with different proof like DNA and fossils. “I believe that may reconcile a few of the debates,” he stated.