Sixty-six million years ago, an asteroid struck the Earth and created a mass extinction event, ending the reign of the dinosaurs. Non-avian dinosaurs, that is. Today’s modern birds can be reasonably described as fully feathered, mostly flighted, small dinosaurs, and now researchers have managed to piece together the impact the asteroid had on their evolution.
A study, published in the journal Current Biology, finds that tree-dwelling birds did not survive the asteroid’s devastating impact on the earth’s forests, and only a few lineages of ground-dwelling birds made it through the mass extinction. These ground-dwelling lineages then diversified into today’s modern birds – many of which returned to the trees.
“We drew on a variety of approaches to stitch this story together,” says lead author Daniel Field from the University of Bath, in the United Kingdom.
“We concluded that the devastation of forests in the aftermath of the asteroid impact explains why tree-dwelling birds failed to survive across this extinction event. The ancestors of modern tree-dwelling birds did not move into the trees until forests had recovered from the extinction-causing asteroid.”
Field, together with a team of researchers from natural history museums and universities in the USA and Sweden, analysed the plant fossil record, and confirmed that global forests collapsed after the asteroid triggered the Cretaceous-Paleogene (K-Pg) extirpations.
The impact of the asteroid, known as Chicxulub, most likely caused extensive forest fires, followed by acid rain, pushing large quantities of soot into the atmosphere, potentially blocking photosynthetic activity for several years. This period of darkness is indicated in the fossil record by the proliferation of organisms which thrive on decomposing organic matter.
A second recent Chicxclub-related study published in the journal Science finds that the event also kicked off a period of substantial global warming, with average temperatures jumping by five degrees Celsius and staying elevated for roughly 100,000 years.
Other studies have confirmed a great radiation of bird species following the gradual ecosystem recovery from the K-Pg extinction event, but Field and his team are the first to link evolutionary relationships of living birds, their morphological traits (mainly foot structure) and their ecological habits. Their ancestral ecological reconstructions showed that the most recent common ancestor of all living birds most likely was ground-dwelling.
“Today, birds are the most diverse and globally widespread group of terrestrial vertebrate animals – there are nearly 11,000 living species,” Field says.
“Only a handful of ancestral bird lineages succeeded in surviving the K-Pg mass extinction event 66 million years ago, and all of today’s amazing living bird diversity can be traced to these ancient survivors.”
Tanya Loos is an ecologist and science writer based in regional Victoria, Australia.
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