Dino-Killing Mass Extinction Boosted Bird Evolution, Study Says

The Cretaceous-Tertiary mass extinction — an event 65 million years ago that wiped out the dinosaurs and was triggered by a massive asteroid that slammed into Earth — led to acceleration in the rate of genetic evolution among its avian survivors, and these survivors were much smaller than their pre-extinction relatives, according to a new study.

This is the ‘Liliput Timeline.’ Image credit: Cornell Lab of Ornithology.

“There is good evidence that size reductions after mass extinctions may have occurred in many groups of organisms,” said Cornell University Ph.D. candidate Jacob Berv, lead author on the study, published in the journal Systematic Biology.

“All of the new evidence we have reviewed is also consistent with a Lilliput Effect affecting birds across the Cretaceous-Tertiary mass extinction (also called K-Pg extinction, K-T extinction, Cretaceous-Paleogene extinction or end-Cretaceous extinction).”

“Smaller birds tend to have faster metabolic rates and shorter generation times,” added co-author Dr. Daniel Field, an evolutionary paleobiologist at the University of Bath, UK.

“Our hypothesis is that these important biological characters, which affect the rate of DNA evolution, may have been influenced by the Cretaceous-Tertiary event.”

The team jumped into this line of inquiry because of the long-running ‘rocks and clocks’ debate.

Different studies often report substantial discrepancies between age estimates for groups of organisms implied by the fossil record and estimates generated by molecular clocks.

Molecular clocks use the rate at which DNA sequences change to estimate how long ago new species arose, assuming a relatively steady rate of genetic evolution.

“But if the Cretaceous-Tertiary extinction caused avian molecular clocks to temporarily speed up, this could explain at least some of the mismatch,” the authors said.

“Size reductions across this extinction would be predicted to do exactly that,” Berv said.

“The bottom line is that, by speeding up avian genetic evolution, the Cretaceous-Tertiary mass extinction may have temporarily altered the rate of the avian molecular clock,” Dr. Field added.

“Similar processes may have influenced the evolution of many groups across this extinction event, like plants, mammals, and other forms of life.”

The researchers also suggest that human activity may even be driving a similar Lilliput-like pattern in the modern world, as more and more large animals go extinct because of hunting, habitat destruction, and climate change.

“Right now, the planet’s large animals are being decimated — the big cats, elephants, rhinos, and whales. We need to start thinking about conservation not just in terms of functional biodiversity loss, but about how our actions will affect the future of evolution itself,” Berv said.

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Jacob S. Berv Daniel J. Field. Genomic Signature of an Avian Lilliput Effect across the K-Pg Extinction. Systematic Biology, published online July 13, 2017; doi: 10.1093/sysbio/syx064