Tree of life for modern birds reveals rapid increase in diversity 66 million years ago

The largest and most complete study of modern bird genomes to date has resulted in the reconstruction of the bird family tree, challenging traditional views on the evolutionary history of birds.

The study published in the journal Nature combines the genomic data of more than 360 bird species with data from nearly 200 bird fossils. It’s the outcome of nearly a decade of research involving scientists from across the globe working on the Bird 10,000 Genomes Project (B10K), which aims to sequence the complete genomes of every living bird species.

“Our study has resolved some previous disputes about the bird family tree and added new nuance to the textbook knowledge of bird evolution,” says lead author Josefin Stiller, a biologist at the University of Copenhagen in Denmark.

Divergence times for 363 bird species based on 63430 intergenic loci. Credit josefin stiller
Divergence times for 363 bird species based on 63,430 intergenic loci. Credit: Josefin Stiller

There are about 10,000 species of living birds which form 3 major clades. About 5% of species belong to either the Palaeognathae – which includes flightless species like the ostrich, cassowary, and emu – or the Galloanseres, which include landfowl and waterfowl.

The other 95% of all bird species form a third diverse clade: the Neoaves.

This latest study indicates most Neoaves appeared within a very small evolutionary window of only 5 million years, during a period of rapid diversification following the Cretaceous–Paleogene extinction event 66 million years ago.

Dr Jacqueline Nguyen, avian palaeontologist at the Australian Museum and Flinders University and co-author of the study, says that “by combining evidence from nearly 200 bird fossils [they] were able to pinpoint an extremely important period of bird diversification that happened immediately after the extinction of the dinosaurs.”

A photograph of a man and a woman, surrounded by taxidermised birds of many species
Evolutionary bioligist, Professor Simon Ho, from the University of Sydney, and avian palaeontologist Dr Jacqueline Nguyen, from the Australian Museum and Flinders University, surrounded by a collection of bird specimens at the Australian Musem in Sydney. Credit: James Alcock/Australian Museum.

The team found that this timeframe coincided with remarkable genetic and morphological changes among birds, including greater mutation rates, smaller body sizes, and larger brains, and larger effective population sizes.  

“This illustrates the power of comparative genomics: by comparing genomes of living species, we can uncover traces of events that happened 66 million years ago,” adds Stiller.

The findings also give scientists the clearest picture of the bird family tree so far, particularly within the Neoaves. The new tree challenges the previous organisation of Neoaves by re-classifying it into four major sub-groups: Mirandornithes, Columbaves, Telluraves, and a newly proposed group the researchers have named ‘Elementaves’.

Relationships for 363 bird species based on 63430 intergenic loci. Credit josefin stiller
Relationships for 363 bird species based on 63,430 intergenic loci. Credit: Josefin Stiller

Inspired by the four elements of earth, air, water and fire, the group includes birds that are successful on land, in the sky, and in water – like penguins, pelicans, hummingbirds, and shorebirds.

“Our work has changed many traditional views on the evolutionary history of birds,” says Guojie Zhang, senior author of the paper and professor of evolutionary biology in Zhejiang University, China.

“This new family tree will serve as a solid backbone for mapping the evolutionary history of all bird species with important implications for ornithological research and biodiversity studies.”

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