Mapping the “Big Bang” of Bird Evolution
by AMNH on
The story of avian origins is now coming to light thanks to an ambitious international collaboration that has mapped the genomes of nearly 50 species ranging from ducks to vultures.
The Avian Phylogenomics Consortium, which involves more than 200 scientists from 80 institutions, including the American Museum of Natural History, has sequenced, assembled, and compared full genomes of 48 species representing all major branches of modern birds. The first round of analyses from this four-year project suggests some remarkable new ideas about bird evolution and supports conclusions about long-debated relationships.
“These new findings not only resolve some long-standing questions about avian history but open up a new era in our study of avian biology,” said Joel Cracraft, a curator in the Museum’s Department of Ornithology and an author of a flagship paper published in a December 12 special issue of Science.
Scientists already knew that birds experienced a rapid burst of evolution around the time of the mass extinction that wiped out non-avian dinosaurs 66 million years ago. But the family tree of modern birds has confused biologists for centuries, and the molecular details of how they arrived at their spectacular diversity—more than 10,000 species, compared to about 5,000 species of mammals—is poorly known.
Because modern birds split into species early and in quick succession, they did not evolve enough distinct genetic differences at the genomic level to clearly determine their early branching order. To resolve the timing and relationships of modern birds, consortium authors used whole-genome DNA sequences of species including a crow, duck, falcon, parakeet, crane, ibis, woodpecker, eagle, and others to infer the bird species tree.
The whole-genome analysis dates the evolutionary expansion of Neoaves, a group that includes songbirds, raptors, parrots, herons, doves, penguins, and most other birds, to the time of the Cretaceous-Paleogene extinction event 66 million years ago—contradicting the idea that Neoaves blossomed 10 to 80 million years earlier.
Based on these new genomic data, only a few bird lineages were present prior to the mass extinction, including the ratite birds (ostriches, kiwis) and the lineage leading to ducks and geese and to the pheasants and their allies. The radiation after the extinction event gave rise to more than 10,000 Neoaves species that comprise 95 percent of all bird species living with us today.
The new family tree for birds, presented in a flagship paper in Science, is based on whole-genome data that resolves the early branches of Neoaves. A key, and unexpected, finding is early divergence between very different-looking birds. For example, the new findings show that flamingoes are more closely related to grebes and pigeons than they are to other waterbirds, and that falcons are more closely related to parrots and passerines (a group that includes songbirds) than they are to eagles, hawks, or vultures.
The findings also indicate that the common ancestor of core landbirds, which include songbirds, parrots, woodpeckers, owls, eagles, and falcons, was an apex predator.
The flagship paper is one of eight reporting the findings in the December 12 issue of Science and one of 23 appearing this month in journals that include Genome Biology, GigaScience, and other journals.
For more information, see the consortium’s press release.