Bird diversity took flight only after the extinction of non-avian dinosaurs

In a paper published in Science, an international team of scientists has determined the relationships between every order of modern-day birds, confirming the hypothesis that these groups only arose once dinosaurs went extinct.

The collaborative effort brought together over 100 scientists from diverse fields including genetics, palaeontology, bird biology, mathematics, and even avian neurobiology. The team used fossil evidence and the complete genomes of almost 50 species from every bird order to create the avian evolutionary tree.

The study resolved two competing theories about the evolution of birds, suggesting that all modern day orders of birds exploded in diversity only after the non-avian (non-bird) dinosaurs went extinct. This sudden appearance of groups is called ‘big bang radiation’, said Associate Professor Simon Ho, the geneticist in charge of estimating the timescales of bird evolution for the study.

“The general idea is that when the dinosaurs went extinct, it opened up a lot of niche space that allowed birds as well as mammals to diversify. At that time in geological history we find that a lot of the modern groups of mammals and birds first appeared in the fossil record. Well [now] we’ve actually found that with the molecular data as well,” explained Ho.

Associate Professor Ho said that the evolutionary tree generated by this study is robust and unlikely to be overturned soon. The study is powerful partly because it used complete bird genomes, said Simon. Previous comparisons have mostly used the physical characteristics of birds, which can be misleading. “Different groups end up evolving the same traits because of similar lifestyles,” he said, “the analysis of genomes has brought us lots of unexpected relationships.”

Seriemas — a bird species involved in this study, and one whose unique ancestry was resolved. Photo: Manfred Werner/CC/Flickr.

Apart from estimating when these early bird groups arose, the research also uncovered many other surprises. “One of the surprising relationships,” said Ho, “is that the sister group of Passerines — that’s all the song birds, the largest group of birds — is actually parrots.”

This means that the Passerines, with members like sparrows, crows, and lyrebirds, are more closely related to parrots than any other bird group. “They have no morphological similarities, and basically, there’d be no morphologist in the world who would group those two together. That was really unexpected.” Though this theory was first suggested by another genetics study, the current study certainly confirmed it.

Furthermore, the results from this study predicted some characteristics of the common ancestor shared by song birds and parrots. Since modern-day Passerines and parrots can make complex songs and vocalisations, the ancestor to these groups may have also possessed these abilities. This ancestral bird would have lived around 55 million years ago and was perhaps an apex predator.

Among other findings, the study confirmed that water-birds and land-birds form two separate and ‘self-contained’ groups. The study also confirmed two carnivorous groups of birds – falcons and seriemas – as unrelated to other raptors such as eagles.

The next step is the ‘Bird Genome 10K Project’, a long-term collaborative endeavour to catalogue the genomes of every species of bird in an effort to understand the evolutionary relationships of all birds.

Originally published in November 2014 on Think Inc. and the University of Sydney's School of Biological Sciences newsletter.