By Angus Dalton
From the ashes of the asteroid strike that killed the dinosaurs, the ancestors of modern birds arose in an evolutionary blitz that would eventually bring albatross to Atlantic skies, emus to the outback and lorikeets to our windowsills.
Australian scientists have contributed to the largest and most complete study of bird evolution to date. This new tree of life, they say, confirms most modern bird groups evolved within a tiny five-million-year evolutionary window, bursting into the ecological chasm left by the dinosaurs.
Evolutionary biologist Professor Simon Ho (right) and bird paleontologist Dr Jacqueline Nguyen.Credit: James Alcock
The question of when modern birds arose has long dogged scientists and pitted evolutionary biologists against each other in fierce debate.
“Every time a new study is published, there’s basically a different story about how birds are related to each other. There’s lots of conflict,” said co-author of the research Professor Simon Ho, an evolutionary biologist at the University of Sydney.
Only in February, another study claimed modern birds arose 100 million years ago amid the dinosaurs’ reign and that the mass asteroid extinction 66 million years ago had “limited impact on birds’ evolution”.
“But now, because we’ve got the largest data set that we’ve ever used for studying birds, we think we’ve got the most confident estimate,” Ho said.
Dr Jacqueline Nguyen with a hoatzin specimen at the Australian Museum. The bird remains an evolutionary enigma. Right: A live hoatzin in South American rainforest.Credit: James Alcock/Alamy
Scientists crunched the billion letter-long genomes of 363 birds and analysed 187 fossils for the study, published in Nature on Tuesday.
Dr Jacqueline Nguyen was part of the study’s fossil team. In 2013, she identified a 16- to 23 million-year-old fragment of fossilised magpie leg bone and named the ancient species Kurrartapu johnnguyeni – in honour of her father, who had died from leukaemia.
“Now it’s been used to estimate when all living birds appeared, so this humble little fossil has actually had quite an important role in our understanding of bird evolution,” said Nguyen, a bird palaeontologist from the Australian Museum and Flinders University.
The researchers believe only two modern bird groups were around at the time of the dinosaurs: the flightless ratites, which now includes emus, ostriches and cassowaries; and fowl, including the ancestors of chickens, ducks, swans and geese.
The fossilised magpie leg bone was one of almost 200 fossils used to build the evolutionary timeline, according to Dr Nguyen.Credit: Dr Jacqueline Nguyen/The Australian Museum
But these groups account for only 5 per cent of bird species. The rest are within the Neoaves clade (a group with a common ancestor), comprising birds as diverse as kingfishers, boobies, toucans, sparrows, owls, penguins, woodpeckers and wedge-tailed eagles. Their ancestors, Nguyen said, emerged in a “big bang” evolution event after the dinosaurs disappeared.
The sub-categories of the Neoaves include a “magnificent seven”, ranging from vultures in the first category to flamingoes in the seventh. Then there are the three intriguing groups of “orphaned orders” – whose ancestries have long been a mystery.
The evolutionary orphans include cranes, shorebirds and gulls. The new analysis has shed new light on these bird species and where they slot into the tree of life.
One bird remains a stubborn enigma: the swamp-dwelling, blue-faced, red-eyed hoatzin, which sports a spiky orange mohawk-style crest. The chicken-sized South American bird is the last of its lineage and the sole creature in the third orphaned order.
“It’s very much a punk bird,” Nguyen said. “It’s the only bird that ferments leaves in its gut using bacteria, kind of like cows. Because of that, unfortunately, it smells like manure.”
The study also lends more evidence to the idea that songbirds – which make up half of all bird species and include willie wagtails, magpies and honeyeaters – evolved 50 million years ago in Australia.
“It’s pretty amazing when you think about it – nearly half of the world’s birds can trace their ancestry back to Australia,” Nguyen said.
The Examine newsletter explains and analyses science with a rigorous focus on the evidence. Sign up to get it each week.