Quail-like birds may have beaten the asteroid
Scientists have long wondered just how many birds survived the asteroid impact in Mexico that wiped out the rest of the dinosaurs some 66 million years ago.
Now, they may have an answer: very few, and mostly small ones.
A new study reported by Science magazine suggests that widespread forest fires would have made it impossible for tree-dependent birds to survive – meaning the avian diversity of today likely arose from just a few ground-dwelling survivors.
Not everyone agrees with this scenario, but Daniel Ksepka, a paleontologist at the Bruce Museum in Greenwich, Connecticut, calls it an “elegant” hypothesis. “It’s nice, kind of a eureka moment.”
Molecular biologists and paleontologists have long debated the origins of bird diversity. Some argued, based on molecular data, that many groups of birds emerged unscathed from the asteroid impact in Chicxulub that killed off so many other species.
More recent molecular evidence, combined with fossil finds, has convinced others that most bird groups did perish. Those researchers argue that the vast array of bird shapes, sizes, and lifestyles emerged quickly after the great extinction event.
Daniel Field, a vertebrate paleontologist at the University of Bath in the UK and his colleagues recently marked up the avian family tree and noticed that tree-dwelling species—which today vastly outnumber ground-dwelling species—had ground-based ancestors.
And the skeletons of the pre and post-impact fossils were different as well. Before the impact, there seemed to be many tree-loving species. But those species were missing in the postimpact fossils.
The spore and pollen data suggested why so many of the tree-dwellers died: forests thrived before the impact but not after, most likely because the asteroid set off a firestorm, they report.
After the impact, fossil evidence from North America suggests ferns were the major flora for about 1000 years.
Among modern birds, it appears that only five groups predate the impact, including species like today’s ostriches, ducks, and chickens. Their impact-surviving ancestors were probably small ground-dwellers, like quail, Field says. They likely survived on seeds banked in the soil, what Ksepka calls “a food source that’s pre-packaged for preservation.”
Understandably, there are skeptics. “It’s difficult to conclude all forests disappeared globally based on [just] evidence from northern areas,” says Alan Cooper, a molecular evolutionist at the University of Adelaide.
Claiming too much
Joel Cracraft, an evolutionary biologist at the American Museum of Natural History in New York City, thinks forests may have disappeared in North America, but he has doubts about the rest of the world. “They are trying to claim too much,” he says.
However, David Penny, an evolutionary biologist at Massey University in Palmerston North, New Zealand thinks the paper “does need to be taken seriously. Although not involved in the work, he, Cracraft, and others want to see more work done on what birds did survive and where, and when.