fossils

Sparrow-sized fossil rewrites bird history after asteroid impact

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Julio
Lacerda

Staff Artist and Writer
The tiny fossil of a tree-climbing bird shows they evolved and radiated quicker than previously thought after the asteroid impact that killed off the non-avian dinosaurs 66 million years ago.

Nowadays it’s common knowledge that birds are a surviving group of dinosaurs. All the avian creatures around today, from ostriches to hummingbirds, are descendants of very bird-like species similar to the movie star Velociraptor and the famous “first bird”, Archaeopteryx. But even though some birds did survive the cataclysmic event that wiped out their cousins, it wasn’t all birds that made the cut.


Living among the other dinosaurs were very strange birds, including some with teeth and clawed fingers. Yet only a few bird lineages survived the extinction, with all the ones alive today tracing their ancestry back to these hardy groups. For a while, scientists thought this radiation from the ancestral stock to all the 10,000 species alive today took quite a bit of time to take off.


But a tiny fossil found in New Mexico shows that this evolutionary boom started happening quite earlier than originally thought. About the size of a sparrow, Tsidiiyazhi abini (“little morning bird” in the Navajo language, as an homage to the ancestral residents of the land it was found in) lived between 62.5 and 62.2 million years ago. That’s not very long after the asteroid hit, and the remarkable thing is that Tsidiiyazhi looks pretty much like a bird you can see at any park. In fact, it’s a relative of mousebirds, a group of small birds that live in Africa to this day.


What’s more, Tsidiiyazhi is the oldest known tree-dwelling modern bird. It had semi-zygodactyl feet, which means one of its toes could rotate to point forwards or backwards. Some fully zygodactyl birds include parrots and woodpeckers, with two toes pointing forwards and another two pointing permanently backwards. This configuration helps them get a firm grip on branches and grants them sure footing on trees, something that Tsidiiyazhi would have been reasonably good at with its transitional feet.


The discovery of Tsidiiyazhi has some important implications on the bird evolution timeline. For instance, it shows that the mousebird family itself appeared at least 6 million years earlier than previously believed. And if by 62 million years ago mousebirds were already distinct from other bird groups, it means that the split between several modern bird families must have happened even earlier.


This, together with the discovery of other extinct modern birds like Waimanu, a 60-million-year-old penguin from New Zealand, shows that bird diversification was well underway in just a few million years after the Cretaceous mass extinction. It’s a similar story to that of our own mammal lineage, and a testament to how this massive die-off gave the underdogs a chance to shine.


Read the original research in PNAS.

Image Credit: Earth Archives

34f1d64c52c45a6bdce31bc5e48b86cc

Julio
Lacerda

Staff Artist and Writer


http://sulc.us/ka9yh
http://www.eartharchives.org/articles/sparrow-sized-fossil-rewrites-bird-history-after-asteroid-impact/