Science & Environment

Fossil sheds light on bird evolution after asteroid strike

Artist’s impression of Tsidiiyazhi abini Image copyright Sean Murtha
Image caption Artist’s impression of Tsidiiyazhi abini

The fossil of a tiny bird that lived 62 million years ago confirms that birds evolved very rapidly after the asteroid strike that wiped out the dinosaurs.

The sparrow-sized tree-dweller lived ''just a geological blink of an eye" after the mass extinction.

Bird fossils from that time period are very rare.

Analysis suggests the ancestors of most modern birds, from owls to woodpeckers, had taken to the wing within four million years of the asteroid strike.

Like mammals, the birds that survived the extinction were able to expand and diversify to become one of the most successful animal groups on Earth.

Analysis of the fossil and its relationship to other members of the bird family tree suggests as many as 10 major bird groups had appeared within four million years of the extinction.

Dr Daniel Ksepka, curator of science at Bruce Museum in Greenwich, Connecticut, said Tsidiiyazhi abini was a very special little bird for several reasons.

''It is very old, very small, and had zany little feet,'' he explained.

''The age is between 62.2 and 62.5 million years, just a geological blink of the eye after the asteroid impact that wiped out the dinosaurs.''

Image copyright Pnas
Image caption Some of the fossilised bones of the bird

DNA evidence suggests birds recovered rapidly from the extinction event 66 million years ago that wiped out most animals on land, including flying reptiles, dinosaurs and primitive birds.

The origins of modern birds can be traced back to this time. However, bird fossils from this era in geological history are very rare because their bones are so small and delicate.

This has made it difficult to resolve how modern birds arose and diversified, leading to some controversy. The discovery of Tsidiiyazhi abini, an ancient species of mousebird, is a new source of evidence.

''When we place the bird in the evolutionary tree, it reveals that other closely related groups must have also split off by then because they occupy lower branches,'' Dr Ksepka told the BBC.

''So this discovery shows not only mousebirds but things like owls, raptors, the Coraciimorphae (a group that includes birds like kingfishers and woodpeckers) and many other groups were all showing up just a short time after the asteroid impact that wiped out the dinosaurs.''

Tsidiiyazhi abini, or ''little morning bird'' was found in 62.5-million-year-old rocks in the Nacimiento Formation of New Mexico.

Dr Thomas Williamson was on a fossil hunting trip with his twin sons, when the birds' bones came to light.

''They discovered an unusually rich site that had some skeletons of small mammals,'' the curator of Palaeontology at the New Mexico Museum of Natural History and Science explained.

''Over the next several months, I collected some bulk samples from the site and within these I discovered the bones of a small bird.''

Image copyright Thomas Williamson
Image caption Dr Williamson's twin sons at the site where the fossils were discovered

He said the new birds were close to modern mousebirds (Coliiformes), a group now found only in Africa, but which was geographically more widespread in the Palaeogene [from 66 million years ago to 23 million years ago].

The bird was able to flip the fourth toe on its foot to face backwards - something that is useful for climbing and grasping. This feature is also seen in other birds, such as modern owls.

Tsidiiyazhi lived at a time when the planet was undergoing great change, with placental mammals and flowering plants also diversifying rapidly.

The bird lived in forests and dined on fruits and seeds from flowering plants.

Today, there are more than 10,000 living species of bird.

The research is published in the journal PNAS.

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