Image caption The fossilised jawbone is nearly twice the length of that of an ostrich, the largest bird found on Earth today

An enormous jawbone found in Kazakhstan is further evidence that giant birds roamed - or flew above - the Earth at the same time as the dinosaurs.

Writing in Biology Letters, researchers say the new species, Samrukia nessovi, had a skull some 30cm long.

If flightless, the bird would have been 2-3m tall; if it flew, it may have had a wingspan of 4m.

The find is only the second bird of such a size in the Cretaceous geologic period, and the first in Asia.

The only other evidence of a bird of such a size during the period was a fossilised spinal bone found in France and reported in a 1995 paper in Nature.

Sharing space

An overwhelming majority of the birds known from the period would have been about crow-sized, but Dr Darren Naish of the University of Portsmouth said that a second find of an evidently different species suggests that large birds were common at the time.

"This fossil is only known from its lower jaw, so unfortunately we can't say anything at all with certainty about the shape and form of the whole animal.

"If it was flightless and sort of ostrich-shaped, it would have been maybe 2-3m tall and somewhere over 50kg," he explained to BBC News. "If it was a flying animal, then maybe it was shaped like a big albatross or a condor."

Dr Naish also wondered about the dinosaurs with which the enormous birds shared their space.

"I think the really interesting thing is that they're living alongside the big dinosaurs we know were around at the time: big tyrannosaurs, long-necked sauropods, duck-billed dinosaurs," he said. "That opens up loads of questions about ecological interactions that we can only speculate about.

"People have said there weren't big birds when there were big pterosaurs, but now we know there were."