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A fossil from China that’s 150 million years old may be the world’s earliest known bird. The discovery shows that the short tails characteristic of modern birds evolved much earlier than previously thought.

Birds evolved from theropods, a group of dinosaurs that included tyrannosaurs and velociraptors, during the Jurassic period. Archaeopteryx, discovered in 1861, has long been considered one of the earliest birds in the fossil record. But its position on the evolutionary tree is debated because, despite having feathered wings, Archaeopteryx is more similar to non-avian theropods in having a long, reptilian tail.

The new fossil was found in Zhenghe County in Fujian province in November 2023 and has been given the species name Baminornis zhenghensis. Only the trunk, forelimb, pelvis and part of the hindlimb are preserved.

Baminornis lived at the same time as Archaeopteryx but it has a short tail like those of modern birds, pushing back the date of this evolutionary innovation by 20 million years.

“A short tail is widely regarded as aerodynamically beneficial, and the reduction of the tail constitutes the most dramatic change during the dinosaurs-bird transition,” says at the Chinese Academy of Sciences in Beijing, a member of the team that analysed the fossil.

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Weighing 140 to 300 grams, Baminornis was much smaller than Archaeopteryx – about the size of a quail – and it would have looked more like modern birds than Archaeopteryx did, says Wang.

Some parts of its body, such as its hands, retained the ancestral morphology of dinosaurs, while its pectoral and pelvic anatomy were similar to modern birds. “This demonstrates that different body regions evolved independently,” Wang says.

“In light of all this, I would say Baminornis is probably the oldest unambiguous record of birds.”

It is thought that Archaeopteryx could fly only for short bursts, like a pheasant, but Wang and his colleagues say ���������Դǰ��Ծ���’s features suggest it was a better flyer than its famous contemporary.

at Ohio University says the new find is an “amazing fossil,” illustrating “the mosaic of dinosaur and bird features in some very early representatives of the bird-like theropods”.

“These first, very dinosaur-like birds, which are represented by a wonderful diversity of shapes, sizes, and peculiar anatomies are not included among modern birds,” O’Connor says. “You will see these referred to as stem birds or ‘early bird-like dinosaurs.’”