New early bird species revealed by fossils unearthed in China

The oldest known bird with a short, modern tail has been discovered.

When birds first evolved, they would have initially been very dinosaur-like. While some of their ancestral features stood the test of time, such as feathers, others would be lost as these animals adapted for life in the skies.

One of the key changes on this evolutionary journey was the development of a short tail. Relatives of birds from the Jurassic, such as Archaeopteryx, have bony, feathered tails that help them to balance on land, but would be heavy and cumbersome in flight.

Modern birds, in contrast, have much shorter tails. Until recently, however, this crucial characteristic was only known from early bird fossils dated from the Cretaceous, millions of years later. The discovery of Baminornis zhenghensis finally provides the evidence that short tails were a Jurassic innovation.

Professor Min Wang, the study’s lead author, says, “Previously, the oldest record of short-tailed birds is from the Early Cretaceous. Baminornis zhenghensis is the sole Jurassic and the oldest short-tailed bird yet discovered, pushing back the appearance of this derived bird feature by nearly 20 million years.”

Discovered in Fujian Province, China, palaeontologists hope that the unearthing of Baminornis will herald more early bird fossils.

Professor Daniel Field, who researches bird evolution at the University of Cambridge, adds, “The new discovery suggests that other, and hopefully better preserved, representatives of early birds could be found from this region.

“If so, these fossils would further clarify our understanding of bird evolution at the end of the Jurassic Period.”

The findings of the study were published in the journal Nature.

Birds in the Jurassic

Birds are the last living dinosaurs. They evolved out of feathered species of dinosaurs, such as Velociraptor and Deinonychus.

The group of animals containing birds and their closest relatives is known as the avialans, which are believed to have first evolved during the Jurassic. One of the most famous species normally included as part of this group is Archaeopteryx, which was important in demonstrating the link between birds and dinosaurs.

While this species is sometimes described as the first bird, other scientists would describe it as bird-like. Archaeopteryx’s long, bony tail is one of the features that show it comes very early in the evolutionary history of modern birds.

“In living birds, a shortened tail is associated with shifting the body’s centre of mass and lightening the body for flight,” explains Daniel. “The vestiges of the ancestral long bony tail that came before it remain as a structure known as the pygostyle.

“The pygostyle helps to anchor the muscles that allow the tail feathers to help steer the bird and generate lift during flight. So, the appearance of a shortened tail in Mesozoic birds was probably directly associated with the refinement of flight.”

Unearthing Baminornis

Currently, the oldest evidence of this style of tail was first uncovered during a dig in 2023. Among Jurassic turtles and other aquatic reptiles, palaeontologists found the fossils of two ancient birds.

One of these animals was represented by just one bone, so the team resisted naming it in the hope of more fossils being revealed in the future. But Baminornis, named for where it was found, was important and complete enough to warrant describing it as a species in its own right.

“Baminornis is very important because it provides us with the first direct evidence that relatively advanced birds originated back in the Jurassic rather than later in the Cretaceous,” says Daniel. “Having a more accurate temporal framework for understanding bird evolution allows us to refine our understanding of the rate of major evolutionary changes and their environmental underpinnings.”

While Baminornis is currently a landmark species in the history of birds, it also raises more questions about how these animals evolved. Some later avialans, like Jehelornis, had long tails, so it’s still uncertain when short tails became a consistent feature of birds.

On the one hand, Baminornis might have developed its short tail independently, with other birds undergoing similar changes later. On the other hand, Jehelornis might have reverted to an older style of tail during the course of its own evolution.

Other questions remain about how Baminornis would have flown. It doesn’t appear to have the breast bone modern birds attach their flight muscles to, so it may have had a different flying style to its modern relatives.

As more Jurassic fossils are revealed, the path that birds took to the sky will gradually become clearer.