New species of birds from the Cretaceous had a long pintail

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Chinese paleontologists have identified a new species of bird pengornithid enantiornithine with a pair of elaborate tail feathers.

An illustration showing what Yuanchuavis Kompsosoura could have looked like in life. Image credit: Haozhen Zhang.

The enantiorniths are the most successful Mesozoic group of birds, arguably representing the first global avian radiation.

They are known exclusively from the Cretaceous period, mainly from fossils discovered in Asia, and generally considered to be the sister of Ornithuromorpha, the group in which all living birds are nested.

The new species is part of the Pengornithidae family, one of the first groups of divergent enantionithines.

Appointed Yuanchuavis Kompsosoura, he lived around 120 million years ago in what is now northeast China and belonged to the famous Jehol Biota.

It was a small bird, about the size of a blue jay, but its tail was over 150% of its body length.

Yuanchuavis Kompsosoura had a fan of short feathers at the base, then two extremely long feathers, ”said Dr Jingmai O’Connor, a paleontologist at the Field Museum.

“The long feathers were dominated by the central spine, called the rachis, then variegated at the end.”

“The combination of a short-tailed fan with two long feathers is called a pintail, we see it in some modern birds like the souimangas and quetzals.”

“We have never seen this combination of different types of tail feathers before in a fossil bird.”

Yuanchuavis kompsosoura fossil, with illustration indicating the tail feathers of the fossil.  Scale bar - 2 cm.  Image credit: Min et al., Doi: 10.1016 / j.cub.2021.08.044.

Fossil Yuanchuavis Kompsosoura, with an illustration indicating the tail feathers of the fossil. Scale bar – 2 cm. Image credit: Min et al., doi: 10.1016 / j.cub.2021.08.044.

Yuanchuavis Kompsosoura is the first documented occurrence of a pintail at Enantiornithes.

“In particular, the morphology preserved in Yuanchuavis Kompsosoura essentially represents a combination of the two tail morphologies previously recognized in other enantionithins which are most closely related to Yuanchuavis KompsosouraSaid Dr Wang Min, a researcher at the Chinese Academy of Sciences.

“Its tail fan is aerodynamically functional, while elongated central paired plumes are used for display, which together reflect the interplay between natural and sexual selection.”

In other words, Yuanchuavis Kompsosoura might have flown well, but his long tail feathers that might have helped him find mates didn’t make the flight any easier – his fancy tail was literally a drag.

This balance between natural and sexual selection has interested scientists since Darwin’s time: if evolution produces organisms that are better able to respond to the pressures of the world around them, then why would an animal develop traits that make it harder to steal or more noticeable? to its predators?

“Scientists call a trait like a fancy big tail an ‘honest signal’ because it is damaging, so if an animal with it is able to survive with this handicap it is a sign that it is really in good shape,” Dr O’Connor said. .

“A female bird would look at a male with awkward, bulky tail feathers and think, ‘Dang, if he’s able to survive even with such a ridiculous tail, he must have some really good genes.’

“It is well known that sexual selection plays a central role in speciation and recognition in modern birds, attesting to the enormous extravagant feathers, ornaments, voices and dances,” said Dr. Wang.

“However, it is notoriously difficult to say whether a given fossilized structure is shaped by sexual selection, given the imperfect nature of the fossil record.”

“Therefore, the well-preserved tail feathers of this new fossil bird provide new information on how sexual selection has shaped the avian tail from an early age. “

“The complexity that we see in Yuanchuavis KompsosouraFeathers is linked to one of the reasons we hypothesize that living birds are so incredibly diverse, as they can separate into different species simply by differences in plumage and differences in song, ”said Dr O’Connor.

“It’s amazing that Yuanchuavis Kompsosoura suggests that this kind of plumage complexity may already have been present in the Lower Cretaceous.

The study was published in the journal Current biology.

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Min Wang et al. An Enantiornithine bird from the Lower Cretaceous with a pintail. Current biology, published online August 16, 2021; doi: 10.1016 / j.cub.2021.08.044


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