Impressive but impractical feather headdress: The peacock concept is apparently already astonishingly old: Even in the Cretaceous period there were birds that invested in attractiveness at the expense of the functionality of their plumage. This is proven by the fossil of a presumably male specimen of a new representative of the extinct bird group of the enantiornithes. The animal had two tail feathers that protruded far and were apparently shaped by the principle of sexual selection. The male splendor also allows conclusions to be drawn about the habitat and behavior of the Cretaceous bird species, say the researchers.
The evolution of birds goes back a long way: It is assumed that the ancestors of the feathered aerial acrobats evolved from two-legged dinosaurs during the Jurassic and Cretaceous Ages. Initially, two lines emerged: the ancestors of today’s birds and the so-called enantiornithes. They resembled modern birds, but had special wing characteristics and mostly snout-like beaks with teeth. Although they were the dominant form of birds in the Cretaceous Period and produced considerable diversity, all enantiornithes fell victim to mass extinction as a result of the asteroid impact 66 million years ago.
Tail feathers – longer than the body
A Sino-US research team has now added an interesting new member to the group of known Enantiornithes species. The fossil, which has been preserved in great detail, was discovered in sedimentary rocks of the Jehol Biota in north-eastern China, which is 120 million years old. Scientists named the species Yuanchuavis kompsosoura. As they report, probably only the males of this species distinguished a literally outstanding feature: At the end of the approximately 23 centimeter long bird’s body sat two at least 30 centimeter long tail feathers.
“In addition, the animal had a fan made of short tail feathers at the base,” says co-author Jingmai O’Connor of the Field Museum in Chicago. The combination of this element with long tail feathers is known as the pintail and is known from the males of some modern bird species, the researcher explains. “We have never seen this combination of different types of tail feathers in any other fossil bird,” emphasizes the paleontologist. As he and his colleagues explain, the tail fan of Yuanchuavis was aerodynamically functional, but the two extremely elongated feathers were more of a hindrance when flying. Obviously, therefore, they were only used for display. “This reflects the interplay between natural and sexual selection,” explains first author Ming Wang from the Chinese Academy of Sciences in Beijing.
Sexual selection is emerging
The founder of the theory of evolution, Charles Darwin, was already interested in this balance between natural and sexual selection. It is now assumed that traits such as an extravagant tail are a kind of “honest signal” of the genetic quality of a male, which females can use as a guide when choosing a partner. “If an animal is able to survive with such a handicap, it is a sign that it is really fit,” explains O’Connor. Wang says: “This new discovery clearly shows how the interplay of natural and sexual selection has shaped the tails of birds since their earliest history”.
As the scientists finally report, knowledge of today’s species with tail feather features similar to those of Yuanchuavis provides clues about the way of life of the Cretaceous bird. Due to the cost-benefit ratio, only species have produced such extravagant tail feathers that are not necessarily dependent on optimal flight ability. “Birds that live in harsher environments and need to be able to fly really well, such as seabirds, typically have short tail feathers. “Elongated birds, on the other hand, tend to live in dense, resource-rich environments like forests, where less specialization in flying is required,” says O’Connor.
There are also indications of Yuanchuavi’s intraspecific behavior, he continues: “If you see extravagant elements in a bird, it is usually a male that does not care very much about its young,” says O’Connor. Because large, conspicuous feathers require more resources, so that the male can hardly invest in raising children. There is also the risk that its plumage will draw attention to the location of the nest. Accordingly, at Yuanchuavis a rather simple female has taken over most of the work in rearing the young.
Source: Field Museum, specialist article: Current Biology, doi: 10.1016 / j.cub.2021.08.044