Bird with unusually long fingers found fossilized in amber

Get to know the old bird who had toes longer than his legs. The researchers discovered a bird's foot dating back to 99 million years ago, preserved in amber and endowed with a third hyper-stretched toe. The study, published in the journal Current biology on July 11, suggests that this bird may have used his toes to extract food from tree-carrying trucks. This is the first time that such a foot structure is observed in birds, whether they are extinct or alive.

"I was very surprised to see amber," said the first author, Lida Xing, of the University of Geosciences of China (Beijing). "This shows that ancient birds were much more diverse than we thought, and they had developed many features to adapt to their environment."

To study the fossil Cretaceous period, Xing and his colleagues scanned amber with the help of a micro-CT and created a three-dimensional reconstruction of the foot. They found that the third toe of the bird, measuring 9.8 millimeters, was 41% longer than the second toe and 20% longer than its tarsometatosis, a bone located in the lower part of the birds' feet. The team compared the ratios with those of 20 other extinct birds of the same era and 62 live birds. No bird has a foot that looks like this one.

The researchers named him Elektorornis chenguangi. Elektorornis means "amber bird" and is part of a group of extinct birds called Enantiornithes, the most abundant type of bird known from the Mesozoic era. Enantiornithines are thought to have died out during the Cretaceous-Paleogene extinction event about 66 million years ago, as were dinosaurs. They do not have live descendants.

Based on the fossil record, the team estimated that the Elektorornis was smaller than a sparrow and was arboreal, meaning that it spent most of its time in the trees rather than than on the ground or in the water.

"The elongated toes are what we see commonly in arboreal animals because they have to be able to grab those branches and wrap around them," says Jingmai O. Connor, co-author of the Chinese Academy of Sciences. "But to the best of our knowledge, this extreme difference in toe length has never been seen before."

The amber in which the foot was found, measuring 3.5 cm long and weighing 5.5 grams, was discovered around 2014 in the Hukawng Valley in Myanmar. In the Mesozoic era, the valley was full of trees producing resin, a sticky substance that flowed from the bark of trees. Plants and small animals, such as geckos and spiders, are often trapped in resin and fossilize with amber after millions of years. Scientists have discovered many extinct animals, including the oldest known bee and a feathered dinosaur tail, in the amber of this valley.

Xing got the amber from a local amber trader, who did not know which animal belonged to this strange foot.

"Some traders thought it was a lizard foot because lizards tend to have long toes," says Xing. "Although I've never seen a bird's claw that looks like this before, I know it's a bird." Like most birds, this foot has four fingers, while the lizards have five. "

It is unclear why the amber bird has evolved so unusually. The only known animal with disproportionately long numbers is the aye-aye. The aye-aye is a lemur that uses its long, medium-sized finger to catch larvae and insects in tree trunks for food. Therefore, the researchers suggest that Elektorornis would have used his toe for the same purpose.

"It's the best estimate we can have," said O & # 39; Connor. "No bird with a similar morphology could be considered a modern analogue for this fossil bird – many ancient birds probably did things completely different from those of live birds." This fossil exposes a different ecological niche than these early birds Experimented then, they evolved. "

The team hopes to be able to extract proteins and pigments from some feathers exposed on the surface of amber. According to Xing, this data could help them better understand the bird's adaptation to the environment, for example whether or not he had a camouflaged plumage.