99-Million-Year-Old Burmese Amber Preserves Feathers of Immature Enantiornithine Bird

Jul 7, 2023 by News Staff

 

The specimen provides the first unequivocal evidence of immature feathers in the Mesozoic fossil record.

A small piece of Burmese amber preserving feathers interpreted as belonging to a juvenile enantiornithine bird: (A) amber with the dorsal surface of the feather cluster exposed; (B) ventral surface exposed; (C) close up of the ventral surface (region marked in B); (D) close up of the ventral surface region marked in (C); (E) close up of the ventral surface region marked in (D); (F) close up of the dorsal surface marked in (A, larger rectangle); (G) close up of the dorsal surface marked in (A, smaller rectangle). Dotted lines indicate desiccation surfaces. Scale bars – 0.5 mm in (A, B, D and F), 0.1 mm in (C); 0.3 mm in (E); and 0.2 mm in (G). Anatomical abbreviations: ipl – immature plumaceous feather; ipn – immature pennaceous feather; ks – keratinous sheath; pf – probable filamentous ‘protofeathers.’ Image credit: O’Connor et al., doi: 10.1016/j.cretres.2023.105572.

Today, baby birds are on a spectrum in terms of how developed they are when they’re born and how much help they need from their parents.

Altricial birds hatch naked and helpless; their lack of feathers means that their parents can more efficiently transmit body heat directly to the babies’ skin.

Precocial species, on the other hand, are born with feathers and are fairly self-sufficient.

All baby birds go through successive molts — periods when they lose the feathers they have and grow in a new set of feathers, before eventually reaching their adult plumage.

Molting takes a lot of energy, and losing a lot of feathers at once can make it hard for a bird to keep itself warm.

As a result, precocial chicks tend to molt slowly, so that they keep a steady supply of feathers, while altricial chicks that can rely on their parents for food and warmth undergo a simultaneous molt, losing all their feathers at roughly the same time.

Hypothetical molt cycle in juvenile enantiornithine birds: (A) hatchling bird with sparse natal body plumage; (B) rapid molt; (C) juvenile with juvenal plumage including fully developed rachis dominated feathers. Image credit: O’Connor et al., doi: 10.1016/j.cretres.2023.105572.

The cluster of immature feathers preserved a piece of amber from the Hukawng Valley in Kachin Province in northeastern Myanmar is the first definitive fossil evidence of juvenile molting.

The 99-million-year-old specimen reveals a baby bird whose life history doesn’t match any birds alive today.

“This specimen shows a totally bizarre combination of precocial and altricial characteristics,” said Dr. Jingmai O’Connor, a researcher at the Field Museum of Natural History.

“All the body feathers are basically at the exact same stage in development, so this means that all the feathers started growing simultaneously, or near simultaneously.”

However, this bird was almost certainly part of a now-extinct group called Enantiornithes, which were highly precocial.

The authors hypothesize that the pressures of being a precocial baby bird that had to keep itself warm, while undergoing a rapid molt, might have been a factor in the ultimate doom of Enantiornithes.

“Enantiornithines were the most diverse group of birds in the Cretaceous, but they went extinct along with all the other non-avian dinosaurs,” Dr. O’Connor said.

“When the asteroid hit, global temperatures would have plummeted and resources would have become scarce, so not only would these birds have even higher energy demands to stay warm, but they didn’t have the resources to meet them.”

A paper on the findings was published in the journal Cretaceous Research.

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Jingmai O’Connor et al. 2023. Immature feathers preserved in Burmite provide evidence of rapid molting in enantiornithines. Cretaceous Research 149: 105572; doi: 10.1016/j.cretres.2023.105572

While an asteroid impact 66 million years ago wiped off all species of dinosaurs, many bird species survived the mass extinction event. In two new studies, researchers suggest that the process of molting -- shedding and regrowing feathers -- hold the key to understanding why some species were able to escape oblivion. Watch this episode of #PureScience with @MohanaBasu to learn more.

Ancient amber reveals how some birds survived asteroid-induced mass extinction

This amber has been described as the "first definitive fossil evidence of juvenile molting."

Mrigakshi Dixit
Created: Jul 07, 2023 

Feathers from a baby bird that lived 99 million years ago, preserved in amber.

Birds were the only dinosaur group to survive the horrific asteroid strike that caused a mass extinction about 66 million years ago.

However, not all of the birds living at the time survived. That has created the baffling enigma that paleontologists have been attempting to unravel for decades – how did some avian ancestors survive while others perished?

Now, two new studies have zeroed in on one possible trait – molting.
Molting in modern birds

Molting is a process in which birds shed and re-grow their feathers. Feathers are formed of keratin, the same protein that produces human hair and fingernails.

Birds rely on feathers to execute a range of functions, including flying, swimming, camouflage, attracting mates, staying warm, and shielding their skin against the sun's rays.

Feathers, on the other hand, are complicated structures that cannot be repaired, which is why they molt.

“Molt is something that I don't think a lot of people think about, but it is fundamentally such an important process to birds because feathers are involved in so many different functions,” said Jingmai O’Connor, associate curator of fossil reptiles at Chicago’s Field Museum, in an official release.

Modern birds generally molt once a year in a “sequential” pattern. This means they only replace a few feathers at a time over a period of a few weeks. This permits them to fly even when they are molting.

While other bird species lose all of their feathers at once and regenerate within a few weeks, the authors emphasize that this is unusual and is normally found in non-avian aquatic birds such as ducks.
Ancient amber hold the secret

The researchers examined the molting process in archaic birds in two recent studies.

The researchers could look back into prehistoric times, thanks to the 99 million years old fossils. What they discovered were baby bird feathers preserved in amber.

This amber has been described as the "first definitive fossil evidence of juvenile molting."

Interestingly, the specimen exhibited a rare mix of characteristics not found in any other living baby bird species.

This was determined based on their capacity to make feathers as well as their dependency on their parents. Some newborn birds, known as Altricial birds, hatch naked and require extensive parental care before they can be left alone. Precocial species, on the other hand, are born with feathers and grow up on their own. Despite this, all newborn birds go through molts, which take a lot of energy.

Illustration of what a newly hatched Enantiornithine bird may have looked like.

“This specimen shows a totally bizarre combination of precocial and altricial characteristics. All the body feathers are basically at the exact same stage in development, so this means that all the feathers started growing simultaneously, or near simultaneously,” explained O’Connor.

The team believes this specimen belonged to the Enantiornithines, a now-extinct precocial group of birds.

Enantiornithines were doomed because the infant bird needed to stay warm while simultaneously going through a rapid molting phase – with no support at hand.

“When the asteroid hit, global temperatures would have plummeted and resources would have become scarce, so not only would these birds have even higher energy demands to stay warm, but they didn’t have the resources to meet them,” noted O’Connor.

Enantiornithines are thought to be one of the most diversified families of birds to live during the Cretaceous period. These birds, just like the mighty dinosaurs, were unable to withstand the conditions of the asteroid's impact and eventually went extinct. However, some ancestors of modern birds that molted once a year could have survived this massive asteroid impact. And this paved the way for the evolution of birds that we see today, like robins, pigeons, and many others.

The findings have been published in the journals Cretaceous Research and Communications Biology.