Tag Archives: feathers

Fossil friday: ancient feathers help explain how cassowaries got shiny

New research is helping scientists understand what ancient feathers look like — and why cassowaries are so shiny.

Cassowaries are flightless, blue-headed birds, with distinctive feet that are designed to run, not perch. Along with emus, ostriches, and kiwi birds (to whom they’re related) cassowaries are part of a lineage (the paleognath family) that split off from more ‘normal’ birds like chickens, ducks, and songbirds 100 million years ago. And, while we do know that the songbird family produces its iridescent colors through the physical structure of their feathers, we didn’t know how the cassowaries got their shine.

Sampling map of the two fossils from the Green River Formation, Wyoming.
Panels on the right show fossil melanosomes similar to black (sample 5, C) and iridescent melanosomes in livingbirds (samples 7 and 8 / D and E).
Image credits Chad M. Eliason and Julia A. Clarke2, (2020), Science.

But two fossils described in a new study in the journal Science Advances helps answer that question, while also telling us of how birds used to look 52 million years ago.

Old feathers

“A lot of times we overlook these weird flightless birds. When we’re thinking about what early birds looked like, it’s important to study both of these two sister lineages that would have branched from a common ancestor 80 million or so years ago,” says Chad Eliason, a staff scientist at the Field Museum and the paper’s first author.

Humans and other mammals create color in their skin or hair/fur through the use of pigments, mostly melanin. Birds and insects, however, also use the microscopic structure of their tissues to produce some of their colorations, such as the dazzling iridescent, glossy, or rainbow effects on their feathers and wings.

The cellular constructs that carry pigment are called melanosomes, and different shapes or arrays of melanosomes are used to produce the range of colors we see in nature. Birds’ feathers use keratin in a similar way, altering its microscopic structure to change the way it reflects light (and thus the color we perceive them to be). Their structure also creates the perception of texture (such as matte or glossy) through the way they reflect light.

Different mechanisms of gloss production in birds.
Image credits Chad M. Eliason and Julia A. Clarke2, (2020), Science.

But these color-creating structures haven’t been found in fossilized paleognath feathers up to now. The team, who has a background in structural color analysis of birds and dinosaurs, found that cassowary feathers also produce structural colors, but by using a different approach than modern birds. Instead of having these structures in their barbules (tiny structures that cover the feathers), they concentrate them in the rachis, the middle trunk of the feather. Their blue heads are also a product of structural coloring, the team explains.

The team then looked at a 52-million-year-old relative of the cassowary, known as the Claxavis bird. It lived in today’s Wyoming and is known from some exceptionally well-preserved fossils that include feather imprints, making it ideal for this study.

“You can look at a fossil slab and see an outline of where their feathers were, because you kind of see the black stain of melanin that’s left over, even after 50 million years or so,” explains Eliason. “We peeled off little flakes of the fossil from the dark spots of melanin, and then we used scanning electron microscopes to look for remnants of preserved melanosomes.”

The melanosomes in the fossilized barbules were long and thin, having the rough shape of green beans, which the team found is associated with iridescence in modern birds. The team says this is strong evidence in favor of ancient paleognath feathers exhibiting structural color. Furthermore, this study also provides the first evidence of structural color in the feathers of paleognaths, helping us understand how cassowaries got so shiny.

Despite this, the team doesn’t know why the two bird families evolved different mechanisms for such coloration. Eliason believes that flightlessness allowed these birds more room to experiment with their feathers, as they didn’t need to keep them aerodynamic.

“Needing to be able to fly is a very strong stabilizing force on wing shape,” says Eliason. “Losing that constraint, that need to fly, might result in new feather morphologies that produce gloss in a way that a flying bird might not.”

“[The findings] give us a glimpse into the time when dinosaurs were going extinct and the birds were rising,” he adds. “Studying these paleognaths gives us a better understanding of what was happening there because you can’t just study neognaths (modern birds); you need to study both sister clades to understand their ancestors.”

The paper “Cassowary gloss and a novel form of structural color in birds” has been published in the journal Science Advances.

Caudipteryx robot.

Feathered dinosaurs may have accidentally developed flying — while running

Flying is a pretty nifty way of moving around very fast. New research is looking into the dinosaurs’ earliest attempts at flight, an effort which ultimately led to the birds of today.

Caudipteryx Hendrickx.

Reconstruction of Caudipteryx Hendrickx at the Sauriermuseum of Aathal, Switzerland.
Image credits Christophe Hendrickx.

Two-legged dinosaurs likely started dabbling in active flight while running, new research reveals. The findings provide new insight into how these reptiles evolved the ability to fly, a debate that’s been raging ever since 1861 and the discovery of Archaeopteryx. The results point to an alternative evolutionary path that didn’t rely on an intermediate gliding phase, suggesting that the two types of flight have different origins.

Dinos of a feather flap their wings together

“Our work shows that the motion of flapping feathered wings was developed passively and naturally as the dinosaur ran on the ground,” says lead author Jing-Shan Zhao of Tsinghua University, Beijing. “Although this flapping motion could not lift the dinosaur into the air at that time, the motion of flapping wings may have developed earlier than gliding.”

To the best of our knowledge, dinosaurs perfected gliding-type flight much earlier than active flight. The sensible assumption, then, would be that active flight developed from gliding — the two are very similar, mechanically. However, Zhao and his colleagues weren’t convinced. The team studied Caudipteryx, the most primitive non-flying dinosaur known to have had feathered “proto-wings.” It weighed around 5 kilograms, very little for a dinosaur, and looked like a miniature, feathered, beaked T-Rex.

The first part of the research revolved around understanding how Caudipteryx moved about. Using a mathematical approach called modal effective mass theory, the team looked at how the various parts of this dinosaur’s body fared during running, how they moved, and what mechanical forces they were subjected to. From these calculations, the team estimates that running speeds between about 2.5 to 5.8 meters per second would have created forced vibrations that caused the Caudipteryx’s wings to flap. So far, so good — previous research has estimated that Caudipteryx could reach running speeds of up to 8 meters per second, so it could easily achieve the speed interval calculated by the team.

Caudipteryx robot.

Caudipteryx robot used in the tests.
Image credits Talori et al., (2019), PLOS.

Then came the fun part: in order to check their results, the team constructed a life-sized robot Caudipteryx and made it run at different speeds. This step confirmed the initial findings — running motions in the 2.5 to 5.8 meter per second range caused a flapping motion of the wings. To double-double check the results, the team also fitted artificial wings on a young ostrich. Here too, running caused the wings to flap. Longer and larger wings providing a greater lift force, the team notes.

So the first part of this hypothesis seems to pan out. Zhao says that the next step is to analyze the lift and thrust of Caudipteryx’s feathered wings during the passive flapping process, to see if the animal could actually sustain flight over meaningful distances, or just tended to hop around.

The paper “Identification of avian flapping motion from non-volant winged dinosaurs based on modal effective mass analysis” has been published in the journal PLOS Computational Biology.

Wilson's Bird of Paradise.

Birds-of-paradise males need more than looks to get a girlfriend

Female birds-of-paradise are very picky with their mates, new research shows.

Wilson's Bird of Paradise.

Wilson’s Bird of Paradise (Diphyllodes respublica).
Image credits Serhanoksay / Wikimedia.

Birds-of-paradise didn’t get their name for naught. The males of the species are renowned for their incredible plumage, complex calls, and dazzling dance moves. However, all this fluff isn’t enough to convince the discerning objects of their affections. A new study reports that the female preference may also be tied to where the males ply their courting: on the ground or up in the trees.

Flirts from paradise

Most of the 40 known species of bird-of-paradise live in New Guinea and northern Australia. For the study, the team analyzed 961 video and 176 audio clips retrieved from the Cornell Lab’s Macaulay Library archive. They also drew on 393 museum specimens from the American Museum of Natural History in New York City. Based on this material, they say that certain behaviors and traits are correlated, as follows:

  • The number of colors on a male and the number of different sounds he makes. The more colors he sports, the larger his repertoire.
  • Dance complexity and the number of sounds a male can produce. The most dazzling dancers also have the widest range of sounds they weave into their songs.
  • Males that display in a group (a lek) tend to have more colors. The team believes this helps them stand out better amid the competition, canceling out some of the drawbacks of the lek.

Victoria's riflebird.

A male (black, top) Victoria’s riflebird (Ptiloris victoriae) displays for a female (brown, bottom). Victoria’s riflebirds are also birds-of-paradise, native to northeastern Queensland, Australia.
Image credits Francesco Veronesi / Wikipedia.

According to the study, female preference drives the evolution of physical and behavioral traits that make the species’ males so distinctive. Lead author Russell Ligon says that females evaluate not only how attractive a male is, but also how well he sings and dances. Their preference for certain combinations of traits results in what his team calls a “courtship phenotype” — the phenotype is an individual’s traits determined by both genetics and environment.

Because females pick and choose mates based on a combination of characteristics (rather than a single one), males have had ample opportunity to ‘experiment’ with their courtship displays, the team reports. This led to the large variation seen in the species’ courting behaviors today — if females were looking for a single characteristic, all the males would simply try to double down on it. Of course, it also helps that the birds have few natural predators to interrupt all the romancing.

Female scrutiny may also have a surprising effect: determining whether a male will perform courting behavior on the ground or up in the trees. The researchers say that location matters when selecting the best approach to impress potential mates:

“Species that display on the ground have more dance moves than those displaying in the treetops or the forest understory,” explains Edwin Scholes, study co-author and leader of the Cornell Lab’s Bird-of-Paradise Project.

“On the dark forest floor, males may need to up their game to get female attention.”

Males of species that display above the canopy — where there is less interference from trees and shrubs to block sounds — sing more complex songs. Their dance moves, however, are less elaborate.

The paper has been published in the journal PLOS Biology.

The tip of a tail and plumage from a 99-million-year-old dinosaur. Credit: RSM/ R.C. McKellar

Beautiful 99-million-year-old dinosaur feather trapped in amber speaks of feathery evolution

The tip of a tail and plumage from a 99-million-year-old dinosaur. Credit: RSM/ R.C. McKellar

The tip of a tail and plumage from a 99-million-year-old dinosaur. There are also two extinct ants trapped inside.Credit: RSM/ R.C. McKellar

Birds are literally dinosaurs being the direct descendants of theropods. That’s not to say, however, that feathers appeared with birds. Scientists know from imprints encased in fossils that some dinosaurs sported feathers as early as 145 million years ago. These fossils are pretty rare and, moreover, only offer a two-dimensional glimpse of what dino feathers were like. Fossilized dino feathers trapped in amber, however, can teach us much more.

One such fossil was found by Lida Xing, a researcher from the China University of Geosciences in Beijing — and it was all by accident. Xing was strolling through an amber market in Myanmar when an item on sale caught his eye. The vendor told him he was looking at tree resin with some plant remains trapped inside. Xing hoped it was actually some animal part inside and bought it to bring home to study.

When he performed a CT scan in his lab, Xing was amazed to find that it was a feather, complete with the tip of a tail. The excitement was doubled when a close examination revealed it actually belonged to a dinosaur — a 99-million-year-old one to boot. It’s not clear right now which dinosaur it belonged to, but it might be a juvenile coelurosaur — a clade of theropods that more closely resemble birds than carnosaurs.

The well preserved amber specimen could prove very important for settling an age-old debate of how feathers evolved. Generally, biologists study bird embryos to get a sense of how feathers appeared millions of years ago but absent time capsules (feather fossils are very rare) we stand the risk of making too many assumptions. Specifically, one assumption is that the ‘velcro’ that keeps feathers together came before the underlying structural form. Some say the velcro appeared later, following the main stem of the feather developed to create bristly feathers.

A close-up of the blade-like barbules. Credit: R.C. McKellar

A close-up of the blade-like barbules. Credit: R.C. McKellar

Xing’s amber suggests even primitive feathered dinosaurs had velcro-like hooks called barbules that help feathers lie flat atop each other. The barbules seemed to hold in place loose feathers that dangled all over the place, not at all like the stiff pinions that modern birds use for flight.

“If you look at them, they’re kind of waving all over the place,” says Matthew Carrano, curator of Dinosauria at the Smithsonian’s National Museum of Natural History. “If you had a really structured feather and you had these barbules, they shouldn’t be floating all over the place. They should be pretty stiff.”

What we can glean from the fossil is that barbules came first, preceding the shaft. It’s also clear that this dinosaur didn’t fly and instead used the feathers for insulation, as reported in the journal Current Biology.

That’s not all. Inside the amber scientists also found insects: two ants belonging to an extinct group called Sphecomyrminae and some cockroach remains. The tissue around the tail bone contains ferrous iron, the remains of hemoglobin from the blood of the sparrow-sized juvenile dinosaur.

All of this information, and much more to follow, was gleaned from a single amble fossil. One that would’ve been turned into a nice necklace or pair of earrings were it not for a watchful paleontologist. Who knows what other treasures lie casually hidden in Myanmar amber fairs.

Dinosaur feathers found preserved in museum amber

Instead of digging through layers of rocks, a few paleontologists focused their efforts on ‘digging’ through museum collection instead – and their efforts were quite successful. Their unique approach led to the discovery of never-before seen structures, which they think are something called dino-fuzz.

dinofuzz

The fluffy structures trapped in the small bits of ancient amber may represent some of the earliest evolutionary experiments leading to feathers, according to researchers. They combed through thousands of small to minuscule samples before finding the ‘good’ 80 million years samples: 11 coin-sized amber traps with traces of ancient feathers and fuzz. Some of them resembled modern feathers (some fit for flying, some fit for diving), while some were the ‘fuzz’; unlike fossils, feathers trapped in amber have another advantage: their colors are also preserved.

dinofuzz2

The oldest bird, Archaeopterix, inhabited the Earth about 150 million years ago, and the oldest known feathered dinosaur, Anchiornis huxleyi, lived some 151-160 million years ago. Both creatures had modern style feathers, and paleontologists have little information about the earlier stages of feather evolution: the flexible, unbranched filaments—often called protofeathers, and sometimes called ‘dinofuzz’.

Ryan McKellar, a paleontologist at the University of Alberta in Canada, and his colleagues provided some much needed information, not by gathering new samples, but by reanalizing old samples. Although some of the feathers and protofeathers appear nearly transparent, others are heavily pigmented and probably were, in life, a deep brown, dark gray, or black.

dinofuzz3

The Results are published in Science.

All pictures via Science/AAAS.