Posts Tagged ‘Feathers’
Last post, we discussed a new type of pigment discovered in the feathers of living penguins. With a little bit of evolutionary tree-based reasoning, it is possible to project the distribution of this color back into the fossil record as well. In his blog Illuminating Fossils, Dr. Daniel Thomas does just that. Check out the post to see how we can reconstruct the color of the fossil penguin Madrynornis. You can also learn more about Madrynornis in this past post.
Color is one of the things that draws people to birds. If one is not filled with wonder upon seeing a pink flamingo, an iridescent hummingbird or a rainbow macaw, it may be time for some serous introspection. Not all colors are created by the same means. Birds use a dazzling array of biological strategies to create color. Many of these come from pigments. Melanin, a pigment that is also found in our own skin and hair, generates colors like grey and reddish brown. Porphyrins create colors including bright greens and reds. Some pigments come from external sources – carotenoids are made by plants, but birds like cardinals and goldfinches gain their colors by harvesting these pigments from seeds. Some pigments can even leave traces in the fossil record. The fossil penguin Inkayacu paracasensis preserves feathers with melanosomes, the organelles that hold melanin inside feathers.
Aside from pigments, colors can be generated by structure – created by the way the feather refracts light. An example is the blue color generated by nanostructures in the Little Blue Penguin. Birds can even produce colors outside the visual light spectrum. Many species, including the King Penguin, have ultraviolet markings that they can see but humans cannot (more on this in a future post).
Recently, Dr. Daniel Thomas and colleagues reported a new type of bird pigment known to occur only in penguins. This pigment is responsibly for the yellow “ninja mask” of the Yellow-Eyed Penguin (Megadyptes antipodes) as well as the rakish yellow plumes of the Eudyptes penguins (the group the includes Macaronis and Rockhoppers). It is also seen in the rich orange neck feathers of King and Emperor Penguins (Aptenodytes). Dr. Thomas and his team used Raman Spectroscopy to unravel the chemical composition of this pigment. Surprisingly, the composition turned out not to match any of the previously known major classes of color-generating chemicals (carotenoids, melanins, porphyrins, psittacofulvins and metal oxides).
One additional interesting implication reported in the study is that the pigment is most likely synthesized directly by penguins. This is because penguins will grow the brightly colored yellow or orange feathers regardless of their diet – we see them in penguins gobbling down fish, squid, or krill in different wild populations and in zoos where food is carefully regulated. So, it does not appear they are gaining the color from their food like flamingos, which turn white if they don’t consume certain invertebrate prey.
Thomas, DB, McGoverin CM., McGraw KJ. James HF, Madden O. 2013. Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins. Journal of the Royal Society Interface:10, 20121065.
David Stephens at National Geographic snapped this picture of a rare white penguin on the Aitcho Islands. This Chinstrap Penguin (Pygoscelis antarcticus) is not albino, it is leucistic. Albino animals lack pigment, typically because of a flaw in an enzyme involved in producing melanin. You may remember learning a little about penguin melanin in the fossil penguin Inkayacu. Leucistic animals are able to form melanin, but generally have a mix of cells that produce melanin and cells that cannot. This results in a “washed out” appearance in cases like the penguin below. Whatever triggered the condition (typically a gene mutation is involved), the penguin ended up with light brownish coloration on its back instead of the black coloration of normal Chinstrap Penguins. Notice, though, that the beak and part of the feet are still black. Leucism often affects a particular area of a bird rather than the entire individual. White penguins turn up in the wild every year. However, it appears that either the mutations associated with leucism are recessive or the condition harms the penguins by ruining their counter-shading camouflage, because second generations have never been documented.
How do birds get their color? Light absorption by pigments is one way color can be produced. Bird feathers have pigments like melanins and carotenoids – we even have evidence for color in the fossil penguin Inkayacu from fossilized melanin-bearing structures. Color can also be produced by physical interactions between light and biological nanostructures. These colors are called structural colors.
Recently the color of Little Blue Penguins was found to be generated by a new type of structural color. As their name implies, Little Blues are both small and wrapped in bluish feathers. A previously unrecognized nanostructure is responsible for the blue feather barbs of these penguins. Structural color can be generated by several different types of structures, such as tiny spheres or channels. However, researchers were surprised to find a completely unknown nanostructural arrangement in the penguin feathers. At the subcellular level, Little Blue Penguin feather barbs are composed of parallel b-keratin nanofibres organized into densely packed bundles. Essentially, the miniscule structures scatter light waves so as to give off blue color.
This is an important discovery, because learning how birds make color at the nanostructural level may help scientists synthesize artificial colored structures in the lab. Of course, it also has implications for penguin evolution. We are only beginning to understand how the microstructure of feathers affects their function in the air and under water. Exciting research is on the horizon, and future investigations may yield a better understanding of what exactly makes penguin feathers so efficient at insulation and streamlining.
D’Alba L; Sarananthan V; Clarke JA; Vinther JA; Prum RO; Shawkey MD. 2011. Colour-producing β-keratin nanofibres in blue penguin (Eudyptula minor) feathers. Biology Letters. February 9 doi: 10.1098/rsbl.2010.1163: 1
In the last two posts, we recounted the discovery of the fossil and its feathers hiding in the block. Inkayacu provided one last surprise in the lab. Not only were feathers and skin intact, but the feathers preserved some microscopic structures giving us a glimpse into the color of an extinct penguin.
After finding several different types of feathers, our team carefully removed small samples to explore with Scanning Electron Microscopy. Matthew Shawkey and Liliana D’Alba (working at the University of Akron) and Jakob Vinther (working at Yale University) analysed the microstructure of the feathers and discovered that melanosomes were preserved in some samples. Melanosomes are microscopic organelles that carry pigments. These bean-shaped structures are responsible for generating certain colors in bird feathers, such as black, grey and red. We have melanosomes ourselves, and they play a role in determining hair color. Different sizes and shapes of melanosomes generate different colors in bird feathers, so by measuring the dimensions of the fossil melanosomes, team members were able to estimate the color these fossil feathers would have been in life. Reconstructions of samples from the feathers on the underside of the flipper support a reddish-brown hue, while isolated body contour feathers found in the block of rock encasing the penguin skeleton appear to have been colored grey and reddish brown.
Finding evidence for these colors was unexpected, because most living penguins are black and white. This is a good color scheme for an aquatic predator, because the white underside makes the animal harder to see from below and the black back makes it harder to see from above. A black and white countershaded pattern is employed by many other animals that hunt underwater, such as Razorbills (auks), Killer Whales, and many sharks. We don’t know the entire color scheme of Inkayacu because we only have wing feathers and a few body contour feathers to study. Because the contour feathers were loose in the sediment, we can’t tell whether they were from the front, back or side of the bird. Still, the presence of reddish brown feathers on the underside of the wing suggests an unusual color pattern, perhaps foregoing the standard countershading to create a more seal or dolphin-like solid outline.
It is interesting to note that brown and grey colors do characterize the hatchlings and juveniles of some penguin species. For example, King Penguins in their second molt look like big brown piles of leaves. This raises the question of whether the first specimen of Inkayacu is actually an immature individual. So far, that seems to be unlikely, because all of the bones have a finished texture and elements that remain separate in young birds are fully fused together in the Inkayacu specimen. This evidence strongly supports adult status.
Continuing the story of Inkayacu, we find ourselves in the paleontology lab back in Lima. After being carefully excavated, plastered and transported back to the museum, Pedro the fossil penguin needed to be soaked in water. This helped protect the fossil from the rapid change in environment. After spending several million years in one of the most arid environments on Earth, the fossil was suddenly going to be exposed to the humid airs of Lima. This could spell bad news for the fossil, because salts concentrated in the rock long ago would rapidly expand with moisture – the growing crystals could literally pop the fossil bone apart with tiny fractures, as has happened to desert fossils before. To prevent this, the team soaked the block for several days to draw the salts out into solution, rather then letting them form crystals. Afterwards, the marathon of preparing away the rock could begin. Walter Aguirre of the Museo completed many of the bones, and the US team including Dr. Julia Clarke and students Drew Eddy and Adam Smith (then at NCSU, now at UT Austin), along with Dr. Paul Brinkman and Vince Schneider of the North Carolina Museum or Natural Science traveled several times to join in.
Late into the evening, our team worked in the preparation station of the Museo de Historia Natural painstakingly removing bits of rock matrix from the bones of the penguin using tools like dental picks and needles set in pin vices. Up to this point, we were not sure whether there would be any other soft parts preserved with the skeleton but we proceeded carefully nonetheless, to avoid a careless scratch to the fossil bones. I remember clearing bits of siltstone away from the femur when the moment of revelation came. Julia Clarke flipped over a thin sheet of rock, and there underneath was a spectacular row of wing feathers.
The feathers were so exciting beause they offer our only glimpse into the transition between the normal flight feathers possessed by the flighted ancestors of penguins and the highly modified, scale-like feathers ofmodern penguins. Most living birds have about a dozen large primary flight feathers attached to the bones of the wing tip, but living penguins have several times as many small, stiff feathers in this region, covered by muliple rows of nearly identical scale-like feathers. The rachises, or quills, of the feathers are widened and flattened as well. This helps create a short, stiff flipper – terrible for flying through the air but perfect for propelling the bird through the water.
As preparation of the block continued, we came upon feathers from other parts of the body loose in the matrix. These feathers are body countour feathers, the feathers that help insulate and waterproof the penguin. Several body countour feathers were found near the bones of the leg, but we cannot be sure exactly where they came from because they are no longer attached. These feathers were interesting because of their size. Nearly complete examples measure about 3cm long, which is actually a bit shorter than the feathers of many smaller living penguin species. Possibly, the length of the feathers is related not only to overall size but also to habitat. Playing into this idea, some small Antarctic penguins have countour feathers about 50% longer than those of Inkayacu, which lived in a tropical environment.
The feathers had one more secret in store, and we will cover that in the next post.
Last post, we introduced Inkayacu, the newest fossil penguin species. Over the next three posts, I’d like to write about the way the story took shape. Inkayacu provides a great illustration of how science in paleontology proceeds, because in this discipline advances can come from two equally important events – discoveries of new fossils in the field and applications of new methods in the lab. In this case, there were three big moments of discovery that contributed to the whole story.
Ali Altamirano, one of the authors of the formal Science report, was responsible for the first big discovery. Ali is a Peruvian student gifted with a talent for finding fossils in the desert. Several years ago, while scanning the rocks of the coastal deserts of southern Peru, Ali caught the first glimpse of what may be the most significant bird fossil ever found in Peru. When a team of paleontologists from the Museo de Historia Natural including curator Rodolfo Salas-Gismondi visited the site, they knew instantly this was no ordinary fossil. Exposed near the surface was a scaley foot – 36 million year old bones wrapped in a remarkably well-preserved layer of skin. This startling aspect of the find is what gave Inkayacu the nickname Pedro. The nickname comes from “scaley Pedro”, a scaley (slang for sleazy) character on a popular South American TV show.
Context of a fossil discovery is always important, and in this case it is quite remarkable. Pedro’s skeleton was found in marine rocks, deposited when silts and sands from a coastal ocean environment compacted and lithified over time, and then were thrust up onto the land by plate tectonic action from the ongoing Andean uplift. Indeed, the forces that heaved these oceanic slabs onto the continental crust are still operating today, as witnessed by the devastating earthquake that struck Peru in 2007. Pedro lived in a very different environment than we typically think of when we envision ice-bound penguins at the South Pole. The fossil site is near 14 degrees south latitude, close to the Equator, and so would have had a very warm climate. Furthermore, during the Eocene the Earth was warmer than today. Global sea temperature was several degrees higher on average, and there were no permanant polar ice caps. So, Pedro was living in one of the hottest places on Earth during one of the hottest times in Earth history.
The skeleton of Inkayacu is beautifully well-preserved after such a stenuous 36 million year journal of burial, tectonic displacement, and ultimate exposure in the desert. Below is a collage of most of the bones that were recovered (some are not shown because they were left in the rock so as not to disturb the feathers). If you remember the post on Icadyptes salasi, you will note that the skull is similar to that species, especially in having a very long, pointed beak. The flipper bones are a bit more slender, and also show evidence of key differences in the way the muscles and nerves were arranged that will no doubt lead to important new work on penguin flipper evolution. Of course the attention right now is focused on the feathers, and rightfully so – we’ll delve into what they tell us in an upcoming post.
Julia A. Clarke, Daniel T. Ksepka, Rodolfo Salas-Gismondi, Ali J. Altamirano, Matthew D. Shawkey,, & Liliana D’Alba, Jakob Vinther, Thomas J. DeVries, Patrice Baby (2010). Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers Science : 10.1126/science.1193604 (Pre-print PDF at Science Express)