March 14, 2013
Roughly 150 million years ago, birds began to evolve. The winged creatures we see in the skies today descended from a group of dinosaurs called theropods, which included tyrannosaurs, during a 54-million-year chunk of time known as the Jurassic period. Why the ability to fly evolved in some species is a difficult question to answer, but scientists agree that wings came to be because they must have been useful: they might have helped land-based animals leap into the air, or helped gliding creatures who flapped their arms produce thrust.
As researchers continue to probe the origin of flight, studies of fossils have shown that theropods–particularly coelurosaurian dinosaurs, which closely resemble modern birds—had large feathers on both their fore limbs and hind limbs. However, extensive evidence for these leg feathers didn’t exist in the earliest birds. But now, a new examination of fossils reported today in the journal Science reveals several examples of this four-winged anatomy in modern birds’ oldest common ancestors.
Modern birds have two types of feathers: vaned feathers that cover the outside of the body, and the down feathers that grow underneath them. Researchers studying the approximately 120 million-year-old fossils of 11 primitive birds from the Shandong Tianyu Museum of Natural History in China found that one type of vaned plumage, also known as pennaceous feathers, was neatly preserved in skeletal fossils of these specimens, along each creatures’ hind limbs. After this find, the researchers must have been flying high: The feathers of birds’ wings, known as flight feathers, are long, stiff and asymmetrically shaped pennaceous feathers, similar to those found in the fossils. When fanned together, pennaceous feathers form the broad surfaces of birds’ wingspans—without these surfaces, birds cannot stay aloft.
Pennaceous feathers, which are composed of many flattened barbs, existed in some winged dinosaurs. Finding them on the hind legs of early birds suggests that before birds used two wings to fly, they may have depended on four. Over millions of years, however, birds gradually lost the feathers on this extra set of wings.
The study adds to existing theories that suggest the first birds flew with four wings. Examination of a primitive bird fossil from the Archaeopteryx genus in 2004 revealed long feathers on the animal’s back and legs, which would have aided its gliding ability. Two years later, another study of the crow-sized animal, which lived about 150 million years ago, reported that the prehistoric bird’s feathers resembled those on modern birds’ flight wings.
One of the more complete skeletons examined in today’s study actually showed hind-limb pennaceous feathers along the bone of each leg. The longest feather stretched almost two inches, which is remarkable considering that the legs they covered were between one inch and two and a half inches long. In fact, specimens from a group of birds called Enantiornithes, which externally resemble modern birds, showed symmetrically paired large feathers preserved along their hind leg bones. Such feather arrangement is present in modern birds’ wings.
Researchers speculate that the second set of wings might have provided extra lift or created drag in the air. They might also have helped birds maneuver their airborne bodies.
If these hind wings indeed served a functional purpose in fight, they will earn an important place in bird evolution.
Bird movement is characterized by a combination of feathered arms for flight and legs for walking on land. This study suggests that if walking legs, present in birds today, developed after these feathered hind legs, then the loss of feathers on the back legs—and thus an extra pair of wings—reflects a period of change during which the arms became specialized for flight and the legs, for locomotion.
Today, leg feathers are less well developed than wing feathers—they are usually much smaller and fluffy—and they serve as protection and insulation for the leg. These fluffy bits are sparse too—instead, the legs are covered in scales, which form only if feather growth is inhibited. Studies of modern birds show how this works. As chicks develop from embryos and grow into adults, feathered legs can be transformed into scaled legs, or vice versa, by altering how certain genes are expressed.
The recent revelation about feathers on birds’ hind legs suggest that a similar genetic, and more permanent, change might have occurred early in bird evolution, according to lead researchers. This shift triggered the loss of birds’ hind wings, pushing the creatures down an evolutionary path that would allow them to fly with just two.
March 12, 2013
Neanderthals never invented written language, developed agriculture or progressed past the Stone Age. At the same time, they had brains just as big in volume as modern humans’. The question of why we Homo sapiens are significantly more intelligent than the similarly big-brained Neanderthals—and why we survived and proliferated while they went extinct—has puzzled scientists for some time.
Now, a new study by Oxford researchers provides evidence for a novel explanation. As they detail in a paper published today in the Proceedings of the Royal Society B, a greater percentage of the Neanderthal brain seems to have been devoted to vision and control of their larger bodies, leaving less mental real estate for higher thinking and social interactions.
The research team, led by Eiluned Pearce, came to the finding by comparing the skulls of 13 Neanderthals who lived 27,000 to 75,000 years ago to 32 human skulls from the same era. In contrast to previous studies, which merely measured the interior of Neanderthal skulls to arrive at a brain volume, the researchers attempted to come to a “corrected” volume, which would account for the fact that the Neanderthals’ brains were in control of rather differently-proportioned bodies than ours ancestors’ brains were.
One of the easiest differences to quantify, they found, was the size of the visual cortex—the part of the brain responsible for interpreting visual information. In primates, the volume of this area is roughly proportional to the size of the animal’s eyes, so by measuring the Neanderthals’ eye sockets, they could get a decent approximation of their the visual cortex as well. The Neanderthals, it turns out, had much larger eyes than ancient humans. The researchers speculate that this could be because they evolved exclusively in Europe, which is of higher latitude (and thus has poorer light conditions) than Africa, where H. sapiens evolved.
Along with eyes, Neanderthals had significantly larger bodies than humans, with wider shoulders, thicker bones and a more robust build overall. To account for this difference, the researchers drew upon previous research into the estimated body masses of the skeletons found with these skulls and of other Neanderthals. In primates, the amount of brain capacity devoted to body control is also proportionate to body size, so the scientists were able to calculate roughly how much of the Neanderthals’ brains were assigned to this task.
After correcting for these differences, the research team found that the amount of brain volume left over for other tasks—in other words, the mental capacity not devoted to seeing the world or moving the body—was significantly smaller for Neanderthals than for ancient H. sapiens. Although the average raw brain volumes of the two groups studied were practically identical (1473.84 cubic centimeters for humans versus 1473.46 for Neanderthals), the average “corrected” Neanderthal brain volume was just 1133.98 cubic centimeters, compared to 1332.41 for the humans.
This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals. “Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement. “[They] are likely also to have resulted in less well developed material culture—which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.”
Previous studies have also suggested that the internal organization of Neanderthal brains differed significantly from ours. For example, a 2010 project used computerized 3D modeling and Neanderthal skulls of varying ages to find that their brains developed at different rates over the course of an individual’s adolescence as compared to human brains despite comparable brain volumes.
The overall explanation for why Neanderthals went extinct while we survived, of course, is more complicated. Emerging evidence points to the idea that Neaderthals were smarter than previously thought, though perhaps not smart enough to outmaneuver humans for resources. But not all of them had to—in another major 2010 discovery,a team of researchers compared human and Neanderthal genomes and found evidence that our ancestors in Eurasia may have interbred with Neanderthals, preserving a few of their genes amidst our present-day DNA.
Apart from the offspring of a small number of rare interbreeding events, though, the Neanderthals did die out. Their brains might have been just as big as ours, but ours might have been better at a few key tasks–those involved in building social bonds in particular—allowing us to survive the most recent glacial period while the Neanderthals expired.
March 6, 2013
In 1975, a team of Russian archaeologists announced that they’d made a remarkable find: From a cave in the Altai Mountains of Siberia, they’d unearthed a 33,000-year-old fossil skull that resembled a wolf. In 2011, an anatomical analysis suggested that the fossil was a hybrid of a wolf (with its large teeth) and a dog (with its shortened snout), raising the possibility that it was a partly domesticated wolf—in other words, one of the oldest ancestors of the modern dog ever discovered.
At the time, though, DNA analysis was needed to make certain that the fossil came from an ancestor of man’s best friend. A paper published today in the journal PLOS ONE confirms that fact, indicating that the creature was more closely related to modern dogs than wolves, and forcing scientists to reconsider the dog’s evolutionary family tree.
To come to the finding, a team led by Anna Druzhkova of the Russian Academy of Sciences sequenced mitochondrial DNA taken from one of the skull’s teeth. This type of genetic material comes from an organelle inside each cell called the mitochondria, which has a distinct type of DNA that’s separate from the cell’s normal chromosomes. For each individual, mitochondrial DNA is inherited directly from one’s mother without any modifications and thus remains relatively constant over generations, except for the gradual effect of mutations. Similarities found in such DNA collected from various animals helps scientists understand the evolutionary relationships between species.
The research team compared their sample of mitochondrial DNA from the ancient skull with samples from 70 different modern breeds of dog, along with 30 different wolf and 4 different coyote DNA samples. Their analysis found that the fossil’s DNA didn’t match any of the other samples perfectly, but most closely resembled the modern dog breeds, sharing the most similarities with Tibetian Mastiffs, Newfoundlands and Siberian Huskies in particular.
Scientists know that dogs evolved as a result of the domestication of wolves, but the specific time and location of this domestication is still poorly understood—and this discovery further complicates that picture. Most experts agree that dogs predate the invention of agriculture (which happened roughly 10,000 years ago), but some say that domestication may have occurred as long as 100,000 years ago.
This finding—and the previous radiocarbon dating of the skull which established its age—set that event to at least 33,000 years ago. However, dogs may have been domesticated from wolves multiple times, and this breed of Siberian dog may have actually gone extinct, rather than serving as an ancestor for modern dogs. Archaeological evidence indicates that, with the onset of the last glacial maximum (around 26,000 years ago), humans in this area of Siberia may have stopped domesticating dogs, maybe due to food scarcity. In that case, an independent domestication elsewhere may have led to the dogs of today.
On the other hand, domestication in the vicinity of the Altai Mountains, as evidenced by this finding, may have led to the geographic spread of dogs elsewhere in Asia and Europe, even if they died out in Siberia. Previously, many have suggested that the first domestication occurred in the Middle East or East Asia, but this skull could force scientists to rethink their theories. The research team behind the analysis notes that finding more ancient dog remains will help us in putting together the puzzle.
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March 5, 2013
Antarctica, as you might expect, gets pretty darn cold: Temperatures as low as -40 degrees Fahrenheit are often recorded during the winter. For the creatures who live there, this extreme cold demands innovative survival strategies that enable the loss of as little heat as possible.
Scientists recently discovered that Emperor Penguins—one of Antarctica’s most celebrated species—employ a particularly unusual technique for surviving the daily chill. As detailed in an article published today in the journal Biology Letters, the birds minimize heat loss by keeping the outer surface of their plumage below the temperature of the surrounding air.
At the same time, the penguins’ thick plumage insulates their body and keeps it toasty. A team of scientists from Scotland and France recently came to the finding by analyzing thermal images (below) of penguins taken at a coastal Emperor breeding colony in Adélie Land, an area of Antarctica claimed by France.
The researchers analyzed thermographic images like this one taken over roughly a month during June 2008. During that period, the average air temperature was 0.32 degrees Fahreinheit. At the same time, the majority of the plumage covering the penguins’ bodies was even colder: the surface of their warmest body part, their feet, was an average 1.76 degrees Fahrenheit, but the plumage on their heads, chests and backs were -1.84, -7.24 and -9.76 degrees Fahrenheit respectively. Overall, nearly the entire outer surface of the penguins’ bodies was below freezing at all times, except for their eyes and beaks.
The scientists also used a computer simulation to determine how much heat was lost or gained from each part of the body—and discovered that by keeping their outer surface below air temperature, the birds might paradoxically be able to draw very slight amounts of heat from the air around them. The key to their trick is the difference between two different types of heat transfer: radiation and convection.
The penguins do lose internal body heat to the surrounding air through thermal radiation, just as our bodies do on a cold day. Because their bodies (but not surface plumage) are warmer than the surrounding air, heat gradually radiates outward over time, moving from a warmer material to a colder one. To maintain body temperature while losing heat, penguins, like all warm-blooded animals, rely on the metabolism of food.
The penguins, though, have an additional strategy. Since their outer plumage is even colder than the air, the simulation showed that they might gain back a little of this heat through thermal convection—the transfer of heat via the movement of a fluid (in this case, the air). As the cold Antarctic air cycles around their bodies, slightly warmer air comes into contact with the plumage and donates minute amounts of heat back to the penguins, then cycles away at a slightly colder temperature.
Most of this heat, the researchers note, probably doesn’t make it all the way through the plumage and back to the penguins’ bodies, but it could make a slight difference. At the very least, the method by which a penguin’s plumage wicks heat from the bitterly cold air that surrounds it helps to cancel out some of the heat that’s radiating from its interior.
And given the Emperors’ unusually demanding breeding cycle (celebrated in the documentary March of the Penguins), every bit of warmth counts. Each winter, they trek from
inland coastal locations to the coast inland—walking as far as 75 miles—where they breed and incubate their eggs. After the females lay eggs, the males incubate them by balancing them on top of their feet in a pouch for roughly 64 days. Since they don’t eat anything during this entire period, conserving calories by giving up as little heat as possible is absolutely crucial.
February 13, 2013
Indonesia’s numerous islands (18,307 to be exact) house a wealth of avian biodiversity, yet scientists speculate that many of the country’s bird species have yet to be discovered or categorized. But ornithologists are celebrating today as a new species of owl joins the list, taking filling in one more spot in the catalog of the archipelago’s animals.
In 2003, George Sangster, a Dutch ornithologist from Stockholm University, and his wife were exploring the forested foothills of Lombak, an island just east of Bali. While traipsing through the forest at night, Sangster picked up on an owl call he did not recognize. Coincidentally, just a few days later Ben King, an ornithologist from the American Museum of Natural History, heard those same calls from the jungle and also suspected they came from an unknown species.
“It was quite a coincidence that two of us identified this new bird species on different parts of the same island, within a few days of being on the island, especially considering that no-one had noticed anything special about these owls in the previous 100 years,” Sangster said in a statement.
Locals on Lombak, it turned out, were familiar with the species. Known as burung pok–roughly translated as “pook,” a mimic of the owl’s hoots–the birds turned out to be a common feature of the nocturnal landscape. But locals on neighboring islands, however, said they had never heard of the bird and did not recognize its unusual call.
Here, you can hear the little Indonesian owl hooting into the night, which the researchers describe as “a single whistle without overtones:
Although birders and scientists alike love owls, surprisingly not much is known about those species’ biology, including how they relate to one another on an evolutionary scale. Lately, however, researchers have been working double time to get a grip on owls. In 1975, for example, scientists knew of 146 species, and that number leapt to 250 as of 2008. One driver behind this jump in species numbers was the realization that owl calls could lend clues (PDF) to classifying different types of owls. Owls hoot to attract mates and recognize one another as the same, so animals evolved calls unique to their species. In some cases, owls previously classified as the same species were split in two primarily on the basis of their calls.
Sangster, King and two other researchers from Sweden and Australia got together and were able to photograph the owls by playing back recordings of the call to attract several of the hooting culprits. Digging through old records, the researchers found that the owls matched specimens collected back in 1896 by Alfred Everett, a British administrator who was based in Borneo and spent his spare time collecting natural history curios. That same year, Ernest Hartlet, a naturalist who reported on Everett’s field work, accurately noted that “the cry is a clear but not very loud ‘pwok,’ like that of [O.] lempiji, but somewhat different in tone.”
Though Hartlet and Everett came close to identifying the new species, they fell just short of making the leap. Since then, no one had collected or observed this type of owl, according to records from the American Museum of Natural History and the Natural History Museum at Tring, in the U.K.
All of this evidence, the team concluded in a PLoS ONE paper, pointed to the discovery of a new species of owl.
Because the new owl shows dramatically less individual variation to its brown and cream-speckled feather patterns than similar species found on neighboring islands, the scientists hypothesize that ancestors of the Lombok owls may have been isolated and trapped on their island many years before by a catastrophic volcanic eruption. Starting with just a handful of individuals, the animals then could have slowly rebuilt their populations, eventually evolving into a unique lineage.
The species, they report, is the first bird known to be unique to Lombok. The authors named the new bird Otus jolandae, after Sangster’s wife, Jolanda.