Tuesday, March 26, 2013

Uncovering Africa's Oldest Known Penguins

Only one penguin species lives in Africa today -- the endangered black-footed penguin, or Spheniscus demersus. But newly found fossils confirm that as many as four penguin species coexisted on the continent in the past. (Credit: Photo by Daniel Thomas)

Mar. 26, 2013 — Africa isn't the kind of place you might expect to find penguins. But one species lives along Africa's southern coast today, and newly found fossils confirm that as many as four penguin species coexisted on the continent in the past. Exactly why African penguin diversity plummeted to the one species that lives there today is still a mystery, but changing sea levels may be to blame, the researchers say.

The fossil findings, described in the March 26 issue of the Zoological Journal of the Linnean Society, represent the oldest evidence of these iconic tuxedo-clad seabirds in Africa, predating previously described fossils by 5 to 7 million years.

Co-authors Daniel Thomas of the National Museum of Natural History and Dan Ksepka of the National Evolutionary Synthesis Center happened upon the 10-12 million year old specimens in late 2010, while sifting through rock and sediment excavated from an industrial steel plant near Cape Town, South Africa.

Jumbled together with shark teeth and other fossils were 17 bone fragments that the researchers recognized as pieces of backbones, breastbones, wings and legs from several extinct species of penguins.

Based on their bones, these species spanned nearly the full size spectrum for penguins living today, ranging from a runty pint-sized penguin that stood just about a foot tall (0.3 m), to a towering species closer to three feet (0.9 m).

Only one penguin species lives in Africa today -- the black-footed penguin, or Spheniscus demersus, also known as the jackass penguin for its loud donkey-like braying call. Exactly when penguin diversity in Africa started to plummet, and why, is still unclear.

Gaps in the fossil record make it difficult to determine whether the extinctions were sudden or gradual. "[Because we have fossils from only two time periods,] it's like seeing two frames of a movie," said co-author Daniel Ksepka. "We have a frame at five million years ago, and a frame at 10-12 million years ago, but there's missing footage in between."

Humans probably aren't to blame, the researchers say, because by the time early modern humans arrived in South Africa, all but one of the continent's penguins had already died out.
A more likely possibility is that rising and falling sea levels did them in by wiping out safe nesting sites.

Although penguins spend most of their lives swimming in the ocean, they rely on offshore islands near the coast to build their nests and raise their young. Land surface reconstructions suggest that five million years ago -- when at least four penguin species still called Africa home -- sea level on the South African coast was as much as 90 meters higher than it is today, swamping low-lying areas and turning the region into a network of islands. More islands meant more beaches where penguins could breed while staying safe from mainland predators.

But sea levels in the region are lower today. Once-isolated islands have been reconnected to the continent by newly exposed land bridges, which may have wiped out beach nesting sites and provided access to predators.

Although humans didn't do previous penguins in Africa in, we'll play a key role in shaping the fate of the one species that remains, the researchers add.

Numbers of black-footed penguins have declined by 80% in the last 50 years, and in 2010 the species was classified as endangered. The drop is largely due to oil spills and overfishing of sardines and anchovies -- the black-footed penguin's favorite food.

"There's only one species left today, and it's up to us to keep it safe," Thomas said.

Story Source:
The above story is reprinted from materials provided by National Evolutionary Synthesis Center (NESCent), via EurekAlert!, a service of AAAS.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:
  1. Daniel B. Thomas, Daniel T. Ksepka. A history of shifting fortunes for African penguins. Zoological Journal of the Linnean Society, 2013; DOI: 10.1111/zoj.12024

National Evolutionary Synthesis Center (NESCent) (2013, March 26). Uncovering Africa's oldest known penguins. ScienceDaily. Retrieved March 26, 2013, from http://www.sciencedaily.com­ /releases/2013/03/130326101606.htm

Monday, March 18, 2013

The Early Bird Loses an Ovary

ScienceNOW - Up to the minute news from Science
on 17 March 2013,
Sunny side up. The follicles (close-up, inset) preserved in the fossilized ovary of this 125-million-year-old bird (main image), provide insights into the reproductive biology of these early birds and into bird evolution. 
Credit: Aijuan Shi; Zhonghe Zhou (inset)
The dinosaurs most closely related to today's birds were super egg producers. Known as maniraptorans, these bipedal creatures had two functional ovaries and produced a large number of eggs per clutch. Living species of birds, on the other hand, have only one functional ovary, typically on the left side of the body, and most produce only a few eggs at a time. When and why did today's flyers ditch a reproductive organ? Newly described fossils of early birds may hold the answer.

All the fossils in this study come from rocks laid down as sediments about 125 million years ago in northeastern China. Despite the poor bone preservation in two of the fossils, all include the well-preserved remains of ovaries and mature or nearly mature follicles, structures within the ovaries that contain developing eggs—the first such fossils of early birds known to do so, says Zhonghe Zhou, a paleontologist with the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. One set of remains represents Jeholornis, a long-tailed bird about the size of a pigeon.

Neither of the other fossils is preserved well enough to identify its species, Zhou notes, but each represents a bird somewhat larger than a sparrow. Each of the fossils included only one ovary—which, as in modern birds, appears to be located on the left side of the body.

Analyses by Zhou and his colleagues showed that the structures assumed to be follicles weren't seeds, because they weren't located in parts of the body where stomach contents would typically be found. The structures also weren't gastroliths, or stomach stones, because such stones typically retain their three-dimensional shape, whereas these structures appeared to have been soft tissue because they had been somewhat flattened before they were preserved.

"These are really incredible fossils," says Stephen Brusatte, a vertebrate paleontologist at the University of Edinburgh in the United Kingdom who wasn't involved in the study. Preservation of soft tissues is exceedingly rare, he notes, but "to have ovarian follicles preserved is just amazing."
The fossils furnish information about the reproductive habits of these animals. In one of the birds, some of the bones in the creature's wing weren't fully fused, Zhou says. That suggests that the creature wasn't an adult, hinting that females of its species became sexually mature before they were fully grown, he and his colleagues report online today in Nature.

One of the fossilized ovaries includes at least 20 mature or near-mature follicles. That's a sign that unlike modern birds, early birds probably laid a large number of relatively small eggs in a single clutch, Brusatte says. "We don't have any fossil nests of early birds, but this tells us that the reproductive biology of early birds was quite different than modern birds."

Some scientists have assumed that the evolutionary loss of one functional ovary—a weight-saving change that might have proved beneficial to flying birds—took place early in avian evolution. Until the new study, paleontologists hadn't unearthed any evidence for the notion that early birds, like their modern-day kin, had only one ovary.

The findings even provide hints about how early birds cared for their young, says Richard Prum, an evolutionary ornithologist at Yale University. Previous analyses of fossil dinosaur nests have suggested that in birds' closest dinosaur relatives, which laid large clutches of eggs, males sat on the nests and presumably cared for the hatchlings. That's also true of some of today's birds—including ratites, a group that includes ostriches and emus—which typically lay eggs in several nests and then leave the childcare to males. "So, large clutch size in early birds is strong evidence for male care," Prum contends.

The new findings "are very exciting," says Frankie Jackson, a vertebrate paleontologist at Montana State University, Bozeman. Besides revealing that even early birds had reproductive biology significantly different from that of their closest dinosaur kin, they provide a new approach to estimate the brood size and the onset of sexual maturity in adults. These reproductive traits—including the loss of one of the ovaries, which probably would have rendered egg-laden females significantly lighter—likely had a substantial impact on the evolution of flight, she notes. That development may even have helped some bird lineages survive the mass extinctions in the wake of an asteroid impact that claimed the dinosaurs 66 million years ago.


Saturday, March 16, 2013

Penguin Ancestor swimming with the predators

From the Eocene -
Icadyptes salasi, an unnamed protocetid, Ocucajea picklingi, and Supayacetus muizoni

The Rise and Fall of Four-Winged Birds

Look at the leg of almost any bird and you’ll see feathers covering the thigh but scales covering everything from the ‘knee’ downwards. There are a couple of exceptions—some birds of prey look like they’re wearing baggy trousers and golden eagles have fluffy foot feathers for insulation. But for the most part, living birds have naked lower legs.

It wasn’t always this way. We know that birds evolved from small two-legged, meat-eating dinosaurs that were covered in simple fuzzy feathers. Those on their arms eventually became longer and flatter, evolving from hollow tubes into flat asymmetrical vanes. They transformed from “dino-fuzz” into flight feathers, and their arms transformed into wings.

Meanwhile, it’s tempting to think that the feathers on their hind legs gradually became smaller and gave way to scales. But that’s not how it happened. For a start, we know that some small dinosaurs had long feathers on their legs as well as their arms. And now, 11 newly analysed fossils tell us that some early birds shared the same feature. These specimens suggest that some of our feathered friends had four wings.

It was an ornithologist called William Beebe who first suggested that early birds might have passed through a four-winged gliding stage on their way to evolving true flapping flight. That was in 1915 and though Beebe’s idea was fanciful, there wasn’t much strong evidence behind it.

Then, in 2003, the prolific Chinese dinosaur-hunter Xing Xu found an actual four-winged dinosaur. He called it Microraptor gui. Xu saw the outlines of feathers clearly splaying from the creature’s legs as well as its arms. These were clearly traces of long, flat and asymmetric plumes, much like those that keep today’s flying birds aloft. While it lived, Microraptor probably looked like a starling wearing flares. Xu suggested that it may have used its leg wings to help it glide, while others later suggested that it could have flown like a biplane.

Xu went on to find other dinosaurs with long leg feathers, such as Anchiornis, Pedopenna and Xiaotingia. For a time, it looked like these feathers disappeared before true birds arrived on the scene, but Xu is now back with 11 new fossils that discount that idea.

Confuciusornis. From Zheng et al, 2013. Science/AAAS
Confuciusornis. From Zheng et al, 2013. Science/AAAS

The specimens include species like Sapeornis, Confuciusornis, Cathayornis, and Yanornis. All of them are early birds, perched on primitive branches of the group’s family tree. All of them lived in China during the Cretaceous period. And all of them had four wings, with long feathers on their legs.
You can see them in the images throughout this post—dark shadows protruding from the bones of the lower leg. In some of the specimens, the leg feathers show a stiff, curved central rod (or “rachis”) with symmetrical vanes sticking out from either side. They protrude from the bones at right angles and seem to form a large flat surface.

Xu thinks that these feathers might have helped the owners to fly. They could have produced extra lift or maybe helped the birds to turn more easily. But other scientists who work on the evolution of flight are not convinced. “[Xu] has basically just taken a punt that because the feathers were stiff, they were probably aerodynamic in function,” says Michael Habib from the University of Southern California. “It is a bit of a weak argument.”

Habib thinks that the long asymmetric leg feathers of Microraptor probably did play some role in gliding or flying, but the smaller plumes of other baggy-legged species “might have merely been there because of a developmental quirk”. If some genes are producing large feathers on the front limbs, “it might not take much to tweak a set onto the hind limbs too,” he says.

Kevin Padian from the University of California, Berkeley agrees. He points out that no one has actually done any proper tests to show if the leg feathers were involved in flight. They would certainly have created drag, but they could only have provided lift if they sat in a flat sheet like the wings of modern birds. Xu claims that they were, but Padian says that the feathers could just have been flattened into a plane as they became fossilised.  “It hasn’t been shown that this is really an aerodynamically competent wing,” he says.

Nonetheless, both Habib and Padian praise Xu’s work. “It’s a great study because it establishes that leg feathers were widely distributed,” says Padian. From beginnings as small outgrowths, leg feathers became dramatically bigger in some of the dinosaur groups on the evolutionary line leading to birds. They eventually shrank away again before disappearing entirely and being replaced by scales.
Scenario for the evolution of leg feathers. From Zheng et al, 2013. Science/AAAS
Scenario for the evolution of leg feathers. From Zheng et al, 2013. Science/AAAS

Of course, like any evolutionary story, this one could be falsified or complicated by the next cool discovery. Xu says that if he discovered early birds or feathered dinosaurs with extensive scales on their feet, that would spell trouble for his hypothesis. “But personally, I am quite confident with our scenario,” he says.

Why did the leg feathers, having first become large, eventually disappear? Xu thinks that it was because the birds set their two pairs of limbs towards different ends—the front pair for flying and the hind pair for walking or running. At the same time, they might have moved from life in the trees to life on the ground, or near water. Under all these scenarios, long leg feathers would have just got in the way, and were soon lost.

Something similar may have happened in other flying animals. For example, the earliest flying insects tend to have four wings, while some of the most competent flyers like, well, flies, only have two. The second pair has evolved into a pair of gyroscopes called halteres. “In the early evolution of flight, different animal groups always try to use as much surface as possible,” says Xu. “Once the major flight organ is well developed, the animal just fires the other organs.”

Xu’s 11 specimens all came from private collectors and had been housed at the Shandong Tianyu Museum of Nature for roughly a decade. The museum contains over 2,000 specimens of early birds, many of which preserve beautiful traces of feathers, skin and more. In fact, the museum’s treasure trove of riches is so huge that it has turned into a backlog. There’s simply too much good stuff there to go through. “It took a while for me to realize how important these specimens are,” says Xu. “These days, we are working hard to extract new information from these wonderful specimens and hopefully can produce more interesting results in future.”

Reference: Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang & Xu. 2013. Hind Wings in Basal Birds and the Evolution of Leg Feathers. Science http://dx.doi.org/10.1126/science.1228753


Saturday, March 9, 2013

Penguin Hookers. Really. (Your Humorous Science of the Day)

Posted by Alex Falcone on Thu, Mar 7, 2013 

Very important information has recently come to my attention. Some penguins are prostitutes.
 We all know humans do it. Some people will even show their boobs to a prison guard for a chocolate chip cookie, but penguins?! Those adorable animals dressed like banquet waiters who engage in Morgan Freeman-narrated lifelong monogomy? Yes. They're prostitutes.

It's not exactly new news but an alert reader Jake H. pointed me towards a 1998 study that somehow didn't make it to my daily reading habits because it's too amazing. Apparently when the small rocks they use to make nests get scarce, some penguins will exchange sexual favors for them. Not only do they prostitute themselves, they do it for pebbles!

According to this excellent Wikipedia article, prostitution has also been observed in chimpanzees, Capuchin monkeys, and the crab-eating macaque. That's not super surprising: chimpanzees and Capuchins are gross. And of course something called a "crab-eating macaque" would sell its body (am I right ladies?). But penguins? PENGUINS? I feel let down.

Read some more about the behavior (and make sure to hear Morgan Freeman's voice in your head):
The female penguins observed under the study were coupled with males. The females will go outside alone to collect pebbles, but the males did not suspect their female partners. According to the observations and analysis made by Hunter, the prostitute penguins targeted single males, because if instead they picked a male penguin with a partner, the male penguin's current partner will come in conflict with the prostitute female.
All that stuff about sitting on the egg waiting for their partners to come back is less romantic when you know they're being cuckolded. You're not a faithful husband penguin, you're a fool. While you're making dinner for your unborn chick, your woman is out Roxanning it up for building materials, perhaps sucking a macaque or two.

Today is a sad, sad day. Well, some day in 1998 was a sad day, but I've fallen behind on my penguin sex Wikipedia reading.


Thursday, March 7, 2013

Researchers find emperor penguins outer feathers colder than surrounding air

March 7, 2013 by Bob Yirka report
Emperor penguin body surfaces cool below air temperature
Thermal image of penguin. Credit: Université de Strasbourg and Centre National de la Recherche Scientifique (CNRS), Strasbourg, France
(Phys.org) —A research team made up of members from France and the U.K. has discovered that when in cold temperatures, the outer feathers of the emperor penguin are actually colder than the surrounding air. As the team describes in their paper published in the journal Biology Letters, they discovered the unusual thermal properties of the penguin's feathers while studying the birds in their natural environment using infrared imaging.
To gain a better understanding of how emperor are able to withstand extremely low temperatures for months at a time, the research team ventured down to Terre Adélie, Antarctica, during June 2008. There they took hundreds of infrared of penguins that had moved slightly apart from the others—that allowed for full body images to be taken and minimized the collective warming that occurs as the animals huddle together.

Upon examining the multicolored images, the researchers were surprised to discover that the outer feathers that cover most of the penguins' body, were actually four to six degrees Celsius colder than the surrounding air. With most other birds, and animals, the air around their bodies is warmer. The researchers explain that the apparent anomaly appears to be due to what they describe as "extreme radiative cooling." It's similar to frost building up on surfaces on a cold morning. It happens with the penguins when their protective coat radiates more heat into the colder sky than is absorbed from the surrounding air—this causes the temperature at the surface of their feathers to fall below that of the surrounding air. The end result, the researchers report, is that the penguins are able to draw very tiny amounts of heat back to their feathers from the surrounding air, helping them to conserve energy. It's not much, the researchers conclude, but when trying to survive in a very for very long periods of time, every little bit helps.

In looking at the thermal images, the researchers also noted that the birds do have a few "hot" spots—eyes, beak and feet, where heat escapes. The eyes in particular, bright red in the photos, suggest that penguins must take care to protect such vulnerable areas from bitter wind. They note that earlier studies have found that the more at-risk areas of the penguins' body have special blood vessels that help to conserve heat.

More information: Emperor penguin body surfaces cool below air temperature, Published online Biology Letters, March 6, 2013. doi: 10.1098/rsbl.2012.1192

Emperor penguins Aptenodytes forsteri are able to survive the harsh Antarctic climate because of specialized anatomical, physiological and behavioural adaptations for minimizing heat loss. Heat transfer theory predicts that metabolic heat loss in this species will mostly depend on radiative and convective cooling. To examine this, thermal imaging of emperor penguins was undertaken at the breeding colony of Pointe Géologie in Terre Adélie (66°40′ S 140° 01′ E), Antarctica in June 2008. During clear sky conditions, most outer surfaces of the body were colder than surrounding sub-zero air owing to radiative cooling. In these conditions, the feather surface will paradoxically gain heat by convection from surrounding air. However, owing to the low thermal conductivity of plumage any heat transfer to the skin surface will be negligible. Future thermal imaging studies are likely to yield further insights into the adaptations of this species to the Antarctic climate.

Press release