Monday, July 6, 2009

54-MILLION-YEAR-OLD SKULL REVEALS EARLY EVOLUTION OF PRIMATE BRAINS

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Researchers at the University of Florida and the University of Winnipeg have developed the first detailed images of a primitive primate brain, unexpectedly revealing that cousins of our earliest ancestors relied on smell more than sight.

The analysis of a well-preserved skull from 54 million years ago contradicts some common assumptions about brain structure and evolution in the first primates. The study also narrows the possibilities for what caused primates to evolve larger brain sizes. The study is scheduled to appear online the week of June 22 in the Proceedings of the National Academy of Sciences.

The skull belongs to a group of primitive primates known as Plesiadapiforms, which evolved in the 10 million years between the extinction of the dinosaurs and the first traceable ancestors of modern primates. The 1.5-inch-long skull was found fully intact, allowing researchers to make the first virtual mold of a primitive primate brain.

“Most explanations on the evolution of primate brains are based on data from living primates,” said lead author Mary Silcox, an anthropologist at the University of Winnipeg and research associate at UF’s Florida Museum of Natural History. “There have been all these inferences about what the brains of the earliest primates would look like, and it turns out that most of those inferences are wrong.”

Researchers used CT scans to take more than 1,200 cross-sectional X-ray images of the skull, which were combined into a 3-D model of the brain.

“A large and complex brain has long been regarded as one of the major steps that sets primates apart from the rest of mammals,” said Florida Museum vertebrate paleontologist and study co-author Jonathan Bloch. “At our very humble beginnings, we weren’t so special. That happened over tens of millions of years.”

The animal, Ignacius graybullianus, represents a side branch on the primate tree of life, Bloch said. “You can think of it as a cousin of the main line lineage that would have given rise ultimately to us.”

In previous research, Bloch and Silcox established that Plesiadapiforms were transitional species. Ignacius was similar to modern primates in terms of its diet and tree-dwelling but did not leap from tree to tree like modern fast-moving primates.

In many ways, the early primate behaved like living primates but with a brain that was one-half to two-thirds the size of the smallest modern primates. This means that factors such as tree-dwelling and fruit-eating can be eliminated as potential causes for primates evolving larger brain sizes, Silcox said, because “the smaller brained Ignacius was already doing those things.”

The mold suggests a “startling combination” of features in the early primate that requires a rethinking of primate brain evolution, said Florida State University anthropologist Dean Falk, who was not involved in the study.

“Hypotheses about early primate brain evolution often link keen smell with nocturnal insect-eating, and a more recently evolved increase in visual processing with fruit-eating in arboreal habitats,” Falk said.

The move to larger brain size occurred during an evolutionary burst that happened 10 million years after the extinction of the dinosaurs. At that point, visual features in the brain became much more prominent while the olfactory bulbs became proportionately smaller.

More than likely, Bloch said, this change in brain structure and size was related to primates living in closed canopy forests that brought trees closer together and allowed for more leaping. But answering that will require the discovery and analysis of new fossils.

Changes in brain size and brain structure in the early stages of primate evolution have generated enormous debates for decades. But until now, fossil evidence has been lacking.

Many models of the ancestral primate brain are based on tree shrews, which come from southeast Asia and are distantly related to humans. But with some 70 million years of evolution between them and humans, “it turns out tree shrew brains are not a good model,” Silcox said.

University of Florida

EXOPLANET’S TITLED ORBIT CHALLENGES THEORIES OF PLANET FORMATION

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An international team of astronomers has discovered an exoplanet whose orbit is steeply titled from the plane of the star’s equator, a finding that contradicts theories about how planetary systems form.

The new observations conducted at the W. M. Keck Observatory in Hawaii provide a clear, solid measurement of the planet’s distinctive tilt, determining the angle of the orbit to be about 37 degrees from the star’s equator. The results appear in the online edition of the Astrophysical Journal and will be published in an upcoming August issue.

Astronomers discovered the planet, called XO-3b, because it passes directly in front of the star as seen from Earth - an event called a transit - thus causing a slight dimming of the star’s light. That dimming can be detected with a powerful telescope connected to a highly sensitive light meter, or photometer. Of the more than 350 exoplanets discovered so far, fewer than two dozen have been discovered through this transit method.

Detecting the planet itself was relatively easy, as it dimmed the star’s light by about one percent. But to go one step further and measure the angle of its orbit, even with such powerful tools, means that “we have to be sneaky about it,” said physicist and the paper’s lead author Joshua Winn of the Massachusetts Institute of Technology in Cambridge, Mass.

He explained that if a planet crosses the star’s disk at an angle relative to the star’s rotation, it causes a distinctive pattern that changes the overall color of the star, as measured by a highly sensitive spectrograph. In this study, astronomers John Asher Johnson of the University of Hawaii and Andrew Howard of the University of California Berkeley (UCB) used the Keck I telescope’s High Resolution Echelle Spectrometer, or HIRES, to confirm hints of such a spectral signature, which another team observed but could not verify last year.

Observing a misalignment of the planet’s orbit relative to the star’s equator is a “remarkable result,” and completely contradicts simple theories of planet formation, said astronomer and paper coauthor Geoff Marcy of UCB.

“In all models of planet formation, a young star is surrounded by a flattened disk of gas and dust, like a fried egg with the yellow yolk, the star, in the middle and the white, the gas and dust, extending outward from the equator of the ‘yolk’,” he explained.

The planets form by collecting the dust and gas together within that disk. The theories naturally explain how the planets in the Solar System reside in a flat plane that slices through the equator of the Sun. Other planetary systems show a similar architecture.

“What is shocking about this planetary system is that the planet orbits in a plane that is grossly misaligned with its star’s equator,” Marcy said.

XO-3b, is about 13 times as massive as Jupiter, yet orbits its star with a period, or “year,” of just 3.5 days. Jupiter, by contrast, takes almost 12 years to make one orbit. The planet is considered a “hot Jupiter,” meaning it resembles the Solar System’s largest planet yet is much hotter due to its proximity to its parent star.

The planet, as with all hot Jupiters, most likely didn’t form at its current orbit, but rather formed much farther out from the star, then migrated inward to its present position. Planet formation theory suggests the gravitational attraction of other planets as well as debris in the disk might tug on planets, slightly disrupting their orbit. Close encounters between or among planets, however, has enough force to significantly change the planet’s trajectory.

In the case of XO-3b, it seems “some other planet gravitationally yanked on this poor planet, jerking it out of its original circular orbit,” Marcy said. It “suffered from a gravitational close encounter. It survived, but was left in a wacky orbit.”

Astronomers are interested in exploring exoplanets, especially oddballs such as XO-3b, to help refine theories of planetary formation and to understand the kinds of variations that may be possible in the Universe. Astronomers want to “see how the dice get rolled in other planetary systems,” Winn said.

NASA’s recently launched Kepler Mission will help astronomers discover increasing numbers of exoplanets, he explained. The Keck telescopes will then be used to follow-up the space-based observations to learn more about the planets’ masses and orbits.

By discovering and observing more oddball exoplanets, astronomers will determine how often planets suffer from close encounters. And, if a large number of exoplanets are observed to have titled orbits, scientists might be able to conclude that close encounters are common during the young lives of planets, Marcy said.

Keck Observatory

CHANGES IN BRAIN ARCHITECTURE MAY BE DRIVEN BY DIFFERENT COGNITIVE CHALLENGES

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Scientists trying to understand how the brains of animals evolve have found that evolutionary changes in brain structure reflect the types of social interactions and environmental stimuli different species face.

The study is the first to compare multiple species of related animals, in this case social wasps, to look at how roles of individuals in a society might affect brain architecture. The research looks at brain structure differences between species, asking how the size of different brain regions relates to each species' social complexity and nest architecture.

"It looks as if different brain regions respond to specific challenges. It is important to find these relationships because they can tell us which challenges guide brain evolution," said Sean O'Donnell, a University of Washington associate professor of psychology and co-author of the study.

O'Donnell and lead author Yamile Molina, who just completed work on her doctorate at the UW, looked at the brains of eight New World social wasp species from Costa Rica and Ecuador.

"One idea is that social interactions themselves put on demands for advanced cognitive abilities. We are interested in finding out exactly which social and environmental factors favor an increase in a given brain region," said Molina.

The UW researchers captured queens and female workers from colonies of the eight wasp species and examined their brains. For the most part, males usually don't play an important behavioral role in a social wasp colony's labor and other activities, according to O'Donnell. However, a follow-up study will look at the male wasp brain structure.

In examining the female wasps, the researchers found strong evidence that queens, rather than workers, have distinct brain structure that matches the species' cognitive challenges.

Social wasps form colonies differently and build two types of nests. In more primitive wasps, a queen mates and flies away separately to establish a small colony. Among the more advanced social wasps, several young queens and a group of workers leave a colony as a swarm to establish a new colony that has a much larger population. Independent founders and a few swarm founders build open-comb nests, while most swarm founders build enclosed nests with interiors that are much darker.

Molina and O'Donnell found that queens from open-comb nests had larger central brain processing regions that are devoted to vision than queens from closed-nest colonies. Queens from enclosed nests, where vision isn't as important and where they rely on chemical communication through pheromones, had larger antennal lobes to process chemical messages than queens from open nests.

Among independent-founding wasps, where queens regulate the behavior of a colony, queens had larger vision-processing regions (called mushroom body collars) than their workers. But among swarm-founders, which have a decentralized form of colony regulation, workers had larger mushroom body collars and larger optic lobes than queens.

"We can learn things about ourselves from a whole variety of animals. When neurobiologists use animal models they often look to rodents and primates," said Molina. "I would argue social insects like wasps are like us in some ways and should be an important model as well. In this study we found that it's not being social, but how you are social that explains brain architecture. The brain can be a mirror reflecting what an animal is using it for."

University of Washington

DOLPHINS GET A LIFT FROM DELTA WING TECHNOLOGY

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Laurens Howle and Paul Weber from Duke University teamed up with Mark Murray from the United States Naval Academy and Frank Fish from West Chester University, to find out more about the hydrodynamics of whale and dolphin flippers. They publish their finding that some dolphins' fins generate lift in the same way as delta wing aircraft on 26 June 2009 in The Journal of Experimental Biology at http://jeb.biologists.org/.

Using Computer tomography scanning of the fins of seven different species ranging from the slow swimming Amazon River dolphin and pygmy sperm whale to the super-fast striped dolphin, the team made scaled models of the flippers of each species. Then they measured the lift and drag experienced by the flipper at inclinations ranging from -45deg. to +45deg. in a flow tunnel running at a speed that would have been the equivalent of 2m/s for the full scale fin.

Comparing the lift and drag coefficients that the team calculated for each flipper at different inclination angles, they found that the flippers behave like modern engineered aerofoils. Defining the flippers' shapes as triangular, swept pointed or swept rounded, the team used computer simulations of the fluid flows around the flippers and found that sweptback flippers generate lift like modern delta wing aircraft. Calculating the flippers' efficiencies, the team found that the bottle nose dolphin's triangular flippers are the most efficient while the harbour porpoise and Atlantic white-sided dolphin's fins were the least efficient.

Commenting that environmental and performance factors probably play a significant role in the evolution of dolphin and whale flipper shapes and their hydrodynamics, Howle and his colleagues are keen to find out more about the link between the flippers' performances and the environment that whales and dolphins negotiate on a daily basis.

The Company of Biologists

OBSIDIAN 'TRAIL' PROVIDES CLUES TO HOW HUMANS SETTLED, INTERACTED IN KURIL ISLANDS

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Using X-ray fluorescence spectrometers, archaeologists from the University of Washington and the Smithsonian Institution have found the origin of 131 flakes of obsidian, a volcanic glass. These small flakes were discarded after stone tools were made from obsidian and were found at 18 sites on eight islands in the Kurils. The flakes were found with other artifacts that were dated over a time period spanning about 1,750 years, from 2500 to 750 years before the present.

The Kuril Archipelago stretches for nearly 800 miles between the northern-most Japanese island of Hokkaido and the Kamchatka Peninsula in Russia. Despite the islands' volcanic origin, there are no known local sources of obsidian.

"A key quality of obsidian is you can create a very sharp edge. Obsidian flakes easily and fractures in a way that is predictable. When it was available people have used it," said Colby Phillips, lead author of the new study and an anthropology doctoral student at the University of Washington. His co-author is Robert Speakman of the Smithsonian's Museum Conservation Institute.

Obsidian is formed when magma is extruded from a volcano and can be geochemically identified Phillips said. That's because the obsidian from each volcano has a unique chemical signature based on the amount of elements such as rubidium, zirconium and strontium in the glass. Archaeologists gather obsidian samples from volcanoes to create a data base of chemical signatures and compare archaeological samples collected in the field to the data base.

Phillips and Speakman pinpointed the Kuril flakes they analyzed to four locations on Hokkaido and five sources on Kamchatka. The majority of the flakes, slightly more than 60 percent, originated in Kamchatka.

Human occupation of the Kurils began about 4,000 years ago at the southern end of the island chain near Hokkaido and gradually spread northward. And where humans went they carried obsidian with them.

"Obsidian only makes up about 8 percent of the stone tools and the waste left from their manufacture, but it shows up at all sites and over all time periods," said Phillips. "Obsidian may have played a role in maintaining social and trade networks as people migrated across the Kurils. Our work suggests social relationships can be important in local and regional areas. Here we have people living in an isolated area that is covered by fog and clouds and subject to tsunamis, volcanic eruptions and earthquakes. So it would be advantageous to have connections with other people. The fact that we have a material such as obsidian throughout the islands shows people were proactive in maintaining ties in the prehistoric era."

The researchers found a basic pattern of obsidian distribution in the islands. Obsidian from Hokkaido was primarily found in the Southern Kurils with a few samples discovered in the Central Kurils. Kamchatka obsidian was only found in the Central and Northern Kurils.

The Southern Kurils are separated from the other islands in the chain by the 70-mile-wide Bussol Strait. Phillips believes that at some time it became too costly to make the dangerous ocean crossing, and people in the central and northern islands began trading for Kamchatka obsidian.

Since the research was accepted for publication, Phillips and Speakman have analyzed the sources of an additional 700 obsidian flakes and their results mirror the newly published data.

(Photo: Colby Phillips)

University of Washington

NEW FOSSIL TELLS HOW PIRANHAS GOT THEIR TEETH

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How did piranhas — the legendary freshwater fish with the razor bite — get their telltale teeth? Researchers from Argentina, the United States and Venezuela have uncovered the jawbone of a striking transitional fossil that sheds light on this question. Named Megapiranha paranensis, this previously unknown fossil fish bridges the evolutionary gap between flesh-eating piranhas and their plant-eating cousins.

Present-day piranhas have a single row of triangular teeth, like the blade on a saw, explained the researchers. But their closest relatives — a group of fishes commonly known as pacus — have two rows of square teeth, presumably for crushing fruits and seeds. "In modern piranhas the teeth are arranged in a single file," said Wasila Dahdul, a visiting scientist at the National Evolutionary Synthesis Center in North Carolina. "But in the relatives of piranhas — which tend to be herbivorous fishes —the teeth are in two rows," said Dahdul.

Megapiranha shows an intermediate pattern: it's teeth are arranged in a zig-zag row. This suggests that the two rows in pacus were compressed to form a single row in piranhas. "It almost looks like the teeth are migrating from the second row into the first row," said John Lundberg, curator at the Academy of Natural Sciences in Philadelphia and a co-author of the study.

If this is so, Megapiranha may be an intermediate step in the long process that produced the piranha's distinctive bite. To find out where Megapiranha falls in the evolutionary tree for these fishes, Dahdul examined hundreds of specimens of modern piranhas and their relatives. "What's cool about this group of fish is their teeth have really distinctive features. A single tooth can tell you a lot about what species it is and what other fishes they're related to," said Dahdul. Her phylogenetic analysis confirms their hunch — Megapiranha seems to fit between piranhas and pacus in the fish family tree.

The Megapiranha fossil was originally collected in a riverside cliff in northeastern Argentina in the early 1900s, but remained unstudied until paleontologist Alberto Cione of Argentina's La Plata Museum rediscovered the startling specimen —an upper jaw with three unusually large and pointed teeth — in the 1980s in a museum drawer.

Cione's find suggests that Megapiranha lived between 8-10 million years ago in a South American river system known as the Paraná. But you wouldn't want to meet one today. If the jawbone of this fossil is any indication, Megapiranha was a big fish. By comparing the teeth and jaw to the same bones in present-day species, the researchers estimate that Megapiranha was up to 1 meter (3 feet) in length. That's at least four times as long as modern piranhas. Although no one is sure what Megapiranha ate, it probably had a diverse diet, said Cione.

Other riddles remain, however. "Piranhas have six teeth, but Megapiranha had seven," said Dahdul. "So what happened to the seventh tooth?"

"One of the teeth may have been lost," said Lundberg. "Or two of the original seven may have fused together over evolutionary time. It's an unanswered question. Maybe someday we'll find out."

(Photo: © Ray Troll, 2005)

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