Precambrian Life Discovered in China (Image 1 and 2)

This photo shows an exceptionally preserved eukaryotic fossil (field of view about 0.15 millimeters in width) from the Doushantuo Formation (635 to 551 million years old), a fossil site near Weng'an, South China. High-resolution geochemical data from the formation indicates that the early diversification of eukaryotes may have coupled with episodic oxygenation of oceans during the Ediacaran Period. (Date of Image: 2008)

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 Research by Shuhai Xiao, a professor of geobiology at Virginia Tech, has found evidence that animals may have existed before the Cambrian period (542 to 488 million years ago) in the Precambrian period, which spans from 4.5 billion years ago to the beginning of the Cambrian period.

In 1997, Xiao and colleagues discovered in the Doushantuo Formation, thousands of 600 million-year-old embryo microfossils. Then in 2000, Xiao's team reported the discovery of a tubular, coral-like animal in a later stage of development than embryonic.

Xiao and colleagues are trying to learn more about these animals that are between the embryonic and adult stages. Only 80 have been recovered that have an advanced to intermediary stage of development; the rest have been early stage embryos. These intermediate stage embroyos have a coiled, tubular embryo imbedded in their egg case. The egg cases have a groove on the surface that consists of three clockwise coils. The researchers used microfocus X-ray computed tomography imaging to virtually peel off the egg case and expose the embryo inside. The tubular embryo is also coiled, with three clockwise coils; some specimens showed signs of uncoiling.

"We think it's safe to say these are juvenile or adult stage organisms," Xiao says. "Uncoiling indicates these embryos would have grown into the tubular organisms that we discovered earlier in our research."

The researchers believe the embroyos were animals similar to corals. Although these creatures were soft-bodied, without skeletons, they were well preserved in rocks that predate the Cambrian period. Xiao says this supports the existence of animals in the Precambrian period. "We didn't see the animal fossil, but we saw the trace of the animal," says Xiao, who along with colleagues estimates this animal to be at least 550 million years old (or about 9 million years before the Cambrian period).

Xiao and colleagues are also studying the connection between the rate of evolution, which accelerated in the Cambrian period, and oxygen. Xiao says that one of the reasons the number of animals species exploded during the early Cambrian may have been oxygen. "Suddenly there was more oxygen," says Xiao, "and we know that almost all animals need oxygen to survive."

Evidence of several oxidation events during the time period suggests a connection between oxidation and evolution. Kathleen McFadden, who was a Ph.D. student with Xiao at the time, studied the ratio of carbon and sulfur in the million-year-old rocks at the Yangtze Gorges of South China and determined from the carbon/sulfur cycles, that several significant oxidation events occurred as life was forming.

McFadden and colleagues meticulously analyzed layers of rock at the site of an ancient sea in the Yangtze Gorges. The layers of sediment represent millions of years of deposits. McFadden went through road cuts, bed by bed, measuring and describing the exposed rock and taking small rock samples every few feet. She collected about 200 samples. While the triggers for the oxidation events are still not clear, "these events recorded in the ocean were probably related to oxygen in the atmosphere reacting with sediments on land," McFadden says. Xiao notes that after each oxidation event, there is more diversification of species.

Future research for Xiao includes exploring how these Precambrian animals were preserved and determining if animals in the Cambrian period are descended from the Precambrian animals or can be linked to that period.

This four-celled animal embryo was extracted from 600 million-year-old rocks in Guizhou Province, South China. The cells, magnified using a scanning electron microscope, are about 0.65 millimeters in diameter. (Date of image: 2004

More About This Image

 Research by Shuhai Xiao, a professor of geobiology at Virginia Tech, has found evidence that animals may have existed before the Cambrian period (542 to 488 million years ago) in the Precambrian period, which spans from 4.5 billion years ago to the beginning of the Cambrian period.

In 1997, Xiao and colleagues discovered in the Doushantuo Formation, thousands of 600 million-year-old embryo microfossils. Then in 2000, Xiao's team reported the discovery of a tubular, coral-like animal in a later stage of development than embryonic.

Xiao and colleagues are trying to learn more about these animals that are between the embryonic and adult stages. Only 80 have been recovered that have an advanced to intermediary stage of development; the rest have been early stage embryos. These intermediate stage embroyos have a coiled, tubular embryo imbedded in their egg case. The egg cases have a groove on the surface that consists of three clockwise coils. The researchers used microfocus X-ray computed tomography imaging to virtually peel off the egg case and expose the embryo inside. The tubular embryo is also coiled, with three clockwise coils; some specimens showed signs of uncoiling.

"We think it's safe to say these are juvenile or adult stage organisms," Xiao says. "Uncoiling indicates these embryos would have grown into the tubular organisms that we discovered earlier in our research."

The researchers believe the embroyos were animals similar to corals. Although these creatures were soft-bodied, without skeletons, they were well preserved in rocks that predate the Cambrian period. Xiao says this supports the existence of animals in the Precambrian period. "We didn't see the animal fossil, but we saw the trace of the animal," says Xiao, who along with colleagues estimates this animal to be at least 550 million years old (or about 9 million years before the Cambrian period).

Xiao and colleagues are also studying the connection between the rate of evolution, which accelerated in the Cambrian period, and oxygen. Xiao says that one of the reasons the number of animals species exploded during the early Cambrian may have been oxygen. "Suddenly there was more oxygen," says Xiao, "and we know that almost all animals need oxygen to survive."

Evidence of several oxidation events during the time period suggests a connection between oxidation and evolution. Kathleen McFadden, who was a Ph.D. student with Xiao at the time, studied the ratio of carbon and sulfur in the million-year-old rocks at the Yangtze Gorges of South China and determined from the carbon/sulfur cycles, that several significant oxidation events occurred as life was forming.

McFadden and colleagues meticulously analyzed layers of rock at the site of an ancient sea in the Yangtze Gorges. The layers of sediment represent millions of years of deposits. McFadden went through road cuts, bed by bed, measuring and describing the exposed rock and taking small rock samples every few feet. She collected about 200 samples. While the triggers for the oxidation events are still not clear, "these events recorded in the ocean were probably related to oxygen in the atmosphere reacting with sediments on land," McFadden says. Xiao notes that after each oxidation event, there is more diversification of species.

Future research for Xiao includes exploring how these Precambrian animals were preserved and determining if animals in the Cambrian period are descended from the Precambrian animals or can be linked to that period.

This text was taken from the story "Scientist Searches for Clues About the Beginnings of Life" that appeared in Virginia Tech's Research magazine, Winter 2010.

Credit: Shuhai Xiao

Iridescent, Feathered Dinosaur: New Evidence That Feathers Evolved to Attract Mates

The detailed feather pattern and color of Microraptor--a pigeon-sized, four-winged dinosaur that lived about 120 million years ago--had a glossy iridescent sheen.

Its tail was narrow and adorned with a pair of streamer feathers, suggesting the importance of display in the early evolution of feathers, say scientists reporting the findings in this week's issue of the journal Science.

By comparing the patterns of pigment-containing organelles from a Microraptor fossil to those in modern birds, the scientists determined that the dinosaur's plumage was iridescent with a glossy sheen like the feathers of a modern crow.

The new fossil is the earliest record of iridescent color in feathers.

A reconstruction of Microraptor will help scientists approach the controversy of how dinosaurs began the transition to flight.

"Specifying the color and iridescence of feathers in avian dinosaurs was not possible 20 years ago," says H. Richard Lane, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.

"This development, in combination with the arrangement of tail feathers, is leading to a deeper understanding of the early development of avian plumage signalling. "

Since it was discovered as the first four-winged dinosaur in 2003, Microraptor has been at the center of questions about the evolution of feathers and flight.

Scientists have proposed aerodynamic functions for various feathery features such as its tail, forewing shape and hind limbs.

Once thought to be a broad, teardrop-shaped surface, or with a shape more like that of a paper airplane meant to help generate lift, Microraptor's tail fan is actually much narrower with two elongate feathers off its tip.

The researchers believe the tail feathering may have been ornamental, and likely evolved for courtship and other social interactions and not as an adaptation for flight.

"Most aspects of early dinosaur feathering continue to be interpreted as fundamentally aerodynamic, optimized for some aspect of aerial locomotion," says Julia Clarke, a paper co-author and paleontologist at The University of Texas at Austin (UT-Austin).

"Some of these structures were clearly ancestral characteristics that arose for other functions and stuck around, while others may be linked to display behaviors or signaling of mate quality," she says.

Feather features were shaped by early locomotor styles, Clarke believes. "But, as any birder will tell you, feather colors and shapes may also be tied with complex behavioral repertoires and, if anything, may be costly in terms of aerodynamics."

Modern birds use feathers for many different things, ranging from flight to thermoregulation to mate-attracting displays, says Matt Shawkey, a paper co-author and biologist at the University of Akron.

"Iridescence is widespread in modern birds, and is frequently used in displays," says Shawkey. "The evidence that Microraptor was largely iridescent suggests that feathers were important for display even relatively early in their evolution."

The feather color displayed by many modern birds is partially produced by arrays of pigment-bearing organelles called melanosomes, about a hundred of which can fit across a human hair.

Generally found in a round or cigar-like shape, a melanosome's structure is constant for a given color. Iridescence arises when narrow melanosomes are organized in stacked layers.

After a breakthrough by Jakob Vinther of UT-Austin in 2009, paleontologists started analyzing the shape of melanosomes in well-preserved fossilized feather imprints.

By comparing these patterns to those in living birds, scientists can infer the color of dinosaurs that lived many millions of years ago.

Paleontologists deduced that Microraptor was iridescent when Shawkey discovered that melanosomes in the most common iridescent feathers were uniquely narrow.

Information on the feather color of a variety of dinosaurs has recently come to light.

The first color map of an extinct dinosaur showed black-and-white spangles, red coloration and grey body color in a species called Anchiornis.

Based on the new data from Microraptor and other findings, a complex color repertoire that includes iridescence is likely ancestral to a group of dinosaurs called Paraves that originated at least 140 million years ago.

It includes dinosaurs like Velociraptor as well as Archaeopteryx, Anchiornis and living birds.

"This study gives us an unprecedented glimpse of what this animal [Microraptor] looked like when it was alive," says Mark Norell, paper co-author and paleontologist at the American Museum of Natural History (AMNH).

Clarke, Norell and an AMNH team, including AMNH researchers Mick Ellison and Rui Pei, worked closely to analyze the bony anatomy and digital overlays of the feathering in the new specimen and in eight previously described Microraptor specimens.

The scientists studied feathering, and melanosome shape and density, from a Microraptor fossil.

To come to their conclusions, the researchers worked closely with Quanguo Li, Ke-Qin Gao and Meng Qingjin at the Beijing Museum of Natural History.

The samples and preservation of melanosomes were assessed by Vinther and compared to a database of melanosomes from a variety of modern birds assembled by Shawkey and Liliana D'Alba at the University of Akron.

Along with NSF, the U.S. Air Force Office of Scientific Research, the Natural Science Foundation of China, the Beijing Municipal Bureau of Human Resources, and the Beijing Academy of Science and Technology also funded the research.

-NSF-

NASA's Wise Raises Doubt About Asteroid Family Believed Responsible for Dinosaur Extinction

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Trent J. Perrotto

Headquarters, Washington                               

 

Whitney Clavin

Jet Propulsion Laboratory, Pasadena, Calif.

WASHINGTON -- Observations from NASA's Wide-field Infrared Survey Explorer (WISE) mission indicate the family of asteroids some believed was responsible for the demise of the dinosaurs is not likely the culprit, keeping the case open on one of Earth's greatest mysteries.

While scientists are confident a large asteroid crashed into Earth approximately 65 million years ago, leading to the extinction of dinosaurs and some other lifeforms on our planet, they do not know exactly where the asteroid came from or how it made its way to Earth. A 2007 study using visible-light data from ground-based telescopes first suggested the remnant of a huge asteroid, known as Baptistina, as a possible suspect.

According to that theory, Baptistina crashed into another asteroid in the main belt between Mars and Jupiter about 160 million years ago. The collision sent shattered pieces as big as mountains flying. One of those pieces was believed to have impacted Earth, causing the dinosaurs' extinction.

Since this scenario was first proposed, evidence developed that the so-called Baptistina family of asteroids was not the responsible party. With the new infrared observations from WISE, astronomers say Baptistina may finally be ruled out.

"As a result of the WISE science team's investigation, the demise of the dinosaurs remains in the cold case files," said Lindley Johnson, program executive for the Near Earth Object (NEO) Observation Program at NASA Headquarters in Washington. "The original calculations with visible light estimated the size and reflectivity of the Baptistina family members, leading to estimates of their age, but we now know those estimates were off. With infrared light, WISE was able to get a more accurate estimate, which throws the timing of the Baptistina theory into question."

WISE surveyed the entire celestial sky twice in infrared light from January 2010 to February 2011. The asteroid-hunting portion of the mission, called NEOWISE, used the data to catalogue more than 157,000 asteroids in the main belt and discovered more than 33,000 new ones.

Visible light reflects off an asteroid. Without knowing how reflective the surface of the asteroid is, it's hard to accurately establish size. Infrared observations allow a more accurate size estimate. They detect infrared light coming from the asteroid itself, which is related to the body's temperature and size. Once the size is known, the object's reflectivity can be re-calculated by combining infrared with visible-light data.

The NEOWISE team measured the reflectivity and the size of about 120,000 asteroids in the main belt, including 1,056 members of the Baptistina family. The scientists calculated the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as originally proposed.

This calculation was possible because the size and reflectivity of the asteroid family members indicate how much time would have been required to reach their current locations -- larger asteroids would not disperse in their orbits as fast as smaller ones. The results revealed a chunk of the original Baptistina asteroid needed to hit Earth in less time than previously believed, in just about 15 million years, to cause the extinction of the dinosaurs.

"This doesn't give the remnants from the collision very much time to move into a resonance spot, and get flung down to Earth 65 million years ago," said Amy Mainzer, a study co-author and the principal investigator of NEOWISE at NASA's Jet Propulsion Laboratory (JPL) in Pasadena. Calif. "This process is thought to normally take many tens of millions of years." Resonances are areas in the main belt where gravity nudges from Jupiter and Saturn can act like a pinball machine to fling asteroids out of the main belt and into the region near Earth.

The asteroid family that produced the dinosaur-killing asteroid remains at large. Evidence that a 10-kilometer asteroid impacted Earth 65 million years ago includes a huge, crater-shaped structure in the Gulf of Mexico and rare minerals in the fossil record, which are common in meteorites but seldom found in Earth's crust. In addition to the Baptistina results, the NEOWISE study shows various main belt asteroid families have similar reflective properties. The team hopes to use NEOWISE data to disentangle families that overlap and trace their histories.

"We are working on creating an asteroid family tree of sorts," said Joseph Masiero, the lead author of the study. "We are starting to refine our picture of how the asteroids in the main belt smashed together and mixed up."

JPL manages and operated WISE for NASA's Science Mission Directorate. The spacecraft was put into hibernation mode after it scanned the entire sky twice, completing its main objectives. The principal investigator, astronomer Edward Wright, is at UCLA.

The mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan.

The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

For more information about WISE, visit http://www.nasa.gov/wise.

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