By studying the chemical composition of dinosaur teeth, scientists have determined that some sauropods had body temperatures as warm as those of mammals.
Robert Eagle, an evolutionary biologist at the California Institute of Technology, and colleagues analyzed 11 dinosaur teeth from sauropods. The researchers report their findings in the current issue of the journal Science.
Camarasaurus, a sauropod found in the United States, could reach a length of 66 feet and weigh up to 15 tons. The researchers estimated its body temperature to be about 96.3 degrees Fahrenheit.
Brachiosaurus, a larger sauropod that could grow to 75 feet and 40 tons, was even warmer, about 100.8 degrees Fahrenheit.
A normal human temperature is about 98.6 degrees Fahrenheit.
“So the first conclusion we could draw from that was that these large dinosaurs didn’t have temperatures as cold as modern crocodiles and alligators,” Dr. Eagle said.
But that does not mean that the dinosaurs had internal thermostats to keep body temperature constant independent of the environment, the way mammals and birds do. For one thing, the dinosaurs must have had “the capacity to retain environmental heat just as a function of being so large,” Dr. Eagle said. And they must have had ways to prevent themselves from overheating, he added.
“They might have had physical adaptations, like an internal air sac system, or they may have been seeking out shade in the hottest part of the day,” he said. Or they may have used their long necks and tails to release heat.
In conducting their studies, the researchers looked at the bonding between two isotopes — carbon-13 and oxygen-18 — in bioapatite, a mineral found in dinosaur teeth.
The number of bonds in the mineral correlates with the animals’ temperatures, Dr. Eagle said.
Last year, his team published a preliminary study in which they similarly determined the temperatures of crocodiles, aquarium sharks and alligators by studying dental enamel.
Source The New York Times
Notable events, developements and publications in science and technology this week. Updated daily.
Showing posts with label Paleontology. Show all posts
Showing posts with label Paleontology. Show all posts
Friday, June 24, 2011
Thursday, June 16, 2011
Breeding with Neanderthals helped humans go global
WHEN the first modern humans left Africa they were ill-equipped to cope with unfamiliar diseases. But by interbreeding with the local hominins, it seems they picked up genes that protected them and helped them eventually spread across the planet.
The publication of the Neanderthal genome last year offered proof that Homo sapiens bred with Neanderthals after leaving Africa. There is also evidence that suggests they enjoyed intimate relations with other hominins including the Denisovans, a species identified last year from a Siberian fossil.
But what wasn't known is whether the interbreeding made any difference to their evolution. To find out Peter Parham of Stanford University in California took a closer look at the genes they picked up along the way.
He focused on human leukocyte antigens (HLAs), a family of about 200 genes that is essential to our immune system. It also contains some of the most variable human genes: hundreds of versions - or alleles - exist of each gene in the population, allowing our bodies to react to a huge number of disease-causing agents and adapt to new ones.
The humans that left Africa probably carried only a limited number of HLA alleles as they likely travelled in small groups. Worse, their HLAs would have been adapted to African diseases.
When Parham compared the HLA genes of people from different regions of the world with the Neanderthal and Denisovan HLAs, he found evidence that non-African humans picked up new alleles from the hominins they interbred with.
One allele, HLA-C*0702, is common in modern Europeans and Asians but never seen in Africans; Parham found it in the Neanderthal genome, suggesting it made its way into H. sapiens of non-African descent through interbreeding. HLA-A*11 had a similar story: it is mostly found in Asians and never in Africans, and Parham found it in the Denisovan genome, again suggesting its source was interbreeding outside of Africa.
Parham points out that because Neanderthals and Denisovans had lived outside Africa for over 200,000 years by the time they encountered H. sapiens, their HLAs would have been well suited to local diseases, helping to protect migrating H. sapiens too.
While only 6 per cent of the non-African modern human genome comes from other hominins, the share of HLAs acquired during interbreeding is much higher. Half of European HLA-A alleles come from other hominins, says Parham, and that figure rises to 72 per cent for people in China, and over 90 per cent for those in Papua New Guinea.
This suggests they were increasingly selected for as H. sapiens moved east. That could be because humans migrating north would have faced fewer diseases than those heading towards the tropics of south-east Asia, says Chris Stringer of the Natural History Museum in London.
Parham presented his work at a Royal Society discussion meeting on human evolution in London last week.
Source New Scientist
Life after Snowball Earth
New fossils suggest rapid recovery of life after global freeze.
Scanning electron microscopy images reveal a microscopic, oval-shaped shell with tapered ends, from which an organism’s feet may have extended. The surface of the shell is made up of tiny bits of silica, aluminum and potassium, which the organism likely collected from the environment and glued to form armor.
The first organisms to emerge after an ancient worldwide glaciation likely evolved hardy survival skills, arming themselves with tough exteriors to weather a frozen climate.
Researchers at MIT, Harvard University and Smith College have discovered hundreds of microscopic fossils in rocks dating back nearly 710 million years, around the time when the planet emerged from a global glaciation, or “Snowball Earth,” event. The fossils are remnants of tiny, amoeba-like organisms that likely survived the harsh post-glacial environment by building armor and reaching out with microscopic “feet” to grab minerals from the environment, cobbling particles together to make protective shells.
The discovery is the earliest evidence of shell building, or agglutination, in the fossil record. The team found a diversity of fossils, suggesting life may have recovered relatively quickly following the first major Snowball Earth event. The researchers report their findings in an upcoming issue of Earth and Planetary Science Letters.
The widely held Snowball Earth theory maintains that massive ice sheets covered the planet from pole to pole hundreds of millions of years ago. Geologists have found evidence of two major snowball periods — at 710 and 635 million years ago — in glacial deposits that formed close to the modern equator. Fossil records illustrate an explosion of complex, multicellular life following the more recent ice age. However, not much is known about life between the two major glaciations — a period of about 75 million years that, until now, exhibited few signs of life.
“We know quite well what happened before the first Snowball, but we have no idea what happened in between,” says Tanja Bosak, assistant professor of geobiology at MIT, and the paper’s lead author. “Now we’re really starting to realize there’s a lot of unexpected life here.”
Ice Age armor
Bosak’s colleagues, Francis Macdonald of Harvard and Sara Pruss of Smith, trekked to northern Namibia and Mongolia to sample cap-carbonate rocks — the very first layers of sediment deposited after the first ice age. The team hauled the samples back to Cambridge, where Bosak dissolved the rocks in acid. She plated the residue on slides and looked for signs of fossilized life. “It’s a little bit like looking at clouds, trying to pick out shapes and seeing if anything’s consistent,” Bosak says.
Peering at the sludge through a microscope, she discovered a sea of tiny dark ovals, each with a single notch at its edge. To get a closer look, Bosak used scanning electron microscopy to create high-resolution, three-dimensional images, revealing hollow, 10-micron-thick shells. Fossils from Namibia were mostly round; those from Mongolia, more tube-like. Most fossils contained a slit or neck at one end, from which the organism’s pseudopodia, or feet, may have protruded.
Bosak analyzed the shells’ composition using X-ray spectroscopy, finding a rough patchwork of silica, aluminum and potassium particles that the organism likely plucked from the environment and glued to its surface.
Bosak says these single-celled microbes may have evolved the ability to build shells to protect against an extreme deep-ocean environment, as well as a potentially growing population of single-celled species, some of which may have preyed on other organisms.
A Snowball window
“We can now say there really were these robust organisms immediately after the first glaciation,” Bosak says. “Having opened this kind of window, we’re finding all kinds of organisms related to modern organisms.”
The closest modern relative may be testate amoebae, single-celled microbes found in forests, lakes and peat bogs. These tiny organisms have been known to collect particles of silica, clay minerals, fungi and pollen, cementing them into a hard cloak or shell. Bosak says testate amoebae were extremely abundant before the first Snowball Earth, although there is no robust evidence that the plentiful protist evolved its shell-building mechanism until after that ice age.
Bosak’s guess is that the post-glacial environment was a “brine” teeming with organisms and newly evolved traits. She says the group plans to return to Mongolia to sample more rocks from the same time period, and hopes other researchers will start to investigate rates of evolutionary change in similar rocks.
Andrew Knoll, the Fisher Professor of Natural History and professor of earth and planetary sciences at Harvard, says the group’s findings point to a potentially rich source of information about the kinds of life able to persist between glacial periods.
“To date, we’ve known very little about life between the two large ice ages,” Knoll says. “With this in mind, the new discoveries are truly welcome.”
Source MIT
The first organisms to emerge after an ancient worldwide glaciation likely evolved hardy survival skills, arming themselves with tough exteriors to weather a frozen climate.
Researchers at MIT, Harvard University and Smith College have discovered hundreds of microscopic fossils in rocks dating back nearly 710 million years, around the time when the planet emerged from a global glaciation, or “Snowball Earth,” event. The fossils are remnants of tiny, amoeba-like organisms that likely survived the harsh post-glacial environment by building armor and reaching out with microscopic “feet” to grab minerals from the environment, cobbling particles together to make protective shells.
The discovery is the earliest evidence of shell building, or agglutination, in the fossil record. The team found a diversity of fossils, suggesting life may have recovered relatively quickly following the first major Snowball Earth event. The researchers report their findings in an upcoming issue of Earth and Planetary Science Letters.
The widely held Snowball Earth theory maintains that massive ice sheets covered the planet from pole to pole hundreds of millions of years ago. Geologists have found evidence of two major snowball periods — at 710 and 635 million years ago — in glacial deposits that formed close to the modern equator. Fossil records illustrate an explosion of complex, multicellular life following the more recent ice age. However, not much is known about life between the two major glaciations — a period of about 75 million years that, until now, exhibited few signs of life.
“We know quite well what happened before the first Snowball, but we have no idea what happened in between,” says Tanja Bosak, assistant professor of geobiology at MIT, and the paper’s lead author. “Now we’re really starting to realize there’s a lot of unexpected life here.”
Ice Age armor
Bosak’s colleagues, Francis Macdonald of Harvard and Sara Pruss of Smith, trekked to northern Namibia and Mongolia to sample cap-carbonate rocks — the very first layers of sediment deposited after the first ice age. The team hauled the samples back to Cambridge, where Bosak dissolved the rocks in acid. She plated the residue on slides and looked for signs of fossilized life. “It’s a little bit like looking at clouds, trying to pick out shapes and seeing if anything’s consistent,” Bosak says.
Peering at the sludge through a microscope, she discovered a sea of tiny dark ovals, each with a single notch at its edge. To get a closer look, Bosak used scanning electron microscopy to create high-resolution, three-dimensional images, revealing hollow, 10-micron-thick shells. Fossils from Namibia were mostly round; those from Mongolia, more tube-like. Most fossils contained a slit or neck at one end, from which the organism’s pseudopodia, or feet, may have protruded.
Bosak analyzed the shells’ composition using X-ray spectroscopy, finding a rough patchwork of silica, aluminum and potassium particles that the organism likely plucked from the environment and glued to its surface.
Bosak says these single-celled microbes may have evolved the ability to build shells to protect against an extreme deep-ocean environment, as well as a potentially growing population of single-celled species, some of which may have preyed on other organisms.
A Snowball window
“We can now say there really were these robust organisms immediately after the first glaciation,” Bosak says. “Having opened this kind of window, we’re finding all kinds of organisms related to modern organisms.”
The closest modern relative may be testate amoebae, single-celled microbes found in forests, lakes and peat bogs. These tiny organisms have been known to collect particles of silica, clay minerals, fungi and pollen, cementing them into a hard cloak or shell. Bosak says testate amoebae were extremely abundant before the first Snowball Earth, although there is no robust evidence that the plentiful protist evolved its shell-building mechanism until after that ice age.
Bosak’s guess is that the post-glacial environment was a “brine” teeming with organisms and newly evolved traits. She says the group plans to return to Mongolia to sample more rocks from the same time period, and hopes other researchers will start to investigate rates of evolutionary change in similar rocks.
Andrew Knoll, the Fisher Professor of Natural History and professor of earth and planetary sciences at Harvard, says the group’s findings point to a potentially rich source of information about the kinds of life able to persist between glacial periods.
“To date, we’ve known very little about life between the two large ice ages,” Knoll says. “With this in mind, the new discoveries are truly welcome.”
Source MIT
Tuesday, June 14, 2011
Building a dinosaur from a chicken Can scientists convince birds to evolve backward .. into dinosaurs?
One of the most controversial topics in science during the past many decades has been the debate over the origin of birds: did they evolve from dinosaurs or reptiles? This debate quieted down for awhile until the discovery of an important new fossil in the nineteenth century. This fossil, known today as the Berlin specimen of Archaeopteryx (pictured above), led to fresh insights, thus reigniting this debate. Today, it is fairly well-accepted by the scientific community that birds are a special lineage of theropod dinosaurs.
When you look closely at the above fossil, you can see similarities as well as clear morphological differences between Archaeopteryx and, say, a chicken. Archaeopteryx has fingers instead of wings, Archaeopteryx has a long bony tail instead of a short bony nubbin and, if you look closely, you can also see that Archaeopteryx has teeth -- all of which birds lack.
But ornithologists and birders are familiar with one peculiar South American bird, the hoatzin, Opisthocomus hoazin, whose chicks possess claws on two of their wing digits -- almost like Archaeopteryx! But hoatzins aren't unique: curious traits, traits that had been lost during evolution, sometimes pop up in domestic livestock and even in humans -- chickens with teeth, horses with extra toes and humans with tails, for example. These features, known as atavisms, result from errors in gene regulation: genes are either "turned on" (expressed) or "turned off" (suppressed) at the incorrect times during development. Atavistic traits are reminders of the evolutionary past.
Knowing this, renown paleontologist Jack Horner has spent much of his career trying to turn back the evolutionary clock by reconstructing a dinosaur. He's found dinosaur fossils with extraordinarily well-preserved blood vessels and soft tissues, but never intact DNA. So instead of using the Jurassic Park method to recreate dinosaurs, he's taking a different approach. Mr Horner is taking a living descendant of the dinosaur -- chickens -- and genetically engineering them to reactivate ancestral traits -- including teeth, tails, and even hands. He's making a "chickenosaurus". In this fascinating video, Mr Horner reviews recent dinosaur discoveries and talks about his plans for recreating a "chickenosaurus":
Jack Horner studied geology and zoology but did not complete his bachelor's degree due to his inability to pass the required foreign language courses (he is somewhat dyslexic and could not read adequately in German). However, he did complete his senior thesis on the fauna of the Bear Gulch Limestone in Montana, which is one of the most famous Mississippian fossil sites in the world. He currently is Curator of Paleontology at the Museum of the Rockies and also serves in a number of academic capacities. In recognition of his achievements and contributions to the field of paleontology, he was awarded an Honorary Doctorate of Science in 1986 by the University of Montana and in 2006 by the Pennsylvania State University. In 1986, he was also awarded the prestigious MacArthur Fellowship. Mr Horner further discusses his plans to reconstruct a "chickenosaurus" in his 2009 book, How to Build a Dinosaur: Extinction Doesn't Have to Be Forever [Amazon UK; Amazon US].
Source The Guardian
Friday, June 10, 2011
Meteorite holds clues to organic chemistry of the early Earth
Washington, DC— Carbonaceous chondrites are a type of organic-rich meteorite that contain samples of the materials that took part in the creation of our planets nearly 4.6 billion years ago, including materials that were likely formed before our Solar System was created and may have been crucial to the formation of life on Earth. The complex suite of organic materials found in carbonaceous chondrites can vary substantially from meteorite to meteorite. New research from Carnegie's Department of Terrestrial Magnetism and Geophysical Laboratory, published June 10 in Science, shows that most of these variations are the result of hydrothermal activity that took place within a few million years of the formation of the Solar System, when the meteorites were still part of larger parent bodies, likely asteroids.
Organic material in carbonaceous chondrites shares many characteristics with organic matter found in other primitive samples, including interplanetary dust particles, comet 81P/Wild-2, and Antarctic micrometeorites. It has been argued by some that this similarity indicates that organic material throughout the Solar System largely originated from a common source, possibly the interstellar medium.
A test of this common-source hypothesis stems from its requirement that the organic diversity within and among meteorites be due primarily to chemical and thermal processing that took place while the meteorites were parts of their parent bodies. In other words, there should be a relationship between the extent of hydrothermal alteration that a meteorite experienced and the chemistry of the organic material it contains.
If--as many have speculated--the organic material in meteorites had a role to play in the origin of life on Earth, the attraction of the common-source hypothesis is that the same organic material would have been delivered to all bodies in the Solar System. If the common source was the interstellar medium, then similar material would also be delivered to any forming planetary system.
The research team—led by Christopher Herd of the University of Alberta, Canada, and including Carnegie's Conel Alexander, Larry Nittler, Frank Gyngard, George Cody, Marilyn Fogel, and Yoko Kebukawa—studied four meteorite specimens from the shower of stones, produced by the breakup of a meteoroid as it entered the atmosphere, that fell on Tagish Lake in northern Canada in January 2000. The samples are considered very pristine, because they fell on a frozen lake, were collected without hand contact within a few days of landing and have remained frozen ever since.
The samples were processed and analyzed on the microscopic level using a variety of sophisticated techniques. Examination of their inorganic components indicated that the specimens had experienced large differences in the extent of hydrothermal alteration, prompting an in-depth examination of their organic material. The team demonstrated that the insoluble organic matter found in the samples has properties that span nearly the entire range found in all carbonaceous chondrites and that those properties correlate with other measures of the extent of parent body alteration. Their finding confirms that the diversity of this material is due to processing of a common precursor material in the asteroidal parent bodies.
The team found large concentrations of monocarboxylic acids, or MCAs, which are essential to biochemistry, in their Tagish Lake samples. They attributed the high level of these acids to the pristine nature of the samples, which have been preserved below zero degrees Celsius since they were recovered. There was variety in the types of MCAs, which they determined could also be due to alterations that took place on the parent bodies.
The samples also contained amino acids—the essential-for-life organic building blocks used to create proteins. The types and abundances of amino acids contained in the samples are consistent with an extraterrestrial origin, and were clearly also influenced, albeit in a complex way, by the alteration histories of their host meteorites.
"Taken together these results indicate that the chemical and thermal processing common to the Tagish Lake meteorites likely occurred when the samples were part of a larger parent body that was created from the same raw materials that formed our Solar System," said Larry Nittler of Carnegie's DTM. "These samples can also provide important clues to the source of organic material, and life, on Earth."
Source ScienceAlert!
Organic material in carbonaceous chondrites shares many characteristics with organic matter found in other primitive samples, including interplanetary dust particles, comet 81P/Wild-2, and Antarctic micrometeorites. It has been argued by some that this similarity indicates that organic material throughout the Solar System largely originated from a common source, possibly the interstellar medium.
A test of this common-source hypothesis stems from its requirement that the organic diversity within and among meteorites be due primarily to chemical and thermal processing that took place while the meteorites were parts of their parent bodies. In other words, there should be a relationship between the extent of hydrothermal alteration that a meteorite experienced and the chemistry of the organic material it contains.
If--as many have speculated--the organic material in meteorites had a role to play in the origin of life on Earth, the attraction of the common-source hypothesis is that the same organic material would have been delivered to all bodies in the Solar System. If the common source was the interstellar medium, then similar material would also be delivered to any forming planetary system.
The research team—led by Christopher Herd of the University of Alberta, Canada, and including Carnegie's Conel Alexander, Larry Nittler, Frank Gyngard, George Cody, Marilyn Fogel, and Yoko Kebukawa—studied four meteorite specimens from the shower of stones, produced by the breakup of a meteoroid as it entered the atmosphere, that fell on Tagish Lake in northern Canada in January 2000. The samples are considered very pristine, because they fell on a frozen lake, were collected without hand contact within a few days of landing and have remained frozen ever since.
The samples were processed and analyzed on the microscopic level using a variety of sophisticated techniques. Examination of their inorganic components indicated that the specimens had experienced large differences in the extent of hydrothermal alteration, prompting an in-depth examination of their organic material. The team demonstrated that the insoluble organic matter found in the samples has properties that span nearly the entire range found in all carbonaceous chondrites and that those properties correlate with other measures of the extent of parent body alteration. Their finding confirms that the diversity of this material is due to processing of a common precursor material in the asteroidal parent bodies.
The team found large concentrations of monocarboxylic acids, or MCAs, which are essential to biochemistry, in their Tagish Lake samples. They attributed the high level of these acids to the pristine nature of the samples, which have been preserved below zero degrees Celsius since they were recovered. There was variety in the types of MCAs, which they determined could also be due to alterations that took place on the parent bodies.
The samples also contained amino acids—the essential-for-life organic building blocks used to create proteins. The types and abundances of amino acids contained in the samples are consistent with an extraterrestrial origin, and were clearly also influenced, albeit in a complex way, by the alteration histories of their host meteorites.
"Taken together these results indicate that the chemical and thermal processing common to the Tagish Lake meteorites likely occurred when the samples were part of a larger parent body that was created from the same raw materials that formed our Solar System," said Larry Nittler of Carnegie's DTM. "These samples can also provide important clues to the source of organic material, and life, on Earth."
Source ScienceAlert!
Earth-bound asteroids carried ever-evolving, life-starting organic compounds
Detailed analysis of the most pristine meteorite ever recovered shows that the composition of the organic compounds it carried changed during the early years of the solar system
(Edmonton) Detailed analysis of the most pristine meteorite ever recovered shows that the composition of the organic compounds it carried changed during the early years of the solar system. Those changed organics were preserved through billions of years in outer space before the meteorite crashed to Earth.The research team, led by University of Alberta geologist Chris Herd, analyzed samples of a meteorite that landed on Tagish Lake in northern British Columbia in 2000. Variations in the geology of the meteorite samples were visible to the naked eye and indicated the asteroid, from which the meteorite samples originated, had gone through substantial changes.
The researchers began looking for variations in the organic chemistry that corresponded with variations in the meteorite's geology. Herd says they found a surprising correlation, which gave researchers a snapshot of the process that altered the composition of organic material carried by the asteroid. Among the organic compounds studied were amino acids and monocarboxylic acids, two chemicals essential to the evolution of the first, simple life forms on Earth.
Herd says the finding shows the importance of asteroids to Earth's history.
"The mix of prebiotic molecules, so essential to jump-starting life, depended on what was happening out there in the asteroid belt," said Herd. "The geology of an asteroid has an influence on what molecules actually make to the surface of Earth."
Herd says that, when the asteroid was created by the accumulation of dust around the infant sun, it contained ice. The ice warmed and turned to water, which began percolating and altering the organic compounds buried in the rock.
The Tagish Lake meteorite is considered to be one-of-a-kind because of its landing and handling. It was January when the meteorite exploded at an altitude of 30 to 50 kilometres above Earth and rained meteorite fragments down on the frozen, snow-covered lake. The individual who recovered the samples consulted with experts beforehand and avoided any contamination issues.
Herd says the meteorite's pristine state enabled the breakthrough research. "The variations in the organic makeup are true to what was happing inside the asteroid," said Herd. "This is exactly what has been orbiting in the asteroid belt for the last 4.5 billion years."
Source EurekaAlert!
Tuesday, June 7, 2011
Ancient armor Fossils from the Yukon reveal protective plates for microscopic organisms.
In summer 2007, two geologists armed with rock hammers and a shotgun hiked through the Yukon, looking for fossils. For two weeks, Phoebe Cohen, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences, and Francis Macdonald, an assistant professor of geology at Harvard University, set up camp along the Alaska-Canada border in a remote mountain range accessible only via helicopter.
The shotgun came in handy: Macdonald fired it once to scare off a grizzly bear. And the rock hammers proved invaluable — the team worked them against mountainsides, chiseling out rock samples. They hauled the rocks back to Cambridge and made a surprising discovery: The ancient carbonate contained hundreds of incredibly well-preserved fossils resembling tiny, shield-like plates.
An image of the microfossil Characodictyon taken with a scanning electron microscope. This fossil was extracted using very weak acid from a carbonate rock. It's about 20 microns long - one-fifth the width of a human hair.
Cohen, who was a Harvard PhD student at the time, says single-celled organisms may have produced the plates as armor, in a process called biomineralization. Today, many organisms have evolved the ability to produce mineral structures: Mollusks generate shells, and mammals and birds form bone. The 700-million-year-old fossils Cohen found may be the oldest evidence of biomineralization; Cohen, Macdonald and co-authors reported the finding this week in the journal Geology.
Plating up
In 1979, researchers from the University of Alaska identified strange fossils in the Yukon region — not in carbonate, but in sections of glasslike rock called chert. But it wasn’t clear then just how old the fossils were. During their expedition, Cohen and Macdonald found the same fossils for the first time in carbonate.
In the lab, they were able to date the rock, and the fossils, to between 717 million and 812 million years old, placing them in the middle of the Neoproterozoic era — a time period in which single-celled organisms likely flourished just prior to the first "Snowball Earth" event, in which vast ice sheets likely covered the planet. Cohen says these microorganisms were most likely killed off in the global freeze, but the fossils they left behind may give researchers clues to the complexity of life just before the planet froze over.
“These fossils … fit in with a huge diversity of other single-celled eukaryotic organisms that seem to have evolved approximately at the same time,” Cohen says.
To get a better look at the fossils, Cohen and Macdonald dissolved rock samples in weak acid, and mounted the residue on stubs. With collaborators at the University of California at Los Angeles, they then created high-resolution, three-dimensional images of the microscopic fossils using scanning electron microscopy. The images revealed plates, each about 20 microns wide, arranged in a honeycomb pattern, with teeth-like spines jutting out and rimming the perimeter.
It’s unclear which modern organisms might be related to these fossils, but on close examination, Cohen observed similarities between the ancient fossil patterns and those formed by modern-day coccolithophores — spherical, single-celled algae found in enormous blooms throughout the ocean. These tiny organisms create mineralized plates within their vacuoles, ultimately extruding the plates to the surface to form protective coverings.
Cohen and her co-authors believe the tiny fossil plates they observed may have formed via a similar process. But exactly why simple organisms evolved such a complex process is still a mystery.
“It takes a lot of effort, energy and just sheer biomass to create these [plates],” Cohen says. “One of the big questions is: Why are these organisms making these intricate, detailed, morphologically complex structures?”
One theory is that spines and plates may help small organisms stay afloat. Today, coccolithophores are found within the photic zone of the ocean, at depths where light can reach. Maintaining a “sweet spot” within this zone enables plankton to grow and thrive — an advantage their ancient counterparts may also have evolved.
The plates may also have served as armor. Hard mineral coverings may have put off predators for two reasons: protective shields simply make it harder to get at an organism, and a plate’s mineral composition may have made the organisms less appealing to nutrient-seeking predators.
“It’s a good possibility that these fossil plates functioned in defense against predators,” says Susannah Porter, an associate professor of geological sciences at the University of California at Santa Barbara who was not involved in the research. “This would be significant if true, for it would be some of the earliest evidence for complex food webs, that consist not only of primary producers … but also organisms that actively prey on other living organisms.”
Cohen hopes the results will spur more researchers to investigate other such early signs of complex life, in rocks of the same time period from around the world.
“These fossils are really small and hard to find,” Cohen says. “And maybe the fossils are there, we just have to look for them.”
Source MIT
The shotgun came in handy: Macdonald fired it once to scare off a grizzly bear. And the rock hammers proved invaluable — the team worked them against mountainsides, chiseling out rock samples. They hauled the rocks back to Cambridge and made a surprising discovery: The ancient carbonate contained hundreds of incredibly well-preserved fossils resembling tiny, shield-like plates.
Cohen, who was a Harvard PhD student at the time, says single-celled organisms may have produced the plates as armor, in a process called biomineralization. Today, many organisms have evolved the ability to produce mineral structures: Mollusks generate shells, and mammals and birds form bone. The 700-million-year-old fossils Cohen found may be the oldest evidence of biomineralization; Cohen, Macdonald and co-authors reported the finding this week in the journal Geology.
Plating up
In 1979, researchers from the University of Alaska identified strange fossils in the Yukon region — not in carbonate, but in sections of glasslike rock called chert. But it wasn’t clear then just how old the fossils were. During their expedition, Cohen and Macdonald found the same fossils for the first time in carbonate.
In the lab, they were able to date the rock, and the fossils, to between 717 million and 812 million years old, placing them in the middle of the Neoproterozoic era — a time period in which single-celled organisms likely flourished just prior to the first "Snowball Earth" event, in which vast ice sheets likely covered the planet. Cohen says these microorganisms were most likely killed off in the global freeze, but the fossils they left behind may give researchers clues to the complexity of life just before the planet froze over.
“These fossils … fit in with a huge diversity of other single-celled eukaryotic organisms that seem to have evolved approximately at the same time,” Cohen says.
To get a better look at the fossils, Cohen and Macdonald dissolved rock samples in weak acid, and mounted the residue on stubs. With collaborators at the University of California at Los Angeles, they then created high-resolution, three-dimensional images of the microscopic fossils using scanning electron microscopy. The images revealed plates, each about 20 microns wide, arranged in a honeycomb pattern, with teeth-like spines jutting out and rimming the perimeter.
It’s unclear which modern organisms might be related to these fossils, but on close examination, Cohen observed similarities between the ancient fossil patterns and those formed by modern-day coccolithophores — spherical, single-celled algae found in enormous blooms throughout the ocean. These tiny organisms create mineralized plates within their vacuoles, ultimately extruding the plates to the surface to form protective coverings.
Cohen and her co-authors believe the tiny fossil plates they observed may have formed via a similar process. But exactly why simple organisms evolved such a complex process is still a mystery.
“It takes a lot of effort, energy and just sheer biomass to create these [plates],” Cohen says. “One of the big questions is: Why are these organisms making these intricate, detailed, morphologically complex structures?”
One theory is that spines and plates may help small organisms stay afloat. Today, coccolithophores are found within the photic zone of the ocean, at depths where light can reach. Maintaining a “sweet spot” within this zone enables plankton to grow and thrive — an advantage their ancient counterparts may also have evolved.
The plates may also have served as armor. Hard mineral coverings may have put off predators for two reasons: protective shields simply make it harder to get at an organism, and a plate’s mineral composition may have made the organisms less appealing to nutrient-seeking predators.
“It’s a good possibility that these fossil plates functioned in defense against predators,” says Susannah Porter, an associate professor of geological sciences at the University of California at Santa Barbara who was not involved in the research. “This would be significant if true, for it would be some of the earliest evidence for complex food webs, that consist not only of primary producers … but also organisms that actively prey on other living organisms.”
Cohen hopes the results will spur more researchers to investigate other such early signs of complex life, in rocks of the same time period from around the world.
“These fossils are really small and hard to find,” Cohen says. “And maybe the fossils are there, we just have to look for them.”
Source MIT
Monday, May 30, 2011
Researchers solve mammoth evolutionary puzzle: The woollies weren't picky, happy to interbreed
A DNA-based study sheds new light on the complex evolutionary history of the woolly mammoth, suggesting it mated with a completely different and much larger species.
The research, which appears in the BioMed Central's open access journal Genome Biology, found the woolly mammoth, which lived in the cold climate of the Arctic tundra, interbred with the Columbian mammoth, which preferred the more temperate regions of North America and was some 25 per cent larger.
"There is a real fascination with the history of mammoths, and this analysis helps to contextualize its evolution, migration and ecology" says Hendrik Poinar, associate professor and Canada Research Chair in the departments of Anthropology and Biology at McMaster University.
Poinar and his team at the McMaster Ancient DNA Centre, along with colleagues from the United States and France, meticulously sequenced the complete mitochondrial genome of two Columbian mammoths, one found in the Huntington Reservoir in Utah, the other found near Rawlins, Wyoming. They compared these to the first complete mitochrondrial genome of an endemic North American woolly mammoth.
"We are talking about two very physically different 'species' here. When glacial times got nasty, it was likely that woollies moved to more pleasant conditions of the south, where they came into contact with the Columbians at some point in their evolutionary history," he says. "You have roughly 1-million years of separation between the two, with the Columbian mammoth likely derived from an early migration into North American approximately 1.5-million years ago, and their woolly counterparts emigrating to North America some 400,000 years ago."
"We think we may be looking at a genetic hybrid," says Jacob Enk, a graduate student in the McMaster Ancient DNA Centre. "Living African elephant species hybridize where their ranges overlap, with the bigger species out-competing the smaller for mates. This results in mitochondrial genomes from the smaller species showing up in populations of the larger. Since woollies and Columbians overlapped in time and space, it's not unlikely that they engaged in similar behaviour and left a similar signal."
The samples used for the analyses date back approximately 12,000 years. All mammoths became extinct approximately 10,000 years ago except for small isolated populations on islands off the coast of Siberia and Alaska.
Source EurekaAlert!
The research, which appears in the BioMed Central's open access journal Genome Biology, found the woolly mammoth, which lived in the cold climate of the Arctic tundra, interbred with the Columbian mammoth, which preferred the more temperate regions of North America and was some 25 per cent larger.
"There is a real fascination with the history of mammoths, and this analysis helps to contextualize its evolution, migration and ecology" says Hendrik Poinar, associate professor and Canada Research Chair in the departments of Anthropology and Biology at McMaster University.
Poinar and his team at the McMaster Ancient DNA Centre, along with colleagues from the United States and France, meticulously sequenced the complete mitochondrial genome of two Columbian mammoths, one found in the Huntington Reservoir in Utah, the other found near Rawlins, Wyoming. They compared these to the first complete mitochrondrial genome of an endemic North American woolly mammoth.
"We are talking about two very physically different 'species' here. When glacial times got nasty, it was likely that woollies moved to more pleasant conditions of the south, where they came into contact with the Columbians at some point in their evolutionary history," he says. "You have roughly 1-million years of separation between the two, with the Columbian mammoth likely derived from an early migration into North American approximately 1.5-million years ago, and their woolly counterparts emigrating to North America some 400,000 years ago."
"We think we may be looking at a genetic hybrid," says Jacob Enk, a graduate student in the McMaster Ancient DNA Centre. "Living African elephant species hybridize where their ranges overlap, with the bigger species out-competing the smaller for mates. This results in mitochondrial genomes from the smaller species showing up in populations of the larger. Since woollies and Columbians overlapped in time and space, it's not unlikely that they engaged in similar behaviour and left a similar signal."
The samples used for the analyses date back approximately 12,000 years. All mammoths became extinct approximately 10,000 years ago except for small isolated populations on islands off the coast of Siberia and Alaska.
Source EurekaAlert!
Thursday, May 19, 2011
Early mammals were brainy and nosy
The early Jurassic might be famous as the point in prehistory that dinosaurs began to grow into giants, but something else was growing larger at that time too: the brains of early mammal-like animals. That could be because smell and touch were vital for their survival during the age of the dinosaurs.
My, what big olfactory bulbs you have (Image: Matt Colbert/University of Texas at Austin).
In the 1980s, palaeontologist Timothy Rowe visited the fossil collection at Harvard University with an earnest request: could he please crack open a rare, 190-million-year-old skull of a tiny mammal to determine the shape of its brain? The eyes of Harvard's curators widened behind their spectacles; their lips pursed; their brows wrinkled.
"The standard response was, 'No way! Sit on your hands and be patient, and sooner or later we'll have non-destructive techniques to answer those questions,'" Rowe recalls. "It was so frustrating because I really wanted to know what the brain was like, but these fossils were treated like a Rembrandt or a Vermeer."
Three decades later, Rowe's waiting is over. His team at the University of Texas at Austin recently used high-resolution X-ray computed tomography (CT) to create 3D maps of the skulls of two ancient mammals, faithfully reproducing the shapes of the brains they once contained. The digital moulds suggest that their brains evolved to meet the need for acute senses of smell and touch.
There will be mammals
Rowe examined fossil Jurassic skulls from China, remains of the pygmy shrew-like creatures Morganucodon oehleri and Hadrocodium wui – animals so old that they may in fact be forerunners to true mammals.
Mammals have rather large brains for their body size compared with other animals. The difference is the neocortex: a six-layered hunk of brain tissue that is much larger and more complex in mammals. As expected, the digital brains of the early mammals had big neocortices – but something else contributed to their overall size.
Staring back at Rowe from the computer screen were two prominent bumps on the front of the brains: the olfactory bulbs, where smell is processed (see image, top right). The bulbs were much larger than Rowe expected, suggesting that smell was extremely important for early mammals, just as it is for certain mammals today, such as bears and bloodhounds.
Tucked in the wrinkly folds of the digital brains the researchers found evidence of strong motor coordination skills and a keen sense of touch. Rowe speculates that the animals depended on specialised hair follicles attached to nerves to learn about their environments, as some mammals now use whiskers. We know that even these early mammals were covered in hair because a fossil of one of them, Castorocauda lutrasimilis, remarkably preserves evidence of a thick pelt that covered its body.
"The story of becoming a mammal is the story of developing the most sensitive and high-resolution olfactory system," says Rowe, "and secondary to that is touch and motor skills."
Respectable smell
"It's a beautifully done paper," says Lori Marino, who studies the evolution of mammalian brains at Emory University in Atlanta, Georgia. "It's important work because up to now we haven't had a whole lot of information about what parts of the brain have expanded in different groups. It tells us something about our preconceptions of how the mammalian brain evolved: it wasn't just the neocortex that expanded. It gives a new respectability to smell."
The evident importance of smell and touch to these tiny proto-mammals hints at their lifestyle. The 190-million–year-old animals probably navigated dark burrows and skittered through leaf litter hunting insects – activities greatly helped by sensitive smell and touch.
"Having a great sense of smell is also consistent with the idea these mammals may have been nocturnal," explains Rowe. Despite recent evidence of nocturnal behaviour in dinosaurs, it's generally thought that most of these animals were active at day and asleep at night. "That's when the mammals came out. With a great sense of smell, it doesn't matter if it's dark," he says. "Smell might be what made it possible for early mammals to come out and find food and mates. In the early Jurassic, that was what drove their evolution."
Source New Scientist
Monday, May 16, 2011
Anthropologist discovers new fossil primate species in West Texas
AUSTIN, Texas–Physical anthropologist Chris Kirk has announced the discovery of a previously unknown species of fossil primate, Mescalerolemur horneri, in the Devil's Graveyard badlands of West Texas.
Mescalerolemur lived during the Eocene Epoch about 43 million years ago, and would have most closely resembled a small present-day lemur. Mescalerolemur is a member of an extinct primate group – the adapiforms – that were found throughout the Northern Hemisphere in the Eocene. However, just like Mahgarita stevensi, a younger fossil primate found in the same area in 1973, Mescalerolemur is more closely related to Eurasian and African adapiforms than those from North America.
This is Mescalerolemur horneri's partial upper jaw (in two pieces, at left) and partial lower jaw (at right) (scales = 2 mm).
"These Texas primates are unlike any other Eocene primate community that has ever been found in terms of the species that are represented," says Kirk, associate professor in the Department of Anthropology at The University of Texas at Austin. "The presence of both Mescalerolemur and Mahgarita, which are only found in the Big Bend region of Texas, comes after the more common adapiforms from the Eocene of North America had already become extinct. This is significant because it provides further evidence of faunal interchange between North America and East Asia during the Middle Eocene."
By the end of the Eocene, primates and other tropically adapted species had all but disappeared from North America due to climatic cooling, so Kirk is sampling the last burst of diversity in North American primates. With its lower latitudes and more equable climate, West Texas offered warm-adapted species a greater chance of survival after the cooling began.
Kirk says Marie Butcher, a then undergraduate who graduated with degrees in anthropology and biology from The University of Texas at Austin, found the first isolated tooth of Mescalerolemur in 2005. Since that time, many more primate fossils have been recovered by Kirk and more than 20 student volunteers at a locality called "Purple Bench." This fossil locality is three to four million years older than the Devil's Graveyard sediments that had previously produced Mahgarita stevensi.
"I initially thought that we had found a new, smaller species of Mahgarita," Kirk says.
However, as more specimens were prepared at the Texas Memorial Museum's Vertebrate Paleontology Lab, Kirk realized he had discovered not just a new species, but a new genus that was previously unknown to science.
Fossils of Mescalerolemur reveal it was a small primate, weighing only about 370 grams. This body weight is similar to that of the living greater dwarf lemur. Mescalerolemur's dental anatomy reveals a close evolutionary relationship with adapiform primates from Eurasia and Africa, including Darwinius masillae, a German fossil primate previously claimed to be a human ancestor. However, the discovery of Mescalerolemur provides further evidence that adapiform primates like Darwinius are more closely related to living lemurs and bush babies than they are to humans.
For example, the right and left halves of Mescalerolemur's lower jaws were two separate bones with a joint along the midline, a common trait for lemurs and bush babies. Mahgarita stevensi, the closest fossil relative of Mescalerolemur, had a completely fused jaw joint like that of humans.
"Because Mescalerolemur and Mahgarita are close relatives, fusion of the lower jaws in Mahgarita must have occurred independently from that observed in humans and their relatives, the monkeys and apes" Kirk says.
The new genus is named Mescalerolemur after the Mescalero Apache, who inhabited the Big Bend region of Texas from about 1700-1880. The species name, horneri, honors Norman Horner, an entomologist and professor emeritus at Midwestern State University (MSU) in Wichita Falls, Texas. Horner helped to establish MSU's Dalquest Desert Research Site, where the new primate fossils were found.
Kirk and his colleague Blythe Williams of Duke University will publish their findings in the Journal of Human Evolution article, "New adapiform primate of Old World affinities from the Devil's Graveyard Formation of Texas."
Source EurekaAlert!
Mescalerolemur lived during the Eocene Epoch about 43 million years ago, and would have most closely resembled a small present-day lemur. Mescalerolemur is a member of an extinct primate group – the adapiforms – that were found throughout the Northern Hemisphere in the Eocene. However, just like Mahgarita stevensi, a younger fossil primate found in the same area in 1973, Mescalerolemur is more closely related to Eurasian and African adapiforms than those from North America.
"These Texas primates are unlike any other Eocene primate community that has ever been found in terms of the species that are represented," says Kirk, associate professor in the Department of Anthropology at The University of Texas at Austin. "The presence of both Mescalerolemur and Mahgarita, which are only found in the Big Bend region of Texas, comes after the more common adapiforms from the Eocene of North America had already become extinct. This is significant because it provides further evidence of faunal interchange between North America and East Asia during the Middle Eocene."
This is Mescalerolemur horneri's partial right lower jaw (scale = 2 mm).
Kirk says Marie Butcher, a then undergraduate who graduated with degrees in anthropology and biology from The University of Texas at Austin, found the first isolated tooth of Mescalerolemur in 2005. Since that time, many more primate fossils have been recovered by Kirk and more than 20 student volunteers at a locality called "Purple Bench." This fossil locality is three to four million years older than the Devil's Graveyard sediments that had previously produced Mahgarita stevensi.
"I initially thought that we had found a new, smaller species of Mahgarita," Kirk says.
However, as more specimens were prepared at the Texas Memorial Museum's Vertebrate Paleontology Lab, Kirk realized he had discovered not just a new species, but a new genus that was previously unknown to science.
Fossils of Mescalerolemur reveal it was a small primate, weighing only about 370 grams. This body weight is similar to that of the living greater dwarf lemur. Mescalerolemur's dental anatomy reveals a close evolutionary relationship with adapiform primates from Eurasia and Africa, including Darwinius masillae, a German fossil primate previously claimed to be a human ancestor. However, the discovery of Mescalerolemur provides further evidence that adapiform primates like Darwinius are more closely related to living lemurs and bush babies than they are to humans.
For example, the right and left halves of Mescalerolemur's lower jaws were two separate bones with a joint along the midline, a common trait for lemurs and bush babies. Mahgarita stevensi, the closest fossil relative of Mescalerolemur, had a completely fused jaw joint like that of humans.
"Because Mescalerolemur and Mahgarita are close relatives, fusion of the lower jaws in Mahgarita must have occurred independently from that observed in humans and their relatives, the monkeys and apes" Kirk says.
The new genus is named Mescalerolemur after the Mescalero Apache, who inhabited the Big Bend region of Texas from about 1700-1880. The species name, horneri, honors Norman Horner, an entomologist and professor emeritus at Midwestern State University (MSU) in Wichita Falls, Texas. Horner helped to establish MSU's Dalquest Desert Research Site, where the new primate fossils were found.
Kirk and his colleague Blythe Williams of Duke University will publish their findings in the Journal of Human Evolution article, "New adapiform primate of Old World affinities from the Devil's Graveyard Formation of Texas."
Source EurekaAlert!
Saturday, May 14, 2011
Featherweight Relative of the T. Rex Is Found
Researchers working in the western Gobi Desert in Mongolia have discovered the almost complete skeleton of a tyrannosaurid dinosaur that was less than 3 years old when it died, younger and smaller than any previously known. The animal, Tarbosaurus bataar, is the closest relative of Tyrannosaurus rex, the predator that lived at the same time in North America.
In life, the specimen weighed less than 70 pounds, compared with the six-ton weight of a full-grown T. bataar, the researchers report in The Journal of Vertebrate Paleontology. The researchers were able to determine its age by microscopic examination of one of the leg bones, which reveal periodic pauses in growth, similar to the rings of a tree trunk.
The skulls of adult tyrannosaurids have extremely strong bones, especially those of the jaw, capable of tremendous twisting and bending forces. But the juvenile’s skull bones are more delicate, its teeth much thinner and its jaw much weaker. This suggests that a young T. bataar would be more likely to take its prey by stealth and speed rather than the overwhelming power its parents could use. In other words, T. bataar changed its diet as it matured, unlike some other predatory dinosaurs.
“This is one of the clearest pictures we have of these dinosaurs,” said Lawrence M. Witmer , a professor of paleontology at Ohio University and the senior author of the study. “It gives us the best glimpse into the changing lifestyles of these animals as they grew.”
Source The New York Times
The almost complete skeleton of a tyrannosaurid dinosaur that was less than 3 years old when it died.
The skulls of adult tyrannosaurids have extremely strong bones, especially those of the jaw, capable of tremendous twisting and bending forces. But the juvenile’s skull bones are more delicate, its teeth much thinner and its jaw much weaker. This suggests that a young T. bataar would be more likely to take its prey by stealth and speed rather than the overwhelming power its parents could use. In other words, T. bataar changed its diet as it matured, unlike some other predatory dinosaurs.
“This is one of the clearest pictures we have of these dinosaurs,” said Lawrence M. Witmer , a professor of paleontology at Ohio University and the senior author of the study. “It gives us the best glimpse into the changing lifestyles of these animals as they grew.”
Source The New York Times
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