Why Do Dinosaur Skeletons Look So Weird?
ScienceDaily (Feb. 16, 2012) — Many fossilized dinosaurs have been found in a twisted posture. Scientists have long interpreted this as a sign of death spasms. Two researchers from Basel and Mainz now come to the conclusion that this bizarre deformations occurred only during the decomposition of dead dinosaurs.
More or less complete and articulated skeletons of dinosaurs with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. This posture, also known from Archaeopteryx, has been fascinating paleontologists for more than 150 years. It was called “bicycle pose” when talking with a wink, or “opisthotonic posture” in a more oppressive way of speaking.
The latter alludes to an accessory symptom of tetanus, well known in human and veterinarian medicine. Usually, an “opisthotonic posture” like that is the result of vitamin deficiency, poisoning or damage to the cerebellum.
Basically, the cerebellum is a brain region that controls fine muscle movement, which includes the body’s antigravity muscles that keep the head and tail upright. If the cerebellum ceases to function, the antigravity muscles will clench at full force, tipping the head and tail back, and contracting the limbs.
A syndrome like that as a petrified expression of death throes was discussed for the first time about 100 years ago for some vertebrate fossils, but the acceptance of this interpretation declined during the following decades. In 2007, this “opisthotonus hypothesis” was newly posted by a veterinarian and a palaeontologist. This study, generously planned, received much attention in the public and the scientific community.
Now, five years later, two scientists from Switzerland and Germany have re-evaluated the revitalized “opisthotonus hypothesis” and examined one of its icons, the famous bipedal dinosaur Compsognathus longipes from the “Solnhofen Archipelago” (Germany). It is widely acknowledged that this 150-millions-years-old land-living dinosaur was embedded in a watery grave of a tropical lagoon.
“In our opinion, the most critical point in the newly discussed scenario of the preservation of an opisthotonic posture in a fossil is the requirement that terrestrial vertebrates must have been embedded immediately after death without substantial transport. But consigning a carcass from land to sea and the following need of sinking through the water column for only a few decimetres or meters is nothing else” says sedimentologist Achim Reisdorf from University of Basel’s Institute of Geology and Paleontology.
Biomechanics in Watery Graves Convinced that the back arching was generated, not by death throes, but by postmortem alterations of a decaying carcass, the researchers made experiments with plucked chicken necks and thoraxes, immersed in water. Submersed in water, the necks spontaneously arched backwards for more than 90°. Ongoing decay for some months even increased the degree of the pose. Thorough preparation and dissection combined with testing revealed that a special ligament connecting the vertebrae at their upper side was responsible for the recurved necks in the chickens. This ligament, the so-called Ligamentum elasticum, is pre-stressed in living chickens, but also in dead ones.
“Veterinarians may often have to do with sick and dying animals, where they see the opisthotonic posture in many cases. Vertebrate palaeontologists, however, who want to infer the environment in which the animals perished and finally were embedded have to elucidate postmortem processes and biomechanical constraints too” says palaeontologist Michael Wuttke from the Section of Earth History in the General Department for the Conservation of Cultural History Rhineland Palatinate in Mainz (Germany).
“A strong Ligamentum elasticum was essential for all long necked dinosaurs with a long tail. The preloaded ligament helped them saving energy in their terrestrial mode of life. Following their death, at which they were immersed in water, the stored energy along the vertebra was strong enough to arch back the spine, increasingly so as more and more muscles and other soft parts were decaying” conclude the researchers. “It is a special highlight that, in the Compsognathus specimen, these gradual steps of recurvature can be substantiated, too. Therefore, biomechanics is ruling the postmortem weird posture of a carcass in a watery grave, not death throes.”
Entire Genome of Extinct Human Decoded from Fossil
ScienceDaily (Feb. 7, 2012) — The Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany, has completed the genome sequence of a Denisovan, a representative of an Asian group of extinct humans related to Neandertals.
In 2010, Svante Pääbo and his colleagues presented a draft version of the genome from a small fragment of a human finger bone discovered in Denisova Cave in southern Siberia. The DNA sequences showed that this individual came from a previously unknown group of extinct humans that have become known as Denisovans. Together with their sister group the Neandertals, Denisovans are the closest extinct relatives of currently living humans.
The Leipzig team has now developed sensitive novel techniques which have allowed them to sequence every position in the Denisovan genome about 30 times over, using DNA extracted from less than 10 milligrams of the finger bone. In the previous draft version published in 2010, each position in the genome was determined, on average, only twice. This level of resolution was sufficient to establish the relationship of Denisovans to Neandertals and present-day humans, but often made it impossible for researchers to study the evolution of specific parts of the genome. The now-completed version of the genome allows even the small differences between the copies of genes that this individual inherited from its mother and father to be distinguished.
On February 8 the Leipzig group makes the entire Denisovan genome sequence available for the scientific community over the internet.
“The genome is of very high quality,” says Matthias Meyer, who developed the techniques that made this technical feat possible. “We cover all non-repetitive DNA sequences in the Denisovan genome so many times that it has fewer errors than most genomes from present-day humans that have been determined to date.”
The genome represents the first high-coverage, complete genome sequence of an archaic human group — a leap in the study of extinct forms of humans. “We hope that biologists will be able to use this genome to discover genetic changes that were important for the development of modern human culture and technology, and enabled modern humans to leave Africa and rapidly spread around the world, starting around 100,000 years ago” says Pääbo. The genome is also expected to reveal new aspects of the history of Denisovans and Neandertals.
The group plans to present a paper describing the genome later this year. “But we want to make it freely available to everybody already now” says Pääbo. “We believe that many scientists will find it useful in their research.”
The project is made possible by financing from the Max Planck Society and is part of efforts since almost 30 years by Dr. Pääbo’s group to study ancient DNA. The finger bone was discovered by Professor Anatoly Derevianko and Professor Michail Shunkov from the Russian Academy of Sciences in 2008 during their excavations at Denisova Cave, a unique archaeological site which contains cultural layers indicating that human occupation at the site started up to 280,000 years ago. The finger bone was found in a layer which has been dated to between 50,000 and 30,000 years ago.
Fossils in South Africa Reveal Dinosaur Nesting Site: 190 Million Years Old
ScienceDaily (Jan. 23, 2012) — An excavation at a site in South Africa has unearthed the 190-million-year-old dinosaur nesting site of the prosauropod dinosaur Massospondylus — revealing significant clues about the evolution of complex reproductive behaviour in early dinosaurs.
A new study, published in the Proceedings of the National Academy of Sciences (PNAS), was led by Canadian palaeontologist Prof. Robert Reisz, a professor of biology at the University of Toronto at Mississauga, and co-authored by Drs. Hans-Dieter Sues (Smithsonian Institute, USA), Eric Roberts (James Cook University, Australia), and Adam Yates (Bernard Price Institute (BPI) for Palaeontological Research at Wits).
The study reveals clutches of eggs, many with embryos, as well as tiny dinosaur footprints, providing the oldest known evidence that the hatchlings remained at the nesting site long enough to at least double in size.
Prof. Bruce Rubidge, Director of the BPI at Wits, says: “This research project, which has been ongoing since 2005 continues to produce groundbreaking results and excavations continue. First it was the oldest dinosaur eggs and embryos, now it is the oldest evidence of dinosaur nesting behaviour.”
The authors say the newly unearthed dinosaur nesting ground is more than 100 million years older than previously known nesting sites.
At least ten nests have been discovered at several levels at this site, each with up to 34 round eggs in tightly clustered clutches. The distribution of the nests in the sediments indicate that these early dinosaurs returned repeatedly (nesting site fidelity) to this site, and likely assembled in groups (colonial nesting) to lay their eggs, the oldest known evidence of such behaviour in the fossil record.
The large size of the mother, at six metres in length, the small size of the eggs, about six to seven centimetres in diameter, and the highly organised nature of the nest, suggest that the mother may have arranged them carefully after she laid them.
“The eggs, embryos, and nests come from the rocks of a nearly vertical road cut only 25 metres long,” says Reisz. “Even so, we found ten nests, suggesting that there are a lot more nests in the cliff, still covered by tons of rock. We predict that many more nests will be eroded out in time, as natural weathering processes continue.”
The fossils were found in sedimentary rocks from the Early Jurassic Period in the Golden Gate Highlands National Park in South Africa. This site has previously yielded the oldest known embryos belonging to Massospondylus, a relative of the giant, long-necked sauropods of the Jurassic and Cretaceous periods.
“Even though the fossil record of dinosaurs is extensive, we actually have very little fossil information about their reproductive biology, particularly for early dinosaurs,” says David Evans, a University of Toronto at Mississauga alumnus and a curator of Vertebrate Palaeontology at the Royal Ontario Museum.
“This amazing series of 190 million year old nests gives us the first detailed look at dinosaur reproduction early in their evolutionary history, and documents the antiquity of nesting strategies that are only known much later in the dinosaur record,” says Evans.
Ancient domesticated dog skull found in Siberian cave: 33,000 years old
ScienceDaily (Jan. 23, 2012) — A 33,000-year-old dog skull unearthed in a Siberian mountain cave presents some of the oldest known evidence of dog domestication and, together with an equally ancient find in a cave in Belgium, indicates that modern dogs may be descended from multiple ancestors.
If you think a Chihuahua doesn’t have much in common with a Rottweiler, you might be on to something.
An ancient dog skull, preserved in a cave in the Altai Mountains of Siberia for 33,000 years, presents some of the oldest known evidence of dog domestication and, together with equally ancient dog remains from a cave in Belgium, indicates that domestication of dogs may have occurred repeatedly in different geographic locations rather than with a single domestication event.
In other words, man’s best friends may have originated from more than one ancient ancestor, contrary to what some DNA evidence previously has indicated.
“Both the Belgian find and the Siberian find are domesticated species based on morphological characteristics,” said Greg Hodgins, a researcher at the University of Arizona’s Accelerator Mass Spectrometry Laboratory and co-author of the study that reports the find.
“Essentially, wolves have long thin snouts and their teeth are not crowded, and domestication results in this shortening of the snout and widening of the jaws and crowding of the teeth.”
The Altai Mountain skull is extraordinarily well preserved, said Hodgins, enabling scientists to make multiple measurements of the skull, teeth and mandibles that might not be possible on less well-preserved remains. “The argument that it is domesticated is pretty solid,” said Hodgins. “What’s interesting is that it doesn’t appear to be an ancestor of modern dogs.”
The UA’s Accelerator Mass Spectrometry Laboratory used radiocarbon dating to determine the age of the Siberian skull.
Radioactive carbon, or carbon-14, is one of three carbon isotopes. Along with naturally occurring carbon dioxide, carbon-14 reaches the surface of Earth by atmospheric circulation, where plants absorb it into their tissues through photosynthesis.
Animals and humans take in carbon-14 by ingesting plants or other animals that have eaten plants. “Carbon-14 makes it into all organic molecules,” said Hodgins. “It’s in all living things.”
“We believe that carbon-14 production is essentially constant over time,” said Hodgins. “So the amount of carbon-14 present in living organisms in the past was similar to the levels in living organisms today. When an animal or plant dies, the amount of carbon-14 in its remains drops at a predictable rate, called the radioactive half-life. The half-life of radiocarbon is 5,730 years.”
“People from all over the world send our laboratory samples of organic material that they have dug out of the ground and we measure how much carbon-14 is left in them. Based on that measurement, and knowing the radiocarbon half-life, we calculate how much time must have passed since the samples had the same amount of carbon-14 as plants and animals living today.”
The researchers use a machine called an accelerator mass spectrometer to measure the amount of radioactive carbon remaining in a sample. The machine works in a manner analogous to what happens when a beam of white light passes through a prism: White light separates into the colors of the rainbow.
The accelerator mass spectrometer generates a beam of carbon from the sample and passes it through a powerful magnet, which functions like a prism. “What emerges from it are three beams, one each of the three carbon isotopes,” said Hodgins. “The lightest carbon beam, carbon-12, bends the most, and then carbon-13 bends slightly less and carbon-14 bends slightly less than that.”
The relative intensities of the three beams represent the sample’s carbon mass spectrum. Researchers compare the mass spectrum of an unknown sample to the mass spectra of known-age controls and from this comparison, calculate the sample’s radiocarbon age.
At 33,000 years old, the Siberian skull predates a period known as the Last Glacial Maximum, or LGM, which occurred between about 26,000 and 19,000 years ago when the ice sheets of Earth’s last ice age reached their greatest extent and severely disrupted the living patterns of humans and animals alive during that time. Neither the Belgian nor the Siberian domesticated lineages appear to have survived the LGM.
However, the two skulls indicate that the domestication of dogs by humans occurred repeatedly throughout early human history at different geographical locations, which could mean that modern dogs have multiple ancestors rather than a single common ancestor.
“In terms of human history, before the last glacial maximum people were living with wolves or canid species in widely separated geographical areas of Euro-Asia, and had been living with them long enough that they were actually changing evolutionarily,” said Hodgins. “And then climate change happened, human habitation patterns changed and those relationships with those particular lineages of animals apparently didn’t survive.”
“The interesting thing is that typically we think of domestication as being cows, sheep and goats, things that produce food through meat or secondary agricultural products such as milk, cheese and wool and things like that,” said Hodgins.
“Those are different relationships than humans may have with dogs. The dogs are not necessarily providing products or meat. They are probably providing protection, companionship and perhaps helping on the hunt. And it’s really interesting that this appears to have happened first out of all human relationships with animals.”
North America’s Biggest Dinosaur Revealed
ScienceDaily (Dec. 7, 2011) — New research from Montana State University’s Museum of the Rockies and the State Museum of Pennsylvania has unveiled enormous bones from North America’s biggest dinosaur.
In a paper published Dec. 6 in Acta Palaeontologica Polonica, MSU researcher Denver W. Fowler and coauthor Robert M. Sullivan from Harrisburg, Pa., describe two gigantic vertebrae and a femur that the team collected in New Mexico from 2003 to 2006. Carrying the vertebrae alone took most of a day and was a “killer” because the paleontologists carried them 1.2 miles through 100-degree heat, Fowler said.
The bones belong to the sauropod dinosaur Alamosaurus sanjuanensis: a long-necked plant eater related to Diplodocus. The Alamosaurus roamed what is now the southwestern United States and Mexico about 69 million years ago.
“Alamosaurus has been known for some time; its remains were first described in 1922 from the Naashoibito beds of New Mexico. Since then, more bones have been discovered in New Mexico, Utah, some really nice material from Texas, and Mexico, including a few partial skeletons,” Fowler said.
The sheer size of the new bones caught the researchers by surprise, however.
“We used to think that a fully grown Alamosaurus measured around 60 feet long and weighed about 30 tons; but a 2009 study by another MSU researcher, Dr. Holly Woodward, found that a femur thought to belong to an adult was still growing,” Fowler said. “This told us that Alamosaurus got even bigger, but we didn’t imagine that it could get quite this big.”
How big? The enormity of the new bones puts Alamosaurus in the same size league as other giant sauropods from South America, including Argentinosaurus which weighed about 70 tons, and is widely considered to be the biggest dinosaur of all.
“Over the past 20 years, Argentinean and Brazilian paleontologists have been unearthing bigger and bigger dinosaurs, putting the rest of the world in the shade,” Fowler said. “However, our new finds not only show that Alamosaurus is newly recognized as the biggest dinosaur from North America, but also that it was right up there with the biggest South American species: the US is back in the fight for the No.1 spot.”
Although comparison of the new Alamosaurus bones with the South American species gave the researchers an idea of size, giant specimens of sauropods like Alamosaurus and Argentinosaurus are only known from very fragmentary remains offering only a tantalizing glimpse of what a complete Alamosaurus might look like, Fowler said.
“We’d love to find more complete material,” Fowler continued. “Fortunately, Alamosaurus bones are quite common in the Naashoibito of New Mexico, so we have a good chance of going back and finding more, but in order to dig up one of the world’s biggest dinosaurs you need one of the world’s biggest dinosaur digging teams and large digging equipment.”
The Pennsylvania State Museum field crew is typically just two or three people, so there are limits on how many bones can be collected in one season, Fowler said. Even so, many new and important specimens have been recovered over the past 10 to 15 years, including new species, and other members of the fauna including the iconic carnivore Tyrannosaurus.
“We found a shed Tyrannosaurus tooth with another Alamosaurus neck bone that we were excavating,” Fowler said. “The Tyrannosaurus may have lost its tooth while feeding on an Alamosaurus carcass.”
The Alamosaurus discovery goes beyond just “size” bragging-rights, and may have important implications for other dinosaurs, Fowler said. Recent discoveries by paleontologist Jack Horner’s paleo lab at the Museum of the Rockies have emphasized the importance of understanding growth and ontogeny in interpreting dinosaur evolution.
“Increasingly, we’re finding that very large or small individuals often look very different, and are often described as different species,” Fowler said. “Our findings show that Alamosaurus was originally described based on immature material, and this is a problem as characteristics that define a species are typically only fully gained at adult size. This means that we might be misinterpreting the relationships of Alamosaurus and possibly other sauropod dinosaurs too.”
LARGE NEST OF JUVENILE DINOSAURS, FIRST OF THEIR GENUS EVER FOUND
The findings were reported in the most recent issue of the Journal of Paleontology.
David Fastovsky, URI professor of geosciences, said the bowl-shaped nest measuring 2.3 feet in diameter was found in the Djadochta Formation at Tugrikinshire, Mongolia.
“Finding juveniles at a nest is a relatively uncommon occurrence, and I cannot think of another dinosaur specimen that preserves 15 juveniles at its nest in this way,” he said.
The analysis of the 70-million-year-old nest by Fastovsky and his colleagues found that all 15 dinosaurs — at least 10 of which are complete specimens — were about
the same size and had achieved the same state of growth and development, suggesting they represent a single clutch from a single mother. The discovery also indicates that the young dinosaurs remained in the nest through the early stages of postnatal development and were cared for by their parents.
Protoceratops grew to about 6 feet long and may have taken as long as 10 years to reach full size. Those Fastovsky found in the nest were likely less than one year old when they died.
“I suspect that the preserved animals were rapidly buried by the shifting, accumulating sands that must have constituted the bulk of sedimentation in this setting,” he said. “Death likely occurred during a desert sandstorm. My guess is that the initial and present-day dryness contributed significantly to the superb preservation, not just of Protoceratops, but of all the fossils from this unit.”
Fastovsky calls Protoceratops “a fascinating and unexpected mass of contradictions.” It is an herbivore that lived in a sand sea much like the Sahara Desert and likely bestowed significant parental care on a relatively large number of offspring, perhaps because it lived where mortality was quite high.
A wide variety of theropod dinosaurs lived in Mongolia at the time, some of which, including the notorious Velociraptor, probably ate young Protoceratops‘.
“Juvenile Protoceratops mortality may have been rather high, not only from predation but from a potentially stressful environment, and large clutches may have been a way of ensuring survival of the animals in that setting,” he said. “Nonetheless, if preservation is any indicator of abundance in life, then during the time represented by the Djadochta Formation, Protoceratops were a very common feature of Mongolian Late Cretaceous desert landscapes.”
Oldest Fossils Found
Team Claims It Has Found Oldest Fossils
By NICHOLAS WADE
Published: August 21, 2011
A team of Australian and British geologists have discovered fossilized, single-cell organisms that are 3.4 billion years old and that the scientists say are the oldest known fossils on earth.
David Wacey
Their assertion, if sustained, confirms the view that life evolved on earth surprisingly soon after the Late Heavy Bombardment, a reign of destruction in which waves of asteroids slammed into the primitive planet, heating the surface to molten rock and boiling the oceans into an incandescent mist. The bombardment, which ended around 3.85 billion years ago, would have sterilized the earth’s surface of any incipient life.
The claim is also a new volley in a long-running conflict over who has found the oldest fossil.
The new microfossils are described in Sunday’s issue of Nature Geoscience by a team led by David Wacey of the University of Western Australia and Martin D. Brasier of the University of Oxford. The fossils were found in sandstone at the base of the Strelley Pool rock formation in Western Australia.
The sandstone, 3.4 billion years ago, was a beach on one of the few islands that had started to appear above the ocean’s surface. Conditions were very different from those of today. The moon orbited far closer to earth, raising huge tides. The atmosphere was full of methane, since plants had not yet evolved to provide oxygen, and greenhouse warming from the methane had heated the oceans to the temperature of a hot bath.
It was in these conditions, the geologists believe, that organisms resembling today’s bacteria lived in the crevices between the pebbles on the beach. Examining thin slices of rock under the microscope, they have found structures that look like living cells, some in clusters that seem to show cell division.
Cell-like structures in ancient rocks can be deceiving — many have turned out to be artifacts formed by nonbiological processes. In this case, the geologists have gathered considerable circumstantial evidence that the structures they see are biological. With an advanced new technique, they have analyzed the composition of very small spots within the cell-like structures. “We can see carbon, sulfur, nitrogen and phosphorus, all within the cell walls,” Dr. Brasier said.
Crystals of fool’s gold, an iron-sulfur mineral, lie next to the microfossils and indicate that the organisms, in the absence of oxygen, fed off sulfur compounds, Dr. Brasier and his colleagues say.
Microfossils — the cell-like structures found in ancient rocks — have become a highly contentious field, both because of the pitfalls in proving that they are truly biological and because the scientific glory of having found the oldest known fossil has led to pitched battles between rival claimants.
The honor of having found the most ancient microfossil has been long been held by J. W. Schopf, a paleobiologist at the University of California, Los Angeles. In 1993, Dr. Schopf reported his discovery of fossils 3.465 billion years old in the Apex chert of the Warrawoona Group in Western Australia, about 20 miles from where the new fossils have been found. Those would be some 65 million years older than the new find, but Dr. Schopf’s claim was thrown in doubt in 2002 when Dr. Brasier attacked his finding, saying the fossils were not biological but just mineral artifacts.
With the new discovery, Dr. Brasier has dropped the second shoe, claiming to find microfossils that are or may be the oldest known, if and when Dr. Schopf’s are knocked out of the running.
The Nature Geoscience article published on Sunday does not claim discovery of the earth’s oldest microfossils. That assertion was made in a press release issued by the University of Oxford, where Dr. Brasier is a professor in the department of earth sciences.
Dr. Brasier said the article submitted to Nature Geoscience had made such a claim, but the reviewers questioned the advisability of doing so, and the senior author, Dr. Wacey, “decided to acquiesce on this particular point.”
Dr. Schopf did not respond to an e-mail seeking his comments. “Bill Schopf still very strongly defends his original claim, and is working to validate it,” said Roger Buick, an earth scientist at the University of Washington.
Dr. Buick said there was no consensus on Dr. Schopf’s microfossils, but that “the majority opinion is that they are probably not biological and probably not as old as claimed.”
The team led by Dr. Wacey and Dr. Brasier has made a “pretty good case,” Dr. Buick said, because the many different analytic techniques they have used “lend credence to the argument in a way that many other previously reported discoveries of particularly ancient microfossils have not.”
Does that mean the new microfossils are the oldest known? “If these are valid, and if we discount the Schopf microfossils, these would be the oldest known, though not by much,” Dr. Buick said.
Rocks older than 3.5 billion years have been so thoroughly cooked as to destroy all cellular structures, but chemical traces of life can still be detected. Chemicals indicative of life have been reported in rocks 3.5 billion years old in the Dresser Formation of Western Australia and, with less certainty, in rocks 3.8 billion years old in Greenland.
“This struggle to be the owner of the world’s oldest microfossils is really not the crux of the battle for understanding the early development of life anymore,” Dr. Buick said.
Andrew H. Knoll, an earth scientist at Harvard, said in a brief e-mail from a Moscow airport that the researchers had not proved their point that the fossils, when alive, fed on sulfur compounds. But he did not take sides on the dispute between Dr. Brasier and Dr. Schopf.
Dr. Buick said: “You’ve got to realize how divisive this microfossil war has been over the last decade. Most people just want it to be over. If claim and counterclaim go back and forth for a decade, it sounds like we don’t know what we’re doing.”