Amazing Science

Most species of gigantic animals that once roamed Australia had disappeared by the time people arrived, a major review of the available evidence has concluded.

 

The research challenges the claim that humans were primarily responsible for the demise of the megafauna in a proposed "extinction window" between 40,000 and 50,000 years ago, and points the finger instead at climate change.

 

An international team led by the University of New South Wales, and including researchers at the University of Queensland, the University of New England, and the University of Washington, carried out the study. It is published in the Proceedings of the National Academy of Sciences.

 

"The interpretation that humans drove the extinction rests on assumptions that increasingly have been shown to be incorrect. Humans may have played some role in the loss of those species that were still surviving when people arrived about 45,000 to 50,000 years ago -- but this also needs to be demonstrated," said Associate Professor Stephen Wroe, from UNSW, the lead author of the study.

 

"There has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big-game hunting," he said.

 

About 90 giant animal species once inhabited the continent of Sahul, which included mainland Australia, New Guinea and Tasmania.

 

"These leviathans included the largest marsupial that ever lived -- the rhinoceros-sized Diprotodon - and short-faced kangaroos so big we can't even be sure they could hop. Preying on them were goannas the size of large saltwater crocodiles with toxic saliva and bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth," said Associate Professor Wroe.

 

The review concludes there is only firm evidence for about 8 to 14 megafauna species still existing when Aboriginal people arrived. About 50 species, for example, are absent from the fossil record of the past 130,000 years.

“Living” molecules, meaning intact cellular structures that haven’t fossilized, were recently retrieved from 350-million-year-old remains of aquatic sea creatures uncovered in Ohio, Indiana, and Iowa, according to a study that will appear in the March issue of the journal Geology.

 

The animals- crinoids- were spindly and had feathered arms. Their relatives today are called by the plant-like name “sea lily.”

 

The retrieved molecules are quinones, which function as pigments or toxins (to help ward off predators) and are still found in modern sea lilies. The molecules aren’t DNA, unfortunately, but they can reveal other things about past life, such as the color of long gone animals.

 

“There are lots of fragmented biological molecules — we call them biomarkers — scattered in the rock everywhere,” William Ausich, professor in the School of Earth Sciences at Ohio State and co-author of the paper, said in a press release. “They’re the remains of ancient plant and animal life, all broken up and mixed together. But this is the oldest example where anyone has found biomarkers inside a particular complete fossil. We can say with confidence that these organic molecules came from the individual animals whose remains we tested.”

 

The ultra ancient crinoids appear to have been buried alive in storms during the Carboniferous Period. At that time, North America was covered with vast inland seas. The skeletal remains of the buried-alive crinoids filled with minerals over time, but some of the pores containing organic molecules were miraculously sealed intact.

It's been more than 30 years since UC Berkeley researchers first suggested that the extinction of the dinosaurs was probably linked to a massive comet or asteroid impact, known as Chicxulub, off the Yucatan coast. The idea was that the collision from space, which left a 110-mile-wide crater off the coast of Mexico, would have cast off debris that wrapped all the way around Earth, altering the climate and resulting in the global extinction.

 

But that story hasn't passed muster everywhere. Because different methods of estimating when the extinction and the impact occurred have yielded different answers -- some studies concluded that the asteroid hit as much as 300,000 years before dinosaurs went extinct -- some people have argued that other circumstances, including volcanic eruptions or climate change, must have had more to do with the dinosaurs' end than a whopper of an asteroid.

Now, using highly refined methods of determining the ages of rocks, another team from Berkeley has demonstrated that the extinction and the impact occurred at almost exactly the same time: just over 66 million years ago. 

 

"The impact was clearly the final straw that pushed the Earth past the tipping point," said study lead author and UC Berkeley earth scientist Paul Renne, in a statement. "We have shown that these events are synchronous to within a gnat's eyebrow."

 

To arrive at the more accurate dates, Renne and his team looked at isotopes of argon in rocks created by the Chicxulub impact, known as tektites, found in Haiti.  The scientists also used the dating technique to assign an age to altered volcanic ash deposits from the Hell Creek Formation in Montana that are known to coincide with the boundary between the Cretaceous period, when dinosaurs like Tyrannosaurus rexand Velociraptor still roamed Earth, and the Paleogene period, when they disappeared.

 

The results showed that the impact and the extinctions happened at essentially the same time, within the range of uncertainty in the measurements.  The scientists suggested that brief cold snaps in the late Cretaceous period had already put stress on "a global ecosystem that was well adapted to the long-lived preceding Cretaceous hothouse climate." The asteroid pushed the ecosystem over the edge, they said.

Asteroids 2, dinosaurs 0. The infamous space rock that slammed into Earth and helped wipe it clean of large dinosaurs may have been a binary – two asteroids orbiting each other.

 

The dino-killing asteroid is usually thought of as a single rock with a diameter of 7 to 10 kilometres, but it may really have been two widely separated rocks with that combined diameter.

 

The surprise conclusion comes from a re-evaluation of the proportion of asteroid craters on Earth that were formed from binary impacts. It could also spell bad news for those hoping to protect our world from catastrophic collisions in future.

 

Earth bears the scars of twin-asteroid impacts: the Clearwater Lakes near Hudson Bay in Canada, for instance, are really twin craters that formed about 290 million years ago. Examples like Clearwater are rare, though. Just 1 in 50 of craters on Earth come in such pairs.

 

That is a puzzle because counts of the rocks zooming around in the vicinity of Earth suggest binaries are far more common. "It's been known for 15 years that about 15 per cent of near-Earth asteroids are binary," says Katarina Miljković at the Institute of Earth Physics in Paris, France. All else being equal, 15 per cent of Earth's impact craters should be the result of twin impacts. Why does the real figure appear so much lower?

 

Miljković and her colleagues have found an explanation. They ran computer simulations of binary asteroids hitting Earth and found that they often form a single crater.

 

This makes sense, given that a crater can be 10 times the diameter of the asteroid that made it. The team found that only unusual cases involving two small, widely separated asteroids are guaranteed to form a pair of distinct craters. The researchers' simulations confirmed that such binary asteroids are rare enough to explain why paired craters account for only 2 per cent of all Earth's craters.

 

An obvious implication is that binary asteroids hit Earth more often than the crater record appears to suggest – with ramifications for efforts to prevent future impacts.

Many fossils are tinted with color, but few have had their pigments chemically analyzed. Now, researchers are reporting the oldest pigment molecules extracted from fossils of a known organism—namely, approximately 340 million-year-old fossils of marine animals called crinoids, which are related to sea cucumbers, starfish, and urchins.

 

The techniques used to measure the pigments could be easily applied to other tinted fossils, says Christina E. O’Malley, who did the analysis with paleontologist William I. Ausich and chemist Yu-Ping Chin, all of Ohio State University. In addition to reconstructing the color palette of ancient organisms, O’Malley hopes that organic molecules preserved in ancient fossils could help unravel phylogenetic relationships among fossilized and contemporary organisms.

 

Crinoid fossils can vary in color from white to brown and reddish purple, O’Malley says. After taking about a gram of sample from fossils of three crinoid species, Barycrinus rhombiferus, Cyathrocrinites iowensis, and Elegantocrinus hemiohaericus, the team identified a complex mixture of pigments that corresponded to aromatic or polyaromatic quinones.

 

This is not the first time researchers have identified pigment residues on fossils, although it is an emerging field. For example, in 2011, paleochemists identified the feather color of ancient winged dinosaurs from 120 million-year-old fossils, some 220 million years younger than the crinoid fossils.

A new DNA analysis method reveals how ancient skeletons would have looked in the flesh and even predicts hair and eye color.

For years, when museums, textbooks or other outlets attempted to illustrate what a particular ancient human skeleton would have looked like in the flesh, their method was admittedly unscientific—they basically had to make an educated guess.

 

Now, though, a group of researchers from Poland and the Netherlands has provided a remarkable new option, described in an article they published in the journal Investigative Genetics on Sunday. By adapting DNA analysis methods originally developed for forensic investigations, they’ve been able to determine the hair and eye color of humans who lived as long as 800 years ago.

 

The team’s method examines 24 locations in the human genome that vary between individuals and play a role in determining hair and eye color. Although this DNA degrades over time, the system is sensitive enough to generate this information from genetic samples—taken either from teeth or bones—that are several centuries old (although the most degraded samples can provide information for eye color only).

 

As a proof of concept, the team performed the analysis for a number of people whose eye and hair color we already know. Among others, they tested the DNA of Władysław Sikorski, a former Prime Minister of Poland who died in a 1943 plane crash, and determined that Sikorski had blue eyes and blonde hair, which correctly matches color photographs.

 

For example, in the paper, the researchers analyzed the hair and eye color for a female skeleton buried in the crypt of a Benedictine Abbey near Kraków, Poland, sometime between the 12th and 14th centuries. The skeleton had been of interest to archaeologists for some time, since male monks were typically the only people buried in the crypt. The team’s analysis showed that she had brown eyes and dark blond or brown hair.

 

The team is not sure yet just how old a skeleton has to be for its DNA to be degraded beyond use—the woman buried in the crypt was the oldest one tested—so it’s conceivable that it might even work for individuals who’ve been in the ground for more than a millenium. The researchers suggest this sort of analysis could soon become part of a standard anthropological toolkit for evaluating human remains.

It’s relatively easy for scientists to see the signature of droughts and other climate events in the prehistoric past by digging into underground or seafloor sediments, or drilling into ancient ice. In order to say exactly when these events happened, though, you need a reliable natural dating method, and even the best of these is flawed.

 

However, one of the most familiar of these timelines, known as radiocarbon dating, just got a lot more precise. According to a paper published in the journal Science, measurements from the bottom of Japan’s Lake Suigetsu have allowed scientists to improve the technique dramatically.

 

Now, thanks to those lake sediments, scientists can narrow that range down to just 10 years or less -- but only if the sample is between 11,000 and 53,000 years old. Younger and there hasn't been enough breakdown in the radioactive carbon. Older, and the lake's sediments don't go back that far.

This impressive achievement comes thanks to Lake Suigetsu’s calm waters, and also from the lucky fact that the plant matter that drifts into the water and sinks to the bottom is light-colored in winter and dark in summer. The result: alternating layers under the lake bottom that make it easy to identify every year, one after the other, going well back into the last Ice Age.

The strongest and biggest bird of prey that ever lived was the Haast’s Eagle (Harpagornis moorei) of New Zealand, and it became extinct around the 1400s soon after the Maori settled the South Island of New Zealand.

 

H. moorei was powerful enough to attack and prey on giant flightless birds, the moa, weighing 10 to 15 times their own body weight. Comparatively to its body size, the Haast’s Eagle’s wingspan was short, at about 9 feet. It’s believed that the raptor would swoop down at speeds of nearly 50 mph to attack the moa. It used its talons to kill them on the ground and didn’t carry off its prey.

 

It’s believed that the Haast’s Eagle and moa evolved due to island gigantism, a phenomenon in which animals isolated from other, more diverse populations, end up much larger than they would be on mainland. When the Maori first arrived in New Zealand, there were no land animals. Birds and reptiles evolved to fill up these empty ecological niches that would have been typically filled up by larger mammals.

 

Evolutionarily speaking, Haast’s Eagle took the place of the apex predator that hunted grazers, a space taken up by the moa species. When the Maori hunted the moa to extinction in the 1400s, barely a century after their arrival, there was no prey large enough to sustain the Haast’s Eagles, so they became extinct quickly. No evidence has been found that Haast’s Eagle preyed on humans, but researchers believe it was big and strong enough to do so.

Each winter rainwater from the land above made its way through the cave's ceiling and dripped onto the floor. As each layer of the stalagmite formed, oxygen and carbon isotopes within these raindrops were captured and preserved inside the rock. Now, thousands of years later, a team led by Oxford University scientists is using the data locked inside this stalagmite to get a glimpse of the ancient winter climate of Western North America. 

 

The team's results show that in recent prehistory the region has seen rapid shifts between dry and warm and wet and cold periods. The findings hint at the importance of the Pacific Decadal Oscillation – a pattern of climate variability that changes every 50-70 years – to this area.

 

'We picked Oregon because it's around this latitude where winter storms hit the West coast of North America, it is representative for an area stretching from California to British Columbia,' Vasile Ersek of Oxford University's Department of Earth Sciences, lead author of the report, told me. Water resources in the region are highly dependent on winter rainfall, without the winter rains the land is arid. 

 

'Most other ways of estimating past climate, like tree ring data, only tell us about summers, when plants are growing,' Vasile explains. 'This work gives us a unique insight into winter climate over thousands of years with an unprecedented combination of length, detail and dating accuracy. 'Moreover, because the cave is only around 70 km from the Pacific Ocean, and directly affected by processes occurring over the ocean, it also represents a record of past climate variability in the Eastern Pacific where detailed records of past climate are otherwise very hard to obtain.'

 

The stalagmite record suggests that there have been important variations in both rainfall and temperature (c.1 degree Celsius) over the last 13,000 years – with the region's climate switching between extreme dry-warm and wet-cold periods within just a few decades. But those hoping that this cave rock might tell us about man's influence on the climate will be disappointed; after bearing witness to so many winters its record-keeping stopped before the industrial age began.

Modern day birds may simply be dinosaurs that never grew up druing development, researchers say.

 

Evolutionary biologist Arkhat Abzhanov of Harvard University noted an apparent resemblance between the skulls of juvenile dinosaurs and adult birds and decided to do a more comprehensive study. With graduate student Bhart-Anjan Bhullar, he used CT scanners to examine dozens of skulls, including modern birds, theropods -- the dinosaurs most closely related to birds -- and earlier dinosaur species. By identifying various landmarks on the skulls, they were able to track how the skull shapes had changed over the years.

 

"We examined skulls form the entire lineage that gave rise to modern birds," Abzhanov said. "We looked back approximately 250 million years, to the Archosaurs, the group which gave rise to crocodiles and alligators as well as modern birds. Our goal was to look at these skulls to see how they changed, and try to understand exactly what happened during the evolution of the bird skull."

 

What they found was surprising. Early dinosaurs underwent vast morphological changes as they aged. Among other things, their snouts grew longer and their heads grew flatter. The skulls of juvenile and adult birds, in contrast, are remarkably similar. They concluded that the evolutionary changes that produced birds were a phenomenon known as paedomorphosis. "We can see that the adults of a species look increasingly like the juveniles of their ancestors," Abzhanov said. In the case of birds, he added, the phenomenon is caused by a process called progenesis, in which the descendants reach sexual maturity earlier. Birds can take as little as 12 weeks to reach maturity, while dinosaurs required months or years. Concluded Abzhanov: "When we look at birds, we are actually looking at juvenile dinosaurs."

The Great Oxidation Event occured around 2.3 billion years ago, when it was no longer possible for newly created oxygen to be captured in chemical compounds. Instead, it started to accumulate as oxygen in the oceans and in the atmosphere. Before this event, in the Earth's early atmosphere, there were only traces of free oxygen. All life was based exclusively on anaerobic processes - chemical reactions that did not require oxygen. With the emergence of cyanobacteria that oxidized water with the help of light and produced oxygen as a by-product, the conditions for life on Earth gradually began to transform.

 

New research by scientists at the University of Bristol and Boston University suggests that the evolution of multicellularity coincided with increased diversification of cyanobacteria and the Great Oxidation Event. Cyanobacteria are among the most diverse prokaryotic phyla, with morphotypes ranging from unicellular to multicellular filamentous forms, including those able to irreversibly differentiate in form and function. It has been suggested that cyanobacteria raised oxygen levels in the atmosphere around 2.45–2.32 billion years ago during the Great Oxidation Event and dramatically changing life on the planet. 

However, little is known about the possible interplay between the origin of multicellularity, diversification of cyanobacteria, and the rise of atmospheric oxygen. The team tested whether the evolution of multicellularity overlapped with the Great Oxidation, and whether multicellularity is associated with significant shifts in diversification rates in cyanobacteria.

 

The results indicate an origin of cyanobacteria before the rise of atmospheric oxygen. The evolution of multicellular forms coincided with the onset of the Great Oxidation Event and an increase in diversification rates, suggesting that multicellularity could have played a key role in triggering cyanobacterial evolution. In prior studies, geochemists challenged the simple notion of an up-only trend for early oxygen and provided the first compelling direct evidence for a major drop in oxygen after The Great Oxidation event some, which was critical for the origin and evolution of the first forms of eukaryotic life. The second big step in the up-only hypothesis occurred almost two billion years later, coinciding with the first appearances and earliest diversification of animals.

Mesolithic hunter-gatherers living on a meat-dominated, grain-free diet had much healthier mouths that we have today, with almost no cavities and gum disease-associated bacteria, a genetic study of ancient dental plaque has revealed.

 

An international team of researchers, led by a group at the Australian Centre for Ancient DNA, University of Adelaide, extracted DNA from dental plaque from 34 prehistoric northern European human skeletons, and traced the changes in the nature of oral bacteria from the last hunter-gatherers to Neolithic and medieval farmers and modern individuals.

 

"Dental plaque represents the only easily accessible source of preserved human bacteria," says lead author Dr Christina Adler, now associate lecturer in dentistry at the University of Sydney.

 

The researchers found the composition of bacteria changed with the introduction of farming and again 150 years ago during the Industrial Revolution.

 

In contrast to the hunter-gatherer and early agriculturist diet, a modern diet full of refined carbohydrates and sugars has given us mouths dominated by cavity-causing bacteria.

 

"What we found was that the early [hunter-gatherer] groups really had a lot lower frequencies of any of the disease-associated bacteria compared to what you see today [and] that the number of species per person's mouth, or the diversity, was much higher in the past," says Adler.

 

However, while the researchers noted that bacteria associated with dental cavities such as S. mutans became dominant around the time of the Industrial Revolution, the frequency of bacteria associated with periodontal diseases such as gingivitis has not changed much since farming began.

 

This may have implications for the notion that gum disease and associated bacteria are a significant contributor to the recent increase in conditions such as cardiovascular disease and atherosclerotic plaques, says co-author Professor Alan Cooper, director of the Australian Centre for Ancient DNA.

 

"It has been suggested that the presence of this permanent inflammation state along the gums was promoting an immune inflammatory response, which in turn leads to cardiovascular disease," says Cooper.

 

"The idea was that a recent increase in the bacteria P. gingivalis [which causes gingivitis], was associated with the recent increases in cardiovascular disease, however we could show that this particular species has been fairly stable throughout the farming period."

 

The results will no doubt be good news for advocates of the so-called 'paleolithic diet' - high in meat, low in grains. Cooper says it would be interesting to study the effects of the diet on the bacterial population of the mouths, particularly after reseeding with healthy bacteria.

Scientists using a "more reliable" form of radiocarbon dating have re-assessed fossils from the region and found them to be far older than anyone thought. The work appears in the journal PNAS.

 

Its results have implications for when and where we - modern humans - might have co-existed with our evolutionary "cousins", the Neanderthals.

 

"The picture emerging is of an overlapping period [in Europe] that could be of the order of perhaps 3,000-4,000 years - a period over which we have a mosaic of modern humans being present and then Neanderthals slowly ebbing away, and finally becoming extinct," explained co-author Prof Thomas Higham from the Oxford Radiocarbon Accelerator Unit at the University of Oxford, UK.

 

"What our research contributes is that in southern Spain, Neanderthals don't hang on for another 4,000 years compared with the rest of Europe. And the hunch must be that they go extinct in the south of Spain at the same time as everywhere else," he told BBC News.

 

Though once thought to have been our ancestors, the Neanderthals are now considered an evolutionary dead end.

 

They first appear in the fossil record hundreds of thousand of years ago and, at their peak, dominated a wide range, spanning Britain and Iberia in the west to Israel in the south and Uzbekistan in the east. Our own species, Homo sapiens, evolved in Africa, and displaced the Neanderthals after entering Europe somewhere around the 45,000-year mark.

 

No-one can say for sure what, if any, active role modern humans had in the decline of Europe's Neanderthals.

 

What is clear though is that some mixing must have occurred somewhere at some point. This is evident from DNA studies that prove Neanderthals made a small but significant contribution to the genetics of many modern humans.

However, scientists think this interbreeding could have occurred outside Europe, in the eastern Mediterranean or Middle East region (the area archaeologists call the "Levant"), and quite probably even deeper in time - some 80,000-90,000 years or so ago.

Researchers believe that ancient archaea, similar in shape to this Halobacteria, used aerobic respiration 2.9 billion years ago to produce an active form of vitamin B6

 

Billions of years ago, a tiny, single-celled organism started using oxygen. It is not exactly known when this happened, or why, but a team of scientists has come closer than ever before to finding that out. They have identified the earliest known example of an aerobic metabolism, the process of using oxygen as fuel. The discovery may even provide clues as to where the oxygen came from in the first place.

 

To travel so far back in time, evolutionary bioinformaticist Gustavo Caetano-Anollés of the University of Illinois, Urbana-Champaign, along with colleagues in China and South Korea, did a bit of molecular sleuthing. They scoured published genomes from all groups of organisms-although they didn't include viruses in this study-focusing on pieces of proteins known as domains. These pieces have their own distinguishing shapes that provide clues to the protein's function and can be categorized based on various characteristics. Just like a Victorian house has certain features that set it apart from a Tudor mansion, researchers can tell the difference between different domains based on their shape.

 

The team produced a kind of molecular clock by establishing an evolutionary sequence for single-domain proteins. Caetano-Anollés and his colleagues could then tie that sequence to the geologic timeline. By correlating the appearance of domains integral to events such as the rise of eukaryotes, organisms with membrane-bound cellular structures, they could determine an approximate date for the origin of particular domains. "Molecular clocks aren't perfect," Caetano-Anollés acknowledges. "And sometimes they misbehave. But the [domains] that we sampled that were linked to clear-cut events had good agreement."

 

The researchers found that the most ancient aerobic process was the production of pyridoxal, or the active form of vitamin B6, they report today in Structure. This reaction appeared about 2.9 billion years ago, along with an oxygen-producing enzyme called manganese catalase. This enzyme detoxifies hydrogen peroxide by breaking it down into water and oxygen. Caetano-Anollés hypothesizes that early organisms got the oxygen they needed to produce vitamin B6 from this breakup of hydrogen peroxide. The authors argue that these ancient organisms would have encountered massive amounts of hydrogen peroxide in their environment due to the bombardment of glacial ice by ultraviolet radiation, which can generate the compound.

Taking into consideration its size, an ancient relative of piranhas weighing about 20 pounds delivered a bite with a force more fierce than prehistoric whale-eating sharks, the four-ton ocean-dwelling Dunkleosteus terrelli and – even – Tyrannosaurus rex.

 

The bite force of Megapiranha, which lived 10 million years ago, was extrapolated from the first field measurements of the biting force of Earth’s largest piranha today, Serrasalmus rhombeus or black piranha. One 2 ½ pound fish delivered a bite with a force of 320 newtons, or about 72 pounds, which is 30 times its body weight. The force is nearly three times greater than the bite force of an equivalent size American alligator.

 

Based on the 2 ½ pound piranha and other specimens tested in the wild,  the scientists calculate that Megapiranha paranensis, which weighed approximately 22 pounds, could have had a bite force anywhere from 1,240 to 4,750 newtons  – or 280 to 1,070 pounds – and possibly more.

 

Other scientists have previously estimated that T. rex slammed its jaws shut with 13,400 newtons, or 3,000 pounds of force, but that’s nowhere near 30 times its body weight.

 

Pound for pound, Megapiranha and black piranha have the most powerful bites among carnivorous fishes, living or extinct, the paper said. “For its relatively diminutive size, Megapiranha paranensis’ bite dwarfs other extinct mega-predators” including the enormous whale-eating Carcharodon megalodon and the monstrous Dunkleosteus terrelli, a four-ton armored fish.

While most of its relatives perished with the dinosaurs, a molelike mammal nicknamed the "grave robber" survived the event that killed the dinosaurs, new research finds. Necrolestes patagonensis, whose name translates in part to "grave robber," was among the mammals that lived through thedinosaur mass extinction. The new study finds that the creature lived 45 million years longer than paleontologists realized.

 

Necrolestes was first discovered in fossil form in the Patagonia region of South America in 1891, but little was known about the animal, study researcher John Wible, a mammalogist at the Carnegie Museum of Natural History, said in a statement. Necrolestes' subterranean lifestyle may explain its lucky fate, the researchers reported Monday (Nov. 19) in the journal Proceedings of the National Academy of Sciences.

 

"There's no other mammal in the Tertiary of South America that even approaches its ability to dig, tunnel, and live in the ground," Wible said. "It must have been on the edges, in an ecological niche that allowed it to survive."

Research at the University of Liverpool, using computer models to reconstruct the jaw muscle ofTyrannosaurus rex, has suggested that the dinosaur had the most powerful bite of any living or extinct terrestrial animal. The Liverpool scientists developed a computer model to reverse engineer the animal's bite, a method that has previously been used to predict dinosaur running speeds.

 

An animal's bite force is largely determined by the size of the jaw muscles. Using their computer models, researchers tested a range of alternative muscle values, as it is not precisely known what the muscles of dinosaurs were like. Even with error margins factored in, the computer model still showed that the T. rex had a more powerful bite than previously suggested.

The smallest values predicted were around 20,000 Newtons, while the largest values were as high as 57,000 Newtons, which would be equivalent to the force of a medium sized elephant sitting down on the ground.

The Cretaceous Period of Earth history ended with a mass extinction that wiped out numerous species, most famously the dinosaurs. A new study now finds that the structure of North American ecosystems made the extinction worse than it might have been. The mountain-sized asteroid that left the now-buried Chicxulub impact crater on the coast of Mexico's Yucatan Peninsula is almost certainly the ultimate cause of the end-Cretaceous mass extinction, which occurred 65 million years ago. Nevertheless, "Our study suggests that the severity of the mass extinction in North America was greater because of the ecological structure of communities at the time.

 

 Peter Roopnarine of the California Academy of Sciences and Kenneth Angielczyk of the Field Museum, reconstructed terrestrial food webs for 17 Cretaceous ecological communities. Seven of these food webs existed within two million years of the Chicxulub impact and 10 came from the preceding 13 million years. The findings are based on a computer model showing how disturbances spread through the food web. Roopnarine developed the simulation to predict how many animal species would become extinct from a plant die-off, a likely consequence of the impact. "Besides shedding light on this ancient extinction, our findings imply that seemingly innocuous changes to ecosystems caused by humans might reduce the ecosystems' abilities to withstand unexpected disturbances," Roopnarine said.

 

The team's computer model describes all plausible diets for the animals under study. In one run, Tyrannosaurus might eat only Triceratops, while in another it eats only duck-billed dinosaurs, and in a third it might eat a more varied diet. This stems from the uncertainty regarding exactly what Cretaceous animals ate, but this uncertainty actually worked to the study's benefit.