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Scientists say sabretooth bit like a pussycat

Smilodon jaw bite

In the eyes of the public, the sabre-toothed cat Smilodon ranks alongside Tyrannosaurus rex as the ultimate killing machine of all time. Powerfully built, with upper canines like knives, Smilodon has been portrayed as a fearsome predator of Ice-Age mammals such as mammoth, bison, and elk.

And while most scientists agree that the sabrecat was able to kill these animals thanks to its ferocious fangs, there has been plenty of debate about how it actually used them.

Now a new study, using a computer based technique called Finite Element Analysis (FEA), has tested some of the previous ideas about killing behaviour in Smilodon.

FEA is used by engineers to help design trains, planes, and cars, and allows them to digitally ‘crash test’ their designs to make sure they will work as intended. But biologists can use it to reverse engineer Nature’s designs to find out what sort of forces a structure like a sabrecat skull was able to handle.

Skulls are much more complex then most man-made structures, and to apply the technique to a fossil big cat requires some tricks engineers don’t usually have to handle, but an Australian team based at the University of Newcastle and the University of New South Wales have been working on a method to do just that and the results give scientists new insights into the behaviour of this iconic predator.

Compared to a modern day lion, the sabrecat had a relatively weak bite: for a ~230kg Smilodon the computer models predict a force of about 1000N (~100 kg) at the canines, about the same as the bite force of a 80 kg jaguar and a third of the bite force of ~250 kg lion.

In a Smilodon skull, the available area for jaw muscles is small compared to a lion, but to see if the sabrecat was somehow packing some extra bite in its cheek the team artificially increased the bite force to that of a 230 kg modern big cat.

The result: high stresses in the sabrecat’s jaw (shown as greens, yellows, reds, and white in the model), far higher than in the lion. But if the extra bite force was supplied by the neck muscles instead (so that the sabrecat was driving its whole head – including the teeth – towards the prey) then it handles the forces much better. This suggests that the neck muscles played an important role in generating bite force in Smilodon.

But the real difference between the sabrecat and a modern lion is revealed when the models are subjected to the kind of forces that result from tackling struggling prey – prey that is still on its feet. Lions do this all the time, but when the Smilodon model was exposed to these forces it lit up like a Christmas tree. If there was one thing Smilodon was not doing, it was tackling unrestrained prey.

Sabrecats were well built for wrestling large prey to the ground, and the models show that it needed to do this before trying a bite. Moreover, the killing bite was most likely applied to the prey’s throat, because it is easier to restrain the prey this way. It had to be made with care, but once the bite was done the prey was would have died almost instantly – a handy trick, when the predator needs to keep clear of angry herd-mates and hungry competitors.

A lion can take more than 10 minutes to kill a Cape buffalo – plenty of time for its mates to charge you, or the hyenas to arrive. On the other hand, lions can catch a wide range of different prey, including agile antelope and gazelle.

The sabrecat may have been a highly efficient hunter of large prey, but it was not built to catch smaller, faster animals and when the American megafauna went extinct at the end of the last Ice-Age the specialist predator went with them. This may explain why today we still have lions, tigers, and bears but no sabrecats.

Note: This story has been adapted from a news release issued by The University of Newcastle

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Inca Children Were Fattened-up Before Sacrifice, Hair Samples Show

Hair samples from naturally preserved child mummies discovered at the world’s highest archaeological site in the Andes have provided a startling insight into the lives of the children chosen for sacrifice. Researchers funded by the Wellcome Trust used DNA and stable isotope analysis to show how children as young as 6-years old were “fattened up” and taken on a pilgrimage to their death.

A team of scientists led by Dr Andrew Wilson at the University of Bradford analysed hair samples taken from the heads and from small accompanying bags of four mummies found in the Andes. These included the 15-year old “Llullaillaco Maiden” and the 7-year old “Llullaillaco Boy” whose frozen remains were found in 1999 at a shrine 25m from the summit of Mount Llullaillaco, a 6,739m volcano on the border of Argentina and Chile. The Maiden, described as a “perfect mummy” went on display for the first time last month in Salta, northwest Argentina.

Dr Wilson and colleagues studied DNA and stable light isotopes from the hair samples to offer insight into the lives of these children. Unlike samples of bone collagen and dental enamel, which give an average reading over time, hair growth allows scientists to capture a unique snapshot at different intervals over time, helping build up a picture of how the children were prepared for sacrifice over a period of months.

“By examining hair samples from these unfortunate children, a chilling story has started to emerge of how the children were ‘fattened up’ for sacrifice,” says Dr Wilson, a Wellcome Trust Bioarchaeology Fellow.

It is believed that sons and daughters of local rulers and local communities were chosen for sacrifice, possibly as a way for the ruling Incas to use fear to govern their people. Some girls, know as acllas, were selected from around the age of four and placed under the guardianship of priestesses; some would later be offered as wives to local nobles, others consecrated as priestesses and others offered as human sacrifices.

By analysing stable isotopes found in the hair samples, Dr Wilson and colleagues were able to see that for much of the time prior to sacrifice, the children were fed a diet of vegetables such as potato, suggesting that they came from a peasant background. Stable isotopes of carbon, nitrogen, oxygen and hydrogen from an individual’s diet are deposited in their hair where they can remain unchanged over thousands of years.

However, in the twelve months prior to sacrifice, the isotopic evidence shows that the Maiden’s diet changed markedly to one that was enriched with plants such as maize, considered an “elite” food, and protein, likely to have come from charki (dried llama meat).

“Given the surprising change in their diets and the symbolic cutting of their hair, it appears that various events were staged in which the status of the children was raised” says Dr Wilson. “In effect, their countdown to sacrifice had begun some considerable time prior to death.”

Changes in the isotopes in the hair sample in the final 3-4 months suggest that the children then began their pilgrimage to the mountains, likely from Cuzco, the Inca capital. Whilst scientists cannot be certain how the children died, it is believed that they were first given maize beer (chicha) and coca leaves, possibly to alleviate the symptoms of altitude sickness and also to inure them to their fate. This theory is supported by evidence of coca metabolites that the researchers found in the victims’ hair, and in particularly high concentrations in the Maiden’s.

“It looks to us as though the children were led up to the summit shrine in the culmination of a year-long rite, drugged and then left to succumb to exposure,” says co-author Dr Timothy Taylor, also of the University of Bradford. “Although some may wish to view these grim deaths within the context of indigenous belief systems, we should not forget that the Inca were imperialists too, and the treatment of such peasant children may have served to instil fear and facilitate social control over remote mountain areas.”

Previous research has shown that Llullaillaco Boy appears to have met a particularly horrific end. His clothes were covered in vomit and diarrhoea, features indicative of a state of terror. The vomit was stained red by the hallucinogenic drug achiote, traces of which were also found in his stomach and faeces. However, his death was likely caused by suffocation, his body apparently having been crushed by his textile wrapping having been drawn so tight that his ribs were crushed and his pelvis dislocated.

This research is published in the journal Proceedings of the National Academy of Sciences.

Note: This story has been adapted from a news release issued by the Wellcome Trust

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New light shines on ‘hobbit’

A visual comparison of the hobbit’s wrist bone scaled to the same size as those of a chimpanzee and a modern human. The colors indicated the articular and non-articular bone surfaces.

J.R.R. Tolkien may have talked up their hairy feet, but it is the wrists of hobbits – real hobbits, not the ones in the novelist’s Middle-earth – that interest anthropologists.

An international team of researchers has used ASU’s cutting-edge, three-dimensional imaging technology to help crack the mystery of Homo floresiensis, a 3-foot-tall, 18,000-year-old skeleton nicknamed “The Hobbit.”

The team, led by ASU alumnus Matt Tocheri of the Smithsonian Institution Human Origins Program and ASU doctoral candidate Caley Orr of ASU’s School of Human Evolution and Social Change, used techniques developed at ASU’s Partnership for Research in Spatial Modeling (PRISM) to better place the hobbit on the human family tree. The research was published in the Sept. 21 issue of the journal Science. The work at PRISM was funded by a 3DKnowledge grant from the National Science Foundation.

Four years after they were first discovered on the Indonesian island of Flores, the dozen hobbit skeletons continue to generate heated debate among researchers. Although the skeletons have skull and jaw features similar to modern humans, and the overall structure of creatures that clearly walked on two legs, researchers differ on how best to interpret them.

It is clear that hobbits are a type of hominin – a fossil relative more closely related to humans than to chimpanzees – but while some consider them the bones of a different species of early human, others think they are remnants of a closed community of modern humans with a shared genetic defect or growth disorder.

When the Flores material was first released, they named this new species Homo floresiensis based on a number of features of the cranium and the mandible (jawbone) and its very small stature,” says Orr, who also works in ASU’s Institute of Human Origins. “It had some links in terms of the cranial shape with Homo erectus, an earlier species of hominin, but it’s since been challenged by a number of groups saying, ‘Well, its possible you could explain many of these features as the result of some kind of pathology – microcephaly, and some kind of syndrome that might cause dwarfing.’

Tne approach to answering that question, and to nailing down just where in evolutionary history the hobbit belongs, is to look at the wrist bones.

Modern humans and our closest fossil relatives, the Neanderthals, have wrists that are quite different in shape from those of living apes, older fossil relatives like Australopithecus, or even the earliest members of the genus Homo.

As graduate assistants at ASU, Tocheri and Orr developed a large database of three-dimensional laser scans of primate wrist bones using PRISM. They also developed techniques for comparing the three-dimensional structures of the bones, clustering them into groups such as “great apes” or “modern humans.” Determining which group, if any, the hobbit bones belonged to was simply a matter of getting a hold of some casts of the bones in question, scanning them and comparing them to what they already had.

That is where serendipity stepped in.

While attending a lecture at the Smithsonian Institution by the chief preservationist of the hobbit bones, Tocheri was offered the opportunity to see casts of the skeleton’s wrist.

“Up until then, I had no definitive opinion regarding the hobbit debates,” Tocheri says. “But these hobbit wrist bones do not look anything like those of modern humans. They’re not even close.”

After receiving consent from the research team, Tocheri contacted Orr so that they could pool their data and make the comparison. Just as they suspected, the hobbit bones were nearly indistinguishable from those of an African ape or early hominin-like wrist – nothing at all like wrist bones found in modern humans and Neanderthals.

More importantly, the findings supported the conclusion that hobbits are indeed a branch of early human and not modern humans with some kind of pathology. According to Orr, wrist disorders, even genetic ones, cannot account for such a striking match to early hominin-like wrists.

“Because the development of the wrist bones is so early and the types of pathologies that the critics have talked about tend to occur later on in the development of an individual, it becomes very difficult for pathology to account for a wrist looking the way it does in the hobbit,” he says. “And although there are certainly pathologies that can affect the wrist, it would be highly unlikely that they would produce the anatomy that we are seeing.”

The overall skeletal features of the hobbits, combined with Tocheri and Orr’s wrist analysis, also provides valuable clues as to how long ago the hobbit split from the human family tree.

Humans and Neanderthals share a common ancestor with “modern” wrist bones dating back to about 800,000 years ago, so anthropologists can say with confidence that the hobbits predate that ancestor. Unfortunately, they cannot bracket the dates beyond that, because of a lack of wrist material from other early hominins such as Homo erectus.

Still, the finding, by providing some confirmation of the human ancestor hypothesis, could cause quite a stir in the Shire, as Tolkien might say.

“I think it will make an impact because there are a lot of people who hadn’t made up their minds about the Flores material,” Orr says. “The data are good, and they tell an interesting story that people will definitely consider in terms of making up their mind of what the Flores fossils are – whether they are a distinct species or not.”

Note: This story has been adapted from a news release issued by Arizona State University

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10 Million year old chips reveal link between fish diet and evolution

Head-on view of a stickleback with small teeth lining the mouth. The stickleback has been stained to show the skeleton.

Chips from 10 million years ago have revealed new insights into fish diets and their influence on fish evolution, according to new research featured in this week’s issue of the journal Science. The chips were found, along with scratches, on the teeth of fossil stickleback fish and reveal for the first time how changes in the way an animal feeds control its evolution over thousands of years.

This kind of study, which was funded by the Natural Environment Research Council, has previously not been possible because although fossils preserve direct evidence of evolutionary change over thousands and millions of years, working out exactly what a long-dead fossil animal was eating when it was alive, and establishing a link between feeding and evolution, is very difficult.

The stickleback tooth chips and scratches were formed 10 million years ago as part of the normal process of tooth wear while the fish were alive and feeding in a large lake in what is now Nevada. “Like footprints in sand, the wear on teeth preserves a trail of evidence of how a fish feeds and what it feeds on,” says Dr Mark Purnell from the University of Leicester, lead author on the report. “The difficult bit was learning how to read that trail.”

The research team, based at the universities of Leicester, UK, and Stony Brook, USA, captured living stickleback (of the common or garden pond variety), fed them different kinds of food in different conditions and then examined their teeth using a powerful electron microscope. The team also looked at the teeth of wild stickleback, which had been feeding naturally, from Alaskan lakes.

Professor Paul Hart, also from the University of Leicester, explains: “The teeth might be tiny, but we discovered a very clear picture. Stickleback that feed from lake bottoms have very different tooth wear from those that eat water fleas and the like which swim around in open water”. The fossil teeth have almost exactly the same wear patterns as living stickleback but they have changed through time.

Dr. Mike Bell, from Stony Brook University adds, “Stickleback are spiky little characters, with armour and spines on their sides and along their backs. We found that evolutionary changes in these characteristic features were closely linked to shifts in feeding away from the lake bottom. As feeding changed over thousands of years, the stickleback in the fossil sequence evolved to have fewer spines.”

Scientifically, this is highly significant. That feeding and diet is an important control on evolution is exactly what would be expected from evolution by natural selection, but this is the first time that this aspect of Darwin’s theory has been directly testable using fossils that record real evolutionary change over many thousands of years. “We now know that by looking at microscopic chips and scratches on fish teeth we can investigate important evolutionary questions that were previously in the realm of the unknowable” concludes Purnell.

Note: This story has been adapted from a news release issued by the University of Leicester

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New technique breaks ground on North Slope dinosaur research

This spring, researchers excavated a 20-meter tunnel into the permafrost on the banks of the Colville River to continue research on polar dinosaurs. – Photo Credit: Kevin May/UA Museum of the North

Until this year, digging for dinosaurs along the North Slope’s Colville River in Alaska meant working on a narrow beach, with steep bluffs on one side and the river’s swift, cold waters on the other.

Over the years, University of Alaska Museum of the North staff, students and volunteers collected more than 8,000 teeth and bones from the area, the most productive dinosaur-bearing area in the world’s polar regions. But most of the specimens were shattered into small pieces after being exposed to millennia of freeze-thaw cycles.

Researchers often wondered what they would find if they dug beyond the active layer of the permafrost. Would they find more intact specimens?

This year gave museum staff and collaborators a chance to test this theory and uncover new ground in dinosaur research as they worked in a 20-meter-deep tunnel dug into the side of the bluff.

The project was no small undertaking. In March, museum staff, colleagues from Australia and a mining crew spent three weeks in the frozen North excavating the tunnel. Then, they sealed the tunnel, returned home and waited for the summer field season, returning in August when conditions would be more conducive to field work. When they arrived, they had more work cut out for them: high waters from the spring melt left two feet of ice on the floor of the tunnel.

“We spent the first week just clearing the ice out of the tunnel before we could even begin to excavate the specimens,” says museum operations manager and paleontologist Kevin May, one of the principal investigators on the project. “Even after that, the work was slow going.”

In three weeks, the museum research team–May, museum earth science curatorial assistant Amanda Hansen, University of Alaska Anchorage geology professor emeritus Anne Pasch, and volunteers Kelly May and Cindy Schraer–excavated approximately 30 centimeters into the frozen ground in two plots, each a meter square. Working outside on the banks, they could have excavated a meter deep in the same amount of time.

The long hours and hard work in the freezing tunnel paid off. The team recovered more than a hundred specimens. Many of the specimens are in excellent condition, including hadrosaur teeth and bones; tyrannosaurid and troodontid teeth; and tiny vertebrae from an as-yet-unidentified dinosaur species, possibly new to Alaska. Outside the tunnel, the team also found a pachyceplalosaur jaw fragment, potentially representing a new species. The dinosaurs date to the late Cretaceous period and are approximately 70 million years old.

“This summer’s work has given us a much better sense of the size and shape of the Liscomb bed,” says May, referring to a productive dinosaur bone bed discovered in 1961 by Shell Oil Company geologist Robert Liscomb. “Before this summer, we knew the bed extended along the river bluff for about 100 meters, but we had no idea how far the deposit extended into the bluff. Now, we know that it is at least six meters wide at the tunnel site, and likely even wider. There will be plenty of work there to keep us busy for years to come.”

The museum’s work this summer was supported, in part, by a $20,000 contribution from North Slope oil producer ConocoPhillips. The donation helped fund expenses including a boat to transport crew members between the research site and the field camp, lighting for the tunnel and other supplies. ConocoPhillips also provided in-kind support including transporting an air compressor to power jackhammers used to clear the ice from the tunnel, fuel for generators and other logistical support.

In addition to the museum research team, the field crew included researchers from Australia’s Museum Victoria, independent television producer Ruth Berry and cinematographer Paul Warren. Using footage from the spring tunnel excavation, the summer field work and supplemental interviews, Berry is working on a documentary for the public television program NOVA, a production of WGBH-Boston, as well as a documentary for the Australian Broadcasting Company. The productions have the potential to bring international attention to the museum’s North Slope dinosaur research.

Note: This story has been adapted from a news release issued by the University of Alaska, Fairbanks