IN THE LAST DAYS OF SABRE-TOOTH CAT

Sabre-tooth cat skull

Sabre-tooth cats, one of the most fearsome cats of all time, rule the land of the North America in the ice age. They are the top predator of the land of North America in the Ice Age. Huge preys like the Bison, horses are the main prey of the Sabre-Tooth Cat. The normal temperature of the North America never exceeded more than 40 degree in the complete Ice age era. In that time most probably the land of North America is not like this. Most probably the places are not dry and there exist huge forests with big trees and grasslands. This forest and the grasslands create huge covers for the Sabre-Tooth Cats to hunt. If we see the bone structure of the Sabre-Tooth Cat, we find that, the sabre-tooth cats are much heavier than other big cats of today. This indicates they are much slower than today’s cat. So they must be much more dependent on their sneak attack. So the covers from the grasslands and the forests with huge trees are very much in favour of them – That makes the Sabre-tooth cat the top predator of the entire North America in the ice age.

Now we are entering 10,000 years ago from today. The time is changing. It is the End of the Ice age era. The climate is changing rapidly. The ice is melting rapidly. The forestland with huge trees and grasslands become the place of much drier open field with short grasses. That is making the most of the herbivorous megafauna migrate. But surprisingly one megafauna is looking like very much adoptable with this environmental change – It is the Bison. And actually in this new environmental condition the bison are more comfortable and their population increases in those open field.

Imaginary body of the Sabre-tooth cat

After ruling the North America, now suddenly the Sabre-tooth is losing its grip in the wild. In fact they are decreasing rapidly. In the time of the ice age the maximum temperature never crossed 40 degree, but now the temperature is much higher, the lands become drier; the big land forests and the grasslands are gone. These cause a huge problem to the sabre-tooth cat to hunt. We know the sabre-tooth cats hunting completely depends on the fact that how much they are capable of being camouflaged. Since all the big tree forests and grasslands are now gone and they are replaced by the open fields, Sabre-tooth cats are losing their chance of being unseen. We can simply say the climate is betraying the Sabre-tooth cats in these days. Also the numbers of the Bison population increasing now – This gives the bison herds a lot of more pairs of eyes to watch their backs. So they can see the cat from a long distance and can run away. Sabre-tooth cat figure is not built to chase down a prey and hunt it down, as they are much slower than modern world cheetah, lions, tigers etc.

This new world makes the Sabre-tooth cats food less. They started to decrease from the world only because of the food. In their last days, the sabre-tooth cats lived a life where they can see their prey standing not too far from them but still out of their reach.

The last sabre-tooth cat – a female cat, most probably has two kids. She tried to hunt bison for many times but failed every time. Then she abandoned its kids and travelled long for food. It finally reaches the La Brea Tar Pit and sees some dead or trapped animals. She entered the tar pit and got trapped in the tar and died there.

The Last Sabre-Tooth Cat died like this and The Sabre-Tooth Cat extinct from the world.

Diverse gene pool critical for tigers' survival, say experts

New research by Stanford scholars shows that increasing genetic diversity among the 3,000 or so tigers left on the planet is the key to their survival as a species.

Iconic symbols of power and beauty, wild tigers may roam only in stories someday soon. Their historical range has been reduced by more than 90 percent. But conservation plans that focus only on increasing numbers and preserving distinct subspecies ignore genetic diversity, according to the study. In fact, under that approach, the tiger could vanish entirely.

"Numbers don't tell the entire story," said study co-author Elizabeth Hadly, the Paul S. and Billie Achilles Professor in Environmental Biology at Stanford and senior fellow at the Stanford Woods Institute for the Environment. She is a co-author of the study, which was published April 17 in the Journal of Heredity.

That research shows that the more gene flow there is among tiger populations, the more genetic diversity is maintained and the higher the chances of species survival become. In fact, it might be possible to maintain tiger populations that preserve about 90 percent of genetic diversity.

Rachael Bay, a graduate student in biology at Stanford's Hopkins Marine Station and the lead author of the study, said, "Genetic diversity is the basis for adaptation."

Loss of diversity

The research focused on the Indian subcontinent, home to about 65 percent of the world's wild tigers. The scientists found that as populations become more fragmented and the pools of each tiger subspecies shrink, so does genetic diversity. This loss of diversity can lead to lower reproduction rates, faster spread of disease and more cardiac defects, among other problems.

The researchers used a novel framework, based on a method previously employed to analyze ancient DNA samples, to predict what population size would be necessary to maintain current genetic diversity of tigers into the future. The authors believe this new approach could help in managing populations of other threatened species.

The results showed that for tiger populations to maintain their current genetic diversity 150 years from now, the tiger population would have to expand to about 98,000 individuals if gene flow across species were delayed 25 years. By comparison, the population would need to grow to about 60,000 if gene flow were achieved immediately.

Neither of these numbers is realistic, considering the limited size of protected tiger habitat and availability of prey, among other factors, according to the researchers.

Limited habitat

"Since genetic variability is the raw material for future evolution, our results suggest that without interbreeding subpopulations of tigers, the genetic future for tigers is not viable," said co-author Uma Ramakrishnan, a former Stanford postdoctoral scholar in biology and current researcher at the National Centre for Biological Sciences in Bangalore, India.

Because migration and interbreeding among subspecies appear to be "much more important" for maintaining genetic diversity than increasing population numbers, the researchers recommend focusing conservation efforts on creating ways for tigers to travel longer distances, such as wildlife corridors, and potentially crossbreeding wild and captive tiger subspecies.

"This is very much counter to the ideas that many managers and countries have now - that tigers in zoos are almost useless and that interbreeding tigers from multiple countries is akin to genetic pollution," said Hadly. "In this case, survival of the species matters more than does survival of the exclusive traits of individual populations."

Understanding these factors can help decision-makers better address how development affects populations of tigers and other animals, the study noted.

Conservation efforts for other top predators have shown the importance of considering genetic diversity and connectivity among populations, according to the report. One example is Florida panthers: since individuals from a closely related panther subspecies were introduced to the population, Florida panthers have seen a modest rise in numbers and fewer cases of genetic disorders and poor fitness.

Almost seven million birds perish at communication towers in North America each year

Every year nearly 7 million birds die as they migrate from the United States and Canada to Central and South America, according to a new USC study published on April 25 in the journal PLoS ONE.

The birds are killed by the 84,000 communication towers that dot North America and can rise nearly 2,000 feet into the sky, according to the authors of "An Estimate of Avian Mortality at Communication Towers in the United States and Canada."

Placing that figure in context, the Exxon Valdez oil spill killed 250,000 birds and the Empire State building is 1,250 feet high.

"This is a tragedy that does not have to be," said lead author Travis Longcore, associate professor in the USC Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences.

The taller the tower the greater the threat, the study found. The 1,000 or so towers above 900 feet accounted for only 1.6 percent of the total number of towers. Yet these skyscraper towers killed 70 percent of the birds, about 4.5 million a year, Longcore said.

Most of the birds spent winter in places like the Bahamas and summer in Canada. With names like the Common Yellowthroat and the Tennessee Warbler, they could fit in the palm of one's hand.

"These birds eat insects and keep our forests healthy," Longcore said. "They are quite beautiful. We have a long history of appreciating birds. Millions of people watch birds."

However, the birds are not generally killed by running into the tower itself but the dozens of cables, known as guy wires, that prop up the thin, freestanding structure, Longcore said.

During bad weather, the birds were pushed down by cloud cover and flew at lower altitudes. The clouds also removed navigation cues, such as stars, leaving only the blinking or static red lights of towers.

The blinking did not fool the birds, but towers with a static red light resulted in more dead birds.

Estimated annual avian mortality from communication towers by Bird Conservation Region. High mortality estimates in Peninsular Florida and Southeastern Coastal Plain reflect the more numerous and taller communication towers in these regions.

"In the presence of the solid red lights, the birds are unable to get out of their spell," Longcore said. "They circle the tower and run into the big cables holding it up."

Longcore estimated that changing the steady-burning lights on the 4,500 towers greater than 490 feet tall (about 6 percent of the total) could reduce mortality about 45 percent, or about 2.5 million birds. The study also recommended that businesses share towers to reduce their number and build more freestanding towers to reduce the need for guy wires.

In 2005, Longcore and his colleagues started collecting and analyzing data from field studies that counted the number of bird kills at communication towers across the United States. The team only used findings that documented bird kills for at least a year and in some cases for several decades.

The numbers were scrutinized to find the average bird mortality based on height, the guy wires and the types of lights affixed to the tower.

The team then matched up tower types, sizes and attributes of 38 tower studies, applying those findings to the 84,000 towers across Canada and the United States in preparation for the new publication, which also was submitted to the Federal Communications Commission.

"One of the things this country has been great about is saying we care about not losing species on our watch," Longcore said. "With these towers, we are killing birds in an unnatural way. This is senseless."

The study, which does not include shorter towers that typically are used for mobile telephone transmission, focused on towers taller than 180 feet, which typically provide TV and radio frequencies.

The study's authors included Catherine Rich and Beau MacDonald of The Urban Wildlands Group, Pierre Mineau, Daniel G. Bert and Erin Mutrie of Environment Canada, Lauren M. Sullivan of UCLA, Sidney A. Gauthreaux of Clemson University, Michael Avery of the U.S. Department of Agriculture/Wildlife Services, Albert M. Manville of U.S. Fish and Wildlife Service, Emilie Travis and David Drake of the University of Wisconsin and independent scholar Robert L. Crawford.

The study was funded in part by The Urban Wildlands Group, Environment Canada, the American Bird Conservancy and Defenders of Wildlife.

All teeth and claws? New study sheds light on dinosaur claw function

Theropod dinosaurs, a group which includes such famous species asTyrannosaurus rex and Velociraptor, are often regarded as carnivorous and predatory animals, using their sharp teeth and claws to capture and dispatch prey. However, a detailed look at the claws on their forelimbs revealed that the form and shape of theropod claws are highly variable and might also have been used for other tasks

Inspired by this broad spectrum of claw morphologies, Dr Stephan Lautenschlager from Bristol's School of Earth Sciences studied the differences in claw shape and how these are related to different functions.

His research focussed on the therizinosaurs, an unusual group of theropods which lived between 145 and 66 million years ago. Therizinosaurs were very large animals, up to 7m tall, with claws more than 50cm long on their forelimbs, elongated necks and a coat of primitive, down-like feathers along their bodies. But in spite of their bizarre appearance, therizinosaurs were peaceful herbivores.

Dr Lautenschlager said: "Theropod dinosaurs were all bipedal, which means their forelimbs were no longer involved in walking as in other dinosaurs. This allowed them to develop a whole new suite of claw shapes adapted to different functions."

In order to fully understand how these different claws on the forelimbs were used, detailed computer models were created to simulate a variety of possible functions for different species and claw morphologies.

The dinosaur claws were also compared to the claws of mammals, still alive today, whose function (that is, how and for what the claws are used) is already known.

In the course of evolution, several theropod groups, including therizinosaurs, changed from being carnivores to become plant-eaters. This new study reveals that, during this transition, theropod dinosaurs developed a large variety of claw shapes adapted to specific functions, such as digging, grasping or piercing.

Dr Lautenschlager said: "It's fascinating to see that, with the shift from a carnivorous to a plant-based diet, we find a large variety of claw shapes adapted to different functions. This suggests that dietary adaptations were an important driver during the evolution of theropod dinosaurs and their transition to modern birds."

A 'smoking gun' on Ice Age megafauna extinctions

It was climate that killed many of the large mammals after the latest Ice Age. But what more specifically was it with the climate that led to this mass extinction? The answer to this is hidden in a large number of sediment samples from around the Arctic and in the gut content from permafrozen woolly rhinos, mammoth and other extinct ice age mammals.

It was climate that killed many of the large mammals after the latest Ice Age. But what more specifically was it with the climate that led to this mass extinction? The answer to this is hidden in a large number of sediment samples from around the Arctic and in the gut content from permafrozen woolly rhinos, mammoth and other extinct ice age mammals.

It is a bit of a shift in paradigm Willerslev and co-workers publish in this week's edition of the journalNature. The common image of a light-brown grass-steppe dominating the northern hemisphere during the Ice Age does not hold any longer. The landscape was far more diverse and stable than today, and big animals like woolly rhino and mammoth fed on grasses and particularly on protein-rich forbs. But at the Last Glacial Maximum 25,000 -- 15,000 years ago, at a time when the climate was at its coldest and driest, a major loss of plant diversity took place. The animals barely survived.

After the Ice Age ended about 10,000 years ago it became warmer again. After the large reduction of plant diversity during the Last Glacial Maximum another kind of vegetation now appeared. One of the key food sources of the large mammals- the protein-rich forbs -- did not fully recover to their former abundance. This likely proved fatal for species like woolly rhino, mammoth, and horse in Asia and North America. Even though it became warmer again after the end of the Ice Age the old landscapes did not return.

Professor Eske Willerslev, a researcher of ancient DNA and director of the Centre for GeoGenetics at the Natural History Museum of Denmark, says: "We knew from our previous work that climate was driving fluctuations of the megafauna populations, but not how. Now we know that the loss of protein-rich forbs was likely a key player in the loss of the ice age megafauna. Interestingly one can also see our results in the perspective of the present climate changes. Maybe we get a hold on the greenhouse gases in the future. But don't expect the good old well-known vegetation to come back when it becomes cooler again after the global warming. It is not given that the 'old' ecosystems will re-establish themselves to the same extent as before the warming. It's not only climate that drives vegetation changes, but also the history of the vegetation itself and the mammals consuming it."

Footprints from past ecosystems

Professor Christian Brochmann, a botanist at the Natural History Museum at the University of Oslo in Norway, states: "We show that the permafrost contains a vast, frozen DNA archive left as footprints from past ecosystems, and that we can dechiffer this archive by exploring the collections of plants and animals stored in Natural History Museums. Using DNA from museum collections as reference, we could identify the different plant species that co-occurred with extinct ice age mammals."

Dr. Mari Moora and Professor Martin Zobel, vegetation ecologists from the University of Tartu, Estonia, say: "For the first time, ecologists have been able to piece together the characteristics of more complete plant communities occurring in the Arctic during the last 50,000 years. The new information shows clearly that the vegetation of the Late Pleistocene was rich in forbs but lost considerable diversity at the peak of the ice age. Different plant communities, with graminoids and woody plants prevailing, then started to develop during the Holocene."

Dr. Pierre Taberlet, an ecologist at the CNRS in France, further states: "We should realise that the results presented in this paper would have never been obtained without a very broad collaboration (30 teams from 12 countries) involving the following scientific areas: ancient DNA, palaeo-ecology, taxonomy, molecular ecology, community ecology, zoology, bioinformatics, molecular genetics, and geology. Whereas competition among scientists often is believed to be the main stimulus promoting global scientific output, this study clearly demonstrates that extensive collaboration is a viable alternative."

'Smoking gun'

The article in Nature elaborates on the Willerslev group's results from 2011 where the researchers pointed at climate as the culprit for the mass extinction of some of the large mammals'. But in 2011 the researchers lacked a 'smoking gun'. Now they got it! 242 permafrost sediment samples and eight fossil samples from large mammals from around the Arctic have been dated and analysed for DNA. The data shows that the likely main reason for the mass extinction of the large mammals after the latest Ice Age is changes in the vegetation.

Key points

• So far the common image of much of the northern hemisphere during the latest Ice Age has been of a landscape dominated by grass steppe. The new results show this to be exaggerated. The landscape was far more diverse and dominated by protein-rich forbs. After the Ice Age the forbs became rarer and some of the large forb-eating mammals went extinct or near-extinct.
• Severe climate changes put an extreme stress on animals and plants. After the Last Glacial Maximum the composition of the ecosystems changed. New kinds of vegetation invaded -- but without the large herbivores following. When debating the impact of climate change one should not expect the return of the former ecosystems even though the climate change may be reversed.

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