* Astronomy

 NOVA - Ice Age Death Trap

In the Rocky Mountains, archeologists uncover a unique fossil site packed with astonishingly well-preserved bones of mammoths, mastodons, and other giant extinct beasts. The discovery opens a highly focused window on the vanished world of the Ice Age in North America.

Title: A phase-space model for Pleistocene ice volume
Authors: John Z. Imbrie, Annabel Imbrie-Moore, Lorraine E. Lisiecki

We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. Terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90 ±90 degrees before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model produces an orbitally driven increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused, at least in part, by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system.

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The extinction of many large mammals at the end of the Ice Age may have packed an even bigger punch than scientists have realised. To the list of victims such as woolly mammoths and saber-toothed cats, a Smithsonian-led team of scientists has added one more: a highly carnivorous form of wolf that lived in Alaska, north of the ice sheets.
Wolves were generally thought to have survived the end-Pleistocene extinction relatively unscathed. But this previously unrecognised type of wolf appears to have vanished without a trace some 12,000 years ago.
The study, which will be published in the June 21 online issue of Current Biology, combined genetic and chemical analyses with more conventional palaeontological study of the morphology, or form, of the fossilised skeletal remains. This multifaceted approach allowed the researchers to trace the ancient wolves genetic relationships with modern-day wolves, as well as understand their role in the ancient ecosystem.

"Being able to say all of those thingshaving a complete pictureis really unusual" - lead author Jennifer Leonard, a research associate with the Smithsonian Genetics Program, and currently at Uppsala University in Sweden.

The researchers extracted mitochondrial DNA from the fossil wolf bones preserved in permafrost and compared the sequences, called haplotypes, with those of modern-day wolves in Alaska and throughout the world. The fossils showed a wide range of haplotypesgreater in fact than their modern counterpartbut there was no overlap with modern wolves. This was unexpected.

"We thought possibly they would be related to Asian wolves instead of American wolves because North America and Asia were connected during that time period. That they were completely unrelated to anything living was quite a surprise" - Jennifer Leonard.

The result implies that the Alaskan wolves died out completely, leaving no modern descendents. After the extinction, the Alaskan habitat was probably recolonised by wolves that survived south of the ice sheet in the continental United States, Leonard said.
The ancient Alaskan wolves differed from modern wolves not only in their genes, but also in their skulls and teeth, which were robust and more adapted for forceful bites and shearing flesh than are those of modern wolves. They also showed a higher incidence of broken teeth than living wolves.

"Taken together, these features suggest a wolf specialised for killing and consuming relatively large prey, and also possibly habitual scavenging" - Jennifer Leonard.

Chemical analyses of the bones back up this conclusion. Carbon and nitrogen isotope values of the Alaskan wolf bones are intermediate between those of potential prey speciesmammoth, bison, musk ox and caribousuggesting that their diet was a mix of these large species.
The cause of Pleistocene extinction (called the megafaunal extinction because of the large size of many of its victims) is controversial. It has been variously blamed on human hunting or climate change, or on a combination of factors as the Ice Age waned.
For the specialised Alaskan wolves, the story is perhaps less complicated.

"When their prey disappeared, these wolves did as well. There may be other extinctions of unique Pleistocene forms yet to be discovered" - Jennifer Leonard.

But the results of this study also imply that the effects of the extinction were broader than previously thought.

Source : Smithsonian