Hyenas another european mammal extinct at the end of the last ice age

Spanish researchers have published a new paper on the extinction of spotted hyenas (Crocuta crocuta, the same species dominant in Africa) in Europe and Asia. Apparently hyenas lived without much trouble in the Mediterranean areas of Eurasia until c. 10,000 years ago, when they became extinct. This is also the time of the end of the last Ice Age.

Lead researcher Sara Varela says that climate change in the past was not directly responsible for the extinction of the spotted hyena in southern Europe, but it was a factor in its disappearance.

Source: Science Daily, illustration from Wikipedia.

Ref. Sara Varela et al., Were the Late Pleistocene climatic changes responsible for the disappearance of the European spotted hyena populations? Hindcasting a species geographic distribution across time. Quaternary Science Reviews 2010. Pay per view.

More on megafauna and humans: Iberian peninsula

There is an interesting article at Science Daily today that adds important information for one of the discussions that have arisen in Leherensuge recently: did humans caused megafauna extinctions?

The answer is clearly no. Not directly at least. Woolly mammoths are known to have existed in the Iberian peninsula, specially but not only in the North, not just in the Neanderthal (Middle Paleolithic) period but specially in the Upper Paleolithic period, when modern humans were already established and thriving in the region.

These species lived alongside different human cultures. There is evidence in some sites of the Basque country, Navarra and Catalonia that the Neanderthals coexisted with the mammoths and the reindeer at specific times. However, the majority of evidence of these faunae coincides with the periods of the Gravettian, Solutrean and Magdalenian cultures.

The most important detail for me is the word Magdalenian. We know with some certainty that population grew quickly in the Magdalenian period, after the Last Glacial Maximum, yet megafauna was still there and seems rather abundant.

The key element for the vanishing of these large herbivores in Iberia was the end of the Ice Age, when forests became the dominant feature of a warmed up landscape in which these animals, adapted to cold and steppe, could not survive.

There is however an ill-understood gap in the 31-26 Ka period (Aurignacian period, which in Iberia lasts from c. 30 Ka to c. 22 Ka. BP uncalibrated), when the megafauna findings are lacking.

Ref. Diego J. Álvarez-Lao and Nuria García, Chronological distribution of Pleistocene cold-adapted large mammal faunas in the Iberian Peninsula. Quaternary International, 2010. Pay per view.

Cave bears extinct on human and climate pressure

That seems to be the conclusion of a mostly European research:

Mathias Stiller et al. Withering Away—25,000 Years of Genetic Decline Preceded Cave Bear Extinction. Molecular Biology and Evolution 2010. Pay per view.

Abstract

The causes of the late Pleistocene megafaunal extinctions are still enigmatic. Although the fossil record can provide approximations for when a species went extinct, the timing of its disappearance alone cannot resolve the causes and mode of the decline preceding its extinction. However, ancient DNA analyses can reveal population size changes over time and narrow down potential causes of extinction. Here, we present an ancient DNA study comparing late Pleistocene population dynamics of two closely related species, cave and brown bears. We found that the decline of cave bears started approximately 25,000 years before their extinction, whereas brown bear population size remained constant. We conclude that neither the effects of climate change nor human hunting alone can be responsible for the decline of the cave bear and suggest that a complex of factors including human competition for cave sites lead to the cave bear's extinction.

Cave bears went extinct roughly at the time of the Last Glacial Maximum, 25-18,000 years ago.

See also:
· Article at Science Daily
· Leherensuge: Mammoths died because of forest expansion.

Mammoths died off because of forest expansion

That is the conclusion reached by Brian Huntley and colleagues of Durham University, UK, as reported by BBC (sorry but I cannot find a more direct reference at this time).

According to the British scientists, after running several models for the extinction of mammoth and other megafauna of the Ice Age, the model that is most plausible is that they went extinct because of loss of grasslands and not human hunters' pressure.

During the height of the ice age, mammoths and other large herbivores would have had more food to eat. But as we shifted into the post-glacial stage, trees gradually displaced those herbaceous ecosystems and that much reduced their grazing area.

Update (Aug 19):

Found the relevant paper:

Judy R. M. Allen et al., Last glacial vegetation of northern Eurasia. Quaternary Science Reviews, 2010. Pay per view.

There is also an alternative news article at Science Daily (typically a literal transcription from the press release) that uses maybe less absolute terms than the BBC one:

The change from productive grasslands across large areas of northern Eurasia, Alaska and Yukon to less productive tundra-like habitats had a huge effect on many species, particularly on the large herbivores like the woolly rhinoceros and woolly mammoth. Mammoths and other mega-mammals found it increasingly difficult to find food. We believe that the loss of food supplies from productive grasslands was the major contributing factor to the extinction of these mega-mammals.

Snowball Earth confirmed

New geological research has confirmed the theory that Earth went through a phase of extreme cooling some 717 million years ago, with all, absolutely all the oceans covered in ice, at least seasonally, as well as the land. This extreme ice age is known technically as the Sturtian glaciation.

This mountain, now at Yukon, was once a tropical coral reef (light grey area) and shows cover by glaciar deposits (darker top).

However there is some discussion on how could life survive such extreme circumstances, more so when it's the period when the earliest animals are thought to have appeared first. It is possible that even in such extreme conditions, there would be seasonal patches of open water allowing for photosynthesis. Another possibility is that this early life was in fact adapted to hydrothermal vents in the deep ocean, not needing of solar input (extremophiles).

Was Earth once like Enceladus?

Source: Science Daily.

Bering strait closure caused the end of last Ice Age in the long run

A very interesting new climate theory the one mentioned today at Science Daily: while the cooling of Earth was caused by orbit perturbations, leading to the closure of Bering Strait and the formation of the Beringia isthmus, this last caused such perturbation in global oceanic currents that in the long run sentenced the Ice Age to its end.

The Atlantic Ocean is saltier than the Pacific, what leads to water flowing from this latter to the former. This circulation can only go through the south or via the Arctic Ocean. With Bering Strait closed, Atlantic salinity grew and the North Atlantic Conveyor (Gulf Stream) was enhanced leading to a gradual meltdown of the North Atlantic Ice sheets (in North America and Northern Europe), which in turn lead to higher sea levels and eventually to the reopening of the Bering Strait and the stabilization of climate in the Holocene.

It took many many thousand years though.

Younger Dryas began in just few months

Research by scientists of the University of Saskatoon (Canada) has found that the arrival of the last cold phase of the late Ice Age, known as the Younger Dryas stadial, took place in few months.

Submilimetrical slicing of fossil sediments at Lough Monreagh in Ireland showed that biological activity stopped within months, a year at most. It would be like taking Ireland and moving it up to Svalbard, in the Arctic Ocean, said led researcher William Patterson.

This is even shorter than the time suggested by less precise measurements in Greenland's ice sheet, that suggested an onset of the big freeze in one to three years.

It is believed that this cold period was triggered by melting of ice sheets due to global warming at the end of the Ice Age, causing the Gulf Stream, which keeps Europe quite warmer than normal for its latitude, to stop flowing. The Younger Dryas period lasted some 14 centuries, from 12,900 to 11,500 years ago.

Source: New Scientist.
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The rich enviroment of Southern Iberia in the Ice Age

Just a quick note: a new study led by J.S. Carrión (behind paywall) concludes that the area near Gibraltar, and overall in southern Iberia, was very rich and quite warm in the Upper Paleolithic, with a vegetation that included pines, oaks and other deciduous trees.

While Carrión emphasizes before the media this as the enviroment of the last Neanderthals, the dates given, 32,000-11,000 years ago, rather suggest the period of AMH (H. sapiens) occupation of the area, who arrived there c. 28,700 BP (uncalibrated oldest date for Gorham's Cave Aurignacian).

Gorham's Cave today (above) and as it could have been in the Ice Age (below),
as reconstructed by the Museum of Gibraltar .

Direct source: divulgative article at Science Daily.
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Sharp warm spikes at the end of the Ice Age.

A University of Colorado team researching the Greenland ice sheet has found that two sudden warm epysodes happened just before the definitive end of the Ice Age some 10,000 years ago.

The first one was c. 14,700 BP and lasted till c. 12,900 BP. Then deep freeze conditions were back agains for some 1200 years until the second sudden warming (11,700 BP) that preluded the definitive end of the Ice Age.

But the most important finding is that the warming happened in such a brief period as 50 years, with the reorganization of atmospheric circulation being as quick as only one or two years!

We have analyzed the transition from the last glacial period until our present warm interglacial period, and the climate shifts are happening suddenly, as if someone had pushed a button.

The origin of the sudden changes seems to be in the tropical belt but it doesn't seem like the researchers can pinpoint the ultimate trigger of such a climatic change.

While these abrupt climate changes could really alter radically the life of Paleolithic hunter-gatherers, for the case of Europe, the first one seems to imply some continuity: Magdalenian was dominant in the SW and expanded to Central Europe about that date. The second one preludes the Paleolithic, with the gradual diversification of Magdalenian culture but it doesn't show lack of continuity either. Fully diversified Epipaleolithic cultures (Azilian, Sauveterrean, etc.) are only found since c. 10,000 BP, some time after the second peak, when the Ice Age had already become history.

(Via Science Daily)