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.

'Clovis impact' theory finds new support

I briefly mentioned two weeks ago that the Clovis impact theory had been rejected. The argument being that nanodiamonds (lonsdaleite or n-diamonds) were not such but mere graphene.

But now researchers from US universities, working with Greenland ice cores, have found the controversial "diamonds" in an ice layer roughly dated to that same fateful date of c. 12,900 years ago. Furthermore, the analysis seems to confirm these are genuine n-diamonds and that:

... the shape and size of the Greenland n-diamonds suggest that they formed not by shock metamorphism but rather by processes such as high-temperature CVD and/or high-explosive detonation, which duplicate conditions known to occur during a cosmic impact.

The authors also examined lonsdaleite from Caravaca (Spain) and Needles Point (New Zealand), concluding that they also seem to support the impact theory.

Of course, it is possible that the NDs in Greenland formed through some as-yet undiscovered natural process other than cosmic impact; however, that seems unlikely, since intense diamond research spanning more than a century indicates that the formation of NDs, and lonsdaleite in particular, requires extraordinary temperature, pressure and redox conditions that rule out natural processes that occur either on or below the surface of the Earth (DeCarli and others, 2002).

The theory known as 'Clovis imapact' or 'Younger Dryas event' claims that a sizable meteorite hit Earth, possibly in North America, c. 12,900 years ago, causing the cold millennium known as Younger Dryas, just before the definitive post-glacial warming that marks the beginning of the end of the Paleolithic era. This impact would have been decisive in the megafauna extinctions that defined that time

Ref. Andrei V. Kurbatov et al., Discovery of a nanodiamond-rich layer in the Greenland ice sheet. Journal of Glaciology, 2010. (Direct PDF link).

Found originally at Science Daily.

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.

'Clovis impact' theory rejected

No nanodiamonds are found.

I reported last year on the novel theory that a meteorite may have caused megafauna extinction in North America (specially) at the end of Pleistocene. This theory relied heavily on alleged evidence of nanodiamonds (carbon spherules containing lonsdaleite, a carbon crystal likened to diamonds and found only in meteorites).

This evidence seems now to be nowhere. That is at least what Tyrone Daulton of Washington University claims: that it is nothing but graphene (graphite) what has been mistaken for lonsdaleite, an error that had happened before.

Source: Science Daily (no paper linked and too lazy to search it myself).

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.

More evidence for Clovis-age meteorite impact

The controversial extra-terrestrial explanation for the extinction of North American megafauna some 13,000 years ago, has now got further evidence.

A team lead by Douglas J. Kennet has found nanodiamonds mixed with sooth in sediments dated to 12,900 years ago at the Channel Islands of California. These nanodiamonds are typically created under the massive pressures and heat of a meteoric impact, as the one some believe caused the pre-Clovis extinction.

The smoking gun?

The date of this event matches with the extinction of the of so many American large mammals, like the horse. Earlier this year, the same team found similar nanodiamonds at several North American locations.

The findings suggest that it was not humans who massacred the megafauna but actually something much more powerful arriving from outer space.

Source: Science Daily.
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Not a meteorite but a supervolcano

The old theory of what killed the dinosaurs, along with 65% of contemporary species, was an impact of a meteorite from outer space has been dismissed by recent methodic research that shows that the Chicxulub crater at Yucatan is actually 300,000 years older than the K/T event and that it actually caused the extinction of no known species whatsoever.

Instead the eruption of a supervolcano in India and the radical climatic alterations it caused was the responsible for the massive extinction.

Read more at Science Daily.

This basically removes any major pretext for the meteorite-hunting paranoia, of likely hidded military goals, that we have been bombed with in the media. It's not imposible that a sizeable meteorite hits us sometime in the (likely quite distant future) but it won't kill us as species. Instead it is much more likely that we kill ourselves by means of unconsiderate global warming (no need of a supervolcano this time: we do it on our own arrogant idiocy).
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Mammoth mtDNA wholly sequenced from hair

Source: Science Daily: Woolly Mammoth Gene Study Changes Extinction Theory.

The study, published in PNAS, has several interesting findings:

Mammoths were not one but two species, that had diverged one million years ago, one of which became extinct c. 45,000 BP, some time before modern humans arrived to their habitats.

Both mammoth species had low genetic diversity, what is curious for an animal that ranged from Europe to North America.

The mtDNA of mammoths was a lot more complex than their elephant relatives, either African or Asian.

They managed to generate and compare 18 complete mitochondrial DNA sequences, a unique feat in the field of aDNA studies. They could make it because they worked with hair, not with bone, what evidences that hair preserves aDNA much better than any bone tissue.