Lost Giants: Did Mammoths Vanish Before, During and After Humans Arrived?

[Jack Linthicum]

The Scientific American offers a popularized version of the question
and, as is its wont, makes no decision. One study says the megafauna
disappeared before man came to the Americas, thereby placing in
question all those "butchering" sites. Another study says the Clovis
people hunted the megafauna to extinction. A conclusion which is
countered by the third study that has the megafauna and horse
surviving for another 3 thousand or more years after the earliest
dated human evidence. Not really archaeology but probably the sort of
article that would provide easy reference for an argument on any of
the three theories.

News - December 14, 2009
Lost Giants: Did Mammoths Vanish Before, During and After Humans
Arrived?
Three studies seem to disagree as to when mammoths, saber-toothed cats
and other North American megafauna disappeared

By Charles Q. Choi

Before humans arrived, the Americas were home to woolly mammoths,
saber-toothed cats, giant ground sloths and other behemoths, an array
of megafauna more impressive than even Africa boasts today.
Researchers have advanced several theories to explain what did them in
and when the event occurred. A series of discoveries announced in the
past four weeks, at first glance apparently contradictory, adds fresh
details to the mystery of this mass extinction.

One prominent theory pegs humans as the cause of the demise, often
pointing to the Clovis people, who left the earliest clear signs of
humans entering the New World roughly 13,500 years ago. The timing
coincides with the disappearance of megafauna, suggesting the Clovis
hunted the animals to extinction or infected them with deadly disease.
Another hypothesis supposes that climate was the culprit: it had swung
from cold to warm twice, including a 1,300-year-long chill known as
the Younger Dryas; such abrupt shifts might have overwhelmed the
creatures’ abilities to adapt.

To pin down when the megafauna vanished, paleoecologist Jacquelyn Gill
of the University of Wisconsin–Madison and her colleagues analyzed
fossil dung, pollen and charcoal from ancient lake sediments in
Indiana. The dung of large herbivores harbors a fungus known as
Sporomiella , and its amounts in the dung gives an estimate of how
many mammoths and other megafauna were alive at different points in
history. Pollen indicates vegetation levels, and charcoal signals how
many fires burned; the extent of flora and wildfires is related to the
presence of herbivores, the researchers say in the November 20
Science. Without megaherbivores to keep them in check, broad-leaved
tree species such as black ash, elm and ironwood claimed the
landscape; soon after, buildups of woody debris sparked a dramatic
increase in wildfires. Putting these data together, Gill and her team
conclude that the giant animals disappeared 14,800 to 13,700 years ago
—up to 1,300 years before Clovis.

A different study, however, suggests that this mass extinction
happened during Clovis. Zooarchaeologist J. Tyler Faith of George
Washington University and archaeologist Todd Surovell of the
University of Wyoming carbon-dated prehistoric North American mammal
bones from 31 different genera (groups of species). They found that
all of them seemed to meet their end simultaneously between 13,800 to
11,400 years ago, findings they detailed online November 23 in the
Proceedings of the National Academy of Sciences USA.

But if ancient DNA recovered from permafrost is any sign, megafauna
survived in the New World millennia after humanity arrived. As the
permafrost in central Alaska cracked during springtime thaws, water
that held DNA from life in the region leaked in, only to freeze again
during the winter. As such, these genes can serve as markers of “ghost
ranges” — remnant populations not preserved as fossil bones.

Looking at mitochondrial DNA, evolutionary biologist Eske Willerslev
of the University of Copenhagen and his colleagues suggest mammoths
lasted until at least 10,500 years ago (as did horses, which actually
originated in the Americas only to vanish there until the Europeans
reintroduced them). The Proceedings of the National Academy of
Sciences USA published those findings online December 14.

Although the three papers appear to conflict with one another, they
could be snapshots from the beginning, middle and end of a mass
extinction. “If they seem to disagree, it is for the same reason as in
that fable about the three blind men trying to describe an elephant —
or mammoth?— by touching different parts of it,” says ecologist
Christopher Johnson of James Cook University in Australia, who did not
take part in any of the studies.

Johnson suggests the fungus research is superb evidence for when the
decline began, but it is not as good at confirming exactly when the
extinction was completed, especially over larger areas where sparse
populations might have persisted. The DNA finds, on the other hand,
can detect late survivors, he says, “maybe very close to the actual
time that the last individuals were alive, at least in Alaska.” The
bones analyzed from the period roughly in between show that the
extinction process afflicted many species simultaneously. Those
fossils came from the contiguous U.S., which back then was separated
from Alaska by the massive Laurentide and Cordilleran ice sheets and
so, Faith notes, could explain why the pattern of extinction differed
up there.

So what caused the decline? The jury’s still out, says Willerslev’s
collaborator Ross MacPhee of the American Museum of Natural History in
New York City. Johnson notes that archaeologists are turning up
evidence of humans in the New World before Clovis, and he suggests
they overhunted the megafauna. The beautifully crafted fluted spear
points linked with the Clovis might reflect strategies that developed
once the giants became rare and harder to hunt, Johnson adds.

Even if scientists cannot definitively finger the killer, research
into the megafauna disappearance “is directly relevant today because
we are in the middle of a mass extinction and one for which we know
the cause — us,” Gill says. “Large animals are among the most
threatened today,” she points out, and no one wants Africa to follow
the ancient experience of the Americas.

http://www.scientificamerican.com/article.cfm?id=lost-giants-did-mammoths