[Aztlan] 13,800 year-old Megafauna die off in North America

[Bruce Rogers]

Listeros,

Since we have had some recent interest in large 
mammals in Mesoamerica, it is timely that this 
post from a reviewer at the Los Angeles Times 
reports on an article just published in the 
journal Science.  I have added a few comments in 
[brackets]. 



Scientists zero in on reason for mammoths' demise
By John Johnson Jr. - john.johnson at latimes.com
November 20, 2009

The sediment beneath an Indiana lake is providing 
clues. One thing is clear: A meteor didn't kill 
off the mammoths, mastodons and other large 
plant-eaters, as previously theorized.

About 15,000 years ago, North America was home to 
an astonishing number of large plant-eating 
mammals -- giant sloths, mastodons, and mammoths. 
A thousand years later, they were all gone, wiped 
from the face of the Earth with sudden finality. 
[Since a mammoth kill and subsequent BBQ dating 
to about 8800 years ago was located in Actun 
Loltún in the central Sierrita de Ticul about 50 
km south of Merida in Yukatán, there may have 
been pockets of mammoths still holding out well 
past the general extirpation date quoted here. 
Further, a dwarf species of mammoth, Mammuthus 
exilis, existed on Santa Rosa Island in the 
Channel Islands west of Los Angeles.  In 1994, an 
AMS 14C date of 12,840 + 410 was obtained from an 
intact, undisturbed skeleton, a date close to the 
first human remains so far found on the island 
(>11,000 years ago).] 

  Scientists have floated a variety of possible 
explanations for this mass die-off, from climate 
change to a cataclysmic asteroid impact. But now 
a team of American researchers may be closing in 
on the answer, hidden in the thousands-of-year 
old muck of an Indiana lake.

  To track the population of large herbivores, 
scientists analyzed the pollen, charcoal and 
fungus in ancient sediments beneath Appleman 
Lake, a 35-foot-deep body of water [located east 
of Chicago near the Indiana, Michigan, and Ohio 
States join] left behind when the last ice age 
ended 20,000 years ago.  The research focused on 
the amounts of the fungus Sporormiella present in 
the sediments, according to Jacquelyn Gill, a 
graduate student at the University of Wisconsin, 
Madison and a co-author of the paper appearing in 
today's issue of the journal Science.

  Because the fungus is commonly found in the dung 
of large plant-eaters, its prevalence in the 
fossil record should be a direct measure of 
population density, Gill said. The research team 
found that the decline of the large mammals 
started about 14,800 years ago -- and was 
virtually complete a thousand years later.

  "About 13.8 thousand years ago, the number of 
[fungus] spores drops dramatically," Gill said.

  In the end, a total of 34 types of large animal 
disappeared [including ground sloths the size of 
a one ton truck].

  According to Gill and the other researchers, 
from the University of Wyoming and Fordham 
University in New York, these dates eliminate 
several possible reasons for the mass extinction 
that were put forward previously.

  The first is habitat loss due to a changing 
climate. Around this time, tree species such as 
black ash, elm and ironwood began spreading 
across the landscape of North America. According 
to Gill, the die-off of the big mammals predated 
this change. In fact, the loss of the big 
herbivores may have helped precipitate it. 
Without the large plant-eaters around to keep 
them in check, the tree species were free to 
colonize the countryside.

  Another theory suggested that a comet or meteor 
impact that occurred about 12,900 years ago could 
have wiped out the big mammals in the same way 
that a similar, but larger, impact is believed to 
have killed off the dinosaurs. The new timeline 
shows the extinction event was already over when 
that impact took place, Gill said.

  A third theory held that the animals were wiped 
out by a so-called "blitzkrieg" of hunting by 
Clovis culture humans. The Clovis culture is 
distinguished by the fluted spear points used by 
hunters to bring down large animals. But 
according to Gill, the die-off was already 
underway before the Clovis hunters arrived. "This 
was already happening before humans adopted the 
Clovis tool kit," Gill said.

  The new evidence doesn't mean humans didn't play 
a central role in the decline of megafauna, said 
Christopher Johnson, a professor of biology at 
James Cook University in Australia who wrote an 
accompanying perspective article in Science. 
Even if the Clovis hunters, with their advanced 
technology, did not start the decline, "they were 
certainly part of the story, and probably account 
for the final demise," Johnson said.  "My view of 
all the evidence . . . is that human hunting was 
the sole cause of the megafaunal extinction, and 
that other factors such as climate change had 
nothing to do with it."

Gill isn't ready to go that far.

  "What we've been able to do is start to 
eliminate some hypotheses" for the die-off, she 
said.  "We're not ruling out humans so far," she 
said, but she doesn't feel she has enough 
evidence to point a finger at human hunters. She 
said that her research is continuing at the lake 
and that more discoveries may be coming.


Cheers,
  Bruce Rogers, earth scientist on a good megafauna BBQ day