The Early Holocene Survival of Late Pleistocene Megafauna in the Americas

Most Pleistocene species of North American megafauna stopped occurring in the fossil record about 12,000 calender years ago.  It is remarkable how consistently the latest terminal radiocarbon dates of Pleistocene megafauna cluster around this time boundary.  Specimens that date to younger than this boundary are always questioned and resubmitted for another round of radiocarbon dating till a more believable result is attained, or they are dismissed as “contaminated” samples.  One notable exception to this rule was the discovery that mammoths survived on the Pribiloff Islands, located between Siberia and Alaska, until about 4000 calender years ago.  (See:https://markgelbart.wordpress.com/2013/09/15/the-late-extinction-of-the-pribiloff-island-mammoths/).  Another accepted exception are some of the fossils of dwarf ground sloths found on Carribean islands.  They also date to just a few thousand years ago.  However, these late survival sites are considered special cases explained by the isolation of islands.  The consistent terminal radiocarbon dates on the mainland suggested to scientists a fairly rapid extinction event.  Explanations include sudden climate change, a “blitzkrieg” human hunting overkill scenario, or a comet impact.  Any evidence that Pleistocene megafauna survived for thousands of years past the boundary of 12,000 BP  destroys all 3 of these explanations.

The fossil record is reliably incomplete because over 99% of animals that ever lived never became fossilized or preserved.  I hypothesize the final radiocarbon dates cluster around 12,000 BP because this is the last time these species were common enough in the environment to be preserved.  After this date, many of these species still existed but in isolated populations in areas with low human density and therefore were less likely to become preserved.  My hypothesis is supported by studies of sedaDNA in Alaska permafrost that show mammoths lived for 2200 years later than the last dated bone for this species, and horses were present here for 3700 years past the commonly accepted extinction date for this species in America. (See:https://markgelbart.wordpress.com/2011/02/24/csi-pleistocene-alaska/).

The Devil’s Den site in Florida also yielded early Holocene radiocarbon dates on megafauna bones. (See:https://markgelbart.wordpress.com/2012/07/08/the-devils-den-fossil-site-may-have-been-located-in-one-of-the-last-refuges-of-the-megafauna/).  These dates were obtained during the early 1970’s before improvements in radiocarbon dating were developed.  As far as I can determine, these specimens have not been redated.  If they haven’t, they should be.

Fossil remains of now extinct megafauna from 2 sites in South America also date to the early Holocene.  At the La Moderna site in Argentina, scientists excavated the remains of guanacos, paleollama, Amerihippus (an extinct species of horse), onohippus (a half-ass), deer, macrauchenia, toxodon, armadillo, glyptodont,  megatherium, and glossotherium.  Humans butchered many guanacos at this site as well as horse,  ground sloth, and glyptodont.  I think this is the only site where evidence of a human-butchered glyptodont has ever been found.  Only the bones of the most edible parts of the ground sloth were found here–evidence the beast was killed elsewhere, and the choice cuts carried to this site.  The calender year dates at this site average to between 7800 BP-8300 BP.

Glyptodon old drawing.jpg

Evidence humans butchered a glyptodont was found at the La Moderna site in Argentina.

At the Camp Laborde site also in Argentina, scientists excavated rhea (an ostrich like bird), the fossil remains of 2 species of glyptodont, a megatherium associated with 2 quartz tools, peccary, llama, cavy, viscacha, and a canid closely related to the extinct Falkland’s wolf.  Humans evidentally butchered the megatherium ground sloth here too.  The average calender year dates found here range between 8500 BP-9000 BP. 

The Falkland Island’s wolf became extinct in 1876.  Fossils of a closely related species were found at the Camp Laborde site.

The cavy or Patagonian mara (Dolichotis patagonus).  Fossils of this species were also found at the Camp Laborde site.  Although it looks like a hare, it is actually in the rodent family.  An example of convergent evolution. 

Lagostomus maximus-1-WilhelmaZoo-Stuttgart.JPG

The plains viscacha (Lagostomus maximus).  It is closely related to the chinchilla.  Fossils of this species were found at Camp Laborde.

The Falkland Island’s Wolf was hunted to extinction on the island by 1876.  A close relative lived on the mainland of South America until about 1600 years ago.  The species was nicknamed “the foolish dog” because it showed no fear of humans.  This canid was the only native terrestrial mammal on the Falkland Islands.  DNA evidence suggests it colonized the Falklands by traversing a narrow landbridge that must have existed 16,000 years ago.

The authors of the below referenced study use evidence from Camp Laborde  to reject the “blitzkrieg” overkill model of extinction.  (It’s kind of ironic that they use evidence of humans exploiting megafauna as evidence against overkill.)  They believe humans didn’t rapidly overkill megafauna because many of these species still existed in areas of South America with low human density until well into the Holocene.  However, they do believe a combination of climatic and anthropogenic change doomed South American megafauna.  I disagree with their reasoning and believe that if humans never colonized South America, most of these species would still be extant. Humans were ultimately responsible for megafaunal extinctions, but it took thousands of years rather than hundreds to completely wipe them out.  Pollen evidence from this study does not support climate change as a cause of extinction.  This site was a humid grassland during the early Holocene…just like the pampas of modern day Argentina.

Reference:

Politis, Gustavo; Pablo Messeneo

“The Camp Laborde Site: New Evidence for the Holocene Survival of Pleistocene Megafauna in the Argentine Pampas.”

Quaternary International 191 2008

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2 Responses to “The Early Holocene Survival of Late Pleistocene Megafauna in the Americas”

  1. Paleotool Says:

    Reblogged this on BLACKWATER LOCALITY #1.

  2. markgelbart Says:

    Thanks.

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