North America - Giant Beasts!
When humans first entered North America is
hotly debated. However, many scientists believe that humans arrived
comparatively recently, long after the end of the last major glaciation
(about 20,000 calendar years ago). The earliest radiocarbon dates
documenting human presence in either North or South America that
are widely accepted are only on the order of 12,000-13,000 years
ago (about 14,000 calendar years ago).
The most obvious difference concerns the mammalian
megafauna. Today there are only about a dozen species of
North American mammals that are megafaunal (greater than 100
lbs in body size). As recently as 11,000 calendar years ago,
there were more than three times that number.
| Whatever the exact date may turn out to be, we
know from the archeological and paleontological records that,
when humans first arrived in the New World, they entered a faunal
landscape that greatly differed from the one that we live in
to all these mammals?
Their ranks included
the Woolly Mammoth, a close relative of living elephants, and
Giant Ground Sloths whose closest living relatives are the comparatively
tiny Tree Sloths of South America. In addition to these species,
there were American horses, American camels, American lions, and
a host of less familiar creatures. Within a period possibly as
short as 400 years, the last representatives of these species
(and many others, to a total of perhaps 135 on both continents)
had become extinct.
"Megafaunal" by whose standards?
Scientists use different definitions of what counts as a large
When talking about the end-Pleistocene extinctions, for example,
some scientists refer to any animal over 5 kg as "large." Using
this definition, about 90% of the genera dying out in North
America 11,000 calendar years ago could be described as large.
Other scientists restrict the term "megafaunal" to refer to
any animal over 100 lbs (~44 kg). Under this definition, only
about three-quarters of the species that went extinct fit the
Megafaunal by anyone's standards!
Man standing next to the bones of a Woolly Mammoth leg in the AMNH collection.