2018-04-19 23:15:36 UTC
mammals, not only in North America, but everywhere.
"Over the past 125,000 years, the average size of mammals on the Earth
has shrunk. And humans are to blame.
That's the conclusion of a new study of the fossil record by
paleo-biologist Felisa Smith of the University of New Mexico.
Smith studied fossils going back 65 million years, when dinosaurs died
and mammals came into their own. Many of the early mammals went on to
get big. Among the giant creatures: "Llamas and camels and sloths and
five species of pronghorn [antelope] actually," she says, "and certainly
mammoths. And then lots of really cool predators, like Arctodus, the
short faced bear." The short-faced bear stood 11 feet tall, about the
shoulder height of some species of ancient camel."
"Looking back over the most recent 125,000 years of the fossil record,
Smith found that when humans arrived someplace, the rate of extinction
for big mammals rose. She says it basically came down to hunger.
"Certainly humans exploit large game," she says, "probably because they
are tasty"and because a bigger animal makes for a bigger meal.
But humans did other things besides hunting that hastened the
disappearance of big mammals. They burned forests and grasslands that
big mammals used. They competed with the big carnivores for game. They
brought dogs with them that made them better hunters.
Over time, Smith says, the downsizing of mammals affected the
environment in ways you might not imaginefor example, in the erosion of
the land. "When a large animal walks up a hill," Smith explains, "it
zig-zags a lot, whereas a small animal walks up more directly, and that
has an impact because water follows those game trails down, so erosion
and vegetation and what-not are affected by that.""