WASHINGTON: Mammal body
size decreased significantly during at least two ancient global warming events
millions of years ago, a new study has found.
A similar outcome is possible in response to human-caused climate change, according to a University of Michigan paleontologist and his colleagues.
Researchers have known for years that mammals such as primates
and the groups that include horses and deer became much smaller during a period
of warming, called the Paleocene-Eocene Thermal Maximum (PETM), about 55
million years ago.
Now, Philip Gingerich and his colleagues have found evidence
that mammalian "dwarfing" also occurred during a separate, smaller
global warming event that occurred about 2 million years after the PETM, around
53 million years ago.
"The fact that it happened twice significantly increases
our confidence that we're seeing cause and effect, that one interesting
response to global warming in the past was a substantial decrease in body size
in mammalian species," said Gingerich, a professor of earth and
environmental sciences.
Researchers concluded that decreased body size "seems to be
a common evolutionary response" by mammals to extreme global warming
events, known as hyperthermals, "and thus may be a predictable natural
response for some lineages to future global warming."
The PETM lasted about 160,000 years, and global temperatures
rose an estimated 9 to 14 degrees Fahrenheit at its peak.
The smaller, later event analysed in the latest study, known as
ETM2 (Eocene Thermal Maximum 2), lasted 80,000 to 100,000 years and resulted in
a peak temperature increase of about 5 degrees Fahrenheit.
Teeth and jaw fossils of early hoofed mammals and primates that
spanned this later climatic event were collected in Wyoming's Bighorn Basin,
and the size of molar teeth was used as a proxy for body size.
The researchers found that body size decreased during ETM2, but
not as much as the dwarfism seen in PETM fossils.
For example, the study revealed that a lineage of early horses
the size of a small dog, called Hyracotherium, experienced a body-size decrease
of about 19 per cent during ETM2.
The same horse lineage
showed a body-size decrease of about 30 per cent during the PETM. After both
events, the animals rebounded to their pre-warming size.
The study was presented at the annual meeting of the Society of
Vertebrate Paleontology in Los Angeles.
