ETSU scientists: Beavers have been shaping North America for 7 million years
This work is altering our understanding of ecosystems
Famous for their habits of downing trees and damming rivers, beavers leave a major impact on their environments. In fact, scientists have said that beavers change their surroundings more than any other animal besides humans.
And new research suggests that these rodents have been modifying forests and rivers
for millions of years.
These insights come from a study published in the journal “Palaeontologia Electronica”
by Kelly Lubbers, bonebed paleontologist at The Mammoth Site in South Dakota and an
alumnus of East Tennessee State University’s paleontology master’s program, and Dr.
Joshua Samuels, associate professor in the ETSU Department of Geosciences and curator at the Gray Fossil Site & Museum.
Modern North American beavers belong to the species Castor canadensis, and they are
often compared with the extinct species Castor californicus, found in the fossil record
between about 2 and 7 million years ago. The two species are so similar that some
researchers have questioned whether they are truly distinct species. The main factor
that distinguishes them: their size, with the extinct C. californicus being generally
larger.
“Size alone is not a good metric for distinguishing species,” said Lubbers, “so we
wanted to take a closer look and see if we could find any other similarities or differences
that might tell us if they really should be considered different species.”
To do so, the team took extensive measurements on more than 120 beaver specimens, including skulls and skeletons of modern and fossil
beavers from all over North America. Comparing the results, they found only minor
differences between the modern and extinct species, including significant overlap
in their body size. This suggests the two might not represent wholly separate species,
but instead a single lineage showing subtle changes over time.
These strong similarities also indicate that the extinct beavers had a similar lifestyle
to their modern relatives, suggesting that North American environments have been shaped
by beaver activity for the last 7 million years.
“Based on our findings, I am quite confident that Castor californicus would have had
a lifestyle and ecology indistinguishable from living beavers,” said Samuels.
“This means that like beavers today,” added Lubbers, “we can infer that C. californicus
was semiaquatic, consuming fibrous plant matter and modifying ecosystems by felling
trees and dam building.”
The researchers said that more work will be needed to determine confidently whether
these beavers represent the same species, including further study on particular parts
of the beavers’ bodies.
“Castor californicus was initially described as a separate species based on its teeth,”
said Lubbers. “I think by comparing the teeth of fossil and extant beavers, this will
give us a better indication as to whether they really are separate species or not.”
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