 A Larch Forest Today
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Sept. 25, 2003 — A prehistoric beaver pond unearthed in freezing northern Canada has proved to be a treasure trove of fossilized plants and animals — and provides some stark new insights into the powerful impact that climate change can have on living things.
Richard Tedford, of the American Museum of Natural History and Richard Harington, of the Canadian Museum of Nature, report their findings in today's issue of the journal Nature.
The researchers report that the pond environment has been preserved in rich detail — right down to wood featuring beaver teeth-cuts — in a deep peat deposit on chilly Ellesmere Island in Canada. It was laid down in the Early Pliocene epoch, some four to five million years ago, they said.
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"Today, the pond is 2,000 miles north of the present tree line, and its winter climate is about 15 degrees Celsius colder than the Early Pliocene one," the report said. "The fossilized remains illustrate the flora and fauna that lived in the region millions of years ago, during a period of interaction between Asia and North America."
The fossils and their links — or absence of links — with living species on the two continents reveal how mobile species were able to move across the Bering land bridge that has joined them at various times of low sea levels, the scientists said.
Some animals disappeared from North America during the Ice Age but their descendants lived on or evolved into new species in Asia. Others, such as an extinct type of bear, had moved from Asia to North America only to die out there.
The island's peat accumulated in a pond, which, when it existed, was surrounded by larch (a type of conifer) forests that grew in a warm, moist climate. Average temperatures were then probably about 11 degrees warmer in summer and 15 degrees warmer in winter — roughly equivalent to conditions today in Labrador, Canada.
A mass of beaver-cut sticks — up to 28 inches long and 2 inches wide — together with cobbles in silty sand overlain by the peat may be the core of a dam made by a Dipoides beaver, an extinct "Old World" species only distantly related to modern-day beavers, the report said.
The remains of other species found in the pond — including a wolverine, an Asian badger, a three-toed horse and a small deerlet — have their closest living relatives in eastern Asia, not North America. The deerlet's closest modern-day relative, for example, is a Siberian musk deer.
"The beaver pond sediments of Ellesmere Island record a fauna adapted to the most northerly terrestrial climates of the Early Pliocene," Tedford and Harington reported. "Those that have living descendants are all inhabitants of woodlands."
Pollen and other plant fossils reveal that when the beaver-dam was built, the area was in coastal hills and surrounded by open larch woodland that was far more diverse in plant and animal life than the present-day Arctic tree line.
"The peat contains well-preserved plant remains, with rooted larch tree trunks up to three meters [10 feet] tall and many beaver-cut branches and saplings." Pollen remains and the types of animals found there confirm that the woodlands had a rich grassy understorey as well.
The trees included many living species, but also extinct kinds of larch, spruce and a pine closely related to the living Japanese stone pine. Alder and birch trees also grew near the pond. The researchers said the variety of trees at the time was greater than that found today in comparable North American forests.
Among the rich haul of other animal fossils is a type of rabbit, an extinct member of the dog family, a shrew and 16 species of beetles.
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