The Early Eocene was a time of high species
turnover among Mammals (and other groups), driven by two periods of extreme
global warming, the Paleocene-Eocene Thermal Maximum about 55.8 million years
ago and the Early Eocene Climatic Optimum, between about 53 and 50 million
years ago. During the Early Eocene many of the Mammal groups which had survived
the End Cretaceous Extinction disappeared, and were replaced by representatives
of modern groups which persist to this day.
This makes Early Eocene Mammalian faunas of
particular interest to palaeontologists, although examples of such faunas are
somewhat rare, leading to a patchy understanding of Early Eocene Mammalian
biogeography. In North America Mammal remains are known from Ellesmere Island
in the Canadian High Arctic and the Western Interior of the United States,
particularly Colorado and Wyoming, but are unknown from the rest of the
continent.
In a paper published in the Journal ofVertebrate Palaeontology on 8 July 2014, Jaelyn Eberle of the University of Colorado Museum of Natural History and Department of Geological Sciences at the
University of Colorado at Boulder, Natalia Rybczynski of Palaeobiology at the
Canadian Museum of Nature and David Greenwood of the Department of Biology at
Brandon University describe two Mammal specimens from the Driftwood Creek Beds
(part of the Oota Lake Group) in Driftwood Canyon Provincial Park, east of
Smithers in northern British Columbia.
The Driftwood Canyon Provincial Park was
established in 1967 in order to protect the fossils there, after the landowner
donated the site to the Province of British Columbia. The site has yielded
extensive plant remains, predominantly Conifers (Redwoods, Cedars, Firs,
Larches, Spruces, Pines and Golden Larches) with some broadleaved deciduous
Angiosperms (Alders, Birches, Sassafrasses, Elms and members of the Oak Family)
and other plants (Ginko and the Fern Azolla, which forms floating mats on
still or slow moving waterways). The site has also yielded numerous Fish and Insect fossils,
as well as some Bird remains, which have yet to be formally described. The site
also has interbedded volcanic ashes, which allow for accurate isotopic dating,
which currently dates the site at 51.77 million years old, within the Early
Eocene Climatic Optimum. The site has been interpreted as a the bed of a small
lake in an area surrounded by dense, conifer-dominated, woodland, with annual
temperatures averaging 10-15˚C and seldom falling bellow freezing.
Driftwood Canyon fossil
site. (A) map showing location of Driftwood Canyon Provincial Park and other key
Eocene; (B) image of the north cliffface showing lake beds, and positions
of radiometrically dated volcanic ash and the level at which the Erinaceid
fossil was collected. Eberle et al. (2014).
The first specimen described is a right
maxilla (upper jawbone) with some teeth, thought to have come from an
Erinaceomorph Lipotyphlan (Hedgehog). It is named as Silvacola acares, where ‘Silvacola’
means ‘forest-dweller’ and ‘acares’
means ‘tiny’ as the specimen is very small for a Hedgehog. Hedgehogs have
previously been described from the Late Palaeocene of Central Alberta and
Southern Saskatchewan and the Eocene of Wyoming.
Right maxilla of Silvacola acares in labial view. Eberle et al. (2014).
The second specimen described is a partial
right dentary (lower jawbone), again with some teeth intact, of a Tapir. This
is referred to the Early to Middle Eocene genus Heptodon, though not confidently assigned due to the fragmentary
nature of the material. Tapirs are thought to be good proxies for forested
environments (modern Tapirs are strict forest dwellers and there are no known
fossil Tapirs from deposits where forests can be ruled out), supporting the
current palaeoenvironmental interpretation of the Driftwood Creek deposits.
Right dentary assigned to
cf. Heptodon in labial view. Eberle et al. (2014).
See also…
Silky Lacewings (Psychopsidae) are a group of...
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