Fossil leaves on the Interstate
Posted 3/4/2011 12:03 AM by Ian Miller | Comments
The American West is the best place on Earth to be a
paleontologist. For the better part of the last 500 million years,
sand, silt and mud have accumulated on vast stretches of the
continent, entombing spectacular evidence of past life as fossils.
These sediments form layers, which are the pages of the epic that
is the evolution of multicellular life on Earth. Today, these
sediments are sometimes found in small basins sandwiched between or
flanking major mountain ranges and other times found in enormous
pre-Rocky Mountain deposits dissected by modern mountains and
What's so amazing about being a paleontologist in the American
West is that more often than not there are fossils RIGHT
under your feet! For instance, the rocks beneath Front Range
communities from Fort Collins to Pueblo are absolutely packed with
fossils. Just about anywhere you dig you can find fossils of
leaves, shells, mammals, reptiles and dinosaurs.
Some of the most exquisite fossil sites in Colorado have been
found during road and building construction. The Denver Museum of
Nature and Science partners with the Colorado Department of
Transportation (CDOT) to dig and collect fossil sites found on
State road projects. Just this last Tuesday, March 1, CDOT
paleontologist Steve Wallace, museum volunteer Steve Wagner, and I
explored a new fossil leaf site found at I-25 and Alameda, right in
the middle of the City of Denver. Steve had noticed some nice
fossil leaves in slabs of rock turned up by an excavator a few days
earlier and we returned to make a representative collection for the
One of the most remarkable things about the rocks in the Denver
Basin (the area from Fort Collins to Colorado Springs to Limon) is
that they record the Cretaceous-Tertiary (KT) boundary, which marks
the end of the dinosaurs. Because the Denver Basin was filling with
sand and mud between 68 and 64 million years ago, it's as if the
sediments were a tape recorder running when the Cretaceous ended.
We use the fossils in these Cretaceous and Tertiary rocks to
understand how life and the earth changed across the KT boundary.
All told, we have more than 400 fossil leaf sites in the Denver
Basin spanning the KT boundary.
Though we just collected them last Tuesday, we know that the
leaves we dug are Cretaceous in age for two reasons. First, we've
extensively mapped the Denver Basin, so we know what age rocks are
underfoot based on our maps; and second, these species of plants
occur only during the Cretaceous. This is really cool because,
despite the fact that we have more than 400 fossil leaf sites in
the Denver Basin, our sampling is lopsided and many of our sites
occur in early Tertiary rocks. As a result, this site will provide
significant information about what Colorado forests were like when
dinosaurs roamed Denver.
Right now, all the fossils are drying slowly in tightly wrapped
in industrial strength toilet paper (our preferred fossil leaf
transport medium!). In a few months, we'll unwrap them and our
trained team of Museum volunteers will prepare them, then we'll
catalog and begin to study them. In the meantime, stay tuned for
updates on this new fossil site.
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