Big Cedar Ridge, Wyoming
If you like milkshakes (and I do, with double malt), this was the trip to go on. The dig site was located just minutes from
Dirty Sally's in Tensleep, and our leader, Dr. Kirk Johnson, made sure we didn't work too long without recharging our batteries.
Happy workers find more fossils!
Big Cedar Ridge is a unique site in the Meeteetse Formation of northern Wyoming that preserves a beautiful snapshot of
the botanical communities of the late Cretaceous (71 million years ago). The Meeteetse is sandwiched between the Lance
Formation and the Lewis Shale in this part of the Bighorn Basin. It is recognizable at the surface by its grey color and popcorn-like texture.
The bentonitic tuff, remnant of ashfalls from volcanoes in Montana and Idaho, covered everything and fossilized the plants in
situ and in three dimensions. For this reason, Big Cedar Ridge is called a "Plant Pompeii". Whole plants can be found instead of
just the detached leaves common at other sites. Herbaceous vegetation is preserved here, while it is not frequently found at
other paleobotanical locations.
The paleobotanical community varies with the paleoterrain and is represented by one of three characteristic assemblages: ferns
and palms growing on an organic silty substrate, small angiosperms in disturbed areas, and a fern-cycad flora on peaty soil. We
were split up into small groups, all working different sites along the east face of the ridge. I requested a cycad site and was assigned
to quarry 13 (maybe that's why I never found any cycads, although it was a productive locality for other types of plants). We
were collecting for the Denver Museum of Natural History
, and after Kirk inspected our finds and took what he wanted, we
were allowed to keep what was left.
Our spot was on the nose of a small knoll jutting east from the main line of the ridge, which runs north-south and offered a little
bit of protection from the strong westerly breeze. In fact, most of the time, conditions were very nice for digging. It was
sunny, probably in the mid-80°s, and breezy. The first day it might have been a little hotter, but our shade canopy held up for most of
the day before succumbing to a particularly strong gust. The wind kept it from really being too hot. The scenery was beautiful:
multicolored badlands and not a soul around for miles except the other members of our crew. It was nice and quiet,
and delightfully, no one in my group had the inclination to tote a ghetto blaster to the dig site, so we got to drink in the blissful
solitude for hours. For me, it was especially refreshing, because my dad kept the kids entertained at the campground in Worland while
my mom and I looked for fossils.
We found one small pinnate frond that Kirk told us was a type of conifer, and some fragments of palm fronds, but most of the
palms came from sites further along the ridge where other members of our crew were digging. Our best find was numerous examples of
a type of fern which had radially arranged leaflets, like an oxalis, but which resembled the pinnae of a maidenhair fern. Kirk told
us it was a floating fern which inhabited the surface of pond areas like modern duckweed does. I guess that's why it's associated
with a peaty substrate, which may have been what we were calling hash layers, bedding planes just covered with thousands of
minute plant fragments, so many that they colored the layer a darker grey than the rest of the rock.
Studies of the Big Cedar Ridge flora have shown that angiosperms (especially dicots), while they were extremely
diverse, constituted but a small fraction of the plants in the overall flora at the time. They were not yet dominant over the ferns
and gymnosperms that held sway earlier in the Mesozoic. In later times, they would paint the landscape with the bold splashes of
their flowers, but 71 million years ago at Big Cedar Ridge, things were still mostly just green. The only angiosperms present in
any quantity were the monocotyledonous fan palms.
The weekend ended too soon, as fun times always do. We went on to Billings to visit my sister while most of the rest of the
crew headed back to Denver. The museum got a lot of good fossils, and I even came home with some nice pieces of ferns and
palm fronds to add to my collection. Thanks, Kirk!
