About 34 million years ago, near what is now Florissant, Colorado, there was a large lake, dammed up by volcanic mudflows.
Thick blooms of algae allowed fragile material like leaves and insects to rest on the surface of the lake, but those blooms periodically died off and settled to the bottom, taking the entrapped material down with them.
There were perhaps three active volcanoes about 15 miles away. The occasional big eruption would quickly drop down a thick layer of yellowish-white pumice, but numerous smaller eruptions would leave fine ash to erode by rainfall and be deposited in the lake as sediment, and the nutrients in that sediment would allow another algal bloom. Each time this couplet of events happened, a new layer of “paper shale” formed.
And now, between those layers of shale, we find exquisitely preserved fossils of delicate material that normally does not fossilize.
The example you see above in the main photo is one of these.
My daughter discovered it on April 11 as she sat on our front porch here in Massachusetts and carefully split a long, rectangular piece of Florissant shale with an X-ACTO blade.
You can see that the head of this 34 million-year-old insect is covered by a thin layer of pumice, which, I can attest, is not very easy to remove. You also see a big ball of pumice next to the insect, which was probably dropped down by a comparatively large eruption that launched it through the air.
Naturally, we wondered exactly what the bug is, but fortunately I was able to contact Ricardo Pérez-de la Fuente, who is now a Research Fellow at the Museum of Natural History at Oxford University. He is the man who, as a postdoctoral researcher at Harvard, identified and digitized a huge collection of insect fossils, the great majority of which are from Florissant. If anyone on Earth knows what this could be, he does.
He kindly got right back to me — I mean within an hour — and said:
That looks like a nematoceran dipteran (a midge) to me, maybe belonging to the family Bibionidae or Mycetophilidae, and likely a female.
In case you wanted to fully expose the head, you might want to use the head of a needle to very carefully expose the layer of rock, first attempting to peel off ashy layer that is away from the fossil and then getting closer to the fossil. In any case, these type of endeavours are always challenging and risky, and so I would not recommend touching the fossil unless you clearly see that the rock gets exposed easily.
I haven’t quite been brave enough to attempt that yet.
For comparison, here is an especially nice specimen from the collection of Florissant Fossil Beds National Monument, a nematoceran dipteran of some sort. The fragile nature of these fossils is evident even when they are carefully collected by experts:
The Nematocera, by the way, include mosquitoes, crane flies, gnats, black flies, and midges.
What makes these stand out to me in fossil form is that they have four smaller legs up front and two much-larger legs in back. You can see that in modern-day Bibio johannis (black gnat):
Back in 1883, the U.S. Geological Survey put out one of the first reports of fossil characterization from the area, and sure enough, Mycetophilidae and Bibionidae are mentioned. Based on this and the widely variable condition of specimens you see in today’s Harvard collection, my daughter is lucky to have found a specimen as whole as she did:
Even though my daughter spends a lot of time doing things you might expect a teenager to do — video games, cheerleading, singing, political activism — when she hears that a box of shale is coming, she gets visibly excited about it.
I have to say that when it comes to getting kids — and adults! — interested in science, there is no substitute for this direct kind of experience. Whether it’s cracking open shale, seeing a planet or nebula through a telescope, paddling on a bioluminescent bay, or yes, even making something explode, people can suddenly get very interested in things like families of Diptera! I mean, who wouldn’t be excited about discovering a living thing that hasn’t seen the light of day in 34 million years? Who wouldn’t want to know what it is?
If you’re wondering where the shale came from, I'll let you in on a little secret: There is a little quarry down the road from the Florissant Fossil Beds National Monument, and if you send an email to Nancy, she will pack up some shale and ship it to you.
Be advised: You may go through several bags full, layer after layer, without finding much of anything, but if you just keep at it, something cool is going to come out. We have been through probably 200 or 300 pieces of shale, and we have found a winged ant, a sequoia branch, a tiny snail, and stems and leaves of a legume plant.
But now we add perhaps the coolest one of all… the star of today is the fly!