This is an Great Block of a Green River Fungus Gnat Fossil. But this insect has exceptional detail and preservation. This is a Fossil March Fly trapped in the layers of rock well known from a classic site. The preservation and detail is exquisite.
These Colorado Insects are Eocene in age, and are 50 Million years old. They come from the Green River Formation.
This formation is known for the insects and leaves coming from that area and this Fungus Gnat Fossil is in a block of rock and shows outstanding detail. Because the fossilization is exceptional for these small invertebrates you can actually see the detail. These are not trapped in Amber but they are locked inside rock. This rock is a vert fine grained sediment that preserved these insects beautifully this Fungus Gnat Fossil displays very well. But there are many other organisms buried in the sediment as well. Fossils such as these provide an excellent snapshot as to what life was like then. And it also shows the wide diversity of insect life that we still see today.
Because this Fungus Gnat Fossil was trapped in mud or a mud flow and was buried very quickly it shows quality detail. But it did not completely decay immediately. Because they were preserved in that fine mud and exhibit great detail. The Green River is known for the excellent preservation of fossils but here they are quite small.