The Fossils
From the National Park Service comes this bit of scientific wisdom:
This 50-million year old lake bed is one of the richest fossil localities in the world. Recorded in limestone are dynamic and complete paleoecosystems that spanned two million years. Preservation is so complete that it allows for detailed study of climate change and its effects on biological communities.
Well, it ain't limestone. So much for the government geniuses. Here's the real scoop from Fossil Museum:
Class actinopterygii, the ray-finned bony fishes, comprise almost half of all known species of vertebrates, some 20,000 extant species. There are numerous locations worldwide that are noted for wondrous preservation of bony fishes, and the Green River formation that covers some 25,000 square miles of SW Wyoming, west Colorado and east Utah is one of them. The formation is one of the largest lacustrine (i.e., lake) sedimentary accumulations in the world, averages some 2,000 feet thick, and spans the period 40 to 50 million years ago during the Eocene Epoch of the Cenozoic Era.
The Green River Formation is actually a heterogeneous complex of lakes differential in ecological, geological characteristics, timeframe and hence fauna and flora. The complex comprises three primary lakes formed as a consequence of drainage from tectonic highlands envolved in the uplift of the Rocky Mountains during Tertiary time. Fossil lake, centered in Southwest Wyoming, is the smallest and appeared briefly during the early Eocene. The Lake Gosiute deposits span the period from Lower to Middle Eocene, and the largest deposit from Lake Uinta that ranges across the Utah-Colorado border, spans most of the Eocene Epoch.
During the Eocene, based on the fossil record, the region was sub-tropical to temperate. Some 60 vertebrate taxa have been described from the formation, as well as abundant invertebrates and plants. Green river has been noted for its well-preserved fish since mid-way through the 19th century. The unusually excellent preservation of the Green River fish fossils is usually attributed to a combination of two factors: 1) a cold period during the Eocene that would have caused dead fish to sink faster due to a less inflated swim bladder; and 2) the great depth of the lakes and the consequent anoxic conditions that would have often prevented scavengers from disturbing the carcasses.
The majority of fish fossils are taken from the Fossil L area from two layers: 1) the so-called 18-inch layer; and 2) the spilt fish layer (aka the F1 layer). The best preserved fish come from the 18-inch layer. Because the sediment is highly laminated, the fish can often be removed nearly whole. This layer, in the area near Fossil Butte, does indeed average about 18 inches in thickness, and represents some 4,000 (years) of deposition. The composition of the limestone (actually oil shale - where do they keep getting limestone from?) indicates that the layer was formed in deep water far from shore. By contrast, the so-called split-fish layer is unlaminated making extraction and preparation of the best fossil fish far more difficult. The layer is about six feet thick, and the fauna indicates water that was better circulated than that associated with the 18-inch layer. Some 19 genera of Eocene fish come from the Green River formation.
Here is a diagram of the stratigraphy of Fossil Lake, the unit that the Kemmerer quarries are located in. The "sandwich beds" are better known as the split-fish layers.
Of course the coolest thing about the Green River formation is the fossils themselves. I suggest you start your visit at the Fossil Butte National Monument on Highway 30 west of town; they have a tour and great fossils and information in the visitor's center. June-August, Visitor Center Hours 8:00a-7:00p; Winter Visitor Center Hours 8-4:30 (September through May). Closed winter Holidays.
Here are some fish from my and other collections; you won't find many of these but the Knightia and Diplomystus are extremely common in the quarries, while Prisacacara, Phareodus, and Mioplosus are fairly common. Stingrays, gars, bowfins, etc. are so rare you will probably only see parts lol. The Diplomystus dentatus, was a large predator, up to 26", but most you will find are juveniles, common up to 6" or so.
>A Diplomystus dentatus from the share dig quarry (Charlie Nunn's) north of town
This adult Diplo is mine from the 18-inch layer and is about 14" long.
This is Knightia alta, relatively common in the quarries. It's a small herring that swam about the deeper parts of the lakes eating plankton in huge schools. Every other fish ate them lol. This one is from Warfield's old quarry in the F1 layer south of town.
This is Knightia eoceana , extremely common in the quarries. In fact, 95+% of the fish you dig will be these. It's a herring too and every other fish except Knightia alta ate them :) This one is from Warfield's old quarry too.
This is the head of a large perch, Priscacara liops ("Prisky" to the diggers - it's easier to pronounce :). They grew up to 15" long and ate snails, crustaceans, fish, and probably just about anything else. This is a good example of why you need to keep track of where you are in the layers; the diggers who found this will recover the rest of the fish as they get deeper into the rock. From Charlie Nunn's quarry.
This is a juvenile Priscacara serrata from the 18-inch layer.
This is my Priscacara hypsacantha from Nunn's quarry. They preyed on ostracods (aka fairy shrimp). They are relatively common in the quarries.
This is a sucker, Notogoneus osculus, closely related to living suckers. They must be pretty rare because I have never heard of one from the split-fish layer.
Mioplosus labracoides, a predator that grew up to 20" long. Yikes! From the 18-inch layer, and I wish it was mine but it's not!
And this is the fearsome Phareodus testis, the coolest fish in the quarries (IMHO). They are related to the Amazonian arrowana and they ate FISH! I have a 14" one that I found at Warfield's old quarry south of town. You will find many exploded fish in the quarries (aka "Explodeodus"!) but very few whole ones. If you do find a whole one be prepared to pay a couple hundred dollars for it.
Lepiosteus atrox, an extinct gar. These are the prize fish of the quarries and grew up to 66" long! There are a few beautiful gar at all the galleries in town and at the monument. They ate anything that moved. If you find one don't expect to keep it unless you are willing to pay big money for it. As in thousands of dollars. Many thousands :(
