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GREEN RIVER FOSSIL FISH FOR SALE
Dig Your Own Fossil Fish In Wyoming
The Fossil Lake Safari located near Kemmerer, Wyoming is operated by FossilEra Adventures. This adventure offers visitors of all ages the unique experience of being able to find their own fossils. You can split rock from the 50 million year old Fossil Lake, one of the world’s most biodiverse and prolific fossil formations in the entire world. Customers get to keep the fossils that you find!
What Is The Green River Formation?
The Green River Formation is effectively a record of the sedimentation of a group of intermountain lakes in what is now present-day Wyoming, Colorado and Utah. One of the largest sediment deposition formations, the Green River Formation spans 25,000 square miles and maintains a near uniform depth of about 2,000 feet deep. During the Eocene, this area, as indicated by the fossil record, had a sub-tropical to temperate climate. These conditions were enough to support a vast ecosystem that was teeming with life. Because of those conditions, we now get to enjoy a fossil bed with rich biodiversity. While a slew of different animals have been extracted from the lake beds, the phenomenal preservation of the many fish species are what draws paleontologists and the casual collector to the bountiful offerings of the Green River Formation.
Fossil Lake is physically the smallest of the three sites and also provides a record of the shortest amount of time. This lake is located in the southwest corner of Wyoming, tiptoeing just along the eastern border of Utah. Researchers place estimates of Fossil Lake’s fossils between 53 and 51 million years ago. Fossil Lake is further subdivided into three members, of which the Fossil Butte Member is the most relevant for fossil collection. This singular location is easily responsible for the majority of the fossils and discoveries from the Green River Formation. As such it is the origin of most of the fossil fish on the market and the source of much of the information we have about Eocene fossils in North America.
The Lake Gosiute Sediments, containing fossils dating from 53 to 49 million years ago, is the second largest of the ancient lakes and is believed to have had a tumultuous history and an ever-shifting shoreline. Lake Gosiute has five members that represent a wider time frame than Fossil Lake but has less overall abundance. Located in the southwest quadrant of Wyoming and dipping into the northern reaches of Utah, Lake Gosiute’s fauna is seeming very different from that of Fossil Lake and Lake Uinta. The presence of catfish and sucker species indicate that it had a more hospitable lake bed than Fossil Lake did, despite a shifting climate.
The final region is the Lake Uinta Sediments that sits almost completely in northeast Utah and just barely crosses the western border of Colorado. Its six members span from 56 to 44 million years ago, offering not only some of the earliest fauna from the area, but some of the most recent, right before the entire lake system dried up. It is the largest of the three lakes and, coincidentally, the first lake to form and the last to dry up. It is generally believed to be rather shallow and lagoon-like. This lake has the lowest amount of vertebrate, including fish, fossils of all three locations. However, Lake Uinta has the greatest variety of plant and insect fossils of any of the Green River Formation’s members. It also sports one of the thickest accumulations of lake sediments of any formation in the world, at a thickness of 7,000 feet. Lake Uinta is important, not just for its wealth of information about the Eocene epoch in North America, but also because it is believed to hold 1 trillion barrels of oil.
What Can Be Found In The Green River Formation?
There are 19 separate genera and 27 species of fish from the Green River Formation but many are extremely rare and the validity of some species are contested by experts. All of these fish are ray-finned fishes, with the exception of the two cartilaginous, stingray genera. Fish of the genus Knightia, Diplomystus, and Cockerellites are the most common species within the formation with Knightia occurring 50% more frequently than Diplomystus in a distant second place. Phareodus and Mioplosus are relatively uncommon finds, but still well recorded. Outside of the five aforementioned genera, Green River fish become increasingly rarer and rarer. The rarest fish include: the gars (Family Lepiosteidae), stingrays (Order Myliobatiformes), catfish (Family Ictaluridae), and suckers (Family Catostomidae).
Besides fossil fish, the Green River Formation also preserves exceptional plant material, insects, and, on very rare occasions, birds, mammals, and crocodilians. These fossils are also phenomenal display pieces and have helped paleontologists unlock clues to North America’s post-Western Interior Seaway past. Tetrapods are exceptionally rare, with only 1 of every 5,000 to 10,000 fossils quarried being a reptile, amphibian, mammal, or bird. The earliest known bat fossil (Onychonycerteris finneyi) was discovered in the Fossil Butte Member of the Green River Formation and allows paleontologists a glimpse at the early evolution of bats.
Why Are Fish From The Green River Formation So Well Preserved?
These fossil fish are preserved in very fine sediments that were deposited continuously for 6 million years. Each year two distinct layers were deposited, one during the growing season and the other during the dry season. The average thickness of these fine layers is about .2mm. Scientists attribute the excellent preservation of these fish to two major environmental factors. The first is that the lakes were quite deep and lacking sufficient oxygen for excessive disruption of deceased fish by scavengers. The depth was important because the environment was colder, causing reduced inflation of the fish’s swim bladder, which in turn reduces buoyancy and allows perished fish to sink faster than in warmer waters where bladders exhibit less shrinkage. These factors, coupled with rapid and consistent deposition of sediment assisted with efficient, consistent fossilization of dead organisms.
The Fish
Knightia - These fish are by and large the most abundant and prolific fish from the Green River Formation. They are clupeid fish, which are related to modern herring, and average between 3 and 5 inches with a maximum size of 10 inches. Much like modern herring, Knightia was apt to school throughout its life in the pursuit of its favorite food, plankton. There are two recognized species of Knightia, K. eoceana and K. alta. K. eocana is the more common of the two and is substantially more abundant in Fossil Lake deposits, whereas K. alta tends to appear in higher frequency in Lake Gosiute members. Mass mortality plates have produced significant evidence of the enormity of school sizes for Knightia species, with a few large plates averaging 100 fish per square meter. Over the decades it’s likely that over one million individual Knightia have been been collected and overall they represent about 50% of the fossil fish found in the formation.
Diplomystus - The second most common fish fossils belong to the genus Diplomystus. Also a herring-esque fish, D. dentatus was rather prolific in the Fossil Butte Member representing approximately 25-30% of all fossil fish found. Diplomystus is one of the only Green River Formation species to spawn mid-lake and do most of their hunting nearshore on the fry of smaller fish species. These fish are often described as hatchet shaped, with an upturned snout and a continuous anal fin that runs to their tail fin. They can often reach lengths of over a foot in length, maxing out around 2 feet long.
Priscacara and Cockerellites - Easily the most consistently mixed up and contested genera from the Green River Formation, Priscacara and Cockerellites are the major representatives of the Perciformes, in Eocene deposits. P. serrata and C. liops are each recognized as belonging to their own, respective genus, though this taxonomic classification is tenuous and constantly debated. Cockerellites liops was, for a long while, labeled as Priscacara liops, and some scientists still view them as such. The primary visual differences between the two are the number of anal spines present and a difference in size. Generally, Cockerellites average 4 inches long and top out at just over 5 inches. Anything exceeding that length will most likely be Priscacara. Cockerellites was a schooling fish frequently found in mid-lake deposits, while Priscacara is more common in rocks representing a near-shore environment. These two genre represent about 5% of the fish found in the formation.
Mioplosus - Of all the predatory fish in the Green River Formation, Mioplosus is the fish most often found dead with a smaller fish in its mouth. These perch-pikes are the epitome of speedy predatory fish. They have slender fusiform bodies with a deeply forked tail fin and parallel rear dorsal and ventral fins. Their mouth is packed with sharp teeth ready to make any smaller fish into a swim-thru meal. Mioplus can reach lengths of about 15 inches, though most fossils are under a foot long. They have a similar abundance to Cockerilites within the Fossil Lake deposits.
Phareodus - Related to modern arowanas, these bony tongue fish are one of the more sought after of the uncommon fish from Fossil Lake. They were ridiculously predatory and assumedly quite successful. Another species that is sometimes found fossilized mid-gulp, Phareodus has a nearly unmistakable look that is a collector favorite. Their mosaic scale patterns, slender, flowing pectoral fins and parallel, oar-like, rear anal and dorsal fins are some of the dead giveaways of Phareodus. Also their teeth; they have a huge set of razor sharp teeth that preserve extremely well. There are two recognized Phareodus species, P. encaustus and P. testi, within the Green River Formation. For a relatively uncommon fossil fish, both species occur at roughly the same frequency with the Fossil Butte Member. While most phareodus specimens are under a foot long, they can reach fairly impressive sizes of two feet in length. They represent less than 1% of the fossil fish found in the Fossil Lake deposits.
Gars - One of the most coveted of the Green River fish, there are three recognized species under the genus Lepisosteus, L. simplex, L. cuneatus, and L. bemisi. These fish rarely appear in Fossil Lake, limited to about 150 collected specimens. Gars are one of the more resilient species within all of the lakes. This persistence could be one of the major reasons they make rather scarce fossils. These long, slender predators create some of the most stunning fossil displays, especially when the dark black preservation of the 18-inch layer is highlighted by their dense overlapping scales. Paleontologists explain the “abundance” of gar fossils in Lake Uinta over many other species as a byproduct of their ability to survive the extreme environmental shifts until the lake completely dried up. Gars have the unique ability to breathe oxygen from the air if water levels are low, placing them in a privileged position to outlast the average fish. The mass die-offs of other species provided the gar with an easy food source during periods of stagnation; a theory that also explains the lack of fish fossils that are commonly observed in other formations.
Stingrays - These bottom-dwelling beauties are one of the finest display fish that come out of the Green River Formation. With two separate genera, the stingrays are one of the rarer fish that are primarily found in the nearshore deposits of Fossil Lake, though they are also very rarely found in Lake Gosiute and Lake Uinta. Quarriers estimate that 1 out of every 2,500 fish found at Fossil Lake is a stingray. This is most likely due to the lack of viable lake bottom habitats in Fossil Lake. The two species of stingray present in the Green River Formation are Heliobatis radians and Asterotrygon maloneyi, of which H. radians is extremely more prevalent. A. maloneyi, or the Eocene Fat-tailed stingray, is only known from roughly 30 specimens. The two species are distinguished by the width of the base of the stinger and a difference in overall length, with H. radians generally reaching greater lengths.
Notogoneus - A type of beaked sandfish, Notogoneus belongs to the Gonorynchidae family. There are currently five extant species within the family that live in the tropical waters between India and southeast Asia, with Notogoneus being the last of the family to swim in North American waters. These fish had beaked mouths that lacked teeth; an adaptation suited for bottom feeding and scavenging. Because of a lack of middle aged specimens within Fossil Lake, scientists infer that this genus spent most of its life in connecting rivers, only returning to the lake to spawn and die in the deeper regions of the lake. The average length of the adult fossils found mid-lake is 18 inches long. These fish make up about 1% of the 18-inch layer fauna of Fossil Lake but are absent from many of the other layers.
Paddlefish - Unlike their modern North American relatives, the Green River Formation paddlefish were predatory instead of being filter feeders. These fish, from the genus Crossopholis, are characterized by their long snouts, or “paddles” that protrude from the front of their heads. The snouts of modern paddlefish are filled with electro-receptors that allow for underwater navigation in water with poor visibility. Based on the relatively low amount of morphological differences between Eocene and modern paddlefish, it is assumed that Crossopholis paddles provided a similar function at a more primitive level. These fish are known to max out at 59 inches, just shy of 5 feet long, and comprise 0.002% of the fish fossils found in the Fossil Butte Member. Some of their scarcity is attributed to them leaving the lake in preference of rivers and streams as hunting grounds. Like their relatives the sturgeon, paddlefish have a spine made of cartilage, making complete fossils even rarer. Initially Crossopholis fossils were discarded because of their incomplete nature, often only found with head and tail intact.
Mooneyes - A largely insectivorous group, the Mooneyes of Family Hiodontidae are relatively rare fossils within the Green River Formation, though they are prevalent enough to mention. They average 6 inches in length but have been recorded up to 10 inches, and extant Mooneye individuals max out at 20 inches. The only confirmed species is Eohiodon falcatus, which had a fusiform body plan and a deeply forked tail. They look like a shorter, ovular Mioplosus, but much closer in overall size to Phareodus. Mooneye fossils have been found in Eocene deposits of Asia, providing further evidence of the linkage between the North American and Asian continents.
Catfish - Catfish are some of the most rare fossil fish from the Green River Formation as a whole, and are essentially absent from Fossil Lake. The two known catfish genera (Astephus and Hypsidoris) appear most frequently in Lake Gosiute and occasionally in Lake Uinta. The catfish lifestyle is much better supported by these shallow lakes than the deep anoxic environment of Fossil Lake. The connecting rivers and streams would have been much kinder to catfish from the Fossil Lake region and would explain their lack of a fossil record in that locality. Both catfish genera average 7 inches in length and top out around 12 inches. These numbers hold true for Astephus and, given a lack of material, are reasonable estimates for Hypsidoris.
Bowfins - The family Amiidae is characterized by a lengthy arching dorsal fin, hence the moniker, bowfin. Two species of bowfin appear in the fossil fauna of the Green River Formation, Amia pattersoni and Cyclurus gurleyi. Both fish are rare in the Green River Formation fossil record, but of the two, C. gurleyi is slightly more rare. These fish reached fairly large sizes in comparison to other common fishes. C. gurleyi had a fusiform football shape and molariform teeth that were good for eating the mollusks and arthropods in nearshore habitats. This species maxed out at about 3 feet long, but little is known for drawing an average length because of the lack of collected material. A. pattersoni had an elongate body plan and long, slender jaws that made them hearty predators of other fish. There are more adult A. pattersoni fossils at the nearshore deposits than of the other bowfin species. The largest recorded A. pattersoni specimen was about 4.6 feet long, and most of the fossilized bowfins of this species measure over 3 feet in length. Juveniles of both species are exceptionally rare.
Gosiutichthys - This species of clupiform fish is commonly found in mass mortality plate fossils. Not uncommon for herring, these school mortality plates are often observed in Knightia fossils as well. These fish are far more common in the Lake Gosiute Sediments than Fossil Lake, even gaining its genus name from the lake in which they are found. Gosiutichthys average between 2 and 4 inches long and rarely occur as individuals in the fossil record. They are a staple of the Laney Shale Member fauna which dates back to around 49 million years ago.
How Do The Fish Get Out Of The Quarries And On To Our Website?
There are several commercial quarries operating within the Green River Formation. Many of them offer pay-per-dig opportunities to tourists and fossil enthusiasts. The fossil fish that we have for sale are purchased wholesale from these quarries. The quarries dig fish from the two primary fish layers at Fossil Lake– the split fish layer (sometimes called the sandwich beds) and the 18-inch layer.
A view of one of the commercial quarries where fossils from the Green River Formation are collected.
The split fish layer occurs where the fish “split out“ near the surface of the bedding plane, often at the lake’s shoreline and often have a rust-orange coloring. Fish from the 18-inch layer are usually buried deeper under the surface of the rock, which coincides with a mid-to-deep-lake environment. The 18-inch layer offers better preservation, a result of finely laminated layers, but requires significantly more time and skill to collect and prepare. However, you rarely find bottom-dwelling species in the 18-inch layer because of the anoxic environment of the lake bed.
An unprepared fossil fish from the 18 inch layer. The fossil is totally under the surface of the rock.
At FossilEra we offer fossil fish for sale from both of these layers, though the 18-inch layer specimens are typically much more expensive due to the amount of extra time and effort involved. Granted, the results and quality of the fossil display are well worth the higher price.