Fossil Fish Species

Fossil fish are the most common fossil finds from the Fossil Butte Member (FBM). So far, 27 species of fish have been discovered in the FBM. The diversity of species and the abundance of fossils, together allow scientists to understand the ecosystem of Fossil Lake.
stingray with long and skinny ray
H. radians FOBU11823 specimen

NPS Photo

Stingrays - 2 Species Identified: Heliobatis radians & Asterotrygon maloneyi

Order Myliobatiformes

  • Family Heliobatidae - H. radians
  • Family Asterotrygonidae - A. maloneyi
Stingrays have cartilaginous skeletons (lacking bones), so it is rare to find more than their teeth or stings fossilized. Currently, the FBM is the only place in the world where articulated, complete freshwater stingray fossils have been discovered. So many are found, that even the life cycles of the ancient species can be studied. One A. maloneyi specimen was found with several baby stingrays scattered around it.
There are almost 200 modern stingray species.
  • Most are bottom-dwellers and feed on bottom-dwelling invertebrates, such as shrimp and crayfish.
  • Stingray fossils are found in association with these species, indicating their ancient diet was similar to their modern relatives'.
  • Modern freshwater stingrays are found in tropical river systems of South America and Asia.

large fish with smaller fish surrounding it and inside belly
C. magnicaudatus FOBU7217 specimen

NPS Photo

Paddlefish - Crossopholis magnicaudatus

Order Acipenseriformes, Family Polydontidae
C. magnicaudatus is often preserved with fish in the stomach, indicating this species was a predator. This fossil species is most commonly found in shallow-water deposits, but very few juveniles have been discovered. This could possibly indicate that C. magnicaudatus matured and spawned in connecting rivers before migrating to Fossil Lake as an adult.
This species' name comes from the thousands of tiny, fringed scales covering its body, crossopholis meaning 'fringed scale.'
The maximum known size of this fossil species is 4 feet.
long fish with diamond shape scales covering entire body
A. simplex FOBU788 specimen

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Gars - 4 Species Identified: Lepisosteus bemisi & Atractosteus simplex & Atractosteus atrox & Masillosteus janei

Order Lepisosteiformes, Family Lepisosteidae
Seven living gar species are found in freshwaters of North America, Central America, and Cuba. Of the 4 Fossil Lake gar species, all but one are very similar to modern gars.
M. janei lacked the long jaw and sharp teeth characteristic of modern gars. M janei. teeth were instead rounded and flat, ideal for crushing small invertebrates like snails and crayfish. This gar species is primarily found in association with these fossil invertebrates.
Outside of the FBM, gar scales are much more common fossils than complete skeletons. The gars' characteristic, diamond-shaped scales have historically been used by humans as arrowheads and on protective breastplates. There tough scales offer significant protection from would be predators.
Modern gar species often migrate up rivers to spawn. This is one explanation for the lack of juvenile gar fossils found in the FBM.
flattened fish skeleton
A. pattersoni FOBU7218 specimen

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Bowfins - 2 Species Identified: Cyclurus gurleyi & Amia pattersoni

Order Amiiformes, Family Amiidae
The genus Cyclurus is not known to have survived past the Eocene Epoch, possibly dying out about 35 million years ago. The closely related Amia genus survives today with the North American A. calva species.
The long jaw and pointed teeth found on A. pattersoni specimens are indicators of a possible apex predator.
The crushing jaws found on C. gurleyi specimens suggest an invertebrate diet.
small fish with deep belly and forked tail
D. dentatus FOBU791 specimen

NPS Photo

Ray-finned Fish - Diplomystus dentatus

Order Ellimmichthyiformes, Family Paraclupeidae
The last known species of the Ellimmichthyiformes order went extinct sometime in the middle Eocene. D. dentatus is a primitive relative of the modern day herring. The genus Diplomystus is also known from fossil deposits in China.
D. dentatus is the 2nd most common fossil fish found from Fossil Lake. Specimens ranging from embryonic size (about 0.7 inches) to full-grown adults (about 26 inches) are common. Smaller-sized specimens are more commonly found in mid-lake than near-shore deposits. This suggests that D. dentatus spawned in open water.
This species' upturned mouth indicates it fed at the surface of Fossil Lake. D. dentatus specimens are commonly found with other fish stuck in their mouths, including other D. dentatus specimens.
flattened fish skeleton with forked tail
K. alta FOBU13444 specimen

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Herrings - 2 Species Identified: Knightia eocaena & Knightia alta

Order Clupeiformes, Family Clupeidae
The Clupeidae family has an estimated 50 modern freshwater species. Clupeidae species can lay as many as 200,000 eggs at once, allowing species to multiply quickly. Modern species are also prone to mass die offs.
K. eocaena is:
  • The most common fish found from Fossil Lake.
  • The most commonly found articulated vertebrate fossil in the world.
  • The Wyoming state fossil.
Both K. eocaena and K. alta are frequently discovered in mass mortality plates, some containing up to 100 fish per square meter. This suggests that, like their modern relatives, the Knightia species were sensitive to environmental changes.
K. eocaena specimens of all sizes are found in mass mortality plates, indicating this species schooled as both a juvenile and adult. The average adult size of K. eocaena specimens is about 6 inches, though specimens as large as 10 inches have been found.
long fish with non-forked tail and bony head
N. osculus BYU-I specimen

NPS Photo

Beaked Sandfish - Notogoneus osculus

Order Gonorynchiformes, Family Gonorynchidae
N. osculus was the last survivor of the Gonorynchiformes order in North America. There are 5 modern species in the Gonorynchidae family. They inhabit tropical marine regions of the Indo-Pacific Oceans.
Very young juveniles and large adults are the only N. osculus specimens found from Fossil Lake. This could indicate that N. osculus was a migratory species. Their lifecycle may have consisted of:
  • Hatching in Fossil Lake
  • Migrating to connecting streams to mature
  • Returning to Fossil Lake as an adult to spawn and die
N. osculus had a down-turned, sucker-like mouth. Its toothless mouth suggests that this was a bottom-feeding species. The highly salty water conditions at the bottom of Fossil Lake should have excluded most scavengers and bottom-feeders. Yet, N. osculus is found exclusively in deep-water deposits. This suggests that N. osculus spent most of its life outside of Fossil Lake in connecting rivers and streams.
round shaped fish with spiky fins on top
C. liops FOBU428_1 specimen

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Perches - 7 Species Identified: Mioplosus labracoides & Cockerellites liops & Priscacara serrata & 2 undescribed Priscacara species & Hypsiprisca hypsacantha & 1 undescribed Hypsiprisca species

Order Perciformes

  • Family Latidae - M. labracoides
  • Family Moronidae - C. liops, P. serrata, H. hypsacantha, and undescribed Priscacara & Hypsiprisca species
M. labracoides specimens:
  • are characterized by 2 dorsal fins and a forked tail
  • known to reach 20 inches
  • juveniles commonly found in mass mortalities and adults found alone, indicating M. labracoides traveled in schools as a juvenile and became solitary as an adult
  • juvenile and adult specimens often found preserved with smaller fish in the jaw or stomach
C. liops specimens:
  • known found as isolated specimens and in mass mortalities, indicating that C. liops traveled in schools throughout its life
  • known to reach a maximum size of 6 inches
  • body shape is similar to members of the modern Centrarchidae family (the sunfish family)
When you visit Fossil Butte National Monument, look for an enlarged bronze sculpture of C. liops on our entrance sign!
small fish with bony fins and opened sucker mouth
A. squamifrons FOBU11234 specimen

NPS Photo

Mystery Fish - Asineops squamifrons

Order Unknown, Family Asineopidae
  • known as the "mystery fish"
  • lacks identifiable traits to place in an order
  • A. squamifrons assigned its own family
  • appears to have gone extinct in the middle Eocene
  • characterized by short dorsal spines, rounded tail margin, tiny sharp teeth, and large mouth
  • known from isolated specimens and mass mortalities
  • may be primitive, spiny-rayed fish
big bellied fish
P. testis FOBU11245 specimen

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Bony-Tongue Fish - 2 Species Identified: Phareodus encaustus & Phareodus testis

Order Osteoglossiformes, Family Osteoglossidae
Living members of the Osteoglossidae family:
  • include 10 modern species
  • live exclusively in tropical freshwaters
  • found in South America, Africa, Asia, and Australia
  • mouth-brooders (parents hold eggs and hatchlings in their mouths)
Phareodus fossils:
  • adult specimens usually found alone, but juveniles known from mass mortalities
  • indicates that Phareodus schooled as a juvenile and became solitary as an adult
  • often preserved with smaller fish in their jaws and stomach, indicating they were predators
  • rearward oriented fins on back and underside, adaptation for speed
  • large, sharp teeth
  • max known size of P. encaustus: 30 inches
  • max known size of P. testis: 20 inches
small fish with opened sucker mouth and forked tail
A. brachyptera FOBU11240 specimen

NPS Photo

Trout-Perch - Amphiplaga brachyptera

Order Percopsiformes, Family Percopsidae
The Percopsidae family has one modern genus with 2 species. They are restricted to freshwater rivers and lakes of North America.
A. brachyptera is the earliest known member of the Percopsidae family, and is known exclusively from Fossil Lake deposits.
Larval-size A. brachyptera specimens are almost completely absent from the FBM. This suggests that A. brachyptera spawned in rivers.
A. brachyptera is also never found in mass mortality plates, indicating this species was solitary and not a schooling fish.
oval shaped fish with forked tail
H. falcatus FOBU11237 specimen

NPS Photo

Mooneye - Hiodon falcatus

Order Hiodontiformes, Family Hiodontidae
Living members of the Hiodon genus:
  • include 2 species
  • found exclusively in freshwater
  • known only from North America
  • reach about 20 inches in length
  • primarily feed on insects
Fossil specimens of the Hiodon genus are known from both North America and Asia. H. falcatus is almost exclusively found in near-shore sediment from Fossil Lake. Most specimens are between 4 and 6 inches long, though some are as large as 10 inches.

Last updated: November 17, 2022

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