Fossil Arthropod Species

There are over one million living arthropod species today. Arthropods are invertebrate animals (having no backbone or spine) with a hard, external skeleton (known as an exoskeleton), segmented bodies, and jointed appendages.

See some of the arthropod fossils on display in our museum exhibits.

Freshwater seed shrimp (ostracods) are the most common arthropod fossil found in the Fossil Butte Member (FBM).
Bechleja rostrata shrimp fossil with long antennaenext to fossil fish, additional fish tail in corner
Bechleja rostrata with Diplomystus dentatus catalog number FOBU11821

NPS Photo

Shrimp - Bechleja rostrata

Order Decapoda, Family Palaemonidae
The Bechleja genus appears to have gone extinct sometime during the Eocene. Living members of the Palaemonidae family includes over 900 species that live in freshwater and marine waters. They are also known as prawns and are primarily carnivores.
Procambarus primaevus crayfish fossil with large front claws
Procambarus primaevus catalog number FOBU11926

NPS Photo

Crayfish - Procambarus primaevus

Order Decapoda, Family Cambaridae
Living members of the Procambarus genus include 160 species primarily found in warm freshwaters in North America and Central America.
Spider fossil with 8 visible long legs and large body
Lycosidae (wolf spider) catalog number FOBU13456

NPS Photo

Spiders - 3 Unidentified Species

Order Aranae
  • Family Thomisidae (crab spider)
  • Family Salticidae (jumping spider)
  • Family Lycosidae (wolf spider)
Spiders are very uncommon fossil specimens in the FBM. It is possible this is because spiders' soft bodies are prone to fast decay or spiders may have been eaten before they could break water tension and sink to the bottom of Fossil Lake.

Three families have been identified from the FBM, but no species have been described. Together, the 3 families contain thousands of modern species. None of these species of spider use a web to catch prey.


Insect fossils in the Fossil Butte Member (FBM) exist only as very thin carbon stains on the rock. Unlike fossil vertebrates (animals with a backbone), their skeletons are not visible beneath the rock. Insect specimens are found when the splitting rock layers split directly on the carbon stain.
Tynskyagrion brookae dragonfly fossil with white lines one third of the way down the wings. From Green River Formation.
Tynskyagrion brookae damselfly catalog number FOBU448

NPS Photo

Dragonflies & Damselflies

Order Odonata
  • Suborder Zygoptera (damselflies)
  • Suborder Epiprocta (dragonflies)

Living members of the Odonata order are diurnal (active during the day) predator insects. They are exclusively freshwater insects during nymph state (juvenile stage).

The FBM has produced several Odonata specimens. No dragonflies are described as of yet, but there are seven described damselfly species: Carlea eocenica, Labandeiraia riveri, Zacallites cockerelli, Dysagrion integrum, Tenebragrion shermani, Tenebragrion tynskyi and Tynskysagrion brookeae. The presence of nymph specimens indicate Fossil Lake was a freshwater lake.

light impression of fossil cricket body with long antennae
Orthoptera catalog number FOBU11854

NPS Photo


Order Orthoptera, Family Gryllidae
Of the Orthopteran order, which includes katydids, grasshoppers, locusts, and crickets, only cricket and grasshopper specimens are known from the FBM. None have been described as species, yet the crickets closely resemble the living family Gryllidae (true crickets). Living members of the Gryllidae family are nocturnal, omnivorous, and an important food source for amphibians, reptiles, and other arthropods.


Order Plecoptera

Fossils of stonefly nymphs have been found in the FBM. Modern stoneflies will spend 1-4 years as aquatic nymphs and live for several weeks as winged adults. The sole purpose of adulthood for these insects is to breed. To find a mate they “drum” the ground with their abdomen. Each drumming pattern is specific to the species.

A water strider fossil with four legs extended back behind its abdomen. From Green River Formation.
Water strider, catalog number FOBU1393

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True Bugs

Order Hemiptera

While “bug” is a name usually applied to any small insect or arachnid with more than four legs, Hemipterans are a diverse order of insects formally referred to as true bugs. They are characterized by their sucking mouthparts and partially reinforced front wings. All bugs from the FBM are undescribed, but they have been grouped into the following families:

· Scuterellidae (shield-backed / jewel bugs)

· Petatomidae (stink bugs)

· Cicadidae (cicadas)

· Gerridae (water striders)

· Cixiidae (primitive plant hoppers)

· Achilidae (achilid leaf hoppers)

· Fulgoridae (fulgorid leaf hoppers)

Many Hemipterans are adapted to an herbivorous lifestyle, using their specialized mouthparts to extract plant juices. However, some are carnivorous; the water strider, a common Hemipteran in the FBM, uses its four hind legs to “skate” on the water’s surface and grabs smaller insect prey using its two front legs.

A beetle fossil with alternating black and white zigzag pattern on the wings and one visible antenna that looks like a dotted line curving down towards the wing. From Green River Formation.
Beetle fossil, catalog number FOBU13518

NPS Photo


Order Coleoptera

Beetles are the most diverse group of animals on the planet with over 350,000 described species and many more awaiting description. Their incredible diversity is still being processed, which makes the classification and description of fossil species difficult. None of the FBM Beetles have been described, but have been grouped into the following families:

· Buprestidae (jewel/ metallic wood-boring beetles)

· Carabidae (ground beetles)

· Curculionidae (weevils)

· Cupepidae (reticulated beetles)

The largest (up to 2 in.) and most common FBM beetles are Buprestids. This family still exists, and are known for having bright, iridescent exoskeletons. Adults lay eggs in wood and the larvae eat the surrounding wood. When they metamorphose into adults, they consume mostly leaves.

Bee fossil with veins visible in wings and one antenna curled into a loop. From Green River Formation.
Bee fossil, catalog number FOBU17461a

NPS Photo

Ants, Bees, and Wasps

Order Hymenoptera

Ants, wasps, and bees are all known for forming some of the most intricate social structures in the entire animal kingdom. These societies are generally composed of a reproductive queen, sterile workers, and soldiers that defend the hives/ colonies. The flightlessness of ants makes them uncommon in the FBM, but bees and wasps are comparatively more common. All of the FBM Hymenopterans are undescribed, but three families of wasp are recognized:

· Vespidae (paper wasps, hornets, yellow jackets)

· Ichneumonidae (parasitoid/ scorpion wasps)

· Scollidae (flower wasps)

The evolution of bees and wasps is closely tied to the evolution and diversification of flowering plants. The relationship between the FBM insects and the plant life in the area is evident due to the frequency of leaves found with predation from insects. The circular patterns in some leaves suggest a relative of modern leaf-cutter bees.


Moths and Butterflies

Order Lepidoptera

Although lepidopterans are uncommon, the damage their caterpillars did to leaves 52-million years ago is frequently recorded in stone. All modern moths have a long, straw-like appendage for drinking nectar called a proboscis. At least two families are known from the FBM:

· Saturniidae (royal and giant silk moths)

· Pterophoridae (plume moths)

Another lepidopteran family known from the FBM is Papilionoidea, which includes true butterflies. The fossil butterflies here are some of the first true butterflies to appear in the fossil record.

Plecia pealei March fly fossil viewed from side with wings extended above and legs extended below. From Green River Formation.
Plecia pealei, catalog number FOBU11292

NPS Photo


Order Diptera

Flies are, by far, the most abundant insect fossils in the FBM: over 90% are flies, and 80% are from just one species. That one species is Plecia pealei, a relative of today’s March flies (Bibioinidae). March flies are sometimes called “love bugs” because they are frequently seen mating and thus produce a lot of offspring. The resulting swarms are a likely explanation for their fossil commonality. In addition to March flies, these other fly families are known from the FBM:

· Stratiomyidae (soldier flies)

· Tipulidae (crane flies)

· Sciaridae (dark-winged fungus gnats)

· Empididae (dagger flies)

· Chironomidae (non-biting midges)

Last updated: January 31, 2024

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