The Green River Formation is famous for the many fish, birds, and mammal species immaculately preserved in the fine lakebed sediment, but perhaps more impressively, that fine grain sediment was also perfect for preserving the many insects that made these ancient lakes their home. Among the insects found are flies, crickets, dragonflies, beetles, and more. Some of these specimens are so well preserved, patterns and pigments can be seen in the fossils themselves.
Whip-tail Stingray (Eocene)
Heliobatis radians was a freshwater stingray found exclusively in the fossil lakebeds of the Green River Formation in the Western United States. Like modern marine stingray species, Heliobatis radians has a flat body and barbed stingers on their long tails for defense. When not searching for food, these stingrays buried themselves in the fine-grained mud at the bottom of the lakes, which served to preserve a handful of these unique stingrays. The conditions for preservation were so optimal that even the radial pattern of their fin supports are sometimes present in the fossils. This striking pattern provided inspiration for their name, “Heliobatis”, which translates to “sun rays” in latin.
Knightia eocaena were small (typically 3 to 6 inches long) schooling fish whose fossils are largely found in the Green River Formation of the Western United States. Knightia eocaena were an integral part of the ecology of the region during the Eocene as they were the primary prey item for larger fish like Diplomystus dentatus as well as the various birds, snakes, and turtles that lived in or near the lakes. As such, their fossils are plentiful in the rock quarries of the Green River Formation and easily accessible for fossil collectors. Modern relatives of the Knightia eocaena like herring, sardines, and shads remain vital to commercial fish markets and marine food chains.
Mioplosus labracoides was a freshwater fish whose fossils are found almost exclusively in the ancient lakebeds of the Green River Formation. They grew to about 16 inches and are easily recognized by their elongated body shape and forked tailfins. Adult Mioplosus labracoides were likely solitary animals, as their fossils are not typically found near others of their species, but juvenile specimens of Mioplosus are often found within schools.
Priscacara serrata is an extinct species of bass-like fish whose fossils are found almost exclusively in the Green River Formation located in Western United States. These fish had striking dorsal spikes that make them a favorite among fossil collectors. They grew up to 16 inches and occasionally are found with smaller fish lodged in their mouth or throats, suggesting that they had a tendency to choke on larger food items. Their primary source of food was small arthropods and mollusks and possessed tooth-pads in their throats that helped grind up the hard components of their prey.
Cockerellites liops is an extinct species of schooling fish that lived in the lakes of the Green River Formation during the Eocene epoch. These fish were small with rounded, sunfish-like profiles, growing up to 6 inches in length. They had small mouths and are assumed to have fed on zooplankton and insects. They are known for their prominent spiny dorsal fins that were likely used both for defense and stabilization while swimming.
Diplomystus dentatus was a freshwater fish whose fossils are commonly found in the Green River Formation of the American West. It was distantly related to modern herrings, sardines, and anchovies. Their upturned mouths were perfectly shaped for feeding on smaller fish that congregated near the surface of the water from below. In fact, the fossils of Diplomystus dentatus are often found with Knightia eocaena fossils in their mouths, throats, and stomachs.
Icaronycteris index is an extinct species of bat that is found exclusively in the Green River Formation in the American West. The genus Icaronycteris contains the oldest species of bats ever found (about 50 million years old) and has been instrumental in teaching us about the evolution of bats. Because bat bones are lightweight and delicate, there are currently no complete specimens of older relatives of the Icaronycteris index (and the slightly older Icaronycteris gunnelli), which shrouds the bat lineage in mystery. The fine grain of the Green River Formation’s sediment has allowed for a few complete preserved skeletons of these early bats, and hopefully their prior lineage will be discovered in future excavations.
What is known is that these first true bats were small, used echolocation to hunt insects in midair, had long tails, a claw on their thumb and index ‘fingers’, and had membranous wings.
Messelornis nearctica was a terrestrial bird which was likely non-adept at flight. It was omnivorous and ate fish, fruits, and seeds. Messelornis nearctica is one of several bird species associated with in the Green River Formation in the American West.
The Notogenus osculus was a bottom feeding fish found in the Green River Formation of the American West. It had a toothless mouth that essentially vacuumed detritus off the lake floors and grew up to about 35 inches long. The large quantity of sub adult fossils (about 18 inches long) of Notogenus osculus found in the ancient lakebeds of the Green River Formation suggest that these fish likely spawned in the lakes before continuing their journey down connecting streams and rivers for the rest of their life cycle.
The Squalicorax falcatus, or the Crow Shark, was a mid-sized predatorial shark species that lived during the Cretaceous period, whose fossil teeth are found in North America, Europe, and North Africa. It grew to be about 16 feet long and preyed on fish, mosasaurs, and sea turtles. A Crow Shark tooth was found imbedded in the foot bone of a hadrosaur, showing that they even scavenged land animals that were swept out to sea.
Primobucco mcgrewi was a small, long-legged roller (a bird group defined by their intricate arial maneuvers during courtship). Rollers like Primobucco hunt insects mid-flight, as well as small amphibians and snakes.
The specimens pictured here were prepared by hand in the Earth Experience Paleo Lab.
Presbyornis pervetus was a long-legged waterfowl that filter fed along the shorelines of the lakes that made up the Green River Formation environment with its duck-like beak. It was a member of the Anseriformes family, meaning it was related to modern ducks, geese, and swans.
Amia pattersoni was a large bowfin fish–– so called because of the arcing curve of their dorsal fin –– that lived throughout North America, Asia, and Europe from the late Cretaceous to the early Eocene. They are one of several bowfin species found in the Green River Formation. They were predators of the freshwater environs of Green River and are often found fossilized with smaller fish in their mouths or stomachs.
Paddlefish are a relatively rare find in the Green River Formation, making up only 0.02% of the fish fossils excavated there. Specimens of the Crossopholis magnicaudatus range from about 1 to 5 feet in length and had a bony protrusible jaw (jaws that lunge forward independently of the skull) used to hunt smaller fish, unlike its closest modern relative, the Polyodon, which exclusively filter feeds.
Pterodactylus kochi was a small pterosaur that lived in southern Germany during the Jurassic period. Often depicted as giant avian terror, pterodactyls in reality were a smaller variety of pterosaur, with a wingspan of 1 to 4 feet. The Pterodactylus kochi was particularly small with a 18 inch wingspan.
Pterodactylus kochi lived and hunted amongst the lagoons and archipelagos of ancient Germany. They ate small schooling fish, insects, crustaceans, and any other small animal they could catch. Much of what we know about this species is thanks to the incredibly well- preserved specimen from the Solnhofen Limestone.
The idea that birds are dinosaurs is still relatively fresh in the general zeitgeist, but paleontologists have been investigating this connection since the discovery of the first fossils of Archaeopteryx lithographica were unearthed in 1861. Since then, more fossils have been found which further support the link between birds and theropod dinosaurs of old.
Like some modern birds, they ate small mammals, lizards, amphibians, and insects. Unlike modern birds, the Archaeopteryx had teeth instead of a hard beak. It also had claws at the bend of its wings that scientists think they used to grab onto trees as they glided through the canopy. As for flight, there is still a debate over whether they could truly take flight as easily as modern birds. It is possible that they relied on gliding from tree to tree like a sugar glider or required a running start with little hops to take off flying.
Compsognathus was a genus of small theropod dinosaur that lived in Europe during the Jurassic period. Compsognathus, sometimes nicknamed ‘Compie’, is among the smallest dinosaurs, not accounting for modern birds, growing anywhere between 2 and 3 feet in length and weighing up to 8 lbs. The Solnhofen specimen was even smaller, about 30 inches long from nose to tail and weighing between 1 and 3 lbs, but this specimen was later determined to be a juvenile. It is thought that the Compsognathus would use its speed, agility, and sharp teeth to ambush small prey like lizards, insects, and possibly even small pterosaurs. Unlike their depiction in popular media, it is unlikely that they hunted in socially active groups.
In the waters of old Baravia, Germany, the Tharsis dubius, a small carnivorous ray-finned fish made their home. These tiny fish fed by sucking plankton and other tiny prey items into their mouths. Fossils of the Tharsis have shown that they often choked on their prey and died of suffocation.
Dakotaraptor was a mid-sized carnivorous theropod dinosaur discovered in the South Dakota region of the Hell Creek Formation. At an estimated 16 feet in length from nose to long feathered tail, the Dakotaraptor bridges the gap between the gigantic tyrannosaurids like the Nanotyrannus and smaller theropods like the Pectinodon. The Dakotaraptor is the second largest raptor species discovered, only dwarfed by the Utahraptor. Most of fossils found of this animal are individual teeth.
Did you know Tennessee has a state fossil? Pterotrigonia thoracica was a bivalve that lived in the shallow seas that covered much of the middle of North America during the Cretaceous (Western Interior Seaway). Pterotrigonia thoracica was chosen as the state fossil due to its abundant fossils found in the Coon Creek Formation in West Tennessee.
Plesiosaurs were marine reptiles that lived during the age of the dinosaurs. Though not dinosaurs themselves, Plesiosaurs are well-known for their distinctive body shape which inspired the famous cryptid, the Loch Ness Monster. While many believers argue that a Plesiosaur could still be in Loch Ness in Scotland, they all unfortunately went extinct at the same time at the non-avian dinosaurs following the K-Pg Impact. Their diet was comprised of fish and cephalopods. Plesiosaurs came in different shapes and sizes; some where large and long-necked like the Zarafasaura oceanis who had short faces with long necks, while some like the Pliosaurus had short necks and large heads.
The first complete Plesiosaur fossil was found by famous female paleontologist Mary Anning in 1823.
Toxochelys was a genus of sea turtle that live in the Western Interior Seaway, and its fossils are found in the United States and Canada. Toxochelys lived a similar life as modern sea turtles, feeding mostly on jellyfish, squids, mollusks, crustaceans, and marine vegetation. However, Toxochelys was larger, growing up to 6 feet in length.
This specimen was found by museum staff in the Coon Creek Formation in Tennessee.
Little is known about the Paronychodon. The only fossils found as of yet of this group of theropds are teeth like the one pictured here. These mysterious carnivorous dinosaurs lived in North America during the late Cretaceous, and similar teeth have also been found in Eurasia, which may indicate that this genus could have been fairly far spread.
The Nanotyrannus is a newly confirmed genus of therapod dinosaur that lived alongside the Tyrannosaurus rex at the end of the Cretaceous period. For years, scientists debated over whether this smaller was a teenage T. rex or its own distinct species. In 2025, the researchers at North Carolina Museum of Natural Sciences determined that the theropod in their famous fossil “The Dueling Dinosaurs” was fully-grown at the time of death. This discovery settled the debate once and for all. Now that the two species are officially split, our understanding of both the Nanotyrannus and the T. rex are forever changed.
One of the most famous and beloved dinosaurs, the Tyrannosaurus rex, was the king of Hell Creek back during the late Cretaceous. Its name translates to “king of the tyrant lizards”, which it earned by being one of the biggest theropod dinosaurs (12 feet tall and 40 feet long) and possessing the greatest bite force of any land animal ever (8,000 – 12,800 lbs. per square inch). The T. rex is often noted for its large head full of long sharp teeth which was ideal for taking big bites out of its big prey like the Triceratops or Edmontosaurus.Its small arms are also cause for conversation; some scientists think their small (approx. 3 feet) arms were a trade-off for its large head, which was much more useful than long arms would have been considering its very large prey items. It is also possible that T. rex simply ‘grew out’ of their arms, as younger T. Rex specimens have for more proportional limbs.
At Earth Experience, you can see a full-scale T. rex model named Frank and get a feel for just how big these tyrants were.
The Champsosaurus was a large aquatic reptile that lived in slow-moving freshwater rivers, swamps, and ponds during the Cretaceous period and into the Paleogene epoch. Champsosaurus was an odd-looking animal, with a crocodile-like body and an elongated snout which was useful in ambush hunting for fish. Despite their similarities to crocodilians, they are not closely related.
The Triceratops was a tank-sized herbivore that lived up to the end of the age of the dinosaurs. The Triceratops had several defining features like its three horns used to defend against T. rex attacks and a beak it used to shear tough plants to eat. The purpose of its large fan-like structure on the back of its head called the ‘frill’ is still a matter of debate. Some think the frill was a defensive measure to protect its neck from the devastating bite of a T. rex, while others think it likely displayed distinctive colors or patterns to attract mates and be recognizable to other Triceratops. There are even theories that it was used as thermoregulation, as the frill was full of veins that could have allowed the animal’s blood to cool.
At Earth Experience, we have been lucky enough to be able to work on a Triceratops skull from the Hell Creek Formation in Montana. Our specimen is likely a subadult, meaning that even with its large size, full grown Triceratops would still be slightly bigger. Due to erosion, our skull is missing its horns, which is unfortunately common with Triceratops fossils. It does still have a lot of its frill still protected in its plaster jacket until more of the base skull is prepared and stabilized. Come see this work-in-progress in person!
Amongst the fossil bones and teeth of dinosaurs, paleontologists occasionally find fossilized dinosaur egg material. As you might expect, dinosaur eggs are rarely found due to their delicate nature, and it is generally hard to determine what type of dinosaur may have once been inside. However, finding the eggs, or better yet, the nests tell us a lot about dinosaur behavior. Some fossils of Oviraptor dinosaurs have been found on top of their eggs, indicating that they cared for their eggs like modern birds. Other larger species buried their eggs rather than brood as their weight would have done more harm than good.
With modern technology, our understanding of dinosaur eggs has improved further. It is possible to perform a CT scan on dinosaur eggs, which makes it possible for scientists to learn more about dinosaur embryos and their development.
Pectinodon bakkeri was a small bird-like dinosaur in the theropod family. Little is known for certain about the Pectinodon due to scant fossil evidence aside from the animal’s comb-like teeth. By comparing the teeth to other small theropods, it is assumed that Pectinodons was a small, agile, feathered predator. Its few fossils have largely come from the Lance Formation in Wyoming.
Little is known about the Richardoestesia because there has not been a lot of fossil evidence for this morphogenus. What is known about this group comes from fossil teeth like the one pictured here, which have been found in Southern Canada, Northwest United States, and even in some locations in Asia and Europe. From the teeth found, scientists believe this group of dinosaurs were carnivorous theropods. More fossil evidence needs to be found before more conclusions can be drawn about this mysterious group.
Pachycephalosaurus was a bipedal herbivorous dinosaur which is best known for its odd, dome-shaped growth on top of its head. Scientists have not yet come to an agreement on what their hard heads were used for; some think they may have used them to ram others of their species, while others think it was for display to impress potential mates. Others yet think their noggins were used for a combination of the two.
The Ankylosaurus was a large, armored dinosaur that lived in North American during the Cretaceous period. The Ankylosaurus was like a living tank, covered in spiky osteoderms (bony-plates) which protected it from large predators like the T. rex, and had a large club tail which they would use as a bone-cracking weapon against predators or fellow Ankylosaurus. Ankylosaurus were herbivores and ate low growing vegetation like ferns, horsetails, and fallen fruit.
One of the best-preserved dinosaur specimens ever found was a Borealopelta, another genus of Ankylosaur, which still has the osteoderms, some skin, and even the stomach contents of its last meal preserved. You can learn more about this specimen and even see it in person at the Royal Tyrell Museum in Alberta, Canada.
Thescelosaurus was a genus of ornithischian (bird-hipped) dinosaurs that made its home in North America. Thescelosaurs were beaked herbivores that grew to be 10-13 feet long. By studying its cranial structure, scientists have come to believe that the Thescelosaurus relied on a keen sense of smell to find buried roots and tubers to eat.
Stygimys is a genus of extinct mammals that originated in the Late-Cretaceous and lived in North America and Northeastern Asia. Like most mammals of the time, they were small and rodent-like in nature and belonged to the multituberculates, which is a now extinct order of mammals defined by their unique, knobby teeth.
Didelphodon was an omnivorous and likely scavenging mammal that lived during the Cretaceous period. It was one of the largest mammals at the time, yet only grew about 3 feet long. It had sharp teeth and a strong bite force, which helped it crack the shells of turtles, clams, and snails. It also likely ate eggs, aquatic vegetation, and the carcasses of dinosaurs.
Struthiomimus was a mid-sized theropod dinosaur (about 13 feet from beak to tail). The name Struthiomimus literally translates to “ostrich mimic”, which is an apt name, as this dinosaur heavily resembled modern flightless birds. Besides its ostrich-like appearance, the Struthiomimus is perhaps best known for its estimated speed. Scientists think these animals could run 30-50 miles per hour, similar to modern Grizzly Bears, Lions, and conveniently, ostriches.
Coniophis precedens was roughly 7cm long and one of – if not the – first ever snake species. Coniophis precedens acts as a ‘missing-link’ species, demonstrating that snakes diverged from terrestrial lizards as opposed to marine reptiles. Like modern snakes, it had no limbs, but it had not yet developed the jaw structure found in modern snakes which allows them to eat larger prey. This means that Coniophis precedens would have had to eat smaller prey items like salamanders and lizards.
Habrosaurus dilates is an extinct type of salamander whose fossils are commonly found in the Lance and Hell Creek Formations in the Western United States and Southern Part of Canada. It was about the size of a modern Hellbender salamander and munched on small, shelled animals like crayfish or snails. Habrosaurus dilates was one of the lucky species that survived the K-pg Impact extinction event.
Myledaphus bipartitus was a freshwater ray whose fossils have been found in Western United States and Canada. Myledaphus bipartitus was related to modern rays and guitarfish. Most of the fossils found have been fossil teeth which were used to crush the shells of clams and other bivalves.
Gar fish are long-bodied freshwater fish who possess armored scales along their bodies. Gars belonging to Lepisosteidae first developed in the early Cretaceous, but ancestors to these Gar first show up in the fossil record during the Jurassic Period. Gars are often called ‘living fossils’ as they have gone virtually unchanged over the last 100 million years. There is plenty of fossil evidence for the Gar in the Hell Creek Formation; their armored scales fossilize very well and appear a bit like shards of obsidian among the dirt.
Cyclurus fragosus was a species of bowfin fish that is most often found in the Hell Creek Formation.Cyclurus are thought to be the closest relatives of modern bowfins, but much smaller than their extant counterparts, only growing between 4 and 12 inches long.
The Edmontosaurus annectens was a species of Hadrosaur that lived during the Cretaceous period in the modern US and Canada. Many Edmontosaurus annectens fossils come from the Hell Creek Formation, where they lived among Triceratops, T. rex, and other smaller ceratopsians and theropods.
One of the only dinosaur fossils ever found in Tennessee was a chevron (a part of the spine) from what is thought to be Edmontosaurus annectens. It is likely that the animal had died near or in a river and was washed out into the Western Interior Seaway where it fossilized. You can see this chevron at Earth Experience Museum.
The Mecochirus longimanatus is an extinct species of lobster-like crustacean whose fossils can be found in the Solnhofen Limestone of Bavaria, Germany. It is named for its extra long appendages that were likely used for feeding.
Horseshoe crabs have been around for about 450 million years, surviving all five major extinction events. You may notice that this particular species found in the Solnhofen Limestone, Mesolimulus walchi, looks a lot like modern horseshoe crabs. Their body plan has been so successful that they have not had to change very much at all to survive into the modern era. While Mesolimulus walchi may be extinct, its modern relative still thrive in the oceans today.
The Solnhofen Limestone has not only preserved the bodies of the crabs, but also their footprints!
Aeger tipularius was a species of shrimp that lived in the waters of the archipelago of modern Bavaria Germany. These shrimps are very well preserved by the fine grain of the Solnhofen Limestone.
Unlike stalked crinoids, the Saccocoma pectinata was a free-floating species that fed on plankton. It is believed that the Saccocoma pectinata could swim using its feathered arms to propel itself through the water. These crinoids have been excellently preserved in the Solnhofen Limestone with some specimens even retaining their feathery arm structures.
The Solnhofen Limestone is responsible for some of the best-preserved insect fossils from the Mesozoic. The fine grained sediment allowed for immaculate preservation of wing structures, body segments, and even coloration patterns. The preservation of insect species tells us about the type of environment of ancient Germany. For example, the presence of dragonflies and water striders tells us that the area was had laden with lagoons and bodies of freshwater.
Rhamphorhynchus was a small pterosaur that lived in Europe during the Jurassic, most often found in the Solnhofen Limestone of Germany. Rhamphorhynchus is one of the best understood pterosaurs due to the excellent preservation in some of the fossils found, even including the wing membranes, skin, and stomach contents. Rhamphorhynchus had sharp teeth which it used to catch fish and other sea creatures and was an agile flier with an approximately 3-foot wingspan.
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