Paleontology in Oregon refers to paleontological research occurring within or conducted by people from the U.S. state of Oregon. Oregon's geologic record extends back approximately 400 million years ago to the Devonian period, before which time the state's landmass was likely submerged under water. Sediment records show that Oregon remained mostly submerged until the Paleocene period. The state's earliest fossil record includes plants, corals, and conodonts. Oregon was covered by seaways and volcanic islands during the Mesozoic era. Fossils from this period include marine plants, invertebrates, ichthyosaurs, pterosaurs, and traces such as invertebrate burrows. During the Cenozoic, Oregon's climate gradually cooled and eventually yielded the environments now found in the state. The era's fossils include marine and terrestrial plants, invertebrates, fish, amphibians, turtles, birds, mammals, and traces such as eggs and animal tracks.
Oregon has a long tradition of paleontological research. Local Native Americans devised myths to explain fossils. By the mid-19th century local fossils had come to the attention of formally trained scientists, and modern research has produced data on climate change and extinction.
The Oligocene dawn redwood Metasequoia occidentalis is the Oregon state fossil.
There are no known rocks in Oregon from Precambrian times. Geologists infer that the area now occupied by Oregon must have been submerged deep on the ocean floor during that period.
Paleozoic Era Oregon's oldest known rock formations are found in the Blue Mountains and the Klamath Mountains. The state's oldest individual rock is a limestone near Suplee dated to nearly 400 million years ago, during the Devonian period of the Paleozoic era. These deposits include conodonts as well as extinct corals and brachiopods, indicating a shallow marine environment. Most of Oregon would remain under water until the Cenozoic era.
Starting in the Carboniferous period, a series of volcanic archipelagos formed in the region. Islands in these chains would have hosted warm, wet terrestrial environments. Fossils in Oregon's oldest floral assemblage, dating to the Late Carboniferous period, implies a lagoon ecosystem. Fossils in the assemblage include horsetails, ferns, scale trees, and conifer tree seeds. Formations of similar age also include shallow water invertebrates indicating that Oregon's volcanic islands were surrounded by coral reefs, which is consistent with Charles Darwin's theory of reef formation.
Island chains continued to form over Oregon through the Permian period. Fossil assemblages from that time are therefore similar to those from the Carboniferous, although none have been found that include any Permian plant life. One species of Permian snail found in Oregon, Acteonina permiana, lends credence to the theory of plate tectonics because of its resemblance to contemporary Eurasian species. Fragmentary remains of Permian trilobites, including the endemic species Cummingella oregonensis, have been found in the state's Coyote Butte Formation.
Mesozoic Era Oregon remained covered by shallow seaways throughout the Mesozoic era. Rising temperatures throughout the era led to rising sea levels. Oregon's fossil flora and fauna track these environmental changes with the addition of species adapted to deeper water or more tropical terrestrial conditions.
A new series of tropical islands emerged during the Triassic period, formed by the merging of the state's older volcanic chains. The only plant fossil from Oregon's Triassic formations is Diplopora oregonensis. As in the Paleozoic, shallow water invertebrates made up Oregon's Triassic fauna. These include sponges, ammonites, radiolarians, brachiopods, and the belemnite Aulacoceras. The trace fossil Chondrites, a species of fodinichnid, has been found in the same formations. Although corals have also been found in these assemblages, paleontologists debate the presence of true coral reefs in the region during the Triassic. The oldest vertebrate fossils in Oregon's fossil record appear in Triassic-aged limestones in the Wallowa Mountains. These fossils, including vertebrae, ribs, and a partial skull, have been assigned to the early ichthyosaur genus Shastasaurus. Additionally, a new genus of basal thalattosaur has been recovered from the Brisbois Member of the Vester Formation in Central Oregon near the community of Suplee.The breakup of the Pangaean supercontinent during the transition to the Jurassic period created a subduction zone in Oregon's ancient seaway, burying older rock formations and giving way to new volcanic island chains. Oregon's Jurassic invertebrates, such as the reef-building clam Lithiolus problematicus and the mussel-like Buchia piochii, indicate shallow sea environments similar to those of the state's late Triassic. Among Oregon's Jurassic-aged vertebrate fossils are the remains of marine crocodiles known as Zoneait. These crocodiles likely shared Oregon's Jurassic seaways with ichthyosaurs. Plant fossils from Oregon's Jurassic period show that the terrestrial environment became warmer and wetter, creating swampy conditions. These fossils, from the Coon Hollow Formation and others of similar age, include ferns, quillworts, cycads, and conifers.
Oregon's islands collided with the Laramidian continent at the end of the Jurassic, creating a new western coastline during the Cretaceous period. This coastline later developed through a combination of sea level change and mountain uplift. Global temperatures reached their maximum during the mid-Cretaceous, melting mountain ice and increasing global sea levels. As sea levels rose the Pacific grew to cover more of Oregon's landmass, eventually stopping at the base of a coastal mountain range. These mountains blocked oceanic weather systems, creating a tropical rainy environment along the ancient Oregonian coast. Although the mountain range ran along that Cretaceous coast, it was different from Oregon's modern Coast Range.
Because of the spread of seaways over Oregon during the Cretaceous, plant remains from that time period tend to be rare in the region. Those that have been found come from the state's southwest and northeast, which indicate the presence of small islands in those areas during the period. Plant fossils from these areas tend to be endemic to the region. These include species of the fern Dicksonia, cycads Ctenis and Ctenophyllum, conifers Podozamites and Taxites, seeds of the palm Attalea, and the tree-fern Tempskya. The tree-fern fossils have been found associated with ammonites, suggesting the location of an ancient shoreline. Other Cretaceous invertebrates in the region are similar to those found in Jurassic formations. Cretaceous formations in Oregon tend to include a wider variety of trace fossils, including the fodinichnids Planolites, Skolithos, Glossifungites, and Arenicolites. Oregon's oldest known crustacean, a unique species named Hoploparia riddlensis, is also of Cretaceous age.
Oregon's vertebrates become more diverse in its Cretaceous fossil record. An amateur discovery in 2005, popularly dubbed "Mitchell's Monster," shows that short-necked plesiosaurs roamed the state's Cretaceous seas along with ichthyosaurs. Other sites nearby in Wheeler County have yielded the remains of Oregon's only known pterosaur, attributed to Bennettazhia oregonensis, as well as teeth from the extinct goblin shark Scapanorhynchus. Only two non-avian dinosaur fossils have been found in Oregon, and both are isolated bones in marine rocks, which evidently bloated and floated out to sea. One is the pedal phalanx of a large (5 m long) ornithopod, intermediate in size and morphology between Tenontosaurus and Eolambia, from the Early Cretaceous (Albian) Hudspeth Shale near Mitchell, Oregon. The other is a sacrum fragment, attributable to a hadrosaur similar to Lambeosaurus, recovered from Late Cretaceous (Campanian) sandstones at Cape Sebastian on the southern Oregon coast.
There is no geological record in Oregon of the K-Pg boundary or of the event that ended the Mesozoic era.
Cenozoic Era Oregon's paleoenvironment in the Cenozoic reflected the era's overall global cooling trend, shifting from tropical to temperate to glacial climates. Westward shift in the state's shoreline brought a more diverse terrestrial fauna, including a variety of extinct land mammals.
The state's earliest Paleogene deposits record an environment that was warm and wet, similar to the modern American southeast. Fossils from this time include pollen and leaves from ferns, spongeplants, hazelnuts, water elms, laurels, and horsetails. Trees that would become more common when temperatures later cooled, including alder and birch, made their first appearance along Oregon's Paleogene coastline. Invertebrate foramenifera from the Paleogene have been reported from sediments in Coos County, but their identity remains disputed.
Oregon's mid-to-late Paleogene fossil record is split between the ocean-covered western part of the state and the terrestrial east, where mammals made their first appearance in the state's fossil record.
In western Oregon's ocean, the new Cascadia subduction zone laid the foundations for Oregon's modern Coast Range and improved ocean productivity, prompting diversification among the state's fauna. At least 25 species of mollusk, including several snails, are known from the Fern Ridge Dam area alone. Other marine invertebrates include echinoderms, foramenifera, brachiopods, scaphopods, shrimp, and crabs. Shark teeth from over a dozen genera have been found at a variety of sites, including the Rocky Point Quarry to the west of the Nehalem River. These genera include dogfish, horn sharks, comb-toothed sharks, makos, tiger sharks, white sharks, and an archaic basking shark. Bony fish included mahi mahi, conger eels, rattails, ancestral billfish, cod, hake, and rockfish. Marine birds in the area included auks, the local species Hydrotherikornis oregonus, and the pelican-like Phocavis maritimus. The state's only known fossil egg was found in associated rock formations. The subduction zone's volcanic activity also formed the Cascade volcanic arc, which blocked moist air from the Pacific and created the state's High Desert. This is when Oregon's fossil-rich John Day Fossil Beds were first laid down. The earliest fossils in John Day indicate a subtropical terrestrial environment. The assemblage is rich in fossil seeds, fruit nuts, and associated woods, and is one of the few places in the world where all three are preserved in a single location. The flora included cinnamon, cycads, palms, the primitive sycamore Platanophyllum angustilobus, walnuts, magnolias, figs, grapes, coffee trees, cashews, and bananas. The state's earliest known land mammals—including the rhinoceros Hyrachyus, the early horse Orohippus, and the brontothere Telmatherium—browsed these flora. Among the area's predators was Patriofelis, a cat-like creodont. These mammals shared the ecosystem with crocodiles in the genus Pristichampsus and the tortoise Hadrianus.