Paleontology in Colorado refers topaleontological research occurring within or conducted by people from theU.S. state ofColorado.Thegeologic column of Colorado spans about one third of Earth's history.Fossils can be found almost everywhere in the state but are not evenly distributed among all theages of the state's rocks.[1] During the earlyPaleozoic, Colorado was covered by a warm shallowsea that would come to be home to creatures likebrachiopods,conodonts,ostracoderms,sharks andtrilobites. This sea withdrew from the state between theSilurian andearlyDevonian leaving a gap in the localrock record. It returned during theCarboniferous. Areas of the state not submerged were richly vegetated and inhabited byamphibians that left behindfootprints that would later fossilize. During thePermian, the sea withdrew andalluvial fans andsand dunes spread across the state. Manytrace fossils are known from these deposits.
The sea returned during theTriassic, while exposed areas were a richly vegetatedcoastal plain that was home todinosaurs. Colorado was again submerged by a sea during theCretaceous period that was home toplesiosaurs up to 70 feet long. During the early part of theCenozoic era,rainforests grew in Colorado. Later, another rich flora and fauna would come to be preserved in theFlorissant beds, where bothrhinoceroses anduintatheres lived. More recently the state's modernprairies began to form and the state was home to creatures likebison,camels,horses, andmammoths. LocalNative Americans have devisedmyths to explain local fossil bones and dinosaur footprints. By the late 19th century, local fossils had attracted the attention of formally trained scientists. Major finds include theLate Jurassic dinosaurs of theMorrison Formation and the Cenozoic plants and mammals of the Florissant beds. TheJurassic plated dinosaurStegosaurus armatus is the Coloradostate fossil.Stegosaurus is also thestate dinosaur of Colorado.
NoPrecambrian fossils are known from Colorado, so the state's fossil record does not begin until thePaleozoic.[2] At the start of the Paleozoic, Colorado was located near theequator. The state was submerged under a warm shallowsea.[2] At least part of Colorado was covered by shallow water during theMiddle Ordovician. At the time, Colorado was home to invertebrates likearticulated brachiopods,conodonts,gastropods,ostracods,pelecypods,sponges,trilobites, andworms (known from trace fossils). Contemporary vertebrates included armoredjawless fish calledostracoderms.[3] Sometime between theSilurian and earlyDevonian the sea withdrew from the state. While the sea was gone local sediments were eroded away rather than deposited. During theCarboniferous the absent sea returned, although some areas of the state remained dry land. Brachiopods, crinoids, sharks, and trilobites inhabited the sea. A rich variety of plants grew in Colorado's terrestrial environments. Examples includeCalamites,conifers, andlycopods.Mountain ranges were being raised in the western part of the state by geologic forces.[2] During theCarboniferous,footprints were laid down in Colorado by earlytetrapods that would later fossilize.[4] That being said, Colorado is not generally a good source of Carboniferous aged fossils.[1] Western Colorado had a series ofalluvial fans during thePermian when theCutler Group was being deposited. Preserved in thesesediments are tracks referred to theichnospeciesLimnopus cutlerensis, which may have been left by atemnospodylamphibian.[5] During the Permian the sea withdrew once more from the state. In its place were fields of sand dunes. Tracks left by ancient insects and reptiles were preserved in these dune deposits.[2] Also like the Carboniferous, despite the presence of contemporary trace fossils, the fossil record of Permian life in Colorado is relatively poor compared to states likeKansas andTexas.[1]
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Seawater returned to Colorado during the ensuingTriassic period, although it left significant areas of the state uncovered.[2] These terrestrial areas included coastal floodplains vegetated by conifers and inhabited by creatures likeamphibians anddinosaurs.[2] TheLate Triassic also saw the formation of many footprints that would later fossilize. These are preserved in the sediments of theChinle Formation of the northwestern part of the state.[6] A chicken to turkey sizedtheropoddinosaur left behind footprints of the ichnogenusAgialopous. These tracks contain large number of the ichnogenusRhynchosauroides, which resembleslizard footprints. The Chinle of Colorado also bears the greatest known abundance of the ichnogenusGwynnedichnium.[7] Both Triassic amphibians and reptiles left behind footprints near what is now theFall Creek Post Office.[3]
During theLate Jurassic deposition of the sediments now known as theMorrison Formation, bothsauropods andtheropods left behind footprints.[8] Only two large tracksites of fossil footprints are known from the Morrison Formation and both of them are located in Colorado.[8] A tracksite called Rancho del Rio preserves both sauropod and theropod tracks. The Rancho del Rio site is located along theColorado River in central Colorado. The other large tracksite is the Purgatoire Valley tracksite of the eponymousPurgatoire River in southeastern Colorado.[8] The Purgatoire Valley tracksite is 400 meters at its widest and contains four track-bearing strata. One of the four track bearing strata bears more than 1,300 individual prints.[9] A series of five parallel trackways left by young sauropods provides important evidence for dinosaur social behavior.[10] The trackways of young sauropods found at the Purgatoire Valley site fill important gaps in the local body fossil record, as the vast majority of sauropods skeletal remains in the Morrison come from grown individuals.[11]
Much of Colorado was covered by an expanding sea during the ensuingCretaceous period.[2] This sea is known as theWestern Interior Seaway.[12] Algae, fish, molluscs, and marine reptiles inhabited its waters.[2] ThemosasaurPlatecarpus was one such marine reptile.[13] When theGraneros Shale was being deposited in Colorado, theplesiosaurThalassomedon lived in the state.[14] This was a truly huge plesiosaur that could exceed 45 feet in length.[15] Beyond the shores of this sea were forests and swamps where early flowering plants grew. Later in the Cretaceous, the sea withdrew. Dinosaurs were still present, but the vegetation had undergone significant changes. The forests were now made of broadleafed trees and palms. At this point the local Rocky Mountains began to rise.[2] During theCretaceouscephalopods with coiled shells and clams were preserved atMonument Creek.[16]Fish were present in Coloradan waters and left behindscales that would later fossilize. On land the flora also left behindleaves that would later fossilize.[16] The sediments of theBenton Formation preserved bothinvertebrates andmarine reptiles.[16] ThebivalveOstrea congesta was preserved in the ColoradoNiobrara Formation.[3] The Niobrara's vertebrate life includedsharks, which left behind fossil teeth.[16] Colorado was home to bivalves and straight shelled cephalopods when the Pierre shale was being deposited.[16] The Pierre shale are mound-shapedbioherms up to 15 inches in diameter.[3] A sixty to seventy footplesiosaur was preserved in what is nowBaca County, which is in the southeastern region of the state.[17] Marinemollusks were preserved in theFox Hills Formation.[16]Oysters and other mollusks were preserved in the sediments now composing theDakota Formation. Aspects of the Coloradan flora were also preserved from this time. The most common plant fossils of the Dakota are the leaves ofdeciduous trees. Other contemporary plants includedferns andpalms.[18]
The uplift of the Rocky Mountains persisted into the early part of theCenozoic era. They were surrounded byrainforests at this point in prehistory. Areas in the state with lower elevation became the sites of vast lakes. Fish, insects, and leaves would end up entombed in sediments deposited by these lakes.[2] After the start of the Cenozoic, earlyPaleoceneturtles left behind fossils near modernGolden.[19] The Coloradan flora of the ensuingEoceneepoch left behind plant fossils like ferns, palm leaves, andpetrified wood.[20] Animal life of northwestern Colorado during the Eocene included the primitive horseEohippus, earlytitanotheres, anduintatheres.[19] A rich flora grew in Colorado during theOligocene. At least 150 different kinds of plants from this epoch are preserved in what is now theFlorissant beds of Colorado. Among the members of this flora weresequoia trees with trunks up to17+1⁄2 feet in diameter. More than a thousand different kinds ofinsect have been documented among the same beds.[16]Beetles were among the Florissant insects.[19] A diverse mammalian fauna inhabited this ancient forest.[16] Members included animals resembling giantpigs,rhinoceroses, and titanotheres. During thePliocene, Colorado was home to creatures likerhinoceroses and giant pig-like animals. The state's modern prairies formed during the Quaternary.[2] Colorado was shaken byvolcanic eruptions. The state's climate gradually cooled as the Cenozoic proceeded. The rainforests gave way tosequoia forests andgrasslands.[2]Pleistocene Colorado had a diverse mammal fauna. Among them wereArchidiskodon, a relative of modernelephants.[21]Bison,camels,horses, andmammoths also inhabited the state at this time.[2]
Not far fromGrand Junction is a tall cottonwood tree called theUte Council Tree. Close by is an obviousdinosaurtrack site. The Ute had a myth regarding these tracks that justified the tree as a significant meeting place, although the contents of the tale are now lost.[22]Oglala Lakota historianJohnson Holy Rock has described an old story about a Lakota hunting party traveling through northeastern Colorado who were caught during an exceptionally violent thunderstorm while camping. They thought the violence of the storm was due to theThunder Birds being angry and trying to kill something with theirlightning. When morning came, the Lakota hunters went down onto the plain where the storm was most intense. There they found the carcass of an animal with an unusual long nose who was "so strange that they wondered how it managed to eat."[23] This story may be based on the region's abundant fossils. Candidates for the unusual remains found after the storm includebrontotheres,entelodonts, orproboscidean remains. Johnson Holy Rock, who told the story, was inclined to think of the animal as a proboscidean or gianttapir.[24]
Around March 1877 a man namedOramel Lucas discovered sauropod bones in a valley calledGarden Park located a few miles north ofCanon City. He wrote toEdward Drinker Cope andO. C. Marsh, the famous rival paleontologists of theBone Wars to alert them about his discovery. Although Marsh never responded, Cope did, and Oramel Lucas and his brother Ira began digging up local fossils and sending them to Cope. These turned out to be the remains of a new species. By August of the same year, Cope had formally named the animal excavated by the Lucas brothersCamarasaurus supremus. This species may have been the most massive known in the entireMorrison Formation, with estimated putting its body weight at more than 100,000 lbs.[25] Later, a crew working on behalf of O. C. Marsh underMudge andWilliston started a quarry nearby. They made several important finds like the new speciesAllosaurus fragilis andDiplodocus longus. Following the initial excavations in the quarry field work stopped until 1883. That year brothersMarshall andHenry Felch reopened excavations there, again on behalf of O. C. Marsh. They worked for five year collecting many dinosaurs already known from the formation, but also the new speciesCeratosaurus nasicornis.[26]
In 1890 paleontologistCharles D. Walcott found broken pieces of the bony plates embedded in the skin ofMiddle Ordovicianjawless fish known asostracoderms. These fossils were the oldest known vertebrate remains in the world at the time. The rocks preserving the fossils were gray and reddish sandstone deposited by shallow water. Other fossils found alongside the ostracoderms livedarticulated brachiopods,conodonts,gastropods,ostracods,pelecypods,sponges,trilobites, andtrace fossils left byworms.[3]
After the Felch brothers ended their field work, the so-called Marsh-Felch quarry lay unworked for twelve years. However, in 1900William Utterback began fieldwork in the area underJohn Bell Hatcher for theCarnegie Museum of Natural History. In the two ensuing years of field work Utterback found many skeletons of previously knowndinosaurs, but also the new genusHaplocanthosaurus. This was the smallest known sauropod species of the Morrison Formation.[27] Around 1920 major fossil finds occurred inOligocene deposits Colorado shares withSouth Dakota. Dozens of articulated skeletons and skulls were uncovered. Among them were animals resembling giantpeccaries andrhinoceroses, as well asentelodonts andbrontotheriids. One notable rhinoceros discovery had occurred inWeld County.[19] In 1925 small duckbilled dinosaurs were discovered in eastern Colorado.[3] Later, in 1955, theAmerican Museum of Natural History uncovered a stone block in south-central Colorado preserving several EoceneEohippus skeletons.[19]
In 1960Malcolm McKenna discovered two earlyPaleoceneturtles on behalf of the American Museum of Natural History onSouth Table Mountain. The following year, curator of theUniversity of Colorado Museum atBoulder discovered even more turtles of that age at the same place.[19] In the summer of 1961 a major discovery happened south ofDenver inDouglas County, at a site known as Lamb Spring. Charles Lamb, the owner of a tract of land used forcattlegrazing, wasdredging out the bottom of a watering hole for the cattle. A great abundance of bones were discovered under the thin layer of mud at the bottom of the watering hole. The owners alerted paleontologists at Denver about the find. The researchers at Denver passed on word of the find to theSmithsonian Institution ofWashington D.C. In response, theNational Science Foundation funded an expedition coordinated by the Smithsonian Institution to the wateringhole. The lowest bones in the deposit were left byColumbian mammoths. Higher in the deposit the excavators uncoveredbison,camels, andhorses. By the end of the summer, 13 gigantic cases containing a total of 341 fossil bones were shipped to theNational Museum in Washington D.C.[21] The site is now managed and protected as Lamb Spring Archaeological Preserve. In the spring of 1963, road work inLimon County near the town ofLimon uncovered amammoth tooth andtusk.[21]
In 1965, theFlorissant fossil beds were proposed as a potentialfederal preserve.[16]Peter Robinson studied theMiocene fossil vertebrates ofMiddle Park during the mid-1960s. These fossils were discovered a short distance northwest of Denver. By 1964 he had discovered the skull of a relatively large camel.[19] Another notable discovery during his research program was the seventh knownmicrofauna site in the park.[28] More recently, in 1982, theJurassic plated dinosaurStegosaurus armatus was designated the Coloradostate fossil.Stegosaurus was also designated the Coloradostate dinosaur that same year.[29]
Elaine Anderson was born inSalida on January 8,1936.[30] Anderson would come to be known primarily for her book,The Pleistocene Mammals of North America and her research on Ice Age carnivores.[31]
Myra Keen was born inColorado Springs in1905.[32] She would go on to become one of the world's foremost paleomalacologists.[32]
Elaine Anderson died inDenver on March 26,2002 at age 66.[31]
Malcolm McKenna died inBoulder on March 3,2008.[33] McKenna was best known for publishing a comprehensive classification of mammals.[33]
Charles Repenning died inLakewood on January 5,2005.[34] Repenning is known for research into fossildesmostylians andshrews.[35]
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