Yellowstone Paleo Survey: Fossil Chronology

Fossil Chronology

The earliest fossilsfound in Yellowstone date from the middle Cambrian period, approximately 510 million years before the present.

Geologic Period Type of Formation/ Location Reported Fossils in Yellowstone

PALEOZOIC All known sedimentary rocks are marine; approx. thickness of 3,000 feet; exposures in Gallatin Range, Barronette Peak, Abiathar Peak, eastern portion of Buffalo Plateau, isolated outcrops along Slough and Soda Butte Creeks, Birch Hills, and the Snake River. Fossils reported from Paleozic rocks by Deiss (1936), Duncan (1937), Girty (1899), Grant (1965), and Walcott (1899).

Middle Cambrian Flathead Sandstone: outcrops in southern Gallatin Range, on Buffalo Plateau, and west of Bison Peak. The Crowfoot Ridge section includes a one-foot thick zone of sandy oolitic hematite beds that contain small brachiopods (Deiss 1936), the only known fossils from Flathead Sandstone.
Wolsey Shale: outcrops in Gallatin Range and on Buffalo Plateau. Only the trilobite trace fossil Cruziana; evident in the Crowfoot Ridge area in the Gallatin Mountains. Alokistocare, Anoria, Bolaspis, Glyhaspis, Hyolithes, and Westonia reported from sections outside the park.
Meagher Limestone: outcrops in southern Gallatin Range, on Buffalo Plateau, and west of Slough Creek. Deiss(1936) indicates fossils are rare; a few fragments of trilobites have been observed. Kootenia, Ehmania, and Glyphaspis are reported from exposures outside the park.
Park Shale: poorly exposed in the park; at Crowfoot Ridge in Gallatin Range and small outcrop at easternmost Slough Creek.
None.

Late Cambrian Pilgrim Limestone: Well-exposed in northeast corner of park along Soda Butte Creek, on east canyon wall of Buffalo Creek near Slough Creek, upper portion of Buffalo Plateau, and in Gallatin Range. Contains three units:
•Lower unit of interbedded ribboned limestone, glauconitic oolitic limestone, and less common limestone pebble conglomerate. The ribboned limestone is rich in trilobite fragments.
• Middle unit consists of coarse-grained glauconitic limestone pebble conglomerate. Contains abundant fossil fragments.
• Upper unit of mottled oolitic limestone. None.
Snowy Range Formation: exposed in Gallatin Range and on Buffalo Plateau. Wayne Hamilton collected trilobite spines in 1995 from a unit he believed to be Snowy Range (pers. commun.).
• Dry Creek Shale Member. None.
• Sage Limestone Member: composed of algal columns as much as a foot in diameter. Collenia magna beds occur on Buffalo Plateau (Grant 1965); includes many fossiliferous beds.
• Grove Creek Limestone Member: only known exposure is on Three Rivers Peak; contains some algal dolomite or vertical algal columns. Contains brachiopods and trilobite fragments in lower sections; Billingsella in the top sections.
Gallatin Limestone: limited exposure in the Birch Hills area. Park exposures not yet surveyed for fossils—currently no data available.

Ordovician Crinoids, brachiopods, bryozoans, and ostracods.

Devonian Jefferson Formation (late): exposed on Three Rivers Peak and in northeast corner of park. Isolated beds containing stromatoporoids; one horizon with small horn corals.
Three Forks Formation (late): well-exposed on Three Rivers Peak; also in Gallatin Range and in northeast corner of park. Fossils are relatively rare. A few brachiopods have been identified.
Darby Formation: small exposure just north of the Fox Creek patrol cabin in Snake River area. None in the park.

Mississippian Lodgepole Limestone (Madison Group): best exposure is on south face of Bannock Peak; thick exposures also near northeast entrance. Abundant fossils, mainly corals, brachiopods, and crinoid fragments; coarse-grained beds made up almost entirely of fossils or fossil fragments are common. Biostratigraphy described in Girty (1899). Hamilton reported collecting horn corals and brachiopods in northeast section of park in 1995 (pers. commun.).
Mission Canyon Limestone (Madison Group): well-exposed on south face of Bannock Peak, Crowfoot Ridge and in northeast corner of park. Many beds contain abundant brachiopods and corals; some beds of coquinas made up of fossil fragments.
Madison Limestone (Madison Group): exposed in southern portion of park in Birch Hills and in Snake River area. Park exposures not yet surveyed for fossils—no data available.

Pennsylvanian Amsden Formation (early to middle Pennsylvanian): thickest section is on Bannock Peak. None.
Quadrant Sandstone: The type locality is on Quadrant Mountain. None.
Tensleep Sandstone: Exposed in southern portion of park in Birch Hills and Snake River area. None.

Permian Shedhorn Sandstone: widely exposed in Gallatin Range, especially on Quadrant Mountain and Bannock Peak. Phosphatized fish bones common in some beds, especially the more phosphatic sandstone beds.
Phosphoria Formation: limited exposures in Birch Hills and Snake River area of the park; equivalent to Park City Formation in Idaho, Utah, and Wyoming. Remains of Helicoprion, a shark with a sprial tooth-whorl.


MESOZOIC Exposed only in Gallatin Range and on east side of Mt. Everts. Ruppel (1982) reports that extensive collections of fossils were described and illustrated by Stanton (1899) and Knowlton (1899).

Triassic Dinwoody Formation (early): exposed south of Fawn Pass and on Quadrant Mountain; possibly present in Birch Hills and in Snake River area of park. None.
Woodside Formation (early): a red colored unit is exposed on Quadrant Mountain and in upper valley of Fawn Creek. None.
Thaynes Formation: exposed near Fawn Creek and south of Fawn Pass. Ruppel reports the age is uncertain, as no fossils have been found.
Chugwater Formation: known only from exposures in southern part of park; outcrops in Birch Hills and in Snake River area. Park exposures not yet surved—no available data.

Jurassic Jurassic rocks in Fawn Pass and at head of Fan Creek were described by Crickmay (1936), who also reported on fossils collected from them. Extensive list reported by Crickmay (1936) and in Gallatin Range described by Stanton (1899).
Sawtooth Formation (Ellis Group): marine unit with three lithologic units; best exposures are in Fawn Pass, head of Fan Creek, and East Fork of Fan Creek. Middle limestone member contains abundant fossils.
Rierdon Formation (Ellis Group: Late Jurassic): marine unit exposed in Fawn Pass, head of Fan Creek and East Fork of Fan Creek. Not as richly fossiliferous as underlying Sawtooth Formation.
Swift Formation (Ellis Group: Late Jurassic): marine unit exposed in Fawn Pass and Fan Creek. Abundant fragments of fossils all cemented by calcite.
Sundance Formation: possibly exposed in Snake River area along park's south boundary. None.
Morrison Formation: non-marine unit northwest of Fawn Pass, at head of Stellaria Creek, and possibly along park's south boundary in Snake River area. In 1995 George Engleman surveyed Little Quadrant Mountain, an area identified on park geologic map as having surficial Morrison exposures, but he could not find evidence of any Morrison outcrops or fossils (Engleman, pers. commun. 1996). Upper beds yielded fragments from the end of a leg bone of a moderately large dinosaur, but these bone pieces were too fragmentary to permit more positive identification (G. Edward Lewis, written communication 1967); these same beds contain abundant fossil wood.

Cretaceous Cretaceous sedimentary rocks in northern park measure nearly 4,000- feet thick. Kootenai Formation, Thermopolis Shale, Mowry Shale, Frontier Sandstone, Cody Shale, Telegraph Creek Formation, and Eagle Sandstone are best exposed on ridge southwest of Electric Peak. Cody Shale and younger Cretaceous units are well-exposed on Mount Everts. Cretaceous rocks were described by Fraser, Waldrop, and Hyden (1969).
(Lower) Cretaceous • Kootenai Formation Upper part contains distinctive "gastropod limestone" with poorly preserved molds of gastropod shells.
• Thermopolis Shale: composed of dirty sandstones and inter-bedded finer-grained rocks. Ostrea anomioides Meek (Cobban, pers. commun. 1967).
• Mowry Shale. Some beds in upper part of formation contain abundant fish scales.
(Upper) Cretaceous • Frontier Sandstone. Fish teeth can be found in some of the sandstone beds.
• Cody Shale. The middle sandstone member contains distinct Inoceramus fauna and is much more fossiliferous than rest of Cody Shale (Cobban, pers. commun. 1967). Cody Shale on Mount Everts was studied in detail by Fox (1939), who described faunal zones.
• Telegraph Creek Formation. Possible remains of plesiosaur and tortoise come from just below Eagle Sandstone on Mount Everts.
• Eagle Sandstone. None.
• Everts Formation: Type section is on Mount Everts. None.
• Bacon Ridge Sandstone: exposed in Snake River area. None.
• Landslide Creek Formation: exposed on the northeast slope of Mount Everts. None.
• Harebell Formation: widely exposed in Snake River area; present on Big Game Ridge, Mount Hancock, Chicken Ridge, Barlow Peak, and Channel Mountain. Only from areas just outside park.


CENOZOIC A thick sequence of tertiary volcanic and volcaniclastic rocks blanket much of the park. Volcaniclastic and sedimentary beds contain abundance paleobotanical material; there is good potential for vertebrate fossils from the selayers.

Tertiary (Eocene Epoch) Absaroka Volcanic Supergroup:
• Sepulcher Formation: known from Gallatin Range, especially Sepulcher Mountain and Bighorn Peak; also exposed on Blacktail Deer Plateau and just west of Tower Junction. Petrified wood deposits.
• Lamar River Formation: well-exposed on cliffs in Lamar Valley including Specimen Ridge, along Soda Butte Creek, and throughout northeastern park. Contains 27 layers of petrified forest.
• Wapiti Formation: large exposures in upper Lamar River area, around Miller Creek and to east boundary near Hoodoo Basin. East flank of Absarokas contain Bridgerian vertebrate fossils.
• Langford Formation (Middle Eocene): Extensively exposed in park, including Lamar Valley, Mirror Plateau, Washburn Range, and throughout peaks east of Yellowstone Lake; characterized by William Fritz as one of younger Absaroka Volcanic Supergroup units; consists of extensive andesite pile of tuffaceous sandstone, volcanic conglomerate pyroclastic flow deposits, lava flows, and shallow intrusive bodies. Contains fossil plant material uncovered during East Entrance road construction; all leaf material belongs to genus Macginitiea, in the sycamore family.
• Wiggins Formation: extensive exposures in southeastern portion of park. Uintan fossil mammals have been reported only in areas outside of park.

More Recent Fossils

Pleistocene. The primary paleontological resources from the Pleistocene epoch are fossil diatoms and pollen, including lacustrine deposits with sedges that date to 13,600 B.P. Fontanallis moss mats and diatomites on the shore of Mary Bay have been dated to 11,000 B.P. The windward side of Dot Island and possibly Stevenson Island have undated Fontanallis and diatomite.

Pleistocene gravels, such as those near the north boundary of the park, may have some potential for Pleistocene vertebrate fossils. An elk antler poacher in the park claimed to find very large bones that were thought to possibly be mammoth tusk. Paul Miller provided the park staff with a photo of the alleged site, which is believed to be within the park. Greg McDonald, who examined photographs of the alleged mammoth tusk, concluded that the specimen was travertine (pers. commun. 1996).

Dave Love collected a bison skull from Rainbow Hot Spring which Skinner at Harvard identified as Bison occidentalis and returned to the park museum. It was last seen hanging on the wall of the old research office before the Yellowstone Center for Resources moved to its present location; its current whereabouts are unknown.

A bison skull is exposed in a dune sand cap in the middle of the west side of Stevenson Island, which is lower in elevation than the north and south ends of the island. Paleosols (fossil soils) have also been reported on the island (Hamilton pers. commun. 1996).

Holocene. One of the most significant paleontological resources in Yellowstone is the subfossil material of 36 mammal species that were collected from ten stratigraphic units in Lamar Cave. This sequence of faunal remains provides information related to late Holocene mammalian diversity, with the oldest specimen dated to 1695 B.P. Except for the prairie vole (Microtus ochrogaster), all of the species found in the cave are present in Yellowstone today. The presence of the wolf (Canis lupus) in late Holocene deposits supports the belief that wolves have been part of the Yellowstone ecosystem for hundreds of years.

The paleontological material from Lamar Cave suggests the potential for additional fossil material from other caves in the park. At present the superintendent has closed all caves. Accounts dating back 120 years indicate that a sinkhole on Mammoth Terraces contained some faunal remains, and Hamilton has reported seeing bones there. The sinkhole must be entered using a ladder and in recent years has been barricaded.

After bones found in McCartney Cave in the parade ground across from the Superintendent's house and accessioned into the park collection were apparently discarded, Hamilton collected more in 1982. Larry Agenbroad at Northern Arizona University C14 dated (collagen) the material, probably Bison, to about 100 years ago (Hamilton pers. commun. 1996). Because of high carbon dioxide (CO2) and radon gas levels, an air pack is required to enter the cave.

The Powerline fossil locality near Le Hardy Rapids preserves Holocene silicified plant fragments (Carex) and other leaf impressions that have been dated to before 7280 B.P. The material can be found on the surface near the road with log barricade (powerline access), across a dry creek approximately one-half mile upstream from the rapids (Hamilton pers. commun. 1996).

Taxonomy