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The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or
Clarkforkian The Clarkforkian North American Stage, on the geologic timescale, is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 56,800,000 to 55,400,000 years BP lasting . Considered t ...
,
Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually ...
and
Bridgerian The Bridgerian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 50,300,000 to 46,200,000 years BP lasting . It is usually c ...
in the NALMA classification.Willwood Formation
at
Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was crea ...
.org
Neasham & Vondra, 1972


Description

It consists of fine grained clastic rocks ( mudstone and shale) interbedded with medium grained clastic rocks ( sandstone) and sporadic conglomerates. The formation underlies portions of the
Bighorn Basin The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming in the United States. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Big ...
of Big Horn,
Hot Springs A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by ci ...
, Park and
Washakie Washakie (1804/1810 – February 20, 1900) was a prominent leader of the Shoshone people during the mid-19th century. He was first mentioned in 1840 in the written record of the American fur trapper, Osborne Russell. In 1851, at the urging ...
counties of Wyoming.


Dating

Radiometric dating of volcanic tuffs, combined with comparisons with other formations using magnetostratigraphy, using numerous samples from various levels of the formation suggest an age range of 55 – 52 million years ago, placing the Paleocene-Eocene boundary near the base of the formation.Tauxe et al., 1994


Fossil content

Trace fossils have been found in the Willwood Formation.Bown & Kraus, 1982 Fossil birds include ''
Gastornis ''Gastornis'' is an extinct genus of large flightless birds that lived during the mid Paleocene to mid Eocene epochs of the Paleogene period. Fossils have been found in Europe, Asia and North America, with the remains from North America origina ...
'', '' Neocathartes'' and ''
Paracathartes ''Paracathartes'' is a genus of extinct bird from the Wasachtian horizon of lower Eocene Wyoming. One species, ''Paracathartes howardae'' has been described. It is a paleognathous bird, turkey-like in stature and size, that probably resembled ...
''. A fossil
alligatorid The family Alligatoridae of crocodylians includes alligators, caimans and their extinct relatives. Phylogeny The superfamily Alligatoroidea includes all crocodilians (fossil and extant) that are more closely related to the American alligator t ...
, namely '' Orthogenysuchus'', was also found in this formation.


Mammals


Afrotheres


Apatotheres


Bats


Cimolestans


Eulipotyphlans


Ferae


Leptictids


Marsupials


Multituberculates


Primatomorphs


Rodents


Ungulates


Reptiles


Birds


Crocodilians


Squamates


Testudines


Amphibians


Fish


Invertebrates


Invertebrate ichnotaxa


Gastropods


Plants


Wasatchian correlations


See also

*
List of fossiliferous stratigraphic units in Wyoming This article contains a list of fossil-bearing stratigraphic units in the state of Wyoming, U.S. Sites See also * Paleontology in Wyoming Paleontology in Wyoming includes research into the prehistoric life of the U.S. state of Wyoming a ...
*
Paleontology in Wyoming Paleontology in Wyoming includes research into the prehistoric life of the U.S. state of Wyoming as well as investigations conducted by Wyomingite researchers and institutions into ancient life occurring elsewhere. The fossil record of the US s ...
*
Tatman Formation The Tatman Formation is a Wasatchian geologic formation in Wyoming. It preserves fossils dating back to the Ypresian stage of the Eocene period.Wasatch Formation The Wasatch Formation (Tw)Shroba & Scott, 2001, p.3 is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana Wyoming, Utah and western Colorado.167:SAPOTL.0.CO;2 Geologic formations of the United States Paleocene Series of North America Eocene Series of North America Paleogene geology of Wyoming Thanetian Stage Ypresian Stage Bridgerian Clarkforkian Wasatchian Limestone formations Mudstone formations Shale formations of the United States Sandstone formations of the United States Conglomerate formations Fluvial deposits Lacustrine deposits Ichnofossiliferous formations Fossiliferous stratigraphic units of North America Paleontology in Wyoming