# Willwood Formation

The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.

## 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 of Big Horn, Hot Springs, Park and Washakie 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.

## Fossil content

Trace fossils have been found in the Willwood Formation. Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.

### Mammals
#### Afrotheres

Afrotheres reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Apheliscus | A. sp. | Upper Gray Bull. | | A macroscelidean. | |

#### Apatotheres

Apatotheres reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Apatemys | A. bellulus | Lysite and Lost Cabin Zone. | | Also found in the Wind River Formation. |
| Apatemys | A. chardini | Middle and possibly lower Gray Bull zone. | | The smallest species of the genus. |
| Apatemys | A. kayi | | | The oldest known species of the genus. |
| Apatemys | A. sp., cf. A. rodens | Eastern side of Red Butte, and north of Sheep Mountain. | YPM 23476, 30582, AMNH 48999. | 3 very large specimens of Apatemys. |

#### Bats

Bats reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| cf. Icaronycteris | cf. I. sp. | Locality SC-29, Park County, Wyoming. | 3 fragmentary specimens. | | |

#### Cimolestans

Cimolestans reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Azgonyx | A. gunnelli | Localities SC-67, SC-308 and SC-351. | | A tillodont. |
| Azgonyx | A. sp. | Locality SC-67. | | A larger tillodont than A. gunnelli. |
| Coryphodon | C. sp. | Localities FG-61, SC-67 and SC-139. | | A pantodont. |
| Didelphodus | D. absarokae | Lower Gray Bull to the upper part of the Lysite zones. | | A palaeoryctid. |
| Ectoganus | E. bighornensis | Localities HG-3 and SC-67. | | A taeniodont. |
| Ectoganus | E. copei | | USGS 3838, with postcrania. | A taeniodont. |
| Ectoganus | E. gliriformis | | A fragmentary femur (PU 13173). | A taeniodont. |
| Esthonyx | E. bisculatus | | Jaws, teeth and a few postcranial remains. | A tillodont. |
| Esthonyx | E. spatularius | Bighorn Basin, and locality SC-67. | Fragmentary left dentary. | A tillodont. |
| Megalesthonyx | M. hopsoni | Buffalo Basin. | | A tillodont. |
| cf. Palaeoryctes | cf. P. sp. | | "USGSD 1661, 2151, 3711". | A palaeoryctid. |
| Palaeosinopa | P. incerta | Lower to upper Gray Bull zone,Bighorn Basin. | | A pantolestid also found in the Wind River and San Jose formations. |
| Palaeosinopa | P. lutreola | Middle and upper Gray Bull zone, Bighorn Basin. | | A pantolestid. |
| Palaeosinopa | P. veterrima | Lower Gray Bull through Lysite zones, Bighorn Basin. | More than 50 specimens. | A pantolestid. |
| Palaeosinopa | P. sp. | Lower part of the formation. | UM 69722 (a partial skull and mandible). | A pantolestid. |
| cf. Pararyctes | cf. P. sp. | "Yale locality 363 at the 190-m level of the Willwood Formation in the Elk Creek Facies". | UW 7028. | A palaeoryctid. |

#### Eulipotyphlans

Eulipotyphlans reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Auroralestes | A. simpsoni | Lower part of the formation, Sand Creek Facies. | UW 9616 (right P4-M2) and YPM 35156. | An erinaceid, originally named Eolestes. |
| Batodonoides | B. vanhouteni | Locality SC-303, situated at the 2,110 m level of the formation. | Maxilla and dentaries. | A geolabidid. |
| Centetodon | C. neashami | "Lower middle Gray Bull and upper Gray Bull zones". | | A geolabidid. |
| Centetodon | C. patratus | | UCMP 44954 and YPM 23088, possibly also UCMP 44957, 44958, 44959. | A geolabidid. |
| Creotarsus | C. lepidus | "Lower Gray Bull beds, Coon Creek, Garland Road, Bighorn Basin". | "AMNH 16169, left ramus with P4-M2, and associated tarsal bones". | An animal of enigmatic affinities but may be an erinaceomorph. |
| cf. Dartonius | cf. D. jepseni | | "YPM 30559, fragment of left ramus with P4-M1 and trigonid of M2". | An erinaceid, originally referred to as "Leptacodon" jepseni. |
| Dormaaliidae | Dormaaliid, sp. A | Sand Creek Facies. | UW 7048, 9627. | An amphilemurid. |
| Eolestes | E. simpsoni | Lower part of the formation, Sand Creek Facies. | UW 9616 (right P4-M2) and YPM 35156. | Now renamed to Auroralestes. |
| Insectivora (?) | gen. et. sp. indeterminate | YPM locality 355, lower part of the middle Gray Bull zone. | "YPM 30860, fragment of right ramus with M1(?) and trigonid of M2(?)". | Teeth which may represent an unusual insectivore or microchiropteran. |
| cf. Leipsanolestes | cf. L. sp. | Sand Creek Facies. | UW 9672, a left molar. | An erinaceid. |
| Leptacodon | cf. "L." jepseni | | "YPM 30559, fragment of left ramus with P4-M1 and trigonid of M2". | Actually an erinaceid, now reassigned to a new genus, Dartonius. |
| Leptacodon | L. rosei | Localities SC-188 and SC-29, Park County, Wyoming. | 3 dentaries, 2 maxillae, several isolated teeth and possibly a metatarsal. | A nyctitheriid. |
| Leptacodon | Cf. L. sp. | | A single lower molar. | A nyctitheriid. |
| Limaconyssus | L. habrus | Locality SC-29, Park County, Wyoming. | Left dentary. | A nyctitheriid. |
| Macrocranion | M. nitens | Uppermost part of the lower Gray Bull zone to the upper part of the Lysite zone. | | An amphilemurid. |
| Parapternodus | P. antiquus | Lower part of the formation. | YPM 31169, fragment of left ramus with M2-3. | An apternodontid. |
| Plagioctenodon | P. krausae | Sand Creek Facies. | | A nyctitheriid. |
| Plagioctenodon | cf. P. krausae | Locality SC-29, Park County, Wyoming. | An isolated first or second lower incisor and the buccal half of an upper molar. | A nyctitheriid. |
| Plagioctenodon | P. savagei | YPM locality 104, lower part of the formation. | "YPM 34257, right P3-M2". | A nyctitheriid. |
| Pontifactor | P. sp. | | "UW 8584, 9621, 9649, 9681, 9683, 9710, 9721, 9732, 9733, 10449, 10455, 10456". | A nyctitheriid. |
| Scenopagus | S. hewettensis | UW locality V -73020. | UW 8998 and possibly UW 9738, 10450. | An amphilemurid. |
| Scenopagus | S. sp. | Middle Gray Bull zone. | | An amphilemurid, at least 2 species represented by inadequate material, at least one is probably new. |
| Talpavoides | T. dartoni | Lower part of the formation. | | An amphilemurid. |
| Wyonycteris | W. chalix | Locality SC-29, Park County, Wyoming. | "UM 76910, a right dentary". | A nyctitheriid, originally believed to be a bat. |

#### Ferae

Ferae reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Acarictis | A. ryani | Locality SC-67. | A broken right molar and a left molar. | A hyaenodont. |
| Alocodontulum | A. atopum | | YRM 30790 and USGS 7208. | A palaeanodont. |
| Arfia | A. junnei | Localities SC-67, SC-69, SC-79, SC-121, SC-308 and SC-348. | | A hyaenodont. |
| Arfia | A. sp. | Southern Bighorn Basin. | Fragmentary postcranial remains. | A hyaenodont. |
| Cf. Asiabradypus | Cf. A. sp. | Locality SC-67. | An edentulous right lower jaw (UM 87859m). | A palaeanodont. |
| Didymictis | D. leptomylus | Localities MP-40, SC-67 and SC-79. | Skull and teeth. | A viverravid. |
| Didymictis | D. protenus | | Multiple postcranial specimens. | A viverravid. |
| Dipsalidictis | D. platypus | Localities SC-67 and SC-141. | | An oxyaenid. |
| Dipsalidictis | D. transiens | Localities SC-79 and SC-67. | An upper left canine and a trigonid of a molar. | An oxyaenid. |
| Miacis | M. winkleri | Localities SC-67, SC-348 and SC-350. | 3 fragmentary dentaries. | A miacid. |
| Miacis | cf. M. sp. | | USGS 7161. | A miacid. |
| Oxyaena | O. forcipata | | Relatively complete skeletal remains. | An oxyaenid. |
| Oxyaena | O. gulo | | USGS 7186. | An oxyaenid. |
| Oxyaena | O. intermedia | | Fragmentary postcrania. | An oxyaenid. |
| Oxyaena | O. platypus | | | Now moved to the genus Dipsalidictis. |
| Palaeanodon | P. ignavus | | Partial skeletons including postcrania. | A palaeanodont. |
| Palaeanodon | P. nievelti | Localities SC-67 and SC-121. | | A palaeanodont. |
| Palaeonictis | P. occidentalis | | "Hind foot skeleton and associated fragments". | An oxyaenid. |
| Palaeonictis | P. sp. | Locality SC-67. | Trigonid of a right molar. | An oxyaenid. |
| Prolimnocyon | P. atavus | Bighorn Basin. | Partial skeleton. | A hyaenodont. |
| Prolimnocyon | P. eerius | Localities SC-67 and possibly SC-139. | Crushed skull. | A hyaenodont. |
| Prototomus | P. deimos | Localities SC-67 and SC-349. | 4 fragmentary specimens. | A hyaenodont. |
| Prototomus | P. sp. | | 4 specimens. | A hyaenodont. |
| Tritemnodon | T. sp. | | 2 specimens with postcrania. | A hyaenodont. |
| ?Uintacyon | ?U. sp. | | | A miacid. |
| Viverravus | V. bowni | Locality SC-67, and locality SC-29, Park County, Wyoming. | | A viverravid. |
| Viverravus | V. politus | Locality SC-67. | A left maxilla. | A viverravid. |
| Vulpavus | cf. V. canavus | | 3 specimens. | A miacid. |

#### Leptictids

Leptictids reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Palaeictops | P. bicuspis | | | Also found in the Wind River Formation. |
| Prodiacodon | P. tauricinerei | Mostly in the Gray Bull zone, one or two specimens in the Bighorn Basin Lysite zone. | | |
| Prodiacodon | P. sp. | Middle Gray Bull zone. | YPM 26013, 26040, possibly 26026. | |

#### Marsupials

Marsupials reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Mimoperadectes | M. labrus | Localities SC-67 and SC-69. | Left dentary. | | |
| Peradectes | P. cf. P. chesteri | | 2 isolated teeth. | | |

#### Multituberculates

Multituberculates reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Ectypodus | E. powelli | Locality SC-29, Park County, Wyoming. | 10 isolated teeth from at least 2 individuals. | A neoplagiaulacid. | |
| Ectypodus | E. tardus | Locality SC-67. | Tooth crowns. | A neoplagiaulacid. | |

#### Primatomorphs

Primatomorphs reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Absarokius | A. abbotti | | | An omomyid. |
| Absarokius | A. metoecus | | | An omomyid. |
| Anemorhysis | A. pattersoni | Upper part of the formation. | | An omomyid. |
| Anemorhysis | A. wortmani | Upper part of the formation. | | An omomyid. |
| Arapahovius | A. advena | Northwest Wyoming. | | An omomyid. |
| Arctodontomys | A. wilsoni | Locality SC-67. | Small sample of teeth. | A microsyopid. |
| Bownomomys | B. americana | | | An omomyid, formerly listed as a species of Teilhardina. |
| Bownomomys | B. crassidens | | | An omomyid, formerly listed as a species of Teilhardina. |
| Cantius | C. abditus | | A substantially complete skull and mandible. | An adapiform. |
| Cantius | C. torresi | Localities SC-67 and SC-69. | | An adapiform. |
| Carpolestes | C. cf. C. nigridens | Locality SC-29, Park County, Wyoming. | A right dentary. | A carpolestid. |
| Chlororhysis | C. incomptus | Upper part of the formation. | | An omomyid. |
| Micromomys | M. willwoodensis | Clark's Fork Basin. | | A micromomyid. |
| Microsyops | M. latidens | Southern Bighorn Basin. | Over a thousand specimens. | A plesiadapiform. |
| Cf. Niptomomys | Cf. N. sp. | Locality SC-67. | An edentulous right dentary. | A microsyopid. |
| Phenacolemur | P. praecox | Localities SC-67 and SC-348. | Right and left dentaries. | A paramomyid. |
| Phenacolemur | P. willwoodensis | Upper part of the formation. | | A paramomyid. |
| Pseudotetonius | P. ambiguus | | | An omomyid. |
| Steinius | S. annectens | Northwest Wyoming. | | An omomyid. |
| Steinius | S. vespertinus | | "AMNH 16835, fragment of a left ramus with M1 through M3". | An omomyid. |
| Strigorhysis | S. sp., cf. S. bridgerensis | | | An omomyid. |
| Tatmanius | T. szalayi | Northwest Wyoming. | | An omomyid. |
| Teilhardina | T. americana | | | Now moved to the genus Bownomomys. |
| Teilhardina | T. crassidens | | | Now moved to the genus Bownomomys. |
| Teilhardina | T. tenuicula | | | An omomyid. |
| Tetonius | T. homunculus | | | An omomyid. |
| Tetonius | T. matthewi | | | An omomyid. |
| Tetonius | T. sp. | | | An omomyid. |
| Tinimomys | T. graybullensis | | The lingual half of a right upper molar. | A microsyopid. |
| Worlandia | cf. W. sp. | Locality SC-29, Park County, Wyoming. | 2 isolated teeth. | A plagiomenid colugo. |

#### Rodents

Rodents reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Acritoparamys | Cf. A. atavus | Locality SC-67. | A small isolated lower incisor (UM 86003m). | |
| Acritoparamys | A. atwateri | Localities SC-67, SC-308 and SC-351. | Several dentaries and teeth. | |
| Franimys | F. sp. | | "ACM 10524 (a skull with the right P4 and M2-M3, edentulous mandible, and several postcranial elements)". | |
| Notoparamys | N. costilloi | Upper part of the formation. | 18 specimens. | Also known from the Huerfano Formation. "Pseudotomus" coloradensis and Leptotomus loomisi are probably junior synonyms. |
| Paramys | P. taurus | Localities SC-67, SC-139 and SC-350. | Jaw fragments and incisors. | |

#### Ungulates

Ungulates reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Anacodon | A. ursidens | | | An arctocyonid. |
| Bunophorus | cf. B. grangeri | | USGS 16470 (a very incomplete skeleton). | A dichobunid originally listed as cf. Wasatchia dorseyana. |
| Cardiolophus | C. radinskyi | | UM 64913. | An isectolophid. |
| Copecion | C. davisi | Localities BR-2, SC-51, SC-67, SC-69, SC-79, SC-139, SC-308, SC-345, SC-348, SC-349 and SC-351. | | A phenacodontid. |
| Chriacus | C. badgleyi | Localities SC-67, SC-79, SC-121 and SC-342. | | An arctocyonid. |
| Chriacus | C. sp. | | Several skeletal specimens. | An arctocyonid. |
| Diacodexis | D. ilicis | Localities SC-67 and SC-308. | | A dichobunid. |
| Diacodexis | D. metsiacus | | Several specimens, including a near-complete skeleton. | A dichobunid. |
| Dissacus | D. praenuntius | Park County, Wyoming. | Teeth, jaw elements & bone fragments. | A mesonychid. |
| Dissacus | D. serior | USGS locality D-1754, Bighorn Basin, Wyoming. | Left dentary fragments (USGS 27612). | A mesonychid. |
| Dissacus | D. willwoodensis | Bighorn Basin, Wyoming. | Mandibles. | A mesonychid. |
| Ectocion | E. osbornianus | Locality SC-67 and SC-351. | 2 fragmentary dentaries. and a single postcranial association. | A phenacodontid. |
| Ectocion | E. parvus | Localities HG-3, SC-67, SC-69, SC-121, SC-139, SC-182, SC-308 and SC-351. | | A phenacodontid. |
| Hapalodectes | H. anthracinus | University of Wyoming locality V-73086, Wyoming. | Teeth (USGS 9628). | A mesonychian |
| Hapalodectes | H. leptognathus | | A fragmentary specimen (USGS 5912). | A mesonychian. |
| Heptodon | cf. H. calciculus | Wind River Basin. | Remains of a subadult with postcrania. | |
| Homogalax | H. protapirinus | Bighorn Basin. | A skull (YPM(PU) 16168), and several other specimens. | An isectolophid. |
| Homogalax | cf. H. protapirinus | | At least 2 specimens. | An isectolophid. |
| Hyopsodus | H. loomisi | Localities SC-67, SC-69, SC-79, SC-121, SC-308 and SC-342. | | A hyopsodontid. |
| Hyopsodus | H. powellianus | | "AMNH 4147, right mandible fragment with M1 through M3". | A hyopsodontid. |
| Lambdotherium | L. popoagicum | Multiple localities | | A brontotherid. |
| Meniscotherium | M. priscum | Locality SC-67(?) | Left dentary fragment. | A phenacodontid. |
| Pachyaena | P. gigantea | YPM localities 131 & 149, Wyoming. | Jaw elements & teeth. | A mesonychid. |
| Pachyaena | P. gracilis | USGS locality D-1640. | Maxillary fragments (USGS 7185). | A mesonychid. |
| Pachyaena | P. ossifraga | Locality SC-348. | Trigonid of a right molar. | A mesonychid. |
| Pachyaena | P. sp. | | Postcranial material. | A mesonychid. |
| Phenacodus | P. cf. P. intermedius | Localities SC-67 and SC-141. | | A phenacodontid. |
| Phenacodus | P. primaevus | | Near complete skeletons. | A phenacodontid. |
| Phenacodus | P. vortmani | | Near complete skeletons. | A phenacodontid. |
| Princetonia | P. yalensis | Locality SC-121(?) | Right dentary. | An arctocyonid. |
| Sifrhippus | S. grangeri | Locality SC-67. | 2 isolated teeth. | An equid, formerly considered a species of Hyracotherium. |
| Sifrhippus | S. sandrae | Localities FG-61, SC-67, SC-69, SC-79, SC-121 and SC-139. | | An equid, formerly considered a species of Hyracotherium. |
| Thryptacodon | T. antiquus | | | An arctocyonid. |
| Thryptacodon | T. barae | Localities MP-38 and SC-121. | | An arctocyonid. |
| Thryptacodon | T. olseni | | | An arctocyonid. |
| Thryptacodon | T. sp. | | 2 partial skeletons. | An arctocyonid. |
| Wasatchia | cf. W. dorseyana | | USGS 16470 (a very incomplete skeleton). | Now a junior synonym of Bunophorus. |
| Xenicohippus | | Lower part of the Upper Willwood Formation. | | A hyracotheriine. |

### Reptiles

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

#### Birds

Birds reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Anachronornis | A. anhimops | Clark Quadrangle, Park County, Wyoming. | USNM 496700. | An anseriform. |
| Anseriformes Familia Incertae sedis | | Clark Quadrangle, Park County, Wyoming. | USNM 496701 (right quadrate missing the pterygoid condyle); USNM 496702 (fragmentary right femur consisting of only the proximal and distal ends). | Generally similar to Anachronornis & Danielsavis. |
| Aves indet. | | Localities SC-67 and SC-121. | A cervical vertebra and proximal part of a carpometacarpus. | An indeterminate bird. |
| Calcardea | C. junnei | | "UM 76882, anterior part of sternum, partial left coracoid. nearly complete right coracoid, partial left humerus. two nearly complete vertebrae. fragmentary left and right tarsometatarsi, and several phalanges, all probably representing a single individual bird." | Originally thought to be a heron, now thought to be related to Vastanavis. |
| Diatryma | D. gigantea | | Several specimens. | Now deemed a junior synonym of Gastornis. |
| Eogeranoides | E. campivagus | | "Fragmentary tibiotarsus and tarsometatarsus remains". | A dubious geranoidid, may be a junior synonym of Paragrus prentici. |
| Gastornis | G. gigantea | | Several specimens. | A gastornithiform. |
| Geranoides | G. jepseni | Elk Creek, Bighorn Basin. | | A geranoidid, now deemed a junior synonym of Palaeophasianus meleagroides. |
| Microolithus | M. wilsoni | | Partial eggs. | Fossil bird eggs. |
| Palaeophasianus | "P." incompletus | | "A fragmentary distal end of a tarsometatarsus". | A very large possible geranoidid, may actually belong to the genus Paragrus or be outside Geranoididae entirely. |
| Palaeophasianus | P. meleagroides | Elk Creek, Bighorn Basin. | | A geranoidid. |
| Palaeophasianus | ?P. sp. | | AMNH 5156. | A geranoidid. |
| Paracathartes | P. howardae | | | A lithornithid. |
| Paragrus | P. prentici | | | A geranoidid. |
| Primoptynx | P. poliotauros | | Specimen including all major postcranial bones. | A large owl. |
| Sandcoleus | S. copiosus | Clark Quadrangale, Park County, Wyoming. | "Two articulated partial skeletons and a number of other elements". | A sandcoleid mousebird. |

#### Crocodilians

Crocodilians reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Allognathosuchus | A. sp. | Localities SC-67, SC-139, SC-342 and SC-349. | | An alligatorid. |
| Crocodilia indet. | | Localities SC-67, SC-69 and SC-121. | Dermal scutes and vertebral centra. | May represent either large Allognathosuchus or small Borealosuchus. |
| Borealosuchus | B. sp. | Localities SC-67, SC-79, SC-139, SC-342, SC-345 and SC-350. | | |
| Orthogenysuchus | O. olseni | | | A caiman. |
| Boverisuchus | B. sp. | Locality SC-348. | A single tooth (UM 83817m). | |

#### Squamates

Squamates reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Anguidae indet. | | | 2 fragmentary dentaries (UM 76872 and 76873). | A very small anguid lizard. |
| Anguimorpha | | | A dentary, maxilla and 1 or 2 premaxillae (UM 76874–76875, 76878-76879(?), and 768811). | A gerrhonotine or diploglossine. |
| Anguimorpha | Anguimorph CG | | "UCMP 150871, 150872 (jaw frag-ments), 150920 (jaw fragment), 150969 (parietal fragment),151038 (left frontal), 151067 (right maxilla fragment), 151095 (right maxilla fragment), 167499 (right maxilla fragment), 167553 (left maxilla fragment)". | |
| Anniealexandria | A. gansi | UCMP locality V99019. | Skull fragments and vertebrae. | An amphisbaenian. |
| Anolbanolis | A. banalis | UCMP locality V99019. | | An iguanian. |
| Apodosauriscus | A. thermophilus | UCMP locality V99019. | Skull fragments. | An anguid. |
| Blutwurstia | B. oliviae | Clarks Fork Basin. | | A xenosaurid. |
| cf. Eodiploglossus | cf. E. sp. CG | | "UCMP 150916 (right maxilla fragment), 150919 (right frontal), 150962 (partial left frontal), 151070, 151071 (skull fragments), 167338 (partial right frontal), 167426 (left maxilla fragment), 167447 (left maxilla fragment), 167456 (jaw fragment),?167527 (right pterygoid fragment), 167602 (right dentary fragment), 400180 (right maxilla fragment)". | An anguid. |
| Gaultia | G. silvaticus | UCMP locality V99019. | | A glyptosaurine. |
| Gerrhonotinae | Gerrhonotine CG | | Skull fragments. | An alligator lizard. |
| Glyptosaurinae | Glyptosaurine CG | | "UCMP 151033 (right maxilla fragment), ?151068 (left pterygoid fragment), 151935 (parietal fragment), 167269 (parietal fragment),?167613 (right palatine fragment)." | A glyptosaurine. |
| Iguanidae | Iguanid CG | | "UCMP 151078 (right dentary fragment), 400156 (partial right postorbital), 400169 (partial right squamosal)". | An iguanid lizard. |
| Lacertilia indet. | | Localities SC-67 and SC-308. | Vertebrae. | Indeterminate lizards. |
| Melanosaurus | M. maximus | | A frontal, numerous osteoderms and vertebrae. | A glyptosaurine. |
| Palaeoxantusia | P. sp. CG | | Skull fragments. | A night lizard. |
| Proxestops | Cf. P. sp. | Locality MP-40. | UM 88170m (2 osteoderms). | A glyptosaurine. |
| Proxestops | P. sp. CG | | Skull fragments. | A glyptosaurine. |
| Provaranosaurus | cf. P. sp. CG | | "UCMP 167299 (right dentary fragment)". | A xenosaurid. |
| cf. Saniwa | cf. S. sp. CG-1 | | "UCMP 150921 (jaw fragment with partial tooth), 151099 (premaxilla), 167572 (jaw fragment with tooth)". | A varanid. |
| cf. Saniwa | cf. S. sp. CG-2 | | "UCMP 150873 (right dentary fragment with tooth), 150971 (tooth), 167324 (distal right humerus), 167336 (edentulous left dentary fragment), 167355 (parietal fragment)". | A varanid. |
| Suzanniwana | S. patriciana | UCMP locality V99019. | | An iguanid. |
| Varanoidea | | | A dentary and maxilla (UM 76876 and 768771). | One or possibly 2 species of Parasaniwa or Provaranosaurus-like varanoids. |
| Xantusiidae | Xantusiid CG | | "UCMP 150827 (right maxilla fragment), 150965 (maxilla fragment), 150970 (right maxilla fragment), 167413 (left frontal fragment), 167495 (right maxilla fragment), 167575 (premaxilla), 167599 (right maxilla fragment), 167600 (left maxilla fragment)". | A night lizard. |

#### Testudines

Testudines reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Chelonia indet. | | Localities SC-67, SC-121 and SC-348. | Several pieces of the carapace and plastron. | Indeterminate medium to large turtles. |
| Echmatemys | E. sp. | Locality SC-67. | Much of the plastron and several peripherals or pleurals from the carapace (UM 83627), and a peripheral (UM 66617m). | |
| Gomphochelys | G. nanus | Southeastern Bighorn Basin, Washakie County, Wyoming. | | A dermatemydid. |
| Cf. Plastomenus | Cf. P. sp. | Localities SC-67 and SC-350. | Fragmentary pieces of the carapace and plastron. | A trionychid. |

### Amphibians

Amphibians reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Anura | | | Distal end of a humerus (UM 76883). | A small frog. | |
| Urodela | | | Numerous vertebrae, UM 76871 (a-j). | A small salamander. | |

### Fish

Fish reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Amia | A. sp. | Localities SC-67 and SC-342. | Isolated cervical vertebrae, and a concretion of broken bones including 1 or 2 tooth-bearing bones likely belonging to Amia. | A bowfin. |
| Cuneatus | C. maximus | | | A large gar. |
| Lepisosteus | L. sp. | | "Mostly diamond-shaped ganoid scales, but some specimens include distinct opisthocoelous vertebrae, basioccipitals and other cranial elements." | A gar. |

### Invertebrates

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

#### Invertebrate ichnotaxa

Invertebrate ichnotaxa reported from the Willwood Formation :
| Ichnogenus | Ichnospecies | Presence | Material | Notes |
| Camborygma | C. litonomos | Polecat Bench. | Prismatic cylindrical structures. | Likely represent crayfish burrows. |
| Cocoon traces | | Polecat Bench. | | |
| Cf. Cylindricum | Cf. C. isp. | Polecat Bench. | "Predominantly vertical, straight to sinuous, unbranched, unlined, and smooth walled shafts with circular cross sections and gently rounded, unenlarged terminations". | Burrows possibly created by beetles, hymenopterans, emerging cicada nymphs, spiders or molluscs. |
| Edaphichnium | E. lubricatum | Polecat Bench. | "Tubular burrows with ellipsoidal fecal pellets". | Formed by substrate feeding by Earthworms or other invertebrates. |
| Naktodemasis | N. bowni | Bighorn Basin. | "Burrows composed of nested ellipsoidal packets backfilled with thin, tightly spaced, menisci subparallel to the bounding packet." | Burrows likely constructed by burrowing bugs or cicada nymphs. |
| cf. Planolites | cf. P. isp. | Polecat Bench. | | Traces made by the feeding of worm-like animals. |
| cf. Steinchnus | S. isp. | Polecat Bench. | | Traces made by invertebrates, possibly beetles or mole crickets. |

#### Gastropods

Gastropods reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes |
| Cf. Albertanella | Cf. A. minuta | | | A pupillid. |
| Discus | D. ralstonensis | | Many individuals (some juvenile specimens). | An endodontid. |
| Elimia or Pleurocera | E. or P. sp. | | Some 25 specimens, many are internal molds. | A pleurocerid. |
| Grangerella | cf. G.(?) phenacodorum | | 2 specimens originally referred to Protoboysia complicata. | A grangerellid. |
| Grangerella | G. sinclairi | | | A grangerellid. |
| Cf. Gyraulus | Cf. G. sp. | Locality SC-69. | A poorly-preserved planispiral internal mold. | A pulmonatan. |
| Hendersonia | H. evanstonensis | | Several specimens, none preserving the operculum. | A helicinid. |
| Holospira | H. sp. | Localities SC-67, SC-139, SC-345 and SC-349. | 7 individuals. | An urocoptid. |
| "Hydrobia" | "H." sp. | Locality SC-69. | "A very small, dextral, high-spired shell with 9 whorls". | A hydrobiid. |
| Cf. Microphysula | Cf. M. sp. | | A single individual. | A sagdid. |
| Oreohelix | O. megarche | | A single specimen (UM(I) 65404). | An oreohelicid. |
| Cf. Pupilla | Cf. P. sp. | | UM(I) 654071. | A pupillid. |

### Plants

Plants reported from the Willwood Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Celtis | C. phenacodorum | | Endocarps. | An urticale. | |

## Wasatchian correlations

Wasatchian correlations in North America :
| Formation | Wasatch | DeBeque | Claron | Indian Meadows | Pass Peak | Tatman | Willwood | Golden Valley | Coldwater | Allenby | Kamloops | Ootsa Lake | Margaret | Nanjemoy | Hatchetigbee | Tetas de Cabra | Hannold Hill | Coalmont | Cuchara | Galisteo | San Jose | Ypresian (IUCS) • Itaboraian (SALMA) Bumbanian (ALMA) • Mangaorapan (NZ) |
| Basin | Powder River Uinta Piceance Colorado Plateau Wind River Green River Bighorn | Piceance | Colorado Plateau | Wind River | Green River | Bighorn | Bighorn | Williston | Okanagan | Princeton | Buck Creek | Nechako | Sverdrup | Potomac | GoM | Laguna Salada | Rio Grande | North Park | Raton | Galisteo | San Juan | Willwood Formation (North America) |
| Country | United States | United States | United States | United States | United States | United States | United States | United States | Canada | Canada | Canada | Canada | Canada | United States | United States | Mexico | United States | United States | United States | United States | United States | | Willwood Formation (North America) |
| Copelemur | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Coryphodon | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Diacodexis | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Homogalax | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Oxyaena | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Paramys | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Primates | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Birds | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Reptiles | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Fish | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Insects | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Flora | | | | | | | | | | | | | | | | | | | | | | Willwood Formation (North America) |
| Environments | Alluvial-fluvio-lacustrine | Fluvial | | | | Fluvial | Fluvio-lacustrine | Fluvial | Lacustrine | Lacustrine | Fluvio-lacustrine | Fluvio-lacustrine | Deltaic-paludal | Shallow marine | Shallow marine | Fluvial | Shallow marine | Fluvial | | Fluvial | Fluvial | Wasatchian volcanoclastics Wasatchian fauna Wasatchian flora |
| Volcanic | Yes | No | No | No | No | No | No | No | Yes | No | Yes | No | Yes | No | No | No | No | No | No | Yes | No | Wasatchian volcanoclastics Wasatchian fauna Wasatchian flora |