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.Willwood Formation at Fossilworks.orgNeasham & 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 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.Tauxe et al., 1994

Fossil content Trace fossils have been found in the Willwood Formation.Bown & Kraus, 1982 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 ApheliscusA. sp. Upper Gray Bull. A macroscelidean.

Apatotheres Apatotheres reported from the Willwood Formation Genus Species Presence Material Notes Images ApatemysA. bellulusLysite and Lost Cabin Zone.Also found in the Wind River Formation.A. chardini Middle and possibly lower Gray Bull zone. The smallest species of the genus. A. kayiThe oldest known species of the genus.A. sp., cf. A. rodensEastern 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. Icaronycteriscf. I. sp. Locality SC-29, Park County, Wyoming.3 fragmentary specimens.

Cimolestans Cimolestans reported from the Willwood Formation Genus Species Presence Material Notes ImagesAzgonyxA. gunnelliLocalities SC-67, SC-308 and SC-351.A tillodont.A. sp.Locality SC-67.A larger tillodont than A. gunnelli.CoryphodonC. sp.Localities FG-61, SC-67 and SC-139.A pantodont.DidelphodusD. absarokaeLower Gray Bull to the upper part of the Lysite zones.A palaeoryctid.EctoganusE. bighornensisLocalities HG-3 and SC-67.A taeniodont.E. copeiUSGS 3838, with postcrania.A taeniodont.E. gliriformisA fragmentary femur (PU 13173).A taeniodont.EsthonyxE. bisculatusJaws, teeth and a few postcranial remains.A tillodont.E. spatulariusBighorn Basin, and locality SC-67.Fragmentary left dentary.A tillodont.MegalesthonyxM. hopsoniBuffalo Basin.A tillodont.cf. Palaeoryctescf. P. sp."USGSD 1661, 2151, 3711".A palaeoryctid.PalaeosinopaP. incerta Lower to upper Gray Bull zone,Bighorn Basin. A pantolestid also found in the Wind River and San Jose formations. P. lutreolaMiddle and upper Gray Bull zone, Bighorn Basin.A pantolestid.P. veterrimaLower Gray Bull through Lysite zones, Bighorn Basin.More than 50 specimens.A pantolestid.P. sp.Lower part of the formation.UM 69722 (a partial skull and mandible).A pantolestid.cf. Pararyctescf. 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 ImagesAuroralestesA. simpsoniLower part of the formation, Sand Creek Facies.UW 9616 (right P4-M2) and YPM 35156.An erinaceid, originally named Eolestes. BatodonoidesB. vanhouteni Locality SC-303, situated at the 2,110 m level of the formation.Maxilla and dentaries. A geolabidid. CentetodonC. neashami"Lower middle Gray Bull and upper Gray Bull zones".A geolabidid.C. patratusUCMP 44954 and YPM 23088, possibly also UCMP 44957, 44958, 44959.A geolabidid.CreotarsusC. 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. Dartoniuscf. D. jepseni"YPM 30559, fragment of left ramus with P4-M1 and trigonid of M2".An erinaceid, originally referred to as "Leptacodon" jepseni.DormaaliidaeDormaaliid, sp. ASand Creek Facies.UW 7048, 9627.An amphilemurid.EolestesE. simpsoniLower 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. Leipsanolestescf. L. sp.Sand Creek Facies.UW 9672, a left molar.An erinaceid.Leptacodoncf. "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.L. roseiLocalities SC-188 and SC-29, Park County, Wyoming.3 dentaries, 2 maxillae, several isolated teeth and possibly a metatarsal.A nyctitheriid.Cf. L. sp.A single lower molar.A nyctitheriid.LimaconyssusL. habrusLocality SC-29, Park County, Wyoming.Left dentary.A nyctitheriid.MacrocranionM. nitensUppermost part of the lower Gray Bull zone to the upper part of the Lysite zone.An amphilemurid.ParapternodusP. antiquusLower part of the formation.YPM 31169, fragment of left ramus with M2-3.An apternodontid.PlagioctenodonP. krausaeSand Creek Facies.A nyctitheriid.cf. P. krausaeLocality SC-29, Park County, Wyoming.An isolated first or second lower incisor and the buccal half of an upper molar.A nyctitheriid.P. savageiYPM locality 104, lower part of the formation."YPM 34257, right P3-M2".A nyctitheriid.PontifactorP. sp."UW 8584, 9621, 9649, 9681, 9683, 9710, 9721, 9732, 9733, 10449, 10455, 10456".A nyctitheriid.ScenopagusS. hewettensisUW locality V -73020.UW 8998 and possibly UW 9738, 10450.An amphilemurid.S. sp.Middle Gray Bull zone.An amphilemurid, at least 2 species represented by inadequate material, at least one is probably new.TalpavoidesT. dartoniLower part of the formation.An amphilemurid. WyonycterisW. 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 ImagesAcarictisA. ryaniLocality SC-67.A broken right molar and a left molar.A hyaenodont.AlocodontulumA. atopumYRM 30790 and USGS 7208.A palaeanodont.ArfiaA. junneiLocalities SC-67, SC-69, SC-79, SC-121, SC-308 and SC-348.A hyaenodont.A. sp.Southern Bighorn Basin.Fragmentary postcranial remains.A hyaenodont.Cf. AsiabradypusCf. A. sp.Locality SC-67.An edentulous right lower jaw (UM 87859m).A palaeanodont.DidymictisD. leptomylusLocalities MP-40, SC-67 and SC-79.Skull and teeth.A viverravid.D. protenusMultiple postcranial specimens.A viverravid.DipsalidictisD. platypusLocalities SC-67 and SC-141.An oxyaenid.D. transiensLocalities SC-79 and SC-67.An upper left canine and a trigonid of a molar.An oxyaenid.MiacisM. winkleriLocalities SC-67, SC-348 and SC-350.3 fragmentary dentaries.A miacid.cf. M. sp.USGS 7161.A miacid.OxyaenaO. forcipataRelatively complete skeletal remains.An oxyaenid.O. guloUSGS 7186.An oxyaenid.O. intermediaFragmentary postcrania.An oxyaenid.O. platypusNow moved to the genus Dipsalidictis.PalaeanodonP. ignavusPartial skeletons including postcrania.A palaeanodont.P. nieveltiLocalities SC-67 and SC-121.A palaeanodont.PalaeonictisP. occidentalis"Hind foot skeleton and associated fragments".An oxyaenid.P. wingi.Locality SC-67.Trigonid of a right molar and a partial mandible possessing multiple teeth (Chester et al., 2010).An oxyaenid.ProlimnocyonP. atavusBighorn Basin.Partial skeleton.A hyaenodont.P. eeriusLocalities SC-67 and possibly SC-139.Crushed skull.A hyaenodont.PrototomusP. deimosLocalities SC-67 and SC-349.4 fragmentary specimens.A hyaenodont.P. sp.4 specimens.A hyaenodont.TritemnodonT. sp.2 specimens with postcrania.A hyaenodont.?Uintacyon?U. sp.A miacid. ViverravusV. bowni Locality SC-67, and locality SC-29, Park County, Wyoming. A viverravid. V. politusLocality SC-67.A left maxilla.A viverravid.Vulpavuscf. V. canavus3 specimens.A miacid.

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

Marsupials Marsupials reported from the Willwood Formation Genus Species Presence Material Notes ImagesMimoperadectesM. labrusLocalities SC-67 and SC-69.Left dentary. PeradectesP. cf. P. chesteri 2 isolated teeth.

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

Primatomorphs Primatomorphs reported from the Willwood Formation Genus Species Presence Material Notes ImagesAbsarokiusA. abbottiAn omomyid.A. metoecusAn omomyid.AnemorhysisA. pattersoniUpper part of the formation.An omomyid.A. wortmaniUpper part of the formation.An omomyid.ArapahoviusA. advenaNorthwest Wyoming.An omomyid.ArctodontomysA. wilsoniLocality SC-67.Small sample of teeth.A microsyopid.BownomomysB. americanaAn omomyid, formerly listed as a species of Teilhardina.B. crassidensAn omomyid, formerly listed as a species of Teilhardina.CantiusC. abditusA substantially complete skull and mandible.An adapiform.C. torresiLocalities SC-67 and SC-69.An adapiform.CarpolestesC. cf. C. nigridensLocality SC-29, Park County, Wyoming.A right dentary.A carpolestid.ChlororhysisC. incomptusUpper part of the formation.An omomyid.MicromomysM. willwoodensisClark's Fork Basin.A micromomyid.MicrosyopsM. latidensSouthern Bighorn Basin.Over a thousand specimens.A plesiadapiform.Cf. NiptomomysCf. N. sp.Locality SC-67.An edentulous right dentary.A microsyopid.PhenacolemurP. praecoxLocalities SC-67 and SC-348.Right and left dentaries.A paromomyid.P. willwoodensisUpper part of the formation.A paromomyid.PseudotetoniusP. ambiguusAn omomyid.SteiniusS. annectensNorthwest Wyoming.An omomyid.S. vespertinus"AMNH 16835, fragment of a left ramus with M1 through M3".An omomyid.StrigorhysisS. sp., cf. S. bridgerensisAn omomyid. TatmaniusT. szalayi Northwest Wyoming. An omomyid.TeilhardinaT. americanaNow moved to the genus Bownomomys.T. brandtiAn omomyid.T. crassidensNow moved to the genus Bownomomys.T. tenuiculaAn omomyid.TetoniusT. homunculusAn omomyid.T. matthewiAn omomyid.T. sp.An omomyid.TinimomysT. graybullensisThe lingual half of a right upper molar.A microsyopid.Worlandiacf. 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 ImagesAcritoparamysCf. A. atavus Locality SC-67.A small isolated lower incisor (UM 86003m). A. atwateriLocalities SC-67, SC-308 and SC-351.Several dentaries and teeth.FranimysF. sp."ACM 10524 (a skull with the right P4 and M2-M3, edentulous mandible, and several postcranial elements)".NotoparamysN. costilloiUpper part of the formation.18 specimens.Also known from the Huerfano Formation. "Pseudotomus" coloradensis and Leptotomus loomisi are probably junior synonyms.ParamysP. taurusLocalities SC-67, SC-139 and SC-350.Jaw fragments and incisors.

Ungulates