Willwood Formation
Geologic formation in Wyoming, United States
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene , or Clarkforkian , Wasatchian and Bridgerian in the NALMA classification .[ 1] [ 2]
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 .[ 3]
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.[ 4]
Fossil content
Trace fossils have been found in the Willwood Formation.[ 5] Fossil birds include Gastornis , Neocathartes and Paracathartes . A fossil alligatorid , namely Orthogenysuchus , was also found in this formation.
Mammals
Afrotheres
Apatotheres
Apatotheres reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Apatemys
A. bellulus
Lysite and Lost Cabin Zone.[ 7]
Also found in the Wind River Formation .[ 7]
A. chardini
Middle and possibly lower Gray Bull zone.[ 7]
The smallest species of the genus.[ 7]
A. kayi
The oldest known species of the genus.[ 7]
A. sp., cf. A. rodens
Eastern side of Red Butte , and north of Sheep Mountain .[ 7]
YPM 23476, 30582, AMNH 48999.[ 7]
3 very large specimens of Apatemys .[ 7]
Bats
Cimolestans
Cimolestans reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Azgonyx
A. gunnelli
Localities SC-67, SC-308 and SC-351.[ 9]
A tillodont .
A. sp.
Locality SC-67.[ 9]
A larger tillodont than A. gunnelli .
Coryphodon
C. sp.
Localities FG-61, SC-67 and SC-139.[ 9]
[ 10]
A pantodont .
Didelphodus
D. absarokae
Lower Gray Bull to the upper part of the Lysite zones.[ 7]
A palaeoryctid .
Ectoganus
E. bighornensis
Localities HG-3 and SC-67.[ 9]
A taeniodont .
E. copei
USGS 3838, with postcrania .[ 10]
A taeniodont .
E. gliriformis
A fragmentary femur (PU 13173).[ 10]
A taeniodont .
Esthonyx
E. bisculatus
Jaws, teeth and a few postcranial remains.[ 10]
A tillodont .
E. spatularius
Bighorn Basin ,[ 11] and locality SC-67.[ 9]
Fragmentary left dentary.[ 9]
A tillodont .
Megalesthonyx
M. hopsoni
Buffalo Basin.[ 12]
A tillodont .
cf. Palaeoryctes
cf. P. sp.
"USGSD 1661, 2151, 3711".[ 7]
A palaeoryctid .
Palaeosinopa
P. incerta
Lower to upper Gray Bull zone,Bighorn Basin .[ 7] [ 13]
A pantolestid also found in the Wind River and San Jose formations.[ 7]
P. lutreola
Middle and upper Gray Bull zone, Bighorn Basin.[ 7] [ 13]
A pantolestid .
P. veterrima
Lower Gray Bull through Lysite zones, Bighorn Basin.[ 7] [ 13]
More than 50 specimens.[ 7]
A pantolestid .
P. sp.
Lower part of the formation.[ 6]
UM 69722 (a partial skull and mandible).[ 6]
A pantolestid .
cf. Pararyctes
cf. P. sp.
"Yale locality 363 at the 190-m level of the Willwood Formation in the Elk Creek Facies".[ 7]
UW 7028.[ 7]
A palaeoryctid .
Eulipotyphlans
Eulipotyphlans reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Auroralestes
A. simpsoni
Lower part of the formation, Sand Creek Facies.[ 7]
UW 9616 (right P4-M2) and YPM 35156.[ 7]
An erinaceid , originally named Eolestes .
Batodonoides
B. vanhouteni
Locality SC-303, situated at the 2,110 m level of the formation.[ 14]
Maxilla and dentaries .[ 14]
A geolabidid .
Centetodon
C. neashami
"Lower middle Gray Bull and upper Gray Bull zones".[ 7]
A geolabidid .
C. patratus
UCMP 44954 and YPM 23088, possibly also UCMP 44957, 44958, 44959.[ 7]
A geolabidid .
Creotarsus
C. lepidus
"Lower Gray Bull beds, Coon Creek, Garland Road, Bighorn Basin ".[ 7]
"AMNH 16169, left ramus with P4-M2, and associated tarsal bones".[ 7]
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".[ 7]
An erinaceid , originally referred to as "Leptacodon" jepseni .[ 15]
Dormaaliidae
Dormaaliid, sp. A
Sand Creek Facies.[ 7]
UW 7048, 9627.[ 7]
An amphilemurid .
Eolestes
E. simpsoni
Lower part of the formation, Sand Creek Facies.[ 7]
UW 9616 (right P4-M2) and YPM 35156.[ 7]
Now renamed to Auroralestes .
Insectivora (?)
gen. et. sp. indeterminate
YPM locality 355, lower part of the middle Gray Bull zone.[ 7]
"YPM 30860, fragment of right ramus with M1(?) and trigonid of M2(?)".[ 7]
Teeth which may represent an unusual insectivore or microchiropteran .
cf. Leipsanolestes
cf. L. sp.
Sand Creek Facies.[ 7]
UW 9672, a left molar.[ 7]
An erinaceid .
Leptacodon
cf. "L. " jepseni
"YPM 30559, fragment of left ramus with P4-M1 and trigonid of M2".[ 7]
Actually an erinaceid , now reassigned to a new genus, Dartonius .[ 15]
L. rosei
Localities SC-188 and SC-29, Park County, Wyoming .[ 8]
3 dentaries, 2 maxillae, several isolated teeth and possibly a metatarsal .[ 8]
A nyctitheriid .
Cf. L. sp.
A single lower molar.[ 8]
A nyctitheriid .
Limaconyssus
L. habrus
Locality SC-29, Park County, Wyoming .[ 8]
Left dentary .[ 8]
A nyctitheriid .
Macrocranion
M. nitens
Uppermost part of the lower Gray Bull zone to the upper part of the Lysite zone.[ 7]
An amphilemurid .
Parapternodus
P. antiquus
Lower part of the formation.[ 7]
YPM 31169, fragment of left ramus with M2-3.[ 7]
An apternodontid .
Plagioctenodon
P. krausae
Sand Creek Facies.[ 7]
A nyctitheriid .
cf. P. krausae
Locality SC-29, Park County, Wyoming .[ 8]
An isolated first or second lower incisor and the buccal half of an upper molar.[ 8]
A nyctitheriid .
P. savagei
YPM locality 104, lower part of the formation.[ 7]
"YPM 34257, right P3-M2".[ 7]
A nyctitheriid .
Pontifactor
P. sp.
"UW 8584, 9621, 9649, 9681, 9683, 9710, 9721, 9732, 9733, 10449, 10455, 10456".[ 7]
A nyctitheriid .
Scenopagus
S. hewettensis
UW locality V -73020.[ 7]
UW 8998 and possibly UW 9738, 10450.[ 7]
An amphilemurid .
S. sp.
Middle Gray Bull zone.[ 7]
An amphilemurid , at least 2 species represented by inadequate material, at least one is probably new.[ 7]
Talpavoides
T. dartoni
Lower part of the formation.[ 7]
An amphilemurid .
Wyonycteris
W. chalix
Locality SC-29, Park County, Wyoming .[ 8]
"UM 76910, a right dentary ".[ 8]
A nyctitheriid , originally believed to be a bat .
Ferae
Leptictids
Leptictids reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Palaeictops
P. bicuspis
Also found in the Wind River Formation .[ 7]
Prodiacodon
P. tauricinerei
Mostly in the Gray Bull zone, one or two specimens in the Bighorn Basin Lysite zone.[ 7]
P. sp.
Middle Gray Bull zone.[ 7]
YPM 26013, 26040, possibly 26026.[ 7]
Marsupials
Marsupials reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Mimoperadectes
M. labrus
Localities SC-67 and SC-69.[ 9]
Left dentary.[ 9]
Peradectes
P. cf. P. chesteri
2 isolated teeth.[ 8]
Multituberculates
Primatomorphs
Rodents
Rodents reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Acritoparamys
Cf. A. atavus
Locality SC-67.[ 9]
A small isolated lower incisor (UM 86003m).[ 9]
A. atwateri
Localities SC-67, SC-308 and SC-351.[ 9]
Several dentaries and teeth.[ 9]
Franimys
F. sp.
"ACM 10524 (a skull with the right P4 and M2-M3, edentulous mandible, and several postcranial elements)".[ 6]
Notoparamys
N. costilloi
Upper part of the formation.[ 23]
18 specimens.[ 23]
Also known from the Huerfano Formation . "Pseudotomus " coloradensis and Leptotomus loomisi are probably junior synonyms .[ 23]
Paramys
P. taurus
Localities SC-67, SC-139 and SC-350.[ 9]
Jaw fragments and incisors.[ 9]
Ungulates
Ungulates reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Anacodon
A. ursidens
[ 10]
An arctocyonid .
Bunophorus
cf. B. grangeri
USGS 16470 (a very incomplete skeleton).[ 10]
A dichobunid originally listed as cf. Wasatchia dorseyana .
Cardiolophus
C. radinskyi
UM 64913.[ 24]
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.[ 9]
A phenacodontid .
Chriacus
C. badgleyi
Localities SC-67, SC-79, SC-121 and SC-342.[ 9]
An arctocyonid .
C. sp.
Several skeletal specimens.[ 10]
An arctocyonid .
Diacodexis
D. ilicis
Localities SC-67 and SC-308.[ 9]
A dichobunid .
D. metsiacus
Several specimens, including a near-complete skeleton.[ 10]
A dichobunid .
Dissacus
D. praenuntius
Park County, Wyoming .[ 9] [ 25]
Teeth, jaw elements & bone fragments.[ 9] [ 25]
A mesonychid .
D. serior
USGS locality D-1754, Bighorn Basin , Wyoming.[ 25]
Left dentary fragments (USGS 27612).[ 25]
A mesonychid .
D. willwoodensis
Bighorn Basin , Wyoming.[ 25]
Mandibles.[ 25]
A mesonychid .
Ectocion
E. osbornianus
Locality SC-67 and SC-351.[ 9]
2 fragmentary dentaries.[ 9] and a single postcranial association.[ 10]
A phenacodontid .
E. parvus
Localities HG-3, SC-67, SC-69, SC-121, SC-139, SC-182, SC-308 and SC-351.[ 9]
A phenacodontid .
Hapalodectes
H. anthracinus
University of Wyoming locality V-73086, Wyoming.[ 25]
Teeth (USGS 9628).[ 25]
A mesonychian
H. leptognathus
A fragmentary specimen (USGS 5912).[ 10]
A mesonychian .
Heptodon
cf. H. calciculus
Wind River Basin.[ 10]
Remains of a subadult with postcrania.[ 10]
Homogalax
H. protapirinus
Bighorn Basin .[ 26]
A skull (YPM(PU) 16168),[ 26] and several other specimens.[ 27] [ 24]
An isectolophid .
cf. H. protapirinus
At least 2 specimens.[ 10]
An isectolophid .
Hyopsodus
H. loomisi
Localities SC-67, SC-69, SC-79, SC-121, SC-308 and SC-342.[ 9]
A hyopsodontid .
H. powellianus
"AMNH 4147, right mandible fragment with M1 through M3".[ 6]
A hyopsodontid .
Hyracotherium
H. grangeri
Locality SC-67.[ 9]
2 isolated teeth.[ 9]
An equid .
H. sandrae
Localities FG-61, SC-67, SC-69, SC-79, SC-121 and SC-139.[ 9]
An equid .
H. sp.
Skeletal remains with postcrania.[ 10]
An equid .
Lambdotherium
L. popoagicum
Multiple localities
A brontotherid .
Meniscotherium
M. priscum
Locality SC-67(?)[ 9]
Left dentary fragment.[ 9]
A phenacodontid .
Pachyaena
P. gigantea
YPM localities 131 & 149, Wyoming.[ 25]
Jaw elements & teeth.[ 25]
A mesonychid .
P. gracilis
USGS locality D-1640.[ 25]
Maxillary fragments (USGS 7185).[ 25]
A mesonychid .
P. ossifraga
Locality SC-348.[ 9]
Trigonid of a right molar.[ 9]
A mesonychid .
P. sp.
Postcranial material.[ 10]
A mesonychid .
Phenacodus
P. cf. P. intermedius
Localities SC-67 and SC-141.[ 9]
A phenacodontid .
P. primaevus
Near complete skeletons.[ 10]
A phenacodontid .
P. vortmani
Near complete skeletons.[ 10]
A phenacodontid .
Princetonia
P. yalensis
Locality SC-121(?)[ 9]
Right dentary.[ 9]
An arctocyonid .
Thryptacodon
T. antiquus
[ 10]
An arctocyonid .
T. barae
Localities MP-38 and SC-121.[ 9]
An arctocyonid .
T. olseni
[ 10]
An arctocyonid .
T. sp.
2 partial skeletons.[ 10]
An arctocyonid .
Wasatchia
cf. W. dorseyana
USGS 16470 (a very incomplete skeleton).[ 10]
Now a junior synonym of Bunophorus .
Xenicohippus
Lower part of the Upper Willwood Formation.[ 28]
A hyracotheriine .
Reptiles
Color key
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
Images
Anachronornis
A. anhimops
Clark Quadrangle, Park County, Wyoming .[ 29]
USNM 496700.[ 29]
An anseriform .
Anseriformes Familia Incertae sedis
Clark Quadrangle, Park County, Wyoming .[ 29]
USNM 496701 (right quadrate missing the pterygoid condyle); USNM 496702 (fragmentary right femur consisting of only the proximal and distal ends).[ 29]
Generally similar to Anachronornis & Danielsavis .[ 29]
Aves indet.
Localities SC-67 and SC-121.[ 9]
A cervical vertebra and proximal part of a carpometacarpus .[ 9]
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."[ 8]
Originally thought to be a heron , now thought to be related to Vastanavis .[ 30]
Diatryma
D. gigantea
Several specimens.[ 31]
Now deemed a junior synonym of Gastornis .
Eogeranoides
E. campivagus
"Fragmentary tibiotarsus and tarsometatarsus remains".[ 32]
A dubious geranoidid , may be a junior synonym of Paragrus prentici .
Gastornis
G. gigantea
Several specimens.[ 31]
A gastornithiform .
Geranoides
G. jepseni
Elk Creek, Bighorn Basin.[ 32]
A geranoidid , now deemed a junior synonym of Palaeophasianus meleagroides.
Microolithus
M. wilsoni
Partial eggs.[ 33]
Fossil bird eggs.
Palaeophasianus
"P." incompletus
"A fragmentary distal end of a tarsometatarsus ".[ 32]
A very large possible geranoidid , may actually belong to the genus Paragrus or be outside Geranoididae entirely.
P. meleagroides
Elk Creek, Bighorn Basin .[ 32]
A geranoidid .
?P. sp.
AMNH 5156.[ 32]
A geranoidid .
Paracathartes
P. howardae
[ 34]
A lithornithid .
Paragrus
P. prentici
[ 32]
A geranoidid .
Primoptynx
P. poliotauros
Specimen including all major postcranial bones.[ 35]
A large owl .
Sandcoleus
S. copiosus
Clark Quadrangale, Park County, Wyoming .[ 36]
"Two articulated partial skeletons and a number of other elements".[ 36]
A sandcoleid mousebird .
Crocodilians
Squamates
Squamates reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Anguidae indet.
2 fragmentary dentaries (UM 76872 and 76873).[ 8]
A very small anguid lizard.[ 8]
Anguimorpha
A dentary, maxilla and 1 or 2 premaxillae (UM 76874–76875, 76878-76879(?), and 768811).[ 8]
A gerrhonotine or diploglossine .[ 8]
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)".[ 38]
Anniealexandria
A. gansi
UCMP locality V99019.[ 38]
Skull fragments and vertebrae.[ 38]
An amphisbaenian .
Anolbanolis
A. banalis
UCMP locality V99019.[ 38]
An iguanian .
Apodosauriscus
A. thermophilus
UCMP locality V99019.[ 38]
Skull fragments.[ 38]
An anguid .
Blutwurstia
B. oliviae
Clarks Fork Basin.[ 39]
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)".[ 38]
An anguid .
Gaultia
G. silvaticus
UCMP locality V99019.[ 38]
A glyptosaurine .
Gerrhonotinae
Gerrhonotine CG
Skull fragments.[ 38]
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)."[ 38]
A glyptosaurine.
Iguanidae
Iguanid CG
"UCMP 151078 (right dentary fragment), 400156 (partial right postorbital), 400169 (partial right squamosal)".[ 38]
An iguanid lizard.
Lacertilia indet.
Localities SC-67 and SC-308.[ 9]
Vertebrae.[ 9]
Indeterminate lizards.
Melanosaurus
M. maximus
A frontal, numerous osteoderms and vertebrae.[ 9]
A glyptosaurine .
Palaeoxantusia
P. sp. CG
Skull fragments.[ 38]
A night lizard .
Proxestops
Cf. P. sp.
Locality MP-40.[ 9]
UM 88170m (2 osteoderms ).[ 9]
A glyptosaurine .
P. sp. CG
Skull fragments.[ 38]
A glyptosaurine .
Provaranosaurus
cf. P. sp. CG
"UCMP 167299 (right dentary fragment)".[ 38]
A xenosaurid .
cf. Saniwa
cf. S. sp. CG-1
"UCMP 150921 (jaw fragment with partial tooth), 151099 (premaxilla), 167572 (jaw fragment with tooth)".[ 38]
A varanid .
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)".[ 38]
A varanid .
Suzanniwana
S. patriciana
UCMP locality V99019.[ 38]
An iguanid .
Varanoidea
A dentary and maxilla (UM 76876 and 768771).[ 8]
One or possibly 2 species of Parasaniwa or Provaranosaurus -like varanoids.[ 8]
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)".[ 38]
A night lizard .
Testudines
Amphibians
Amphibians reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Anura
Distal end of a humerus (UM 76883).[ 8]
A small frog.
Urodela
Numerous vertebrae, UM 76871 (a-j).[ 8]
A small salamander.
Fish
Fish reported from the Willwood Formation
Genus
Species
Presence
Material
Notes
Images
Amia
A. sp.
Localities SC-67 and SC-342.[ 9]
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
[ 41]
A large gar .
Lepisosteus
L. sp.
"Mostly diamond-shaped ganoid scales, but some specimens include distinct opisthocoelous vertebrae, basioccipitals and other cranial elements."[ 9]
A gar .
Invertebrates
Color key
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
Images
Camborygma
C. litonomos
Polecat Bench.[ 42]
Prismatic cylindrical structures.[ 42]
Likely represent crayfish burrows.[ 43] [ 42]
Cocoon traces
Polecat Bench.[ 44]
Cf. Cylindricum
Cf. C. isp.
Polecat Bench.[ 44]
"Predominantly vertical, straight to sinuous, unbranched, unlined, and smooth walled shafts with circular cross sections and gently rounded, unenlarged terminations".[ 42]
Burrows possibly created by beetles , hymenopterans , emerging cicada nymphs, spiders or molluscs .[ 42]
Edaphichnium
E. lubricatum
Polecat Bench.[ 44]
"Tubular burrows with ellipsoidal fecal pellets".[ 45]
Formed by substrate feeding by Earthworms or other invertebrates.
Naktodemasis
N. bowni
Bighorn Basin .[ 46]
"Burrows composed of nested ellipsoidal packets backfilled with thin, tightly spaced, menisci subparallel to the bounding packet."[ 46]
Burrows likely constructed by burrowing bugs or cicada nymphs.[ 42] [ 46]
cf. Planolites
cf. P. isp.
Polecat Bench.[ 44]
Traces made by the feeding of worm-like animals.
cf. Steinchnus
S. isp.
Polecat Bench.[ 44]
Traces made by invertebrates, possibly beetles or mole crickets .
Gastropods
Plants
Wasatchian correlations
See also
References
^ Willwood Formation at Fossilworks .org
^ Neasham & Vondra, 1972
^ "Willwood Formation" . USGS.
^ Tauxe et al., 1994
^ Bown & Kraus, 1982
^ a b c d e f Johnson, Edward (June 1, 2005). "A New Early Eocene Mammalian Fauna from the Great Divide Basin, Southwestern Wyoming: Vertebrate Paleontology, Paleoclimatology, and Biostratigraphy" . Masters Theses .
^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw Bown, T.; Schankler, David M. (1982). "A review of the Proteutheria and Insectivora of the Willwood Formation (Lower Eocene), Bighorn Basin, Wyoming". Geological Survey Bulletin . Vol. 1523. doi :10.3133/B1523 . S2CID 127861247 .
^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak D., Gingerich, Philip (1987). Early Eocene bats (Mammalia, Chiroptera) and other vertebrates in freshwater limestones of the Willwood Formation, Clark's Fork Basin, Wyoming . Museum of Paleontology, University of Michigan. OCLC 17313505 . {{cite book }}
: CS1 maint: multiple names: authors list (link )
^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp Gingerich, Philip D. (1989). New earliest Wasatchian mammalian fauna from the eocene of northwestern Wyoming: composition and diversity in a rarely sampled high-floodplain assemblage . University of Michigan. OCLC 1066072691 .
^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj Rose, Kenneth D. (1990), "Postcranial skeletal remains and adaptations in early Eocene mammals from the Willwood Formation, Bighorn Basin, Wyoming" , Geological Society of America Special Papers , Geological Society of America, pp. 107–134, retrieved September 5, 2022
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