Geologic formation in the northwestern United States
Fort Union Formation Fossils from the Fort Union Formation
Type Geological formation Sub-units Atwell Gulch, China Butte, Ekalaka, Lebo , lower Ludlow, Overland, Rock Bench Quarry, Sentinel Butte , Shotgun, Somber beds, Tongue River , Tullock , upper Ludlow , Polecat Bench Formation Underlies Wasatch Formation Overlies Hell Creek Formation , Lance Formation Primary Sandstone , shale Other Coal Coordinates 47°00′N 104°36′W / 47.0°N 104.6°W / 47.0; -104.6 Approximate paleocoordinates 52°48′N 80°06′W / 52.8°N 80.1°W / 52.8; -80.1 Region Montana , North Dakota Wyoming , Colorado Country United States Extent Powder River Basin
The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming , Montana , and parts of adjacent states. In the Powder River Basin , it contains important economic deposits of coal , uranium , and coalbed methane .[ 1]
Description
The Fort Union is mostly of Paleocene age and represents a time of extensive swamps as well as fluvial and lacustrine conditions. The rocks are more sandy in southwestern Wyoming and more coal-bearing in northeast Wyoming and southeast Montana, reflecting a general change from rivers and lakes in the west to swamps in the east, but all three environments were present at various times in most locations.[ 2]
Coal in the Fort Union in the Powder River Basin occurs mainly in the Tongue River Member, where as many as 32 coal seams total more than 300 feet in thickness.[ 1] One such bed, the Wyodak Coal near Gillette, Wyoming , is as much as 110 feet (34 m) thick. Most of the coals in the Fort Union Formation are ranked subbituminous .[ 3]
Fort Union Formation - stratigraphy
Fossil content
Color key
Notes Uncertain or tentative taxa are in small text ; crossed out taxa are discredited.
Mammals
Cimolestans
Cimolestans reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Crustulus
C. fontanus
Northeastern Montana.[ 4]
Tullock Member.[ 4]
An isolated upper molar.[ 4]
A pantodont .
Leptictids
Marsupials
Primatomorphs
Primatomorphs reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Carpodaptes
C. sp.
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
2 isolated fourth lower premolars.[ 7]
A carpolestid .
Chiromyoides
C. caesor
Hell's Half Acre (UCM locality 78009), Mesa County, Colorado .[ 8]
A single upper incisor (UCM 53515).[ 8]
A plesiadapid .
C. gigas
Piceance Creek Basin , Colorado.[ 8]
Multiple teeth.[ 8]
A plesiadapid .
C. sp.
UCM locality 78060, Colorado.[ 8]
A left molar (UCM 41606).[ 8]
A plesiadapid .
Elphidotarsius
E. shotgunensis
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
Right ramus of mandible & isolated teeth.[ 7]
A carpolestid .
Nannodectes
N. gazini
Fremont County, Colorado .[ 8]
A right maxilla (USGS 16872).[ 8]
A plesiadapid .
Palaechthon
P., near P. alticuspis
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
3 upper molars & 4 lower molars.[ 7]
A plesiadapiform .
P. woodi
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
A lower jaw & 13 isolated teeth.[ 7]
A plesiadapiform .
Palenochtha
P. cf. minor
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
5 lower teeth.[ 7]
A plesiadapiform .
Paromomys
P., near P. depressidens
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
Approximately 12 upper teeth, 8 isolated lower teeth & a jaw fragment.[ 7]
A paromomyid .
Phenacolemur
P. fremontensis
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
A lower jaw & isolated teeth.[ 7]
A paromomyid .
P. cf. frugivorus
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
2 upper molars & 8 isolated lower molars.[ 7]
A paromomyid .
Plesiadapis
P. dubius
Piceance Creek Basin , Colorado.[ 8]
Jaw elements & teeth.[ 8]
A plesiadapid .
P. fodinatus
Piceance Creek Basin , Colorado.[ 8]
Jaw elements & teeth.[ 8]
A plesiadapid .
P. sp.
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
5 lower molars, 3 anterior upper molars & a premolar .[ 7]
A plesiadapid .
Plesiolestes
P. cf. problematicus
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
Approximately 45 isolated teeth.[ 7]
A plesiadapiform .
Pronothodectes
P. intermedius
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
Jaw elements & teeth.[ 7]
A plesiadapid .
Purgatorius
P. janisae
'Harley's Point’ UCMP locality V77087, Garfield County, Montana .[ 9]
Tullock Member.[ 9]
UCMP 150018 (right m1), and UCMP 192398 (left m3).[ 9]
A purgatoriid .
P. mckeeveri
Garfield County, Montana .[ 9]
Tullock Member.[ 9]
Dentary remains & teeth.[ 9]
A purgatoriid .
P. cf. P. mckeeveri
Harley's Point’ UCMP locality V77087, Garfield County, Montana .[ 9]
Tullock Member.[ 9]
UCMP 150019 (right M2), and UCMP 150020 (right M2).[ 9]
A purgatoriid .
Torrejonia
Cf. T. wilsoni
Wind River Basin , Wyoming.[ 7]
Shotgun Member.[ 7]
About 14 lower teeth & possibly 3 upper molars.[ 7]
A plesiadapiform .
Zanycteris
Z. honeyi
UMC locality number 92177, Colorado.[ 10]
Atwell Gulch Member.[ 10]
Right maxilla (UCM 87378).[ 10]
A plesiadapiform .
Ungulates
Ungulates reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Dissacus
D. argenteus
Princeton Quarry, Park County, Wyoming .[ 11]
Upper part of the formation.[ 11]
Jaw elements & teeth.[ 11]
A mesonychid .
D. cf. navajovius
Princeton Quarry, Park County, Wyoming .[ 11]
Upper part of the formation.[ 11]
Jaw elements & teeth.[ 11]
Specimens reassigned to D. argenteus .
D. praenuntius
Park County, Wyoming .[ 11]
Upper part of the formation.[ 11]
Mandible (YPM -PU 16159).[ 11]
A mesonychid also known from the Willwood Formation .
Ectocion
E. mediotuber
Princeton Quarry, Wyoming.[ 12]
Dentary.[ 12]
A phenacodontid .
Periptychus
P. carinidens
Makoshika State Park , Montana.[ 13]
A periptychid also found in the Nacimiento , North Horn , Black Peaks & Animas formations.
Sigynorum
S. magnadivisus
Great Divide Basin , southern Wyoming.[ 14]
China Butte Member.[ 14]
An arctocyonid .
Reptiles
Birds
A partial ornithurine coracoid bone found in this formation is identical to others found in the older Hell Creek Formation . At present, this unnamed species is the only known individual bird species that have survived the Cretaceous–Paleogene extinction event .[ 15]
Crocodilians
Squamates
Squamates reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Anguidae
Genus & species indeterminate
Swain Quarry, Carbon County, Wyoming .[ 18]
Fragmentary jaw elements.[ 18]
An anguid lizard.
cf. Anguidae
Swain Quarry, Carbon County, Wyoming .[ 18]
6 partial dentaries.[ 18]
Provisionally referred to anguid lizards based on size & shape.
Contogenys
cf. C. sloani
Swain Quarry, Carbon County, Wyoming .[ 18]
Posterior part of a right maxilla (AMNH 12069).[ 18]
A skink .
Exostinus
E. cf. E. lancensis
Swain Quarry, Carbon County, Wyoming .[ 18]
4 partial dentaries.[ 18]
A xenosaurid lizard.
E. rugosus
Princeton & Schaff quarries, Park County, Wyoming .[ 17]
Multiple specimens.[ 17]
A xenosaurid lizard.
Glyptosaurinae
Genus & species indeterminate
Swain Quarry, Carbon County, Wyoming .[ 18]
Several jaw remains.[ 18]
A glyptosaurine lizard.
Glyptosaurinae or Odaxosaurinae
Genus & species indeterminate
Swain Quarry, Carbon County, Wyoming .[ 18]
Fragmentary jaw elements & osteoderms.[ 18]
Indeterminate lizard remains.
Machaerosaurus
M. torrejonensis
Swain Quarry, Carbon County, Wyoming .[ 18]
Numerous jaw elements.[ 18]
An anguid lizard also known from the Nacimiento Formation .
Odaxosaurus
O. piger
Swain Quarry, Carbon County, Wyoming .[ 18]
Many fragmentary jaw remains.[ 18]
An anguid lizard.
Oligodontosaurus
O. wyomingensis
Park County, Wyoming .[ 17]
A left mandible (PU 14246).[ 17]
An amphisbaenian .
Palaeosaniwa
cf. P. canadensis
Swain Quarry, Carbon County, Wyoming .[ 18]
Medial part of left dentary (AMNH 15957).[ 18]
A large anguimorph lizard.
Palaeoxantusia
P. fera
Swain Quarry, Carbon County, Wyoming .[ 18]
Numerous jaw elements.[ 18]
A night lizard .
Pancelosaurus
P. piger
Princeton, Fritz & Schaff quarries, Park County, Wyoming .[ 17]
Multiple skull elements.[ 17]
An anguid lizard.
Provaranosaurus
P. acutus
Princeton Quarry, Park County, Wyoming .[ 17]
PU 14243 (left maxilla ), 14561 (anterior portion of left dentary ) & 17145 ( fragment of left maxilla).[ 17]
A palaeovaranid lizard.
cf. P. sp.
Swain Quarry, Carbon County, Wyoming .[ 18]
3 partial dentaries (AMNH 14306, 14307 & 14309).[ 18]
A palaeovaranid lizard.
Rhineuridae
Unidentified genus & species
Fritz Quarry, Park County, Wyoming .[ 17]
An almost complete right dentary & a broken vertebra (PU 18627).[ 17]
An amphisbaenian .
Saniwa
cf. S. sp.
Swain Quarry, Carbon County, Wyoming .[ 18]
2 trunk vertebrae (AMNH 15960 & 16003).[ 18]
A varanid .
Swainiguanoides
S. milleri
Swain Quarry, Carbon County, Wyoming .[ 18]
Jaw elements.[ 18]
An iguanid .
Testudines
Testudines reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Atoposemys
A. entopteros
Montana.[ 19]
Tullock Member.[ 19]
A softshell turtle .
Axestemys
A. montinsana
PTRM Site V02017, Slope County, North Dakota .[ 20]
Numerous skull, limb & shell fragments.[ 20]
A softshell turtle also found in the Melville & Denver formations.
Cardiochelyon
C. rogerwoodi
Reis Quarry, Park County, Wyoming .[ 21]
Partial skeleton (YPM PU14671).[ 21]
A kinosternoid formerly thought to be a platysternid .
Cedrobaena
C. putorius
Cedar Point Quarry, Wyoming.[ 22]
Shell & skull elements.[ 22]
A baenid turtle also found in the Hell Creek Formation .
Hutchemys
H. arctochelys
Burns Mine, Washoe Area, Carbon County, Montana .[ 23]
Tongue River Member.[ 23]
Multiple shell elements.[ 23]
A softshell turtle .
H. rememdium
Fallon County, Montana .[ 23]
Ekalaka Member.[ 23]
A near complete postcranial skeleton (YPM PU 16795) & shell elements.[ 23]
A softshell turtle .
H. sp.
Duffy's Ranch, Sweet Grass County, Montana .[ 23]
YPM PU 11566.[ 23]
A softshell turtle .
Ptychogaster
P. sp.
Princeton Quarry & Reiss Locality, Park County, Wyoming .[ 17]
PU 17794 (fragments of the skull & shell), 14671 & 16443 (shells).[ 17]
A turtle .
Tullochelys
T. montanus
Montana.[ 19]
Tullock Member.[ 19]
A chelydrid turtle also known from the Hell Creek Formation .
Amphibians
Amphibians reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Amphiuma
A. jepseni
Park County, Wyoming .[ 17]
PU 14666 (partial vertebral column), 14668 (partial skull) & 16788 (dislocated vertebrae).[ 17]
An aquatic salamander .
Anura
Incertae sedis
Park County, Wyoming .[ 17]
PU 14662 (distal end of right radioulna), 14663 (proximal end of left radioulna), 14669 (phalanx ), 13372 (right maxilla ).[ 17]
A frog.
Discoglossidae
Undescribed genus & species
Park County, Wyoming .[ 17]
Distal end of right humerus (PU 14670).[ 17]
A frog similar to undescribed discoglossid remains from the Hell Creek Formation .[ 17]
Eorhinophrynus
E. sp.
Princeton & Fritz quarries, Park County, Wyoming .[ 17]
Humeri & vertebrae.[ 17]
A burrowing toad .
Opisthotriton
O. kayi
Princeton Quarry, Park County, Wyoming .[ 17]
Multiple specimens.[ 17]
A salamander .
Scapherpeton
S. tectum
Princeton & Schaff quarries, Park County, Wyoming .[ 17]
PU 20583 (3 broken vertebrae, an atlas , an ilium & a rib) & PU 19500 (a humerus ).[ 17]
A salamander .
Fish
Fish reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Acipenseridae
Morphotype A
Eagle Mine near Bear Creek, Carbon County, Montana .[ 24]
A complete lateral scute (YPM VPPU 17066).[ 24]
A large sturgeon .
Morphotype B
Highway Blowout Site, Fallon County, Montana .[ 24]
Tongue River Member.[ 24]
A complete lateral scute (YPM VPPU 16646).[ 24]
A large sturgeon.
Amia
A. basiloides
Burns Mine and Eagle Mine near Bear Creek, Carbon County, Montana[ 25]
A near complete skull and partial skeleton, isolated vertebra[ 25]
A large bowfin .
Atractosteus
A. grandei
Bowman County, North Dakota .[ 26]
Lowest Danian strata.[ 26]
A large gar .
Cyclurus
C. fragosus
Schaff Quarry, Park County, Wyoming .[ 17]
3 vertebral centra (PU 21174).[ 17]
A bowfin.
Engdahlichthys
E. milviaegis
Montana.[ 27]
Tullock Member.[ 27]
A fairly small sturgeon.
Polyodon
P. tuberculata
Montana.[ 27]
Tullock Member.[ 27]
3 specimens.[ 27]
A paddlefish .
Invertebrates
Bivalves
Gastropods
Plants
Plants reported from the Fort Union Formation
Genus
Species
Locality
Stratigraphic member
Material
Notes
Images
Aesculus
A. hickeyi
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
Leaves.[ 29]
A horse chestnut .
Amersinia
A. obtrullata
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
Fruits.[ 29]
A nyssaceaen , may be produced by the same plant as Beringiaphyllum cupanioides .
Beringiaphyllum
B. cupanioides
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
Leaf (UF 18969-60464).[ 29]
A nyssaceaen , may be produced by the same plant as Amersinia obtrullata .
Browniea
B. serrata
Mexican Hat locality & Custer National Forest, Powder River County, Montana.[ 29] [ 30]
Lebo Member & Tongue River Member.[ 29] [ 30]
Leaves showing signs of insect damage.[ 30]
A nyssaceaen .
Cercidiphyllum
C. genetrix
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves showing signs of insect damage.[ 30]
A katsura tree .
Cornus
C. swingii
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
Leaves.[ 29]
A dogwood .
Davidia
D. antiqua
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Leaves & fruits.[ 29]
A dove tree .
Cf. Dennstaedtia
Cf. D. americana
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
A single specimen of sterile foliage (UF 18969-34532).[ 29]
A fern .
Dicotylophyllum
D. hansonium
Williston Basin , North Dakota.[ 31]
Tongue River Member.[ 31]
Leaves.[ 31]
A dicot .
D. horsecreekium
Williston Basin , North Dakota.[ 31]
Ludlow Member.[ 31]
Leaves.[ 31]
A dicot .
Eostangeria
E. pseudopteris
Sweetwater County, Wyoming .[ 32]
Upper part of the formation.[ 32]
Multiple specimens.[ 32]
A cycad .
Equisetum
E. sp.
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
A single stem (UF 18969-60476A).[ 29]
A horsetail .
"Ficus "
"F." artocarpoides
Mexican Hat locality.[ 30]
Lebo Member.[ 30]
Leaves with signs of hole feeding and insect mining.[ 30]
A fig-tree .
Glyptostrobus
G. europaeus
Mexican Hat locality.[ 30]
Lebo Member.[ 30]
Leafy branches.[ 30]
A conifer .
Juglandiphyllites
J. glabra
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves with insect damage and probable lepidopteran leaf mines .[ 30]
A member of the walnut family .
Lauraceae
Species 1
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaf with piercing and sucking marks from insects.[ 30]
Species 2
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves showing signs of insect damage.[ 30]
Macginistemon
M. mikanoides
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Stamen groups.[ 29]
A platanaceaen .
Macginitiea
M. gracilis
Custer National Forest , Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
A fragmentary leaf (UF 18969-38380).[ 29]
A platanaceaen .
M. nascens
Williston Basin , North Dakota.[ 31]
Ludlow Member.[ 31]
Leaves.[ 31]
A platanaceaen .
Meliosma
M. thriviensis
Williston Basin , North Dakota.[ 31]
Ludlow Member.[ 31]
Leaves.[ 31]
A sabiaceaen .
M. vandaelium
Williston Basin , North Dakota.[ 31]
Tongue River Member.[ 31]
Multiple leaves.[ 31]
A sabiaceaen .
Nordenskioeldia
N. borealis
Custer National Forest, Powder River County, Montana .[ 29]
Tongue River Member.[ 29]
Fruit.[ 29]
A trochodendrale .
Paleonelumbo
P. macroloba
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves.[ 30]
A nelumbonaceaen .
Paranymphaea
P. crassifolia
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves.[ 30]
A nymphaeaceaen .
Phyllites
P. demoresii
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Leaves.[ 29]
Platanus
P. raynoldsii
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves showing signs of insect damage.[ 30]
A plane-tree .
P. sp.
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Leaves.[ 29]
A plane-tree .
Polyptera
P. manningii
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Fruits.[ 30]
A member of the walnut family .
"Populus "
"P". nebrascensis
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaves showing signs of insect damage.[ 30]
A poplar .
Porosia
P. verrucosa
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Fruits.[ 29]
A rutaceaen .
Taxodium
T. olrikii
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
[ 29]
A cypress tree.
Ternstromites
cf. T. aureavallis
Mexican Hat locality, Montana.[ 30]
Lebo Member.[ 30]
Leaf with a gall at the intersection of primary and secondary veins.[ 30]
A theaceaen .
T. paucimissouriensis
Williston Basin , North Dakota.[ 31]
Ludlow & Tongue River Members.[ 31]
Leaves.[ 31]
A theaceaen .
Trochodendroides
T. genetrix
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
A few leaves.[ 29]
A saxifrage .
Ulmites
U. microphylla
Custer National Forest, Powder River County, Montana.[ 29]
Tongue River Member.[ 29]
Leaves.[ 29]
An ulmaceaen .
Zizyphoides
Z. flabella
Mexican Hat locality, Montana & Custer National Forest, Powder River County, Montana.[ 30] [ 29]
Lebo Member & Tongue River Member.[ 30] [ 29]
Leaves showing signs of insect damage.[ 30]
A trochodendrale .
See also
References
^ a b Wyodak Coal, Tongue River Member of the Fort Union Formation, Powder River Basin, Wyoming: "No-Coal Zones" and Their Effects on Coalbed Methane Production , by Mark Ashley, 2005
^ Eocene and Paleocene rocks of the southern and central basins , by Robert E. McDonald, in Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 248
^ Cretaceous and Tertiary coals of the Rocky Mountains and Great Plains regions , by R.M. Flores and T.A. Cross, 1991, in Economic Geology, U.S., Geological Society of America, Decade of North American Geology Series, vol. P-2, p. 547-571.
^ a b c Clemens, William A. (2018-02-17). "A pantodont (Mammalia) from the latest Puercan North American Land Mammal Age (earliest Paleocene) of the Western Interior, USA" . Historical Biology . 30 (1– 2): 183– 188. Bibcode :2018HBio...30..183C . doi :10.1080/08912963.2016.1276178 . ISSN 0891-2963 . S2CID 132830375 .
^ a b c Clemens, W. (January 9, 2015). "(Leptictidae, Mammalia) from the Tullock Member of the Fort Union Formation, Garfield and McCone Counties, Montana, USA" . PaleoBios . 32 (1): 1– 17. doi :10.5070/P9321025382 . S2CID 55974838 .
^ a b c d Johanson, Zerina (November 1996). "New marsupial from the Fort Union Formation, Swain Quarry, Wyoming" . Journal of Paleontology . 70 (6): 1023– 1031. Bibcode :1996JPal...70.1023J . doi :10.1017/S0022336000038725 . ISSN 0022-3360 . S2CID 133554548 .
^ 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 Gazin, C. Lewis (1971). "Paleocene primates from the shotgun member of the Fort Union Formation in the Wind River Basin, Wyoming" . Proceedings of the Biological Society of Washington . 84 : 13– 37. ISSN 0006-324X .
^ a b c d e f g h i j k l Burger, Benjamin J.; Honey, James G. (2008-09-12). "Plesiadapidae (Mammalia, Primates) from the late Paleocene Fort Union Formation of the Piceance Creek Basin, Colorado" . Journal of Vertebrate Paleontology . 28 (3): 816– 825. doi :10.1671/0272-4634(2008)28[816:pmpftl]2.0.co;2 . ISSN 0272-4634 . S2CID 128913932 .
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^ a b c Burger, Benjamin John (2013-10-29). "A new species of the archaic primate Zanycteris from the late Paleocene of western Colorado and the phylogenetic position of the family Picrodontidae" . PeerJ . 1 : e191. doi :10.7717/peerj.191 . ISSN 2167-8359 . PMC 3817582 . PMID 24255808 .
^ a b c d e f g h i O'Leary, Maureen A.; Rose, Kenneth D. (1995-05-12). "New mesonychian dentitions from the Paleocene and Eocene of the Bighorn Basin, Wyoming" . Annals of the Carnegie Museum . 64 (2): 147– 172. Bibcode :1995AnCM...64..147O . doi :10.5962/p.215127 . ISSN 0097-4463 . S2CID 89955337 .
^ a b Thewissen, J. G. M. (1990). "Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra)" . hdl :2027.42/48629 .
^ Shelley, Sarah L.; Williamson, Thomas E.; Brusatte, Stephen L. (2018-07-18). "The osteology of Periptychus carinidens: A robust, ungulate-like placental mammal (Mammalia: Periptychidae) from the Paleocene of North America" . PLOS ONE . 13 (7): e0200132. Bibcode :2018PLoSO..1300132S . doi :10.1371/journal.pone.0200132 . ISSN 1932-6203 . PMC 6051615 . PMID 30020948 . {{cite journal }}
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^ a b McComas, Katie M.; Eberle, Jaelyn J. (May 2015). "A new earliest Paleocene (Puercan) arctocyonid mammal from the Fort Union Formation, Great Divide Basin, Wyoming, and its phylogenetic position among early 'condylarths' " . Journal of Systematic Palaeontology . 14 (6): 445– 459. doi :10.1080/14772019.2015.1066886 . S2CID 127411164 .
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Cenozoic chronostratigraphy of Colorado
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Mesozoic chronostratigraphy of Colorado
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Paleozoic chronostratigraphy of Colorado
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Precambrian chronostratigraphy of Colorado
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