Rodents (Mammalia) from the Early Oligocene (Orellan) Cook Ranch Local Fauna of Southwestern Montana

William W. Korth

doi:10.2992/007.085.0303

Earliest Arikareean (later early Oligocene) Iniyoo local Fauna from Chilapa formation of Santiago Yolomécatl area in northwestern Oaxaca, southern Mexico

Journal of South American Earth Sciences ◽

10.1016/j.jsames.2021.103307 ◽

2021 ◽

pp. 103307

Author(s):

Eduardo Jiménez-Hidalgo ◽

E. Bruce Lander ◽

Isabel Israde-Alcántara ◽

Nadia Wendoline Rodríguez-Caballero ◽

Rosalía Guerrero-Arenas

Keyword(s):

Local Fauna ◽

Southern Mexico ◽

Early Oligocene

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Vertebrate paleontology, geology, and geochronology of the Tapera de López and Scarritt Pocket, Chubut Province, Argentina

Journal of Paleontology ◽

10.1017/s0022336000043080 ◽

1986 ◽

Vol 60 (4) ◽

pp. 920-951 ◽

Cited By ~ 44

Author(s):

Larry G. Marshall ◽

Richard L. Cifelli ◽

Robert E. Drake ◽

Garniss H. Curtis

Keyword(s):

South America ◽

Middle Eocene ◽

Lower Boundary ◽

Vertebrate Paleontology ◽

Early Eocene ◽

Local Fauna ◽

Early Oligocene ◽

Land Mammal ◽

Mammal Faunas ◽

Upper Boundary

Fossil land mammals were collected by G. G. Simpson in 1933–1934 at and near the Tapera de López in central Chubut Province, Patagonia, southern Argentina, from rocks now mapped as the Sarmiento Formation. These fossils are assigned to land mammal faunas of Casamayoran (Early Eocene), Mustersan (Middle Eocene), and Deseadan (late Early Oligocene through Early Miocene) age.40K-40Ar age determinations of eight basalt and two tuff units associated with the Deseadan age local fauna at Scarritt Pocket establish a geochronologic framework that calibrates the biostratigraphic record at this locality. The radioisotope dates obtained at Scarritt Pocket range from 23.4 Ma to about 21.0 Ma, and equate with earliest Miocene time. The Scarritt Pocket local fauna is the youngest dated Deseadan age fauna yet known in South America.Seven other localities have, or were reputed to have, local faunas of Deseadan age associated with dated volcanic units. Six of these localities are in Argentina (Gran Barranca, Cerro Blanco, Valle Hermoso, Pico Truncado, Cañadón Hondo, Quebrada Fiera de Malargüe) and one in Bolivia (Estratos Salla in the Salla-Luribay Basin). The stratigraphic relationships of the volcanic units with these local faunas is discussed, and the taxonomic content of each is reassessed.The Deseadan Land Mammal Age is defined by the earliest record of the land mammal genus Pyrotherium, which is from below a basalt dated at 33.6 Ma at Pico Truncado. Other early records of Pyrotherium occur below basalts dated at about 29 Ma at the Gran Barranca and Valle Hermoso, and from a 28.5 Ma level of the Estratos Salla. Thus, the lower boundary for Deseadan time is about 34 Ma.The youngest record of Pyrotherium is in the upper levels of the Estratos Salla dated at about 24 Ma. However, the Scarritt Pocket local fauna, which lacks Pyrotherium, permits placement of the upper boundary for Deseadan time at about 21.0 Ma. Late Deseadan time is surely, and the end of Deseadan time is apparently, marked by the last record of such groups as Proborhyaeninae (Proborhyaena), Rhynchippinae (Rhynchippus), Archaeohyracidae (Archaeohyrax), and the genera Platypittamys (Octodontidae), Scarrittia (Leontiniidae), Propachyrucos and Prohegetotherium (Hegetotheriidae), and Argyrohyrax (Interatheriidae), as these taxa are recorded in the Scarritt Pocket local fauna. Thus, Deseadan time extends from about 34.0 Ma to about 21.0 Ma, making it the Land Mammal Age with the longest known duration in South America.

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PALEOECOLOGICAL ASPECTS OF WESTERN UNITED STATES NONMARINE OSTRACODS DURING THE EOCENE–OLIGOCENE TRANSITION: THE EARLY OLIGOCENE FAUNAS OF THE RENOVA FORMATION, SOUTHWESTERN MONTANA

Palaios ◽

10.2110/palo.2019.040 ◽

2020 ◽

Vol 35 (4) ◽

pp. 165-174

Author(s):

LUCAS S. ANTONIETTO ◽

LISA E. PARK BOUSH ◽

ROY E. PLOTNICK ◽

ALYCIA L. STIGALL

Keyword(s):

United States ◽

Late Eocene ◽

Western United States ◽

Sedimentary Sequence ◽

Small Lakes ◽

Southwestern Montana ◽

Climatic Variations ◽

Early Oligocene ◽

Volcanic Events ◽

Drought Resistant

ABSTRACT The Renova Formation is a Paleogene sedimentary sequence from southwestern Montana that was deposited in a more extensive basin dominated by mid- to high altitude streams and small-lake paleoenvironments. The sediment infill was dissected during the Miocene–Pliocene into the remnants currently observed in several places, including the Upper Ruby River valley, Medicine Lodge valley and Horse Prairie. Ostracods from these early Oligocene strata belong to five genera of the suborder Cypridocopina: Amplocypris?, Candona (including the species Candona rangliensis? and Candona sp. aff. Candona ohioensis), Cyprois, Eucypris, and Paracypridopsis?. These ostracods, capable of producing drought-resistant eggs, likely inhabited fairly stable small lakes, characterized by arboreal surroundings reminiscent of forests in highland regions that were buffered against the drastic climatic variations of the late Eocene–early Oligocene transition (EOT) during the Eocene–Oligocene climatic deterioration. Further south, climatic change during the EOT, coupled with volcanic events, impacted the establishment of long-lasting, highly diverse ostracod faunas in lowland areas. The Upper Ruby River, Medicine Lodge and Horse Prairie early Oligocene deposits in southwestern Montana may have acted as refugia for Eocene ostracod genera that became extinct elsewhere or represented Lazarus taxa that would later diversify during the Miocene.

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A latest Chadronian (Late Eocene) mammalian fauna from the Cypress Hills, Saskatchewan

Canadian Journal of Earth Sciences ◽

10.1139/e94-116 ◽

1994 ◽

Vol 31 (8) ◽

pp. 1335-1341 ◽

Cited By ~ 2

Author(s):

John E. Storer

Keyword(s):

North America ◽

Strong Evidence ◽

Late Eocene ◽

Mammalian Fauna ◽

Local Fauna ◽

Early Oligocene ◽

Land Mammal

The Kealey Springs West (KSW) local fauna from the Cypress Hills Formation (Eocene to Miocene), Saskatchewan, is probably latest Chadronian in age, and is the northernmost assemblage representing a time near the Eocene–Oligocene boundary in North America. Presence of Pseudocylindrodon neglectus is strong evidence that the assemblage is Chadronian. Herpetotherium valens, Protosciurus, Namatomys cf. N. lloydi, and Centimanomys also suggest a Chadronian age. The assemblage contains Adjidaumo maximus and Palaeolagus cf. P. hemirhizis, species that have been cited as characteristic of the early part of the Orellan Land Mammal Age (early Oligocene), and the typically Orellan Heliscomys hatcheri and Eumys elegans. Several other tara in the KSW assemblage are known from both the Chadronian (late Eocene) and Orellan.

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The first Cenozoic spinicaudatans from North America

Journal of Paleontology ◽

10.1017/jpa.2017.15 ◽

2017 ◽

Vol 91 (3) ◽

pp. 467-476 ◽

Cited By ~ 6

Author(s):

Alycia L. Stigall ◽

Roy E. Plotnick ◽

Lisa E. Park Boush

Keyword(s):

New Species ◽

Calcium Carbonate ◽

North America ◽

Mass Extinction ◽

Fossil Record ◽

Lake Levels ◽

Geochemical Conditions ◽

Southwestern Montana ◽

Early Oligocene ◽

Clam Shrimp

AbstractA new spinicaudatan species,Estherites?jocelynaenew species, is described from more than fiftyspecimens collected from the Medicine Lodge Formation (early Oligocene) of the Beaverhead Basin in southwestern Montana, USA. This is the first spinicaudatan species reported from Cenozoic strata of North America and is the second-youngest fossil clam shrimp described globally. The new species extends the range of the superfamily Estheriteoidea into the Paleogene. Carapaces ofE.?jocelynaen. sp. are preserved as a calcium carbonate replacement of the original chitin-calcium-phosphate structure, which is an uncommon style of preservation for spinicaudatans. The unique preservation coupled with the range extension suggests that the sparse Cenozoic fossil record of spinicaudatans may be partly attributable to preservation bias related to geochemical conditions rather than exclusively to diversity decline following the end-Cretaceous mass extinction. The presence ofE.?jocelynaen. sp. in the Medicine Lodge Formation indicates that lakes in the Beaverhead Basin experienced seasonality and fluctuating lake levels with at least some drying at the lake margins. The ecological inferences support previous paleoenvironmental interpretations based on paleobotanical and other faunal evidence.

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