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The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,808,000 years BP[1]. It is usually considered to start in the early-mid Pliocene epoch and end by the early Pleistocene[2]. The Blancan is preceded by the Hemphillian and followed by the Irvingtonian NALMA stages.

As usually defined, it corresponds to the mid-Zanclean through Piacenzian and Gelasian stages in Europe and Asia. In California, the Blancan roughly corresponds to the mid-Delmontian through Repettian and Venturian to the very early Wheelerian. The Australian contemporary stages are the mid-Cheltenhamian through Kalimnan and Yatalan. In New Zealand, the Opoitian starts at roughly the same time and the Blancan is further coeval with the Waipipian and Mangapanian stages to the early Nukumaruan. Finally, in Japan the Blancan starts coeval with the late Yuian, runs alongside the Totomian and Suchian and ands soon after the start of the Kechienjian.

Dating issuesEdit

The start date of the Blancan has not been fully established. There is general agreement that it is between 4.9[3] and 4.3 mya (million years ago)[4]. The often-cited GeoWhen database places it at 4.75 mya.[1]

There is even stronger disagreement about the end of the Blancan. Some stratigraphers argue for the 1.808 mya date that corresponds better with the end of the Pliocene and the start of the Pleistocene (1.808 mya). This conforms with the extinction of Borophagus, Hypolagus, Paenemarmota, Plesippus, Nannippus, and Rhynchotherium faunal assemblage between 2.2 and 1.8 mya.[2] Other paleontologists find continuity of the faunal assemblages well into the Pleistocene, and argue for an end date of 1.2 mya. This corresponds with the extinction of stegomastodons and related species and the appearance of mammoths in southern North America.[5]

FaunaEdit

The middle of the Blancan, about 2.7 mya, is when the land bridge connection between North and South America was reestablished and taxa like sloths and glyptodonts appeared in North America at the height of the Great American Interchange.[6]

Notable mammalsEdit

Artiodactyla - even-toed ungulates

Carnivora - carnivores

Lagomorpha - lagomorphs

Perissodactyla - odd-toed ungulates

Proboscidea

Rodentia - rodents

Notable birdsEdit

Cathartidae - New World vultures

Charadriiformes

Falconiformes - diurnal raptors

Passeriformes

FootnotesEdit

  1. ^ a b GeoWhen Database - Blancan. Version 1.1.0. Retrieved 2007-NOV-09.
  2. ^ a b Lundelius et al. (1987)
  3. ^ Lindsay et al. (2002)
  4. ^ Cassiliano (1999)
  5. ^ Tedford (1981)
  6. ^ Woodburne & Swisher (1995)
  7. ^ a b Wetmore (1937)
  8. ^ Feduccia (1970)


References Edit

  • Cassiliano, Michael L. (1999): Biostratigraphy of Blancan and Irvingtonian mammals in the Fish Creek–Vallecito Creek section, southern California, and a review of the Blancan-Irvingtonian boundary. J. Vertebr. Paleontol. 19(1): 169–186.
  • Feduccia, J. Alan (1970): Some birds of prey from the Upper Pliocene of Kansas. Auk 87(4): 795-797. PDF fulltext
  • Lindsay, Everett et al. (2002): Recognition of the Hemphillian/Blancan boundary in Nevada. J. Vertebr. Paleontol. 22(2): 429–442. DOI:10.1671/0272-4634(2002)022[0429:ROTHBB]2.0.CO;2 HTML abstract
  • Lourens, L. et al. (2004): The Neogene Period. In: Gradstein, F.; Ogg, J. & Smith, A.G. (eds.): A Geologic Time Scale 2004. Cambridge University Press. ISBN 0-521-78142-6
  • Lundelius, E.L. Jr. et al. (1987): The North American Quaternary Sequence. In: Woodburne, Michael O. (ed.): Cenozoic mammals of North America: geochronology and biostratigraphy: 211–235. University of California Press, Berkeley. ISBN 0-520-05392-3
  • Morgan, Gary S. & Lucas, Spencer G. (2003): Mammalian Biochronology of Blancan and Irvingtonian (Pliocene and Early Pleistocene) Faunas from New Mexico. Bulletin of the American Museum of Natural History 279: 269–320. PDF fulltext
  • Tedford, Richard H. (1981): Mammalian biochronology of the late Cenozoic basins of New Mexico. Geological Society of America Bulletin 92(12): 1008–1022. DOI:10.1130/0016-7606(1981)92<1008:MBOTLC>2.0.CO;2 HTML abstract
  • Wetmore, Alexander (1937): The Eared Grebe and other Birds from the Pliocene of Kansas. Condor 39(1): 40. PDF fulltext DjVu fulltext
  • Woodburne, Michael O. & Swisher, C.C. III (1995): Land mammal high-resolution geochronology, intercontinental overland dispersals, sea level, climate, and vicariance. Society for Economic Paleontology and Mineralogy Special Publications 54: 335–364. ISBN 1-56576-024-7

See also Edit

Neogene period
Miocene
Pliocene
Pleistocene
Holocene
Aquitanian | Burdigalian
Langhian | Serravallian
Tortonian | Messinian
Zanclean | Piacenzian
(Gelasian)
Gelasian | Early
Middle | Late
Boreal | Atlantic
Neogene period
Quaternary
Pliocene
Pleistocene
Holocene
← Neogene | Gelasian Early | Middle | Late  

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