Blancan

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 [http://www.stratigraphy.org/geowhen/stages/Blancan.html GeoWhen Database - Blancan] . Version 1.1.0. Retrieved 2007-NOV-09.] . It is usually considered to start in the early-mid Pliocene epoch and end by the early Pleistocene. 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 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 issues

The start date of the Blancan has not been fully established. There is general agreement that it is between 4.9 [Lindsay "et al." (2002)] and 4.3 mya (million years ago) [Cassiliano (1999)] . The often-cited GeoWhen database places it at 4.75 mya.

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.Lundelius "et al." (1987)] 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. [Tedford (1981)]

Fauna

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. [Woodburne & Swisher (1995)]

Notable mammals

Artiodactyla - even-toed ungulates
* "Platygonus", peccariesCarnivora - carnivores
* "Borophagus", bone-crushing dogs
* "Chasmaporthetes", hyenasLagomorpha - lagomorphs
* "Hypolagus", rabbitsPerissodactyla - odd-toed ungulates
* "Nannippus", horses
* "Plesippus", horses - may belong into "Equus"Proboscidea
* "Rhynchotherium", gomphotheres
* "Stegomastodon", gomphotheresRodentia - rodents
* "Paenemarmota", giant marmots

Notable birds

Cathartidae - New World vultures
* "Sarcoramphus kernense", Kern VultureCharadriiformes
* unknown scolopacid (archaic calidrid or turnstone?)Wetmore (1937)] Falconiformes - diurnal raptors
* "Falco" sp., a falcon [Feduccia (1970)] Passeriformes
* unknown corvid (archaic magpie?)

Footnotes

References

* (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.
* (1970): Some birds of prey from the Upper Pliocene of Kansas. "Auk" 87(4): 795-797. [http://elibrary.unm.edu/sora/Auk/v087n04/p0795-p0797.pdf PDF fulltext]
* (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 [http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634(2002)022%5B0429%3AROTHBB%5D2.0.CO%3B2 HTML abstract]
* (2004): The Neogene Period. "In:" aut|Gradstein, F.; Ogg, J. & Smith, A.G. (eds.): "A Geologic Time Scale 2004". Cambridge University Press. ISBN 0-521-78142-6
* (1987): The North American Quaternary Sequence. "In:" aut|Woodburne, Michael O. (ed.): "Cenozoic mammals of North America: geochronology and biostratigraphy": 211–235. University of California Press, Berkeley. ISBN 0-520-05392-3
* (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. [http://digitallibrary.amnh.org/dspace/bitstream/2246/447/15/B279a12.pdf PDF fulltext]
* (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 [http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2F0016-7606%281981%2992%3C1008%3AMBOTLC%3E2.0.CO%3B2 HTML abstract]
* (1937): The Eared Grebe and other Birds from the Pliocene of Kansas. "Condor" 39(1): 40. [http://elibrary.unm.edu/sora/Condor/files/issues/v039n01/p0040-p0040.pdf PDF fulltext] [http://elibrary.unm.edu/sora/Condor/files/DJVU/v039n01/P0040-P0040.djvu DjVu fulltext]
* (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

* Mount Blanco