The Blancan North American Stage on the

geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...

is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of . Blancan North American Stage
GeoWhen Database. Version 1.1.0. Retrieved 2017-June-26. It is usually considered to start in the early-mid

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. 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 The Piacenzian is in the international geologic time scale the upper stage (stratigraphy), stage or latest age (geology), age of the Pliocene. It spans the time between 3.6 ± 0.005 year#SI prefix multipliers, Ma and 2.58 Ma (million years ago). T ...

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 ends 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 and 4.3 mya (million years ago). 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

(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. 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.

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

sloth Sloths are a Neotropical realm, Neotropical group of xenarthran mammals constituting the suborder Folivora, including the extant Arboreal locomotion, arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of move ...

s and glyptodonts appeared in North America at the height of the Great American Interchange.

Notable mammals

Artiodactyla Artiodactyls are placental mammals belonging to the order (biology), order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof ...

– even-toed ungulates * '' Platygonus'', peccaries Carnivora – carnivores *'' Arctodus'', short-faced bear *'' Hesperocyoninae'', dog-like carnivores * '' Borophagus'', bone-crushing dogs *'' Canis'', wolves * '' Chasmaporthetes'', hyenas *'' Smilodon'', saber-toothed cat *'' Homotherium'', saber-toothed cat *'' Xenosmilus'', saber-toothed cat Lagomorpha – lagomorphs * '' Hypolagus'', rabbits Perissodactyla – odd-toed ungulates * '' Nannippus'', horses * '' Plesippus'', horses – may belong into '' Equus'' * '' Equus giganteus Proboscidea * '' Rhynchotherium'', gomphotheres * '' Stegomastodon'', gomphotheres

Rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

ia – rodents * '' Paenemarmota'', giant marmots Xenarthra * '' Glyptotherium'', giant armadillo

Notable birds

Cathartidae – New World vultures * '' Sarcoramphus kernense'', Kern Vulture Charadriiformes * unknown scolopacid (archaic calidrid or turnstone?) Falconiformes – diurnal raptors * '' Falco'' sp., a falcon Passeriformes * unknown corvid (archaic magpie?)

Dating issues

Fauna

Notable mammals

Notable birds

See also

References

Further reading