Blancan

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The Blancan North American Stage on the

North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of 2.944 million years.[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-

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[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]

Fauna

The middle of the Blancan, about 2.7 mya, is when the

taxa like sloths and glyptodonts appeared in North America at the height of the Great American Interchange.[6]

See also

References

Further reading