Blancan


The Blancan North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology, usually considered to start in the early-mid Pliocene Epoch and end by the mid-Pleistocene. It is typically set from around 4.7 Ma to 1.4 Ma, an estimated duration of about 3.3 million years. The Blancan is preceded by the Hemphillian and followed by the Irvingtonian NALMA stages. The Blancan is named after the fossil site of Mount Blanco in Crosby County, Texas.

Global correlation

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 ends soon after the start of the Kechienjian.

Dating issues

The start date of the Blancan has not been fully established. A widely-used system based on vole fossils defines the start of the Blancan based on the first appearance of Mimomys, Ogmodontomys, and Ophiomys in North America south of Alaska. Ogmodontomys is first reported from California at around 4.7 ± 0.5 Ma. In Nevada, Mammals typical of the Blancan first appear within magnetostratigraphic chron 3n.3r, around 4.98–4.89 Ma.
There is even stronger disagreement about the end of the Blancan. Some stratigraphers historically conflated the end of the Blancan with the extinction of Borophagus, Hypolagus, Paenemarmota, Plesippus, Nannippus, and Rhynchotherium faunal assemblage between 2.2 and 1.8 Ma. Other paleontologists find continuity of the faunal assemblages well into the Pleistocene, and argue for an end date of 1.2 Ma. This corresponds with the extinction of stegomastodons and related species and the appearance of mammoths in southern North America. The end of the Blancan is often defined by the first appearance of mammoths in North America, around 1.4 Ma.

Fauna

The middle of the Blancan, about 2.7 Ma, 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.

Notable mammals

Artiodactyla – even-toed ungulatesPlatygonus, peccaries
Carnivora – carnivoresArctodus, short-faced bearHesperocyoninae, dog-like carnivoresBorophagus, bone-crushing dogsCanis, wolvesChasmaporthetes, hyenasSmilodon, saber-toothed catHomotherium, saber-toothed catXenosmilus, saber-toothed cat
Lagomorpha – lagomorphsHypolagus, rabbits
Perissodactyla – odd-toed ungulatesNannippus, horsesPlesippus, horses – may belong into EquusEquus giganteus
ProboscideaRhynchotherium, gomphotheresStegomastodon, gomphotheres
Rodentia – rodentsPaenemarmota, giant marmots
XenarthraGlyptotherium, giant armadillo

Notable birds

Cathartidae – New World vulturesSarcoramphus kernense, Kern Vulture
Charadriiformes
Falconiformes – diurnal raptorsFalco sp., a falcon
Passeriformes

Blancan fossil sites

From Bell et al. :Aguascalientes: lower Cedazo faunaArizona: St. David Formation, 111 Ranch, Artesia Road, Duncan, Country Club, Bear Springs, Pearson Mesa, Verde faunas