The Chibanian, widely known as the Middle Pleistocene, is an
age in the international
geologic timescale or a
stage in
chronostratigraphy, being a division of the
Pleistocene Epoch within the ongoing
Quaternary Period.[4] The Chibanian name was officially ratified in January 2020. It is currently estimated to span the time between 0.770
Ma (770,000 years ago) and 0.126 Ma (126,000 years ago), also expressed as 770–126 ka. It includes the transition in
palaeoanthropology from the
Lower to the
Middle Paleolithic over 300 ka.
The term Middle Pleistocene was in use as a provisional or "quasi-formal" designation by the
International Union of Geological Sciences (IUGS). While the three lowest ages of the Pleistocene, the
Gelasian, Calabrian and Chibanian have been officially defined, the
Late Pleistocene has yet to be formally defined.[8]
Definition process
The
International Union of Geological Sciences (IUGS) had previously proposed replacement of the Middle Pleistocene by an Ionian Age based on strata found in Italy. In November 2017, however, the Chibanian (based on strata at a site in
Chiba Prefecture, Japan) replaced the Ionian as the Subcommission on Quaternary Stratigraphy's preferred GSSP proposal for the age that should replace the Middle Pleistocene sub-epoch.[9] The "Chibanian" name was ratified by the IUGS in January 2020.[4]
Climate
By early Middle Pleistocene, the
Mid-Pleistocene Transition had changed the
glacial cycles from an average 41,000 year
periodicity present during most of the Early Pleistocene to a 100,000 year periodicity,[10] with the glacial cycles becoming asymmetric, having long
glacial periods punctuated by short warm
interglacial periods.[11] Millennial-scale climatic variability continued to be highly sensitive to precession and obliquity cycles.[12]
Events
The Early-Middle Pleistocene boundary saw the migration of true horses out of North America and into Eurasia.[13] Also around this time, the European mammoth species Mammuthus meridionalis became extinct and was replaced by the Asian species Mammuthus trogontherii (the steppe mammoth). This was coincident with the migration of the elephant genus Palaeoloxodon out of Africa and into Eurasia, including the first appearance of species like the European
straight-tusked elephant (Palaeoloxodon antiquus).[14] With the extinction of Sinomastodon in East Asia at the Early-Middle Pleistocene boundary,
gomphotheres became completely extinct in Afro-Eurasia,[15][16] but continued to persist in the Americas into the Late Pleistocene.[16] There was a major extinction of carnivorous mammals in Europe around the Early-Middle Pleistocene transition, including the giant hyena Pachycrocuta.[17] The mid-late Middle Pleistocene saw the emergence of the
woolly mammoth (Mammuthus primigenius), and its replacement of Mammuthus trogontherii, with the replacement of M. trogontherii in Europe by woolly mammoths being complete by around 200,000 years ago.[14][18] The last member of the
notoungulate family
Mesotheriidae, Mesotherium, has its last records around 220,000 years ago, leaving
Toxodontidae as the sole family of notoungulates to persist into the Late Pleistocene.[19] During the late Middle Pleistocene, around 195,000-135,000 years ago, the
steppe bison (the ancestor of the modern
American bison) migrated across the
Bering land bridge into North America, marking the beginning of the
Rancholabrean faunal stage.[20] Around 500,000 years ago, the last members of the largely European aquatic frog genus Palaeobatrachus and by extension the family
Palaeobatrachidae became extinct.[21]
After analyzing 2,496 remains of
Castor fiber (Eurasian beaver) and
Trogontherium cuvieri found at Bilzingsleben in Germany, a team of scientists concluded that, around 400 ka, hominids in the area hunted and exploited
beavers. They may have been targeted for their meat (based on cut marks on the bones) and skin.[24]
^Cohen, K. M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. (January 2020).
"International Chronostratigraphic Chart"(PDF). International Commission on Stratigraphy. Retrieved 23 February 2020.
^Cohen, K. M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. (January 2020).
"International Chronostratigraphic Chart"(PDF). International Commission on Stratigraphy. Retrieved 23 February 2020.