Bumbanian
The Bumbanian is in Earth's history, a regional level in the terrestrial Paleogene of East Asia. The Bumbanian is the fourth stage in the sequence of land mammal stages in East Asia and following the Gashatan about it (or after) follows the Arshantan. Under the current correlation it corresponds to the lower part of the global Ypresium stage of the Eocene ( Paleogene ) (the upper part of the Ypresium already correlated with a part of above following Arshantan stage). Geochronological it is currently dated to the period 56-52 million years. The Bumbanian is characterized by a wave of immigration of groups of mammals from North America.
Conceptual history
The Bumbanian is after bumban member of the Naran Bulak Formation in Nemegt basin ( at Tsagan Khushu, South Gobi, Mongolia) named. The term first appears Bumbanian (?) In 1986 in an article by Philip Gingerich in the journal Science.
Definition, absolute dating, correlation and subdivision
The beginning of the Bumbanian is characterized by the first appearance of Primates, Perissodactyla, Artiodactyla, and condylarths Ctenodactyloidea. This is also the first appearance of these groups in North America and Europe. In Bumbanian the archaic families Micromomyidae, Plesiadapidae, Paramomyidae and Hyopsodontidae occur the first time in East Asia. In North America, they come before the Paleocene; this indicates a migration of families from North America.
In Bumbanian families Eurymylidae, Mimotonidae, Didymoconidae, Alagomyidae and Prodinoceratidae died out. Typical genera are Rhombomylus and Gomphos.
The border Gashatan / Bumbanian is traditionally correlated with the Paleocene / Eocene boundary. Thus the Bumbanian corresponds to the lower part of the global Ypresium stage. In absolute terms, the Bumbanian corresponds to the period 56-52 million years.
Bumbanian the stage is divided into three biozones:
- Heptodon, type genus: Anatolostylopsis, first appearance: Helaletidae, extinction: Arctostylopidae, Eurymylidae, Mimotonidae and Prodinoceratidae
- Homogalax, first appearance: Lophialetidae, Eomoropidae, Ischyromyidae; Extinction: Multituberclata, Astigalidae, Pseudictopidae, Alagomyidae
- Orientolophus, first appearance: Isectolophidae, Gomphos; Extinction: Cimolestidae