MN 4 (biostratigraphy)
In biostratigraphy, MN 4 is one of the MN zones used to characterize the fossil mammal faunas of the Neogene of Europe. It is preceded by MN 3 and followed by MN 5; together, these three zones form the Orleanian age of the middle Miocene. This zone starts within magnetostratigraphic chron C5Dr, at 18 million years ago, and ends within chron C5Cr, at 17.0 million years ago, although some different correlations have been proposed. The reference locality used to correlate faunas with this zone is La Romieu (southwestern France); other localities include Artesilla and Buñol in Spain , Tägernaustrasse-Jona in Switzerland, Erkertshofen 2 and Petersbuch 2 in Germany, Belchatov C in Poland, and Aliveri in Greece. In this zone, the common muroid rodent "Democricetodon" immigrates into Europe from Asia, followed shortly after by three other muroids: "Megacricetodon", "Eumyarion", and "Anomalomys". "Cricetodon", which later also reaches western Europe, is only present in Greece in MN 4 in Europe. The archaic muroid "Melissiodon" last appears in MN 4, as does "Ligerimys", a member of the extinct rodent family Eomyidae. The dormouse "Glirulus", which occurs in older deposits in Turkey, first appears in Europe; this genus contains a single living  species, the Japanese dormouse ("Glirulus japonicus"). The proboscidean genera—members of the group that includes the elephants—"Archaeobelodon" and "Prodeinotherium" first appear in Europe. The rhinoceros "Diaceratherium" last appears in MN 4 and five other rhinoceros genera, "Plesiaceratherium", "Brachypotherium", "Lartetotherium", "Gaindatherium", and "Hispanotherium", make their first appearance. "Phyllotillon", a member of the related extinct family Chalicotheriidae, migrates into Europe during MN 4. Several artiodactyls, such as the pig "Bunolistriodon", the tragulid "Dorcatherium", the deer-like "Lagomeryx", the bovid-like "Amphimoschus", and the first true bovid of Europe, "Eotragus", first occur during MN 4. The last occurrence of the primitive ruminant "Amphitragulus  also falls in this zone. The immigrant African creodont Hyainailouros" occurs in Europe during MN 4. Among carnivorans, the first occurrences of the mustelid "Leptoplesictis" and the saber-toothed "Prosansanosmilus" fall in MN 4.