The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing lice (Mallophaga); however, recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognized:   Nearly 5,000 species of louse have been identified, about 4,000 being parasitic on birds and 800 on mammals. Lice are present on every continent in all the habitats that their host animals and birds occupy. They are found even in the Antarctic, where penguins carry 15 species of lice (in the genera "Austrogonoides" and "Nesiotinus"). The oldest known record of the group is "Megamenopon rasnitsyni" from the Eocene of Germany, but it is essentially a modern form, belonging to Amblycera, so the group as a whole likely has an origin in the Mesozoic. Lice have been the subject of significant DNA research in the 2000s that led to discoveries on human evolution. The three species of sucking lice that parasitize human beings belong to two genera, "Pediculus" and "Pthirus": head lice ("Pediculus humanus capitis"), body lice ("Pediculus humanus humanus"), and pubic lice ("Pthirus pubis"). Human head and body lice (genus "Pediculus") share a common ancestor with chimpanzee lice, while pubic lice (genus "Pthirus") share a common ancestor with gorilla lice. Using phylogenetic and cophylogenetic analysis, Reed et al. hypothesized that "Pediculus" and "Pthirus" are sister taxa and monophyletic. In other words, the two genera descended from the same common ancestor. The age of divergence between "Pediculus" and its common ancestor is estimated to be 6-7 million years ago, which matches the age predicted by chimpanzee-hominid divergence. Because parasites rely on their hosts, hostparasite cospeciation events are likely. Genetic evidence suggests that our human ancestors acquired pubic lice from gorillas approximately 3-4 million years ago. Unlike the genus "Pediculus", the divergence in "Pthirus" does not match the age of host divergence that likely occurred 7 million years ago. Reed et al. propose a "Pthirus" species host-switch around 3-4 million years ago.