To each his own lice (Image: Vince Smith/Natural History Museum, London) Megamenopon rasnitsyni (left) is a 44-million-year-old louse fossil, collected from the Eckfeld Maar crater near Manderscheid in Germany. It is a close relative of Holomenopon brevithoracicum (right), which parasitises the feathers of waterfowl

They may be irritating and harmful, but lice have their uses. A study of their evolution suggests that the parasitic lice that plague modern birds and mammals began diversifying while dinosaurs ruled the Earth.

That implies their hosts were also diversifying, challenging the popular idea that mammals hid in the shadows during the dinosaur era and only began evolving into new species – or radiating – after the great reptiles died out during the K-T extinction of 65 million years ago.


Because the bird and mammalian fossil record only goes back to just before this extinction, it is tough to determine their family tree during the reign of the dinosaurs.

Vince Smith of London’s Natural History Museum assembled a family tree showing how modern lice groups are related. See a picture of a 44 million year old louse, used in Smith’s study of the louse family tree.

Many lice only parasitise one species. For instance, lice infesting pocket gophers have notches on their heads that are sized to grip the hair of one species, like a lock-and-key mechanism. If a host evolves into two separate species, the louse follows suit in a process called co-speciation.

Lice radiation

Comparing the mammalian and louse tree, the team found eight co-speciations. Smith had found few louse fossils that he could date, but the matches with the mammalian tree allowed him to calibrate dates on the lice tree. This revealed that lice radiated much earlier than we thought, around 115 million years ago, says Smith. That’s 50 million years before dinosaurs went extinct.

Assuming the lice were living on mammals and birds, that fills in some of the void left by the paucity of host fossils from before the K-T boundary, and implies mammals and birds radiated during the age of dinosaurs.

The suggestion is “dramatic”, says Mike Benton of the University of Bristol, UK. Others, such as Tanja Stadler of the Swiss Federal Institute of Technology in Zurich, have suggested that mammals steadily split into more and more species from 100 million years ago (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1016876108).

There may be another explanation for the new lice tree, though, says Smith – that feathered dinosaurs were subject to the bothersome parasites as well. In which case dinosaur speciation would account for the radiation of lice, not mammals.

Journal reference: (Biology Letters, DOI: 10.1098/rsbl.2011.0105)