A new study opens up the possibility that dinosaurs were early – perhaps even the first – animal hosts of lice.
Scientists, who used fossils and molecular data to track the evolution of lice and their hosts, have shown that the ancestors of lice that today feed on birds and mammals began to diversify before a mass extinction event killed off the dinosaurs about 65 million years ago.
"This study lends support to the idea that major groups of birds and mammals were around before the dinosaurs went extinct," said Kevin Johnson, an ornithologist with the State Natural History Survey at the University of Illinois and a principal investigator on the study.
"If the lice were around, we know their hosts were probably around," he added.
Johnson and his colleagues, including co-principal investigator Vincent Smith, built a partial family tree of lice by comparing the DNA sequences of genes from 69 present-day louse lineages.
"Lice are like living fossils. The record of our past is written in these parasites, and by reconstructing their evolutionary history we can use lice as markers to investigate the evolutionary history of their hosts," said Smith.
The researchers used louse, bird and mammal fossils to anchor precise time points in the tree.
These fossils are dated according to the age of the geologic formations in which they were found. This gives only a minimum age for the animal found embedded there, said Johnson.
"If the oldest dove fossil is 20 million years old, we know that doves must have been around at that time. So we know that the split that occurred between doves and the closest relative of doves must have occurred before 20 million years ago," he said.
Johnson said the oldest fossils found so far that resemble modern bird and mammal groups are less than 65 million years old.
This led to the hypothesis that major bird and mammal lineages appeared only after the dinosaurs went extinct.
But more recent studies of the genetic changes in major groups of birds and mammals suggest that many of them were around before the dinosaurs disappeared.
The new study supports this idea, said Johnson.
Many scientists believe that birds are the descendants of feathered dinosaurs.
"So maybe birds just inherited their lice from dinosaurs," said Johnson.
The study appears in Biology Letters.