DUBLIN: A new evolutionary tree for parasitic lice shows that they diversified well before the dinosaurs went extinct, suggesting that an equally diverse group of mammal and bird hosts lived alongside the dinosaurs.
The conventional hypothesis among scientists has been that the mammals and birds came into their own after the dinosaurs went extinct at the Cretaceous-Tertiary boundary (KT) 65 million years ago. This new study shows that lice radiated perhaps 115 to 130 million years ago, which supports an earlier radiation of birds and mammals than previously thought.
“The lice parasites must have been living on something,” said palaeontologist Vincent Smith from the Natural History Museum in London, lead author of the paper in the journal Biology Letters. “Were they living on mammals or birds, or perhaps the ancestors of birds – the feathered dinosaurs?”
A large collection of living louse helped the scientists to construct a lice family tree using molecular dating techniques. An excellently preserved 44 million-year-old bird louse fossil (Megamenopon
rasnitsyni) collected from the crater of the Eckfeld maar near Manderscheid, Germany, was placed on the tree and helped anchor it in time.
The scientists put timescales on their louse evolutionary tree and as lice show particular adaptations to different hosts, the team hypothesised as to what the lice were living on at that time.
The timeline for the lice and their hosts led them to conclude that the mammals and birds prospered well before the KT extinction, and given the early origin of feathers, parasitic lice could have infested the feathered theropod dinosaurs.
Lice infesting dinosaurs
“Either mammals or birds were around much longer than we thought, or lice were on these dinosaurs and then moved onto birds. So either they were on the birds first or they were on the feathered dinosaurs first,” said Smith. “The most likely explanation, looking at the timescales, is the feathered dinosaur theory.”
Palaeontologist Mike Benton of the University of Bristol in the UK said this is an excellent account of the phylogeny of lice and “it makes some interesting predictions about the origins of mammals and birds.”
He notes that it is possible that these early origins of lice suggest modern birds and modern mammals indeed originated perhaps 120 to 150 million years ago, as suggested by some molecular phylogenies of modern birds and mammals.
Alternatively, the lice could have switched from dinosaurs or other groups, in which case you cannot date bird or mammal origins, he said.
Molecular clock for lice
A molecular clock for lice is “cool for its own sake”, said dinosaur expert Gareth Dyke of University College Dublin in Ireland, but is unconvinced by the predictions on mammals and birds, which he describes as “a little contrived”.
Parasites that are specific to hosts and evolve with them can stand as independent markers used to infer the evolutionary history of the hosts. The wide distribution and ancient diversification of bird lice supports a long association between the two, whereas chewing lice on mammals are species poor and patchily distributed.
“There are many lineages of lice that are quite old, much older than we would have expected,” said Smith. The findings suggest that the lice started out on feathers before moving to fur.
The oldest definitive fossil feathers are those of Archaeopteryx from the Late Jurassic around 150 million years ago and fossilised hair dates from 55 million years ago.
Original paper in Biology Letters
Natural History Museum in London
Vincent Smith at the Natural History Museum in London