The evolution of ectoparasitism in insects has occurred independently multiple times, with parasitic species that feed on blood, feathers, or other external tissues exerting profound impacts on the adaptive evolution of their hosts. However, fossil evidence directly revealing such parasitic behaviors is exceptionally rare, especially for Mesozoic parasites that specifically fed on feathers.
Recently, a team led by Prof. Diying Huang from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, published a study in National Science Review. The study reports the discovery of fossilized chewing lice eggs preserved in mid-Cretaceous Burmese amber, marking the first direct evidence of ectoparasitic lice feeding on feathers of stem-group birds during the Mesozoic. This discovery offers valuable insights into the origins of lice and their early coevolution with vertebrate hosts.
The research team identified a rare and unique amber specimen containing fossilized chewing lice eggs affixed to small feather fragments. Two slender feather barbs are preserved within the amber, with each barb hosting a row of regularly spaced, elongated eggs attached along its shaft. Measuring approximately 512 micrometers in length and spaced 526 to 748 micrometers apart, the eggs adhered to the feather shaft using a cement-like substance. Unlike modern bird lice eggs, which exhibit certain structural similarities, the fossilized eggs display distinct differences in attachment area and arrangement.
Microscopic examination and morphological analysis of the feathers suggest that they belonged to enantiornithines, an extinct group of basal birds that were highly diverse and abundant during the Mesozoic. The discovery of these lice eggs in association with enantiornithine feathers strongly supports the hypothesis that Mesozoic bird lice were parasitic on early feathered vertebrates.
Lice are among the most common ectoparasites in modern animals, predominantly infesting birds and mammals. Studies suggest that modern lice originated at least 99 million years ago during the Mesozoic and exhibit distinct ecological and morphological differences from their free-living relatives in the Liposcelididae family. Earlier research had uncovered fossilized adult lice in Burmese amber, but the newly discovered lice eggs provide even more direct evidence of early parasitic behavior. This discovery bolsters the hypothesis that lice established parasitic relationships with basal birds early in their evolutionary history.
The divergence of modern bird lice from mammalian lice is believed to have resulted from an ancient host-switching event. Fossil evidence supports this idea, including the discovery of lice eggs associated with mammalian hair in Eocene Baltic amber. The mid-Cretaceous bird lice eggs described in this study suggest that early enantiornithines may have been among the first hosts to support the evolution of lice from free-living ancestors to obligate parasites.
