The Itchy Feathers of an Ancient Bird
The 115-million-year-old limestones of Lower
Cretaceous Crato Formation (Nova Olinda Member, Upper
Aptian) of Northeast Brazil may have produced the oldest
evidence of feather parasites: An
isolated feather preserved
impressions in the slab and counterslab of a specimen, which
was recently acquired by the Japanese National
Science Museum (Tokyo).
Mesozoic (Age of Dinosaurs- 250 mya - 65 mya) feather impressions are known from a greater number of localities, wide-spread over the whole world (Australia, China, Canada, Germany, Japan, Lebanon, Mongolia, Russia, Spain, U.S.A.). The extraordinary nature of the new finding of a 85-mm-long feather is in the numerous uniform spheres which covered its surface. These small egg-like structures had a diameter of about 75 µm and were arranged separately from each other or in irregular groups of less than 15 spheres.
While publishing this unusual fossil the authors interpreted the spheres on its surface as the eggs of an arthropod parasite (like lice), who not only infested the host's plumage but also laid their eggs on it. Considering the size and shape of their eggs, as well as the fact that they are common among present day birds as one of the most important group of feather-feeders, mites (Arachnida: Acari) are most likely to have caused this infestation. Although the eggs can certainly be associated with the Acari, it will remain questionable whether they belong to a microscavenger or to a feather-parasitic mite.
In view of a great variety of highly specialized recent avian parasites (some species are known amazingly to be restricted to a part of a feather of a single bird species!) some ornithologists conclude that there has been a long co-evolution of feathers and feather parasites over geological time. The current discoveries of feathered dinosaurs, such as Caudipteryx, Sinornithosaurus, Beipiaosaurusand Protarchaeopteryx, and many otherscould suggest that birds inherited their relationship with parasitic lice from their dinosaur ancestors. The adaptive radiation of these feather-feeding ectoparasites may have started as early as the Jurassic period when the first feathers originated in theropod dinosaurs (or maybe earlier if the 'feathers' of Tianyulong, a small bird hipped dinosaur or ornithischian, are 'true' feathers). Maybe the relationship between lice and these animals even pre-dates the occurrence of feathers in which case the mites and lice would have originally utilized other keratinous structures (claws or scales) for feeding and secondarily adapted to feathers.
One question still remains: Who can be identified as the former owner of this infested feather 115 million years ago? Considering the fact, that its shape is almost symmetrical and that its
barbs lack hooked barbules (who are necessary for the formation of a continuous vane area), this feather cannot have had an aerodynamic function. It most resembles the those of large modern flightless birds (ratites), such as Rhea. The animal, which once carried the feather, may have lived under similar ecological conditions and was probably a ground dwelling bird or a feathered dinosaur. Since the feather is known from the Lower Cretaceous of South America, only a few candidates exist- Hesperornis-like diving birds; Patagopteryx (a ground dwelling flightless bird), enantiornithines (small arboreal birds) and non-bird coelurosaurian dinosaurs.
Reference: MARTILL, D.M. & DAVIS, P.G.(2001): A feather with possible ectoparasite eggs from the Crato Formation (Lower Cretaceous, Aptian) of Brazil.- N. Jb. Geol. Paläont. Abh., 219 : 241- 259.