The specimens from Liaoning show evidence that Confuciusornis had feathers along its leg, making this the earliest record of contour feathers
, as distinct from flight feathers.
In their first year, birds typically pass through four plumages, a downy one followed by three that include contour feathers
. The latter are, in order of appearance, juvenal, first-winter, and first-summer plumages.
Diagnosis was based on clinical signs (dystrophic feathers and severe loss of contour feathers
); the presence of viral DNA in a whole-blood sample, as determined by PCR testing; the presence of microscopic lesions (large numbers of histiocytic cells containing intracytoplasmic inclusions typical for circovirus); and positive results of immunohistochemical staining from the bursa of Fabricius and feather follicles.
The feather identification technique involves both examining the microscopic variation in characters in the plumulaceous (downy) barbs that are located at the base of most contour feathers
(12) In described cases of eagles with this syndrome, all remiges and retrices are malformed, (9,13) and contour feathers
are sometimes malformed to varying degrees as well.