Keratin immunoreactivity in the Late Cretaceous birdRahonavis ostromi

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Abstract
Immunohistochemical studies, supported by additional lines of evidence, suggest that original proteinaceous components of keratin claw sheath material may be preserved in the pedal ungual phalanx associated with the primitive bird, Rahonavis ostromi, from the Late Cretaceous of Madagascar. This conclusion is based upon immunohistochemical analyses, and supported by brightfield, transmission, and scanning electron microscopy, mass spectrometry, and x-ray photoelectron spectroscopy. Although keratinous structures such as hair, nails, claws, scales and feathers have been identified in the fossil record, these identifications were based on morphological similarity rather than molecular analyses. Chemical or immunological evidence for the survival of keratin has not previously been established in fossils older than ~33,000 BP. This study demonstrates immunological staining and amino acid composition consistent with the presence of fragments of beta keratin, a protein family unique to reptiles and birds, in the specimen of Rahonavis ostromi.