Ultrastructure and biomolecular composition of sea turtle epidermal remains from the Campanian (Upper Cretaceous) North Sulphur River of Texas

Sammanfattning: A virtually complete and exceptionally preserved adult specimen of the fossil sea turtle Ctenochelys acris from mid-Campanian (Late Cretaceous) strata of North Sulphur River, Texas, USA, retains putative soft tissues in the form of a flexible, brownish film external to the bony carapace. In this work, the film was examined in detail using state-of-the-art methods (e.g. transmission electron microscopy, time-of-flight secondary ion mass spectrometry and in situ immunohistochemistry) in order to elucidate its ultrastructure, chemical composition and, by extension, affini-ty. It is concluded that the film most likely represents a remnant of the dorsal scutes once covering the carapace. In order to provide a contextual framework, three reviews are included: one addressing melanins and melanosomes (pigment organelles); one dealing with keratins and the reptilian epidermis; and one addressing various fossilization processes responsible for the retention of keratinous structures in the rock record.