Fossil records of vertebrate integuments are relatively common in both rocks, as compressions, and amber, as inclusions. The integument remains, mainly the Mesozoic ones, are of great interest due to the panoply of palaeobiological...
moreFossil records of vertebrate integuments are relatively common in both rocks, as compressions, and amber, as inclusions. The integument remains, mainly the Mesozoic ones, are of great interest due to the panoply of palaeobiological information they can provide. We describe two Spanish Cretaceous amber pieces that are of taphonomic importance, one bearing avian dinosaur feather remains and the other, mammalian hair. The preserved feather remains originated from an avian dinosaur resting in contact with a stalactite-shaped resin emission for the time it took for the fresh resin to harden. The second piece shows three hair strands recorded on a surface of desiccation, with the characteristic scale pattern exceptionally well preserved and the strands aligned together, which can be considered the record of a tuft. These assemblages were recorded through a rare biostratinomic process we call "pull off vestiture" that is different from the typical resin entrapment and embedding of organisms and biological remains, and unique to resins. The peculiarity of this process is supported by actualistic observations using sticky traps in Madagascar. Lastly, we reinterpret some exceptional records from the literature in the light of that process, thus bringing new insight to the taphonomic and palaeoecological understanding of the circumstances of their origins. Amber is fossilised resin originating in ancient forests, with a high capacity for exceptional and three-dimensional preservation of biological remains, providing an outstanding source of information from past ecosystems 1. Arthropods are the most common bioinclusions in amber 2,3 , although vertebrate remains are also often found, including those from Amphibia (e.g., 4) and crown group Reptilia (e.g., 5), such as body fossils and dinosaur feathers (e.g., 6,7). Dinosaur feathers and mammalian hair are keratin integumentary structures which constitute the different forms of vertebrate vestiture 8. The term vestiture is used in this paper for the plumage and pelage of amniotes, thus excluding other dermal structures as scales or glands. Cretaceous amber is an important source of knowledge about feathers, in which they are particularly abundant, providing a panoply of palaeobiological evidence (e.g., 6,7,9,10). Recently, a new study has shown feather-like structures in pterosaurs, so these structures could appear in an archosaur ancestor of dinosaurs and pterosaurs or independently in these two groups 11. Feathers are β-keratin integumentary structures 12 which are present in avian and some non-avian dinosaurs and whose origin has been widely studied 13. The feather structure is composed by medulla, cortex and cuticle (inner to outer) 14. Feathers show high morphological variability, even in the same specimen, so their determination is challenging 14. Mammalian remains are rare in amber, and even more so in amber from the Cretaceous 15,16. A partial mam-malian skeleton which could correspond to a solenodontid was reported from the Miocene amber of the Domini-can Republic 17 , but this is a unique finding since mammals are usually represented in amber by hairs, as in, for example, two records of abundant solenodontid-like hair also found in Dominican amber 18. Hair is an α-keratin integumentary structure occurring since before the emergence of crown mammals 19,20. Like feathers, the hair structure is composed of three layers; medulla, cortex and cuticle, going from innermost to outermost 21-23. The hair cuticle consists of approximately rectangular, flattened, keratin scales composed of an exocuticle rich in sulphur and an endocuticle with low sulphur content 21,23. The overlapping of the keratin scales provides the characteristic surface scale pattern (cuticular pattern) of mammalian hair 22,23. The diverse hair surface scale OPEN
