Fossilized skin reveals coevolution with feathers and metabolism in feathered dinosaurs and early birds

Abstract

Feathers are remarkable evolutionary innovations that are associated with complex adaptations of the skin in modern birds. Fossilised feathers in non-avian dinosaurs and basal birds provide insights into feather evolution, but how associated integumentary adaptations evolved is unclear. Here we report the discovery of fossil skin, preserved with remarkable nanoscale fidelity, in three non-avian maniraptoran dinosaurs and a basal bird from the Cretaceous Jehol biota (China). The skin comprises patches of desquamating epidermal corneocytes that preserve a cytoskeletal array of helically coiled α-keratin tonofibrils. This structure confirms that basal birds and non-avian dinosaurs shed small epidermal flakes as in modern mammals and birds, but structural differences imply that these Cretaceous taxa had lower body heat production than modern birds. Feathered epidermis acquired many, but not all, anatomically modern attributes close to the base of the Maniraptora by the Middle Jurassic.

Three‐dimensional soft tissue preservation revealed in the skin of a non‐avian dinosaur

“…; Bell ; Davis ; McNamara et al . ). The preservation of integument is most prevalent in hadrosaurs (Bell ; Davis ).…”

“…; McNamara et al . ). Traces of collagenous material were found in a ‘mummified’ hadrosaurid from North Dakota, USA (Manning et al .…”

Feathered dinosaurs reconsidered: New insights from baraminology and ethnotaxonomy

“…These fossil corneocytes suggest that these animals shed their skin in flakes like mammals or birds. These fossil skin flakes are most similar to those of extant birds as seen in the fossil corneocytes' central globular structures, which resemble dead cell nuclei as seen in depressions in the corneocyte surface in extant birds, but not in extant reptiles or mammals (McNamara et al 2018).…”

“…Beipiaosaurus is known to have had a coat of downy feather-like integument comparable to that of Sinosauropteryx, as well as a secondary coat of quill-like "elongated broad filamentous feathers" (Xu et al 1999;. Recent in-depth study of a Beipiaosaurus fossil (as well as fossils of other Jehol creatures including two dromaeosaurids (Sinornithosaurus and Microraptor) and the Mesozoic bird Confuciusornis) has revealed skin patches in the form of tiny epidermal flakes preserved with nanoscale detail in calcium phosphate (McNamara et al 2018). These fossil corneocytes suggest that these animals shed their skin in flakes like mammals or birds.…”

Exceptionally preserved ‘skin’ in an Early Cretaceous fish from Colombia

“…Exceptional preservation in the fossil record is expressed in a wide range of structures including hair, cells, blood vessels, claw sheaths, feathers, pycnofibers, muscle remains, skin and even the potential remains of original biomolecular constituents (DNA, proteins, lipids) ( Lingham-Soliar & Plodowski, 2010 ; Cadena, 2016 ; Cadena & Schweitzer, 2012 Cleland et al, 2015 ; McNamara et al, 2018a ; Schweitzer, 2011 ; Wiemann et al, 2018 ; Bailleul et al, 2020 ) associated with these structures. The skin is the largest organ of the a vertebrate body, which encloses or covers their entire body.…”