Recent advances in amniote palaeocolour reconstruction and a framework for future research

Abstract

Preserved melanin pigments have been discovered in fossilised integumentary appendages of several amniote lineages (fishes, frogs, snakes, marine reptiles, non‐avialan dinosaurs, birds, and mammals) excavated from lagerstätten across the globe. Melanisation is a leading factor in organic integument preservation in these fossils. Melanin in extant vertebrates is typically stored in rod‐ to sphere‐shaped, lysosome‐derived, membrane‐bound vesicles called melanosomes. Black, dark brown, and grey colours are produced by eumelanin, and reddish‐brown colours are produced by phaeomelanin. Specific morphotypes and nanostructural arrangements of melanosomes and their relation to the keratin matrix in integumentary appendages create the so‐called 'structural colours'. Reconstruction of colour patterns in ancient animals has opened an exciting new avenue for studying their life, behaviour and ecology. Modern relationships between the shape, arrangement, and size of avian melanosomes, melanin chemistry, and feather colour have been applied to reconstruct the hues and colour patterns of isolated feathers and plumages of the dinosaurs Anchiornis, Sinosauropteryx, and Microraptor in seminal papers that initiated the field of palaeocolour reconstruction. Since then, further research has identified countershading camouflage patterns, and informed subsequent predictions on the ecology and behaviour of these extinct animals. However, palaeocolour reconstruction remains a nascent field, and current approaches have considerable potential for further refinement, standardisation, and expansion. This includes detailed study of non‐melanic pigments that might be preserved in fossilised integuments. A common issue among existing palaeocolour studies is the lack of contextualisation of different lines of evidence and the wide variety of techniques currently employed. To that end, this review focused on fossil amniotes: (i) produces an overarching framework that appropriately reconstructs palaeocolour by accounting for the chemical signatures of various pigments, morphology and local arrangement of pigment‐bearing vesicles, pigment concentration, macroscopic colour patterns, and taphonomy; (ii) provides background context for the evolution of colour‐producing mechanisms; and (iii) encourages future efforts in palaeocolour reconstructions particularly of less‐studied groups such as non‐dinosaur archosaurs and non‐archosaur amniotes.

Sediment-encased pressure-temperature maturation experiments chemically simulate natural diagenesis of melanin

“…PCA further supports this position. The sulphur content of extracted melanin originates from benzothiazole moieties of phaeomelanin 19 whereas that of sediment-matured samples could derive from phaeomelanin, unleached keratin breakdown products, or from melanoidin-like polymers 58 . PC3 explains 9.86 % of the variation in the dataset ( Supplementary Fig.…”

“…Exceptional preservation of soft tissues occurs when the dead organism passes several physical and biochemical taphonomic lters that results in selective removal, transformation, or preservation of anatomy and biomolecules 16,17,18 . Efforts in palaeocolour research therefore, must take into account the effects of diagenetic maturation on organic staining, melanosome shapes, and melanin chemistry 3,13,19 so as to achieve higher precision in articulating ecological, physiological, and behavioural hypotheses. Models of exceptional preservation developed from experiments in controlled laboratory settings bene t from the ability of researchers to focus tests on speci c taphonomic variables of interest and to control many potentially confounding ones.…”

Recent advances in heteromorph ammonoid palaeobiology

“…Reports on fossilised colour mostly refer to the presence of pigments in shells or the ink sac (e.g. Roy et al ., 2020).…”

Study of Laser Actions by Bird’s Feathers With Photonic Crystals

“…From the cross-section views of barbs in Figs. 1(e)-(g), the outer cortex, I, combines the keratin and pigments of pisttacofulvin, which manipulates the feather colors revealing red or yellow [16,17]. The middle layer, II, is photonic crystals that represent entirely white and the ratio of the photonic crystals (white area) shows yellow-green feather (S0) > dark-green feather (S1) > red feather (S2) in these images.…”