Interpreting melanin-based coloration through deep time: a critical review

Area of Science:

• Paleontology
• Biochemistry
• Evolutionary Biology

Background:

• Coloration in vertebrates, derived from melanin and carotenoids, is crucial for behavior, including social signaling and sexual display.
• Melanin-containing organelles (melanosomes) are preserved in fossils, but their identification is ambiguous, often confused with bacterial microbodies.

Purpose of the Study:

• To review the challenges in identifying fossil melanosomes and assess the reliability of current diagnostic methods.
• To propose an integrated approach for the definitive detection of ancient melanin pigments and associated microstructures in fossils.

Main Methods:

• Survey of vertebrate and microbial melanization processes.
• Analysis of data types used for interpreting fossil melanosomes.
• Outline of an integrated morphological and geochemical approach.

Main Results:

• Distinguishing fossil melanosomes from bacterial microbodies is problematic, especially with morphological evidence alone.
• Current methods for identifying fossil melanosomes lack definitive diagnostic sufficiency.
• An integrated approach combining morphology and geochemistry is proposed for reliable detection.

Conclusions:

• Reliable identification of fossil melanosomes requires more than morphological data.
• An integrated morphological and geochemical strategy can improve the accuracy of detecting ancient pigment remains.
• This approach will enhance our understanding of the evolution of coloration in extinct animals.