A recent study published in Nature Communications has shed new light on the evolution of vertebrates. Researchers from University College Cork and La Trobe University in Australia have found that the shape and distribution of melanosomes, microscopic pigment granules, vary across different fish groups and tissues. These variations are preserved in fossils dating back over 300 million years, providing a unique window into the sensory biology of ancient animals. The study measured over 23,000 melanosomes from 12 living species and compared them with around 3,000 preserved in fossil fish. The results suggest that melanosomes record more than just an animal's outward appearance, but also its ability to adapt to its environment. The researchers found that the shape and size of melanosomes are linked to their function, with different shapes and distributions corresponding to different roles in regulating light and handling potentially harmful substances. This discovery has significant implications for our understanding of vertebrate evolution. By studying melanosomes, scientists can gain insights into the sensory biology of ancient animals, including their ability to see and respond to their environment. The findings also highlight the importance of considering the functional significance of pigment in vertebrates, rather than just its aesthetic value. The study's lead author, Shaun Collin from La Trobe University, notes that the preservation of melanosomes in fossils provides a unique opportunity to investigate aspects of sensory biology that bones alone cannot reveal. The research team's findings have the potential to revolutionize our understanding of the evolution of vertebrates and the role of pigment in their sensory systems.