An international team of paleontologists, geoscientists and biologists has found via analysis of melanosome patterns in fossilized Mesozoic mammals, that they most likely had dark, uniformly dull fur coloring. In their paper published in the journal Science, the group describes how they created a predictive model to analyze melanosome patterns found in fossilized fur samples.
Over the past decade, scientists have discovered that melanosomes from dinosaur feathers and skin fossils could be used to discover their coloring. Melanosomes are a type of organelle in cells that account for pigmentation. Prior research has shown that patterns in melanosomes can be used to determine feather, fur, or skin coloring.
This has led other research teams to learn about the coloring of many types of dinosaurs. In this new study, the research team wondered if the same might be true for mammals living during the time of dinosaurs.
To find out, the team first analyzed melanosome patterns in 116 mammals that are alive today by using electron microscopy and spectroscopy to capture melanosome patterns. They then used the imagery and melanosome patterns to train a predictive model. Next, they captured imagery the same way from six mammal fossils from the Mesozoic and then used the model to identify patterns. The model suggested that all the creatures under study very likely had dark and uniformly dull coloring.
The researchers suggest their results are not surprising; prior research has suggested that the mammals living during the time of the dinosaurs were small and nocturnal. Most modern small, nocturnal mammals, such as moles and voles, have dark fur and are uniform in color. It makes it hard for predators, such as owls, to see them.
The team suggests that after the dinosaurs went extinct, mammals diversified to fill niches they left behind and developed skin and fur colors better suited to a variety of environments. The researchers conclude by suggesting that the high melanin content in the fur samples they studied could have been beneficial in other ways, such as helping to provide thermoregulation or assisting with mechanical strength.
More information: Ruoshuang Li et al, Mesozoic mammaliaforms illuminate the origins of pelage coloration, Science (2025). DOI: 10.1126/science.ads9734
Journal information: Science
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