Fur colours, which serve many functions, are essential for the evolution of mammal behavior, physiology and habitat preferences. However, little is known about the colour of Mesozoic mammals that co-evolved with dinosaurs. In a new study, scientists from China, Belgium, the Netherlands, the UK and the US used the dataset Melanosome (Melanin-Containing Organelle) We quantitatively measured the morphology and quantitatively measured hair colours of 116 live mammals to reconstruct the colours of six Mesozoic mammals, including the species Yuhalamiidan mammals that were not previously described.

From communication to camouflage, animal colour plays an important role in many behavioral ecological functions.

Some animals exhibit distinct and vivid arrangements like birds, but mammalian fur is generally limited to muted tones due to their dependence on the single pigment melanin.

Mammals lack palettes, but have evolved a diverse and distinctive coat pattern.

However, due to lack of data on pigmentation in extinct mammals, the evolutionary history of hairy colour is not well understood.

Recent studies have shown that melanosomes, which cause pigmentation, can be preserved in fossilized specimens.

A similar technique has successfully reconstructed the colours of dinosaurs, but despite well-preserved fur specimens, it has not been widely applied to fossil mammals.

In the new study, Dr. Ruoshuang Li, a colleague of the Chinese University of Earth Sciences and colleague, analyzed melanosomes in 116 living mammals and created a predictive model to reconstruct the hairy colour based on melanosome morphology.

The authors applied the model to six Mesozoic mammalian forms of fossilized melanosomes, including the newly described euhalamyidan species that lived 158.5 million years ago (Late Jurassic Epoch).

The authors found that the fur of these early mammals was primarily and uniformly dark in colour, with no stripes and spots that adorn many modern mammals.

This suggests that despite evolutionary differences in phylogenetics and ecology, the early mammalian melanin colored systems remained little different.

This is in stark contrast to the diverse melanosome structures found in feathered dinosaurs, early birds and pterosaurs, indicating a distinct evolutionary pattern of mammalian colour.

“The typical modern nocturne mammals, such as the dark, uniformly dull fur found in these species – moles, mice, rats and nocturne bats, support the previous hypothesis that early mammals are also largely nocturne and colored for camouflage,” the researchers said.

“In addition, the high melanin content of the fur may have been beneficial in providing mechanical strength for thermoregulation and protection.”

“Following the Cretaceous – Fat extinction event, mammals rapidly diversified into niches previously occupied by dinosaurs, leading to more diverse melanosome structures and new perage colour strategies that are more suited to a more diverse environment.”

Survey results It was published in the journal today Science.

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rushuang li et al. 2025. Mesozoic mammalian forms illuminate the origin of the colour of the hair. Science 387 (6739): 1193-1198; doi: 10.1126/science.ads9734