Ancient Mammals Wore Dark Fur, New Study Reveals

Scientists have long known that many dinosaurs sported brightly colored feathers. Now, a new study has shed light on the fur coloration of early mammals that once lived alongside them. These ancient mammals likely had dark brown or gray fur—an adaptation that may have played a crucial role in their survival. The findings were recently published in the journal Science.

To reconstruct the coloration of ancient animals, researchers focus on fossils that preserve melanosomes—microscopic structures found in modern animal skin, feathers, and hair that contain melanin pigments. A research team led by Ghent University in the Netherlands compiled a database of fur color and melanosome structure from 116 modern mammal species. Using this data, they developed a model to predict fur color based on the shape of melanosomes. Their results showed that reddish-orange fur is associated with spherical melanosomes, while darker fur corresponds to elongated melanosomes.

The researchers then examined a fossil of an early mammal that lived approximately 160 million years ago in what is now northeastern China. The fossil, which shows evidence of full-body fur and potential gliding ability, contained oval-shaped melanosomes with high concentrations of copper—an indicator of dark brown fur. The lack of zinc in the fossil further ruled out the presence of lighter-colored fur.

These findings support the theory that Mesozoic mammals were primarily nocturnal, with dark fur helping them navigate and regulate body temperature in low-light environments. Researchers suggest that as mammals began to diversify following the extinction of dinosaurs, variations in fur coloration also began to emerge.