What color was the fur of early mammals, back during the time of the dinosaurs? Paleontologists used to think that questions like this were impossible to answer. But then researchers discovered that microscopic structures called melanosomes can be preserved in fossils for hundreds of millions of years as three dimensional molds or imprints.
Melanosomes are organelles within the cell that produce the substances that color the skin, feathers, and fur of animals with backbones. By studying fossil melanosomes, researchers were able to learn the colors of the feathers of dinosaurs and discovered that some were brightly colored.
In 2025, an international team of researchers reported the first study to determine the colors of the fur of mammals from the time of the dinosaurs. The researchers studied exceptionally well preserved fossils of six species of mammals from China that were between one hundred and twenty and one hundred and sixty million years old. All were small animals the size of rats or mice, which is typical for mammals of that time.
First they created a database by studying the melanosome patterns of one hundred and sixteen species of modern mammals with varied fur colors. They studied the melanosomes with electron microscopy and spectroscopy, and the data was used to train a computer model to predict an animal’s fur color. When they used their model on the fossil specimens, they discovered that all of them had dark grey fur. This is similar to modern rats and mice that are active at night. The dark colors can help nocturnal animals hide from hungry predators.
A special thanks goes to Dr. P. David Polly, Professor and chair, Department of Earth and Atmospheric Sciences at Indiana University, for reviewing this script!
Further reading
- Melanosome patterns in mesozoic mammals suggest they had dark, uniformly dull fur coloring
- Dark coats may have helped the earliest mammals hide from hungry dinosaurs
Dinosaur-era mammals’ fur color revealed for first time
R. Li et al. Mesozoic mammaliaforms illuminate the origins of pelage coloration. Science. Vol. 387, March 14, 2025, p. 1193.