Evrim Yazgin
Cosmos science journalist
A new study looking at fossilised structures inside cells hints at our mammal ancestors’ nocturnal past when they lurked in the shadows of dinosaurs.
The research, published in the journal Science, involved a comparative analysis of fossilised melanosomes – organelles inside cells which dictate pigments in the eyes and skin of animals.
Unlike birds and reptiles, mammal colouration is generally muted and reduced to greys and browns. Evolutionary biologists have suggested that this could be due to mammal ancestors being nocturnal creatures where vibrant colours were unnecessary and dark, muted colours aided in camouflage.
Some mammals have, over millions of years, broken out of the mould to develop striking patterns.
Limited data on extinct mammal pigmentation has made it difficult to verify what has long been suspected – that early mammals were pretty monotone.
Studying fossil melanosomes is a relatively new field which has had some success.
Dinosaur melanosomes have been studied to reveal the colour of feathers belonging to creatures which lived more than 100 million years ago. In 2010, a paper published in Nature revealed the Chinese dinosaur Sinosauropteryx, which lived up to 130 million years ago, had a striped tail with reddish-brown feathers.
Such methods haven’t been widely applied to study ancient mammals, however.
The new research analysed melanosomes in 116 living mammals to create a predictive framework with which to infer the colour of ancient mammals.
They then looked at fossilised melanosomes from 6 extinct mammaliaforms – creatures which belong to the group of extinct animals which are ancestors of “true” mammals. One of the extinct animals is a never-before-described species from the Late Jurassic found in China. That animal lived about 158.5 million years ago.
The ancient mammals’ fur was predominantly and uniformly dark. They showed no indications of patterns like stripes and spots.
Dark, dull fur is typical of modern nocturnal mammals like moles, mice, rats and bats. The finds, therefore, support the hypothesis that early mammals were also largely nocturnal and dark coloured for camouflage.
The authors also suggest that high levels of melanin in the fur of early mammals could have helped with regulating body temperature and made the fur stronger for protection.
Early mammals evolved in the shadows of dinosaurs and were small, scurrying creatures. Mammals diversified after the mass extinction event which wiped out the large dinosaurs 66 million years ago. This diversification includes the development of more striking and vibrant coats.
