How mammals avoided being eaten by dinosaurs
Early mammals had dark inconspicuous fur and only came out at night until dinosaurs became extinct, scientists believe.
A study of colouration of mammals that lived in the Mesozoic era – around 150 million years ago – shows that none had developed the array of patterns and colours seen today and were a dark and dusky greyish-brown shade.
The colours are similar to the hue of nocturnal animals, such as moles, mice, rats and bats. Experts say the findings support the hypotheses that early mammals were largely nocturnal and coloured to camouflage them from meat-eating dinosaurs and other predators.
After dinosaurs became extinct approximately 66 million years ago, mammals were able to come out during the day and evolve the spots, stripes and brighter colours exhibited by many creatures today, experts believe.
Dr Matthew Shawkey, associate professor of biology at the University of Ghent, said: 'Evidence suggests that most mammals were nocturnal in the Jurassic/Cretaceous, perhaps to avoid being eaten by dinosaurs.
'It is likely that the extinction of the dinosaurs enabled mammals to take on new habits, including daytime activity, as they were no longer threatened by dinosaurs.
'Mammals rapidly diversified and spread into new niches previously occupied by dinosaurs.'
The findings were only possible because scientists have recently discovered that melanosomes – the cell machinery responsible for pigmentation – can be preserved in fossils.
Scientists looked at the melanosomes from 116 living mammals and compared them to the fossilised versions from six types of Mesozoic mammals from around 158 million years ago to see which fur had the closest match.
The results stand in stark contrast to the varied melanosome structures found in feathered dinosaurs, early birds, and pterosaurs. There also appeared to be no difference in coat colour between male and female mammals.
Writing in the journal Science, the authors said: 'Samples taken from different integumentary locations of each fossil resulted in uniformly dark brown colour, with no evidence of colour patterns such as striping, spots, or counter-shading as seen in extant mammals.
'A nocturnal lifestyle may have enabled these species to avoid predation by diurnal carnivores and, furthermore, may have helped them to survive mass extinction. Darker hairs could help small mammaliaforms to reduce heat loss through insulation
'Our results suggest that the melanosome variation and colour expansion seen in extant mammals may have occurred during their rapid radiation and diversification after the Cretaceous-Paleogene extinction.'
Researchers believe that the high melanin content in their fur could have been beneficial for thermoregulation and providing mechanical strength for protection.
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