Discover how early mammals’ dark coats may have provided a hidden advantage against hungry dinosaurs, and unlock the secrets of their evolutionary success.
Early mammals during the Mesozoic Era likely had uniformly dark coloring, allowing them to blend into nocturnal environments and evade predators. Researchers analyzed melanosomes in preserved hairs from six early mammals and close relatives, discovering that these ancient beasts sported dark gray and brown coats.
Early mammals developed camouflage as a survival strategy to evade predators.
Fossil records show that early mammals, such as Hadrocodium and Sinoconodon, had primitive coats of fur or hair.
These early camouflages likely provided 'protection from the elements' and aided in hunting.
As mammalian evolution progressed, so did the complexity of their camouflage systems.
Some early mammals developed coloration patterns to blend with their surroundings, while others grew longer coats for additional protection.
While modern mammals exhibit a diverse range of fur colors, including spots, stripes, and patterns, the evolution of these traits is underappreciated. Matthew Shawkey, an evolutionary biologist at Ghent University in Belgium, notes that ‘there’s obviously lots of patterns, stripes, spots, blotches, all those types of things… but also fairly diverse colors: grays, yellows, oranges.’ However, details about fossilized mammals’ coat colors remain scarce, save for recent evidence of reddish fur in a 3-million-year-old mouse fossil.
Shawkey and his colleagues used a scanning electron microscope to analyze melanosomes in the hairs of 116 modern mammals, linking their shapes and sizes to the colors they produce. They found that melanosomes responsible for brighter colors, such as reds and oranges, are rounder, while blacks and browns generally come from elongated melanosomes. Applying this predictive power to melanosomes in preserved hairs from six early mammals and close relatives, the team discovered a narrow range associated with dark grays and browns across their bodies.
The early mammals in this study were small creatures much like rodents, shrews, or moles. They likely had coats that helped them blend into their nighttime surroundings and evade predators. Many dinosaurs, especially birds, showcase a vibrant array of colorful feathers, but the diversity of fur color among modern mammals is underappreciated.
Early mammals, also known as prototheres, first appeared around 210 million years ago during the Triassic period.
They were small, insectivorous creatures with simple lungs and a three-chambered heart.
A key characteristic was their ability to produce milk for their young, marking the beginning of lactation in vertebrates.
Early mammalian traits also included hair or fur, although it's unclear whether these early mammals had fully developed hair follicles.
These primitive mammals likely gave rise to the modern groups of monotremes and therian mammals.
Dark, melanin-rich fur may have been useful in other ways. It heats up easily, and potentially helped early mammals stay warm. The dark hairs may have also been particularly tough and wear-resistant, protecting the mammals’ skin. However, it’s unclear whether some early mammals exhibited patterns or bright colors.
Determining when these colorful traits first arose is a natural next step. Shawkey notes that ‘when do we start seeing spots and these patterns? When do we start seeing light browns and oranges and things like that?‘ It’s possible that the extinction of nonavian dinosaurs played a key role in triggering a broader spectrum of colors among mammals.
Mammalian color evolution is a complex and still-unfolding process that spans millions of years.
The earliest known mammals, which lived around 160 million years ago during the Jurassic period, were likely small, insectivorous creatures with dull, brownish coats.
As mammals evolved and diversified, so did their coloration.
By the Cretaceous period (145-100 million years ago), some early primates and rodents began to exhibit more vibrant colors, possibly as a result of adaptations for communication or camouflage.
The modern mammalian palette emerged around 20-30 million years ago during the Oligocene epoch.
Maria McNamara, a paleontologist at University College Cork in Ireland, would like to know if mammals that lived in different biomes or latitudes during the Jurassic Period were similarly dark. ‘We need more papers like this to be published,’ she says. ‘It’s really important to demonstrate that modern paleontology is much more than describing dusty old bones. It’s a thriving analytical science.‘
