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When considering the appearance of early mammals from the Age of Dinosaurs, striking patterns such as zebra stripes or leopard spots were not part of their design. Instead, research indicates that these ancient creatures likely had muted, dark coats configured for camouflage.
According to research published in the March 14 issue of Science, early mammals and their close relatives likely displayed primarily dark colors, an adaptation that enabled them to remain inconspicuous in their nocturnal environments, thereby avoiding the watchful eyes of predators.
While many dinosaurs, including various birds, dazzled with colorful plumage, the modern diversity of mammalian fur colors often goes unnoticed, as pointed out by Matthew Shawkey, an evolutionary biologist at Ghent University in Belgium. He notes the rich variety of fur patterns—stripes, spots, and more—as well as a spectrum of colors ranging from grays and yellows to oranges.
However, the knowledge surrounding the evolution of these colors, especially in the fossil record, remains limited. Shawkey highlights that despite advances in understanding the pigmentation of extinct birds through melanosomes, details about the coloration of fossilized mammals have largely eluded researchers, with a notable exception being a recent finding of reddish fur in a 3-million-year-old mouse fossil.
In their study, Shawkey and colleagues investigated the melanosomes—the pigment-containing structures—in the hairs of 116 extant mammal species and correlated their morphology with color output. This meticulous analysis facilitated the team’s ability to predict potential colors in ancient mammals. Their findings reveal that melanosomes associated with vibrant hues like red and orange were more rounded, while those linked to darker shades of black and brown were more elongated.
Furthermore, the research extended to six early mammalian species, dating back 120 to 167 million years during the Jurassic Period. Despite the diversity seen in contemporary mammals, the preserved melanosomes from these ancient creatures suggested a narrow spectrum of dark brown and gray hues across their coats, indicating a uniform coloration.
The subjects of this study were primarily small, rodent-like mammals, much like today’s shrews or moles. Shawkey observes that given their ecological context—being prey for dinosaurs—it is logical that these mammals evolved to possess a dark, camouflaging fur that allowed them to hide effectively. “They were basically dinosaur food,” he states, emphasizing the need for stealth in their predatory environment.
Despite this tendency toward uniformity among the studied mammals, all displaying muted fur, Shawkey notes the possibility that some extinct species might have exhibited brighter colors or patterns, leaving the door open for future discoveries that might challenge the current monochrome understanding.
Looking ahead, Shawkey emphasizes the significance of identifying when various color traits began to appear in mammals. Understanding the evolution of patterns such as spots or brighter fur colors, as well as their possible correlation with the extinction of nonavian dinosaurs about 66 million years ago, could provide crucial insight into the adaptive strategies of mammals. The post-dinosaur era could have ushered in new daylight habitats that may have facilitated the development of a broader color palette in mammalian species.
However, as Luke Weaver, a paleontologist at the University of Michigan, points out, signs of this diversification may have preceded the extinction event, hinting at an earlier ecological evolution among mammals that allowed them to occupy a wider variety of habitats. Sampling melanosomes from late Cretaceous mammals could yield valuable data on this transitional period at the close of the Age of Dinosaurs.
Meanwhile, Maria McNamara, a paleontologist from University College Cork, advocates for more studies like Shawkey’s to deepen understanding of mammalian evolution across varying biomes and latitudes during the Jurassic. She emphasizes the importance of modern paleontology, particularly in demonstrating its capacity for rigorous analytical methodologies.
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