To get around that problem, the researchers analyzed data from 2,415 species of mammals alive today, their relatedness to other existent mammal species, and their connections to known ancestors. They then used computer algorithms to reconstruct the likely activity patterns of the mammals that lived in the past.
Several theories exist that seek to explain the origins of mammals and their family trees. The researchers, therefore, constructed two different mammalian family trees portraying alternative timelines for the evolution of mammals.
The results show the same phenomenon: Mammals switched to daytime activity shortly after the dinosaurs disappeared.
The scientists found that the ancestors of simian or higher primates, such as monkeys, gorillas and humans, were among the first to give up nocturnal activity.
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The discovery helps to explain why these primates are the only mammals that evolved adaptations to seeing well in daylight. This is largely because all other mammals lack a fovea, which is a small depression in the retina of the eye where visual acuity is highest.
“No mammals, except monkeys and apes, have more than two types of cones — sensitive to short and long light wavelengths — in their retinae, and their vision has been compared to a red-green colorblind human,” Maor said.
According to the “nocturnal bottleneck hypothesis,” Maor said mammals co-existed alongside dinosaurs thanks to the segregation of the two groups’ ecological niches along a temporal day–night axis.
In short, the first mammals essentially evolved to avoid diurnal dinosaurs.
“It follows that when dinosaurs went extinct, they freed niche space to be taken by other species, including mammals, for which the daytime would have been a novel niche,” Maor said. “According to ecological theory, entering a novel niche may allow a species to evade predators and-or competitors present in its original niche, giving it an advantage that may lead to evolutionary success.”