70 million years ago
Although the earliest mammals evolved in the early Mesozoic 200 million years ago they were still in the background 130 million years later during the heyday of dinosaurs. Seventy million years ago was a time of monster reptiles, great forests, and huge chalk cliffs made of microbial shells. For the microbial underlayer of life on Earth did not disappear. Indeed meiotic sex, the kind with two parents contributing an egg and sperm, probably evolved a billion years ago, in the Proterozoic Eon. Animals, plants, and fungi are "late bloomers," only appearing recently on the evolutionary stage. When the bolide (large rock from the sky) hit into the Yucatan area off the Mexico coast sisty-five million years ago, mammals got their chance. We can imagine the gruesome scene. Any herbivorous dinosaurs not killed by shock waves and fire would have slowly starved in the cold dark. Carnivorous ones would have at first dined on their flesh, but they in turn would have died when the meat of the herbivores went rancid. All the while, worms, insects, and other small creatures would have been having their feasts. And on these invertebrates, mammals would have enjoyed a survivor's banquet. Here was the inaugural party, the kicoff event for millions of years of further evolution of mammals. In many places, the recyling of flesh would not have lasted until the light and greenery returned and with it new life. But in some areas it did. That was enough to let mammals emerge into a dinosaur-free world. The brain and body revolution that had allowed our ancestors to steal dinosaur eggs now allowed them to take control over the future. Mammals thus entered evolution's center stage. Nighttime life had given them the ability to regulate their own warmth and be active when nearly every other creature was asleep; more important, it had prepared them in other ways. It had required mothers to feel emotions for their young, their children. Mammals had evolved into devoted parents, not only letting their offspring nestle and huddle into their fur for warmth but also suckling them with mik from their mammary glands (the most primitive mammal, the echidna, does not have teats; its young suck on hairs, which suggests that nursing has its origins in that snuggling up to a mother's warmth). Reptiles had no such care. The emotional attachments of mothers to children in mammals by contrast enabled the rise of other attachments such as friends to friends. Such emotions did much to drive the expansion of the brain. Rising up from reptiles that never dream, mammals had creaed a brain that, after tens of million more years of evolution, could become yours. Learn More
© 2005 by Sciencewriters
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