Within a few million years of the impact the fossil record shows an explosion in mammalian diversity. With dinosaurs gone, mammals could exploit the planet's resources themselves. But when a catastrophic asteroid or comet-maybe a few comets, as some scientists are now arguing-finished off the dinosaurs 65 million years ago, mammals got the most important evolutionary opportunity they would ever have. During the next 145 million years of evolution, the dominance of dinosaurs ensured that our distant mammalian ancestors remained no larger than a cat. All living mammals today, including us, descend from the one line that survived. They were one of several different mammal lineages that emerged around that time. The earliest known mammals were the morganucodontids, tiny shrew-size creatures that lived in the shadows of the dinosaurs 210 million years ago. Nonetheless, the amphibious hippo, with its lawnmower-like diet of up to a hundred pounds (45 kilograms) of grass a night, shares a common lineage with the three-inch-long (7.5-centimeter-long) naked mole rat-a subterranean, tuber-chomping hot dog with teeth, which lives like a termite in large colonies dominated by a queen.ĭeep in their bones, all mammals are related. So many mammals-and such varied shapes and behaviors-throng this land that it's hard to believe any two could have descended from the same ancestor. Meanwhile, one of the few surviving black rhinoceroses in the area wanders stealthily through a stand of high grasses. Quick-witted vervet monkeys dash down from the trees to steal food through the open door of a tourist van. A few miles away elephants-which scientists are just now realizing may come from one of the oldest of the modern mammalian lineages-lumber toward a midday bath in a rain-swollen stream. In a grove of acacia trees a group of giraffes, members of a family of mammals that until 20 million years ago were small forest dwellers, nibble at the top branches. In the nearby Ngorongoro Crater a mother hippopotamus nuzzles her pink newborn in a muddy pond, while a pair of lions leisurely copulate along the roadside. Myriad mammal species graze, gallop, prowl, and wallow in this part of Africa. But the wildebeests are only part of the scene. Moehlman calls it "a place of pilgrimage." Indeed, no place on Earth offers a more spectacular abundance of our fur-bearing, breast-feeding brethren, especially when the wildebeests are on the march. Local Masai women regard the dune as a sacred fertility site. We feel connected to her because she's a fellow mammal." Her brain may not work like ours, but I think there's pain. "She must be feeling emotion, but there's no way to prove it," says Patricia Moehlman, the wildlife biologist who has brought me to Shifting Sands, a 12-foot-high (3.5-meter-high) dune that is itself slowly migrating across the plain. Then, as if in frustration, she charges two jackals on the sidelines of the kill. A few yards away, ears twitching, the mother stands helpless. Within moments it falls victim to the jaws of the hyena. But the inexperienced fawn makes a panicky turn. The mother slows and moves evasively to distract the hungry predator. But a closer look reveals details of high drama.Ī young Grant's gazelle suddenly dashes between the clusters of wildebeests, followed closely by its mother. From a distance the movement seems a serene and constant march toward the southeast, where recent rains have made pastures greener. Others walk with the distended bellies of imminent birth. It is wildebeest calving season, and many of those giant bearded antelope have newborns trailing them. From the top of Shifting Sands dune in the Serengeti Plain of Africa a million mammals are in motion.
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