THE MAMMALIAN VICTORY
65 million years ago, when a huge meteor wiped out the dinosaurs, leaving life on Earth in a state of chaos, the race to become Earth’s new ruler began. Recent research demonstrates that our ancestors were the first to act.
Lucky for us, millions of years ago reptiles and dinosaurs lost their grip on the biosphere. In the gap, mammals rose. Here’s why we did so well.
When a 34 billion tonne rock slammed into a shallow ocean near what is now Mexico at a speed of 30 km/s, it changed Earth’s history. The collision released energy corresponding to 1+ billion nuclear bombs. Burning rocks were flung through the atmosphere, causing wildfires throughout the planet, and huge tsunamis washed up on the shores. For decades, a worldwide cloud of dust blocked out the sunlight, temperatures plummeted, and plants died. After 160 million years of world domination, the large dinosaurs had been wiped out along with 75 % of all life. In the ruins of the lost world, a group of small, lucky survivors, including birds, crocodiles, snakes, and mammals, remained. The planet was waiting to be conquered, and a brutal race began to reach the top of the food chain and become Earth’s new rulers. Today – 65 million years later – scientists finally have a clear impression of the important moments of the struggle.
GREENHOUSE GASES HEALED EARTH
The giant meteor strike marked the end of the Cretaceous and the beginning of the next period in Earth’s history, Paleogene. After decades of darkness and cold, the dust settled, and slow liberation of greenhouse gases from Earth’s interior made sure that the planet became warmer again. Temperatures ended almost 15 degrees above the present average, and the warm climate spread from pole to pole. Lush rainforests and hardwood forests covered most of the land, and the poles were clear of ice. In many ways, Earth had returned to its heyday, but one vital element was gone, leaving a gaping wound in the global eco-system. The huge dinosaurs, that had dominated the planet in the shape of herbivores weighing several tonnes and awesome predators, had died out. Only one single group of dinosaurs, the birds, had survived. Other groups of animals were also in a bad shape, and only about 10 % of the mammals had made it through the disaster.
MANY NEW SPECIES
The evolutionary race in early Paleogene has been a highly debated subject among scientists for years. One group, geneticists, use analysis of modern animals’ genes to calculate, when individual groups of animals evolved. The scientists take a look at the number of differences in the genes of dogs and elephants, etc. As they know how quickly the differences occur, they can calculate, when the two species’ common ancestor must have lived. Such studies have shown that the ancestors of modern
mammals originated at an even pace throughout the Cretaceous (150-65 million years ago), and their evolution only really began to pick up pace more than 10 million years after the demise of the large dinosaurs.
The problem is that the method is very inaccurate, when scientists are to calculate so far back in time. That is the reason why some scientists rely on fossils instead, and fossilized skeletons tell a very different story indeed.
In the most detailed study so far of fossils from the period around the meteor strike, scientists from University College London have provided us with an extremely clear impression of the evolution of early mammals.
The scientists studied several different aspects of the evolution of early mammals. First, they looked at the number of species over time and found that a wealth of new mammal species evolved in early Paleogene. Subsequently, they analysed the variation between species concerning shapes and sizes, discovering that the mammals obtained a huge variety of body types in no time. The results show that the mammals did not hesitate for a single moment. Their evolution ” exploded” at the