Once the Cretaceous period ended, the Cenozoic era began – that’s the time period that we humans are a part of. It’s sometimes called the “rise of the mammals, which isn’t a great name because the first mammals appeared in the Jurassic period. But it wasn’t until the Cenozoic when their populations really exploded.
That’s because until then, dinosaurs had ruled the earth. Early mammals were mostly nocturnal, scurrying around in the dark to stay out of the giant dinosaurs’ way. But after the great extinction event at the end of the Cretaceous, all those reptiles disappeared and mammals could fill all the habitats that the dinosaurs had dominated before.
That’s not to say that there haven’t been other animals alive during the Cenozoic too; reptiles, birds, and fish have roamed the Earth for the last 60 million years as well.
One of the most important species that appeared during the Cenozoic was Homo sapiens . That’s us – it’s another name for today’s humans. We have many adaptations that have helped us survive and spread all over the planet.
One of the most important is that we walk on two legs, rather than being stuck on all four legs like many mammals. Walking upright gave early humans a few advantages: it freed up their arms and hands to carry things like food and tools, and it helped them see things that were a long distance away, like dangerous predators .
We are only species of human that’s alive right now. But before Homo sapiens evolved, there were a few other species of early humans. And surprisingly, some of these different human species lived at the very same time. Since these different species all ate the same foods and lived in the same kinds of habitat, they were in competition with each other for food and space.
Scientists aren’t exactly sure why only one species of human – our own – survived. Homo sapiens may have been the species that was best adapted to use our environments to survive. And now, 200,000 years later after the first Homo sapiens , there are more than seven billion of us humans on the planet.