According to an article published by PBS.org, researchers reported that a fossil found in China is the remains of a tiny, furry animal that was a relative of mammals living today, but lived 195 million years ago in the Early Jurassic period. Hadrocodium wui, had certain key mammalian features 40 million years earlier than had previously been known from the fossil record. The early true mammals were small, insect-eating creatures adapted to nighttime activity. They ranged in size from bumblebee to squirrel-sized, and kept away from predatory dinosaurs. They acquired certain traits that characterize mammals: limbs positioned under the body, an enlarged brain, milk-producing glands, and a diverse array of teeth. In the early Cenozoic era, after the dinosaurs became extinct, the diversity of mammals exploded. In 10 million years, about 130 genera and 4,000 species evolved. These included the first aquatic mammals, whales, flying mammals, bats, as well as rodents and primates.
Question 1
According to the article, the extinction of the dinosaurs was key to the evolution of mammals. The most obvious and immediate result of the dinosaur's extinction with respect to the mammal populations already on Earth was what?