Absolutely not, said Thomas Williamson, a curator of palaeontology at the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico.
It is true that mammals existed during the Mesozoic era (about 251 to 65.5 million years ago) – which is divided into the Triassic, the Jurassic, and the Cretaceous – but they were no larger than the size of a modern-day house cat.
Only after the dinosaurs went extinct 66 million years ago did the mammals grow in size and evolve to what they are today, according to the researchers.
Steve Brusatte, a palaeontologist at the University of Edinburgh said that dinosaurs had been around for approximately 150 million years when the asteroid hit the Earth. Had the asteroid impact not occur, the dinosaurs would have continued to thrive and evolve, he added.
Mammals would have never gotten the chance to evolve and dominate the world, had the dinosaurs not vanished, Brusatte said. Without the evolution of mammals there would also be no primates and therefore no humans.
Although mammals and dinosaurs originated roughly at the same time – during the Triassic period – the dinosaurs had a major advantage since they diversified into thousands of new species, grew to incredibly huge sizes, and spread across the globe.
None of the mammals dominated their environment, and they stayed in the shadows. Fossil evidence shows that early mammals usually ate seeds, insects, and sometimes very small dinosaurs.
Gregory Wilson, an adjunct curator of vertebrate palaeontology at the Burke Museum of Natural History and Culture in Seattle said that following the asteroid impact – which was six miles wide (ten kilometres) – about 75 percent of all mammals died. The mammals that did survive had generalist diets and were quite small.
When the non-avian dinosaurs went extinct, mammals finally had the opportunity to take over the world. The evolved rapidly (within a few hundred thousand years) into new species, grew up to different sizes, and developed diversified diets. According to Williamson, some mammals reached the size of a German Sheppard 500,000 years after the dinosaurs died out.
Currently there are more than five thousand species of mammals worldwide, Brusatte stated.
Image Source: shtfplan