Ever wonder what would happen if that asteroid had never hit our planet 66 million years ago? The film "The Good Dinosaur" envisions long-necked sauropods as farmers who can speak; humans are seen as little more than barn pests.
Scientists have mulled this question, too, and they have theories, if not answers ...
Scott Persons, a paleontologist at the University of Alberta, says that an alternate, dinosaur-filled Earth would definitely mean a different evolutionary path for humans. It's almost certain that we wouldn't be big enough to handle this gun, much less face off against the dino shown here in "Jurassic World."
The reason? Ecological exclusion -- brutal competition for food and other resources.
"There were mammals at the time" of the asteroid impact, Persons says. "But the mammals were all really small; the biggest was the size of a badger."
In fact, before the asteroid hit, your typical mammal looked more like this modern-day shrew.
Published:Caption:Leslie GornsteinPhoto:Mehgan Murphy, Smithsonian's National Zoo
We couldn't get big
That's because, at the time of the asteroid, what the dinosaurs wanted, the dinosaurs got...at the expense of the rest of the ecosystem, which looked more like this guy, a cautious little mammal that lived around the same time as the T. Rex.
Those sizing trends would likely have continued into the modern day, with large dinosaurs hogging the resources that others species would need to grow larger bodies.
"You might have a small tree-dwelling type" of quasi-human, Persons speculates. But a 6-foot-tall Homo sapiens that could live at ground level? With all those T. Rexes stomping around in the same space? Probably not.
"The development that allows dropping down out of trees, down to the ground, is usually associated with larger body size," Persons explains.
"If you have a great big brain stuck on the end of a long neck, that has a huge demand on your heart," Persons explains. One way to relieve that muscle? Grow a smaller head. And, therefore, a smaller brain.
Amazingly, Persons says, if dinosaurs had survived into the modern age, some might very well be having conversations with us.
"It absolutely seems to be the case that in most dinosaur groups, there was a slow but steady progression toward increased intelligence," Persons says. "By the end of the cretaceous, you have the smartest dinosaurs that ever were."
"Their ancestors had normal arms," not the teeny arms associated with the latest T. rex fossils, Persons says. T. rexes also had lost a finger during their evolutionary process, morphing from a three-fingered hand to a two-fingered appendage. Meanwhile, their jaws were getting bigger and nastier. All that adds up to...
The reason why T. rex's jaws were getting bigger? Its prey was getting tougher.
"T. rex was trying to munch on huge horned dinosaurs [like this ceratopsian, whose skull was recently discovered by Persons] and armored dinosaurs. These were the brutes of the herbivores," and were generally getting bigger and harder to chomp on, Persons says.