A boy tries out the interactive T. rex during the media preview March 5, 2019 of "T. Rex: The Ultimate Predator" an at the American Museum of Natural History in New York City. (Image credit: Photo by TIMOTHY A. CLARY/AFP via Getty Images)
Live Science has an interesting post about the size of extant animals. There were larger animals on Earth in the past. There are theories, but the actual reason is complex and may involve multiple factors. Mammals. being endothermic, may be limited in how large they can get due to energy needs.
Prehistoric giants used to populate the Earth. These behemoths included mighty dinosaurs, airplane-size pterosaurs, massive crocodiles and snakes, and even armadillos the size of cars. But today, there are just a few big animals on our planet.
What happened? Why aren't there many giants left anymore?
First of all, there's plenty of fossil evidence that the ancient past really did have larger animals — beasts that were humongous but also larger, on average, than today's creatures, Greg Erickson, a vertebrate paleobiologist at Florida State University in Tallahassee who specializes in ancient reptiles, told Live Science. Ever since scientists unearthed the first known stash of dinosaur bones, in the 19th century, researchers have put forth ideas to explain why giants were common millions of years ago but less so today. But no one can point to one definitive answer, Erickson said. "It's so multifactorial."