Why were there no tiny dinosaurs? You might blame the mammals

WASHINGTON, Aug 6 : Everyone knows dinosaurs got really big. Some of the long-necked plant-eaters were the largest land animals ever on Earth, as shown by Argentinosaurus, perhaps 70 to 90 tons and upwards of 100 feet (30 meters) long. But how about tiny dinosaurs, like the size of a mouse? As far as we know, none ever existed.New research investigates this phenomenon. Scientists employed mathematical models to explore the evolution of body size across vertebrate groups. They determined that energetics and physiology can account for the sizes of mammals, birds that fly and turtles, but these factors fail to explain the absence of really small dinosaurs, aside from their avian descendants.The researchers see other dynamics at play. They hypothesized that because early mammals — most of them