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 65 to 80 tonnes (70 to 90 tons) and upwards of 30 metres (around 100 feet) long. But why were there never 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 hypothesise that because early mammals – most of them puny and shrew-sized – had filled ecological niches for small animals, their presence prevented dinosaurs from evolving tiny body sizes adapted to such niches.
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