Most of the dinosaurs famously went extinct 66 million years ago, when a massive asteroid smashed into the Earth. At the time of that disaster, feathered dinosaurs called maniraptorans, which included the ancestors of modern-day birds, were living alongside well-known ancient characters such as T. rex and Triceratops. But while the asteroid claimed the lives of those larger dinosaurs, however, the smallest ones—the bird-like maniraptorans—survived.
According to new research, it was precisely the birds' miniscule size that saved them. An international team of scientists (including the Smithsonian Institution's National Museum of Natural History paleontologist Matthew Carrano) used fossil bone measurements to estimate the body size of 426 ancient species. Most dinosaurs, they found, quickly evolved into one size—usually a massive one—and then stayed there. Maniraptorans, on the other hand, continued to tweak their body mass for millions of years leading up to the asteroid event. As a result, the maniraptorans ranged in size from 15 grams to three metric tons, the researchers report.
The smallest of those animals were the birds, which could weigh less than two pounds—the lower limit for the smallest dinosaur species, the team writes. Being small, the researchers think, gave the birds a number of advantages. Flight, for one. More importantly, however, their size meant they were able to survive when catastrophe struck. As ScienceNOW puts it: "The researchers argue that being small made it easier for maniraptorans to adapt to a wider variety of habitats, whereas the rest of the dinosaurs, encumbered by their huge bodies and enormous food requirements, simply didn’t make it."