For years, paleontologists have puzzled over a gap in body sizes of meat-eating dinosaurs. There are many small carnivores (10 to 100 kilograms) and large carnivores (over 1,000 kg) in the fossil record, but few in between.
To find out what happened to the medium-sized meat eaters, Schroeder analyzed 43 dinosaur communities that spanned seven continents and existed over 136 million years. This size gap occurred in all communities with megatheropods—the largest carnivorous dinosaurs that weighed 1,000 kilograms or more. Younger megatheropods could have out-competed other medium-sized dinosaurs, Schroeder says.