The diversity of terrifying meat-eating dinosaurs may be a joy for the makers of the Jurassic Park films, but it poses a challenge for paleontologists to explain. There appear to have been too many carnivorous dinosaurs for the available prey. However, a study of the jaws of theropod dinosaurs provides an answer, indicating they cut down on competition by adopting different diets.
It stands to reason that animals can't afford to outgrow their food supply. Even when the largest creatures ever to roam the Earth served as dinner, the world could only support a certain number of carnivores. Moreover, rather than the meat-eaters coming from a large number of species, we'd expect a few to dominate, as is the case at the top of the food chain today.
Yet the fossil record reveals a wide variety of theropod dinosaurs, from the famous Tyrannosaurus rex to velociraptors, which in real life were the size of turkeys. Many of these occurred in different places and times from each other, but some fossil deposits still reveal more meat-eaters than we would expect.
Joep Schaeffer, a masters student at Bristol University, found an explanation for this discrepancy while studying the jaws of 83 species of theropods. The mouthparts of these dinosaurs were different from each other, suggesting they were not feeding on the same prey. It's not surprising T. rex and something as big as a dog were not eating the same meals, but Schaeffer found wide variation in the mouthparts of even the medium and smaller dinosaurs.
For the study in Palaeontology, Schaeffer collected 78 measurements of jaw and teeth characteristics for each theropod species and used three different techniques to analyze the data. He found each method produced fairly similar results in categorizing the jaws.
Schaeffer then divided the theropods into three distinct categories. The tyrannosaurs settled on a common shape of deep jaws and powerful teeth, apparently engineered for eating smaller dinosaurs that needed subduing. All member species of this clade pretty much stuck to the script.
On the other hand, the maniraptoriforms, the closest relatives to modern birds, ate much more varied diets. “The maniraptoriforms were experimenting with a wide range of smaller prey, maybe from small dinosaurs to early mammals and lizards... even some large, juicy insects,” Schaeffer said in a statement.
Some went so far as to diversify their diet into plants, becoming omnivorous or even strictly herbivorous. Even some of those still eating meat adapted their mouths to capturing fast-moving prey, possibly including tree-dwelling species. With so many dietary niches to occupy, it makes sense more species would evolve. Although the maniraptoriforms were the masters of this, other branches of the theropod family also diversified to expand potential diets – only the tyrannosaurs stuck to a single model.