Hungry teenage tyrants help explain puzzling fact about dinosaur diversity

A graphic showing body sizes of modern carnivorous mammals compared with the body sizes of dinosaurs.

Teen dinosaurs, specifically the offspring of enormous meat-eating species like Tyrannosaurus rex, would have been everywhere 100 million years ago. Their voracious and changing appetites would have deeply affected the world around them — to the extent that these adolescent dinosaurs, as they grew, would have limited the number of other dinosaur species they competed with for food, according to new research.

This could help explain something that has long puzzled palaeontologists: why there are relatively few small dinosaurs in the fossil record, particularly in the mid- to late Cretaceous period. New research published in the journal Science on Thursday has shown these carnivores likely occupied niches that might have ordinarily been filled by smaller, meat-eating dinosaurs, with the young punks beating out those smaller species while competing for prey.

“Dinosaur communities were like shopping malls on a Saturday afternoon jam-packed with teenagers,” said Kat Schroeder, a doctoral student in the University of New Mexico’s department of biology, who led the study.”They made up a significant portion of the individuals in a species and would have had a very real impact on the resources available in communities,” she said.

Despite dominating the biodiversity on land for more than 150 million years, dinosaurs were not very rich in species, relatively speaking. Among dinosaurs, large-bodied species weighing more than 1,000 kilograms were the most diverse group.This is completely different from animals in modern ecosystems, where there’s typically greater diversity among smaller-bodied species because they are able to share a wide range of ecological niches and sources of prey.

Researchers believe that the large gap in size between meat-eating dinosaur hatchlings, juveniles and adults and their rapid growth would have meant they had eaten different prey at different life stages. This may have influenced the diversity and unusual body size distribution of dinosaur communities reflected in the fossil record, with teen dinosaurs making up a significant portion of the individuals in a species.

Schroeder and her coauthors collected data from well-known fossil sites from around the globe, including over 550 dinosaur species. Organizing dinosaurs by mass and diet, they examined the number of small, medium and large dinosaurs in each community. Their results showed that there were very few carnivorous dinosaurs weighing between 100 and 1,000 kilograms (220 to 2,200 pounds).Was it possible that these small and midsize dinosaurs existed and we don’t know about it just because they aren’t preserved well in the fossil record?

Not likely, said Schroeder, noting that the gap was consistent across climates, latitudes and different regions. They did, however find tiny species of dinosaur in places where their midsize counterparts were missing. This suggested that the gap was not an issue of preservation in the fossil record. There was more even body-size distribution among plant-eating dinosaurs, and Schroeder said that young plant-eating dinosaurs wouldn’t have impacted their environment in the same way as their carnivorous counterparts.Teen herbivores could eat what their parents ate: Mom and dad consumed the tops of trees, while the younger ones munched on the leaves lower down, she explained. And there is no way a young T. rex could kill and eat a triceratops — they’d have to leave that up to their parents.

Source: CNN