How Plant Eating Dinosaurs Coexisted
July 11, 2013

How Large Plant-Eating Dinosaurs Were Able To Coexist

Lee Rannals for - Your Universe Online

A new study is helping answer a long-standing question about how large, plant-eating dinosaurs could have co-existed successfully over long periods of geological time.

Dr. Jordan Mallon, a post-doctoral fellow at the Canadian Museum of Nature, measured and analyzed the characteristics of nearly 100 dinosaur skulls recovered from the Dinosaur Park Formation in Alberta. He published his results in the journal PLOS ONE.

According to the findings, these mega-herbivores had differing skull characteristics that allowed them to specialize in eating different types of vegetation. His findings support a concept known as niche partitioning, an idea that dates back to the 19th-century studies of Charles Darwin.

Modern mega-herbivores, a category that includes giraffes, elephants, hippos and rhinos, can weigh over 2,200 pounds.

"Today's mega-herbivore communities are not nearly as diverse as those from the Late Cretaceous of Alberta, and most other fossil communities also pale by comparison. So the question is: how does an environment support so many of these large herbivores at once?" asks Mallon.

He tested two hypotheses during his research. The first is whether the availability of food was a limiting factor in species survival. At the time, plants were super-abundant, meaning that the mega-herbivores would not have had to compete for food.

The second hypothesis is that the available food resources were limited and that niche partitioning came into play. This means that there wouldn't have been many plants to go around so that the species had to share available food sources by specializing on different types of vegetation.

"If niche partitioning was in effect, then you would expect to see various dietary adaptations among the coexisting dinosaur species," explains Mallon. "So you would look for differences in the shapes of the skull, in the teeth, and in the beaks that might reflect adaptations for feeding on diverse plants or plant parts." These differences, for example, would reflect whether a dinosaur was adapted to feeding on soft or hard plant tissues.

Neither of the hypotheses had been rigorously tested with such a large sample size. For each of the 100 dinosaur skulls studied, Mallon measured 12 characteristics that are known to relate to diet in modern animals. These include depth of the jaw, angle of the break, size of muscle insertions, and length of the tooth row.

"We can apply those same functional and mechanical principles to dinosaurs to see what they might tell us about niche partitioning," Mallon explains.

As an example, the paleontologist believes that ankylosaurs probably specialized on eating ferns, because they stood low to the ground. This species' wide beaks would have allowed them to feed efficiently on abundant, relatively low-nutrient plants. However, one family within this group had more efficient jaw mechanics that might have enabled them to include tougher planets in their diets.

Mallon says that although different species came and went, the same ecological roles were filled time and again by different species over the 1.5-million year span.

"This tells us that niche partitioning was a viable strategy for the coexistence of these animals," he adds. "The study provides further evidence to explain why dinosaurs were one of the most successful groups of animals to live on this planet."