How large plant-eating dinosaurs were able to coexist

Researchers have decoded the long-standing mystery about how numerous species of large, plant-eating dinosaurs could co-exist successfully over geological time. Dr Jordan Mallon, a post-doctoral fellow at the Canadian Museum of Nature measured and analysed characteristics of nearly 100 dinosaur skulls recovered from the Dinosaur Park Formation in Alberta, Canada. 

Mallon's results indicate that these megaherbivores (all weighing greater than 1,000 kg) had differing skull characteristics that would have allowed them to specialise in eating different types of vegetation. The results, published in the journal PLOS ONE, support a concept known as niche partitioning, which dates to the 19th-century studies of Charles Darwin and came into its own in the 1950s with the development of the science of ecology.

The Dinosaur Park Formation is between 76.5 and 75 million years old and is known for its rich concentration of dinosaur remains. The rock unit has yielded nearly 20 species of megaherbivores from the Late Cretaceous period. Of these, six species would have coexisted at any one time, including two types of ankylosaurs (tank-like armoured dinosaurs), two types of hadrosaurs (duck-billed dinosaurs), and two types of ceratopsids (horn-faced dinosaurs). 

"Today's megaherbivore 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?" Mallon said. Mallon tested two competing hypotheses. The first is that availability of food was not a limiting factor in species survival. Plants may have been either super-abundant, so the megaherbivores did not have to compete for food, or the dinosaurs' metabolisms were relatively low, so the environment could support more species relative to a fauna comprised entirely of high-metabolic animals. 

 The second hypothesis is that the available food resources were limiting and that niche partitioning came into play; in other words, there weren't that many plants to go around so that the species had to share available food sources by specialising 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," said Mallon. These differences, for example, would reflect whether a dinosaur was adapted to feeding on soft or hard plant tissues. 

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