15 March 2012
An advanced set of molars helped a major group of prehistoric mammals survive the extinction event that ended the reign of the dinosaurs 66 million years ago, according to a new study.
In research published today in Nature, evolutionary biologists from Monash University, the University of Washington and the University of Helsinki showed that the rodent-like multituberculate family of mammals possessed an almost unmatched ability to grow and prosper while co-existing with dinosaurs. Their unusual teeth allowed multituberculates to diversify their diet more than other mammals, giving them a major advantage over their contemporaries.
Dr Alistair Evans of Monash University's School of Biological Sciences said many multituberculates greatly increased the number of bumps or tubercles on their teeth meaning they could, unlike other mammals, eat flowering plants that were beginning to become common 90 million years ago.
"It is generally accepted that for millions of years, mammals were unable to develop much due to competition from the dinosaurs. This study shows how multituberculates bucked this trend - they increased from the size of a mouse to the size of a beaver and were able to take on new roles in the ecosystem," Dr Evans said.
"Unusually, they did this prior to the extinction event which killed off the large dinosaurs - generally considered a turning point in mammalian evolution. Compared to other mammals of the time, they were really ahead of the game. Multituberculates also did rather well out of that extinction event, in fact increasing in size and tooth complexity immediately after it."
Led by Dr Gregory Wilson of the University of Washington, the researchers used imaging software to create high-resolution 3D images of the teeth of 41 multituberculate species held in fossil collections around the globe. They analysed the shape and surface texture of teeth, determining their complexity using software designed for working with topography of land surfaces.
“At the height of multituberculate evolution, these animals had teeth as complex as many modern plant-eating mammals – an attribute that certainly contributed to their evolutionary success,” Dr Evans said.
Following the extinction event, multituberculates continued to prosper for another 30 million years until other mammals closed the evolutionary gap. When primates and rodents gained the upper hand in competition for food, multituberculates became extinct.