MONASH (AUS) / U. WASHINGTON (US) — An advanced set of molars helped a group of prehistoric rodent-like mammals survive the extinction event that ended the reign of the dinosaurs 66 million years ago.
In research published in Nature, evolutionary biologists show that the multituberculate family of mammals possessed an almost unmatched ability to grow and prosper while co-existing with dinosaurs. Their unusual teeth allowed them to diversify their diet more than other mammals, giving them a major advantage over their contemporaries.
Many of the animals 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, says Alistair Evans of Monash University‘s School of Biological Sciences.
“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,” Evans says.
“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. They also did rather well out of that extinction event, in fact increasing in size and tooth complexity immediately after it.”
“These mammals were able to radiate in terms of numbers of species, body size and shapes of their teeth, which influenced what they ate,” says lead author Gregory P. Wilson, assistant professor of biology at the University of Washington.
Led by Wilson, the researchers used imaging software to create high-resolution 3-D images of the teeth of 41 multituberculate species held in fossil collections around the globe. They analyzed the shape and surface texture of teeth, determining their complexity using software designed for working with topography of land surfaces.
“If you look at the complexity of teeth, it will tell you information about the diet,” says Wilson. “Multituberculates seem to be developing more cusps on their back teeth, and the bladelike tooth at the front is becoming less important as they develop these bumps to break down plant material.”
“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,” says Evans.
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.
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