Mammals did not emerge from the extinction event unscathed. Before the asteroid strike, Lyson says, the largest mammals were about the size of a raccoon. Immediately after, the biggest mammals were about rat-sized. But in a world without towering dinosaurs, new opportunities opened for mammals.
“Within 100,000 years after the extinction, we have a different type of raccoon-size mammals,” Lyson says, with additional fossils from Corral Bluffs revealing an increase size over time. By the 300,000-year mark, the biggest mammals were about the size of large beavers, and those that lived 700,000 years after the impact could weigh over a hundred pounds, such as Ectoconus ditrigonus, a herbivore unlike any mammal alive today. “This is a hundred-fold increase in body size compared to the mammals that survived the extinction,” Lyson says. Mammals wouldn’t go through this sort of rapid growth again for another 30 million years.
The question facing paleontologists is what spurred this rapid growth. A combination of factors were likely at play. Not only did the dinosaurs that munched mammals disappear, but a warming global climate changed the makeup of forests and allowed for the evolution of new plants. Legumes—energy-rich plants and the ancestors of bean—evolved for the first time. The botanical changes may have helped provide the fuel for mammalian growth, Lyson says, with climate, plants and mammals all tied together in a story of recovery from one of the world’s most devastating mass extinctions.
“For the first time, we are able to link changes in plants and animals together, and more importantly, we are able to place all of these changes in a high-resolution temporal framework,” Lyson says.
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