Study Show Mammals Thrived Despite Dinosaurs

New study which was published in the journal Nature indicates that at least one      group    of

ancient mammals was already expanding 20 million years before the dinosaurs were wiped from the Earth. Analysis of ancient mammal teeth indicates they were able to take off not because dinosaur die-off made way for them, but because they discovered a new food source that others weren’t consuming. Some of the world’s earliest mammals were the multituberculates, a group of small rodentlike animals that first emerged on Earth about 165 million years ago. For the next 80 million years, they stayed small, seeming to evolve slowly while living in a limited number of habitats and eating insects. Researchers once thought the animals were being held back by dinosaurs, which outcompeted them for food sources. The fossil record shows that after the mass extinction event 65 million years ago, dinosaur diversity and density dropped and overall mammal diversity and density increased. Researchers used to think that the mammals succeeded in the absence of the dinosaurs. To test this theory, the researchers looked closely at a specific group of early mammals. They analyzed 41 sets of fossilized teeth from multituberculates. The teeth were scanned into a computer program, which analyzed their complexity. As reported Gregory Wilson of the University of Washington, 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 (or cusps) to break down plant material. This increasing “dental complexity” allowed them to eat a more diverse range of foods. The fossil teeth suggested that about 85 million years ago, body size of these mammals increased and more and more new species appeared, especially after they switched to eating plants.