New Research Shows That North American Mammal Evolution Tracked With Climate Change

The lush North American forests of the late Eocene. 

Mammals first evolved around 250 million years ago. They were restricted to a number of small rodent-like forms, less than a metre in length, for nearly 200 million years. When the dinosaurs became extinct 65 million years ago, mammals were perfectly placed to become the dominant group of vertebrates on Earth. As Europe existed as a series of loosely connected small islands and vast geological upheavals made Asia a difficult place to live, the central hub of this new mammalian empire was North America.

Scientists have discovered six distinct waves of diversification within the North American mammals since the K-T extinction event. The popular theoretical driving factor was climate change, based upon the number of new species. However, as with all theories, and especially ones based upon climate change, the controversy was whether evidence for the theory could be presented in a quantitative fashion. Now a study, conducted by Christine Janis from Brown University, has provided a direct correlation between temperature fluctuations and the different waves of North American mammalian evolution.

With each change in dominant fauna, there is a corresponding change in temperature, where groupings of mammalian species share the common rise, peak and decline with the global temperature of the time. There are also links to the changes in vegetation. For example a period of warming 20 million years ago, during the early Miocene epoch, caused a change in habitat from woodland to savannah. Simultaneously, the predatory birds of the forest went into decline and were replaced by grazing animals such as horses.

'Such perturbations, related to anthropogenic climatic change, are currently challenging the fauna of the world today, emphasizing the importance of the fossil record for our understanding of how past events affected the history of faunal diversification and extinction, and hence how future climactic changes may continue to influence life on earth. ' Such studies will become increasingly important, in understanding how the Earth evolved and how it will fare due to climate change.