Mammals have taken advantage of past climate changes

 The evolution of mammals is strongly correlated with climate, at least for the species in North America who lived in the aftermath of the Cretaceous . This is reflected in a U.S. study that compares the temperature with the demographics of these animals.

Written by Abdullah Al Abbadi/Blue Line News

Paraceratherium, a giant rhinoceros that lived during the Oligocene, is the largest land mammal of all time. © 2011 Ex Machina

The first mammals appeared on Earth date back to over than 220 million years. There are 65 million years, to the end of the Cretaceous , before the fifth mass extinction, they had already filled all the continents. Following this crisis, their numbers have dropped considerably and it is followed by an adaptive radiation. Since then, other stages of diversification – less important however – have occurred and American researchers came to discover its causes.

The population of mammals study in North America over the past 65 million years shows that these animals have suffered six periods of high diversification or high population growth. That is to say that for various species, population peaks were observed at the same times. They are called stages of adaptive radiation.

Climate and population correlation

Typically, an adaptive radiation is initiated by an event that allows species to occupy niches that were previously inaccessible. Either because they were occupied by other species, or because no body had adapted to live there. Thus, diversification allows new species to conquer these habitats neglected by others.

Climate change not always negative

In the case of North American mammals, what are the causes of these episodes? According to researchers, it is mainly climate change. To reach this conclusion, scientists at Brown University have paralleled the demographics of mammals with paleoclimatic data. And in particular temperature, they were able to assess by analyzing the atmospheric concentrations of oxygen. Their results are published in PNAS.

Four of the six evolutionary radiations, explain the researchers, there is a strong correlation with temperature change. Thus, the evolution of mammals would have followed climate change. The immigrations are also responsible for these phases.

This study shows that all episodes of climate change are not penalized for biodiversity, in contrast, probably the one we live right now and that, along with other factors, is now causing the sixth mass extinction .

Selected Source for further read: Brown university News published in 22-Dec-2011

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