There are almost 300 species of squirrels in the world. From terrestrial marmots in North America to gliding squirrels in Southeast Asia, these animals show an outstanding diversity of locomotion modes and ecological specializations. 

In a recent paper in Mammal Review, paleoecologists investigated the factors that have played a role in accelerating the origination (speciation) and disappearance (extinction) of squirrel species. They reconstructed the ecological and evolutionary history of squirrels in order to identify ancestral characteristics  — traits that were present in past squirrel species  — and periods when the distributions of squirrels changed. This allowed them to identify factors associated with squirrel diversification. 

The researchers found that the first squirrels lived exclusively in trees around 40 million years ago. They concluded that the subsequent adaptation to moving on the ground probably boosted speciation in squirrels. Their results show that squirrels in mountains had higher diversification rates than their lowland relatives, reflecting that mountain ranges offer more ecological resources due to a wide variety of habitats. Most importantly, the researchers found that species present in many different habitats are less affected by changes than species in only one kind of habitat, which are prone to go extinct when conditions change. 

Based on their results and the evidence of the impact of past environmental change on biodiversity, the researchers warn that the current anthropogenic climate change, triggered by global warming and deforestation, will provoke the extinction of an important part of squirrel diversity. Moreover, surviving species will suffer a drastic reduction in their distribution, increasing the probability of their extinction, too.