The gliding animals of south-east Asia have something in common with the Himalayas. Both owe their existence to the collision of India with Eurasia around 50 million years ago. In the wake of the continental clash, tall tropical trees spread from the subcontinent and began to dominate Asian rainforests, providing a perfect environment for the evolution of gliding.
South-east Asia's rainforests are famed for their exceptional variety of gliders. Geckos, Draco lizards, flying squirrels, colugos and frogs have all taken to the skies, suggesting the adaptation evolved several times in the region. Now a study by Matthew Heinicke at the University of Michigan at Dearborn and colleagues has found evidence to support a link between the adaptation and the forests' unusual vegetation, which is dominated by dipterocarps – trees that grow unusually tall and typically mature to lack any branches on the lower 30 metres of their trunks.
"It makes more energy sense for a small animal to glide between trees than to climb all the way down one tree and then climb back up another," says Heinicke.
Heinicke and his colleagues looked at the evolutionary history of the animal groups that contain one or more gliding species. Their analysis suggests that gliding evolved independently eight times in the forests, and that six of those evolutionary events occurred between 20 million and 50 million years ago – the time during which dipterocarp trees were first able to spread from India across southeast Asia.