http://www.nature.com/news/2007/070305/full/070305-6.html

Published online: 7 March 2007; | doi:10.1038/news070305-6

Did a 'light' genome help birds take flight?

A smaller genome evolved in dinosaurs, long before birds learned to fly.

Lucy Odling-Smee

Tyrannosaurus rex may have had the genetic 'lightness' to permit flight, long before their descendents took to the skies. NHPA

A study of dinosaur genomes hints that the early evolution of a smaller genome might have been necessary for later vertebrates to take to the skies.

Birds have long been known to have much smaller genomes than mammals and reptiles living on the ground. And a small genome has been linked to both small cell size and high metabolic rate: the lower volume-to-surface ratio of small cells, which don't have much DNA to pack inside, can allow for faster transport of nutrients and signals across the membrane. Thus, some suggest that the energetic demands of flight require birds to have a 'light' genome.

But which came first: flying birds or the smaller genome?