Batty DNA signals climate change
Bats might have evolved because of an abrupt climate warming 50 million years ago, according to genetic research that provides a new evolutionary tree for this unique and enigmatic group of mammals.
An international team of scientists publishes its findings in the current issue of the journal Science.
Found on every continent except Antarctica, bats are the only mammals capable of powered flight.
They are grouped into 18 families based on their anatomy and use of echolocation, a biological form of sonar to locate and track prey. Another six families are known from fossils.
Bats make up more than 20% of all mammals and account for about 1100 species, yet their evolution is poorly understood.
"Their evolutionary history is largely unknown because of a limited fossil record," Dr Emma Teeling from University College Dublin and colleagues write.
They say around 60% of the bat fossil record is missing.
Genetics reveals bats' mysterious past
The researchers compared genetic sequences from each modern bat family to reconstruct the evolutionary relationships between the two main groups of bats: microbats, which use echolocation, and megabats, which do not.
Megabats are large, fruit-eating creatures with small ears that fly during the day in the tropics. Microbats are smaller insect eaters with large ears that use echolocation to find their prey at night.
The researchers analysed portions of 17 genes sampled in all existing bat families and re-analysed a previously published morphological data set that included four extinct families.
The gene sequencing data suggested that bats split away on their evolutionary path in the early Eocene about 52 to 50 million years ago. At that time the average global temperature rose by about 7°C, and plants and insects flourished.
Kings of the night sky
According to Dr Nancy Simmons, a zoologist at the American Museum of Natural History, as flying predators capable of capturing prey on the wing, bats "would have had few competitors for the rich resources of the Eocene night".
Teeling and colleagues' evolutionary tree for bats also provides a clear indication about the geographic origins of bats, which has long been a source of debate, since Eocene bat fossils have been found on most continents.
The research suggests that bats originated in the ancient landmass of Laurasia, possibly in an area now located in North America, during the early Palaeocene, which followed the extinction of the dinosaurs.
None of the fossils of these "protobats" has ever been discovered.
"Teeling et al. provide a new evolutionary tree for bats that helps to explain how, when, and where this extraordinary diversity may have originated," Simmons writes in a commentary in the same issue of Science.