Bat signals

by Lucas Joel
Friday, April 1, 2016

Mystacina tuberculata foraging on New Zealand's South Island. Credit: Rob Morris.

Bats, the only true-flight mammals, first appeared during the Early Eocene after a period of acute global warming known as the Paleocene-Eocene Thermal Maximum. Despite decades of study, however, much remains unknown about bats. Recent discoveries are shedding new light on the natural history of these creatures, which today comprise one of the most diverse mammalian groups.

A fossil dating to the Early Eocene of France belongs to a newly recognized bat species that is one of the world’s oldest known, according to a recent study published in the Journal of Mammalian Evolution. The species, Marnenycteris michauxi, has primitive traits associated with the development of bat flight, and “may have used a flight style midway between gliding and flapping,” wrote Suzanne Hand of the University of New South Wales in Australia and her colleagues.

Another newly discovered bat fossil, this one from the Early Miocene of New Zealand and described in PLOS ONE by a different team led by Hand, suggests the animal, Mystacina tuberculata, walked on four limbs and was three times larger than today’s average bat. “Our discovery for the first time shows that Mystacina bats have been in New Zealand for upwards of 16 million years, residing in habitats with very similar plant life and food sources [as occur in New Zealand today],” Hand said in a statement. Previously, the oldest New Zealand Mystacina fossil came from a 17,500-year-old cave. “This [much older age] helps us understand the capacity of bats to establish populations on islands and the climatic conditions required for this to happen,” Hand said.

Bat species diversity is not spread evenly across all bat groups — the two main modern groups, echolocating bats and nonecholocating fruit bats, include vastly different numbers of families, for example — and scientists have not been sure why. In a statistical study of evolutionary relationships among bat groups published in the journal Evolution, Jeff Shi and Daniel Rabosky of the University of Michigan found that diversity differences are not due to different rates of species evolution within one group compared to another. Species diversification dynamics, it seems, may be more complex than can be understood using currently available methods. “Bats are really cementing their status as a particularly mysterious group of animals [in that] we don’t understand much about their evolution,” Shi says.

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