A re-analysis of a genus of equatorial bats has revealed three species new to science, according to the Field Museum.

In the last half century, yellow-shouldered bats in the New World tropics have seen an increase in species types as new mitochondrial and DNA analysis has cleared up instances of one distinct species being confused for another.

Since 1960 the number of species in the group Sturnira has grown from eight to 22. The three newest editions are described in the open-access journal Zookeys.

To distinguish the bats as new species, the researchers collected live specimens from the New World tropics and paired those with specimens from museum collections. Then, they used tissue samples taken from museum archives or drawn from the newly collected specimens to conduct a thorough genetic analysis of the bats.

Two nuclear and three mitochondrial genes from each tissue were amplified and sequences, giving the researchers nearly 5,000 base pairs of DNA, from more than 120 individuals.

"We chose these genes because they have proven useful for classification of related groups of bats," said lead study author Paúl Velazco. "Mitochondrial sequences tend to be fast-evolving and informative about very recent evolutionary splits, while nuclear genes tend to be slow-evolving and shed light on more ancient divergence events."

The DNA sequencing enabled Velazco and his collaborators to get about 8 million years worth of genetic history out of the bats.

This sequencing data enabled the researchers to take a new look at existing documentation of these bats in museum records and identity incorrectly classified species.

Nearly 20 percent of species in the group Sturnira were misidentified in museum collections, the researchers found.

"The differences between species are often subtle, and difficult to describe in writing. The historic literature lacked access to the visual documentation that we rely on today, such as color photography and digital libraries," said Field Museum mammal curator Bruce Patterson, a study collaborator. "For this reason, small and imprecisely described morphological differences were often overlooked during the original identification of the specimens. This type of error pervades all biological collections."

The research paints a clearer picture of the bats' range. Once thought to exist as far north as Mexico, the scientists determined that the bats are restricted to Bolivia, Brazil, Paraguay, Uruguay, and northern Argentina.

"A curator's job is to bring order out of chaos," Patterson said. "This group of bats offered an excellent opportunity study the process of species formation across the entire New World tropics."