The discovery of a new bat species that went extinct about a thousand years ago brings Hawaii’s grand total of native terrestrial mammals to two. Synemporion keana was described in American Museum Novitates last week. 

Located over 3,800 kilometers (2,360 miles) from any continent, the Hawaiian Islands are one of the planet’s most geographically isolated archipelagos in the world. While the islands host a diversity of unusual plants and animals – many of which are endemic, or only found there – the terrestrial vertebrate fauna is much less diverse than on continental regions. Researchers have long thought that the only living terrestrial mammal endemic to the islands is the Hawaiian hoary bat, Lasiurus cinereus semotus, which dispersed from mainland North America between 10,000 and 7,000 years ago.

"The Hawaiian Islands are a long way from anywhere, and as a result, they have a very unique fauna – its native animals apparently got there originally by flying or swimming," American Museum of Natural History's Nancy Simmons says in a statement. "Besides the animals that humans have introduced to the islands, like rats and pigs, the only mammals that we've known to be native to Hawaii are a monk seal, which is primarily aquatic, and the hoary bat."

However, back in 1981, Francis Howarth of the Bishop Museum discovered the bones of a second, distinctly different bat species embedded in crystals on the wall of a lava tube in Māhiehie Cave on Maui. He and Alan Ziegler, also of the Bishop Museum, went on to identify the skeletal remains of these bats on four other islands: Hawaii, Kauai, Molokai, and Oahu. Altogether, bones and teeth from at least 110 individuals have been found, but the research was put on hold following Ziegler’s death. 

Now, after examining many specimens of this mysterious second bat, Howarth and Simmons have named it Synemporion keana. It was smaller than the horary bat, and it had a well-developed forehead in comparison (pictured below). The genus name comes from Greek "synemporos," for "fellow traveler or companion," a reference to its co-occupation of the tectonically mobile islands with Lasiurus cinereus semotus. The two lived alongside each other for thousands of years. The species name is formed from Hawaiian "ke" plus "ana" for "cave" or "lava tube."

Synemporion keana emerged in the fossil record 320,000 years ago, and it disappeared around 1,100 years ago, shortly after humans colonized the islands. "This extinct bat really is something new, not just a slight variation on a theme of a known genus," Simmons adds. "The new bat contains a mosaic of features from taxa seen on many different continents. At some point, their ancestors flew to Hawaii, but we can't tell if they came from North America, Asia, or the Pacific Islands – they really could have come from anywhere based on what we know now." Future work with DNA extracted from the bones could help researchers puzzle together its evolutionary relationships. 

^{Skull and left dentary of Synemporion keana (A) compared the Hawaiian hoary bat, Lasiurus cinereus semotus (B). American Museum Novitates}