skeleton
March 23, 2016

Newly-discovered Hawaiian bat was the island’s second known native land mammal

The number of known land mammals native to Hawaii has been doubled - to two.

Until recently the only land mammal known native to the island chain was the hoary bat. But fossil evidence has shown that a different species of bat lived alongside the hoary bat for thousands of years before going extinct just before humans arrived on the islands. Scientists believe their extinction may have been related to the coming of humans and the non-native species they brought with them.

"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," said Nancy Simmons, a co-author on the paper and curator-in-charge of the American Museum of Natural History's Department of Mammalogy. "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. So finding that there actually was a different bat - a second native land mammal for the islands - living there for such a long period of time was quite a surprise."

Remains of the bat, Synemporion keana, were first discovered in a lava tube more than 30 years ago. The new study's co-author Francis Howarth, an entomologist at the Bishop Museum in Honolulu, was investigating lava tubes in 1981 and discovered skeletal remains of the bat. Howarth, Bishop Museum mammalogist Alan Ziegler and other colleagues later found remains on four other islands: Hawaii, Kauai, Molokai, and Oahu.

"The initial specimens included skeletons embedded in crystals on the lava tube wall and thus were likely very old," Howarth said. "Ziegler eagerly guided me through the bat collection at the Bishop Museum to identify the bat and show me features to look for in order to find additional material for study."

A small bat with an intriguing past

Ziegler identified that the bat was different from anything else he had seen and began to investigate where it sat in the evolutionary tree. However, he died in 2003, and work on the subject was suspended until Simmons took over with the new study, published in the journal American Museum Novitates.

Synemporion keana, which was smaller than the hoary bat and first appeared in the islands' fossil record around 320,000 years ago, had several mysterious features that have made it difficult for researchers to identify its closest relatives. While being able to confirm that the bat is indeed a second native land mammal for Hawaii, future work with ancient DNA extracted from the fossils will be needed to piece together the whole puzzle.

"This extinct bat really is something new, not just a slight variation on a theme of a known genus," Simmons said. "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."

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Image credit: American Museum Novitates