A Step Closer to Solving A 100-Year Mystery

Mammalogists may be one step closer towards solving a conundrum that has been a subject of much uncertainty for almost a hundred years—on whether Tragulus williamsoni, or Williamson’s mouse-deer, is a valid and distinct species. Mouse-deer, or chevrotains are some of the world’s smallest hoofed animals.

Research findings by mammalogists Dr. Erik Meijaard, Mr. Marcus Chua, and Dr. Will Duckworth present evidence that T. williamsoni is a morphologically distinct taxon. The findings, published last week in the Raffles Bulletin of Zoology, were based on skull measurements of a previously unidentified mouse-deer specimen from Xishuangbanna, Yunnan province, China, stored in the Kunming Natural History Museum of Zoology.

Previously, there was only one known specimen of T. williamsoni, collected from Meh Lem (modern day Phrae province) in 1916 by British zoologist Cecil Boden Kloss. It was initially considered to be a larger subspecies of the lesser mouse-deer, T. kanchil, until a study by Dr. Meijaard in 2004 provisionally elevated it to full species status.

“Due to there only being one type specimen, there was uncertainty as to whether it was indeed a distinct species or an aberrantly large lesser mouse-deer,” said Mr. Chua.

However, a decade ago, Dr. Meijaard got in touch with Professor Wang Ying-Xiang from the Kunming Institute of Zoology, who found two unidentified mouse-deer skulls in the collection of the Kunming Natural History Museum of Zoology that were suspected to be T. williamsoni. Prof. Wang, Dr. Meijaard, and Dr. Duckworth planned to investigate further, but unfortunately, Dr. Wang passed away before they could finish the research.

In late 2016, Mr. Chua contacted Dr. Wang’s former student and mammal curator at the Kunming Natural History Museum of Zoology, Dr. Li Song, for skull measurements and images of the unidentified mouse-deer specimens.

An analysis of the skull measurements of one of the Kunming mouse-deer compared to 59 other mouse-deer skulls of four species from mainland Southeast Asia revealed that the unidentified specimen matched most closely with the 1916 Tragulus williamsoni specimen, and is distinct from the other three mouse-deer species.

Thus, the researchers believe that the results provide support to earlier suggestions that the 1916 Williamson’s mouse-deer specimen is not just an abnormally large individual of T. kanchil or a specimen of T. versicolor. Instead, it suggests that T. williamsoni is a morphologically distinct taxon.

However, the researchers added that more work needs to be done to verify if T. williamsoni is really a valid species.

“Although we have doubled the data with two specimens critically examined that supports the taxonomic status of the Williamson’s mouse-deer, the sample size is still small,” said Mr. Chua.

He added that further research, especially DNA analysis, would be necessary to establish if T. williamsoni is a valid species, and find out its evolutionary relationship to other mouse-deer.

The researchers also emphasise the importance of natural history museum collections in holding valuable information on the natural world that often gets overlooked.

“If not for the Yunnan specimen and their curator, the Williamson’s mouse-deer may still remain an enigma, and it may take many years before we find out more about it,” said Mr. Chua.

“I hope these findings would encourage curators to examine their collection for more clues so that we can find out more about this mysterious mouse-deer,” he added.

Original paper: Meijaard E, Chua MAH & Duckworth JW (2017) Is the northern chevrotain, Tragulus williamsoni Kloss, 1916, a synonym or one of the least-documented mammal species in Asia? Raffles Bulletin of Zoology, 65: 506–514.