WorldWide Drilling Resource

Fossil of an Ancient Otter Species Found in Shuitangba Mine Compiled by Caleb Whitaker, Associate Editor, WorldWide Drilling Resource ® Shuitangba is an open-pit lignite mine located in the Zhaotong Basin of Yunnan Province, China. The basin is one of the many coal-bearing basins of the western South China fold belt. The Shuitangba mine is dated to the end of the Miocene period, about 6 million years ago, and has yielded hundreds of fossilized animals and plants. Due to a short section at the mine, a borehole was drilled in a thicker section several feet away during paleomagnetic analysis of the site. The findings indicated both the fossil and borehole sites were correlated by three distinct layers - lignite, peaty clay, then another layer of lignite. The most significant mammalian fossils occurred in the upper half of the peaty clay. Fossil-bearing layers con- tinue beyond the confines of the mine, but their true extent cannot be estimated because the mine is surrounded by rice paddies in a heavily populated area. The many fossils in the mine are excellently preserved, and the diversity of the specimens means the mine has the potential to provide more understanding about the environment during the latest part of the Miocene period in China. In 2010, researchers discovered a new species of otter preserved within the mine. The fossilized remains of the extinct otter represent one of the largest otters currently known, ranging up to two or three times larger than present-day otters. The otter would have been roughly the size of a wolf, weighing around 110 pounds when it lived 6.2 million years ago. Remarkably, the find included a nearly complete cranium, which is a rare occurrence in the fossil record. However, the cranium was completely flattened to about a 1½ -inch thickness due to distortions caused by the fossilization process, so the bones were fragile and couldn’t be reconstructed physically. Researchers took CT scans of the cranium, then digitally reconstructed it. The CT scan of the cranium was of particular interest because it revealed some badger-like features, especially the animal’s teeth and cranial. The species name of the otter, Siamogale melilutra, is a nod to the Latin meles, which means badger, and lutra, meaning otter. The species is consid- ered a part of the otter family because it shares many features with current otters; however, the badger traits and overall size make it distinctly different from other species of otter. There are some important questions which need to be answered concerning the animal’s size, and how it moved on land and water. For modern animals, a larger carnivore’s size is usually correlated to the size of its prey since size is one of the natural means used by the carnivore to subdue its prey. So, if the prey is larger, then the carnivore must also get larger. Yet, scientist believe this animal likely ate small creatures such as mollusks, which raises the question - why was the otter so large? Shuitangba open-pit lignite mine. Photos by Cleveland Museum of Natural History. 79 WorldWide Drilling Resource ® DECEMBER 2017