Siamogale melilutra had a large, powerful jaw with the enlarged, bunodont (rounded-cusped) teeth typical of many otter lineages. This raises the question of whether these bunodont teeth were inherited by all otters from a common ancestor, or evolved independently in different otter lineages over time because of the evolution of similar adaptations to thrive in similar environments.Credit: Image courtesy of Cleveland Museum of Natural History
Dr. Xiaoming Wang, Curator and Head of Vertebrate Palaeontology at the Natural History Museum of Los Angeles County and Dr. Denise Su, Curator & Head of Paleobotany and Paleoecology at the Cleveland Museum of Natural History have published a paper with colleagues in the Journal of Systematic Paleontology on the discovery of one of the largest otter species ever found. This discovery was made in the Yunnan Province, Southwestern China by an international team of scientists from the United States, France, and China. It represents groundbreaking research into the evolution of a little-known fossil genus of the otter family.
This newly discovered species of otter, Siamogale melilutra, belongs to an ancient lineage of extinct otters that was previously known only from isolated teeth recovered from Thailand. The discovery of a complete cranium, mandible, dentition and various skeletal elements at Shuitangba provides information about the taxonomy, evolutionary history, and functional morphology of this new species.
“While the cranium is incredibly complete, it was flattened during the fossilization process. The bones were so delicate that we could not physically restore the cranium. Instead, we CT-scanned the specimen and virtually reconstructed it in a computer,” said Dr. Su. The CT restoration revealed a combination of otter-like and badger-like cranial and dental feature, hence its species name, “melilutra,” which refers to meles, Latin for badger, and lutra, Latin for otter.
Siamogale melilutra was about the size of a wolf and weighed approximately 110 lbs., almost twice as large as the largest living otters. It had a large and powerful jaw, with enlarged, bunodont (rounded-cusped) cheek teeth. These characteristics appear to have been adaptations for eating large shellfish and freshwater mollusks, both of which were found in abundance at Shuitangba. “From the vegetation and other animal groups found at Shuitangba, we know that it was a swampy, shallow lake with quite dense vegetation,” said Dr. Su.
“Multiple otter lineages have low-crowned bunodont teeth, leading us to ask the question if this was inherited from a common ancestor or if this was convergent evolution based on common dietary behaviors across different species,” said Dr. Wang, lead author of the paper. “Our phylogenetic analysis suggests that bunodont dentition independently appeared at least three times over the evolutionary history of otters.”
The completeness of the specimens from Shuitangba allows the scientists to better understand the evolutionary history of otters and specifically this enigmatic genus from the Miocene, of which there had been little information. The findings from Shuitangba reveal that Siamogale belongs to one of the oldest and most primitive lineages of the otter family, which goes back at least 18 million years in the form of Paralutra from Europe.
The scientists are working to understand other aspects of the life of Siamogale melilutra.
“The discovery of the otter helps solve some questions about otter relationships, but has opened the door to new questions,” said Dr. Wang. For instance, why was it so large, how did it crack open mollusks and shellfish for food, and how did it move in the water and on land?
“Continued studies by our group will address these fundamental questions and give us a more complete picture of its paleobiology,” said Dr. Su.
Xiaoming Wang, Camille Grohé, Denise F. Su, Stuart C. White, Xueping Ji, Jay Kelley, Nina G. Jablonski, Tao Deng, Youshan You, Xin Yang. A new otter of giant size, Siamogale melilutra sp. nov. (Lutrinae: Mustelidae: Carnivora), from the latest Miocene Shuitangba site in north-eastern Yunnan, south-western China, and a total-evidence phylogeny of lutrines. Journal of Systematic Palaeontology, 2017; 1 DOI: 10.1080/14772019.2016.1267666