Recovery of novel osteological specimens (Mammuthus) from the Mammoth Site of Hot Springs, South Dakota, USA.

The Mammoth Site of Hot Springs, South Dakota, USA, is a Pleistocene locality best known for its Columbian mammoth (Mammuthus columbi) remains which were trapped, buried, and preserved in a sinkhole more than 130,000 years ago. Over the past 50 years, more than 5000 specimens have been excavated, many of which remain in situ. In the summers of 2023 and 2024, two unique specimens were excavated from the bonebed: a segment of "predigit" (an ossified, formerly cartilaginous rod of the fat pad), likely a distal prehallux, and a fused proximal sesamoid pair from the digits. Despite both phenomena being well documented in extant elephants, we report the first record of those elements, to our knowledge, in extinct elephants. This finding supports the prediction that "predigit" sesamoids are ancestral for crown group elephants, reflecting the ancient nature of the singular form and function of the feet in proboscideans, related to supporting these giant animals on land.