DESCRIBING A DIMINUTIVE FEMALE MASTODON (MAMMUT PACIFICUS) FROM LATE PLEISTOCENE (RANCHOLABREAN) SOUTHERN CALIFORNIA, USA

Sexual polymorphism in proboscideans can give many insights into their behavior, insights that are especially important when attempting to learn more about the behavior of extinct species like mastodons. Mastodons are currently known to be strongly sexually polymorphic, mostly based on their tusk size. However, confirmed female mastodon fossils are relatively rare; many diagnosable morphological characteristics overlap with those of juvenile mastodons, making identification difficult. To better understand the sexually polymorphic characteristics of mastodons, we are describing the “Oceanside Mastodon” (SDSNH 86541), an adult female mastodon. Discovered in 2002 in Oceanside, CA (North San Diego County), this specimen is composed of a partial skeleton including the complete left tusk, fragments of the right tusk, left m2, right forelimb including humerus, radius, ulna, carpals, and metacarpals, right femur, numerous vertebrae, ribs, and tarsals, making her one of the more complete identifiable female M. pacificus specimens. This specimen can be positively identified as female by a heavily worn m2 that indicates a Laws Age Group of XXII, indicating an AEY (African Elephant Equivalent Years) of approximately 39, despite very small tusk (max 78mm diameter) that could otherwise be attributed to a juvenile. Now housed in the San Diego Natural History Museum (SDNHM), we aim to complete a full anatomical description of this specimen in order to better understand sexual polymorphism-related morphologies in mastodons beyond tusk growth, and thus support future studies into the paleobiology of mastodons, especially those in the western United States