Postcranial functional morphology of the large swamp otter Siamogale melilutra (Lutrinae: Mustelidae: Carnivora) from northeastern Yunnan, south-western China.

Abstract

Siamogale melilutra was a large otter from the Late Miocene site of Shuitangba in Yunnan Province, China. Previous analyses have hypothesized that the species was a molluscivore and a dominant predator in an otherwise depauperate local carnivoran guild. Here we describe limb elements of S. melilutra and perform quantitative analyses to categorize the functional morphology of the species to better understand its role in the predominantly aquatic and near-water environments at Shuitangba. Our results indicate morphological similarities to both semi-aquatic and semi-fossorial modern mustelids. The limbs suggested unspecialized swimming abilities that were probably limited to paddling along the water surface. Multiple traits suggest semi-fossorial capabilities, possibly related to increased hip stabilization and postural maintenance during digging or intensive foraging. Features relating to semi-fossorial capability are consistently in the ranges of those of modern badgers. The combined functionality associated with both fore- and hind limb morphology was consistent with the more primitively generalized morphology of early lutrines. Many features of the limbs reveal the influence of body size that overwhelms or is indistinguishable from functional signals. Results suggest behaviors similar to those of the modern clawless otter Aonyx, which is more reliant on shoreline foraging, often involving digging, and terrestrial locomotion than other modern otters. The large size of S. melilutra likely provided advantages such as increased potential prey size range and the ability to utilize terrestrial resources, although it would have been more constrained by drag-related forces in the water.