Stiffening in the carpus of Prosantorhinus germanicus (Perissodactyla, Rhinocerotidae) from Sandelzhausen (Germany)

Abstract

AbstractProsantorhinusgermanicus is a small, short-legged, teleoceratine rhino from the Miocene of Sandelzhausen (Bavaria, Germany). P.germanicus shows a high variation in some of its carpal bones. A unique modification of the articulation of Intermedium and Carpale 4 is described here. Special emphasis is given to additional articulation facets at the palmar processes of both bones. These additional contacts, working as stop facets, are unique among rhinos and restrict the flexion of the mid-carpal joint. Some individuals show these additional facets which prohibit the flexion within the wrist and therefore stiffen the carpus. Carpale 4 specimens without the additional facets show knob-like structures instead. These knobs are most likely precursory structures of those facets and the facets are fully developed in heavier males. A skeletal sexual dimorphism is not visible in the sample as all bones are in the same size range. The wrist stiffening in the mid-carpal joint supports a greater bodyweight and therefore could coincide with P.germanicus as a proposed dwarfed rhinoceros species. The stiffening can also be interpreted in favor of a semiaquatic mode of life. The stiffened carpus is more resistant against injuries while walking on muddy grounds in a wet environment.