Comparative actualistic study hints at origins of alleged Miocene “coprolites” of Poland (supplementary movie : Tomographic animation of Miocene coprolite from Turów.avi)

Abstract

Excrement-shaped siderite masseshave been the subject of much controversy. They have been variously interpreted either as being coprolites, cololithes or pseudofossils created by mechanical deformation of plastic sediment. Here we reportexcrement-shaped ferruginous masses recovered from the Miocene of Turów mine in south-western Poland. Results of mineralogical, geochemical, petrographic and microtomographical analyses indicate that these masses consist of siderite and iron oxide rather than phosphate, and rarely contain recognizable food residues, which may suggest abiotic origins of these structures. On the other hand, evidence in support of a fecal origin include: (i) the presence of two distinct morphotypes differing in size and shape, (ii) the limited quantity of specimens, (iii) the presence of rare hair-like structures or coalified inclusions and (iv) the presence of rare fine striations on the surface. Importantly, comparative actualistic study of Recent vertebrate feces shows overall resemblance of the first morphotype (sausage-shaped with rare coalified debris) to excrements of testudinoid turtles (Testudinoidea), whose shell fragment was found in the investigated locality. The second morphotype (rounded to oval-shaped with hair-like structures), in turn, is similar to the feces of some snakes (Serpentes), the remains of which were noted in the Miocene of the neighborhood areas.