Morphology and composition of bone-bearing coprolites from the Late Permian Beaufort Group, Karoo Basin, South Africa

Abstract

Bone-bearing coprolites are fossilised faeces of carnivores and as such they provide important information about food webs and feeding strategies of the ancient ecosystem. With this aim we examined the morphology and composition of Late Permian bone-bearing coprolites from the Hoedemaker Member of the Teekloof Formation (Lower Beaufort Group) of the southern Karoo Basin, South Africa. Analysis of the size and shape of 150 specimens collected from this member resulted in the recognition of 5 different morphotypes. Each morphotype is matched to carnivorous taxa within the Tropidostoma Assemblage Zone fauna which biostratigraphically defines the Hoedemaker Member strata in this part of the basin. Morphotype 1 are long cylinder-shaped non-segmented faeces, or possible cololites, rounded at both ends and commonly contain complete small bones as well as bone fragments and were most likely produced by the large gorgonopsians Aelurognathus and Gorgonops torvus. Smaller, tubular Morphotype 2 coprolites are attributed to the smaller therocephalians and juvenile gorgonopsians. Rare double-pointed Morphotype 3 are similar in size and shape to scats of the modern wild cat and we attribute these to the medium-sized gorgonopsians Cyonosaurus and Lycaenops or possibly juveniles of the large gorgonopsian species. Morphotype 4 coprolites are bullet-shaped and are interpreted as disaggregated portions of compound faeces. They are the most common coprolite found in the Hoedemaker mudrocks and are also attributed to small and medium-sized therocephalians and gorgonopsians. Morphotype 5 are rare flattened disc-shaped coprolites that contain abundant fish-scales and are linked to the temnospondyl, Rhinesuchus africanus, the only known piscivore from the Tropidostoma assemblage. Analyses of the microstructure of the bone inclusions within morphotypes 1–4 revealed two distinct tissue types. Bone tissue type A consists of highly vascularised, rapidly-forming bone interpreted as being that of very young perinatal and/or early juvenile therapsids, probably dicynodonts. Judging by the relative abundance of their body fossils, the herbivorous dicynodonts were by far the most abundant tetrapods in the Tropidostoma Assemblage Zone and it is probably that their young, both embryonic and neonatal juveniles, were commonly preyed upon. Some of the larger carnivores swallowed small prey whole, or with minimal mastication, allowing complete limbs to pass through the digestive tract in articulation. Inclusions of bone tissue type B, which consists of poorly-vascularised, slow-growing bone, are interpreted to be the skeletal remains of small parareptiles.