Paleoecology and Paleobiogeography of the Baynunah Fauna

Abstract

The Baynunah Formation has produced a diverse assemblage of plant, invertebrate, and vertebrate fossils that provides the only window onto the terrestrial late Miocene record of the Arabian Peninsula. This chapter reviews and revises the age, biogeography, environments, and ecology of the Baynunah fauna. Biochronological estimates indicate an age of between 8 and 6 Ma, with several indicators favoring the older end of this range. Paleomagnetostratigraphic correlation more precisely favors an age between ~7.7 and 7.0 Ma, and a maximum duration of less than 720 kyr. Rough estimates of sedimentation rate based on assumptions of precessional control of carbonate formation in the upper parts of the Baynunah Formation here tentatively suggest a duration of ~250 kyr. The most common body fossils found are remains of fish (catfish and cichlids), turtles, and crocodiles, indicating the presence of a large but shallow and slow-moving river. A diverse community of mammalian herbivores subsisted along the banks of the Baynunah River, ranging from rodents to proboscideans, and carnivores included a mustelid, hyaenids, and a saber-toothed felid. The fauna, in conjunction with stable isotope data, indicates the presence of a highly seasonal semi-arid environment, characterized by open habitats with C4 grasslands and trees. The most common large mammals are equids, bovids, hippopotamids, and proboscideans. The high abundance of equids in the Baynunah Formation is unlike African late Miocene assemblages and more like those from the eastern Mediterranean, but the underlying ecological reasons for this are not clear. Baynunah species indicate dominantly African biogeographic influences combined with Eurasian elements. Genus-level comparisons indicate that the Baynunah fauna was part of the widespread Old World Savanna Paleobiome that covered much of Africa and Eurasia during the late Miocene. Food web (trophic network) analyses of the large mammals indicate a highly connected community similar to that of the modern Serengeti. Among the largest Baynunah herbivores (giraffids, proboscideans), only juveniles would have been vulnerable to predation, even under scenarios of cooperative hunting. In contrast to the fluvial Baynunah sediments, the underlying Shuwaihat Formation indicates arid conditions, and provides some of the oldest evidence for desertification in the Saharo-Arabian desert belt.