Microfaunal remains from a modern east African raptor roost: patterning and implications for fossil bone scatters

Fish eagles (genus Haliaeetus) potentially have contributed the bones of th eir prey to many late Cenozoic concentrations of vertebrate microfossils. T o evaluate possible biases in the taxa and skeletal elements preserved in a ssemblages accumulated by fish eagles, which could affect paleoecological a nd evolutionary interpretations derived from Cenozoic microfaunal localitie s, a sample of 1883 bones accumulated by modern African fish eagles (H. vor cifer) was collected from a roost near Lake Turkana, Kenya. Characteristics of the bone assemblage include (1) taxonomic composition dominated by fish ; (2) diverse but small sized and ecologically restricted animals including inshore fish, aquatic birds, very small nocturnal mammals (which may have been contributed by other raptors), and small reptiles (possible predators on the roost); (3) poor survivorship for specific categories of skeletal el ements; (4) considerable bone breakage for all but the smallest animals; an d (5) a distinctive pattern of postcranial fragmentation for bird and mamma l elements. The fish eagle element profile has some similarities to those o f other diurnal raptors, but its cumulative signature can be distinguished from those of other bone accumulators and includes characteristics that wou ld also be manifest in fossil assemblages. Examination of fossil microfauna s from the Plio-Pleistocene localities of Kanapoi (Kenya), Inolelo (Tanzani a), and Olduvai Gorge (Tanzania) shows that the patterns of element preserv ation for Kanapoi and Inolelo do not match those of the Lake Turkana fish e agle roost. Nonetheless, some aspects of the Olduvai Gorge FLKN assemblage show taxonomic and skeletal similarites. In light of the selective choices of prey by fish eagles, the fauna recovered from Olduvai Gorge FLKN might n ot accurately reflect faunal diversity or patterns of abundance at this loc ality during the Pleistocene. Because fish eagles of the genus Haliaeetus a re found on three continents, have a fossil record extending to the Miocene , and deposit bones in a habitat conducive to preservation, the taxa preser ved at many other late Cenozoic microfaunal sites also might be biased. The refore, taphonomic profiles of late Cenozoic microfaunal assemblages should be compared against the taphonomic profiles typical of fish eagle roosts b efore faunal characterizations of sites are applied in analyses of paleoeco logical evolution.