Environmental information in a recent bone assemblage: roles of taphonomicprocesses and ecological change

Taphonomic processes have the potential to obscure or enhance original asso ciations between paleoenvironments and organisms through selective destruct ion, post-mortem transport, and time-averaging. Ecological changes through time in habitat utilization by living organisms also can blur distinctions between faunas or floras associated with particular habitats. If taphonomic processes affect habitat specificity in bone assemblages, then this should be revealed in time sequences of remains from particular habitats. We anal yzed Recent surface bone in six habitats of Amboseli National Park, Kenya, to determine whether taxonomic composition varied with the degree of taphon omic alteration las indicated by bent: weathering stage). The dataset consi sted of 1362 separate bone occurrences classified according to their state of weathering. These bone occurrences represented 27 mammalian taxa from bu sh, openwood, densewood, lakebed, plains, and swamp habitats. The distincti veness of the bone assemblages was measured by the quantified Dice coeffici ent, which accounts for both the presence or absence of taxa and their rela tive proportions. The differences among the weathering stage subsamples wer e compared with known environmental changes at Amboseli over the estimated time period of bone accumulation (15-25 years). Habitat distinctiveness bas ed on the bunt: assemblages was lower in subsets with higher weathering sta ges, although not all habitats showed this to the same degree, and open hab itats (e.g., plains, lakebed) generally remained distinct from closed habit ats (densewood, bush). The greatest change in the similarity among habitats occurred between weathering stages 2 and 3, which corresponds to deaths be tween 1969 and 1973, a period of woodland retreat and expansion of open hab itats in the park. We attribute the loss of environmental resolution in the weathered bone subsamples primarily to time-averaging and the shifting of habitat boundaries. The time period represented by these bone assemblages i s small compared to the time-averaged paleosol or land surface assemblages in the fossil record, suggesting that ecological fluctuations can compromis e interpretations of habitat heterogeneity in fossil assemblages. Our study indicates that it is probably the magnitude of ecological changes rather t han time per se that limits resolution. If distinct paleohabitats can be su pported based on time-averaged fossil evidence, however, this implies that ecological fluctuations were not sufficient to homogenize these distinction s over the period of time-averaging. (C) 1999 Elsevier Science B.V. All rig hts reserved.