MODERN AVIAN BONE TAPHONOMY AT THE MICROSCOPIC LEVEL: HISTOMORPHOLOGICAL AND COMPOSITIONAL ANALYSIS

Modern taphonomic studies of bird bones are crucial for a clear interpretation of the avian fossil record. Previous studies have documented rates of decay and disarticulation of avian carcasses and also established rates for bone weathering within a limited range of depositional environments. However, microscopic-level analyses of histomorphological and compositional (i.e., mineralogical) changes to bird bones in modern taphonomic experiments have been lacking. This study employed backscattered electron (BSE) imaging and wavelength-dispersive spectrometry (WDS) to determine if histomorphological and compositional changes could be detected in weathered avian leg (femora and tibiotarsi) bones, exposed over 12 months in varying coastal environments in Georgia and Florida, when compared to unexposed controls. Because female bones may be more susceptible to taphonomic degradation than male bones, differences in the weathering of male and female bones were of special interest.

Analysis of BSE images showed that the subperiosteal bone layer was lost from all specimens regardless of sex, but the medullary tissue of reproducing females tended to be preserved and to protect the endosteal layer from bacterial bioerosion. WDS results indicated no difference between control and exposed bones in terms of alteration in mineral composition, regardless of sex or bone region (periosteal, medial, or endosteal cortical layers). WDS results suggested that the distribution of calcium and phosphate in the bone regions differed based on gender: male bones had higher Ca/P ratios in the periosteal layer; female bones had higher Ca/P ratios in the endosteal layer. These differences could influence dissolution and recrystallization. Overall, male bones were in better taphonomic condition than female bones, despite the presence of medullary tissue, suggesting a possible gender-based bias in the avian fossil record.