A REVIEW AND MODERN FIELD STUDY OF PRESERVATIONAL BIASES AFFECTING THE AVIAN FOSSIL RECORD

The most widely recognized avian fossil locality is the Jurassic limestone of Solnhofen, Germany, where Archaeopteryx was discovered. Many studies have focused on the carbonate deposits of the Solnhofen and their effectiveness in preserving the primitive bird’s bones. However, little attention has concentrated on the range of depositional environments in which avian fossils are found and the taphonomic biases that may be influencing our understanding of the avian record.

To address these understudied aspects, we reviewed 130 scientific articles describing avian remains from the Cretaceous to Recent and found that the majority of specimens are preserved in siliciclastic rather than carbonate environments. Shallow marine depositional settings appear to preserve the most remains, indicating a possible bias toward coastal marine species. Additionally, climate, sex, and age have not been carefully evaluated as sources of taphonomic bias within the avian fossil record.

Based on the results of our review, we conducted yearlong taphonomic studies to investigate the impact of depositional environment (including climate and scavenger activity), age, and sex on avian carcass destruction and bone weathering in two lithologically distinct regions. A total of 24 freshly dead chicken carcasses and 80 femur and tibiotarsus bone pieces were deployed at the siliciclastic (Sapelo Island, Georgia) and carbonate (Key Largo, Florida) sites. At both locations, scavengers provided the most substantial impact on carcass disarticulation and loss. Soft tissue decay was more rapid at the siliciclastic site, but leg bone mean mass loss at the siliciclastic site (mean of 3.12g) was less than the mean mass loss at the carbonate site (mean of 5.36g; p-value of 0.01). Additionally, a greater number of leg bones were preserved in the siliciclastic site (38 compared to 16). At both locations, adult male bones were preserved more frequently and in better condition than other sex and age groups, indicating a possible sex- and age-based bias in the avian fossil record.