Palaeoclimate, environmental factors, and bird body size: A multivariable analysis of avian fossil preservation

For this study, we abstracted data on 693 avian fossil specimens from 398 publications to determine preservation biases in the avian fossil record. Our results show that dissociated wing and leg bones are the most commonly preserved avian skeletal elements and they are preferentially preserved in environments of high erosion and reworking potential—notably continental shelf marine environments. Using bivariate descriptive displays and multivariable regression analyses, we investigated the trends and associations between well-preserved avian specimens (i.e., fully- or partially-articulated) and a variety of taphonomic factors, including depositional environment, body size, and palaeoclimate. The regression model shows that well-preserved specimens are independently associated with depositional environments of low reworking potential commensurate with low energy systems, warm and humid climates, and smaller bird body size. Our results also indicate that fossils of smaller birds are less common than those of larger birds, but they are more often well-preserved. Bivariate analyses revealed that five times as many articulated specimens are found in warm and humid climates as in cool or dry climates, and this association persists in the multivariable regression model. Warm climates, the strongest predictor of better skeletal preservation, may be underestimated as a source of taphonomic bias in the avian fossil record, possibly because of the indirect nature of climate effects. Rapid burial events, such as volcanic ash accumulations and mudflows, are recognised for their influence on preservation, but climate-related storm events may be more important to avian taphonomy than previously understood. Our analyses indicate that geologic processes leading to high quality preservation of avian fossils are closely associated with climate. Additional studies, based both on fossils and modern taphonomic experiments, with improved collection of climate-related data, are needed to advance our understanding of avian taphonomy.