Taphonomic Completeness: A new metric for assessing fossil leaf preservation using the Spitsbergen Cenozoic fossil flora

Abstract

Leaves are the most common type of plant macrofossil found in the plant fossil record; however, comparing leaf preservation quality across plant groups, sites, and time periods is challenging. A new metric was devised that allowed the quality of leaf preservation to be quantitatively measured for leaf fossils preserved from different localities, timepoints and plant life forms, based on a suite of leaf traits. The metric produces a score between 6 (high quality preservation) and 0 (low quality preservation). The leaf traits visible in the Spitsbergen Cenozoic fossil flora were studied to analyse the effect of leaf traits on preservation potential. Non-metric multidimensional scaling indicated that plant life form strongly influenced the leaf traits preserved within the Spitsbergen fossil flora, while stratigraphy had a much weaker effect, indicating that depositional environment and climate influenced preservation less than plant life form. The ‘Taphonomic Completeness’ metric indicated that the gymnosperms and ferns had a significantly higher leaf preservation quality than the woody angiosperms and the herbaceous angiosperms, with the latter group having the lowest quality preservation overall. This result suggests that there may be a bias against the leaves of herbaceous species being preserved in the fossil record, which has implications for interpreting the plant fossil record and how paleo ecosystems functioned. Additionally, the development of this quantitative ‘Taphonomic Completeness’ metric provides a standardised approach that can be widely applied to fossil leaf assemblages from other sites and time periods, allowing robust, large-scale comparisons of preservation quality across fossil floras.