A BLUEPRINT FOR PALEOBIOLOGICAL INQUIRY AT THE INTERSECTION OF TAPHONOMY AND PHYLOGENETICS

Although much work has been devoted to characterizing patterns of fossil record bias, less attention has been paid to whether the phylogenetic information retained in sampled fossils is also systematically biased. In essence, we need to address not just what an incomplete fossil record looks like, but also whether it can be trusted within an evolutionary framework. Here, we present a phylogenetic approach that addresses three crucial questions in assessing the quality of the >242-million-year fossil record of squamates (e.g., lizards, snakes, mosasaurs). Key Question 1: How does fossil incompleteness affect phylogenetic information content in the fossil record? We use an established completeness metric to show that the average fossil squamate species preserves less than 20% of the total characters that can be scored in a phylogenetic dataset. To test if this pattern is rooted in anatomical biases in the fossil record, we also use a dataset of 6,585 specimens and 14,417 skeletal elements to show that marginal tooth-bearing bones and vertebrae are significantly overrepresented as fossils. Key Question 2: Does an anatomically biased squamate fossil record still retain reliable phylogenetic information? Using parsimony and model-based phylogenetic comparative methods, we show that the parts of the squamate skeleton most ubiquitously preserved in the fossil record retain the same level of phylogenetic signal as other rarer parts of the skeleton. These results imply that we can more confidently incorporate incomplete fossils into phylogenetic analyses. Key Question 3: What is the influence of lagerstätten on phylogenetic information content in the fossil record? Unexpectedly, aeolian deposits of the Late Cretaceous Gobi Desert of Mongolia and China preserve an exceptionally complete and phylogenetically diverse lizard assemblage, such that it exerts anomalously high influence on the deep-time structure of squamate evolutionary relationships. These results offer a novel, phylogenetic view on the macroevolutionary effects of lagerstätten in the fossil record. In sum, this work at a critical but largely ignored intersection of paleobiological inquiry provides fresh insight on age-old patterns of fossil record bias, while laying the foundation for future integrative and comparative studies.