PHYLOGENETIC LAGERSTÄTTEN: A NEW TYPE OF LAGERSTÄTTEN RECOGNIZED FROM UPPER CRETACEOUS AEOLIAN DEPOSITS OF THE GOBI DESERT

Localities that contain exceptionally preserved fossils (i.e., lagerstätten) yield unparalleled details concerning ancient organisms’ anatomy, physiology, ecology, behavior, and surrounding ecosystems. These taphonomic anomalies, which occur mostly in low-energy and/or anoxic/hypoxic depositional settings in deep marine, coastal lagoonal, and lacustrine environments, often hold an outsized influence over our understanding of regional and global biodiversity patterns in the rock record (i.e., the “lagerstätten effect”). While the “lagerstätten effect” is widely recognized as a broad-scale paleobiological pattern, parameterizing the extent of this influence has been historically challenging. In this study, we use an established fossil completeness metric to quantify the “lagerstätten effect” on the amount of phylogenetic information available in the fossil record of squamates (e.g., lizards, snakes, amphisbaenians, and mosasaurs). Using published descriptions of 797 fossil squamate species and 16,983 corresponding specimens from 469 localities spanning 242 million years of the group’s evolutionary history, we find that, in addition to traditional lagerstätten deposits (from marine chalks, hypersaline lagoons, lacustrine environments), the aeolian deposits of the Late Cretaceous Gobi Desert of Mongolia and China preserve exceptionally complete squamate anatomical and phylogenetic data. Unlike traditional lagerstätten deposits, the extraordinarily diverse Gobi fossil squamate record has an anomalously large influence on fossil record completeness on continental/global scales compared to all other depositional settings containing squamate fossils. The recognition of “Phylogenetic-lagerstätten” expands the definition of exceptional preservation beyond strictly taphonomic constraints, and invites further assessments of the availability of important evolutionary and ecological information in the rock record amongst other fossil groups.