Transforming turtle systematics: challenges, opportunities and the path ahead

Turtle systematics has a long history at the interface of palaeontology and phylogenetic methodology, supported by a rich fossil record, abundant extant comparative material, and a broadly stable molecular framework for relationships among living clades. Here we review the state of the art in turtle systematics and identify key outstanding problems that continue to limit phylogenetic resolution and macroevolutionary inference. These include the phylogenetic position of the turtle total group among amniotes and the placement of critical early stem taxa; the unclear divergence of crown turtles amid multiple Mesozoic clades of uncertain affinities; the cryptic or missing stem lineages of major crown clades and pronounced asymmetries in fossil representation among sister lineages; unresolved relationships surrounding the origins and early evolution of marine turtles; major post-Eocene knowledge gaps driven by collection bias; and persistent uncertainty regarding rates, modes, and drivers of morphological evolution across deep time. We argue that the next advances in turtle systematics will depend on strengthening the anatomical data pipeline through high-resolution imaging and consistent open-data practices, modernizing inference through wider adoption of Bayesian, total-evidence and time-calibrated phylogenetic frameworks, and increasing integration among museum revision, targeted fieldwork and interdisciplinary collaboration. Together, these steps provide a realistic roadmap for transforming turtle systematics into a more rigorous and broadly influential model system for vertebrate evolution.