Fossils, Phylogenies, Origins Quests and the Crown - The Problem with snakes

CALDWELL, MICHAEL WAYNE; LEE, MICHAEL S. Y.; NYDAM, RANDALL L.; FERNANDO FABIO GARBEROGLIO; APESTEGUÍA, SEBASTIÁN; ALESSANDRO PALCI; SIMÕES, TIAGO R.; AARON LEBLANC; MARK J POWERS; CATIE STRONG

New York

Simposio; Camp '23: Celebrating 100 Years of Charles L. Camp''s Classification of the Lizards; 2023

American Museum of Natural History

Macroevolutionary-scale change can lead to dramatic morphological/molecular divergence between a studied lineage and its sister clade. Snakes are an excellent example of such divergence as compared to other lizard lineages. Nearly two centuries of study have accumulated a massive dataset for fossil and living crown and stem lizards inclusive of snakes (e.g., morphology, whole genomes, transcriptomes, ecologies, behaviors, biogeography, biostratigraphy, etc.). Despite the quality and quantity of these data, consensus remains elusive on foundational knowledge claims such as: 1) Ingroup membership of stem and crown group fossil taxa, their identity, and clade relationships (e.g., †Tetrapodophis, †Parviraptor, Scolecophidians); 2) Sister group relationships of pan-snakes with all other lizards (e.g., Pythonomorpha or Krypteia); and 3) Origins scenarios (e.g., the supposed polarity of “burrowing” vs. “aquatic origins”). As a way forward, we consider that current data are sufficient for reasonable consensus on relative hypotheses of crown and stem snake ingroup and sister group relationships. To reach this consensus, we argue for the use of all lines of evidence and all analytical methods in the testing of that evidence. We recognize that analysis of only the modern crown is unlikely to produce sister group relationships that can address deep node evolution or higher-order questions (e.g., origins scenarios) in the absence of fossil taxa. Further, we propose that origins scenarios be explicitly rooted in patterns of sister group relationships only, because ingroup patterns are uninformative; any other scenario proposals remain as non-empirical as are claims for the ‘discovery’ of ancestors.