CT Scanning.

Scans of Sauripterus, Eusthenopteron, Tiktaalik, and Polypterus were collected at The University of Chicago’s PaleoCT scanning facility using a GE Phoenix v|tome|x 240 kv/180 kv scanner (http://luo-lab.uchicago.edu/paleoCT.html). CT data were reconstructed with Phoenix Datos|x 2 (version 2.3.3) and imported to VGStudio Max (version 2.2) to be cropped and exported as a tiff stack. Neoceratodus and Acipenser were scanned at the Harvard University Center for Nanoscale Systems with the HMXST Micro-CT X-ray imaging system (model HMXST225). Scan settings are presented in SI Appendix, Table S1. CT data were segmented and visualized in Amira 6.5 (FEI Software). Movies were generated by first exporting animations as tiff stacks from Amira and then combining and editing movies using Adobe Premier (version 13.12).