Supplementary Information for: Drivers and mechanisms of convergent forelimb reduction in non-avian theropod dinosaurs.

This study utilises a newly developed methodology to quantify cranial robusticity in theropod dinosaurs and uses this method to test the relationship between cranial robusticity and reduced forelimbs across theropod evolution. We also incorporate linear measurements of the skull and forelimb, and body mass estimates into our analyses. Our results show that reduced forelimbs relative to the skull occurred in at least 5 non-avian theropod lineages. Accounting for body mass indicates that skull robusticity and skull:forelimb are tightly correlated. We postulate that this relationship is the result of a predominant use of the skull in prey-capture and processing in theropods which evolved larger body masses to capture larger prey items. The results of this study may be supplemented by future studies of geometric morphometrics and/or finite element analyses and combined with the results of the cranial robusticity method developed in this study.