The Last Weaponized Arm: Macroevolutionary Trends of Megaraptorid Manual Claw I and Forelimb Integration in medium to large bodied non-avian theropods

Dataset and codes to perform macroeovlutionary analysis of "The Last Weaponized Arm: Macroevolutionary Trends of Megaraptorid Manual Claw I and Forelimb Integration in medium to large bodied non-avian theropods" Abstract From the Jurassic to the Cretaceous, most medium- to large-bodied non-avian theropods evolved toward predominantly head-driven predatory strategies. Megaraptorid dinosaurs represent a striking exception, retaining well-developed forelimbs and hypertrophied manual unguals that have been hypothesized as a key innovation within the clade. However, the macroevolutionary processes underlying the origin and specialization of the megaraptorid claw remain poorly understood. Here, we investigate the macroevolutionary trends of the megaraptorid manual claw by quantifying the shape and size of manual phalanx I-2 (= manual ungual I) using two-dimensional geometric morphometrics and phylogenetic comparative methods. Our results indicate that Megaraptoridae evolved toward a distinct adaptive optimum through a reconfiguration of allometric trajectories, in which a pronounced increase in claw size triggered shape modification. This innovation emerged following an early phase of rapid morphological divergence near the middle early Cretaceous boundary and was subsequently maintained under stabilizing selection throughout the Late Cretaceous, resulting in a highly canalized claw morphology. We further show that medium- to large-bodied non-avian theropods with well-developed forelimbs exhibit strong phylogenetic integration between distal and proximal forelimb elements. Despite this integration, the phalanx-I-2 and the ulna–radius complex evolved at substantially higher evolutionary rates than the humerus, indicating greater morphological evolvability in the ulna-radio and phalanx I-2. Convergence analyses reveal that, although claw size shows limited convergence among distantly related theropods, claw shape remains strongly clade-specific. These results highlight Megaraptoridae as the only medium- to large-bodied carnivorous theropod lineage to retain a highly specialized, forelimb-based predatory strategy until the end of the Cretaceous.