Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution

Therizinosaurs are a group of herbivorous theropod dinosaurs from the
Cretaceous of North America and Asia, best known for their iconically large
and elongate manual claws. However, among Therizinosauria, ungual morphology is highly variable, reflecting a general trend found in derived
theropod dinosaurs (Maniraptoriformes). A combined approach of shape
analysis to characterize changes in manual ungual morphology across theropods and finite-element analysis to assess the biomechanical properties of
different ungual shapes in therizinosaurs reveals a functional diversity related
to ungual morphology. While some therizinosaur taxa used their claws in a
generalist fashion, other taxa were functionally adapted to use the claws as
grasping hooks during foraging. Results further indicate that maniraptoriform
dinosaurs deviated from the plesiomorphic theropod ungual morphology
resulting in increased functional diversity. This trend parallels modifications
of the cranial skeleton in derived theropods in response to dietary adaptation,
suggesting that dietary diversification was a major driver for morphological
and functional disparity in theropod evolution.