Locomotion in ornithischian dinosaurs: an assessment using three-dimensional computational modelling.

Area of Science:

• Paleontology
• Biomechanics
• Evolutionary Biology

Background:

• Ornithischian dinosaurs evolved quadrupedalism independently multiple times from bipedal ancestors, a rare locomotory transition in tetrapod history.
• Previous studies documented osteological and myological changes but lacked biomechanical analysis of these transitions.
• Understanding the biomechanics of locomotion in extinct animals is crucial for reconstructing their evolutionary history.

Purpose of the Study:

• To systematically quantify changes in locomotor muscle function in bipedal and quadrupedal ornithischian dinosaurs.
• To examine similarities and differences in pelvic locomotor muscle moment arms among taxa and lineages.
• To investigate the influence of phylogeny versus functional anatomy on the evolution of quadrupedalism.

Main Methods:

• Utilized three-dimensional computational modeling of major pelvic locomotor muscle moment arms.
• Analyzed data from bipedal and quadrupedal ornithischian dinosaurs, including Thyreophora, Ornithopoda, and Marginocephalia.
• Compared moment arms across individual taxa, between locomotion types, and among major lineages.

Main Results:

• Identified lower moment arms in Chasmosaurus and Hypsilophodon, suggesting potentially poorer locomotor performance.
• Observed higher abductor moment arms in quadrupeds, likely due to wider body morphology.
• Found differences in extensor and medial rotator moment arms between bipeds and quadrupeds, possibly related to hindlimb posture and limb support.

Conclusions:

• Functional anatomy, rather than phylogeny, appears to be the primary driver of changes in muscle moment arms during the evolution of quadrupedalism in ornithischians.
• The independent evolution of quadrupedalism suggests that bipedal ancestry did not constrain functional pathways.
• Differences in moment arms may reflect adaptations to diverse environments and clade-specific behaviors.