Ada J. Klinkhamer, Heinrich Mallison, Stephen F. Poropat, George H.K. Sinapius & Stephen Wroe (2018)
Threeâdimensional musculoskeletal modelling of the sauropodomorph hind limb: the effect of postural change on muscle leverage.
The Anatomical Record (advance online publication)
The biomechanical constraints for life at massive size can be directly observed in the evolutionary history of sauropodomorph dinosaurs. Members of this lineage underwent a number of major postural transitions as they increased in size from relatively small bipedal dinosaurs to massive titanosaurs that include the largest terrestrial animals of all time. To better understand the impact of gigantic size on the biomechanics of sauropods, we used threeâdimensional musculoskeletal modelling to investigate how hind limb musculature was affected, firstly by the development of a quadrupedal stance from a bipedal one, and later in the transition from a narrowâgauge to a wideâgauge stance. Muscle moment arms were measured in four sauropodomorph taxa: the bipedal basal sauropodomorph Plateosaurus engelhardti, the narrowâgauge diplodocid Diplodocus carnegii, the titanosauriform Giraffatitan brancai, and the wideâgauge titanosaur Diamantinasaurus matildae. In Plateosaurus, low moment arm leverage in the hip extensors and knee flexors and extensors was observed suggesting high velocity movement for fast locomotion. A reduction in hip extensor leverage in Diamantinasaurus was found which suggests a reduced role for the hind limb in forward propulsion in titanosaurs. An increase in overall hip adductor leverage and leverage of adductors 1 and 2 in Diamantinasaurus, compared with other taxa studied, might relate to the development of a wideâgauge stance. High knee flexorâextensor leverage in Giraffatitan but not Diamantinasaurus partially refutes the idea that broader femoral condyles in titanosauriforms increased knee torque production capabilities. Sauropodomorph postural changes clearly had an impact on the function and leverage of hind limb muscles.
P. Martin Sander & Jens N.Lallensack (2018)
Dinosaurs: Four Legs Good, Two Legs Bad.
Current Biology 28(19): PR1160-R1163
The quadrupedal Sauropods -- the biggest dinosaurs to walk the Earth -- evolved from bipedal ancestors. Two new early sauropodomorphs from South Africa and Argentina indicate that very large, flexed-limbed sauropodomorphs coexisted with early columnar-limbed sauropods for 20 million years.