Meeting Abstract
Mosasaurs are charismatic marine squamates that were prominent global predators in the Late Cretaceous. Two major clades include most derived mosasaur taxa: Mosasaurinae (Mosasaurus, Plotosaurus, Clidastes) and Russellosaurina (Tylosaurus, Platecarpus, Tethysaurus). With regards to swimming mechanics, most functional analyses have modeled mosasaurs as lateral undulators with most or all propulsion being generated by the tail. However, the large pectoral elements might have been capable of providing significant propulsion and additionally had a major control on the width of the chest cavity, which would impact propulsion due to the resultant drag forces. Mosasaur chest cavity reconstructions are challenging due to the girdle elements and rib cage having cartilaginous extensions which rarely preserve. Most mosasaur pectoral reconstructions are based on conjecture and tend to imply a wider space between the coracoids. Here we present a mosasaur model suggesting three primary trade-offs affected by pectoral breadth: muscle volume and power, drag, and fast start efficiency. Using Plotosaurus as an example, narrowing the pectoral width by 10% of some if its wider estimates reduces the muscle power of the forelimbs, but also results in 2.5 times less drag on the body, and an increased fast start efficiency. Regardless of the pectoral breadth, however, the sternum of Plotosaurus is quite craniocaudally elongate and not affected by chest cavity width, therefore we estimate that Plotosaurus still had significant retraction capacity at the shoulder and this is supported by the shape of the glenoid fossa. This suggests that large derived mosasaurs may have been capable of utilizing a dual caudal and forelimb propulsion system not seen in extant marine tetrapods.
