Elasmosaur (Reptilia: Sauropterygia) neck flexibility: implications for feeding strategies.

Elasmosaurs were extremely long-necked, aquatic reptiles that used four flippers for locomotion. Their distinctive long neck distinguishes them from all other Mesozoic forms, yet the potential uses and constraints of this structure are poorly understood, particularly with regard to feeding. Several associated series of elasmosaurian cervical vertebrae were used to measure ranges of potential flexion. Two-dimensional models, based on a complete specimen of the Late Cretaceous elasmosaur Aphrosaurus furlongi, were created to measure mobility in both vertical and horizontal planes. Accuracy of the models was assessed through comparative analyses with currently extant vertebrate analogues (e.g. snake, turtle, seal). Results suggest that the elasmosaurian neck was capable of a 75-177 degrees ventral, 87-155 degrees dorsal, and 94-176 degrees lateral range of movement depending upon the thickness of cartilage reconstructed between each vertebra. Neck postures such as a 'swan-like' S-shape are shown to be implausible because they require >360 degrees vertical flexion. However, maintenance of a straight neck while swimming, together with considerable lateral and/or ventral movement during prey capture and feeding are feasible.