A new mode of locomotion in mosasaurs: subaqueous flying inPlioplatecarpus marshi

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Abstract
The extinct marine reptiles of the family Mosasauridae supposedly all swam by means of lateral undulation of the body. This paper explores an alternative method of locomotion in some mosasaurs. The enormous pectoral girdle and highly unusual bones of the forelimb of Plioplatecarpus marshi are examined. Their mechanical implications, viewed in the context of the morphology of the animal as a whole, lead to the conclusion that P. marshi swam using subaqueous flight—a previously undescribed mode of swimming in mosasaurs. Paraxial swimming, the use of limbs in active propulsion, in Plioplatecarpus marshi adds yet another unusual characteristic to those distinctive features of the genus previously described in the literature, e.g., the large basioccipital foramen for the basilar artery, large parietal foramen, and huge quadrate. Lastly, it is proposed that paraxial locomotion in P. marshi may have been a special adaptation to a structurally complex environment and to more specific prey forms.