Abstract

New material of Halisaurus platyspondylus allows description of the snout elements for the first time. The specimen was recovered from the Late Maastrichtian New Egypt Formation in Gloucester County, New Jersey. Portions of the frontal, both prefrontals, and the left quadrate are preserved and are nearly identical to the USNM H. platyspondylus specimen. It can be excluded from H. arambourgi by the extensive sutural contact of the prefrontal and ventral frontal. The new material demonstrates development of a relatively broad short skull in H. platyspondylus as in H. arambourgi, and articulations of constituent elements reveal a strong, akinetic snout. This stands in contrast to the elongate, narrow skulls of more basal halisaurines such as Eonatator. This pattern, also seen in derived members of other mosasaurid subfamilies, suggests a shift from high velocity jaw closure for prey acquisition in more basal forms to robust skulls optimized for increased bite force in some more derived forms.

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