THE ABILITY OF MOSASAURS TO PRODUCE UNIQUE PUNCTURE MARKS ON AMMONITE SHELLS

The purpose of this study was to test the claim that certain types of unique puncture marks on ammonite shells could be produced by mosasaur bites. These unique puncture marks are double puncture marks, which are two adjacent holes set within the same indented rim, and puncture marks on only one flank of an ammonite’s shell. The common interpretation of puncture marks in ammonite shells is that they were bite marks from mosasaurs, however, this idea has been challenged, in part with the claim that these two unique types of puncture marks could not be produced by a mosasaur’s bite. To answer this question, this study was divided into two parts. The first part involved measuring the position and orientation of teeth from 202 mosasaur jaw bones and jaw fragments to determine if any had teeth that were crooked enough that they would have tips that were adjacent to one another. Additionally, the distribution and variety of tooth orientations were compared among several mosasaur genera. These comparisons were accomplished by performing univariate statistics using the PAST software package. The second part of this study was to build a replica of a mosasaur skull and use it to crush modern Nautilus shells, to see if puncture marks on only one side of a shell could be experimentally produced. The mosasaur Prognathodon overtoni was used as the model for this replica as this genus is thought to have been the mosasaur most likely responsible for the puncture marks on ammonite shells. The skull replica was made of steel and was used to crush twenty-two Nautilus shells. The crushed shells were then examined and compared to ammonite puncture marks and previous tests in which Nautilus shells were crushed. The results of this study showed that there are a range of tooth orientations in mosasaurs and that in rare cases, adjacent teeth can be found whose tips are close enough to have produced double puncture marks. In addition, the skull replica succeeded in producing puncture marks restricted to one flank of a Nautilus shell’s phragmocone when a partial bite force was applied. These results strengthen the claim that mosasaurs were responsible for the puncture marks found on ammonite shells.