Abstract
Fossil jaw bones and tooth plate batteries from Diodontidae are relatively abundant in shallow marine deposits along the southeastern Atlantic and Gulf Coastal Plains of the U.S.A. Two tooth plate batteries of Diodontidae (Tetraodontiformes) were recently collected from a submerged lag deposit associated with hardbottom limestone scarps and clay exposures of the Pliocene Yorktown Formation on the continental shelf of Onslow Bay, North Carolina. These fossil specimens represent the largest known tooth plate batteries of Diodontidae ever reported globally and measure about 71 mm in maximum width. Micro-computed tomography scans confirm the presence of at least 26 enameloid dental sheets in both specimens. Comparative analyses with extant Diodon spp. and Chilomycterus spp. show that the Onslow Bay tooth plate batteries are most similar to those of Chilomycterus reticulatus although they would have derived from individuals exceeding 1.5 m in standard length. However, direct comparison of tooth plate batteries from large extant specimens similar to 500 mm in length to the Onslow Bay fossil specimens shows that they have an equal or greater number of tooth plates, but are only about half as large. This noticeable size difference suggests the fossil tooth plate batteries may be from a separate taxon, represent exceptionally large, old individuals, or reflect increased body sizes in marine vertebrates due to environmental and climatic factors during the late Cenozoic.