Abstract
A comparative study of rostral morphology of extant mackerel sharks (Lamniformes, Lamnidae) is presented. Based oncomputed tomography (CT) scans of fresh specimens, 3D reconstructions, dried museum chondrocrania and the availableliterature, detailed morphological descriptions of the rostral cartilages are provided for the type species of all three extantlamnid genera, namely Carcharodon carcharias (Linnaeus, 1758), Isurus oxyrinchus Rafinesque, 1810 and Lamna nasus(Bonnaterre, 1788), and compared with those of I. paucus Guitart Manday, 1966 and L. ditropis Hubbs & Follett, 1947.Despite intraspecific variation, the rostral cartilages of all extant lamnids present significant differences that allow genus-and species-level identification, which is especially of use to identify fossil rostral nodes of these particular taxa. The maindifferences were found to be in overall calcification of the rostrum (Lamna > Isurus > Carcharodon), general configura-tion of the rostral open space, position of the base of the lateral rostral cartilages, (non-)abutting lateral cartilages, (absent)rostral keels and shape of the rostral node. In cross section, the base of the rostral node is rounded in Lamna, Y-shaped in Isurus and uncalcified in juvenile and subadult Carcharodon (tesserae absent).
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