FIGURE 1. Simplified family-level phylogenetic hypothesis of Lamniformes showing all extant clades and †Otodontidae (A: dagger [†] indicates extinct), and silhouette depiction of fossil vertebral column of †Otodus megalodon (B). A, Current understanding of lamniform phylogeny demonstrating that a large portion of the phylogenetic tree remains unresolved due to conflicting results based on various molecular and morphological studies (Sternes et al., 2023 and references therein); although the placement of †Otodontidae is tentative and other extinct families are not depicted in this tree, the main point of this illustration is to demonstrate that †Otodontidae lies outside of Lamnidae (both clades highlighted in bold letters) where clades containing one or more species with regional endothermy (indicated by an asterisk [*]) do not share an immediate common ancestry (Sternes et al., 2023). B, Reconstructed vertebral column and its total measured length by Cooper et al. (2022) based on an incomplete associated vertebral set from the Miocene of Belgium; this specific specimen (IRSNB P 9893) was previously estimated to have come from an individual that measured 9.2 m in total length, including the head and caudal fin (Gottfried et al., 1996) based on the modern white shark, not accounted for by Cooper et al. (2022).
FIGURE 2. The distribution of vertebral diameters throughout each vertebral column, where vertebral number ‘1’ represents the anterior-most centrum in each specimen. A, Graph based on Cooper et al.’s (2022) Data S1 for the vertebral column of †Otodus megalodon from the Miocene of Belgium (IRSNB P 9893), where the vertebral column is most certainly incomplete and the vertebral numbers do not necessarily reflect the original anatomical sequence (grey plots represent significantly damaged vertebrae). B, Graph based on CT-scanned data of an extant white shark (Carcharodon carcharias) specimen (LACM 43805-1), where the vertebral column is complete and the vertebral numbers reflect the anatomical sequence.
FIGURE 3. Photographic (*) and CT images (**) of preserved specimens of extant white shark (Carcharodon carcharias) and salmon shark (Lamna ditropis). A, Complete specimen of 126-cm-TL male C. carcharias caught off central California, USA (LACM 43805-1): from top to bottom, external body* and skeleton** in left lateral view and external body** and skeleton** in ventral view. B, Complete specimen of 151 cm TL male L. ditropis caught off central California (FMNH 117475): from top to bottom, external body* and skeleton** in left lateral view and external body* and skeleton** in dorsal view. C, Head specimen of estimated 271-cm-TL male C. carcharias caught off southern Florida, USA (FMNH 38335): from top to bottom, external head* and cranial skeleton** in left lateral view and external head* and cranial skeleton** in dorsal view. All scale bars equal 10 cm.
FIGURE 4. Previous and new schematic interpretations of †Otodus megalodon body form. A dark grey silhouette depicting the previously reconstructed †O. megalodon body form by Cooper et al. (2022) based on the extant white shark, superimposing a light grey outline showing the newly interpreted body form of †O. megalodon which is more elongated than the extant white shark. Note: it must be emphasized that this illustration should be strictly regarded as schematic as the exact extent of body elongation, the shape of the head, and the morphology and positions of the fins remain unknown based on the present fossil record.
