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Known occurrences of Dichichthys species in the Indo–West Pacific. Pink star denotes D. albimarginatus holotype, and pink circle denotes the Papua New Guinea specimen assigned to D. cf. albimarginatus; white star denotes the holotype, and white circle a live individual of D. bigus; orange star denotes the holotype; orange circles for other specimens examined and orange triangle other records not examined of D. melanobranchus; red star denotes holotype and red circle photographic evidence of D. nigripalatum; yellow star denotes the holotype and yellow circles paratypes of D. satoi n. sp.; green circle denotes live individuals of D. sp. (Image © Google 2023, SIO, NOAA, U.S. Navy, NGA, GEBCO).
Source publication
The genus Dichichthys was resurrected for five species previously allocated to the genus Parmaturus in the family Pentanchidae. Supraorbital crests on the chondrocranium distinguish Dichichthys from Parmaturus and other members of the family Pentanchidae. A new family, Dichichthyidae, has been proposed to contain Dichichthys. The sequence of the NA...
Citations
... Furthermore, to identify lamniform-specific trends in body size and proportions, we examined taxa from a range of extant sharks in other clades. In all, our dataset comprises 145 extant species in nine orders (including Lamniformes), 38 families, and 103 genera (Appendix 1; taxonomy and classification follow Ebert et al., 2021, except Dichichthys bigus [Dichichthyidae], which is based on White et al., 2024). In addition, our dataset includes 20 species of Jurassic and Cretaceous (extinct) neoselachians known from complete specimens (i.e., only those fully articulated axial skeletons with preserved body outlines, particularly their head and caudal fin), including four lamniform genera, based on published illustrations of specimens (Appendix 2). ...
... We compiled the neurocranium length (NL; i.e., anteroposterior distance of the skull between the rostral tip and occipital centrum) data from illustrations in the literature in which scale bars and specimen orientation allowed linear calculation of NL as well as radiographic (X-ray or computed tomography) images or neurocranial specimens from non-embryonic shark individuals, each with a known TL. Specifically, we gathered data from the following papers: White (1895), Cappetta (1980), Compagno (1988Compagno ( , 1990, Duffin (1988), Shirai (1992), Goto (2001), Kriwet and Klug (2004), Thies and Leidner (2011), Mollen et al. (2012Mollen et al. ( , 2016, Denton et al. (2018), Weigmann et al. (2020), Pfeil (2021), Vullo et al. (2021Vullo et al. ( , 2024, Jambura et al. (2023), Staggl et al. (2023), Viana and Soares (2023), and White et al. (2024) (Appendices 1-2; note that incomplete fossil specimens or privately owned specimens are not included: e.g., many specimens in Pfeil, 2021). Extant individuals without TL or NL data as well as fossil specimens with missing body parts or unmeasurable TL or NL were not included. ...
... The radiographically examined samples and physical neurocranial specimens used in this study are housed in the following 14 institutions: Academy of Natural Sciences of Drexel University (Ebert et al., 2021;White et al., 2024), the examined taxa account for 96.3% of all known extant shark genera. The remaining 3.7% of the genera not included in this study are: Akheilos (Carcharhiniformes: Scyliorhinidae), Euprotomicroides (Squaliformes: Dalatiidae), Nebrius (Orectolobiformes: Ginglymostomatidae), and Scymnodon (Squaliformes: Somniosidae). ...
Otodus megalodon (Lamniformes: Otodontidae) is an iconic Neogene shark, but the lack of well-preserved skeletons has hampered our understanding of various aspects of its biology. Here, we reassess some of its biological properties using a new approach, based on known vertebral specimens of O. megalodon and 165 species of extinct and extant neoselachian sharks across ten orders. Using the median neurocranial and caudal fin proportions relative to the trunk proportion among non-mitsukurinid/non-alopiid lamniforms, we show that O. megalodon could have had a slender body and possibly reached about 24.3 m in length. Allometric considerations indicate that a stout body plan like the extant white shark (Carcharodon carcharias) for O. megalodon could have incurred excessive hydrodynamic costs, further supporting the interpretation that O. megalodon likely had a slenderer body than C. carcharias. A 24.3-m-long O. megalodon may have weighed around 94 t, with an estimated cruising speed of 2.1–3.5 km h⁻¹. A reanalysis of vertebral growth bands suggests a size at birth of 3.6–3.9 m for O. megalodon, supporting the previous interpretations of its ovoviviparity and embryos’ intrauterine oophagous behavior, but less likely the need for nursery areas. Additional inferred growth patterns corroborated by the known fossil record support the hypothesis that the emergence of C. carcharias during the Early Pliocene is at least partly responsible for the demise of O. megalodon due to competition for resources. These interpretations are working hypotheses expected to serve as reasonable reference points for future studies on the biology of O. megalodon.
