Comment on “An early Miocene extinction in pelagic sharks”

Naylor, Gavin J. P.; Lima, Arthur de; Castro, José Ignacio Fernández del; Hubbell, Gordon; Pinna, Mário C. C. de

doi:10.1126/science.abj8723

Cited by 9 publications

(2 citation statements)

References 3 publications

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“…The placoid scales described here cannot easily be ascribed to any of the taxa based on dermal denticles raised by Johns et al (1997), whose work forms the foundation for taxonomic assignment of placoid scales from the Permian and Triassic of China. Moreover, placoid scales display different morphologies across the body and the number of placoid scale-based genera and species might significantly surpass the actual number of taxa (Naylor et al, 2021). Nevertheless, the placoid scales in this study display the characteristic features found in hybodontiform rather than neoselachian sharks, supporting our general taxonomic assignment here.…”

Section: Discussionmentioning

confidence: 99%

Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB

Wen

Kriwet

Zhang

et al. 2022

Journal of Vertebrate Paleontology

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Hybodontiform shark teeth, cephalic and fin spines as well as placoid scales are reported here for the first time from the continental, Lower Triassic Dongchuan Formation near the village of Zhaojia (Huize County, Yunnan Province) in south-west China. The isolated teeth are assigned to three unidentified hybodontiforms but also to a new species of Parvodus, P. huizodus sp. nov., the oldest record of this small-toothed lonchidiid shark genus, extending its range well down into the Lower Triassic. This new species, together with additional hybodontiform remains, provides new evidence of shark occurrences in the aftermath of the end-Permian mass extinction event, when freshwater environments might have acted as centers of origin rather than refugia for sharks. A review of the species assigned to Parvodus and similar small hybodontiform sharks reveals two distinct ecomorphological groups. Group 1, which is characterized by clutching-type dentitions, includes eight species (three of which remain unnamed) ranging from the Middle Triassic to Lower Cretaceous, while group 2, characterized by cutting-crushing type dentitions, comprises 11 species (six of which remain unnamed) including the type-species, P. rugianus ranging from the Lower Triassic to the Lower Cretaceous. The new fossils documented here reveal that hybodontiforms were already adapted to freshwater environments in the Lower Triassic rather than in the Jurassic in China. http://zoobank.org/urn:lsid:zoobank.org:pub:9FA915B5-C838-4778-95C9-B851676751A4 SUPPLEMENTAL DATA-Supplemental materials are available for this article for free at www.tandfonline.com/UJVP.

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Section: Discussionmentioning

confidence: 99%

Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB

Wen

Kriwet

Zhang

et al. 2022

Journal of Vertebrate Paleontology

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“…The morphology and arrangement of placoid scales can be species-specific and is often used in species identification (Reif, 1985b;Raschi and Tabit, 1992;Deynat, 2000;Gravendeel et al, 2002;Claes and Mallefet, 2009;Dillon et al, 2017;Ferroń and Botella, 2017;Ankhelyi et al, 2018;Duchatelet et al, 2020a). Intraspecific variation of placoid scale morphology is observed at different body regions (Duchatelet et al, 2020a;Feichtinger et al, 2021;Gabler-Smith et al, 2021;Naylor et al, 2021) but, within a dedicated body region, the intraspecific variation is low (authors' pers. obs.).…”

Section: Introductionmentioning

confidence: 99%

Placoid scales in bioluminescent sharks: Scaling their evolution using morphology and elemental composition

et al. 2022

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Elasmobranchs are characterised by the presence of placoid scales on their skin. These scales, structurally homologous to gnathostome teeth, are thought to have various ecological functions related to drag reduction, predator defense or abrasion reduction. Some scales, particularly those present in the ventral area, are also thought to be functionally involved in the transmission of bioluminescent light in deep-sea environments. In the deep parts of the oceans, elasmobranchs are mainly represented by squaliform sharks. This study compares ventral placoid scale morphology and elemental composition of more than thirty deep-sea squaliform species. Scanning Electron Microscopy and Energy Dispersive X-ray spectrometry, associated with morphometric and elemental composition measurements were used to characterise differences among species. A maximum likelihood molecular phylogeny was computed for 43 shark species incuding all known families of Squaliformes. Character mapping was based on this phylogeny to estimate ancestral character states among the squaliform lineages. Our results highlight a conserved and stereotypical elemental composition of the external layer among the examined species. Phosphorus-calcium proportion ratios (Ca/P) slightly vary from 1.8-1.9, and fluorine is typically found in the placoid scale. By contrast, there is striking variation in shape in ventral placoid scales among the investigated families. Character-mapping reconstructions indicated that the shield-shaped placoid scale morphotype is likely to be ancestral among squaliform taxa. The skin surface occupied by scales appears to be reduced in luminous clades which reflects a relationship between scale coverage and the ability to emit light. In luminous species, the placoid scale morphotypes are restricted to pavement, bristle-and spine-shaped except for the only luminescent somniosid, Zameus squamulosus, and the dalatiid Mollisquama mississippiensis. These results, deriving from an unprecedented sampling, show extensive morphological diversity in placoid scale shape but little variation in elemental composition among Squaliformes.

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Taxonomic status of deep-sea sharks Deania calceus and D. hystricosa (Centrophoridae)

Marrero,

Pascual-Alayón,

Martin

et al. 2023

Regional Studies in Marine Science

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Comment on “An early Miocene extinction in pelagic sharks”

Cited by 9 publications

References 3 publications

Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB

Hybodontiform shark remains (Chondrichthyes, Elasmobranchii) from the Lower Triassic of Yunnan Province, China, with comments on hybodontiform diversity across the PTB

Placoid scales in bioluminescent sharks: Scaling their evolution using morphology and elemental composition

Taxonomic status of deep-sea sharks Deania calceus and D. hystricosa (Centrophoridae)

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