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Global taxonomic diversity of sharks, rays, and chimaeras: Family-level patterns and changes in species classification
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Hamid Reza Esmaeili *   |
| Ichthyology and Molecular Systematics Research Laboratory, Zoology Section, Department of Biology, School of Science, Shiraz University, Shiraz, Iran |
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Abstract: (300 Views) |
Quantifying the current taxonomic structure of sharks, rays, and chimaeras (Chondrichthyes) provides an essential, albeit classification-dependent, baseline for biodiversity research and conservation management. In this study, family-level genus and species counts extracted from Eschmeyer’s Catalog of Fishes (21 September 2026) were systematically analysed and validated. The consistency of the taxonomic hierarchy and associated subtotals was assessed, and the resulting taxonomic inventory was compared with two historical benchmarks: the 2015 dataset reported by Weigmann (2016) and the classification reflecting the taxonomic status as of 31 December 2023 compiled by Weigmann et al. (2024). The 2026 extract contains 1,331 accepted species in 218 genera, 68 families, and 14 orders. Batoids account for 702 species (52.7%), sharks for 568 (42.7%), and chimaeras for 61 (4.6%). Carcharhiniformes, Rajiformes, and Myliobatiformes together encompass 871 species (65.4%); the ten richest families contain 788 (59.2%). Species richness is highly unequal among families (median=9; mean=19.6; Gini=0.640), corresponding to an entropy-based effective richness of 31.9 equally represented families. Genus and species count covary across families (Spearman’s ρ = 0.704), but this association is descriptive because both counts share a hierarchical definition. Compared with the 2023 classification, recognized richness increased by a net 65 species (+5.1%), and by 143 (+12.0%) relative to the earlier published checklist with a 2015 cutoff. Family-level changes include taxonomic redistribution: Dichichthyidae was established after the 2023 benchmark and cannot be counted as five entirely new discoveries. One genus-count anomaly (Mitsukurinidae, two genera but one accepted living species) warrants clarification of counting conventions. The audited census documents strong taxonomic concentration and emphasizes that temporal inventory differences should not be equated directly with rates of species discovery.
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| Keywords: Cartilaginous fishes, Batoidea, Elasmobranchii, Holocephali, Taxonomic inventory, Species richness, Taxonomic change, Classification |
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Full-Text [PDF 497 kb]
(112 Downloads)
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Type of Study: Research |
Subject:
Special
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