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Major issues in the origins of ray‐finned fish ( A ctinopterygii) biodiversity
Author(s) -
Sallan Lauren C.
Publication year - 2014
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/brv.12086
Subject(s) - actinopterygii , neoteny , biology , synapomorphy , living fossil , disjunct , taxon , biodiversity , lineage (genetic) , clade , ecology , zoology , evolutionary biology , paleontology , fish <actinopterygii> , phylogenetics , fishery , biochemistry , population , demography , sociology , gene
Ray‐finned fishes ( A ctinopterygii) dominate modern aquatic ecosystems and are represented by over 32000 extant species. The vast majority of living actinopterygians are teleosts; their success is often attributed to a genome duplication event or morphological novelties. The remainder are ‘living fossils’ belonging to a few depauperate lineages with long‐retained ecomorphologies: P olypteriformes (bichirs), H olostei (bowfin and gar) and C hondrostei (paddlefish and sturgeon). Despite over a century of systematic work, the circumstances surrounding the origins of these clades, as well as their basic interrelationships and diagnoses, have been largely mired in uncertainty. Here, I review the systematics and characteristics of these major ray‐finned fish clades, and the early fossil record of A ctinopterygii, in order to gauge the sources of doubt. Recent relaxed molecular clock studies have pushed the origins of actinopterygian crown clades to the mid‐late P alaeozoic [ S ilurian– C arboniferous; 420 to 298 million years ago ( M a)], despite a diagnostic body fossil record extending only to the later M esozoic (251 to 66 M a). This disjunct, recently termed the ‘ T eleost G ap’ (although it affects all crown lineages), is based partly on calibrations from potential P alaeozoic stem‐taxa and thus has been attributed to poor fossil sampling. Actinopterygian fossils of appropriate ages are usually abundant and well preserved, yet long‐term neglect of this record in both taxonomic and systematic studies has exacerbated the gaps and obscured potential synapomorphies. At the moment, it is possible that later P alaeozoic‐age teleost, holostean, chondrostean and/or polypteriform crown taxa sit unrecognized in museum drawers. However, it is equally likely that the ‘ T eleost G ap’ is an artifact of incorrect attributions to extant lineages, overwriting both a post‐ P alaeozoic crown actinopterygian radiation and the ecomorphological diversity of stem‐taxa.