Early evolution of ray-finned fishes: the traditional view

Friedman 2015
summarized “The early evolution of ray-finned fishes” supporting the traditional view, distinct from the large reptile tree (LRT, 1690+ taxa) which includes more varied outgroup taxa.

Friedman reports, “A stable hypothesis of relationships among major modern lineages has emerged over the past decade, supported by both anatomy and molecules.”

By contrast, the LRT adds taxa and shifts several tree topologies (e.g. moray eels, catfish, bichirs among traditional bony fish). The LRT does not support genomic (gene-based) tree topologies.

Friedman reports, “Attribution of fossils to the crowns and apical stems of Cladistia, Chondrostei and Neopterygii is uncontroversial, but placements of Palaeozoic taxa along deeper branches of actinopterygian phylogeny are less secure.”

By contrast, in the LRT Cladistia (Polypterus and kin) are lungfish relatives. Chondrostei (sturgeons + paddlefish + Polypterus and kin) are paraphyletic (not related to each other). Neopterygii are split at the great dichotomy of bony ray-fin fish, with one branch ultimately producing lobefins and tetrapods. So this is another invalid clade that required revision.

Friedman reports, “early ray-finned fishes share lobate pectoral-fin bases with sarcopterygians.”

By contrast, in the LRT lobefin fish arise from ray-finned fishes and earlier from spiny sharks (Fig. 1).

Friedman reports, “The origin of Actinopterygii is minimally constrained to the late Silurian by the first sarcopterygians(, but the mid-Devonian Cheirolepis is the oldest taxon consistently resolved as a ray-fin.”

By contrast, the LRT (subset Fig. 1) documents many more primitive ray fins than Cheirolepis. Unfortunately these more primitive taxa are not yet represented in fossil finds from deeper strata. Many are extant taxa, which should aid study.

Figure x. Newly revised fish subset of the LRT

Figure x. Newly revised fish subset of the LRT

The Early Devonian Dialipina
(Fig. 2) is widely considered to be the oldest articulated actinopterygian. Even so, it nests with Latimeria (the extant coelacanth) in the LRT. So it is 5 million years older and more complete than the oldest coelacanth promoted by Zhu et al. 2012, Euprosteus (known from a cranium in dorsal view). Zhu et al. do not mention Dialipina (Schultze 1968, 1992). We looked at Dialipina earlier here.

Mickle 2015 reported, “Currently, there is no standardized nomenclatural scheme for identifying and naming the bones of the snout in lower actinopterygians and specifically those fishes referred to as palaeoniscoids. A literature review reveals that the same bone names are used by different researchers to identify very different bones.”

Traditionally only some cranial bones are given tetrapod homologies. By contrast in the LRT all cranial bones are given tetrapod homologies, including groups of tiny bones that coalesce to become nasals or single bones that split to become two or more cheek bones. It’s a method that accurately documents homologies.

Friedman M 2015. The Early Evolution of Ray-Finned Fishes. Palaeontology 58(2): 213–228.
Mickle KE 2015. Identification of the bones of the snout in fossil lower actinopterygians—a new nomenclature scheme based on characters. Copeia 103 (4):838–857.
Schultze H-P 1968. Palaeoniscoidea-Schuppen aus dem Unterdevon Australiens und Kanadas und aus dem Mitteldevon Spitzbergens. Bulletin of the British Museum (Natural History) 16: 343–376.
Schultze H-P 1973. Crossopterygier mi heterozerker Schwanzfloss aus dem Oberdevon Kanadas, nebst einer Beschreibung von Onychodontida-Resten aus dem Middledevon Spaniens und aus dem Karbon der USA. Palaeontograhica A 143:188–208.
Schultze H-P 1992. Early Devonian actinopterygians (Osteichthyes, Pisces) from Siberia. Pp. 233–242 in Mark-Kurik, E.: Fossil Fishes as Living Animals. Academy of Sciences of Estonia.
Schultze H-P, and  Cumbaa SL 2001. Dialipina and the characters of basal actinopterygians, p. 315–332. In: Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny and Development. Ahlberg PE (ed.). Systematics Association Special Volume 61, Taylor and Francis, London.
Zhu M, Yu X-B, Lu J, Qiao T, Zhao W and Jia L-T 2012. Earliest known coelocanth skull extends the range of anatomically modern coelacanths to the Early Devonian. Nature Communications 3:772 DOI: 10.1038/ncomms1764

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