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High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian

By Sam Giles, Kara Feilich, Stephanie E Pierce, Matt Friedman

Posted 03 Sep 2021
bioRxiv DOI: 10.1101/2021.09.02.458676

Actinopterygian (ray-finned) fishes represent the principal vertebrate group in aquatic settings. This dominance is often attributed to their apparent success in the aftermath of the end-Devonian extinction. Increases in taxonomic and morphological diversity in the early Carboniferous, coupled with phylogenetic hypotheses implying the survival of few Devonian lineages, contribute to a model of explosive post-extinction radiation. However, most actinopterygian fossils from within a ca. 20 Myr window surrounding the end-Devonian extinction remain poorly known, contributing to uncertainty about these patterns. Here we present detailed anatomical data for an exceptionally preserved but diminutive ray-finned fish from within this gap, ~7 Myr prior to the Devonian-Carboniferous boundary. Representing a new genus and species, it bears a series of derived anatomical features otherwise known only from Carboniferous and younger taxa. It nests phylogenetically within a clade of post-Devonian species and, in an expanded phylogenetic analysis incorporating other previously neglected taxa, draws at least ten lineages of Carboniferous actinopterygians into the Late Devonian. This suggests phenotypically cryptic divergence among ray-finned fishes in the latest Devonian, followed by more conspicuous diversification in feeding and locomotor structures in the Carboniferous. This revised model finds parallels in patterns emerging for other clades, and provides a refined perspective on key events early in the history of a group that today contains half of all living vertebrate species.

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