Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes

Research output: Contribution to journalLetter

Authors

Colleges, School and Institutes

Abstract

Modern ray-finned fishes (Actinopterygii) comprise half of extant vertebrate species and are widely thought to have originated before or near the end of the Middle Devonian epoch (around 385million years ago)1–4. Polypterids (bichirs and ropefish) represent the earliest-diverging lineage of living actinopterygians, with almost all Palaeozoic taxa interpreted as more closely related to other extant actinopterygians than to polypterids5–10. By contrast, the earliest material assigned to the polypterid lineage is mid-Cretaceous in age (around 100million years old)11, implying a quarter-of-a-billionyear palaeontological gap. Here we show that scanilepiforms, a widely distributed radiation from the Triassic period (around 252–201 million years ago), are stem polypterids. Importantly, these fossils break the long polypterid branch and expose many supposedly primitive features of extant polypterids as reversals. This shifts numerous Palaeozoic ray-fins to the actinopterygian stem, reducing the minimum age for the crown lineage by roughly 45 million years. Recalibration of molecular clocks to exclude phylogenetically reassigned Palaeozoic taxa results in estimates that the actinopterygian crown lineage is about 20–40million years younger than was indicated by previous molecular analyses1–4. These new dates are broadly consistent with our revised palaeontological timescale and coincident with an interval of conspicuous morphological and taxonomic diversification among ray-fins centred on the Devonian–Carboniferous boundary12–14. A shifting timescale, combined with ambiguity in the relationships of late Palaeozoic actinopterygians, highlights this part of the fossil record as a major frontier in understanding the evolutionary assembly of modern vertebrate diversity

Details

Original languageEnglish
Pages (from-to)265–268
Number of pages4
JournalNature
Volume549
Issue number7671
Early online date30 Aug 2017
Publication statusPublished - 17 Sep 2017