So far, the Palaeozoic fossil jawless vertebrates have not provided any direct evidence for the organization of the gills, apart from vague impressions—supposedly left by gill filaments—on the bony surface of the gill chamber in certain armoured forms or ‘ostracoderms’ (for example, osteostracans and heterostracans)1. The latter are currently regarded as more closely related to the living jawed vertebrates (crown gnathostomes) than to the living jawless vertebrates (hagfish and lampreys, or cyclostomes)2,3. Here we report the first direct evidence for the position of the gill filaments—possibly supported by gill rays—enclosed by gill pouches in a 370-million year (Myr)-old jawless vertebrate, Endeiolepis, from the Late Devonian fossil fish site of Miguasha, Quebec, Canada. This extinct jawless fish has much the same gill organization as living lampreys, although it possesses an unusually large number of gill pouches—a condition unlike that in any extant vertebrates and that raises questions about gill development4. Endeiolepis is currently regarded as a close relative of anaspids3, a group of 410–430-Myr-old ‘ostracoderms’. Assuming that current vertebrate phylogeny is correct, this discovery demonstrates that pouches enclosing the gills are primitive for vertebrates, but have been subsequently lost in jawed vertebrates.
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Author Contributions J.A.W. discovered the specimen MHNM 01-154 described herein; the other authors have contributed equally to the article.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
This file contains a discussion on synonymy, taphonomy and interpretation of the gill pouches of Euphanerops and Endeiolepis. (DOC 23 kb)
This illustrates the organization and orientation of the gill pouch natural casts in Endeiolepis. (PDF 90 kb)
A simplified phylogenetic tree of euchordates, showing the nodes where gill pouches and gill rays may have appeared and then disappeared. (PDF 134 kb)
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A three-dimensional placoderm (stem-group gnathostome) pharyngeal skeleton and its implications for primitive gnathostome pharyngeal architecture
Journal of Morphology (2017)
Biological Reviews (2016)
Zoological Letters (2016)