title: The Origin of Vertebrate Gills.
abstract: Pharyngeal gills are a fundamental feature of the vertebrate body plan [1]. However, the evolutionary history of vertebrate gills has been the subject of a long-standing controversy [2-8]. It is thought that gills evolved independently in cyclostomes (jawless vertebrates-lampreys and hagfish) and gnathostomes (jawed vertebrates-cartilaginous and bony fishes), based on their distinct embryonic origins: the gills of cyclostomes derive from endoderm [9-12], while gnathostome gills were classically thought to derive from ectoderm [10, 13]. Here, we demonstrate by cell lineage tracing that the gills of a cartilaginous fish, the little skate (Leucoraja erinacea), are in fact endodermally derived. This finding supports the homology of gills in cyclostomes and gnathostomes, and a single origin of pharyngeal gills prior to the divergence of these two ancient vertebrate lineages.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK; Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA. Electronic address: jag93@cam.ac.uk.
authors.forename: J Andrew
authors.initials: JA
authors.lastname: Gillis
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK.
authors.forename: Olivia R A
authors.initials: OR
authors.lastname: Tidswell
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005880:Gills / Q000196:embryology*; D006196:Hagfishes / Q000196:embryology; D014714:Vertebrates / Q000196:embryology*
keywords: chondrichthyan; development; endoderm; evolution; gills; homology; pharyngeal arch; skate; vertebrate