title: Concordia discors: duality in the origin of the vertebrate tail.
abstract: The vertebrate tail is an extension of the main body axis caudal to the anus. The developmental origin of this structure has been a source of debate amongst embryologists for the past century. Some view tail development as a continuation of the morphogenetic processes that shape the head and trunk (i.e. gastrulation). The alternative view, secondary development, holds that the tail forms in a manner similar to limb development, i.e. by secondary induction. Previous developmental studies have provided support for both views. Here I revisit these studies, describing caudal morphogenesis in select vertebrates, the associated genes and developmental defects, and, as a relevant aside, consider the developmental and evolutionary relationships of primary and secondary neurulation. I conclude that caudal development enlists both gastrulation and secondary induction, and that the application of recent high-resolution cell labelling technology may clarify how these discordant programmes interact in building the vertebrate tail.
authors.affiliation: Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada. ghandrig@dal.ca
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Handrigan
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds; D004627:Embryonic Induction / Q000502:physiology*; D005775:Gastrula / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D008322:Mammals; D009024:Morphogenesis / Q000502:physiology; D009420:Nervous System / Q000196:embryology; D010802:Phylogeny; D013623:Tail / Q000196:embryology*; D014714:Vertebrates / Q000196:embryology*; D014981:Xenopus; D015027:Zebrafish