Two spinal cords in birds: novel insights into early avian evolution

Abstract

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Woodbury C. Jeffery 1998Two spinal cords in birds: novel insights into early avian evolutionProc. R. Soc. Lond. B.2651721–1729http://doi.org/10.1098/rspb.1998.0494SectionRestricted accessTwo spinal cords in birds: novel insights into early avian evolution C. Jeffery Woodbury C. Jeffery Woodbury Department of Ornithology, American Museum of Natural History, 79th Street and Central ParkWest, NewYork, New York 10024, USA [email protected] Google Scholar Find this author on PubMed Search for more papers by this author C. Jeffery Woodbury C. Jeffery Woodbury Department of Ornithology, American Museum of Natural History, 79th Street and Central ParkWest, NewYork, New York 10024, USA [email protected] Google Scholar Find this author on PubMed Search for more papers by this author Published:22 September 1998https://doi.org/10.1098/rspb.1998.0494AbstractBirds can be subdivided into two large superordinal assemblages based on differences in the dorsal horn of the spinal grey matter. Palaeognaths (i.e. ratites and tinamous), along with a few other orders of neognathous birds, exhibit the primitive dorsal horn state characteristic of other amniotes wherein cutaneous nerves form a single map of the body surface across the dorsal horn. In contrast, the vast majority of neognaths exhibit a novel, distinctly bifid dorsal horn wherein cutaneous nerves form not one, but two separate maps of the skin, each lying side–by–side. This unusual dorsal horn organization, which has been highly conserved and represents the derived state in birds, may identify a novel, major avian clade. These findings shed new light on historically problematic taxa and the early evolutionary branching sequence among living birds. Most notably, they reveal that the traditional orders Gruiformes, Columbiformes, Cuculiformes and Piciformes are unnatural assemblages. Further, in addition to palaeognaths, these findings suggest that most gruiforms, including buttonquails and mesites, as well as pigeons, cuckoos, woodpeckers and songbirds, represent ancient lineages whose ancestry predates the majority of ‘modern’ birds. The phylogeny of living birds may thus be likened more to a dense bush than the traditional tree, with more than half of all living species arising from a basal side branch. 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