title: Scenarios for the making of vertebrates.
abstract: Over the past 200 years, almost every invertebrate phylum has been proposed as a starting point for evolving vertebrates. Most of these scenarios are outdated, but several are still seriously considered. The short-range transition from ancestral invertebrate chordates (similar to amphioxus and tunicates) to vertebrates is well accepted. However, longer-range transitions leading up to the invertebrate chordates themselves are more controversial. Opinion is divided between the annelid and the enteropneust scenarios, predicting, respectively, a complex or a simple ancestor for bilaterian animals. Deciding between these ideas will be facilitated by further comparative studies of multicellular animals, including enigmatic taxa such as xenacoelomorphs.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Holland
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, USA.
authors.forename: Linda Z
authors.initials: LZ
authors.lastname: Holland
authors.affiliation: Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
authors.forename: Peter W H
authors.initials: PW
authors.lastname: Holland
mesh_terms: D000818:Animals; D000845:Annelida / Q000033:anatomy & histology / Q000145:classification; D007448:Invertebrates / Q000033:anatomy & histology / Q000145:classification; D008954:Models, Biological; D010802:Phylogeny; D012106:Research; D014714:Vertebrates / Q000033:anatomy & histology / Q000145:classification