title: The zootype and the phylotypic stage.
abstract: What is it that defines an animal? The definition provided here, made on the basis of developmental biology, suggests methods for resolving phylogenetic problems.
authors.affiliation: Department of Zoology, University of Oxford, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Slack
authors.forename: P W
authors.initials: PW
authors.lastname: Holland
authors.forename: C F
authors.initials: CF
authors.lastname: Graham
mesh_terms: D000818:Animals; D015870:Gene Expression; D005801:Genes, Homeobox; D009024:Morphogenesis; D010802:Phylogeny