title: Evolutionary innovation and conservation in the embryonic derivation of the vertebrate skull.
abstract: Development of the vertebrate skull has been studied intensively for more than 150 years, yet many essential features remain unresolved. One such feature is the extent to which embryonic derivation of individual bones is evolutionarily conserved or labile. We perform long-term fate mapping using GFP-transgenic axolotl and Xenopus laevis to document the contribution of individual cranial neural crest streams to the osteocranium in these amphibians. Here we show that the axolotl pattern is strikingly similar to that in amniotes; it likely represents the ancestral condition for tetrapods. Unexpectedly, the pattern in Xenopus is much different; it may constitute a unique condition that evolved after anurans diverged from other amphibians. Such changes reveal an unappreciated relation between life history evolution and cranial development and exemplify 'developmental system drift', in which interspecific divergence in developmental processes that underlie homologous characters occurs with little or no concomitant change in the adult phenotype.
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Nadine
authors.initials: N
authors.lastname: Piekarski
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Gross
authors.affiliation: Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hanken
mesh_terms: D000558:Ambystoma mexicanum / Q000196:embryology*; D000818:Animals; D005075:Biological Evolution; D009432:Neural Crest / Q000196:embryology*; D012886:Skull / Q000196:embryology*; D014714:Vertebrates / Q000196:embryology; D014982:Xenopus laevis / Q000196:embryology*