title: Evolution of the head-trunk interface in tetrapod vertebrates.
abstract: Vertebrate neck musculature spans the transition zone between head and trunk. The extent to which the cucullaris muscle is a cranial muscle allied with the gill levators of anamniotes or is instead a trunk muscle is an ongoing debate. Novel computed tomography datasets reveal broad conservation of the cucullaris in gnathostomes, including coelacanth and caecilian, two sarcopterygians previously thought to lack it. In chicken, lateral plate mesoderm (LPM) adjacent to occipital somites is a recently identified embryonic source of cervical musculature. We fate-map this mesoderm in the axolotl (Ambystoma mexicanum), which retains external gills, and demonstrate its contribution to posterior gill-levator muscles and the cucullaris. Accordingly, LPM adjacent to the occipital somites should be regarded as posterior cranial mesoderm. The axial position of the head-trunk border in axolotl is congruent between LPM and somitic mesoderm, unlike in chicken and possibly other amniotes.
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States.|Museum of Comparative Zoology, Harvard University, Cambridge, United States.
authors.forename: Elizabeth M
authors.identifier: http://orcid.org/0000-0001-6481-612X
authors.initials: EM
authors.lastname: Sefton
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States.|Museum of Comparative Zoology, Harvard University, Cambridge, United States.|Department of Organismal Biology and Anatomy, University of Chicago, Chicago, United States.|Department of Geology and Geophysics, Yale University, New Haven, United States.|Yale Peabody Museum of Natural History, Yale University, New Haven, United States.
authors.forename: Bhart-Anjan S
authors.identifier: http://orcid.org/0000-0002-0838-8068
authors.initials: BA
authors.lastname: Bhullar
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States.|Museum of Comparative Zoology, Harvard University, Cambridge, United States.
authors.forename: Zahra
authors.identifier: http://orcid.org/0000-0002-3766-5896
authors.initials: Z
authors.lastname: Mohaddes
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States.|Museum of Comparative Zoology, Harvard University, Cambridge, United States.
authors.forename: James
authors.identifier: http://orcid.org/0000-0003-2782-9671
authors.initials: J
authors.lastname: Hanken
mesh_terms: D000818:Animals; D005075:Biological Evolution; D006257:Head / Q000033:anatomy & histology; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D009333:Neck / Q000033:anatomy & histology*; D013909:Thorax / Q000033:anatomy & histology; D014714:Vertebrates / Q000033:anatomy & histology*
keywords: Axolotl; Caecilian; Coelacanth; developmental biology; evolutionary biology; fate mapping; genomics; muscle development; neck evolution; stem cells