title: Structure and growth pattern of the bizarre hemispheric prominence on the rostrum of the fossil beaked whale Globicetus hiberus (Mammalia, Cetacea, Ziphiidae).
abstract: The rostrum of most ziphiids (beaked whales) displays bizarre swollen regions, accompanied with extreme hypermineralisation and an alteration of the collagenous mesh of the bone. The functional significance of this specialization remains obscure. With the voluminous and dense hemispheric excrescence protruding from the premaxillae, the recently described fossil ziphiid Globicetus hiberus is the most spectacular case. This study describes the histological structure and interprets the growth pattern of this unique feature. Histologically, the prominence in Globicetus is made up of an atypical fibro-lamellar complex displaying an irregular laminar organization and extreme compactness (osteosclerosis). Its development is suggested to have resulted from a protraction of periosteal accretion over the premaxillae, long after the end of somatic growth. Complex shifts in the geometry of this tissue are likely to have occurred during its accretion and no indication of Haversian remodeling could be found. X-ray diffraction and Raman spectroscopy indicate that the bone matrix in the premaxillary prominence of Globicetus closely resembles that of the rostrum of the extant beaked whale Mesoplodon densirostris: apatite crystals are of common size and strongly oriented, but the collagenous meshwork within bone matrix seems to be extremely sparse. These morphological and structural data are discussed in the light of functional interpretations proposed for the highly unusual and diverse ziphiid rostrum. J. Morphol. 277:1292-1308, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Departement Ecologie et Gestion de la Biodiversite, UMR CNRS/MNHN 7179, 'Mécanismes Adaptatifs: des Organismes aux Communautés', 55 rue Buffon, Paris, 75005, France. maitena.dumont@gmail.com.
authors.forename: Maïtena
authors.initials: M
authors.lastname: Dumont
authors.affiliation: Département Histoire de la Terre, Muséum National d'Histoire Naturelle, CNRS-UMR 7207 (CR2P), Bâtiment de Géologie CC 48, 57 rue Cuvier F-75231, Paris Cedex 05, France.
authors.forename: Vivian
authors.initials: V
authors.lastname: de Buffrénil
authors.affiliation: Departement Marine Mammal, Sociedade Galega de Historia Natural, Praza De Canido S/N E-15401, Ferrol, España.
authors.forename: Ismael
authors.initials: I
authors.lastname: Miján
authors.affiliation: Institut Royal des Sciences Naturelles de Belgique, D.O. Terre et Histoire de la Vie, 29 rue Vautier B-1000 Bruxelles, Belgique.
authors.forename: Olivier
authors.initials: O
authors.lastname: Lambert
mesh_terms: D000818:Animals; D001502:Beak / Q000033:anatomy & histology / Q000254:growth & development; D001842:Bone and Bones / Q000033:anatomy & histology; D005580:Fossils / Q000033:anatomy & histology*; D006257:Head / Q000033:anatomy & histology* / Q000254:growth & development; D013059:Spectrum Analysis, Raman; D014907:Whales / Q000033:anatomy & histology* / Q000254:growth & development; D014961:X-Ray Diffraction
keywords: Ziphiidae; bone histology; fossil; hyperdense bone, deep diving; rostrum