title: Patterns in the bony skull development of marsupials: high variation in onset of ossification and conserved regions of bone contact.
abstract: Development in marsupials is specialized towards an extremely short gestation and highly altricial newborns. As a result, marsupial neonates display morphological adaptations at birth related to functional constraints. However, little is known about the variability of marsupial skull development and its relation to morphological diversity. We studied bony skull development in five marsupial species. The relative timing of the onset of ossification was compared to literature data and the ossification sequence of the marsupial ancestor was reconstructed using squared-change parsimony. The high range of variation in the onset of ossification meant that no patterns could be observed that differentiate species. This finding challenges traditional studies concentrating on the onset of ossification as a marker for phylogeny or as a functional proxy. Our study presents observations on the developmental timing of cranial bone-to-bone contacts and their evolutionary implications. Although certain bone contacts display high levels of variation, connections of early and late development are quite conserved and informative. Bones that surround the oral cavity are generally the first to connect and the bones of the occipital region are among the last. We conclude that bone contact is preferable over onset of ossification for studying cranial bone development.
authors.affiliation: Paläontologisches Institut und Museum der Universität Zürich, Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland.|Institute of Biology Leiden (IBL) at Leiden University, Sylviusweg 72, 2333 BE Leiden, the Netherlands.|Museum für Naturkunde, Leibniz-Institut für Evolutions- and Biodiversitätsforschung an der Humboldt-Universität zu Berlin, Invalidenstraße 43, 10115 Berlin, Germany.
authors.forename: Stephan N F
authors.initials: SN
authors.lastname: Spiekman
authors.affiliation: Museum für Naturkunde, Leibniz-Institut für Evolutions- and Biodiversitätsforschung an der Humboldt-Universität zu Berlin, Invalidenstraße 43, 10115 Berlin, Germany.|Senckenberg Center for Human Evolution and Palaeoenvironment (HEP) at Eberhard Karls Universität, Sigwartstraße 10, 72074 Tübingen, Germany.|Eberhard Karls Universität, Hölderlinstraße 12, room: 308g, D-72076 Tübingen, Germany.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Werneburg
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001846:Bone Development; D008394:Marsupialia / Q000254:growth & development*; D010012:Osteogenesis; D012886:Skull / Q000254:growth & development*; D013997:Time Factors