title: Independent origins of middle ear bones in monotremes and therians.
abstract: A dentary of the oldest known monotreme, the Early Cretaceous Teinolophos trusleri, has an internal mandibular trough, which in outgroups to mammals houses accessory jaw bones, and probable contact facets for angular, coronoid, and splenial bones. Certain of these accessory bones were detached from the mandible to become middle ear bones in mammals. Evidence that the angular (homologous with the mammalian ectotympanic) and the articular and prearticular (homologous with the mammalian malleus) bones retained attachment to the lower jaw in a basal monotreme indicates that the definitive mammalian middle ear evolved independently in living monotremes and therians (marsupials and placentals).
authors.affiliation: Museum Victoria, Post Office Box 666E, Melbourne, Victoria 3001, Australia. trich@museum.vic.gov.au
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Rich
authors.forename: James A
authors.initials: JA
authors.lastname: Hopson
authors.forename: Anne M
authors.initials: AM
authors.lastname: Musser
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Flannery
authors.forename: Patricia
authors.initials: P
authors.lastname: Vickers-Rich
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004429:Ear Ossicles / Q000033:anatomy & histology*; D005580:Fossils; D008322:Mammals / Q000033:anatomy & histology* / Q000145:classification; D008334:Mandible / Q000033:anatomy & histology*; D008394:Marsupialia / Q000033:anatomy & histology / Q000145:classification; D009007:Monotremata / Q000033:anatomy & histology* / Q000145:classification; D010802:Phylogeny