title: Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth.
abstract: The modern platypus,Ornithorhynchus anatinus, has an eye structure similar to aquatic mammals; however, platypuses also have a "sixth sense" associated with the bill electro- and mechanoreception that they use without opening their eyes underwater. We hypothesize thatOrnithorhynchusand the Miocene taxonObdurodonhave different sensory capacities, which may have resulted from differences in foraging behavior. To estimate differences in foraging, sensory systems, and anatomical divergence between these monotremes, we compared their skull morphologies. Results indicate that the bill ofObdurodonis more dorsally deflected than that ofOrnithorhynchus, suggesting a pelagic foraging behavior inObdurodoncompared to the bottom-feeding behavior inOrnithorhynchus. The infraorbital foramen ofObdurodon, through which the maxillary nerve passes sensory data from the bill to the brain, is relatively less developed than that ofOrnithorhynchus. Whereas bill-focused sensory perception was likely shared among Mesozoic monotremes, the highly developed electrosensory system ofOrnithorhynchusmay represent an adaptation to foraging in cloudy water. Computed tomography imagery indicates that the enlarged infraorbital canal ofOrnithorhynchusrestricts the space available for maxillary tooth roots. Hence, loss of functional teeth inOrnithorhynchusmay possibly have resulted from a shift in foraging behavior and coordinate elaboration of the electroreceptive sensory system. Well-developed electroreceptivity in monotremes is known at least as far back as the early Cretaceous; however, there are differences in the extent of elaboration of the feature among members of the ornithorhynchid lineage.
authors.affiliation: College of Liberal Arts and Sciences, Mie University, Kurima-machiya-cho 1577, Tsu, Mie 514-8507, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Asahara
authors.affiliation: Department of Acupuncture and Moxibustion, Tokyo Ariake University of Medical and Health Sciences, 2-9-1 Ariake, Koto-ku, Tokyo 135-0063, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Koizumi
authors.affiliation: Department of Biological Sciences, St. Mary's University, One Camino Santa Maria, San Antonio, TX 78228, USA.
authors.forename: Thomas E
authors.identifier: 0000-0001-9488-1512
authors.initials: TE
authors.lastname: Macrini
authors.affiliation: Palaeontology, Geobiology and Earth Archives Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Suzanne J
authors.initials: SJ
authors.lastname: Hand
authors.affiliation: Palaeontology, Geobiology and Earth Archives Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Archer
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005247:Feeding Behavior / Q000502:physiology*; D010987:Platypus / Q000033:anatomy & histology* / Q000502:physiology*
keywords: Monotremes; evolution; ornithorhynchids; trigeminal nerve