title: The stem osteichthyan Andreolepis and the origin of tooth replacement.
abstract: The teeth of gnathostomes (jawed vertebrates) show rigidly patterned, unidirectional replacement that may or may not be associated with a shedding mechanism. These mechanisms, which are critical for the maintenance of the dentition, are incongruently distributed among extant gnathostomes. Although a permanent tooth-generating dental lamina is present in all chondrichthyans, many tetrapods and some teleosts, it is absent in the non-teleost actinopterygians. Tooth-shedding by basal hard tissue resorption occurs in most osteichthyans (including tetrapods) but not in chondrichthyans. Here we report a three-dimensional virtual dissection of the dentition of a 424-million-year-old stem osteichthyan, Andreolepis hedei, using propagation phase-contrast synchrotron microtomography, with a reconstruction of its growth history. Andreolepis, close to the common ancestor of all extant osteichthyans, shed its teeth by basal resorption but probably lacked a permanent dental lamina. This is the earliest documented instance of resorptive tooth shedding and may represent the primitive osteichthyan mode of tooth replacement.
authors.affiliation: Uppsala University, Department of Organismal Biology, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
authors.forename: Donglei
authors.initials: D
authors.lastname: Chen
authors.affiliation: Uppsala University, Department of Organismal Biology, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
authors.forename: Henning
authors.initials: H
authors.lastname: Blom
authors.affiliation: Science for Life Laboratory and Uppsala University, Department of Organismal Biology, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.|European Synchrotron Radiation Facility, 6 rue Jules Horowitz, 38043 Grenoble CEDEX, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Sanchez
authors.affiliation: European Synchrotron Radiation Facility, 6 rue Jules Horowitz, 38043 Grenoble CEDEX, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Tafforeau
authors.affiliation: Science for Life Laboratory and Uppsala University, Department of Organismal Biology, Norbyvägen 18A, SE-752 36 Uppsala, Sweden.
authors.forename: Per E
authors.initials: PE
authors.lastname: Ahlberg
mesh_terms: D000818:Animals; D005399:Fishes; D005580:Fossils; D007568:Jaw / Q000033:anatomy & histology; D008858:Microscopy, Phase-Contrast; D017356:Synchrotrons; D014054:Tomography; D014070:Tooth / Q000033:anatomy & histology* / Q000254:growth & development*