title: Dental ontogeny of a white shark embryo.
abstract: Unlike most viviparous vertebrates, lamniform sharks develop functional teeth during early gestation. This feature is considered to be related to their unique reproductive mode where the embryo grows to a large size via feeding on nutritive eggs in utero. However, the developmental process of embryonic teeth is largely uninvestigated. We conducted X-ray microcomputed tomography to observe the dentitions of early-, mid-, and full-term embryos of the white shark Carcharodon carcharias (Lamniformes, Lamnidae). These data reveal the ontogenetic change of embryonic dentition of the species for the first time. Dentition of the early-term embryos (∼45 cm precaudal length, PCL) is distinguished from adult dentition by 1) the presence of microscopic teeth in the distalmost region of the paratoquadrate, 2) a fang-like crown morphology, and 3) a lack of basal concavity of the tooth root. The "intermediate tooth" of early-term embryos is almost the same size as the adjacent teeth, suggesting that lamnoid-type heterodonty (lamnoid tooth pattern) has not yet been established. We also discovered that mid-term embryos (∼80 cm PCL) lack functional dentition. Previous studies have shown that the maternal supply of nutritive eggs in lamnoid sharks ceases during mid- to late-gestation. Thus, discontinuation of functional tooth development is likely associated with the completion of the oophagous (egg-eating) phase. Replacement teeth in mid-term embryos include both embryonic and adult-type teeth, suggesting that the embryo to adult transition in dental morphology occurs during this period. J. Morphol. 278:215-227, 2017. © 2016 Wiley Periodicals,Inc.
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Taketeru
authors.initials: T
authors.lastname: Tomita
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Miyamoto
authors.affiliation: Department of Human Biology and Anatomy, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kawaguchi
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Toda
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Shin-Ichiro
authors.initials: SI
authors.lastname: Oka
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nozu
authors.affiliation: Zoological Laboratory, Okinawa Churashima Research Center, Okinawa Churashima Foundation, Okinawa, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Sato
mesh_terms: D000818:Animals; D003817:Dentition; D012754:Sharks / Q000196:embryology*; D014070:Tooth / Q000196:embryology*; D055114:X-Ray Microtomography
keywords: Carcharodon carcharias; Lamniformes; embryonic teeth; lamnoid tooth pattern; oophagy