Origin of the unique morphology of the shoulder girdle in turtles

Authors

  • Hiroshi Nagashima,

    Corresponding author
    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
    2. Division of Gross Anatomy and Morphogenesis, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
    • Correspondence

      Hiroshi Nagashima and Shigeru Kuratani, Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), 2-2-3 Minatojima-minami, Kobe 650-0047, Japan. (H.N.)

      T: +81 25 2272048; F: +81 25 2270752; E: nagahiro@med.niigata-u.ac.jp; (S.K.) T: +81 78 3063064; F: +81 78 3063370; E: saizo@cdb.riken.jp

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  • Tatsuya Hirasawa,

    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
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    • These authors contributed equally to this study.
  • Fumiaki Sugahara,

    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
    2. Division of Biology, Hyogo College of Medicine, Hyogo, Japan
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    • These authors contributed equally to this study.
  • Masaki Takechi,

    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
    2. Division of Human Embryology, Iwate Medical University, Iwate, Japan
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  • Ryo Usuda,

    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
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  • Noboru Sato,

    1. Division of Gross Anatomy and Morphogenesis, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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  • Shigeru Kuratani

    Corresponding author
    1. Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), Hyogo, Japan
    • Correspondence

      Hiroshi Nagashima and Shigeru Kuratani, Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB), 2-2-3 Minatojima-minami, Kobe 650-0047, Japan. (H.N.)

      T: +81 25 2272048; F: +81 25 2270752; E: nagahiro@med.niigata-u.ac.jp; (S.K.) T: +81 78 3063064; F: +81 78 3063370; E: saizo@cdb.riken.jp

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Abstract

The shoulder girdle of turtles has a triradiate morphology. Although its dorsal process represents the scapular blade, the skeletal identities of the two ventral processes remain uncertain. To elucidate the question, developmental patterns of the girdles were compared between Chinese soft-shelled turtles, chickens, and mice. Despite the morphological diversity of adults, the initial primordia of the shoulder girdles showed similar morphological patterns. The ventral two processes developed from the anlagen comparable to those of the acromion and the coracoid in other amniotes. The developmental pattern of the acromion is very similar among embryos, whereas that of the coracoid in mammals differs from that in non-mammals, implying that coracoids are not homologous between non-mammals and mammals. Therefore, amniotes have retained the ancestral pattern of the girdle anlage, and the shoulder girdle of turtles has been achieved through a transformation of the pattern in the late ontogenic period.

Ancillary