Scientific Research and Essays

  • Abbreviation: Sci. Res. Essays
  • Language: English
  • ISSN: 1992-2248
  • DOI: 10.5897/SRE
  • Start Year: 2006
  • Published Articles: 2753

Full Length Research Paper

Skeletal ontogeny of Seychelles giant tortoises (Aldabrachelys/Dipsochelys)

Justin Gerlach
133 Cherry Hinton Road, Cambridge CB1 7BX, U.K.
Email: [email protected]

  •  Accepted: 16 February 2012
  •  Published: 31 March 2012

Abstract

The skeletal development of captive bred Seychelles-Aldabra giant tortoises (Dipsochelys/Aldabrachelys) was studied from late embryos to adults based on 93 specimens (45 embyronic). The pattern of ossification is described and the developments of the characters used to distinguish different morphotypes are investigated. The timing of ossification of different bones in this genus is similar to the patterns reported for other taxa with complete chondrification of the skeleton immediately prior to the onset of ossification. By hatching the main bones of the skull, axial skeleton, limbs and plastron are at least partially ossified. In other turtle carapace, ossificiation has started by hatching but in Dipsochelys it does not commence until after hatching. Fusion of carpal and tarsal elements is also delayed. Morphotype differences are apparent in juvenile skeletons in the skull, carapace and fore-limbs. These can be traced to development of structures associated with specific jaw or limb muscles or the effects of muscle action. Three main processes were identified: the progressive development of muscle attachment sites, distortion of cartilage precursors of bones as a result of muscle action, differential growth rates of adjacent bones, differential ossification and differences in the exact form of cartilage bone precursors. These findings shed light on the morphological changes found in different tortoise morphotypes.

 

Key words: Aldabrachelys, Dipsochelys, ontogeny, skeleton growth.