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Galapagos Giant Tortoises (Chelonoidis spp.) Fact Sheet: Physical Characteristics

General Appearance

Notable traits

  • Among the largest (extant) terrestrial reptiles (Blake et al. 2015a)
  • Some traits differ between species and islands (Caccone et al. 1999)
    • Shell shape
    • Maximum adult size
    • Length of neck and limbs
  • Neck
    • Long and thin (Bonin et al. 2006)
  • Bony scales on forelimbs (McDougal 2000)
    • Like most tortoises
    • Called “osteroderms”
  • Head
    • Triangular (Bonin et al. 2006)
    • Upper jaw weakly hooked (Zug 2013)
    • Mandibles with sharp edges for cutting and tearing vegetation (de Vries 1984)
  • Eyes
    • Dark (Standford 2010)
  • Shell (Bonin et al. 2006)
    • Black or brown
      • Fine, light-colored lines along seams between scutes (bony plates of shell)
    • No nuchal scute (scute located centrally at the anterior edge of the carapace)
      • Present in Aldabra tortoises

Shell functions (Chiari et al. 2009)

  • Protection
  • Regulation of body temperature (thermoregulation)
  • Facilitation of mating and reproduction
  • Ability to turn over (“self-righting”)
  • Locomotion
  • Storage of water, fat, and wastes

Carapace shapes (Schafer 1982; Poulakakis et al. 2008; Poulakakis et al. 2015, except as noted)

  • Only living giant tortoise lineage that shows two different shell shapes (Chiari et al. 2009)
  • First described by Van Denburgh (1914)
  • “Saddle-back”
    • Sharply raised anterior opening of the carapace
    • Proposed adaptations
      • To feed on high-growing vegetation in dry habitats
      • To raise head high in competition for dominance
    • Extant Giant Galápagos Tortoises (GGTs): from islands of Española, San Cristóbal, Pinzón
    • Extinct Giant Galápagos Tortoises (GGTs): from islands of Pinta, Floreana, Gernandina
  • “Domed”
    • Rounded
    • Extant GGTs: from islands of Isabela and Santa Cruz
  • Variation within these broad categories (Chiari et al. 2009; Standford 2010)
    • Sometimes called “intermediate”
    • May be influenced by selection pressures and environment-related plasticity

Hatchlings (Bonin et al. 2006)

  • Small, but similar to adults in appearance
  • Shell shape
    • Flat and oval
  • Coloration
    • Uniformly dark or with subtle rings on each scute

Sexual Dimorphism

  • Size differences
    • Males (Bonin et al. 2006)
      • Up to 2-3 times the size of females
    • More pronounced in saddleback species (Standford 2010)
      • Possibly due to harsher environmental conditions
  • Shell shape of males
    • More variation in some species (Chiari et al. 2009)
      • Due to more rapid shell growth
    • Concave plastron (lower shell) (Standford 2010)
      • To facilitate mating
  •  Long tail in males (Standford 2010)
    • Used in mating

Keeping a Healthy Weight

Galapagos Tortoise being weighed by a zookeeper

Weighing a juvenile Galápagos giant tortoise at the San Diego Zoo, 1961.

As adults, Galápagos giant tortoises weigh hundreds of pounds. Males are much heavier than females.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Strong Support

Elephantine foot of a Galapagos tortoise

The sturdy, elephant-like feet of Giant Galápagos Tortoises help to support their heavy bodies.

Image credit: Peter Wilton, made publically available via Wikimedia Commons; CC by 2.0 license.

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