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

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

• 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

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.

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.