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Desert Tortoise (Gopherus agassizii) Fact Sheet: Taxonomy & History

Desert Tortoise (Gopherus agassizii)

Taxonomy and Nomenclature

  • Differences exist in morphology, genetics, physiology, and behavior between Sonoran and Mojave populations (Zylstra & Steidl 2009)
    • Two populations may be separate species (Murphy et al 2007) or subspecies, but classified as same species at present
  • Some researchers have proposed dividing the four gopher tortoises into two separate genera, with G. agassizii in Scaptochelys (Bramble 1982) or Xerobates (Bour & Dubois 1984); others now prefer to use Gopherus for all four species, based on several unique morphologies of these tortoises (Crumly 1984, Ernst & Lovich 2009)
  • Synonyms: Xerobates agassizii Cooper 1863; Xerobates lepidocephalus Ottley & Valazquez-Solis 1989.
  • Common name: desert tortoise, Agassiz's desert tortoise
  • Scientific name
    • Gopherus - from French "gaufre" meaning waffle; used for small mammals making waffle or honeycomb-like multi-chambered burrows (Harper 2010)
    • agassizii - in honor of naturalist Jean Louis Agassiz

 

 

Evolutionary History

  • Turtles are the closest relatives of birds and crocodiles (the archosaurs); they are less closely related to snakes, lizards and the tuatara (Crawford et al. 2012)
  • An early, fully shelled turtle: Proganocheles, 210 million years ago (Late Triassic) (Bonin et al 2006)
    • Turtle origins assumed to be earlier
    • Early in turtle evolution, both terrestrial and semi-aquatic freshwater forms present (Renous et al 2008)
    • Fully marine turtle evolved somewhat later, by Jurassic times.
  • Testudinidae family of turtles probably originated in Asia, according to fossil record. (Le et al 2006)
  • By 34-37 million years ago (Late Eocene), the Testudinidae family had spread from Asia to Europe, North America and Africa.
    • Earliest tortoises probably similar to modern Asian forest tortoises, (Manouria emys). (Stanford 2010)
  • Gopherus fossils: 35-33 million years old (late Eocene to early Oligocene) (McCord 2002) (Reynoso et al 2004)
    • Wyoming, Colorado, Nebraska, South Dakota
  • Two groups of Gopherus tortoises: (Ernst & Lovich 2009)
    • Flavomarginatus-polyphemus group (Bolson tortoise-gopher tortoise)
    • Agassizii-berlandieri group (desert tortoise-Texas tortoise or Berlandier's tortoise)
  • Around 10.5 million years ago (mid-Miocene) desert tortoises may have diverged from Texas tortoises (G. berlandieri) (McCord 2002)
  • Lineages of Sonoran and Mojave tortoises diverged about 5 million years ago (Lamb & McLuckie 2002)
    • Probably after being separated by an early Colorado River drainage
    • Van Devender (2002) suggests, rather, that different rainfall regimes more of a factor for separation
    • Populations are now geographically, genetically, and behaviorally distinct (Murphy et al 2007)
  • Many Gopherus agassizii fossils discovered in California, Arizona, New Mexico and Texas (Late Pleistocene) (McCord 2002)
    • Oldest are no more than 34,000 years old but older records may exist (McCord 2002)
    • By 8,000 years ago, modern distributions achieved (Van Devender & Moodie 1977)
  • Mojave population adapted to winter-rainfall regime, a climate pattern that began at the end of the Pleistocene. (Van Devender 2002)
    • Mojave populations may have been derived from Sonoran ones, once winter rains established at end of Pleistocene.
  • Sonoran (and Sinaloan) tortoises are more like their tropical ancestors, adapted to two rainfall seasons - winter-spring and summer. (Van Devender 2002)

Cultural History

Documentaries

Classification

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia (Laurenti, 1768)

Order: Testudines (Batsch, 1788) – turtles, tortoises, terrapins

Family: Testudinidae (Batsch, 1788) - tortoises

Genus: Gopherus (Rafinesque, 1832) - gopher tortoises, North American tortoises

Species: Gopherus agassizii - desert tortoise

Sources: Integrated Taxonomic Information System (2017)

Also see: Edwards et al. (2016)

Desert Tortoise

Desert Tortoise

The desert tortoise is the largest terrestrial turtle in the United States.

Image credit: © San Diego Zoo Global. All rights reserved.

Page Citations

Bonin et al. (2006)
Bramble (1982)
Crawford et al. (2012)
Crumly (1984)
Ernst & Lovich (2009)
ITIS (2010, 2017)
Le et al. (2006)
McCord (2002)
Murphy et al. (2007)
Zylstra & Steidl (2009)

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