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

Desert Tortoise (Gopherus agassizii)

Taxonomy and Nomenclature

  • Common name
    • Desert tortoises, Agassiz's desert tortoise
  • Scientific name
    • Gopherus  - from French "gaufre" meaning waffle (Harper 2010)
      • Used in reference to small mammals that make waffle- or honeycomb-like multi-chambered burrows
    • agassizii - in honor of naturalist Jean Louis Agassiz (Cooper 1861)
  • Three species of desert tortoises recognized:
    • G. agassizi - found north and west of the Colorado River (Murphy et al. 2011)
    • G. morakai - found south and east of the Colorado River (Murphy et al. 2011)
    • G. evgoodei - found in southern Sonora and northern Sinaloa (Edwards et al. 2016)
  • Murphy et al. (2011) described agassizi using genetic evidence, as well as behavioral and ecological differences
    • Mojave tortoises live in burrows in valleys and on alluvial fans
    • Have a wider shell that is box-like and high domed with longer gular scutes
    • Oviposition is from April to mid-July with 0-3 clutches and 5-16 eggs/year
    • Sonoran desert tortoises (morakai) live in rock crevices, steep slopes and hill tops
    • Oviposition is from early June to early August with 0-1 clutches and 1-12 eggs/year
  • Genus Gopherus includes 6 different species, comprising 2 major sister groups that diverged 4-8 million years ago (Berry and Murphy 2019)
    • G. agassizi, G. berlandieri, G. evgoodei, and G. morafkai
    • G. polyphemus, G. flavomarginalis
  • Population genetics of the desert tortoise species has been largely influenced by historical landscape impediments to movement such as mountain ranges, lakes, rivers, and deserts (Shaffer et al. 2017).

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 Wildlife Alliance. 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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