Desert Tortoises (Gopherus spp.) Fact Sheet: Taxonomy & History

• 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).

• 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)

Documentaries

• Tortoise in Peril (Topic Productions)

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)

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

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

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)