Nile Crocodiles (Crocodylus niloticus & C. suchus) Fact Sheet: Taxonomy & History

Common names

• Nile Crocodile
• African common names (from Harper 2001)
• Mamba, in Swahli
• Garwe, in Shona

Scientific name

• Etymology (from Parker 2009)
• Genus Crocodylus derived from two Greek word kroko meaning "pebble" and deilos meaning "worm"
• Referring to the rough texture of the skin
• Herodotus used "krokodilos" to describe a lizard in the Ionic dialect of Greek
• Later, Ionians applied this term to creatures in Egypt they thought similar
• Specific epithet niloticus in reference to the Nile River in Africa
• Subspecies
• 7 proposed; none officially recognized (Britton 2009)
• Geographical races distinguished mainly by features of their scales (from Trutnau & Sommerlad 2006)
• Variation in numbers, shape, and degree of ossification
• Newly rediscovered dwarfed crocodiles
• Inhabit Mauritania
• Previously considered extirpated
• Believed to be Nile Crocodiles by some
• Others consider them distinctive, based on DNA analysis (Schmitz et al. 2003)
• Assigned the scientific name Crocodylus suchus (Trutnau & Sommerlad 2006)

Position within Reptilia

• Considered diapsids (Benton 1984)
• Have two skull openings behind the eye socket, each of which is roofed by a bony arch
• By modern classification systems, birds are also considered diapsids, although their skull have been highly modified
• Other vertebrates such as mammals are synapsids (one opening) or anapsids such as turtles (no openings)
• Diapsid subdivisions
• Archosauria ("ruling replies")
• Includes modern birds and crocodiles as well as extinct dinosaurs, pterosaurs
• Lepidosauria
• Includes lizards and snakes
• Relationship with birds
• Birds diverged from crocodile-like animals c. 254 million years ago (Mya) (Janke & Arnason 1997)

Order Crocodylia

• Ancestors
• Modern crocodiles descend within the reptiles c. 225 Mya (from Summers 2005; Seymour et al. 2004; Carroll 1988)
• Forerunners similar to the small, active, and bipedal land-based predator Saltoposuchus
• Active, warm-blooded, land-living ancestor
• Later adapted a largely aquatic way of life, leaving terrestrial habitats to the dinosaurs
• Arose in the Late Triassic
  
• Geographic distribution
• Europe, South America, and South Africa
• Sarcosuchus, a distant crocodile-relative, lived in Africa c.110 million years ago (Cretaceous) (from Sereno 2001)
• Animal reached lengths up to twice that of the largest living crocodiles or 12 m (c. 40 ft)
• Crocodile divergence
• Crocodiles, alligators, and caimen branched c. 65 Mya, according to fossil and molecular data
• Closest living relatives
• Birds more closely related to crocodiles than to the lizards (Janke & Arnason 1997)
• Molecular data (similar protein coding genes) and other evidence support this relationship (Janke & Arnason 1997)
• Lepidosaurs (spiny lizards such as Tuatara of New Zealand) and other lizards and snakes are more distantly related to dinosaurs (Benton 1984)
• Historic distribution
• Existed on every continent, except Antarctica, by c. 65 Mya

Family Crocodylidae

• Diversification
• Crocodiles and alligators diverged c.140 Mya (Jurassic/Cretaceous boundary) (Janke et al 2005)
• Modern species of crocodiles began to be distinct around 5-7 Mya (Late Miocene) (Brochu 2001)

Genus Crocodylus

• Origin
• Fossil remains date to 5-7 Mya, in Africa
• Fossil record of Nile Crocodile
• Date to 2.5-3.5 Mya (Late Pliocene), in North and East Africa (Trutnau & Sommerlad 2006)
• Diversity within C. niloticus
• Modern populations geographically unique
• Modern genetic testing supports "distinct evolutionary lineages" within the species (from Hekkala et al 2009)
• Unlike the traditional view of a single Nile Crocodile species adapted to a wide geographic range

Crocodile mummies

• Found in Egyptian tombs (from Trutnau & Sommerlad 2006)
  • In 1827 two crocodile mummies were named by French naturalist Geoffroy Saint Hillaire
    • Crocodylus lacunosus and Crocodylus complanatus

Popular cultural references

• Documentary appearances
  • Deadly Crocodiles of the Nile River – 2014, National Geographic Wild
  • Nile Crocodiles: Diving with a deadly predator – 2013, CBS
    • Anderson Cooper takes an in depth look at the Nile Crocodile in this 13 minute 60 Minutes clip.

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Crocodylia

Family: Crocodylidae

Genus: Crocodylus

Species*: Crocodylus niloticus - Nile Crocodile (eastern Africa, Nile valley, southern Africa)

Species*: Crocodylus suchus - Nile Crocodile (west and central Africa)

*Note that Hekkala et al. (2011) found that although both species have adjacent ranges in Africa, they are not sister species.

Sources: Hekkala et al. (2011); Grigg and Kirshner (2015)

Image credit: © Rhys Davenport from Flickr. Some rights reserved.

Benton (1985)
Brochu (2001)
Brochu & Densmore (2001)
Carroll (1988)
Harper (2001)
Hekkala et al (2009)
Janke & Arnason (1997)
Janke & Arnason (2005)
King & Burke (1997)
Parker (2009)
Summers (2005)
Sereno (2001)
Seymour et al (2004)
Trutnau & Sommerlad (2006)