Dwarf Crocodile (Osteolaemus tetraspis) Fact Sheet: Taxonomy & History

Common names (from ITIS 2015 unless otherwise noted)

• English names
  • Dwarf Crocodile, African Dwarf Crocodile, Broad-nosed Crocodile
    • West African Dwarf Crocodile reserved for O. t. tetraspis subspecies
    • Congo Dwarf Crocodile reserved for O. t. osborni subspecies
      • Also known as Osborn’s Crocodile
  • Broad-fronted Crocodile (Guggisberg 1972; Waitkuwait 1989)
  • West African Stumpy Crocodile (Waitkuwait 1989)
• Spanish names
  • Cocodrilo Chico Africano (Crocodile Specialist Group 1996)
• French names
  • Crocodile Nain (Eaton 2010a)
• German names
  • Stumpfkrokodile (Eaton 2010a)
• Etymology
  • Crocodile from the Latin word crocodilus (and Greek krokodeilos) meaning “lizard” (Brown 1956)

Scientific name

• Etymology
  • Genus Osteolaemus from two Greek words; osteon meaning “bone” and laimosmeaning “throat” (Brown 1956; Gotch 1995)
    • Referring to the four large, bony plates arranged in a square on the nape of the neck; known as a nuchal shield (Gotch 1995)
  • Specific epithet tetraspis from two Greek words; tetra meaning “four” and aspis meaning “a shield”
• Synonyms
  • Osteolaemus osborni
  • Osteoblepharon osborni (Schmidt 1911)
• Taxonomy under debate (from Eaton et al. 2009; Eaton 2010a; Inger 1948 unless otherwise noted)
  • Currently recognized subspecies formerly viewed as distinct species
    • View of subspecific designations has direct implications for conservation (Shirley et al. 2014; Smolensky 2014)
    • Recognize and deter unintended hybridization
    • May change population counts
  • Morphological and molecular studies may lead to elevation of O. t. osborni to its former taxonomic designation (Eaton 2010a; Eaton et al. 2009; Franke et al. 2013; Shirley et al. 2014)
  • Recent research suggests 3 species within the genus Osteolaemus (Eaton et al. 2009; Franke et al. 2013; Shirley et al. 2014; Smolensky et al. 2014)
    • Osteolaemus osborni – Congo River Basin form
    • Osteolaemus tetraspis – Central African form
    • Ostelaemus sp. nov. cf. tetraspis – West African form
  • Additional lineages may be present across current range (Franke et al. 2013), but this may represent a spectrum of genetic diversity [i.e., an Evolutionarily Significant Unit (ESU)] within the newly identified taxonomic lineage in West Africa (Osteolaemus sp. nov. cf. tetraspis) (Shirley et al. 2014)

Archosaurs

• Clade (grouping) members (from Brochu 2001 unless otherwise noted)
  • Extinct
    • Dinosaurs
    • Pterosaurs
  • Extant (living)
    • Birds
    • Crocodilians
      • Crocodiles and their relatives
      • Living members represent a small portion of historic diversity (Brochu 2003)
• Early crocodilians (from Brochu 2003 unless otherwise noted)
  • Represented by alligator-like and gavial-like fossils

Order Crocodylia

• Includes 3 (extant) families (from ITIS 2015 unless otherwise noted)
  • Alligatoridae
    • Includes the alligators and caimans
    • Found predominantly in the Western Hemisphere (Brochu 2003)
      • A single species survives in Asia today (Brochu 2003)
  • Gavialidae
    • Includes the gavials/gharials
  • Crocodylidae
    • Includes the true crocodiles
    • Most recently derived clade (Brochu 2003)
      • Early naming conventions incorrectly classified many fossils within the genus Crocodylus (Brochu 2003)
        • Led to the mistaken view of the group as an ancient lineage (Brochu 2003)
• Evolutionary history (from Brochu 2003 unless otherwise noted)
  • Origins
    • Fossil remains representing each family dated to the Late Cretaceous
      • Formed distinctive groups by 72.1–83.6 million years ago (Mya)
    • Common ancestor of living crocodilians likely lived c. 80-100 Mya (Green et al. 2014)
  • Historical distribution
    • Remains found on every continent
    • Ranged from Antarctica to Ellesmere Island during the Eocene
• Genetic variability (from Green et al. 2014)
  • Genetic similarity contrasts distinctive morphological differences
    • Limited intraspecific (between species) variable and slow karyotype evolution

Family Crocodylidae

• Divided into 3 (extant) genera (from ITIS 2015)
  • Crocodylus
  • Mecistops
  • Osteolaemus
• Fossil record (from Brochu 2003)
  • Earliest fossil forms
    • Dated to c. 66-72 Mya; Prodiplocynodon, from Wyoming
    • Generalized in appearance
  • Historical distribution
    • Spread throughout the Northern Hemisphere by the late Early Tertiary, c. 66-23.03 Mya

Genus Osteolaemus

• Close relatives (from Brochu 2003 unless otherwise noted)
  • Some authorities place Osteolaemus as sister taxon to Crocodylus and Mecistops (Brochu 2010)
  • Recent evidence suggests Osteolaemus as sister taxon to the slender-snouted crocodile (Mecistops cataphractus) which is no longer considered to be a member of Crocodylus; both Osteolaemus and Mecistops are then considered sister taxa to the true crocodiles, Crocodylus (Grigg and Kirshner 2015; Eaton 2010b; Hekkla et al. 2011; Shirley et al. 2014; Shirley at al. 2015)
  • Extinct relations
    • Euthecodon; a bizarre, long-snouted African endemic
      • Skull resembles the head of a sawfish due to laterally protruding alveoli
    • “Crocodylus” robustus; present on Madagascar
      • Resembles an oversized Osteolaemus with prominent, triangular horns (Brochu 2003; Brochu 2007)
• Origin of Osteolaemus
  • With Mecistops, shared a common ancestor with Crocodylus as recently as c. 26 Mya (Shirley et al. 2014)
  • Ancestral Osteolaemus split from a shared ancestor with Mecistops c. 21 Mya (Shirley et al. 2014)
• Number of species within genus (from ITIS 2015; Ray et al. 2001)
  • 1 currently recognized
    • Subspecies, previously described as separate species
      • O. t. osborni
        • Once assigned to its own genus (Schmidt 1911)
      • O. t. tetraspis
    • High levels of genetic variability within the genus

Religious and historical attachment (from Shirley et al. 2009 unless otherwise noted)

• Beliefs related to crocodiles
• Persistence of water is tied directly to crocodiles in Ghana and Côte d'Ivoire
• Water will vanish if crocodiles vanish
• Worshipped as totems
• Guarded and cared for in sacred crocodile pools in West Africa (Kpera 2003; Mosier and Barber 1994)
• Reported for both Nile Crocodile and Dwarf Crocodile
• Guardians of community grain stores

Traditional medicine (from Kpera 2003 unless otherwise noted)

• Crocodile bile believed to be a potent toxin (Shirley et al. 2009)
• Various portions of crocodiles used for medicinal products in Benin (Kpera 2003)
• Heart, lung, head, and teeth believed to cure diseases, such as asthma

Akan culture and art (from Guggisberg 1972)

• Crocodiles often represented in artworks of carved wood

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Crocodylia – crocodiles, alligators, caimans, gharials

Family: Crocodylidae - crocodiles

Genus: Osteolaemus

Species: Osteolaemus tetraspis (Cope 1861)

Subspecies: O. t. osborni - Congo Dwarf Crocodile
Subspecies: O. t. tetraspis - African Dwarf Crocodile, Dwarf Crocodile, West African Dwarf Crocodile, Broad-nosed Crocodile

(Classification according to ITIS 2015 unless otherwise noted)

Akan sword ornament in the form of a crocodile. 

Copper alloy, late 19th or early 20th century.  Image Credit: © Brooklyn Museum from Wikimedia Commons.  Creative Commons License 3.0; some rights reserved.

Brown (1956)
Brochu (1997)
Brochu (2001)
Brochu (2003)
Brochu (2007)
Cope (1861)
Crocodile Specialist Group (1996)
Eaton (2010a)
Eaton et al. (2009)
Franke et al. (2013)
Gotch (1995)
Green et al. (2014)
Guggisberg (1972)
Inger (1948)
ITIS (2015)
Kpera (2003)
Mosier and Barber (1994)
Ray et al. (2001)
Schmidt (1911)
Shirley et al. (2009)
Shirley et al. (2014)
Shirley et al. (2015)
Smolensky (2014)
Waitkuwait (1989)