Dwarf crocodile

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Dwarf crocodile
Temporal range: Miocene - Recent, 11.6–0  Ma [1]
Crocodile nain aquarium porte doree Paris.JPG
At Dorée Tropical Aquarium
CITES Appendix I (CITES) [3]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Order: Crocodilia
Family: Crocodylidae
Subfamily: Osteolaeminae
Genus: Osteolaemus
Species:
O. tetraspis
Binomial name
Osteolaemus tetraspis
Cope, 1861 [4]
Osteolaemus tetraspis Distribution.png
Range of the dwarf crocodile in green

The dwarf crocodile (Osteolaemus tetraspis), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile) or bony crocodile, [5] is an African crocodile that is also the smallest extant (living) species of crocodile.

Contents

Description

Juvenile in Ghana Dwarf Crocodile juv - Ankasa - Ghana 14 S4E1975 (16203014142) (cropped).jpg
Juvenile in Ghana
Orange cave-dwelling dwarf crocodile next to a "normal" aboveground individual in Gabon Cave-dwelling-orange-crocodile.jpg
Orange cave-dwelling dwarf crocodile next to a "normal" aboveground individual in Gabon

Dwarf crocodiles attain a medium adult length of 1.5 m (4.9 ft), though the maximum recorded length for this species is 1.9 m (6.2 ft). Adult specimens typically weigh between 18 and 32 kg (40 and 71 lb), with the largest females weighing up to 40 kg (88 lb) and the largest males weighing 80 kg (180 lb). [6] [7] This makes it the smallest living crocodile species, although the Cuvier's dwarf caiman (Paleosuchus palpebrosus), a member of the family Alligatoridae, is smaller at up to about 1.7 m (5.6 ft). [7] [8] If the Congo dwarf crocodile (O. osborni) is recognized as a valid species, it would be both the smallest crocodile and the smallest crocodilian since it does not surpass 1.2 m (3.9 ft). [9] Adults are all dark above and on their sides, while the underside is yellowish with black patches. [10]

Some individuals living in the caves of Abanda, Gabon, displayed orange patches, apparently due to alkaline bat guano that erodes the skin of the crocodile. [11] Juveniles have a lighter brown banding on body and tails and yellow patterns on the head.

As a result of its small size and heightened vulnerability to predation, this species of crocodile has a heavily armoured neck, back, and tail and also has osteoderms on its belly and underside of neck.

Osteolaemus has a blunt short snout, as long as it is wide, similar to that of a Cuvier's dwarf caiman, probably a result of occupying a similar ecological niche. The dentition consists of four premaxillary teeth, 12 to 13 on the maxilla, and 14 to 15 on the dentary bone.

O. t. tetraspis has lighter colours, a more pointed, upturned snout, and more body armour than O. t. osborni.

Distribution and habitat

Dwarf crocodiles range across tropical regions of Sub-Saharan West Africa and Central Africa. Such a distribution greatly overlaps with that of the slender-snouted crocodile, encompassing countries as far west as Senegal, reaching Uganda in the east, and ranging as southerly as Angola. [2] [9] The last confirmed record from Uganda was in the 1940s, but whether the species, which is easily overlooked, still survives there is unclear (it was always marginal in this country, only occurring in the far southwest). [9]

Dwarf crocodiles live from lowlands to mid-altitude in streams, small rivers, swamps, pools and mangrove, but generally avoid main sections of large rivers. [9] [12] Most of their range is within forested regions, but it may extend into more open regions where the streams or river are well-shaded. They are also found in seasonally-flooded forest. [13] Unlike most crocodiles, dwarf crocodiles only rarely bask in the sun. [9] During the night they may move some distance from water on land. [9] Reports exist of dwarf crocodiles in isolated pools in the savannah. [14] Dwarf crocodiles living long-term in caves are known from western Gabon, [15] which stand out as an isolated genetic group. [16]

Biology and behaviour

Skull from the collection of the Children's Museum of Indianapolis The Childrens Museum of Indianapolis - Dwarf crocodile.jpg
Skull from the collection of the Children's Museum of Indianapolis
Bronx Zoo. Dwarf Crocodile (Osteolaemus tetraspis) 4.jpg
Bronx Zoo.

The dwarf crocodile is a timid and mainly nocturnal reptile that spends the day hidden in pools or burrows, [14] although it occasionally may be active during the day. [9] Foraging is mainly done in or near the water, although it is considered to be one of the most terrestrial species of crocodilian and may expand the feeding pattern to land in extensive forays, especially after rains. [14]

Dwarf crocodiles are generalist predators and have been recorded feeding on a wide range of small animals such as fish, crabs, frogs, gastropods, insects, lizards, water birds, bats and shrews. [9]

[15] [12] In a study in the Democratic Republic of the Congo the primary food item was fish, [9] and in a study in Nigeria the primary food items were gastropods and crabs. [17] In the Congo there is a level of seasonality in its diet, changing from fish in the wet season to crustaceans in the dry season, when fish are less available. [10] Plant material has also been found in the stomach of dwarf crocodiles, but it is suspected that this is ingested by accident. [12] They can survive for relatively long periods without food. [7] During the dry season, dwarf crocodiles often retreat to deep holes. [12]

in the wild in Ghana Dwarf crocodile (Osteolaemus tetraspis) Ankasa.jpg
in the wild in Ghana

True to its solitary, nocturnal nature, a dwarf crocodile digs out a burrow in which to hide and rest during the day, which can sometimes have a submerged entrance. An individual lacking the right conditions to do so usually lives between tree roots that hang over the ponds where it lives.

Reproduction

Interacting closely only in breeding season, female dwarf crocodiles build their nest mounds at the beginning of the wet season, which spans May and June. The nest, situated near the water, is a mound of wet, decaying vegetation that incubates the eggs due to the heat generated by the decomposition of the plant material. A small number of eggs is laid, usually about 10, though in extreme cases up to 20, and they incubate in 85 to 105 days. Hatchlings measure 28 cm when emerging from the eggs. The female guards the nest during the incubation period, and after the eggs hatch, she watches over the young for an unknown period of time, as young can be eaten by a great range of predators (birds, fish, mammals and reptiles, including other crocodiles).

Taxonomy and etymology

The second species has had a somewhat convoluted taxonomical history. It was first described as Osteoblepharon osborni by Schmidt in 1919, based on a few specimens from the Upper Congo River Basin in what is now the Democratic Republic of Congo. However, Inger in a 1948 paper found the specimens wanting of characteristics that would justify a generic separation from Osteolaemus and referred the specimens to Osteolaemus osborni . In 1961, it was reduced to subspecies rank. [18]

A study of morphology published in 2007, and studies of DNA in 2009, 2013 and 2015 indicate that three distinctly different populations of Osteolaemus may merit full species recognition. [19] [20] [21] [22] These are O. tetraspis (Central Africa, except the Congo River Basin), O. osborni (Congo River Basin), and a third possibly unnamed species (West Africa). [20] [22] [14] Uncertainty exists for the population in Nigeria (between O. tetraspis and the possibly unnamed West African species) as it has not been studied. [14] A fourth clade was found in a study of captives in 2013, but where members of this clade live in the wild is unclear. [21] In some regions the species may come into contact. For example, Cameroon is home to both O. tetraspis and O. osborni. [23]

Etymology

The generic name, Osteolaemus, means "bony throat", and is derived from the Ancient Greek όστεον (bone) and λαιμός (throat). The genus was named as such due to the osteoderms found among the scales in the neck and belly.

The specific epithet, tetraspis, means "four shields", and derives from the Ancient Greek τετρα (four) and ασπίς (shield), as the back of the neck has four large, shield-like scales.

Phylogeny

A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodylidae. [24] In 2021, Hekkala et al. were able to use paleogenomics, extracting DNA from the extinct Voay , to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae. [25]

The below cladogram shows the results of the latest study:

Crocodylidae
Osteolaeminae

Brochuchus †

Rimasuchus †

Osteolaemus osborni Osborn’s dwarf crocodile

Osteolaemus tetraspisDwarf crocodile

Crocodylinae

Voay †

Crocodylus

Crocodylus johnstoni Freshwater crocodile

Crocodylus novaeguineae New Guinea crocodile

Crocodylus mindorensis Philippine crocodile

Crocodylus porosus Saltwater crocodile

Crocodylus siamensis Siamese crocodile

Crocodylus palustris Mugger crocodile

Crocodylus suchus West African crocodile

Crocodylus niloticus Nile crocodile

Crocodylus moreletii Morelet's crocodile

Crocodylus rhombifer Cuban crocodile

Crocodylus intermedius Orinoco crocodile

Crocodylus acutus American crocodile

(crown group)
Carcass hanging with monkey. Gibier bord route.jpg
Carcass hanging with monkey.
Handbag of dwarf crocodile leather, Natural History Museum, London. Handbag of West African Dwarf Crocodile.JPG
Handbag of dwarf crocodile leather, Natural History Museum, London.

Conservation

The dwarf crocodile is considered vulnerable by the IUCN, [2] and it is listed on Appendix I of CITES. [9] It is a little-known species, so unlike their more studied relatives, conservationists are often not as aware of how their populations are faring under the growing human pressure over the ecosystems where they abide. Survey data, when available, show some degree of decline, either by hunting for bushmeat or habitat loss due to deforestation. However, it is a widely spread, and presumably numerous overall. [10] In some regions the populations remain healthy, but in others (such as Gambia and Liberia) it has seriously declined and may risk extirpation. [10] Dwarf crocodiles occur in several protected reserves. [12]

Though some skins are used in local manufacturing of leather products, they are of poor quality, so little interest is shown in captive breeding or a sustainable use program. In contrast, they are sometimes hunted for food and part of the bushmeat trade. [9] [10]

Dwarf crocodiles are widely kept and bred in zoos. Based on a study of individuals kept in AZA zoos, captives in North America are primarily O. tetrapis and the possibly unnamed West African species, but there are also some hybrids. [22] Another study of individuals kept at EAZA zoos revealed a similar picture for Europe, but also that there were a few individuals of the fourth clade (native range in the wild unknown) and a single O. osborni. [21]

Related Research Articles

<span class="mw-page-title-main">Crocodile</span> Family of large reptilian carnivores

Crocodiles or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant members of the order Crocodilia, which includes the alligators and caimans, the gharial and false gharial among other extinct taxa.

<span class="mw-page-title-main">Crocodilia</span> Order of mostly large, predatory, semiaquatic reptiles

Crocodilia is an order of semiaquatic, predatory reptiles known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchian, a subset of archosaurs that appeared about 235 million years ago and were the only survivors of the Triassic–Jurassic extinction event. The order includes the true crocodiles, the alligators and caimans, and the gharial and false gharial. Although the term "crocodiles" is sometimes used to refer to all of these, it is less ambiguous to use "crocodilians".

<span class="mw-page-title-main">Crocodylinae</span> Subfamily of crocodiles

Crocodylinae is a subfamily of true crocodiles within the family Crocodylidae, and is the sister taxon to Osteolaeminae.

<span class="mw-page-title-main">False gharial</span> Species of crocodilian

The false gharial, also known by the names Malayan gharial, Sunda gharial and tomistoma, is a freshwater crocodilian of the family Gavialidae native to Peninsular Malaysia, Borneo, Sumatra and Java. It is listed as Endangered on the IUCN Red List, as the global population is estimated at around 2,500 to 10,000 mature individuals.

<i>Crocodylus</i> Genus of reptiles

Crocodylus is a genus of true crocodiles in the family Crocodylidae.

<span class="mw-page-title-main">Orinoco crocodile</span> Species of reptile

The Orinoco crocodile is a critically endangered crocodile. Its population is very small, and they can only be found in the Orinoco river basin in Venezuela and Colombia. Extensively hunted for their skins in the 19th and 20th centuries, it is one of the most endangered species of crocodiles. It is a very large species of crocodilian; males have been reported up to 6.8 m in the past, weighing over 900 kg (2,000 lb), but such sizes do not exist today, 5.2 m being a more widely accepted maximum size. A large male today may attain 4.2 m in length and can weigh up to 450 kg (1,000 lb), while females are substantially smaller with the largest likely to weigh around 225 kg (496 lb). Sexual dimorphism is not as profound as in other crocodilian species. The coloration is light even in adults.

<i>Osteolaemus</i> Genus of crocodiles

Osteolaemus is a genus of crocodiles. They are small, secretive crocodiles that occur in wetlands of West and Middle Africa. They are commonly known as the African dwarf crocodiles. Unlike other crocodiles, Osteolaemus are strictly nocturnal.

<span class="mw-page-title-main">West African slender-snouted crocodile</span> Species of reptile

The West African slender-snouted crocodile, or slender-snouted crocodile, is a critically endangered species of African crocodile. It is one of five species of crocodile in Africa, the other four being the Central African slender-snouted, Nile, West African and dwarf crocodiles.

<i>Mecistops</i> Genus of reptiles

Mecistops is a genus of crocodiles, the slender-snouted crocodiles, native to sub-Saharan Africa.

<i>Euthecodon</i> Extinct genus of crocodilian

Euthecodon is an extinct genus of long-snouted crocodile. It was common throughout much of Africa during the Neogene, with fossils being especially common in Kenya, Ethiopia, and Libya. Although superficially resembling that of gharials, the long snout was a trait developed independently from that of other crocodilians and suggests a diet of primarily fish. Euthecodon coexisted with a wide range of other crocodiles in the areas it inhabited before eventually going extinct during the Pleistocene.

<i>Voay</i> Extinct genus of reptiles

Voay is an extinct genus of crocodile from Madagascar that lived during the Late Pleistocene to Holocene, containing only one species, V. robustus. Numerous subfossils have been found, including complete skulls, noted for their distinctive pair of horns on the posterior, as well as vertebrae and osteoderms from such places as Ambolisatra and Antsirabe. The genus is thought to have become extinct relatively recently. It has been suggested to have disappeared in the extinction event that wiped out much of the endemic megafauna on Madagascar, such as the elephant bird and Malagasy hippo, following the arrival of humans to Madagascar around 2000 years ago. Its name comes from the Malagasy word for crocodile.

<i>Planocrania</i> Extinct genus of reptiles

Planocrania is an extinct genus of eusuchian crocodyliforms from what is now China. Two species are currently known to belong to the genus.

<span class="mw-page-title-main">Crocodyloidea</span> Superfamily of crocodiles

Crocodyloidea is one of three superfamilies of crocodilians, the other two being Alligatoroidea and Gavialoidea, and it includes the crocodiles. Crocodyloidea may also include the extinct Mekosuchinae, native to Australasia from the Eocene to the Holocene, although this is disputed.

Rimasuchus is an extinct genus of crocodile from the Miocene of Egypt and possibly Libya. Only one species - Rimasuchus lloydi - is currently known. It was previously thought to be a species of Crocodylus, but is now thought to be more closely related to the modern African dwarf crocodiles (Osteolaemus).

<span class="mw-page-title-main">Tomistominae</span> Subfamily of reptiles

Tomistominae is a subfamily of crocodylians that includes one living species, the false gharial. Many more extinct species are known, extending the range of the subfamily back to the Eocene epoch. In contrast to the false gharial, which is a freshwater species that lives only in southeast Asia, extinct tomistomines had a global distribution and lived in estuaries and along coastlines.

<span class="mw-page-title-main">Osteolaeminae</span> Subfamily of crocodiles

Osteolaeminae is a subfamily of true crocodiles within the family Crocodylidae containing the dwarf crocodiles and slender-snouted crocodiles, and is the sister taxon to Crocodylinae.

"Crocodylus" megarhinus is an extinct species of crocodile from the Eocene of Egypt. A partial skull was found by British paleontologist Charles William Andrews in the Fayum Depression. Andrews named Crocodylus megarhinus in 1905 on the basis of the holotype skull. A complete skull was also uncovered from Egypt in 1907 but was not recognized as "C." megarhinus until 1927.

<span class="mw-page-title-main">West African crocodile</span> Species of reptile

The West African crocodile, desert crocodile, or sacred crocodile is a species of crocodile related to, and often confused with, the larger and more aggressive Nile crocodile.

Brochuchus is an extinct genus of crocodile known from the Early Miocene Hiwegi Formation of Rusinga Island in Lake Victoria, Kenya; it was originally named as a species of Crocodylus. It contains two species, B. parvidens and B. pigotti. Brochuchus belongs to the family Crocodylidae, which includes all living crocodiles. The closest living relative of Brochuchus is Osteolaemus, the dwarf crocodile. Compared to Osteolaemus, which has a small body and blunt snout, Brochuchus has a more generalized crocodylid anatomy. Brochuchus is characterized by a flat and relatively narrow skull, and although it is larger than Osteolaemus it is smaller than most other crocodylids. It has two prominent bumps on the surface of its snout.

References

  1. ↑ Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ . 9: e12094. doi: 10.7717/peerj.12094 . PMC   8428266 . PMID   34567843.
  2. 1 2 3 Crocodile Specialist Group (1996). "Osteolaemus tetraspis". IUCN Red List of Threatened Species . 1996: e.T15635A4931429. doi: 10.2305/IUCN.UK.1996.RLTS.T15635A4931429.en . Retrieved 19 November 2021.
  3. ↑ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  4. ↑ Osteolaemus tetraspis at the Reptarium.cz Reptile Database. Accessed 17 September 2018.
  5. ↑ "Osteolaemus tetraspis (Cope, 1861)". crocodilian.com. Archived from the original on 21 February 2020. Retrieved 23 September 2019.
  6. ↑ "Dwarf Crocodile". The Animal Files. Retrieved 7 August 2017.
  7. 1 2 3 "The African Dwarf Crocodile". h2g2. 1 June 2010. Retrieved 7 August 2017.
  8. ↑ Britton, Adam. "Paleosuchus". Crocodilians: Natural History & Conservation. Crocodilian.com. Retrieved 9 August 2017.
  9. 1 2 3 4 5 6 7 8 9 10 11 Sprawls, S.; K. Howell; R. Drewes & J. Ashe (2002). A Field Guide to the Reptiles of East Africa. Academic. pp. 276–277. ISBN   978-0-12-656470-9.
  10. 1 2 3 4 5 "Osteolaemus tetraspis". crocodilian.com. 1 June 2010. Retrieved 9 August 2017.
  11. ↑ Shirley, Matthew; Burtner, Brittany; Oslisly, Richard; Sebag, David; Testa, Olivier (2016-09-26). "Diet and body condition of cave-dwelling dwarf crocodiles (Osteolaemus tetraspis , Cope 1861) in Gabon". African Journal of Ecology. 55 (4): 411–422. doi:10.1111/aje.12365.
  12. 1 2 3 4 5 Pauwels; Barr; Sanchez & Burger (2007). "Diet records for the Dwarf Crocodile, Osteolaemus tetraspis tetraspis in Rabi Oil fields and Loango National Park, southwestern Gabon". Hamadryad. 31 (2): 258–264.
  13. ↑ Eaton, M. J., Martin, A. P., Thorbjarnarson, J. B., & Amato, G. (2009). Species-level diversification of African dwarf crocodiles (Genus Osteolaemus): A geographic and phylogenetic perspective. Molecular Phylogenetics and Evolution, 50(3), 496–506. https://doi.org/10.1016/j.ympev.2008.11.009
  14. 1 2 3 4 5 Eaton, M.J. (2010). "Dwarf crocodile Osteolaemus tetraspis" (PDF). In Manolis, S.C.; C. Stevenson (eds.). Crocodiles: Status, Survey and Conservation Action Plan (3 ed.). IUCN Crocodile Specialist Conservation Group. pp. 127–132.
  15. 1 2 "Weird orange crocodiles found gorging on bats in Gabon's caves". New Scientist. 12 October 2016. Retrieved 10 August 2017.
  16. ↑ Hance, Jeremy (2018-01-29). "Orange cave crocodiles may be mutating into new species". the Guardian. Retrieved 2018-01-29.
  17. ↑ Luiselli, L.; Akani, G. C. & Capizzi, D. (1999). "Is there any interspecific competition between dwarf crocodiles (Osteolaemus tetraspis) and Nile monitors (Varanus niloticus ornatus) in the swamps of central Africa? A study from south-eastern Nigeria". Journal of Zoology. 247 (1): 127–131. doi:10.1111/j.1469-7998.1999.tb00200.x.
  18. ↑ Wermuth, H. & R. Mertens (1961). Schildkröten, Krokodile, Brückenechsen. Veb Gustav Fischer Verlag.
  19. ↑ Brochu, C.A. (2007). "Morphology, relationships, and biogeographical significance of an extinct horned crocodile (Crocodylia, Crocodylidae) from the Quaternary of Madagascar". Zoological Journal of the Linnean Society. 150 (4): 835–863. doi: 10.1111/j.1096-3642.2007.00315.x .
  20. 1 2 Eaton, Mitchell J.; Andrew Martin; John Thorbjarnarson & George Amato (March 2009). "Species-level diversification of African dwarf crocodiles (genus Osteolaemus): A geographic and phylogenetic perspective". Molecular Phylogenetics and Evolution. 50 (3): 496–506. doi:10.1016/j.ympev.2008.11.009. PMID   19056500.
  21. 1 2 3 Franke, Franziska Anni; Schmidt, Fabian; Borgwardt, Christin; Bernhard, Detlef; Bleidorn, Christoph; Engelmann, Wolf-Eberhard & Schlegel, Martin (2013). "Genetic differentiation of the African dwarf crocodile Osteolaemus tetraspis Cope, 1861 (Crocodylia: Crocodylidae) and consequences for European zoos". Organisms Diversity & Evolution. 13 (2): 255–266. doi:10.1007/s13127-012-0107-1. S2CID   14636510.
  22. 1 2 3 Shirley, M. H.; Villanova, V. L.; Vliet, K. A. & Austin, J. D. (2015). "Genetic barcoding facilitates captive and wild management of three cryptic African crocodile species complexes". Animal Conservation. 18 (4): 322–330. Bibcode:2015AnCon..18..322S. doi: 10.1111/acv.12176 . S2CID   82155811.
  23. ↑ Smolensky, N.L. (2015). "Co-occurring cryptic species pose challenges for conservation: a case study of the African dwarf crocodile (Osteolaemus spp.) in Cameroon". Oryx. 49 (4): 584–590. doi: 10.1017/S0030605314000647 .
  24. ↑ Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B . 285 (1881). doi: 10.1098/rspb.2018.1071 . PMC   6030529 . PMID   30051855.
  25. ↑ Hekkala, E.; Gatesy, J.; Narechania, A.; Meredith, R.; Russello, M.; Aardema, M. L.; Jensen, E.; Montanari, S.; Brochu, C.; Norell, M.; Amato, G. (2021-04-27). "Paleogenomics illuminates the evolutionary history of the extinct Holocene "horned" crocodile of Madagascar, Voay robustus". Communications Biology. 4 (1): 505. doi: 10.1038/s42003-021-02017-0 . ISSN   2399-3642. PMC   8079395 . PMID   33907305.

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