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 The mugger crocodile (''Crocodylus palustris'') is a medium-sized broad-snouted crocodile, also known as mugger and marsh crocodile. It is native to freshwater habitats from south-eastern Iran to the Indian subcontinent, where it inhabits marsh ...

) or bony crocodile, is an African

crocodile Crocodiles (family (biology), family Crocodylidae) 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 more loosely to include ...

that is also the smallest

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

(living) species of crocodile.

Description

Dwarf crocodiles attain an adult length of . Adult specimens typically weigh between . This makes it the smallest living crocodile species, although the Cuvier's dwarf caiman (''Paleosuchus palpebrosus''), a member of the family

Alligatoridae The family (biology), family Alligatoridae of crocodylians includes alligators, caimans and their extinct relatives. Phylogeny The superfamily Alligatoroidea includes all crocodilians (fossil and extant) that are more closely related to the Am ...

, is smaller at up to about . If the Congo dwarf crocodile (''O. osborni'') is recognized as a valid species, it would be both the smallest crocodile and the smallest

crocodilian Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

since it does not surpass . Adults are all dark above and on their sides, while the underside is yellowish with black patches. Some individuals living in the caves of Abanda, Gabon, displayed orange patches, apparently due to alkaline bat

guano Guano (Spanish from ) is the accumulated excrement of seabirds or bats. Guano is a highly effective fertiliser due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. Guano was also, to a le ...

that erodes the skin of the crocodile. 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 Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...

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 In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

. The

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

consists of four

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry teeth, 12 to 13 on the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

, and 14 to 15 on the

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

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 The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

regions of

Sub-Saharan Sub-Saharan Africa is the area and regions of the continent of Africa that lie south of the Sahara. These include Central Africa, East Africa, Southern Africa, and West Africa. Geopolitically, in addition to the list of sovereign states and ...

West Africa and Central Africa. Such a distribution greatly overlaps with that of the slender-snouted crocodile, encompassing countries as far west as

Senegal Senegal, officially the Republic of Senegal, is the westernmost country in West Africa, situated on the Atlantic Ocean coastline. It borders Mauritania to Mauritania–Senegal border, the north, Mali to Mali–Senegal border, the east, Guinea t ...

, reaching

Uganda Uganda, officially the Republic of Uganda, is a landlocked country in East Africa. It is bordered to the east by Kenya, to the north by South Sudan, to the west by the Democratic Republic of the Congo, to the south-west by Rwanda, and to the ...

in the east, and ranging as southerly as

Angola Angola, officially the Republic of Angola, is a country on the west-Central Africa, central coast of Southern Africa. It is the second-largest Portuguese-speaking world, Portuguese-speaking (Lusophone) country in both total area and List of c ...

. 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). Dwarf crocodiles live from lowlands to mid-altitude in streams, small rivers, swamps, pools and

mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...

, but generally avoid main sections of large rivers. 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. Unlike most crocodiles, dwarf crocodiles only rarely bask in the sun. During the night they may move some distance from water on land. Reports exist of dwarf crocodiles in isolated pools in the

savannah A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

. Dwarf crocodiles living long-term in caves are known from western

Gabon Gabon ( ; ), officially the Gabonese Republic (), is a country on the Atlantic coast of Central Africa, on the equator, bordered by Equatorial Guinea to the northwest, Cameroon to the north, the Republic of the Congo to the east and south, and ...

, which stand out as an isolated genetic group.

Biology and behaviour

The Childrens Museum of Indianapolis - Dwarf crocodile

The dwarf crocodile is a timid and mainly

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

reptile that spends the day hidden in pools or burrows, although it occasionally may be active during the day. 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. Dwarf crocodiles are generalist predators and have been recorded feeding on a wide range of small animals such as fish, crabs, frogs,

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s, insects, lizards, water birds, bats and

shrew Shrews ( family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to dif ...

s. In a study in the Democratic Republic of the Congo the primary food item was fish, and in a study in Nigeria the primary food items were gastropods and crabs. 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. Plant material has also been found in the stomach of dwarf crocodiles, but it is suspected that this is ingested by accident. They can survive for relatively long periods without food. During the dry season, dwarf crocodiles often retreat to deep holes.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 Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...

, 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

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

s 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 In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon), and these groups are given ...

history. It was first described as ''Osteoblepharon osborni'' by Schmidt in 1919, based on a few specimens from the Upper

Congo River Basin The Congo River, formerly also known as the Zaire River, is the second-longest river in Africa, shorter only than the Nile, as well as the third-largest river in the world list of rivers by discharge, by discharge volume, following the Amazon Ri ...

in what is now the

Democratic Republic of Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...

. 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. A study of

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

published in 2007, and studies of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

in 2009, 2013 and 2015 indicate that three distinctly different populations of ''Osteolaemus'' may merit full species recognition. These are ''O. tetraspis'' (

Central Africa Central Africa (French language, French: ''Afrique centrale''; Spanish language, Spanish: ''África central''; Portuguese language, Portuguese: ''África Central'') is a subregion of the African continent comprising various countries accordin ...

, except the Congo River Basin), ''O. osborni'' (Congo River Basin), and a third possibly unnamed species (

West Africa West Africa, also known as Western Africa, is the westernmost region of Africa. The United Nations geoscheme for Africa#Western Africa, United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Gha ...

). Uncertainty exists for the population in

Nigeria Nigeria, officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf of Guinea in the Atlantic Ocean to the south. It covers an area of . With Demographics of Nigeria, ...

(between ''O. tetraspis'' and the possibly unnamed West African species) as it has not been studied. A fourth

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

was found in a study of captives in 2013, but where members of this clade live in the wild is unclear. In some regions the species may come into contact. For example,

Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...

is home to both ''O. tetraspis'' and ''O. osborni''.

Etymology

The generic name, ''Osteolaemus'', means "bony throat", and is derived from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

(bone) and (

throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the Human pharynx, pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the t ...

). The genus was named as such due to the osteoderms found among the scales in the neck and belly. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

, ''tetraspis'', means "four shields", and derives from the Ancient Greek (four) and (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 DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, thymine, cytosine, and guanine. The ...

), and

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

(

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

age) data established the inter-relationships within

Crocodylidae Crocodiles (family Crocodylidae) 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 more loosely to include all extant membe ...

. In 2021, Hekkala ''et al.'' were able to use paleogenomics, extracting DNA from the extinct ''

Voay ''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 distinctiv ...

'', to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae. The below

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

shows the results of the latest study: Gibier bord route

Conservation

The dwarf crocodile is considered vulnerable by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

, and it is listed on Appendix I of

CITES CITES (shorter acronym for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of inte ...

. 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

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s where they abide. Survey data, when available, show some degree of decline, either by hunting for

bushmeat Bushmeat is meat from wildlife species that are Hunting, hunted for human consumption. Bushmeat represents a primary source of animal protein and a cash-earning commodity in poor and rural communities of humid tropical forest regions of the worl ...

or habitat loss due to

deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...

. However, it is a widely spread, and presumably numerous overall. In some regions the populations remain healthy, but in others (such as

Gambia The Gambia, officially the Republic of The Gambia, is a country in West Africa. Geographically, The Gambia is the List of African countries by area, smallest country in continental Africa; it is surrounded by Senegal on all sides except for ...

and

Liberia Liberia, officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to Guinea–Liberia border, its north, Ivory Coast to Ivory Coast–Lib ...

) it has seriously declined and may risk

extirpation Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with extinction, global extinctions. Local extinctions ...

. Dwarf crocodiles occur in several protected reserves. Though some skins are used in local manufacturing of

leather Leather is a strong, flexible and durable material obtained from the tanning (leather), tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffal ...

products, they are of poor quality, so little interest is shown in

captive breeding Captive breeding, also known as captive propagation, is the process of keeping plants or animals in controlled environments, such as wildlife reserves, zoos, Botanical garden, botanic gardens, and other Conservation biology, conservation facilitie ...

or a sustainable use program. In contrast, they are sometimes hunted for food and part of the bushmeat trade. 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. 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''.

Gallery

File:Osteolaemus tetraspis, tooth.JPG, Tooth File:Osteolaemus tetraspis Bronx Zoo.webm,

Bronx Zoo The Bronx Zoo (also historically the Bronx Zoological Park and the Bronx Zoological Gardens) is a zoo within Bronx Park in the Bronx, New York City. It is one of the largest zoos in the United States by area and the largest Metropolis, metropol ...

, USA File:West African Dwarf Crocodile 5.jpg, Pittsburgh Zoo, USA File:Dwarf crocodile Cleveland Zoo 5.4.19 DSC 0058.jpg, Cleveland Zoo, USA File:Osteolaemus tetraspis - Karlsruhe Zoo 02.jpg, Karlsruhe Zoo, Germany File:Osteolaemus tetraspis - Karlsruhe Zoo 01.jpg, Karlsruhe Zoo, Germany File:Osteolaemus tetraspis fg01.JPG,

Berlin Zoological Garden The Berlin Zoological Garden (, ) is the oldest surviving and best-known zoo in Germany. Opened in 1844, it covers and is located in Berlin's Tiergarten (park), Tiergarten. With about 1,380 different species and over 20,200 animals, the zoo pre ...

, Germany File:Stumpfkrokodil (Ostaeolaemus tetraspis).jpg, Aquazoo Löbbecke Museum, Germany File:Stumpfkrokodil Osteolaemus tetraspis Tierpark Hellabrunn-1.jpg,

Tierpark Hellabrunn Hellabrunn Zoo () is a 40 hectare (99 acre) zoological garden in the Bavarian capital of Munich. The zoo is situated on the right bank of the river Isar, in the southern part of Munich near the quarter of Thalkirchen. A high ratio of enclosures ...

, Germany File:Stumpfkrokodil (Osteolaemus tetraspis).JPG, Tierpark Dählhölzli, Switzerland File:Bristol.zoo.westafrican.dwarf.croc.arp.jpg,

Bristol Zoo Bristol Zoo was a zoo in the city of Bristol in South West England. The zoo's stated mission was to "maintain and defend" biodiversity through breeding endangered species, conserving threatened species and habitats and promoting a wider underst ...

, UK File:Stumpfkrokodil Bioparc Fuengirola 02 2014.jpg, Bioparc in

Fuengirola Fuengirola () is a city on the Costa del Sol in the province of Málaga in the autonomous community of Andalusia in southern Spain. It is located on the central coast of the province and integrated into the region of the Costa del Sol and the Com ...

, Spain File:Breedvoorhoofdkrokodil (41389358971).jpg, Wildlands Adventure Zoo, Netherlands File:Reptilarium du Larzac - Osteolaemus tetraspis 01.jpg, Reptilarium du Larzac, France File:Micro Zoo de Saint Malo - Osteolaemus tetraspis 02.jpg, 5 year old female, at Micro Zoo de Saint Malo, France File:Micro Zoo de Saint Malo - Osteolaemus tetraspis 01.jpg, 5 year old female, at Micro Zoo de Saint Malo, France File:Gfp-dwarf-crocodile.jpg File:Crocodile nain du bassin d'Afrique de l'Ouest.jpeg