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• O. t. tetraspis Cope, 1861
• O. t. osborni (Schmidt, 1919) – Congo (or Osborn’s) dwarf crocodile
  

The second subspecies 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.

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. These are O. tetrapis (Central Africa, except the Congo River Basin), O. osborni (Congo River Basin), and a third possibly unnamed species (West Africa). The name afzelii Lilljeborg, 1867 (type locality: Sierra Leone) may be available for the West African species. Uncertainty exists for the population in Nigeria (between O. tetrapis and the possibly unnamed West African species) as it has not been studied. A fourth clade 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 is home to both O. tetrapis and O. osborni.

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). 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). 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). Adults are all dark above and on their sides, while the underside is yellowish with black patches. Individuals living in caves may have orange patches, apparently due to acidic bat guano 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 on its belly and underside of the 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.

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). 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). 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). Adults are all dark above and on their sides, while the underside is yellowish with black patches. Individuals living in caves may have orange patches, apparently due to acidic bat guano 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 on its belly and underside of the 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.

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. 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, 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. 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. Dwarf crocodiles living long-term in caves are known from western Gabon,[18] which stand out as an isolated genetic group.

The dwarf crocodile is a timid and mainly nocturnal 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, gastropods, insects, lizards, water birds, bats and shrews. 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 where 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.
https://en.wikipedia.org/wiki/Dwarf_crocodile

The Orange Cave-Dwelling and Digging Crocodiles

Scientists in Gabon discover orange, cave-dwelling crocodiles

Thursday 28 June 2018 - 1:20 pm


This photograph taken on 11 August 2010, shows an orange cave crocodile captured in a cave in Abanda in the Ogooue-Maritime, in the south-west of Gabon.
LIBREVILLE - The West African state of Gabon is famous for its biodiversity but in a galaxy of spectacular finds, one stands out: orange crocodiles.

Scientists looking for traces of ancient human life stumbled upon the unusual reptiles decade ago as they searched in the gloom of isolated caves in Gabon&39;s southern Omboue region.
"When I approached with the torch in the cave, I saw red eyes... crocodiles!", said geo-archaeologist Richard Oslisly. It was only two years later when they hauled one out into the light that they realised it was orange.
"At first we thought the colour came from their food because we saw that these reptiles ate orange bats," said Oslisly.
The scientists discarded other theories before speculating that lack of light in the Abanda caves may have caused depigmentation and urea in bat droppings may then have induced an orange hue like this: https://youtu.be/Ru2gAI6qKGY

Under this theory, "the bat guano began to attack their skin and transformed their colour," said speleologist Olivier Testa, a member of the research team.
Dwarf crocodiles (Osteolaemus tetraspis) are a well-studied species, but the ones in the cave complex stand out in the way they have adapted to their habitat.

Oslisly, Testa and an American researcher, Matthew Shirley, have carried out multiple expeditions to study the unusual animals, which can grow to 1.7 metres.
"We think these... crocodiles have been in the Abanda caves for around 3,000 years, which correlates fairly well with a time when the sea level fell and this coastal zone became terrestrial once again," Shirley said.
Mapping the cave complex, the scientists found four orange specimens in a community of 40.
The crocodiles of "normal" colour, they discovered, live in grottos which are connected to the surface.
But the orange-coloured ones live in caverns that are accessible today only from vertical shafts.
However, the cave system also has smaller horizontal connections, which are filled with water or dry according to the level of the groundwater.
One possibility is that the orange crocodiles entered their present habitat through narrow openings which they then outgrew and could not return, and their skin eventually changed colour in response to the bat guano.
In the total darkness, the animals survive on a diet of bats and crickets, unlike above-ground crocodiles of the same species which feed on fish and crustaceans.
"It&39;s an especially challenging environment," Shirley said.
A comparison of cave-dwelling and above-ground crocodiles confirms that they have not become separate species.
However, the subterranean creatures -- whether orange or normal colour -- have developed a specific "genetic signature," apparently from adapting to life underground, and this is transmitted from generation to generation, said Shirley.
The crocodile is already a protected species in Gabon, known for its geological and biological diversity, but Oslisly wants the Abanda site to become a "wholly protected sanctuary".
"There&39;s much more to learn in the Abanda caves," he said, pledging to develop the site for "scientific tourism".

A Unique discovery
The Abanda caves in Gabon host a population of cave-dwelling crocodiles. They spent their entire life in these caves and had to adapt to the underground conditions. Who are these unique reptiles living in the caves of Gabon?
How did these crocodiles happen to be trapped in Abanda caves?






We don't have a definite answer to this question. The Abanda cave network is based on a system of faults. Some of the crocodiles live completely isolated from the exterior, the only access being through a 7 m deep shaft.




We think that entrances existed in the past, but they are now filled with sediments, preventing the crocodiles to escape.
One question needs also to be solved, the reason why these crocodiles initially found shelter in these caves. This is in Africa's Gaban county. In them, some rainforest has a lot of water bodies. In them, are some weird caves, scientists on expedition have taken oxygen masks and luminescence torches in dark muddy caves with full of Bat shit, it was difficult to walk. The caves are filled with dense smoke and poisonous gases. After going deep, they saw some big eyes reflections, it was croc but it is orange in colour. As they go deeper, they found numerous crocs there. Finally, they found that these reptiles are going underground by digging tunnels, they formed a tunnel network under that cave. They formed their own habitat inside that cave environment. This was astonishing and first time discovered by these people. They took blood sample 30-40 crocodiles. When they examined their stomach content, they found strangely, some small cave-dwelling creatures, plant materials like algae and mosses. These incredibly rare crocodiles were about 200 in that cave. Nile crocs are known to aestivate in summer or dry season in underground caves dug by them beside river bed to escape drought in advance. But these are only crocodile species which made dark caves as their natural habitats. These were found to be evolving as separate species from dwarf crocodiles and hence, scientists are doing more research on these caves and crocs.
How many of them are there?
During our two expeditions in 2010 and 2011, organised by IRD and Foundation Liambissi, we observed twenty individuals in the caves. Almost all of them could be captured by Matthiew Shirley, who measured them, took samples, marked them and released them.
Are they different from the outside crocodiles?
They look very close to the Dwarf Crocodile, (Osteolaemus tetraspis), however, they differ by several points. They are broader, almost blind, and their skin is orange-coloured, which has never been observed in the dwarf crocodile from the exterior.
The biggest captured specimen was 1.70m long. This length is very high for the species and the crocodile must be very old. We observed several individuals more than one meter long.
Our hypothesis to explain their orange colour is a chemical attack of the skin. They live permanently in a eau croupie dans laquelle fermentent les excréments de chauves-souris. L'odeur est d'ailleurs presque insoutenable.








[attachment=1582][attachment=1584]
And genetically?
The first DNA analysis made in 2010 showed a genetic difference of a few percents between the crocodile inside the caves and the crocodile found elsewhere in Gabon. The population has therefore been isolated for several thousand years. More blood samples have been taken in 2011, both on cave crocodiles and on outside crocodiles. The number of the sample will give statistically significant results.
In the caves, what are their food diet?
These crocodiles live in the absolute darkness. The food is scarce and poorly diversified. We obtained the stomach content by regurgitation and it appears that the cave crocodiles have a very original diet. Whereas outside crocodiles feed on shrimps, crabs, frogs, we found in cave crocodiles' stomachs crickets, bats, insects and a big amount of algae.




What will be the next steps of your research?
We want to know why these crocodiles live in what seems to be an inhospitable environment. Is it to survive a past climate change ? to be protected from predators? Have they just been trapped there?
Many questions a new expedition will bring answers.
You can check here the first results of the 2015 Abanda expedition
http://www.abanda-expedition.org/orange-cave-dwelling-crocodile-012.html

https://www.enca.com/life/scientists-in-gabon-discover-orange-cave-dwelling-crocodiles