Freshwater crocodile Temporal range: Pleistocene–present, | |
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At Rockhampton Zoo | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha |
Clade: | Archosauriformes |
Order: | Crocodilia |
Family: | Crocodylidae |
Genus: | Crocodylus |
Species: | C. johnstoni |
Binomial name | |
Crocodylus johnstoni | |
Range of the freshwater crocodile in black | |
Synonyms [5] [6] | |
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The freshwater crocodile (Crocodylusjohnstoni), also known commonly as the Australian freshwater crocodile, Johnstone's crocodile, and the freshie, is a species of crocodile native to the northern regions of Australia. Unlike its much larger Australian relative, the saltwater crocodile, the freshwater crocodile is not known as a man-eater, although it bites in self-defence, and brief, nonfatal attacks have occurred, apparently the result of mistaken identity.
When Gerard Krefft named the species in 1873, [7] he intended to commemorate the man who first sent him preserved specimens, Australian native police officer and amateur naturalist Robert Arthur Johnstone (1843–1905). [6] [8] However, Krefft made an error in writing the name, and for many years, the species has been known as C. johnsoni. Recent studies of Krefft's papers have determined the correct spelling of the name, and much of the literature has been updated to the correct usage, but both versions still exist. According to the rules of the International Code of Zoological Nomenclature, the epithet johnstoni (rather than the original johnsoni) is correct. [9] [10] [11]
The genus Crocodylus likely originated in Africa and radiated outwards towards Southeast Asia and the Americas, [12] although an Australia/Asia origin has also been considered. [13] Phylogenetic evidence supports Crocodylus diverging from its closest recent relative, the extinct Voay of Madagascar, around 25 million years ago, near the Oligocene/Miocene boundary. [12]
Below is a cladogram based on a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data, [14] as revised by the 2021 Hekkala et al. paleogenomics study using DNA extracted from the extinct Voay . [12]
Crocodylinae |
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The freshwater crocodile is a relatively small crocodilian. Typically, males can grow to a total length (including tail) of 2.3–3.0 m (7.5–9.8 ft) if a dominant male (although there are reported specimens of 4 metres in length (see below)), while females reach a maximum size of 2.1 m (6.9 ft). [9] Males commonly weigh around 70 kg (150 lb), with large specimens up to 100 kg (220 lb) or more, against the female weight of 40 kg (88 lb). [15] In areas such as Lake Argyle and Katherine Gorge, a handful of confirmed 4-metre (13-foot) individuals exist.[ citation needed ] This species is shy and has a slenderer snout and slightly smaller teeth than the dangerous saltwater crocodile. The body colour is light brown with darker bands on the body and tail. These bands tend to be broken up near the neck. Some individuals possess distinct bands or speckling on the snout. Body scales are relatively large, with wide, close-knit, armoured plates on the back. Rounded, pebbly scales cover the flanks and outsides of the legs. [9]
Freshwater crocodiles are found in Western Australia, Queensland, and the Northern Territory. Main habitats include freshwater wetlands, billabongs, rivers, and creeks. This species can live in areas where saltwater crocodiles cannot, and are known to inhabit areas above the escarpment in Kakadu National Park and in very arid and rocky conditions (such as Katherine Gorge, where they are common and are relatively safe from saltwater crocodiles during the dry season). However, they are still consistently found in low-level billabongs, living alongside the saltwater crocodiles near the tidal reaches of rivers.
In May 2013, a freshwater crocodile was seen in a river near the desert town of Birdsville, hundreds of kilometres south of their normal range. A local ranger suggested that years of flooding may have washed the animal south, or it may have been dumped as a juvenile. [16]
A population of freshwater crocodiles has been repeatedly sighted for a number of decades in the Ross River that runs through Townsville. [17] The predominant theory is that the heavy flooding common to the area may have washed a number of the animals in to the Ross River Catchment area.
They compete poorly with saltwater crocodiles, but are saltwater tolerant. [18]
An individual being eaten by an olive python has been filmed; it was reported to have succumbed after a struggle of around five hours. [19]
Eggs are laid in holes during the Australian dry season (usually in August) and hatch at the beginning of the wet season (November/December). The crocodiles do not defend their nests during incubation. From one to five days prior to hatching, the young begin to call from within the eggs. This induces and synchronizes hatching in siblings and stimulates adults to open the nest. If the adult that opens a given nest is the female which laid the eggs is unknown. As young emerge from the nest, the adult picks them up one by one in the tip of its mouth and transports them to the water. Adults may also assist young in breaking through the egg shell by chewing or manipulating the eggs in its mouth. [20]
Feeding in the wild, freshwater crocodiles eat a variety of invertebrate and vertebrate prey. These prey may include crustaceans, insects, spiders, fish, frogs, turtles, snakes, birds, and various mammals. Insects appear to be the most common food, followed by fish. Small prey is usually obtained by a 'sit-and-wait' method, whereby the crocodile lies motionless in shallow water and waits for fish and insects to come within close range, before they are snapped up in a sideways action. However, larger prey such as wallabies and water birds may be stalked and ambushed in a manner similar to that of the saltwater crocodile.
The crocodiles have teeth that have adapted for capturing and holding prey, and food is swallowed without chewing. The digestive tract is short, as their food is relatively simple to swallow and digest. The stomach has two compartments - a muscular gizzard that grinds food, and a digestive chamber where enzymes act on the food. The crocodile's stomach is comparatively more acidic than that of any other vertebrate and contains ridges that lead to the mechanical breakdown of food. Digestion takes place at a faster pace at high temperatures.
The hearts of other reptiles are designed to contain three sections, including two atria and one ventricle. The right atrium, which collects the returned deoxygenated blood and the left atrium, which collects the oxygenated blood collected from pulmonary arteries of the lung, takes the blood to a common ventricle. When just one ventricle is available to receive and mix oxygenated and deoxygenated blood and pump it to the body, the mixture of blood the body receives has relatively less oxygen. Crocodiles have a more complex vertebrate circulatory system, with a four-chambered heart, including two ventricles. Like birds and mammals, crocodiles have heart valves that direct blood flows in a single direction through the heart chambers. When under water, the crocodile's heart rate slows down to one to two beats a minute, and muscles receive less blood flow. When it comes out of the water and takes a breath, its heart rate speeds up in seconds, and the muscles receive oxygen-rich blood. Unlike many marine mammals, crocodiles have only a small amount of myoglobin to store oxygen in their muscles.
Until recently, the freshwater crocodile was common in northern Australia, especially where saltwater crocodiles are absent (such as more arid inland areas and higher elevations). In recent years, the population has dropped dramatically due to the ingestion of the invasive cane toad. The toad is poisonous to freshwater crocodiles, although not to saltwater crocodiles, and the toad is rampant throughout the northern Australian bush. [21] The crocodiles are also infected by Griphobilharzia amoena , a parasitic trematode, in regions such as Darwin. [22]
Although the freshwater crocodile does not attack humans as potential prey, it can deliver a nasty bite. Brief and rapidly abandoned attacks have occurred, and were likely the result of mistaken identity (mistaking a part of the human as a typical prey item). [23] [24] Other attacks have occurred in self defense when the crocodile was touched or approached too closely. [25] No human fatalities are known to have been caused by this species. [25] A few incidents have been reported where people have been bitten whilst swimming with freshwater crocodiles, and others incurred during scientific study. An attack by a freshwater crocodile on a human was recorded at Barramundi Gorge (also known as Maguk) in Kakadu National Park and resulted in minor injuries; the victim managed to swim and walk away from the attack. He had apparently passed directly over the crocodile in the water. In general, though, swimming with this species is still considered safe, so long as they are not aggravated. [26] There has, however, been a freshwater crocodile attack at Lake Argyle. [27]
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.
Crocodylia ) 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".
Crocodylinae is a subfamily of true crocodiles within the family Crocodylidae, and is the sister taxon to Osteolaeminae.
The saltwater crocodile is a crocodilian native to saltwater habitats, brackish wetlands and freshwater rivers from India's east coast across Southeast Asia and the Sundaic region to northern Australia and Micronesia. It has been listed as Least Concern on the IUCN Red List since 1996. It was hunted for its skin throughout its range up to the 1970s, and is threatened by illegal killing and habitat loss. It is regarded as dangerous to humans.
The mugger crocodile is a medium-sized broad-snouted crocodile, also known as mugger and marsh crocodile. It is native to freshwater habitats from southern Iran to the Indian subcontinent, where it inhabits marshes, lakes, rivers and artificial ponds. It rarely reaches a body length of 5 m and is a powerful swimmer, but also walks on land in search of suitable waterbodies during the hot season. Both young and adult mugger crocodiles dig burrows to which they retreat when the ambient temperature drops below 5 °C (41 °F) or exceeds 38 °C (100 °F). Females dig holes in the sand as nesting sites and lay up to 46 eggs during the dry season. The sex of hatchlings depends on temperature during incubation. Both parents protect the young for up to one year. They feed on insects, and adults prey on fish, reptiles, birds and mammals.
The black caiman is a crocodilian reptile endemic to South America. With a maximum length of around 5 to 6 m and a mass of over 450 kg (1,000 lb), it is the largest living species of the family Alligatoridae, and the third-largest crocodilian in the Neotropical realm. True to its common and scientific names, the black caiman has a dark greenish-black coloration as an adult. In some individuals, the pigmentation can appear almost jet-black. It has grey to brown banding on the lower jaw; juveniles have a more vibrant coloration compared to adults, with prominent white-pale yellow banding on the flanks that remains present well into adulthood. The banding on young animals helps with camouflage by breaking up their body outline, on land or in water, in an effort to avoid predation. The morphology is quite different from other caimans but the bony ridge that occurs in other caimans is present. The head is large and heavy, an advantage in catching larger prey. Like all crocodilians, caimans are long, squat creatures, with big jaws, long tails and short legs. They have thick, scaled skin, and their eyes and noses are located on the tops of their heads. This enables them to see and breathe while the rest of their bodies are underwater.
The Nile crocodile is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and central regions of the continent, and lives in different types of aquatic environments such as lakes, rivers, swamps and marshlands. It occasionally inhabits deltas, brackish lakes and rarely also saltwater. Its range once stretched from the Nile Delta throughout the Nile River. Lake Turkana in Kenya has one of the largest undisturbed Nile crocodile populations.
The American crocodile is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas, with populations present from South Florida, the Caribbean islands of Cuba, Jamaica, Hispaniola, and the coasts of Mexico to as far south as Peru, Ecuador, Colombia, and Venezuela.
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.
The Siamese crocodile is a medium-sized freshwater crocodile native to Indonesia, Brunei, East Malaysia, Laos, Cambodia, Myanmar, Thailand and Vietnam. The species is critically endangered and already extirpated from many regions. Its other common names include Siamese freshwater crocodile, Singapore small-grain, and soft-belly.
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.
The Philippine crocodile, also known as the Mindoro crocodile, the Philippine freshwater crocodile, the bukarot in Ilocano, and more generally as a buwaya in most Filipino lowland cultures, is one of two species of crocodiles found in the Philippines; the other is the larger saltwater crocodile (Crocodylus porosus). The Philippine crocodile, the species endemic only to the country, went from data deficient to critically endangered in 2008 from exploitation and unsustainable fishing methods, such as dynamite fishing. Conservation methods are being taken by the Dutch/Filipino Mabuwaya foundation, the Crocodile Conservation Society and the Zoological Institute of HerpaWorld in Mindoro island. It is strictly prohibited to kill a crocodile in the country, and it is punishable by law.
Crocodile attacks on humans are common in places where large crocodilians are native and human populations live. It has been estimated that about 1,000 people are killed by crocodilians each year.
The New Guinea crocodile is a small species of crocodile found on the island of New Guinea north of the mountain ridge that runs along the centre of the island. The population found south of the mountain ridge, formerly considered a genetically distinct population, is now considered a distinct species, Hall's New Guinea crocodile. In the past it included the Philippine crocodile, C. n. mindorensis, as a subspecies, but today they are regarded as separate species. The habitat of the New Guinea crocodile is mostly freshwater swamps and lakes. It is most active at night when it feeds on fish and a range of other small animals. A female crocodile lays a clutch of eggs in a nest composed of vegetation and she lies up nearby to guard the nest. There is some degree of parental care for newly hatched juveniles. This crocodile was over-hunted for its valuable skin in the mid 20th century, but conservation measures have since been put in place, it is reared in ranches and the International Union for Conservation of Nature (IUCN) lists it as being of "Least Concern".
Morelet's crocodile, also known as the Mexican crocodile or Belize crocodile, is a modest-sized crocodilian found only in the Atlantic regions of Mexico, Belize and Guatemala. It usually grows to about 3 metres (10 ft) in length. It is a species at least concern for extinction according to the International Union for Conservation of Nature. The species has a fossil record in Guatemala.
Paludirex is an extinct genus of mekosuchine crocodylian from the Pliocene and Pleistocene of Australia. A large and robust semi-aquatic ambush hunter capable of attaining lengths of up to 5 m (16 ft), it was likely the top predator of Australia's waterways prior to the appearance of modern saltwater crocodiles. Two species are known, the smaller Paludirex gracilis and the larger Paludirex vincenti. A third as of yet unnamed species may have also existed.
Mecistops is a genus of crocodiles, the slender-snouted crocodiles, native to sub-Saharan Africa.
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.
The Cuban crocodile is a small-medium species of crocodile endemic to Cuba. Typical length is 2.1–2.3 m (6.9–7.5 ft) and typical weight 70–80 kg (150–180 lb). Large males can reach as much as 3.5 m (11 ft) in length and weigh more than 215 kg (474 lb). Despite its smaller size, it is a highly aggressive animal, and potentially dangerous to humans.
"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.