Freshwater crocodile
Freshwater crocodile | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Archosauromorpha |
Clade: | Archosauriformes |
Order: | Crocodilia |
Family: | Crocodylidae |
Genus: | Crocodylus |
Species: | C. johnstoni
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Binomial name | |
Crocodylus johnstoni | |
Range of the freshwater crocodile in black | |
Synonyms[5][6] | |
The freshwater crocodile (Crocodylus johnstoni), also known as the Australian freshwater crocodile, Johnstone's crocodile or the freshie, is a species of crocodile endemic to the northern regions of Australia. Unlike their much larger Australian relative, the saltwater crocodile, freshwater crocodiles are not known as man-eaters, although they bite in self-defence, and brief, nonfatal attacks have occurred, apparently the result of mistaken identity.
Taxonomy and etymology
When
Evolution
The
Phylogeny
Below is a
Crocodylinae |
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Description
The freshwater crocodile is a relatively small crocodilian. Males can grow to 2.3–3.0 m (7.5–9.8 ft) long, while females reach a maximum size of 2.1 m (6.9 ft).
Distribution and habitat
Freshwater crocodiles are found in
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.
Biology and behavior
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]
Reproduction
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]
Diet
Feeding in the wild, freshwater crocodiles eat a variety of invertebrate and vertebrate prey. These prey may include crustaceans, insects, spiders, fishes, 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.
Digestive system
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.
Circulation system
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.
Conservation status
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 Australian wilderness.[21] The crocodiles are also infected by Griphobilharzia amoena, a parasitic trematode, in regions such as Darwin.[22]
Relationship with humans
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]
Gallery
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Head of a freshwater crocodile
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Freshwater crocodile basking on a log
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Various skull views of an "Australia crocodile" (Crocodylus johnsoni)
References
- PMID 34567843.
- . Retrieved 13 November 2021.
- ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
- ^ "Crocodylus johnstoni". Integrated Taxonomic Information System.
- ^ ... johnstoni means "of Johnstone", derived from the name of the first European to discover and report it to Krefft. Unfortunately Krefft misspelled the name "johnsoni " in his initial description and his subsequent correction was ignored until 1983 when the nomenclature was reviewed thoroughly by Hal Cogger (Cogger 1983). Although the majority of scientific literature, including all Australian Federal, State and Territory legislation has been using "johnstoni " correctly since then, the uncorrected version is still popular especially in the US on the basis of a later taxonomic review (King and Burke 1989) that ignored Cogger's revision. http://crocodilian.com/cnhc/csp_cjoh.htm Crocodilian Species List, Crocodylus johnstoni (KREFFT, 1873).
- ^ a b "Crocodylus johnsoni ". The Reptile Database. www.reptile-database.org.
- ^ "Crocodylus johnsoni Krefft 1873 (crocodile)". PBDB.
- ISBN 978-1-4214-0135-5
- ^ a b c Britton, Adam. "Crocodylus johnstoni ". Florida Museum of Natural History. Retrieved 16 June 2009.
- ^ "International Commission on Zoological Nomenclature". www.iczn.org.
- ^ Cogger H (1983). Reptiles and Amphibians of Australia. Reed.
- ^ PMID 33907305.
- S2CID 7254442.
- PMID 30051855.
- ^ "26 fresh water crocodiles hatched at Vandalur zoo - Times of India". articles.timesofindia.indiatimes.com. Archived from the original on 17 May 2013. Retrieved 12 January 2022.
- ^ "Crocodile turns up in river near Birdsville". Australian Broadcasting Corporation. 23 May 2013. Retrieved 25 May 2013.
- ^ "'Scared the crap out of each other': Freshwater croc that attacked woman accidentally hit with oar". ABC News. 28 February 2022. Retrieved 19 May 2022.
- .
- ^ "Snake eats crocodile in battle at Australian lake". The Daily Telegraph. 6 March 2014. Archived from the original on 6 March 2014.
- S2CID 85800873.
- ^ "Crocodiles falling victim to cane toads". ABC News. 29 December 2008.
- JSTOR 3282558.
- ^ CrocBITE, Worldwide Crocodilian Attack Database: Australian freshwater crocodile, 1 November 2013 Archived 28 January 2021 at the Wayback Machine. Charles Darwin University, Northern Territory, Australia.
- ^ CrocBITE, Worldwide Crocodilian Attack Database: Australian freshwater crocodile, 6 April 2006 Archived 10 March 2022 at the Wayback Machine. Charles Darwin University, Northern Territory, Australia.
- ^ a b Hines, K.N.; Skroblin, A. (2010). "Australian Freshwater Crocodile (Crocodylus johnstoni) attacks on humans". Herpetological Review. 41 (4): 430–433.
- ^ "How Embarressing". aebrain.blogspot.com. 26 September 2003.
- .
Further reading
- Boulenger GA (1889). Catalogue of the Chelonians, Rhynchocephalians, and Crocodiles in the British Museum (Natural History). New Edition. London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). x + 311 pp. + Plates I–VI. (Crocodilus johnstonii, pp. 279–280).
- ISBN 978-0643100350.
- Gray JE (1874). "On Crocodilus johnstoni, Krefft". Proc. Zool. Soc. London 1874: 177–178 + Plate XXVII.
- Krefft G (1873). "Remarks on Australian Crocodiles, and Description of a New Species". Proc. Zool. Soc. London. 1873: 334–335. (Crocodilus johnsoni, new species, p. 335).