Crocodile

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Crocodile

  1. 1. CrocodileFrom Wikipedia, the free encyclopediaFor other uses, see Crocodile (disambiguation).For differences between alligators and crocodiles, see Crocodilia#Differences between alligators andcrocodiles.CrocodilesTemporal range: 55–0MaPreЄЄOSDCPTJKPgNEocene – RecentNile crocodile (Crocodylus niloticus)
  2. 2. Estuarine crocodile (Crocodylus porosus)Scientific classificationKingdom: AnimaliaPhylum: ChordataClass: ReptiliaClade: CrocodylomorphaOrder: CrocodyliaFamily: CrocodylidaeSubfamily: CrocodylinaeCuvier, 1807Type speciesCrocodylus niloticusLaurenti, 1768GeneraCrocodylusOsteolaemus
  3. 3. Mecistops (proposed)Worldwide distribution of crocodilesCrocodiles (subfamily Crocodylinae) or true crocodiles are large aquatictetrapods that live throughoutthe tropics in Africa, Asia, the Americas andAustralia. Crocodylinae, in which all its members areconsidered true crocodiles, is classified as a biological subfamily. A broader sense of the termcrocodile,Crocodylidae, that includes the tomistoma, was excluded in this article since new genetic studiesreveal the possibility of tomistoma as a close relative of thegharial.[1]This article applies the term crocodileonly to the species within the subfamily of Crocodylinae. The term is sometimes used even more loosely toinclude all extant members of the order Crocodilia: which includes all members of Crocodylidae, includingthe tomistoma, the alligators and caimans (familyAlligatoridae) and the gharials (family Gavialidae), and therest of Crocodylomorpha, which includes all of the prehistoric crocodile relatives and ancestors.Although they appear to be similar to the untrained eye, crocodiles, alligators and the gharial belong toseperate biological families. The gharial having a very unique and narrow snout is easier to distinguish,while morphological differences are more difficult to spot in crocodiles and alligators. The most obviousexternal differences are visible in the head with crocodiles having narrower and longer heads, with a moreV-shaped than a U-shaped snout compared to alligators and caimans. Another obvious trait is the upperand lower jaws of the crocodiles are the same width, and teeth in the lower jaw fall along the edge oroutside the upper jaw when the mouth is closed; therefore all teeth are visible unlike an alligator; whichpossesses small depressions in the upper jaw where the lower teeth fit into. Also when the crocodilesmouth is closed, the large fourth tooth in the lower jaw fits into a constriction in the upper jaw. For hard-to-distinguish specimens, the protruding tooth is the most reliable feature to define the family,the species belongs to.[2]Crocodiles have more webbing on the toes of the hind feet and can bettertoleratesaltwater due to specialized salt glands for filtering out salt, which are present but non-functioning inalligators. Another trait that separates crocodiles from other crocodilians, are the much higher levelsof aggression.[3]All reptiles, with the exception of Testudines, are all scaled diapsids, but crocodiliansare archosaurs, which means they are genetically closer to birds and the extinct dinosaurs, than otherreptiles are.Although all crocodiles are anatomically and biologically similar;their size,morphology, behavior and ecology somewhat differs between species. However, they have manysimilarities in these areas as well. All crocodiles are semiaquaticand tend to congregatein freshwater habitats such as rivers, lakes, wetlands and sometimes in brackish water and saltwater. Theyare carnivorous animals, feeding mostly on vertebrates such as fish, reptiles, birds and mammals, and
  4. 4. sometimes on invertebrates such as molluscs and crustaceans, depending on species and age. Allcrocodiles are tropical species that unlike alligators, are very sensitive tocold. They first separated fromother crocodilians during the Eocene epoch, about 55 million years ago.[4]A lineage, including the restof Crocodylomorpha, have been around for at least 225 million years, survived multiple mass extinctions,but today, due to habitat destruction and poaching, many species are at the risk of extinction, some beingclassified as critically endangered.Contents[hide]1 Etymology2 Species3 Characteristicso 3.1 Size4 Biology and behavioro 4.1 Senses 4.1.1 Vision 4.1.2 Olfaction 4.1.3 Hearing 4.1.4 Toucho 4.2 Hunting and diet 4.2.1 Biteo 4.3 Locomotiono 4.4 Longevityo 4.5 Social behavior and vocalizationo 4.6 Reproduction5 Relationship with humanso 5.1 Danger to humanso 5.2 Crocodile products6 Taxonomy and phylogenyo 6.1 Phylogeny7 See also8 References9 Further reading10 External linksEtymology
  5. 5. The word "crocodile" comes from the Ancient Greek κροκόδιλος (crocodilos), "lizard," used in the phrase hokrokódilos tou potamoú, "the lizard of the (Nile) river". There are several variant Greek forms of the wordattested, including the later form κροκόδειλος (crocodeilos)[5]found cited in many English referenceworks.[6]In the Koine Greek of Roman times, crocodilos and crocodeilos would have been pronouncedidentically, and either or both may be the source of the Latinized form crocodīlus used by the ancientRomans.Crocodilos or crocodeilos is a compound of krokè ("pebbles"), and drilos/dreilos ("worm"),although drilos is only attested as a colloquial term for "penis".[6]It is ascribed to Herodotus, andsupposedly describes the basking habits of the Egyptian crocodile.[7]The form crocodrillus is attested in Medieval Latin.[6]It is not clear whether this is a medieval corruption orderives from alternate Greco-Latin forms (late Greek corcodrillos and corcodrillion are attested). A (further)corrupted form cocodrille is found in Old French and was borrowed into Middle English as cocodril(le).The Modern English form crocodile was adapted directly from the Classical Latincrocodīlus in the 16thcentury, replacing the earlier form. The use of -y- in the scientific name Crocodylus (and forms derived fromit) is a corruption introduced by Laurenti (1768).SpeciesA total of 14 extant species have been recognized. Further genetic study is needed for the confirmation ofproposed species under the genus Osteolaemus, which is currently monotypic.Species name Image Distribution Description/CommentsAmericancrocodile(Crocodylus acutus)Throughout theCaribbeanBasin, including many oftheCaribbeanislands andSouth Florida.A larger sized species, with grayishcolor and a prominent V-shaped snout.Prefers brackish water but also inhabitslower stretches of rivers andtrue marine environments. This speciesis one of the rare species that exhibitssea-going behavior regularly, whichexplains the great distributionthroughout theCaribbean. It is alsofound in hypersaline lakes such as LagoEnriquillo, in the Dominican Republic,which has one of the largestpopulations of this species.[8]Dietconsists mostly of aquatic andterrestrial vertebrates. Classifiedas Vulnerable, but certain localpopulations under greater threat.
  6. 6. Slender-snoutedcrocodile(Crocodylus cataphractus)Central andWestern Africa A medium sized species with a narrowand elongated snout. Livesin freshwater habitats within tropicalforests of the continent. Feeds mostlyon fish but also other small to mediumsized vertebrates. Possibly belongs toitsown monotypicgenus, Mecistops.[9]Insufficient data on conservation.Orinococrocodile(Crocodylus intermedius)Colombia andVenezuela This is a large species with a relativelyelongated snout and a pale tancoloration with scattered dark brownmarkings. Lives primarily inthe Orinoco Basin. Despite having arather narrow snout, preys on a widevariety of vertebrates, including largemammals. It is a CriticallyEndangered species.Freshwatercrocodile(Crocodylus johnsoni)Northern Australia A smaller species with a narrow andelongated snout. It has a light browncoloration with darker bands on bodyand tail. Lives in rivers withconsiderable distance from the sea, toavoid confrontations with saltwatercrocodiles. Feeds mostly on fishandother small vertebrates.Philippinecrocodile(Crocodylus mindorensis)Endemic to thePhilippines This is a relatively small species with arather broader snout. It has heavydorsal armor and a golden-brown colorthat darkens as the animal matures.Prefers freshwater habitats and feeds ona variety of small to medium sizedvertebrates. This species isCriticallyEndangered and in fact is the mostseverely threatened species ofcrocodile.[10]Moreletscrocodile(Crocodylus moreletii)Atlantic regionsof Mexico,Belize andGuatemalaA small to medium sized crocodile witha rather broad snout. It has a darkgrayish-brown color and is found inmostly variousfreshwater habitats.Feeds on mammals, birds and reptiles.It isConservation Dependent.
  7. 7. Nilecrocodile(Crocodylus niloticus)Sub-saharan Africa A large and aggressive species with abroad snout, especially in olderanimals. It has a dark bronze colorationand darkens as the animal matures.Lives in a variety of freshwater habitatsbut is also found in brackish water. It isan apex predator that is capable oftaking a wide arrayof African vertebrates, including largeungulates and other predators.[11]Thisspecies is listed asLeast Concern.New Guineacrocodile(Crocodylus novaeguineae)The island ofNew Guinea A smaller species of crocodile withgrey-brown color and dark brown toblack markings on the tail. The younghave a narrower V-shaped snout thatbecomes wider as the animal matures.Prefers freshwater habitats, eventhough is tolerant to salt water, in orderto avoid competition and predation bythe saltwater crocodile. This speciesfeeds on small to mid-sized vertebrates.Muggercrocodile(Crocodylus palustris)The Indiansubcontinentandsurrounding countriesThis a modest sized crocodile with avery broad snout and an alligator-likeappearance. It has dark-grey to browncoloration with enlarged scutes aroundthe neck, making it a considerablyheavy armored species. Prefers slowmowing rivers, swampsand lakes. It canalso be found in coastal swamps butavoids areas populated by saltwatercrocodiles.[12]Feeds on a wide array ofvertebrates.Saltwatercrocodile(Crocodylus porosus)ThroughoutSoutheastAsia,NorthernAustralia and surroundingwatersThe largest living reptile and mostaggressive of all crocodiles. It is a big-headed species and has a relativelybroad snout, especially when older. Thecoloration is pale yellow with blackstripes when young but dark greenish-drab colored as adults. Livesin brackish and marine environments aswell as lower stretches of rivers. Thisspecies has the greatest distribution ofall crocodiles. Tagged specimensshowed long-distance marine travelingbehavior. It is the apexpredator throughout its range and preyson virtually any animal within its reach.It is classified as Least Concern withseveral populations under greaterrisk.[13]
  8. 8. Cubancrocodile(Crocodylus rhombifer)Found only in the ZapataSwamp of CubaIt is a small but extremely aggressivespecies of crocodile thatprefers freshwater swamps.[14]Thecoloration is vibrant even as adults andthe scales have a "pebbled" appearance.It is a relatively terrestrial species withagile locomotion on land, sometimesdisplays terrestrial hunting. The snoutis broad with a thick upper-jaw andlarge teeth. The unique characteristicsand fossil record indicates a ratherspecialized diet in the past, preying onmegafauna such as the giant sloth. Thisspecies sometimes displays pack-hunting behavior, which might havebeen the key to hunting large species inthe past, despite its small size.[15]Todaymost prey are small to medium sizedvertebrates. It is Critically Endangered,and yet the remaining wild populationis under threat of hybridization.[16]Siamesecrocodile(Crocodylus siamensis)Indonesia,Brunei, EastMalaysia andsouthernIndochinaA fairly small sized crocodile thatprefers freshwater habitats. It has arelatively broad snout and olive-greento dark green coloration. It feeds on avariety of small to mid-sizedvertebrates. Listed as CriticallyEndangered, but might be alreadyextinct in the wild, status isunknown.[17]Desertcrocodile(Crocodylus suchus)Western andCentral Africa Recent studies revealed that this isdistinct species from the larger Nilecrocodile.[18][19]It is much smaller witha slightly narrower snout and is muchsmaller compared to its larger cousin.Dwarfcrocodile(Osteolaemus tetraspis)Western Africa It is the smallest of all livingcrocodiles. Belongs to itsownmonotypic genus, however newstudies indicate there might be two oreven three distinct species.[20]It is aheavily armored species with uniformblack coloration in adults but juvenileshave a lighter brown banding. Lives inthe tropical forests of Western Africa.Feeds on small vertebrates and largeaquatic invertebrates. It is a fairlyterrestrial species and exhibitsterrestrial hunting, especially at night.
  9. 9. This species is classified as Vulnerable.For information on Tomistoma or false gharial, that is recently not considered as a true crocodile,see Tomistoma.CharacteristicsCrocodiles are similar to alligators and caimans; for their common characteristics and differencesbetween them, see Crocodilia.Crocodiles, like dinosaurs, have the abdominal ribs modified into gastralia.A crocodile’s physical traits allow it to be a successful predator. Its external morphology is a sign ofits aquatic and predatory lifestyle. Its streamlined body enables it to swim swiftly, it also tucks its feet tothe side while swimming, which makes it faster by decreasing water resistance. They have webbedfeet, though not used to propel the animal through the water, allows them to make fast turns andsudden moves in the water or initiate swimming. Webbed feet are an advantage in shallower water,where the animal sometimes moves around by walking. Crocodiles have a palatal flap, a rigid tissue atthe back of the mouth that blocks the entry of water. The palate has a special path from the nostril tothe glottis that bypasses the mouth. The nostrils are closed during submergence. Likeother archosaurs, crocodilians are diapsid, although their post-temporal fenestrae are reduced. Thewalls of the braincase are bony, but lack supratemporal and postfrontal bones.[21]Their tongues are notfree, but held in place by a membrane that limits movement; as a result, crocodiles are unable to stickout their tongues.[22]Crocodiles have smooth skin on their bellies and sides, while their dorsal surfacesare armoured with large osteoderms. The armoured skin has scales and is thick and rugged, providingsome protection. They are still able to absorb heat through this armour, as a network ofsmall capillaries allows blood through the scales to absorb heat. Crocodilian scales have poresbelieved to be sensory in function, analogous to the lateral line in fishes. They are particularly seen ontheir upper and lower jaws. Another possibility is that they are secretory, as they produce an oilysubstance which appears to flush mud off.[21]Size
  10. 10. A saltwater crocodile in captivitySize greatly varies between species, from the dwarf crocodile to the saltwater crocodile. Speciesof Osteolaemus grow to an adult size of just 1.5 m (4.9 ft) to 1.9 m (6.2 ft),[23]whereas the saltwatercrocodile can grow to sizes over 7 m (23 ft) and weigh 2,000 kg (4,400 lb).[24]Several other largespecies can reach over 5.2 m (17 ft) long and weigh over 900 kg (2,000 lb). Crocodilians showpronounced sexual dimorphism, with males growing much larger and more rapidly thanfemales.[21]Despite their large adult sizes, crocodiles start their lives at around 20 cm (7.9 in) long. Thelargest species of crocodile is the saltwater crocodile, found in eastern India, northern Australia,throughout South-east Asia, and in the surrounding waters.The largest crocodile ever held in captivity is an estuarine–Siamese hybrid named Yai (Thai: ,meaning big) (born 10 June 1972) at the Samutprakarn Crocodile Farm and Zoo, Thailand. Thisanimal measures 6 m (20 ft) in length and weighs 1,114.27 kg (2,456.5 lb).[25]The longest crocodile captured alive is Lolong, which was measured at 6.17 m (20.24 ft) and weighedat 1,075 kg (2,370 lb) by a National Geographic team in Agusan del Sur Province, Philippines.[26][27][28]Biology and behaviorCrocodiles are similar to alligators and caimans; for their common biology and differences betweenthem, see Crocodilia.Crocodilians are more closely related to birds and dinosaurs than to most animals classified asreptiles, the three families being included in the group Archosauria (ruling reptiles). Despite theirprehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles,a crocodile has a cerebral cortex, a four-chambered heart, and the functional equivalent of adiaphragm, by incorporating muscles used for aquatic locomotion into respiration.[29]Saltglands are present in the tongues of crocodiles and they have a pore opening on the surface ofthe tongue, which is a trait that separates them from alligator. Salt glands are dysfunctional inAlligatoridae.[21]Its function appears to be similar to those in marine turtles. Crocodiles do nothave sweat glands and release heat through their mouths. They often sleep with their mouthsopen and may even pant like a dog.[30]Senses
  11. 11. Crocodile eyeCrocodiles have acute senses, an evolutionary advantage that makes them successful predators.The eyes, ears and nostrils are located on top of the head, allowing the crocodile to lie low in thewater, almost totally submerged and hidden from prey.VisionCrocodiles have very good night vision, and are mostly nocturnal hunters. They use thedisadvantage of most prey animals poor nocturnal vision, to their advantage. The light receptorsin crocodilians’ eyes include both cones and numerous rods, so it is assumed all crocodilians cansee colors.[31]Crocodiles have vertical-slit shaped pupils, similar to domestic cats. Oneexplanation for the evolution of slit pupils is that they exclude light more effectively than a circularpupil, helping to protect their eyes during daylight.[32]On the rear wall of the eye is a tapetumlucidum which reflects incoming light back onto the retina, thus utilizing the small amount of lightavailable at night to best advantage. In addition to the protection of the upper and lower eyelids,crocodiles have a nictitating membrane which can be drawn over the eye from the inner cornerwhile the lids are open. The eyeball surface is thus protected under the water while a certaindegree of vision is still possible.[33]OlfactionCrocodilian sense of smell is also very well developed, aiding them to detect prey or animalcarcasses that are either on land or in water, from far away. It is possible that crocodiles useolfaction in the egg prior to hatching.[33]Chemoreception in crocodiles is especially interesting because they hunt both in terrestrial and inaquatic surroundings. Crocodiles have only one olfactory chamber and the vomeronasal organ isabsent in the adults[34]indicating all olfactory perception is limited to the olfactory system.Behavioral and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. When above water, crocodilesenhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of thefloor of the pharynx.[35][36]Unlike turtles, crocodiles close their nostrils when submerged, soolfaction underwater is unlikely. Underwater food detection is presumably gustatory and tactile.[37]Hearing
  12. 12. Crocodiles can hear well; their tympanic membranes are concealed by flat flaps that may beraised or lowered by muscles.[21]TouchCaudal: The upper and lower jaws are covered with sensory pits, visible as small, black speckleson the skin, the crocodilian version of the lateral line organs seen in fish and many amphibians,though arising from a completely different origin. These pigmented nodules encase bundlesof nerve fibers innervated beneath by branches of the trigeminal nerve. They respond to theslightest disturbance in surface water, detecting vibrations and small pressure changes as smallas a single drop.[38]This makes it possible for crocodiles to detect prey, danger and intruders,even in total darkness. These sense organs are known as Domed Pressure Receptors (DPRs).[39]Post-Caudal: While alligators and caimans have DPRs only on their jaws, crocodiles have similarorgans on almost every scale on their bodies. The function of the DPRs on the jaws is clear; tocatch prey, but it is still not clear what is the function of the organs on the rest of the body. Thereceptors flatten when exposed to increased osmotic pressure, such as that experienced whenswimming in sea water hyper-osmotic to the body fluids. When contact between the integumentand the surrounding sea water solution is blocked, crocodiles are found to lose their ability todiscriminate salinities. It has been proposed that the flattening of the sensory organ in hyper-osmotic sea water is sensed by the animal as ―touch‖, but interpreted as chemical informationabout its surroundings.[39]This might be why in alligators they are absent on the rest of thebody.[40]Hunting and dietNile crocodile attacking wildebeestCrocodiles are ambush predators, waiting for fish or land animals to come close, then rushing outto attack. Crocodiles mostlyeat fish, amphibians, crustaceans, molluscs,birds, reptiles, mammals andoccasionally cannibalize on smaller crocodiles. What a crocodile eats varies greatly with species,size and age. From the mostly fish-eating species like the Mecistops and freshwater crocodiles tothe larger species like the Nile crocodile and the saltwater crocodile that prey on large mammals,such as buffalo, deerand wild boar, diet shows great diversity. Diet is also greatly affected by sizeand age of the individual within the same species. All young crocodiles hunt
  13. 13. mostly invertebrates and small fish. Gradually moving onto larger prey. As cold-blooded predators, they have a very slow metabolism, so they can survive long periods withoutfood. Despite their appearance of being slow, crocodiles have a very fast strike and aretop predators in their environment, and various species have been observed attacking and killingother predators such as sharks and big cats.[41][42]Crocodiles have the most acidic stomach of any vertebrate. They can easily digest bones, hoovesand horns. The BBC TV[43]reported that a Nile crocodile that has lurked a long time underwater tocatch prey builds up a large oxygen debt. When it has caught and eaten that prey, it closes itsright aortic arch and uses its left aortic arch to flush blood loaded with carbon dioxide from itsmuscles directly to its stomach; the resulting excess acidity in its blood supply makes it mucheasier for the stomach lining to secrete more stomach acidto quickly dissolve bulks of swallowedprey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomachstones), which may act as ballast to balance their bodies or assist in crushing food,[21]similar togrit ingested by birds. Herodotusclaimed that Nile crocodiles had a symbiotic relationship withcertain birds, such as the Egyptian plover, which enter the crocodiles mouth andpick leeches feeding on the crocodiles blood; with no evidence of this interaction actuallyoccurring in any crocodile species, it is most likely mythical or allegorical fiction.[44]Even a cruising crocodile is difficult to locateBiteSince they feed by grabbing and holding onto their prey, they have evolved sharp teeth forpiercing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. Theteeth are not well-suited to tearing flesh off of large prey items as is the dentition and claws ofmany mammalian carnivores, the hooked bills and talons of raptorial birds, or the serrated teeth ofsharks. However, this is an advantage rather than a disadvantage to the crocodile since theproperties of the teeth allow it to hold onto prey with the least possibility of the prey animal toescape. Otherwise combined with the exceptionally high bite force, the flesh would easily cutthrough; thus creating an escape opportunity for the prey item. The jaws can bite down withimmense force, by far the strongest bite of any animal. The bite of a large crocodiles bite is morethan 5,000 lbf (22,000 N), which was measured in a 5.5 m (18 ft) Nile crocodile, on thefield,[45]compared to just 335 lbf (1,490 N) for a Rottweiler, 670 lbf (3,000 N) for a great white
  14. 14. shark, 800 lbf (3,600 N) for a hyena, or 2,200 lbf (9,800 N) for an American alligator.[46][47]A 5.2 m(17 ft) long saltwater crocodile has been confirmed as having the strongest bite force everrecorded for an animal in a laboratory setting. It was able to apply a bite force value of 3,700 lbf(16,000 N), and thus surpassed the previous record of 2,125 lbf (9,450 N) made by a 3.9 m (13 ft)long American alligator.[48][49]Taking the measurements of several 5.2 m (17 ft) crocodiles asreference, the bite forces of 6-m individuals were estimated at 7,700 lbf (34,000 N).[8]The study,lead by Dr. Gregory M. Erickson, also shed light to the larger, extinct species of crocodilians.Since crocodileanatomy has changed only slightly for the last 80 million years, current data onmodern crocodilians can be used to estimate the bite force of extinct species. An 11 to 12 metres(36–39 ft) long Deinosuchus would apply a force of 23,100 lbf (103,000 N), twice that of the latest,higher bite force estimations of Tyrannosaurus.[8]The extraordinary bite of crocodilians is a resultof their anatomy. The space for the jaw muscle in the skull is very large, which is easily visiblefrom the outside as a bulge at each side. The nature of the muscle is so stiff, it is almost as hardas bone to touch, as if it were the continuum of the skull. Another trait is that most of the muscle ina crocodiles jaw is arranged for clamping down. Despite the strong muscles to close the jaw,crocodiles have extremely small and weak muscles to open the jaw. Crocodiles can thus besubdued for study or transport by taping their jaws or holding their jaws shut with largerubberbands cut from automobile inner tubes.LocomotionA crocodile, in a farm, gaping to thermoregulateCrocodiles are very fast over short distances, even out of water. The land speed record for acrocodile is 17 km/h (11 mph) measured in a galloping Australian freshwatercrocodile.[50]Maximum speed varies from species to species. Certain species can indeed gallop,including Cuban crocodiles, New Guinea crocodiles, African dwarf crocodiles, and even small Nilecrocodiles. The fastest means by which most species can move is a kind of "belly run", where thebody moves in a snake-like fashion, limbs splayed out to either side paddling away franticallywhile the tail whips to and fro. Crocodiles can reach speeds of 10 or 11 km/h (around 7 mph)when they "belly run", and often faster if slipping down muddy riverbanks. Another form oflocomotion is the "high walk", where the body is raised clear of the ground. Crocodiles may
  15. 15. possess a form of homing instinct. In northern Australia, three rogue saltwater crocodiles wererelocated 400 kilometres by helicopter, but had returned to their original locations within threeweeks, based on data obtained from tracking devices attached to the reptiles.[51]LongevityMeasuring crocodile age is unreliable, although several techniques are used to derive areasonable guess. The most common method is to measure lamellar growth rings in bones andteeth—each ring corresponds to a change in growth rate which typically occurs once a yearbetween dry and wet seasons.[52]Bearing these inaccuracies in mind, it can be safely said that allcrocodile species have an average lifespan of at least 30-40 years, and in the case of largerspecies an average of 60-70 years. The oldest crocodiles appear to be the largest species. C.porosus is estimated to live around 70 years on average, with limited evidence of some individualsexceeding 100 years.[53]One of the oldest crocodiles on record died in a zoo in Russia at anestimated age of 115. Unfortunately data on this specimen is limited. A male freshwater crocodileat the Australia Zoo is estimated to be 130 years old. He was rescued from the wild by BobIrwin and Steve Irwin after being shot twice by hunters. As a result of the shootings, this crocodile(known affectionately as "Mr. Freshy") has lost his right eye.[54]Social behavior and vocalizationCrocodiles are the most social of reptiles. Even though they do not form social groups, manyspecies congregate in certain section of arivers, tolerating each other at timesof feeding and basking. Most species are not highly territorial, with the exception of the saltwatercrocodile; which is a highly territorial and aggressive species. A mature male will not tolerate anyother males at any time of the year. Most of the species however, are more flexible. There is acertain form of hierarchy in crocodiles, where the largest and heaviest males are at the top; havingaccess to the best basking site, females and priority during a group feeding of a big kill or carcass.A good example to the hierarchy in crocodiles would be the case of the Nile crocodile. Thisspecies clearly displays all of these behaviors. Studies in this area are not thorough, and manyspecies are yet to be studied in greater detail.[55]Mugger crocodiles are also known to showtoleration in group feedings and tend to congregate to certain areas. However males of all speciesare aggressive towards each other during mating season, to gain access to females.Crocodiles are also the most vocal of all reptiles, producing a wide variety of sounds duringvarious situations and conditions, depending on species, age, size and sex. Depending on thecontext, some species can communicate over 20 different messagesthroughvocalizations alone.[56]Some of these vocalizations are made during socialcommunication, especially during territorial displays towards the same sex and courtship with theopposite sex; the common concern being reproduction. Therefore most conspecificvocalization ismade during the breeding season, with the exception being year-round territorial behavior in somespecies and quarrels during feeding. Crocodiles also produce different distress calls and in
  16. 16. aggressive displays to their own kind and other animals; notably other predatorsduring interspecific predatory confrontations over carcasses and terrestrial kills.Specific vocalisations include -Chirp: When about to hatch, the young make a ―peeping‖ noise, which encourages the female toexcavate the nest. The female then gathers the hatchlings in her mouth and transports them tothe water, where they remain in a group for several months, protected by the female[57]Distress call: A high-pitched call mostly used by younger animals that alerts other crocodiles toimminent danger or an animal being attacked.Threat call: A hissing sound that has also been described as a coughing noise.Hatching call: Emitted by females when breeding to alert other crocodiles that she has laid eggsin her nest.Bellowing: Male crocodiles are especially vociferous. Bellowing choruses occur most often in thespring when breeding groups congregate, but can occur at any time of year. To bellow, malesnoticeably inflate as they raise the tail and head out of water, slowly waving the tail back and forth.They then puff out the throat and with a closed mouth, begin to vibrate air. Just before bellowing,males project an infrasonic signal at about 10 Hz through the water which vibrates the ground andnearby objects. These low-frequency vibrations travel great distances through both air and waterto advertise the males presence and are so powerful they result in the water appearing to dance’.ReproductionCrocodile eggsCrocodiles reproduce by laying eggs, which are either laid in hole or mound nests, depending onspecies. A hole nest is usually excavated in sand and a mound nest is usually constructed out ofvegetation. Nesting period ranges from a few weeks up to six months. Courtship takes place in aseries of of behavioral interactions that include a variety of snout rubbing and submissive displaythat can take a long time. Mating always takes place in water, where the pair can be observedmating several times. Females can build or dig several trial nests which appear incomplete andabandoned later. Egg laying usually takes place at night and about 30-40 minutes.[58]Females arehighly protective of their nests and young. The egg are hard shelled but translucent at the time ofegg-laying. Depending on the species crocodile, a number of 7-95 eggs are laid.
  17. 17. Crocodile embryos do not have sex chromosomes, and unlike humans, sex is not determinedgenetically. Sex is determined by temperature, where at 30 °C (86 °F) or less most hatchlings arefemales and at 31 °C (88 °F), offspring are of both sexes. A temperature of 32 °C (90 °F) to 33°C (91 °F) gives mostly males whereas above 33 °C (91 °F) in some species continues to givemales but in other species resulting in females, which are sometimes called as high-temperaturefemales.[59]Temperature also affects growth and survival rate of the young, which may explainthe sexual dimorphism in crocodiles. The average incubation period is around 80 days, and also isdependent on temperature and species that usually ranges from 65 to 95 days.[60]At the time ofhatching, the young start calling within the eggs. They have an egg-tooth at the tip of their snouts,which is developed from the skin, helps them pierce out of the shell. Hearing the calls, he femaleusually excavates the nest and sometimes takes the unhatched eggs in her mouth, slowly rollingthe eggs to help the process. The young is usually carried to the water in the mouth. A groupof hatchlings is called a pod or crèche and may be protected for months.[58]Relationship with humansDanger to humansMain article: Crocodile attacksCrocodile warning sign, Trinity Beach, Queensland, AustraliaThe larger species of crocodiles are very dangerous to humans, mainly because of their ability tostrike before the person can react. The saltwater crocodile and Nile crocodile are the mostdangerous, killing hundreds of people each year in parts of Southeast Asia and Africa.The mugger crocodile, American crocodile, American alligator and black caiman are alsodangerous to humans.Crocodile productsMain article: Crocodile farm
  18. 18. Crocodile leather wallets from a Bangkokcrocodile farmChiang Mai crocodile leather beltCrocodiles are protected in many parts of the world, but they also are farmed commercially. Theirhides are tanned and used to make leather goods such as shoes and handbags; crocodile meat isalso considered a delicacy. The most commonly farmed species are the saltwater and Nilecrocodiles, while a hybrid of the saltwater and the rare Siamese crocodile is also bred in Asianfarms. Farming has resulted in an increase in the saltwater crocodile population in Australia, aseggs are usually harvested from the wild, so landowners have an incentive to conserve theirhabitat. Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags,belts, hats, and shoes.Crocodile meat is consumed in some countries, such as Australia, Ethiopia, Thailand, SouthAfrica and also Cuba (in pickled form); it can also be found in specialty restaurants in some partsof the United States. The meat is white and its nutritional composition compares favourably withthat of other meats.[citation needed]It tends to have a slightly higher cholesterol level than othermeats.[citation needed]Crocodile meat has a delicate flavour; some describe it as a cross betweenchicken and crab.[citation needed]Cuts of meat include backstrap and tail fillet.Crocodile oil has been used for various purposes.Taxonomy and phylogenyMost species are grouped into the genus Crocodylus. The other extant genus, Osteolaemus,is monotypic (as is Mecistops, if recognized).
  19. 19. Distribution of crocodilesCrocodile farming in AustraliaA bask of crocodiles
  20. 20. American crocodile at La Manzanilla, Jalisco, MexicoA skull of the extinct Voay robustusSubfamily CrocodylinaeGenus CrocodylusCrocodylus acutus,American crocodileCrocodylus cataphractus,slender-snouted crocodile (studiesinDNA andmorphology suggest this species may bemore basal thanCrocodylus, so belongs in its own genus, Mecistops).[61]Crocodylus intermedius, Orinoco crocodileCrocodylus johnsoni, freshwater crocodile, or Johnstones crocodileCrocodylus mindorensis, Philippine crocodileCrocodylus moreletii, Morelets crocodile or Mexican crocodileCrocodylus niloticus, Nile crocodile or African crocodile (the subspecies foundin Madagascar is sometimes called the black crocodile)Crocodylus novaeguineae, New Guinea crocodileCrocodylus palustris, mugger, marsh or Indian crocodileCrocodylus porosus, saltwater crocodile or estuarine crocodile
  21. 21. Crocodylus rhombifer, Cuban crocodileCrocodylus siamensis, Siamese crocodile (may be extinct in the wild)Crocodylus suchus, West African crocodile, desert or sacred crocodileGenus OsteolaemusOsteolaemus tetraspis, dwarf crocodile (There has been controversy as towhether or not this is actually two species; recent (2010) DNA analysis indicatethree distinct species: O. tetraspis, O. osborni and a third, currently unnamed.)Genus †EuthecodonGenus †Rimasuchus (formerly Crocodylus lloydi)Genus †Voay Brochu, 2007 (formerly Crocodylus robustus)PhylogenyThe cladogram below follows the topology from a 2012 analysis of morphological traits byChristopher A. Brochu and Glenn W. Storrs. Many extinct species of Crocodylus might representdifferent genera. C. suchus was not included because its morphological codings were identical tothese of C. niloticus. However, the authors suggested that it could be explained by their specimensampling, and considered the two species to be distinct.[62]Crocodylinae†"Crocodylus" pigotti†"Crocodylus" gariepensis†Euthecodon arambourgii†Euthecodon brumpti†Rimasuchus lloydi†Voay robustusOsteolaemus osborniOsteolaemus tetraspisMecistops cataphractusCrocodylus†C. checchiai†C. palaeindicus†C. anthropophagus†C. thorbjarnarsoni
  22. 22. C. siamensisC. palustrisC. porosusC. johnsoniC. mindorensisC. novaeguineaeC. raninusC. acutusC. intermediusC. rhombiferC. moreletiiSee alsoCrocodilian armorSewer alligatorThe Crocodile HunterAncient Egypt:Sobek - Crocodile godCrocodilopolisReferences1. ^ Gatesy, Jorge; Amato, G.; Norell, M.; DeSalle, R.; and Hayashi, C. (2003). "Combinedsupport for wholesale taxic atavism in gavialine crocodylians". Systematic Biology 52 (3):403–422.doi:10.1080/1063515035019703.2. ^ "Crocodilian Biology Database - FAQ - Whats the difference between a crocodile and analligator". Flmnh.ufl.edu. Retrieved 2009-04-05.3. ^ Guggisberg, C.A.W. (1972). Crocodiles: Their Natural History, Folklore, and Conservation.Newton Abbot: David & Charles. p. 195. ISBN 0-7153-5272-5.
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