Crocodilia

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Crocodilia_table_infobox_0

Crocodilia

Temporal range: Late CretaceousRecent 83.5–0 Ma PreꞒ O S D C P T J K Pg NCrocodilia_header_cell_0_0_0

Scientific classification CrocodiliaCrocodilia_header_cell_0_1_0
Kingdom:Crocodilia_cell_0_2_0 AnimaliaCrocodilia_cell_0_2_1
Phylum:Crocodilia_cell_0_3_0 ChordataCrocodilia_cell_0_3_1
Class:Crocodilia_cell_0_4_0 ReptiliaCrocodilia_cell_0_4_1
Clade:Crocodilia_cell_0_5_0 EusuchiaCrocodilia_cell_0_5_1
Order:Crocodilia_cell_0_6_0 Crocodilia

Owen, 1842Crocodilia_cell_0_6_1

SubgroupsCrocodilia_header_cell_0_7_0

Crocodilia (or Crocodylia, both /krɒkəˈdɪliə/) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. Crocodilia_sentence_0

They first appeared 95 million years ago in the Late Cretaceous period (Cenomanian stage) and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Crocodilia_sentence_1

Members of the order's total group, the clade Pseudosuchia, appeared about 250 million years ago in the Early Triassic period, and diversified during the Mesozoic era. Crocodilia_sentence_2

The order Crocodilia includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharial and false gharial (family Gavialidae). Crocodilia_sentence_3

Although the term 'crocodiles' is sometimes used to refer to all of these, crocodilians is a less ambiguous vernacular term for members of this group. Crocodilia_sentence_4

Large, solidly built, lizard-like reptiles, crocodilians have long flattened snouts, laterally compressed tails, and eyes, ears, and nostrils at the top of the head. Crocodilia_sentence_5

They swim well and can move on land in a "high walk" and a "low walk", while smaller species are even capable of galloping. Crocodilia_sentence_6

Their skin is thick and covered in non-overlapping scales. Crocodilia_sentence_7

They have conical, peg-like teeth and a powerful bite. Crocodilia_sentence_8

They have a four-chambered heart and, somewhat like birds, a unidirectional looping system of airflow within the lungs, but like other non-avian reptiles they are ectotherms. Crocodilia_sentence_9

Crocodilians are found mainly in lowlands in the tropics, but alligators also live in the southeastern United States and the Yangtze River in China. Crocodilia_sentence_10

They are largely carnivorous, the various species feeding on animals such as fish, crustaceans, molluscs, birds, and mammals; some species like the Indian gharial are specialised feeders, while others like the saltwater crocodile have generalised diets. Crocodilia_sentence_11

Crocodilians are typically solitary and territorial, though cooperative feeding does occur. Crocodilia_sentence_12

During breeding, dominant males try to monopolise available females. Crocodilia_sentence_13

Females lay eggs in holes or in mounds and, unlike most other non-avian reptiles, care for their hatched young. Crocodilia_sentence_14

Some species of crocodilians are known to have attacked humans. Crocodilia_sentence_15

The largest number of attacks comes from the Nile crocodile. Crocodilia_sentence_16

Humans are the greatest threat to crocodilian populations through activities that include hunting, poaching, and habitat destruction, but farming of crocodilians has greatly reduced unlawful trading in wild skins. Crocodilia_sentence_17

Artistic and literary representations of crocodilians have appeared in human cultures around the world since Ancient Egypt. Crocodilia_sentence_18

The earliest known mention of the story that crocodiles weep for their victims was in the 9th century; it was later spread by Sir John Mandeville in 1400 and then by William Shakespeare in the late 16th century and early 17th century. Crocodilia_sentence_19

Spelling and etymology Crocodilia_section_0

Crocodilia and Crocodylia have been used interchangeably for decades starting with Schmidt's redescription of the group from the formerly defunct term Loricata. Crocodilia_sentence_20

Schmidt used the older term Crocodilia, based on Owen's original name for the group. Crocodilia_sentence_21

Shortly after, Wermuth opted for Crocodylia as the proper name for this redescribed group, basing it on the type genus Crocodylus (Laurenti, 1768). Crocodilia_sentence_22

Dundee—in a revision of many reptilian and amphibian names—argued strongly for Crocodylia to be the spelling for the group. Crocodilia_sentence_23

However, it was not until the advent of cladistics and phylogenetic nomenclature that a more solid justification for assuming one spelling over the other was proposed. Crocodilia_sentence_24

Prior to 1988, Crocodilia/Crocodylia was a group that encompassed the modern-day animals (the crown group) as well as their more distant relatives now in the larger groups called Crocodylomorpha and Pseudosuchia. Crocodilia_sentence_25

Under its current definition Crocodylia is restricted to only the most recent ancestor of today's modern-day crocodilians (alligators, crocodiles, and gharials). Crocodilia_sentence_26

This distinction is more important for paleontologists studying crocodilian evolution. Crocodilia_sentence_27

As such, the alternate spellings Crocodilia and Crocodylia are still used interchangeably in the neontological literature. Crocodilia_sentence_28

Crocodilia appears to be a Latinizing of the Greek κροκόδειλος (crocodeilos), which means both lizard and Nile crocodile. Crocodilia_sentence_29

Crocodylia, as coined by Wermuth, in regards to the genus Crocodylus appears to be derived from the ancient Greek κρόκη (kroke)—meaning shingle or pebble—and δρîλος or δρεîλος (dr(e)ilos) for "worm". Crocodilia_sentence_30

The name may refer to the animal's habit of basking on the pebbled shores of the Nile. Crocodilia_sentence_31

Morphology and physiology Crocodilia_section_1

Crocodilians range in size from the Paleosuchus and Osteolaemus species, which reach 1–1.5 m (3 ft 3 in–4 ft 11 in), to the saltwater crocodile, which reaches 7 m (23 ft) and weighs up to 2,000 kg (4,400 lb), though some prehistoric species such as the late Cretaceous Deinosuchus were even larger at up to about 11 m (36 ft) and 3,450 kg (7,610 lb). Crocodilia_sentence_32

They tend to be sexually dimorphic, with males much larger than females. Crocodilia_sentence_33

Though there is diversity in snout and tooth shape, all crocodilian species have essentially the same body morphology. Crocodilia_sentence_34

They have solidly built, lizard-like bodies with elongated, flattened snouts and laterally compressed tails. Crocodilia_sentence_35

Their limbs are reduced in size; the front feet have five digits with little or no webbing, and the hind feet have four webbed digits and a rudimentary fifth. Crocodilia_sentence_36

The skeleton is somewhat typical of tetrapods, although the skull, pelvis and ribs are specialised; in particular, the cartilaginous processes of the ribs allow the thorax to collapse during diving and the structure of the pelvis can accommodate large masses of food, or more air in the lungs. Crocodilia_sentence_37

Both sexes have a cloaca, a single chamber and outlet at the base of the tail into which the intestinal, urinary and genital tracts open. Crocodilia_sentence_38

It houses the penis in males and the clitoris in females. Crocodilia_sentence_39

The crocodilian penis is permanently erect and relies on cloacal muscles for eversion and elastic ligaments and a tendon for recoil. Crocodilia_sentence_40

The gonads are located near the kidneys. Crocodilia_sentence_41

The eyes, ears and nostrils of crocodilians are at the top of the head. Crocodilia_sentence_42

This allows them to stalk their prey with most of their bodies underwater. Crocodilia_sentence_43

Crocodilians possess a tapetum lucidum which enhances vision in low light. Crocodilia_sentence_44

While eyesight is fairly good in air, it is significantly weakened underwater. Crocodilia_sentence_45

The fovea in other vertebrates is usually circular, but in crocodiles it is a horizontal bar of tightly packed receptors across the middle of the retina. Crocodilia_sentence_46

When the animal completely submerges, the nictitating membranes cover its eyes. Crocodilia_sentence_47

In addition, glands on the nictitating membrane secrete a salty lubricant that keeps the eye clean. Crocodilia_sentence_48

When a crocodilian leaves the water and dries off, this substance is visible as "tears". Crocodilia_sentence_49

The ears are adapted for hearing both in air and underwater, and the eardrums are protected by flaps that can be opened or closed by muscles. Crocodilia_sentence_50

Crocodilians have a wide hearing range, with sensitivity comparable to most birds and many mammals. Crocodilia_sentence_51

They have only one olfactory chamber and the vomeronasal organ is absent in the adults indicating all olfactory perception is limited to the olfactory system. Crocodilia_sentence_52

Behavioural and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. Crocodilia_sentence_53

When above water, crocodiles enhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of the floor of the pharynx. Crocodilia_sentence_54

The well-developed trigeminal nerve allows them to detect vibrations in the water (such as those made by potential prey). Crocodilia_sentence_55

The tongue cannot move freely but is held in place by a folded membrane. Crocodilia_sentence_56

While the brain of a crocodilian is fairly small, it is capable of greater learning than most reptiles. Crocodilia_sentence_57

Though they lack the vocal folds of mammals and the syrinx of birds, crocodilians can produce vocalisations by vibrating three flaps in the larynx. Crocodilia_sentence_58

They appear to have lost their pineal organ, but still show signs of melatonin rhythms. Crocodilia_sentence_59

Locomotion Crocodilia_section_2

Crocodilians are excellent swimmers. Crocodilia_sentence_60

During aquatic locomotion, the muscular tail undulates from side to side to drive the animal through the water while the limbs are held close to the body to reduce drag. Crocodilia_sentence_61

When the animal needs to stop, steer, or manoeuvre in a different direction, the limbs are splayed out. Crocodilia_sentence_62

Crocodilians generally cruise slowly on the surface or underwater with gentle sinuous movements of the tail, but when pursued or when chasing prey they can move rapidly. Crocodilia_sentence_63

Crocodilians are less well-adapted for moving on land, and are unusual among vertebrates in having two different means of terrestrial locomotion: the "high walk" and the "low walk". Crocodilia_sentence_64

Their ankle joints flex in a different way from those of other reptiles, a feature they share with some early archosaurs. Crocodilia_sentence_65

One of the upper row of ankle bones, the astragalus, moves with the tibia and fibula. Crocodilia_sentence_66

The other, the calcaneum, is functionally part of the foot, and has a socket into which a peg from the astragalus fits. Crocodilia_sentence_67

The result is that the legs can be held almost vertically beneath the body when on land, and the foot can swivel during locomotion with a twisting movement at the ankle. Crocodilia_sentence_68

The high walk of crocodilians, with the belly and most of the tail being held off the ground, is unique among living reptiles. Crocodilia_sentence_69

It somewhat resembles the walk of a mammal, with the same sequence of limb movements: left fore, right hind, right fore, left hind. Crocodilia_sentence_70

The low walk is similar to the high walk, but without the body being raised, and is quite different from the sprawling walk of salamanders and lizards. Crocodilia_sentence_71

The animal can change from one walk to the other instantaneously, but the high walk is the usual means of locomotion on land. Crocodilia_sentence_72

The animal may push its body up and use this form immediately, or may take one or two strides of low walk before raising the body higher. Crocodilia_sentence_73

Unlike most other land vertebrates, when crocodilians increase their pace of travel they increase the speed at which the lower half of each limb (rather than the whole leg) swings forward; by this means, stride length increases while stride duration decreases. Crocodilia_sentence_74

Though typically slow on land, crocodilians can produce brief bursts of speed, and some can run at 12 to 14 km/h (7.5 to 8.7 mph) for short distances. Crocodilia_sentence_75

A fast entry into water from a muddy bank can be effected by plunging to the ground, twisting the body from side to side and splaying out the limbs. Crocodilia_sentence_76

In some small species such as the freshwater crocodile, a running gait can progress to a bounding gallop. Crocodilia_sentence_77

This involves the hind limbs launching the body forward and the fore limbs subsequently taking the weight. Crocodilia_sentence_78

Next, the hind limbs swing forward as the spine flexes dorso-ventrally, and this sequence of movements is repeated. Crocodilia_sentence_79

During terrestrial locomotion, a crocodilian can keep its back and tail straight, since the scales are attached to the vertebrae by muscles. Crocodilia_sentence_80

Whether on land or in water, crocodilians can jump or leap by pressing their tails and hind limbs against the substrate and then launching themselves into the air. Crocodilia_sentence_81

Jaws and teeth Crocodilia_section_3

The snout shape of crocodilians varies between species. Crocodilia_sentence_82

Crocodiles may have either broad or slender snouts, while alligators and caimans have mostly broad ones. Crocodilia_sentence_83

Gharials have snouts that are extremely elongated. Crocodilia_sentence_84

The muscles that close the jaws are much more massive and powerful than the ones that open them, and a crocodilian's jaws can be held shut by a person fairly easily. Crocodilia_sentence_85

Conversely, the jaws are extremely difficult to pry open. Crocodilia_sentence_86

The powerful closing muscles attach at the median portion of the lower jaw and the jaw hinge attaches to the atlanto-occipital joint, allowing the animal to open its mouth fairly wide. Crocodilia_sentence_87

Crocodilians have some of the strongest bite forces in the animal kingdom. Crocodilia_sentence_88

In a study published in 2003, an American alligator's bite force was measured at up to 2,125 lbf (9,450 N). Crocodilia_sentence_89

In a 2012 study, a saltwater crocodile's bite force was measured even higher, at 3,700 lbf (16,000 N). Crocodilia_sentence_90

This study also found no correlation between bite force and snout shape. Crocodilia_sentence_91

Nevertheless, the gharial's extremely slender jaws are relatively weak and built more for quick jaw closure. Crocodilia_sentence_92

The bite force of Deinosuchus may have measured 23,000 lbf (100,000 N), even greater than that of theropod dinosaurs like Tyrannosaurus. Crocodilia_sentence_93

Crocodilian teeth vary from blunt and dull to sharp and needle-like. Crocodilia_sentence_94

Broad-snouted species have teeth that vary in size, while those of slender-snouted species are more uniform. Crocodilia_sentence_95

The teeth of crocodiles and gharials tend to be more visible than those of alligators and caimans when the jaws are closed. Crocodilia_sentence_96

The easiest way to distinguish crocodiles from alligators is by looking at their jaw line. Crocodilia_sentence_97

The teeth on the lower jaw of an alligator fit into sockets in the upper jaw, so only the upper teeth are visible when the mouth is closed. Crocodilia_sentence_98

The teeth on the lower jaw of a crocodile fit into grooves on the outside of the top jaw making both the upper and lower teeth visible when the mouth is closed. Crocodilia_sentence_99

Crocodilians are homodonts, meaning each of their teeth are all of the same type (they do not possess different tooth types, such as canines and molars) and polyphyodonts and able to replace each of their approximately 80 teeth up to 50 times in their 35 to 75-year lifespan. Crocodilia_sentence_100

They are the only non-mammalian vertebrates with tooth sockets. Crocodilia_sentence_101

Next to each full-grown tooth there is a small replacement tooth and an odontogenic stem cell in the dental lamina in standby, which can be activated when required. Crocodilia_sentence_102

Tooth replacement slows significantly and eventually stops as the animal grows old. Crocodilia_sentence_103

Skin and scales Crocodilia_section_4

Main article: Crocodilian armor Crocodilia_sentence_104

The skin of crocodilians is thick and cornified, and is clad in non-overlapping scales known as scutes, arranged in regular rows and patterns. Crocodilia_sentence_105

These scales are continually being produced by cell division in the underlying layer of the epidermis, the stratum germinativum, and the surface of individual scutes sloughs off periodically. Crocodilia_sentence_106

The outer surface of the scutes consists of the relatively rigid beta-keratin while the hinge region between the scutes contains only the more pliable alpha-keratin. Crocodilia_sentence_107

Many of the scutes are strengthened by bony plates known as osteoderms, which are the same size and shape as the superficial scales but grow beneath them. Crocodilia_sentence_108

They are most numerous on the back and neck of the animal and may form a protective armour. Crocodilia_sentence_109

They often have prominent, lumpy ridges and are covered in hard-wearing beta-keratin. Crocodilia_sentence_110

The head lacks actual scales and is instead covered in a tight sheet of highly keratinised skin that cracks due to the mechanical stress of the jaws. Crocodilia_sentence_111

The skin on the neck and flanks is loose, while that on the abdomen and underside of the tail is sheathed in large, flat square scutes arranged in neat rows. Crocodilia_sentence_112

The scutes contain blood vessels and may act to absorb or radiate heat during thermoregulation. Crocodilia_sentence_113

Research also suggests that alkaline ions released into the blood from the calcium and magnesium in these dermal bones act as a buffer during prolonged submersion when increasing levels of carbon dioxide would otherwise cause acidosis. Crocodilia_sentence_114

Some scutes contain a single pore known as an integumentary sense organ. Crocodilia_sentence_115

Crocodiles and gharials have these on large parts of their bodies, while alligators and caimans only have them on the head. Crocodilia_sentence_116

Their exact function is not fully understood, but it has been suggested that they may be mechanosensory organs. Crocodilia_sentence_117

Another possibility is that they may produce an oily secretion that prevents mud from adhering to the skin. Crocodilia_sentence_118

There are prominent paired integumentary glands in skin folds on the throat, and others in the side walls of the cloaca. Crocodilia_sentence_119

Various functions for these have been suggested. Crocodilia_sentence_120

They may play a part in communication, as indirect evidence suggest that they secrete pheromones used in courtship or nesting. Crocodilia_sentence_121

The skin of crocodilians is tough and can withstand damage from conspecifics, and the immune system is effective enough to heal wounds within a few days. Crocodilia_sentence_122

Circulation Crocodilia_section_5

The crocodilian has perhaps the most complex vertebrate circulatory system. Crocodilia_sentence_123

It has a four-chambered heart and two ventricles, an unusual trait among extant reptiles, and both a left and right aorta which are connected by a hole called the Foramen of Panizza. Crocodilia_sentence_124

Like birds and mammals, crocodilians have heart valves that direct blood flow in a single direction through the heart chambers. Crocodilia_sentence_125

They also have unique cog-teeth-like valves that, when interlocked, direct blood to the left aorta and away from the lungs, and then back around the body. Crocodilia_sentence_126

This system may allow the animals to remain submerged for a longer period, but this explanation has been questioned. Crocodilia_sentence_127

Other possible reasons for the peculiar circulatory system include assistance with thermoregulatory needs, prevention of pulmonary oedema, or faster recovery from metabolic acidosis. Crocodilia_sentence_128

Retaining carbon dioxide within the body permits an increase in the rate of gastric acid secretion and thus the efficiency of digestion, and other gastrointestinal organs such as the pancreas, spleen, small intestine, and liver also function more efficiently. Crocodilia_sentence_129

When submerged, a crocodilian's heart rate slows down to one or two beats a minute, and blood flow to the muscles is reduced. Crocodilia_sentence_130

When it rises and takes a breath, its heart rate speeds up in seconds, and the muscles receive newly oxygenated blood. Crocodilia_sentence_131

Unlike many marine mammals, crocodilians have little myoglobin to store oxygen in their muscles. Crocodilia_sentence_132

During diving, muscles are supplied with oxygen when an increasing concentration of bicarbonate ions causes haemoglobin in the blood to release oxygen. Crocodilia_sentence_133

Respiration Crocodilia_section_6

Crocodilians were traditionally thought to breathe like mammals, with airflow moving in and out tidally, but studies published in 2010 and 2013 conclude that crocodilians breathe more like birds, with airflow moving in a unidirectional loop within the lungs. Crocodilia_sentence_134

When a crocodilian inhales, air flows through the trachea and into two primary bronchi, or airways, which branch off into narrower secondary passageways. Crocodilia_sentence_135

The air continues to move through these, then into even narrower tertiary airways, and then into other secondary airways which were bypassed the first time. Crocodilia_sentence_136

The air then flows back into the primary airways and is exhaled. Crocodilia_sentence_137

These aerodynamic valves within the bronchial tree have been hypothesised to explain how crocodilians can have unidirectional airflow without the aid of avian-like air sacs. Crocodilia_sentence_138

The lungs of crocodilians are attached to the liver and the pelvis by the diaphragmaticus muscle (analogous of the diaphragm in mammals). Crocodilia_sentence_139

During inhalation, the external intercostal muscles expand the ribs, allowing the animal to take in more air, while the ischiopubis muscle causes the hips to swing downwards and push the belly outward, and the diaphragmaticus pulls the liver back. Crocodilia_sentence_140

When exhaling, the internal intercostal muscles push the ribs inward, while the rectus abdominis pulls the hips and liver forwards and the belly inward. Crocodilia_sentence_141

Because the lungs expand into the space formerly occupied by the liver and are compressed when it moves back into position, this motion is sometimes referred to as a "hepatic piston". Crocodilia_sentence_142

Crocodilians can also use these muscles to adjust the position of their lungs; thereby controlling their buoyancy in the water. Crocodilia_sentence_143

An animal sinks when the lungs are pulled towards the tail and floats when they move back towards the head. Crocodilia_sentence_144

This allows them to move through the water without creating disturbances that could alert potential prey. Crocodilia_sentence_145

They can also spin and twist by moving their lungs laterally. Crocodilia_sentence_146

Swimming and diving crocodilians appear to rely on lung volume more for buoyancy than oxygen storage. Crocodilia_sentence_147

Just before diving, the animal exhales to reduce its lung volume and achieve negative buoyancy. Crocodilia_sentence_148

When submerging, the nostrils of a crocodilian shut tight. Crocodilia_sentence_149

All species have a palatal valve, a membranous flap of skin at the back of the oral cavity that prevents water from flowing into the throat, oesophagus, and trachea. Crocodilia_sentence_150

This enables them to open their mouths underwater without drowning. Crocodilia_sentence_151

Crocodilians typically remain underwater for fifteen minutes or less at a time, but some can hold their breath for up to two hours under ideal conditions. Crocodilia_sentence_152

The maximum diving depth is unknown, but crocodiles can dive to at least 20 m (66 ft). Crocodilia_sentence_153

Digestion Crocodilia_section_7

Crocodilian teeth are adapted for seizing and holding prey, and food is swallowed unchewed. Crocodilia_sentence_154

The digestive tract is relatively short, as meat is a fairly simple substance to digest. Crocodilia_sentence_155

The stomach is divided into two parts: a muscular gizzard that grinds food, and a digestive chamber where enzymes work on it. Crocodilia_sentence_156

The stomach is more acidic than that of any other vertebrate and contains ridges for gastroliths, which play a role in the mechanical breakdown of food. Crocodilia_sentence_157

Digestion takes place more quickly at higher temperatures. Crocodilia_sentence_158

Crocodilians have a very low metabolic rate and consequently, low energy requirements. Crocodilia_sentence_159

This allows them to survive for many months on a single large meal, digesting the food slowly. Crocodilia_sentence_160

They can withstand extended fasting, living on stored fat between meals. Crocodilia_sentence_161

Even recently hatched crocodiles are able to survive 58 days without food, losing 23% of their bodyweight during this time. Crocodilia_sentence_162

An adult crocodile needs between a tenth and a fifth of the amount of food necessary for a lion of the same weight, and can live for half a year without eating. Crocodilia_sentence_163

Thermoregulation Crocodilia_section_8

Crocodilians are ectotherms, producing relatively little heat internally and relying on external sources to raise their body temperatures. Crocodilia_sentence_164

The sun's heat is the main means of warming for any crocodilian, while immersion in water may either raise its temperature by conduction, or cool the animal in hot weather. Crocodilia_sentence_165

The main method for regulating its temperature is behavioural. Crocodilia_sentence_166

For example, an alligator in temperate regions may start the day by basking in the sun on land. Crocodilia_sentence_167

A bulky animal, it warms up slowly, but at some time later in the day it moves into the water, still exposing its dorsal surface to the sun. Crocodilia_sentence_168

At night it remains submerged, and its temperature slowly falls. Crocodilia_sentence_169

The basking period is extended in winter and reduced in summer. Crocodilia_sentence_170

For crocodiles in the tropics, avoiding overheating is generally the main problem. Crocodilia_sentence_171

They may bask briefly in the morning but then move into the shade, remaining there for the rest of the day, or submerge themselves in water to keep cool. Crocodilia_sentence_172

Gaping with the mouth can provide cooling by evaporation from the mouth lining. Crocodilia_sentence_173

By these means, the temperature range of crocodilians is usually maintained between 25 and 35 °C (77 and 95 °F), and mainly stays in the range 30 to 33 °C (86 to 91 °F). Crocodilia_sentence_174

The ranges of the American and Chinese alligator extend into regions that sometimes experience periods of frost in winter. Crocodilia_sentence_175

Being ectothermic, the internal body temperature of crocodilians falls as the temperature drops, and they become sluggish. Crocodilia_sentence_176

They may become more active on warm days, but do not usually feed at all during the winter. Crocodilia_sentence_177

In cold weather, they remain submerged with their tails in deeper, less cold water and their nostrils just projecting through the surface. Crocodilia_sentence_178

If ice forms on the water, they maintain ice-free breathing holes, and there have been occasions when their snouts have become frozen into the ice. Crocodilia_sentence_179

Temperature sensing probes implanted in wild American alligators have found that their core body temperatures can descend to around 5 °C (41 °F), but as long as they remain able to breathe they show no ill effects when the weather warms up. Crocodilia_sentence_180

Osmoregulation Crocodilia_section_9

No living species of crocodilian can be considered truly marine; although the saltwater crocodile and the American crocodile are able to swim out to sea, their normal habitats are river mouths, estuaries, mangrove swamps, and hypersaline lakes, though several extinct species have had marine habitats, including the recently extinct "Gavialis" papuensis, which occurred in a fully marine habitat in the Solomon Islands coastlines. Crocodilia_sentence_181

All crocodilians need to maintain the concentration of salt in body fluids at suitable levels. Crocodilia_sentence_182

Osmoregulation is related to the quantity of salts and water exchanged with the environment. Crocodilia_sentence_183

Intake of water and salts takes place across the lining of the mouth, when water is drunk, incidentally while feeding, and when present in foods. Crocodilia_sentence_184

Water is lost from the body during breathing, and both salts and water are lost in the urine and faeces, through the skin, and via salt-excreting glands on the tongue, though these are only present in crocodiles and gharials. Crocodilia_sentence_185

The skin is a largely effective barrier to both water and ions. Crocodilia_sentence_186

Gaping causes water loss by evaporation from the lining of the mouth, and on land, water is also lost through the skin. Crocodilia_sentence_187

Large animals are better able to maintain homeostasis at times of osmotic stress than smaller ones. Crocodilia_sentence_188

Newly hatched crocodilians are much less tolerant of exposure to salt water than are older juveniles, presumably because they have a higher surface-area-to-volume ratio. Crocodilia_sentence_189

The kidneys and excretory system are much the same as in other reptiles, but crocodilians do not have a bladder. Crocodilia_sentence_190

In fresh water, the osmolality (the concentration of solutes that contribute to a solution's osmotic pressure) in the plasma is much higher than it is in the surrounding water. Crocodilia_sentence_191

The animals are well-hydrated, and the urine in the cloaca is abundant and dilute, nitrogen being excreted as ammonium bicarbonate. Crocodilia_sentence_192

Sodium loss is low and mainly takes place through the skin in freshwater conditions. Crocodilia_sentence_193

In seawater, the opposite is true. Crocodilia_sentence_194

The osmolality in the plasma is lower than the surrounding water, which is dehydrating for the animal. Crocodilia_sentence_195

The cloacal urine is much more concentrated, white, and opaque, with the nitrogenous waste being mostly excreted as insoluble uric acid. Crocodilia_sentence_196

Distribution and habitat Crocodilia_section_10

Crocodilians are reptiles, spending part of their time in water and part on land. Crocodilia_sentence_197

The last surviving fully terrestrial genus, Mekosuchus, became extinct about 3000 years ago after humans had arrived on its Pacific islands, making the extinction possibly anthropogenic. Crocodilia_sentence_198

Typically they are creatures of the tropics; the main exceptions are the American and Chinese alligators, whose ranges consist of the south-eastern United States and the Yangtze River, respectively. Crocodilia_sentence_199

Florida, in the United States, is the only place that crocodiles and alligators live side by side. Crocodilia_sentence_200

Most crocodilians live in the lowlands, and few are found above 1,000 metres (3,300 ft), where the temperatures are typically about 5 °C (9 °F) lower than at the coast. Crocodilia_sentence_201

None of them permanently reside in the sea, though some can venture into it, and several species can tolerate the brackish water of estuaries, mangrove swamps, and the extreme salinity of hypersaline lakes. Crocodilia_sentence_202

The saltwater crocodile has the widest distribution of any crocodilian, with a range extending from eastern India to New Guinea and northern Australia. Crocodilia_sentence_203

Much of its success is due to its ability to swim out to sea and colonise new locations, but it is not restricted to the marine environment and spends much time in estuaries, rivers, and large lakes. Crocodilia_sentence_204

Various types of aquatic habitats are used by different crocodilians. Crocodilia_sentence_205

Some species are relatively more terrestrial and prefer swamps, ponds, and the edges of lakes, where they can bask in the sun and there is plenty of plant life supporting a diverse fauna. Crocodilia_sentence_206

Others spend more time in the water and inhabit the lower stretches of rivers, mangrove swamps, and estuaries. Crocodilia_sentence_207

These habitats also have a rich flora and provide plenty of food. Crocodilia_sentence_208

The Asian gharials find the fish on which they feed in the pools and backwaters of swift rivers. Crocodilia_sentence_209

South American dwarf caimans inhabit cool, fast-flowing streams, often near waterfalls, and other caimans live in warmer, turbid lakes and slow-moving rivers. Crocodilia_sentence_210

The crocodiles are mainly river dwellers, and the Chinese alligator is found in slow-moving, turbid rivers flowing across China's floodplains. Crocodilia_sentence_211

The American alligator is an adaptable species and inhabits swamps, rivers, or lakes with clear or turbid water. Crocodilia_sentence_212

Climatic factors also affect crocodilians' distribution locally. Crocodilia_sentence_213

During the dry season, caimans can be restricted to deep pools in rivers for several months; in the rainy season, much of the savanna in the Orinoco Llanos is flooded, and they disperse widely across the plain. Crocodilia_sentence_214

Desert crocodiles in Mauritania have adapted to their arid environment by staying in caves or burrows in a state of aestivation during the driest periods. Crocodilia_sentence_215

When it rains, the reptiles gather at gueltas. Crocodilia_sentence_216

Dry land is also important as it provides opportunities for basking, nesting, and escaping from temperature extremes. Crocodilia_sentence_217

Gaping allows evaporation of moisture from the mouth lining and has a cooling effect, and several species make use of shallow burrows on land to keep cool. Crocodilia_sentence_218

Wallowing in mud can also help prevent them from overheating. Crocodilia_sentence_219

Four species of crocodilians climb trees to bask in areas lacking a shoreline. Crocodilia_sentence_220

The type of vegetation bordering the rivers and lakes inhabited by crocodilians is mostly humid tropical forest, with mangrove swamps in estuarine areas. Crocodilia_sentence_221

These forests are of great importance to the crocodilians, creating suitable microhabitats where they can flourish. Crocodilia_sentence_222

The roots of the trees absorb water when it rains, releasing it back slowly into the environment. Crocodilia_sentence_223

When the forests are cleared to make way for agriculture, rivers tend to silt up, the water runs off rapidly, the water courses can dry up in the dry season and flooding can occur in the wet season. Crocodilia_sentence_224

Destruction of forest habitat is probably a greater threat to crocodilians than hunting. Crocodilia_sentence_225

Ecological roles Crocodilia_section_11

Being highly efficient predators, crocodilians tend to be top of the food chain in their watery environments. Crocodilia_sentence_226

The nest mounds built by some species of crocodilian are used by other animals for their own purposes. Crocodilia_sentence_227

American alligator mounds are used by turtles and snakes, both for basking and for laying their own eggs. Crocodilia_sentence_228

The Florida red-bellied turtle specialises in this, and alligator mounds may have several clutches of turtle eggs developing alongside the owner's eggs. Crocodilia_sentence_229

Alligators modify some wetland habitats in flat areas such as the Everglades by constructing small ponds known as "alligator holes". Crocodilia_sentence_230

These create wetter or drier habitats for other organisms, such as plants, fish, invertebrates, amphibians, reptiles, and mammals. Crocodilia_sentence_231

In the limestone depressions of cypress swamps, alligator holes tend to be large and deep. Crocodilia_sentence_232

Those in marl prairies and rocky glades are usually small and shallow, while those in peat depressions of ridge and slough wetlands are more variable. Crocodilia_sentence_233

Man-made holes do not appear to have as large an effect. Crocodilia_sentence_234

In the Amazon basin, when caimans became scarce as a result of overhunting in the mid-20th century, the number of local fish, such as the important arapaima (Arapaima gigas), also decreased. Crocodilia_sentence_235

These are nutrient-poor waters, and the urine and faeces of the caimans may have increased primary production by contributing plant nutrients. Crocodilia_sentence_236

Thus the presence of the reptiles could have benefited the fish stock; the number of crocodilians in a stretch of water appears to be correlated with the fish population. Crocodilia_sentence_237

Behavior and life history Crocodilia_section_12

Spacing Crocodilia_section_13

Adult crocodilians are typically territorial and solitary. Crocodilia_sentence_238

Individuals may defend basking spots, nesting sites, feeding areas, nurseries, and overwintering sites. Crocodilia_sentence_239

Male saltwater crocodiles establish year-round territories that encompass several female nesting sites. Crocodilia_sentence_240

Some species are occasionally gregarious, particularly during droughts, when several individuals gather at remaining water sites. Crocodilia_sentence_241

Individuals of some species may share basking sites at certain times of the day. Crocodilia_sentence_242

Feeding Crocodilia_section_14

Crocodilians are largely carnivorous, and the diets of different species can vary with snout shape and tooth sharpness. Crocodilia_sentence_243

Species with sharp teeth and long slender snouts, like the Indian gharial and Australian freshwater crocodile, are specialised for feeding on fish, insects, and crustaceans, while extremely broad-snouted species with blunt teeth, like the Chinese alligator and broad-snouted caiman, specialise in eating hard-shelled molluscs. Crocodilia_sentence_244

Species whose snouts and teeth are intermediate between these two forms, such as the saltwater crocodile and American alligator, have generalised diets and opportunistically feed on invertebrates, fish, amphibians, other reptiles, birds, and mammals. Crocodilia_sentence_245

Though mostly carnivorous, several species of crocodilian have been observed to consume fruit, and this may play a role in seed dispersal. Crocodilia_sentence_246

In general, crocodilians are stalk-and-ambush predators, though hunting strategies vary depending on the individual species and the prey being hunted. Crocodilia_sentence_247

Terrestrial prey is stalked from the water's edge and then grabbed and drowned. Crocodilia_sentence_248

Gharials and other fish-eating species sweep their jaws sideways to snap up prey, and these animals can leap out of the water to catch birds, bats, and leaping fish. Crocodilia_sentence_249

Small animals can be killed by whiplash as the predator shakes its head. Crocodilia_sentence_250

Caimans use their tails and bodies to herd fish into shallow water. Crocodilia_sentence_251

They may also dig for bottom-dwelling invertebrates, and the smooth-fronted caiman will even hunt on land. Crocodilia_sentence_252

Some crocodilian species have been observed to use sticks and branches to lure nest-building birds. Crocodilia_sentence_253

Nile crocodiles are known to hunt cooperatively, and several individuals may feed on the same carcass. Crocodilia_sentence_254

Most species will eat anything suitable that comes within reach and are also opportunistic scavengers. Crocodilia_sentence_255

Crocodilians are unable to chew and need to swallow food whole, so prey that is too large to swallow is torn into pieces. Crocodilia_sentence_256

They may be unable to deal with a large animal with a thick hide, and may wait until it becomes putrid and comes apart more easily. Crocodilia_sentence_257

To tear a chunk of tissue from a large carcass, a crocodilian spins its body continuously while holding on with its jaws, a manoeuvre known as the "death roll". Crocodilia_sentence_258

During cooperative feeding, some individuals may hold on to the prey, while others perform the roll. Crocodilia_sentence_259

The animals do not fight, and each retires with a piece of flesh and awaits its next feeding turn. Crocodilia_sentence_260

Food is typically consumed by crocodilians with their heads above water. Crocodilia_sentence_261

The food is held with the tips of the jaws, tossed towards the back of the mouth by an upward jerk of the head and then gulped down. Crocodilia_sentence_262

Nile crocodiles may store carcasses underwater for later consumption. Crocodilia_sentence_263

Reproduction and parenting Crocodilia_section_15

Crocodilians are generally polygynous, and individual males try to mate with as many females as they can. Crocodilia_sentence_264

Monogamous pairings have been recorded in American alligators. Crocodilia_sentence_265

Dominant male crocodilians patrol and defend territories which contain several females. Crocodilia_sentence_266

Males of some species, like the American alligator, try to attract females with elaborate courtship displays. Crocodilia_sentence_267

During courtship, crocodilian males and females may rub against each other, circle around, and perform swimming displays. Crocodilia_sentence_268

Copulation typically occurs in the water. Crocodilia_sentence_269

When a female is ready to mate, she arches her back while her head and tail submerge. Crocodilia_sentence_270

The male rubs across the female's neck and then grasps her with his hindlimbs, placing his tail underneath hers so their cloacas align and his penis can be inserted. Crocodilia_sentence_271

Mating can last up to 15 minutes, during which time the pair continuously submerge and surface. Crocodilia_sentence_272

While dominant males usually monopolise reproductive females, multiple paternity is known to exist in American alligators, where as many as three different males may sire offspring in a single clutch. Crocodilia_sentence_273

Within a month of mating, the female crocodilian begins to make a nest. Crocodilia_sentence_274

Depending on the species, female crocodilians may construct either holes or mounds as nests, the latter made from vegetation, litter, sand, or soil. Crocodilia_sentence_275

Nests are typically found near dens or caves. Crocodilia_sentence_276

Those made by different females are sometimes close to each other, particularly in hole-nesting species. Crocodilia_sentence_277

The number of eggs laid in a single clutch ranges from ten to fifty. Crocodilia_sentence_278

Crocodilian eggs are protected by hard shells made of calcium carbonate. Crocodilia_sentence_279

The incubation period is two to three months. Crocodilia_sentence_280

The temperature at which the eggs incubate determines the sex of the hatchlings. Crocodilia_sentence_281

Constant nest temperatures above 32 °C (90 °F) produce more males, while those below 31 °C (88 °F) produce more females. Crocodilia_sentence_282

However, sex in crocodilians may be determined in a short interval, and nests are subject to changes in temperature. Crocodilia_sentence_283

Most natural nests produce hatchlings of both sexes, though single-sex clutches do occur. Crocodilia_sentence_284

The young may all hatch in a single night. Crocodilia_sentence_285

Crocodilians are unusual among reptiles in the amount of parental care provided after the young hatch. Crocodilia_sentence_286

The mother helps excavate hatchlings from the nest and carries them to water in her mouth. Crocodilia_sentence_287

Newly hatched crocodilians gather together and stay close to their mother. Crocodilia_sentence_288

For spectacled caimans in the Venezuelan llanos, individual mothers are known to leave their young in the same nurseries, or crèches, and one of the mothers guards them. Crocodilia_sentence_289

Hatchlings of many species tend to bask in a group during the day and disperse at nightfall to feed. Crocodilia_sentence_290

The time it takes young crocodilians to reach independence can vary. Crocodilia_sentence_291

For American alligators, groups of young associate with adults for one to two years, while juvenile saltwater and Nile crocodiles become independent in a few months. Crocodilia_sentence_292

Communication Crocodilia_section_16

The social life of a crocodilian begins while it is still in the egg, because the young start communicating with each other before they are hatched. Crocodilia_sentence_293

It has been shown that a light tapping noise near the nest will be repeated by the young, one after another. Crocodilia_sentence_294

Such early communication may help them to hatch simultaneously. Crocodilia_sentence_295

Once it has broken out of the egg, a juvenile produces yelps and grunts either spontaneously or as a result of external stimuli and even unrelated adults respond quickly to juvenile distress calls. Crocodilia_sentence_296

Vocalisations are frequent as the juveniles disperse, and again as they congregate in the morning. Crocodilia_sentence_297

Nearby adults, presumably the parents, also give signals warning of predators or alerting the youngsters to the presence of food. Crocodilia_sentence_298

The range and quantity of vocalisations vary between species. Crocodilia_sentence_299

Alligators are the noisiest, while some crocodile species are almost completely silent. Crocodilia_sentence_300

Adult female New Guinea crocodiles and Siamese crocodiles roar when approached by another adult, while Nile crocodiles grunt or bellow in a similar situation. Crocodilia_sentence_301

The American alligator is exceptionally noisy; it emits a series of about seven throaty bellows, each a couple of seconds long, at ten second intervals. Crocodilia_sentence_302

It also makes various grunts and hisses. Crocodilia_sentence_303

Males create vibrations in the water to send out infrasonic signals that serve to attract females and intimidate rivals. Crocodilia_sentence_304

The enlarged boss of the male gharial may serve as a sound resonator. Crocodilia_sentence_305

Another form of acoustic communication is the headslap. Crocodilia_sentence_306

This typically starts with an animal in the water elevating its snout and remaining stationary. Crocodilia_sentence_307

After some time, the jaws are opened sharply then clamped shut with a biting motion that makes a loud slapping sound, and this is immediately followed by a loud splash, after which the head may be submerged and copious bubbles produced. Crocodilia_sentence_308

Some species then roar, while others slap the water with their tails. Crocodilia_sentence_309

Episodes of headslapping spread through the group. Crocodilia_sentence_310

The purpose varies, but it seems to be associated with maintaining social relationships, and is also used in courtship. Crocodilia_sentence_311

Dominant individuals may also display their body size while swimming at the water surface, and a subordinate will submit by holding its head at an acute angle with the jaws open before retreating underwater. Crocodilia_sentence_312

Growth and mortality Crocodilia_section_17

Mortality is high for eggs and hatchlings, and nests face threats from floods, overheating, and predators. Crocodilia_sentence_313

Flooding is a major cause of failure of crocodilians to breed successfully: nests are submerged, developing embryos are deprived of oxygen, and juveniles get washed away. Crocodilia_sentence_314

Numerous predators, both mammalian and reptilian, may raid nests and eat crocodilian eggs. Crocodilia_sentence_315

Despite the maternal care they receive, hatchlings commonly fall to predation. Crocodilia_sentence_316

While the female is transporting some to the nursery area, others are picked off by predators that lurk near the nest. Crocodilia_sentence_317

In addition to terrestrial predators, the hatchlings are also subject to aquatic attacks by fish. Crocodilia_sentence_318

Birds take their toll, and in any clutch there may be malformed individuals that are unlikely to survive. Crocodilia_sentence_319

In northern Australia, the survival rate for saltwater crocodile hatchlings is only twenty-five percent, but with each succeeding year of life this improves, reaching sixty percent by year five. Crocodilia_sentence_320

Mortality rates are fairly low among subadults and adults, though they are occasionally preyed on by large cats and snakes. Crocodilia_sentence_321

The jaguar and the giant otter may prey on caimans in South America. Crocodilia_sentence_322

In other parts of the world, elephants and hippopotamuses may kill crocodiles defensively. Crocodilia_sentence_323

Authorities differ as to whether much cannibalism takes place among crocodilians. Crocodilia_sentence_324

Adults do not normally eat their own offspring, but there is some evidence of subadults feeding on juveniles and of adults attacking subadults. Crocodilia_sentence_325

Rival male Nile crocodiles sometimes kill each other during the breeding season. Crocodilia_sentence_326

Growth in hatchlings and young crocodilians depends on the food supply, and sexual maturity is linked with length rather than age. Crocodilia_sentence_327

Female saltwater crocodiles reach maturity at 2.2–2.5 m (7–8 ft), while males mature at 3 m (10 ft). Crocodilia_sentence_328

Australian freshwater crocodiles take ten years to reach maturity at 1.4 m (4 ft 7 in). Crocodilia_sentence_329

The spectacled caiman matures earlier, reaching its mature length of 1.2 m (4 ft) in four to seven years. Crocodilia_sentence_330

Crocodilians continue to grow throughout their lives. Crocodilia_sentence_331

Males in particular continue to gain in weight as they get older, but this is mostly in the form of extra girth rather than length. Crocodilia_sentence_332

Crocodilians can live 35–75 years, and their age can be determined by growth rings in their bones. Crocodilia_sentence_333

Taxonomy and classification Crocodilia_section_18

Evolution Crocodilia_section_19

The main distinguishing characteristic of diapsid tetrapods is the presence of two openings (temporal fenestrae) on either side of the skull behind the eye. Crocodilia_sentence_334

Living diapsids include modern reptiles and birds. Crocodilia_sentence_335

The feature that distinguishes archosaurs from other diapsids is an extra pair of openings in the skull (antorbital fenestrae) in front of the eye sockets. Crocodilia_sentence_336

Archosauria is the crown group containing the most recent common ancestor of crocodilians and birds and all its descendants. Crocodilia_sentence_337

It comprises the Pseudosuchia, the "false crocodiles", and the Avemetatarsalia, which in turn comprises the dinosaurs (including birds) and pterosaurs. Crocodilia_sentence_338

Pseudosuchia is defined as living crocodilians and all archosaurs more closely related to crocodilians than to birds. Crocodilia_sentence_339

The Pseudosuchia–bird split is assumed to have occurred close to the Permian–Triassic mass extinction event. Crocodilia_sentence_340

In modern crocodilians, the antorbital fenestrae are walled off externally and exist merely as sinuses. Crocodilia_sentence_341

They were present in most of their fossil ancestors as small openings. Crocodilia_sentence_342

The crocodylomorphs are the only pseudosuchians to have survived the Triassic–Jurassic extinction event, 201.3 million years ago. Crocodilia_sentence_343

During the early Jurassic period, the dinosaurs became dominant on land, and the crocodylomorphs underwent major adaptive diversifications to fill ecological niches vacated by recently extinguished groups. Crocodilia_sentence_344

Unfolding fossil evidence shows that Mesozoic crocodylomorphs had a much greater diversity of forms than modern crocodilians. Crocodilia_sentence_345

Some became small fast-moving insectivores, others specialist fish-eaters, still others marine and terrestrial carnivores, and a few became herbivores. Crocodilia_sentence_346

The earliest stage of crocodilian evolution was the protosuchians, which evolved in the late Triassic and early Jurassic. Crocodilia_sentence_347

They were followed by the mesosuchians, which diversified widely during the Jurassic and the Tertiary. Crocodilia_sentence_348

Another group, the eusuchians, appeared in the late Cretaceous 80 million years ago and includes all the crocodilians living today. Crocodilia_sentence_349

Protosuchians were small, mostly terrestrial animals with short snouts and long limbs. Crocodilia_sentence_350

They had bony armor in the form of two rows of plates extending from head to tail, and this armor is retained by most modern crocodilians. Crocodilia_sentence_351

Their vertebrae were convex on the two main articulating surfaces, and their bony palates were little developed. Crocodilia_sentence_352

The mesosuchians saw a fusion of the palatine bones to form a secondary bony palate and a great extension of the nasal passages to near the pterygoid bones. Crocodilia_sentence_353

This allowed the animal to breathe through its nostrils while its mouth was open under the water. Crocodilia_sentence_354

The eusuchians continued this process with the interior nostrils now opening through an aperture in the pterygoid bones. Crocodilia_sentence_355

The vertebrae of eusuchians had one convex and one concave articulating surface, allowing for a ball and socket type joint between the vertebrae, bringing greater flexibility and strength. Crocodilia_sentence_356

The oldest known eusuchian is Hylaeochampsa vectiana from the lower Cretaceous of the Isle of Wight in the United Kingdom. Crocodilia_sentence_357

It was followed by crocodilians such as the Planocraniidae, the so-called 'hoofed crocodiles', in the Palaeogene. Crocodilia_sentence_358

Spanning the Cretaceous and Palaeogene periods is the genus Borealosuchus of North America, with six species, though its phylogenetic position is not settled. Crocodilia_sentence_359

The three primary branches of Crocodilia had diverged by the end of the Mesozoic. Crocodilia_sentence_360

The earliest-known members of the group is Portugalosuchus from the Cenomanian (95 million years ago) and after are alligatoroids and gavialoids that lived in North America and Europe during the Campanian (around 83.6–72.1 million years ago). Crocodilia_sentence_361

The first known crocodyloids appeared in the Cenomanian (around 72.1–66.0 million years ago), that lineage must have been present during the Campanian, and the earliest alligatoroids and gavialoids include highly derived forms, which indicates that the time of the actual divergence between the three lineages must have been a pre-Campanian event. Crocodilia_sentence_362

Relationships Crocodilia_section_20

The phylogenetic relationships of crocodilians has been the subject of debate and conflicting results. Crocodilia_sentence_363

Many studies and their resulting cladograms, or "family trees" of crocodilians, have found the "short-snouted" families of Crocodylidae and Alligatoridae to be close relatives, with the long-snouted Gavialidae as a divergent branch of the tree. Crocodilia_sentence_364

The resulting group of short-snouted species, name Brevirostres, was supported mainly by studies which analyzed skeletal features alone. Crocodilia_sentence_365

In 2012, Erickson et al. Crocodilia_sentence_366

produced a phylogeny formed from DNA sequencing to give a maximum likelihood cladogram of the relationships among living crocodilians (excluding the yacare caiman for which no DNA evidence was available). Crocodilia_sentence_367

In this, the existence of a distinct group Brevirostres was rejected, with the long-snouted gavialids more closely related to crocodiles than to alligators. Crocodilia_sentence_368

Taxonomy Crocodilia_section_21

Crocodilia_description_list_0

Crocodilia_unordered_list_1

There are two extant species of Gavialidae: the gharial and the false gharial. Crocodilia_sentence_369

Gharials can be recognised by the long narrow snout, with an enlarged boss at the tip. Crocodilia_sentence_370

They are rare and found only in South Asia. Crocodilia_sentence_371

Crocodilia_unordered_list_2

The extant Alligatoridae are two species in the genus Alligator, and six species of caimans grouped into three genera. Crocodilia_sentence_372

They can be recognised by the broad snout, in which the fourth tooth of the lower jaw cannot be seen when the mouth is closed. Crocodilia_sentence_373

Crocodilia_unordered_list_3

The extant Crocodylidae are fourteen species in the genus Crocodylus, and three species in other genera. Crocodilia_sentence_374

They have a variety of snout shapes, but can be recognised because the fourth tooth of the lower jaw is visible when the mouth is closed. Crocodilia_sentence_375

Crocodilia_description_list_4

Crocodilia_table_general_1

CrocodiliaCrocodilia_table_caption_1
Living and extinct groupsCrocodilia_header_cell_1_0_0

Interactions with humans Crocodilia_section_22

Farming and ranching Crocodilia_section_23

Main article: Alligator farm Crocodilia_sentence_376

Alligators and crocodiles were first farmed in the early 20th century, but the facilities involved were zoo-like and their main source of income was from tourism. Crocodilia_sentence_377

By the early 1960s, the feasibility of farming these reptiles on a commercial scale was investigated in response to the decline of many crocodilian species around the world. Crocodilia_sentence_378

Farming involves breeding and rearing captive stock on a self-contained basis, whereas ranching means the use of eggs, juveniles, or adults taken each year from the wild. Crocodilia_sentence_379

Commercial organisations must satisfy the criteria of the Convention on International Trade in Endangered Species (CITES) by demonstrating that, in the area concerned, they do not adversely impact the wild population. Crocodilia_sentence_380

Alligator and crocodile farming began because of demand for their hides, but now nearly all parts of the animal are put to use. Crocodilia_sentence_381

The side and belly skin make the best leather, the meat is eaten, the gall bladders are valued in East Asia, and the heads are sometimes made into ornaments. Crocodilia_sentence_382

In traditional Chinese medicine, alligator meat is said to cure the common cold and prevent cancer, while various internal organs are believed to have medicinal properties. Crocodilia_sentence_383

Attacks Crocodilia_section_24

Main article: Crocodile attack Crocodilia_sentence_384

See also: Alligator wrestling Crocodilia_sentence_385

Crocodilians are opportunistic predators that are at their most dangerous in water and at the edge of water. Crocodilia_sentence_386

Several species are known to attack humans and may do so to defend their territories, nests, or young; by mistake, while attacking domestic animals such as dogs; or for food, as larger crocodilians can take prey as big as or bigger than humans. Crocodilia_sentence_387

The species on which there is most data are the saltwater crocodile, the Nile crocodile, and the American alligator. Crocodilia_sentence_388

Other species which have sometimes attacked humans are the black caiman, the Morelet's crocodile, the mugger crocodile, the American crocodile, the gharial, and the freshwater crocodile. Crocodilia_sentence_389

The Nile crocodile has a reputation as the biggest killer of large animals, including humans, on the African continent. Crocodilia_sentence_390

It is widely distributed, found in many habitats and cryptically coloured. Crocodilia_sentence_391

From a waiting position with only its eyes and nostrils above the water, it can lunge at drinking animals, fishermen, bathers, or people collecting water or washing clothes. Crocodilia_sentence_392

Once seized and dragged into the water, there is little chance for the victim to escape. Crocodilia_sentence_393

Analysis of attacks show that most take place during the breeding season or when crocodiles are guarding nests or newly hatched young. Crocodilia_sentence_394

Although many attacks go unreported, there are estimated to be over 300 per year, 63% of which are fatal. Crocodilia_sentence_395

Wild saltwater crocodiles in Australia carried out 62 confirmed and unprovoked attacks causing injury or death between 1971 and 2004. Crocodilia_sentence_396

These animals have also caused fatalities in Malaysia, New Guinea, and elsewhere. Crocodilia_sentence_397

They are highly territorial and resent intrusion into their territories by other crocodiles, humans, or boats such as canoes. Crocodilia_sentence_398

Attacks may come from animals of various sizes, but the larger males are generally responsible for fatalities. Crocodilia_sentence_399

As their size increases, so does their need for larger mammalian prey; pigs, cattle, horses, and humans are all within the size range they seek. Crocodilia_sentence_400

Most of the people attacked were either swimming or wading, but in two instances they were asleep in tents. Crocodilia_sentence_401

American alligators are recorded as making 242 unprovoked attacks between 1948 and mid-2004, causing sixteen human fatalities. Crocodilia_sentence_402

Ten of these were in the water and two were on land; the circumstances of the other four are not known. Crocodilia_sentence_403

Most attacks were in the warmer months of the year, though in Florida, with its warmer climate, attacks can happen at any time of year. Crocodilia_sentence_404

Alligators are considered to be less aggressive than either the Nile or saltwater crocodile, but the increase in density of the human population in the Everglades has brought people and alligators into proximity and increased the risk of alligator attacks. Crocodilia_sentence_405

Conversely in Mauritania, where the crocodiles' growth is severely stunted by the arid conditions, the local people swim with them without being attacked. Crocodilia_sentence_406

As pets Crocodilia_section_25

Several species of crocodilian are traded as exotic pets. Crocodilia_sentence_407

They are appealing when young, and pet-store owners can easily sell them, but crocodilians do not make good pets; they grow large and are both dangerous and expensive to keep. Crocodilia_sentence_408

As they grow older, pet crocodilians are often abandoned by their owners, and feral populations of spectacled caimans exist in the United States and Cuba. Crocodilia_sentence_409

Most countries have strict regulations for keeping these reptiles. Crocodilia_sentence_410

In medicine Crocodilia_section_26

The blood of alligators and crocodiles contains peptides with antibiotic properties. Crocodilia_sentence_411

According to National Geographic, these may contribute to future antibacterial drugs. Crocodilia_sentence_412

Conservation Crocodilia_section_27

The main threat to crocodilians around the world is human activity, including hunting and habitat destruction. Crocodilia_sentence_413

Early in the 1970s, more than 2 million wild crocodilian skins of a variety of species had been traded, driving down the majority of crocodilian populations, in some cases almost to extinction. Crocodilia_sentence_414

Starting in 1973, attempted to prevent trade in body parts of endangered animals, such as the skins of crocodiles. Crocodilia_sentence_415

This proved to be problematic in the 1980s, as crocodiles were abundant and dangerous to humans in some parts of Africa, and it was legal to hunt them. Crocodilia_sentence_416

At the Conference of the Parties in Botswana in 1983, it was argued on behalf of aggrieved local people that it was reasonable to sell the lawfully hunted skins. Crocodilia_sentence_417

In the late 1970s, crocodiles began to be farmed in different countries, started from eggs taken from the wild. Crocodilia_sentence_418

By the 1980s, farmed crocodile skins were produced in sufficient numbers to destroy the unlawful trade in wild crocodilians. Crocodilia_sentence_419

By 2000, skins from twelve crocodilian species, whether harvested lawfully in the wild or farmed, were traded by thirty countries, and the unlawful trade in the products had almost vanished. Crocodilia_sentence_420

The gharial has undergone a chronic long-term decline, combined with a rapid short-term decline, leading the IUCN to list the species as critically endangered. Crocodilia_sentence_421

In 1946, the gharial population had been widespread, numbering around 5,000 to 10,000; by 2006, however, it had declined 96–98%, reduced to a small number of widely spaced subpopulations of fewer than 235 individuals. Crocodilia_sentence_422

This long-term decline had a number of causes, including egg collection and hunting, such as for indigenous medicine. Crocodilia_sentence_423

The rapid decline of about 58% between 1997 and 2006 was caused by increasing use of gill nets and the loss of riverine habitat. Crocodilia_sentence_424

The gharial population continues to be threatened by environmental hazards such as heavy metals and protozoan parasites, but as of 2013 numbers are rising, due to the protection of nests against egg predators. Crocodilia_sentence_425

The Chinese alligator was historically widespread throughout the eastern Yangtze River system but is currently restricted to some areas in southeastern Anhui province thanks to habitat fragmentation and degradation. Crocodilia_sentence_426

The wild population is believed to exist only in small fragmented ponds. Crocodilia_sentence_427

In 1972, the species was declared a Class I endangered species by the Chinese government and received the maximum amount of legal protection. Crocodilia_sentence_428

Since 1979, captive breeding programs were established in China and North America, creating a healthy captive population. Crocodilia_sentence_429

In 2008, alligators bred in the Bronx Zoo were successfully reintroduced to Chongming Island. Crocodilia_sentence_430

The Philippine crocodile is perhaps the most threatened crocodilian and is considered by the IUCN to be critically endangered. Crocodilia_sentence_431

Hunting and destructive fishing habits have reduced its population to around 100 individuals by 2009. Crocodilia_sentence_432

In the same year, 50 captive bred crocodiles were released into the wild to help boost the population. Crocodilia_sentence_433

Support from local people is crucial for the species' survival. Crocodilia_sentence_434

The American alligator has also suffered serious declines from hunting and habitat loss throughout its range, threatening it with extinction. Crocodilia_sentence_435

In 1967 it was listed as an endangered species, but the United States Fish and Wildlife Service and state wildlife agencies in the Southern United States stepped in and worked towards its recovery. Crocodilia_sentence_436

Protection allowed the species to recuperate, and in 1987 it was removed from the endangered species list. Crocodilia_sentence_437

Much research into alligator ranching has been undertaken at the Rockefeller Wildlife Refuge, a large area of marshland in the state of Louisiana. Crocodilia_sentence_438

The resulting data has increased understanding of penning, stocking rates, egg incubation, hatching, rearing, and diet, and this information has been used at other establishments around the world. Crocodilia_sentence_439

Income from the alligators kept at Rockefeller Wildlife Refuge contributes to conservation of the marshland. Crocodilia_sentence_440

A study examining alligator farms in the United States showed that they have generated significant conservation gains, and poaching of wild alligators has greatly diminished. Crocodilia_sentence_441

Cultural depictions Crocodilia_section_28

See also: List of fictional crocodiles and alligators Crocodilia_sentence_442

In mythology, religion, and folklore Crocodilia_section_29

Crocodilians have had prominent roles in the myths and legends of various cultures around the world and may even have inspired stories of dragons. Crocodilia_sentence_443

In Ancient Egyptian religion, Ammit, the demoniac devourer of unworthy souls, and Sobek, the god of power, protection, and fertility, are both represented as having crocodile heads. Crocodilia_sentence_444

This reflects the Egyptians' view of the crocodile both as a terrifying predator and an important part of the Nile ecosystem. Crocodilia_sentence_445

The crocodile was one of several animals that the Egyptians mummified. Crocodilia_sentence_446

Crocodiles were also associated with various water deities by peoples of West Africa. Crocodilia_sentence_447

During the Benin Empire, crocodiles were considered the "policemen of the waters" and symbolised the power of the king or oba to punish wrongdoers. Crocodilia_sentence_448

The Leviathan described in the Book of Job may have been based on a crocodile. Crocodilia_sentence_449

In Mesoamerica, the Aztecs had a crocodilian god of fertility named Cipactli who protected crops. Crocodilia_sentence_450

In Aztec mythology, the earth deity Tlaltecuhtli is sometimes represented as a crocodile-like monster. Crocodilia_sentence_451

The Maya also associated crocodilians with fertility and death. Crocodilia_sentence_452

The gharial is featured in the folk tales of India. Crocodilia_sentence_453

In one story, a gharial and a monkey become friends when the monkey gives the gharial fruit but friendship ends after the gharial confess they tried to lure him into this house to eat him. Crocodilia_sentence_454

Similar stories exist in Native American legends, and in the African American folktale of an alligator and Br'er Rabbit. Crocodilia_sentence_455

In a popular Malay folk tale, a mouse deer tricks a group of crocodiles into becoming a bridge for him to cross a river without eating him. Crocodilia_sentence_456

A legend from East Timor tells how a boy rescues a gigantic crocodile that becomes stranded. Crocodilia_sentence_457

In return, the crocodile protects him for the rest of its life, and when it dies, its scaly ridged back becomes the hills of Timor. Crocodilia_sentence_458

One Australian Dreamtime story tells of a crocodile ancestor who had fire all to himself. Crocodilia_sentence_459

One day, a "rainbow bird" stole fire-sticks from the crocodile and gave it to man. Crocodilia_sentence_460

Hence the crocodile lives in water. Crocodilia_sentence_461

In literature Crocodilia_section_30

Ancient historians have described crocodilians from the earliest historical records, though often their descriptions contain as much legend as fact. Crocodilia_sentence_462

The Ancient Greek historian Herodotus (c. 440 BC) described the crocodile in detail, though much of his description is fanciful; he claimed that it would lie with its mouth open to permit a "trochilus" bird (possibly an Egyptian plover) to enter and remove any leeches it found. Crocodilia_sentence_463

The crocodile was one of the beasts described in the late-13th century Rochester Bestiary, based on classical sources, including Pliny's Historia naturalis (c. 79 AD) and Isidore of Seville's Etymologies. Crocodilia_sentence_464

Isidore asserts that the crocodile is named for its saffron colour (Latin croceus, 'saffron'), and that it is often twenty cubits (10 m (33 ft)) long. Crocodilia_sentence_465

He further claimed that the crocodile may be killed by fish with serrated crests sawing into its soft underbelly, and that the male and female take turns guarding the eggs. Crocodilia_sentence_466

Crocodiles have been reputed to weep for their victims since the 9th century Bibliotheca by Photios I of Constantinople. Crocodilia_sentence_467

The story was repeated in later accounts such as that of Bartholomeus Anglicus in the 13th century. Crocodilia_sentence_468

It became widely known in 1400 when the English traveller Sir John Mandeville wrote his description of "cockodrills": Crocodilia_sentence_469

Crocodilia_description_list_5

  • "In that country [of Prester John and by all Ind [India] be great plenty of cockodrills, that is a manner of a long serpent, as I have said before. And in the night they dwell in the water, and on the day upon the land, in rocks and in caves. And they eat no meat in all the winter, but they lie as in a dream, as do the serpents. These serpents slay men, and they eat them weeping; and when they eat they move the over jaw, and not the nether jaw, and they have no tongue."Crocodilia_item_5_39

Crocodilians, especially the crocodile, have been recurring characters in stories for children throughout the modern era. Crocodilia_sentence_470

Lewis Carroll's Alice's Adventures in Wonderland (1865) contains the poem How Doth the Little Crocodile, a parody of a moralising poem by Isaac Watts, . Crocodilia_sentence_471

In J. Crocodilia_sentence_472 M. Barrie's novel Peter and Wendy (1911), the character Captain Hook has lost his hand to the crocodile. Crocodilia_sentence_473

Hook fears the crocodile, but is warned of its approach by the ticking of a clock which it has swallowed. Crocodilia_sentence_474

In Rudyard Kipling's Just So Stories (1902), the Elephant's Child acquires his trunk by having his (short) nose pulled very hard by the Crocodile "on the banks of the great grey-green, greasy Limpopo River". Crocodilia_sentence_475

The newly elongated nose allows him to pick fruit instead of waiting for it to fall, and to do many other useful things. Crocodilia_sentence_476

Roald Dahl's The Enormous Crocodile (1978), illustrated by Quentin Blake, tells how a crocodile wanders the jungle looking for children to eat, trying one trick after another. Crocodilia_sentence_477

In Andrew Fusek Peters' story book, Monkey's Clever Tale, a crocodile is tricked by a monkey. Crocodilia_sentence_478

The monkey asks the crocodile to carry it across a river, promising to give its tail to eat in return, but escaped with the tail intact. Crocodilia_sentence_479

In sports and media Crocodilia_section_31

Crocodilians are sometimes used as mascots for sports teams. Crocodilia_sentence_480

The Canton Crocodiles were a baseball team in the Frontier League, while the University of Florida sport teams are known as the Florida Gators, in reference to the American alligator, and their mascots are Albert and Alberta Gator. Crocodilia_sentence_481

In film and television, crocodilians are represented as dangerous obstacles in lakes and rivers, as in the 1986 Australian comedy film Crocodile Dundee, or as monstrous man-eaters in horror films like Eaten Alive (1977), Alligator (1980), Lake Placid (1999), Crocodile (2000), Primeval (2007) and Black Water (2007). Crocodilia_sentence_482

Some media have attempted to portray these reptiles in more positive or educational light, such as Steve Irwin's wildlife documentary series The Crocodile Hunter. Crocodilia_sentence_483

See also Crocodilia_section_32

Crocodilia_unordered_list_6


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Crocodilia.