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Crocodiles (
family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. Ideally, families would off ...
Crocodylidae) or true crocodiles are large
semiaquatic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
members of the
order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and the habit of achieving a ...
Crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

Crocodilia
, which includes the
alligator An alligator is a crocodilia Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago ...

alligator
s and
caiman A caiman (also cayman as a variant spelling) is an alligatorid The family (biology), family Alligatoridae of crocodylians includes alligators and caimans. Phylogeny The superfamily Alligatoroidea includes all crocodilians (fossil and extan ...

caiman
s (family
Alligatoridae The family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the s ...
), the
gharial The gharial (''Gavialis gangeticus''), also known as the gavial or the fish-eating crocodile, is a crocodilia Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquat ...

gharial
and
false gharial The false gharial (''Tomistoma schlegelii''), also known as the Malayan gharial and the Sunda gharial, is a freshwater crocodilian in the family In human society, family (from la, familia) is a group of people related either by consangui ...

false gharial
(family
Gavialidae Gavialidae is a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subj ...
) among other extinct taxa. Although they appear similar, crocodiles, alligators and the gharial belong to separate biological
families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of families is to maintain the w ...
. The gharial, with its narrow
snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis Convolvulus hawk-moth (''Agrius convolvuli'') feeding with extended probos ...
, is easier to distinguish, while morphological differences are more difficult to spot in crocodiles and alligators. The most obvious external differences are visible in the head, with crocodiles having narrower and longer heads, with a more V-shaped than a U-shaped snout compared to alligators and caimans. Another obvious trait is that the upper and lower jaws of the crocodiles are the same width, and the
teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. ...

teeth
in the lower jaw fall along the edge or outside the upper jaw when the mouth is closed; therefore, all teeth are visible, unlike an alligator, which possesses in the upper jaw small depressions into which the lower teeth fit. Also, when the crocodile's mouth 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
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
'
family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. Ideally, families would off ...
. Crocodiles have more
webbing red, blue and black nylon webbing as used in auto racing harnesses Webbing is a strong Textile, fabric weaving, woven as a flat strip or tube of varying width and fibres, often used in place of rope. It is a versatile component used in climbing ...

webbing
on the toes of the hind
feet The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemist ...

feet
and can better tolerate
saltwater Saline water (more commonly known as salt water) is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the ...
due to specialized
salt gland The salt gland is an organ for excreting excess salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity ...

salt gland
s for filtering out salt, which are present, but non-functioning, in alligators. Another trait that separates crocodiles from other crocodilians is their much higher levels of
aggression Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual. It may occur either reactively or without provocation. In humans, aggression can be caused by various ...
. Crocodile
size Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions (length, width, height, diameter, perimeter), area, or volume. ...

size
,
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
,
behaviour Behavior (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...

behaviour
and
ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biol ...
differ somewhat among
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
. However, they have many similarities in these areas as well. All crocodiles are
semiaquatic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
and tend to congregate in
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...
habitats such as
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river
s,
lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable ove ...

lake
s,
wetland A wetland is a distinct ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles ...

wetland
s and sometimes in
brackish Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) with fresh water together, as in estu ...
water and
saltwater Saline water (more commonly known as salt water) is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the ...

saltwater
. They are
carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization allowed the domestication of animals such as chickens, sheep, rabbi ...
animals, feeding mostly on
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s such as
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
,
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s,
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s and
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s, and sometimes on
invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebra ...
s such as
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil species is es ...
s and
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), der ...
s, depending on species and age. All crocodiles are
tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S; these latitudes correspond to ...

tropical
species that, unlike alligators, are very sensitive to
cold , a common physiological response to cold, aiming to reduce the loss of body heat in a cold environment File:AntarcticaDomeCSnow.jpg, A photograph of the snow surface at Dome C Station, Antarctica a part of the notoriously cold Polar Platea ...

cold
. They separated from other
crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

crocodilia
ns during the
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' ...
epoch, about 55 million years ago. Many species are at the risk of
extinction Extinction is the termination of a kind of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by ...

extinction
, some being classified as critically endangered.


Etymology

The word ''crocodile'' comes from the
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
() meaning 'lizard', used in the phrase , "the lizard of the (
Nile The Nile, , Bohairic , lg, Kiira , Nobiin Nobiin, or Mahas, is a Northern Nubian languages, Nubian language of the Nilo-Saharan languages, Nilo-Saharan language family. "Nobiin" is the genitive case, genitive form of ''Nòòbíí'' ("Nub ...

Nile
) river". There are several variant Greek forms of the word attested, including the later form () found cited in many English reference works. In the
Koine Greek Koine Greek (, , Greek approximately ;. , , , lit. "Common Greek"), also known as Alexandrian dialect, common Attic, Hellenistic or Biblical Greek, was the koiné language, common supra-regional form of Greek language, Greek spoken and written d ...
of
Roman Roman or Romans most often refers to: *, the capital city of Italy *, Roman civilization from 8th century BC to 5th century AD *, the people of ancient Rome *', shortened to ''Romans'', a letter in the New Testament of the Christian Bible Roman ...

Roman
times, and would have been pronounced identically, and either or both may be the source of the
Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s and 1930s to replace traditional writing sy ...
form used by the ancient Romans. It has been suggested, but it is not certain that the word or is a compound of ('pebbles'), and ('worm'), although is only attested as a colloquial term for 'penis'. It is ascribed to
Herodotus Herodotus ( ; grc, Ἡρόδοτος, Hēródotos, ; BC) was an ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), ge ...
, and supposedly describes the basking habits of the Egyptian crocodile. The form is attested in
Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share ...
. It is not clear whether this is a medieval corruption or derives from alternative Greco-Latin forms (late Greek and are attested). A (further) corrupted form is found in
Old French Old French (, , ; Modern French French ( or ) is a Romance language The Romance languages, less commonly Latin or Neo-Latin languages, are the modern languages that evolved from Vulgar Latin Vulgar Latin, also known as Popular o ...
and was borrowed into
Middle English Middle English (abbreviated to ME) was a form of the English language spoken after the Norman conquest of England, Norman conquest (1066) until the late 15th century. The English language underwent distinct variations and developments following ...
as . The
Modern English Modern English (sometimes New English or NE (ME) as opposed to Middle English Middle English (abbreviated to ME) was a form of the English language spoken after the Norman conquest of England, Norman conquest (1066) until the late 15th cen ...

Modern English
form ''crocodile'' was adapted directly from the Classical Latin in the 16th century, replacing the earlier form. The use of ''-y-'' in the scientific name ''
Crocodylus ''Crocodylus'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to ...
'' (and forms derived from it) is a corruption introduced by Laurenti (1768).


Species

A total of 18
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
species have been recognized. Further
genetic study Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist and Augustinia ...
is needed for the confirmation of proposed species under the genus ''
Osteolaemus The dwarf crocodile (''Osteolaemus tetraspis''), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile The mugger crocodile (''Crocodylus palustris''), also called marsh crocod ...
''.


Characteristics

A crocodile's physical traits allow it to be a successful
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

predator
. Its external
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
is a sign of its
aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...
and
predatory Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical envi ...
lifestyle. Its
streamlined.'') Streamlines, streaklines and pathlines are field lines in a fluid flow In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural s ...
body enables it to swim swiftly; it also tucks its feet to the side while swimming, making it faster by decreasing water resistance. Crocodiles have
webbed feet The webbed foot is a specialized limb present in a variety of vertebrates that aids in locomotion. This adaptation is primarily found in semiaquatic species, and has convergently evolved many times across vertebrate taxa. It likely arose fro ...
which, though not used to propel them through the water, allow them to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallow water, where the animals sometimes move around by walking. Crocodiles have a
palatal The palate is the roof of the mouth in humans and other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of ma ...
flap, a rigid tissue at the back of the mouth that blocks the entry of water. The palate has a special path from the
nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose A nose is a protuberance in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic ...
to the
glottis The glottis is the opening between the vocal folds In humans, vocal cords, also known as vocal chords, vocal folds or voice reeds, are folds of tissue in the throat that are key in creating sounds through vocalization. The size of vocal cor ...
that bypasses the mouth. The nostrils are closed during submergence. Like other
archosaur Archosauria ("ruling reptiles") is a clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. ...
s, crocodilians are
diapsid Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are extremely diverse, and include all ...

diapsid
, although their post-temporal fenestrae are reduced. The walls of the braincase are bony but lack supratemporal and postfrontal bones.Grigg, Gordon and Gans, Carl (1993
Morphology And Physiology Of The Crocodylia
, in Fauna of Australia Vol 2A Amphibia and Reptilia, chapter 40, pp. 326–336. Australian Government Publishing Service, Canberra.
Their
tongue The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...

tongue
s are not free, but held in place by a membrane that limits movement; as a result, crocodiles are unable to stick out their tongues. Crocodiles have smooth skin on their bellies and sides, while their dorsal surfaces are armoured with large
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis The dermis or corium is a layer of skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three ...
. The armoured skin has scales and is thick and rugged, providing some protection. They are still able to absorb heat through this armour, as a network of small
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessel ...

capillaries
allows blood through the scales to absorb heat. The osteoderms are highly vascularised and aid in calcium balance, both to neutralize acids while the animal cannot breathe underwater and to provide calcium for eggshell formation. Crocodilian tegument have pores believed to be sensory in function, analogous to the
lateral line The lateral line, also called lateral line system (LLS) or lateral line organ (LLO), is a system of sensory organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory abili ...
in fishes. They are particularly seen on their upper and lower jaws. Another possibility is that they are secretory, as they produce an oily substance which appears to flush mud off.


Size

Size greatly varies among species, from the
dwarf crocodile The dwarf crocodile (''Osteolaemus tetraspis''), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile The mugger crocodile (''Crocodylus palustris''), also called marsh crocod ...

dwarf crocodile
to the
saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They f ...

saltwater crocodile
. Species of the dwarf crocodile ''Osteolaemus'' grow to an adult size of just , whereas the saltwater crocodile can grow to sizes over and weigh over . Several other large species can reach over long and weigh over . Crocodilians show pronounced
sexual dimorphism Sexual dimorphism is the condition where the sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in ...
, with males growing much larger and more rapidly than females. Despite their large adult sizes, crocodiles start their lives at around long. The largest species of crocodile is the saltwater crocodile, found in eastern India, northern Australia, throughout
South-east Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern subregion of Asia, consisting of the regions ...
, and in the surrounding waters. The brain volume of two adult crocodiles was 5.6 cm3 for a
spectacled caiman The spectacled caiman (''Caiman crocodilus''), also known as the white caiman, common caiman, and speckled caiman, is a crocodilian in the family Alligatoridae. It is brownish-, greenish-, or yellowish-gray colored and has a spectacle-like ridge ...

spectacled caiman
and 8.5 cm3 for a larger
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
. The largest crocodile ever held in captivity is a saltwater–Siamese hybrid named Yai ( th, ใหญ่, meaning big; born 10 June 1972) at the Samutprakarn Crocodile Farm and Zoo,
Thailand Thailand ( th, ประเทศไทย), historically known as Siam, () officially the Kingdom of Thailand, is a country in Southeast Asia. It is located at the centre of the Mainland Southeast Asia, Indochinese Peninsula, spanning , wi ...

Thailand
. This animal measures in length and weighs . The longest crocodile captured alive was
Lolong Lolong (died 10 February 2013) was the largest crocodile Crocodiles (family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group ...

Lolong
, a saltwater crocodile which was measured at and weighed at by a National Geographic team in Agusan del Sur Province, Philippines.


Teeth

Crocodiles are
polyphyodont A polyphyodont is any animal whose teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposi ...
s; they are able to replace each of their 80 teeth up to 50 times in their 35- to 75-year lifespan. Next to each full-grown tooth, there is a small replacement tooth and an
odontogenic Tooth development or odontogenesis is the complex process by which tooth, teeth form from embryonic cells, cell growth, grow, and erupt into the human mouth, mouth. For human tooth, human teeth to have a healthy human mouth, oral environment, all ...
stem cell In multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties o ...
in the
dental lamina The dental lamina is a band of epithelial Epithelium () is one of the four basic types of animal Tissue (biology), tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of Cell (biolo ...
in standby that can be activated if required.


Biology and behaviour

Crocodilians are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three families being included in the group Archosauria ('ruling reptiles'). Despite their prehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles, a crocodile has a
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of a ...
and a four-chambered
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
. Crocodilians also have the functional equivalent of a diaphragm by incorporating muscles used for aquatic locomotion into respiration.
Salt gland The salt gland is an organ for excreting excess salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity ...

Salt gland
s are present in the tongues of crocodiles and they have a pore opening on the surface of the tongue, a trait that separates them from alligators. Salt glands are dysfunctional in Alligatoridae. Their function appears to be similar to that of salt glands in
marine turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines Turtles are reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constitut ...
s. Crocodiles do not have sweat glands and release heat through their mouths. They often sleep with their mouths open and may pant like a dog. Four species of freshwater crocodile climb trees to bask in areas lacking a shoreline.


Senses

Crocodiles 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 the water, almost totally submerged and hidden from prey.


Vision

Crocodiles have very good night vision, and are mostly
nocturnal Nocturnality is an animal behavior Ethology is the scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...
hunters. They use the disadvantage of most prey animals' poor nocturnal vision to their advantage. The light receptors in crocodilians' eyes include
cones A cone is a three-dimensional space, three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the Apex (geometry), apex or vertex (geometry), vertex. A cone is fo ...

cones
and numerous rods, so it is assumed all crocodilians can see colours. Crocodiles have vertical-slit shaped pupils, similar to those of domestic cats. One explanation for the evolution of slit pupils is that they exclude light more effectively than a circular pupil, helping to protect the eyes during daylight. On the rear wall of the eye is a
tapetum lucidum The ''tapetum lucidum'' (; from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the ...
, which reflects incoming light back onto the retina, thus utilizing the small amount of light available at night to best advantage. In addition to the protection of the upper and lower eyelids, crocodiles have a
nictitating membrane The nictitating membrane (from Latin ''wikt:nicto, nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the Medial (anatomy), medial canthus to protect and moisten it while ...
(sometimes called a "third eye-lid") that can be drawn over the eye from the inner corner while the lids are open. The eyeball surface is thus protected under the water while a certain degree of vision is still possible.


Olfaction

Crocodilian
sense of smell The sense of smell, or olfaction, is the special sense In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, the ...
is also very well developed, aiding them to detect prey or animal carcasses that are either on land or in water, from far away. It is possible that crocodiles use olfaction in the egg prior to hatching.
Chemoreception A chemoreceptor, also known as chemosensor, is a specialized sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex ...
in crocodiles is especially interesting because they hunt in both terrestrial and aquatic surroundings. Crocodiles have only one olfactory chamber and the
vomeronasal organ The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate). The name is derived fro ...

vomeronasal organ
is absent in the adults indicating all olfactory perception is limited to the olfactory system. Behavioural and olfactometer experiments indicate that crocodiles detect both air-borne and water-soluble chemicals and use their olfactory system for hunting. When above water, crocodiles enhance their ability to detect volatile odorants by gular pumping, a rhythmic movement of the floor of the pharynx. Crocodiles close their nostrils when submerged, so olfaction underwater is unlikely. Underwater food detection is presumably gustatory and tactile.


Hearing

Crocodiles can hear well; their tympanic membranes are concealed by flat flaps that may be raised or lowered by muscles.


Touch

Cranial: The upper and lower jaws are covered with sensory pits, visible as small, black speckles on the skin, the crocodilian version of the
lateral line The lateral line, also called lateral line system (LLS) or lateral line organ (LLO), is a system of sensory organs found in aquatic vertebrates, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory abili ...
organs seen in fish and many amphibians, though arising from a completely different origin. These pigmented nodules encase bundles of
nerve fibers A nerve is an enclosed, cable-like bundle of fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electroc ...
innervated beneath by branches of the trigeminal nerve. They respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes as small as a single drop. 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). Post-Cranial: While alligators and caimans have DPRs only on their jaws, crocodiles have similar organs on almost every scale on their bodies. The function of the DPRs on the jaws is clear; to catch prey, but it is still not clear what the function is of the organs on the rest of the body. The receptors flatten when exposed to increased osmotic pressure, such as that experienced when swimming in sea water
hyperosmotic Tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The ...
to the body fluids. When contact between the integument and the surrounding sea water solution is blocked, crocodiles are found to lose their ability to discriminate salinities. It has been proposed that the flattening of the sensory organ in hyperosmotic sea water is sensed by the animal as "touch", but interpreted as chemical information about its surroundings. This might be why in alligators they are absent on the rest of the body.


Hunting and diet

Crocodiles are
ambush predator Ambush predators or sit-and-wait predators are carnivorous animal A carnivore , meaning "meat eater" (Latin, ''caro'', genitive ''carnis'', meaning "meat" or "flesh" and ''vorare'' meaning "to devour"), is an organism, animal whose food and e ...
s, waiting for fish or land animals to come close, then rushing out to attack. Crocodiles mostly eat
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
,
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s,
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), der ...
s,
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil species is es ...
s,
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s,
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s, and
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s, and they occasionally
cannibalize Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecology, ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documen ...
smaller crocodiles. What a crocodile eats varies greatly with species, size and age. From the mostly fish-eating species, like the slender-snouted and
freshwater crocodile The freshwater crocodile (''Crocodylus johnstoni'' or ''Crocodylus johnsoni''; see below), also known as the Australian freshwater crocodile, Johnstone's crocodile or colloquially as freshie, is a species of crocodile Crocodiles (subfamil ...

freshwater crocodile
s, to the larger species like the
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
and the
saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They f ...

saltwater crocodile
that prey on large mammals, such as buffalo,
deer Deer or true deer are ed s forming the Cervidae. The two main groups of deer are the , including the , the (wapiti), the , and the ; and the , including the (caribou), , the , and the . Male deer of all species (except the Chinese ) as we ...

deer
and
wild boar The wild boar (''Sus scrofa''), also known as the wild swine, common wild pig, Eurasian wild pig, or simply wild pig, is a suid native to much of Eurasia Eurasia () is the largest continental area on Earth, comprising all of Europe and ...

wild boar
, diet shows great diversity. Diet is also greatly affected by the size and age of the individual within the same species. All young crocodiles hunt mostly
invertebrates Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the chordata, chordate subphylum vertebrate, Vertebrat ...
and small
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
, gradually moving on to larger prey. Being
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
ic (cold-blooded) predators, they have a very slow
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
, so they can survive long periods without food. Despite their appearance of being slow, crocodiles have a very fast strike and are top
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

predator
s in their environment, and various species have been observed attacking and killing other
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical env ...

predator
s such as
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s and
big cat The term "big cat" is typically used to refer to any of the five living members of the genus '' Panthera'', namely the lion, tiger, jaguar, leopard, and snow leopard, as well as the non- pantherine cheetah and cougar. Except for the latter thr ...

big cat
s. Crocodiles are also known to be aggressive
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study ...
s who feed upon
carrion Carrion (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in re ...

carrion
and steal from other predators. Evidence suggests that crocodiles also feed upon fruits, based on the discovery of seeds in stools and stomachs from many subjects as well as accounts of them feeding. Crocodiles have the most acidic stomach of any vertebrate. They can easily digest bones, hooves and horns. The
BBC TV BBC Television is a service of the BBC The British Broadcasting Corporation (BBC) is a public service broadcaster, headquartered at Broadcasting House in Westminster, London London is the capital city, capital and List of urban ...
reported that a
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
that has lurked a long time underwater to catch prey builds up a large oxygen debt. When it has caught and eaten that prey, it closes its right
aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta The aorta ( ) is the main and largest in the , originating from the of the and extending down to the , where it into two smaller arteries (the ). T ...

aortic arch
and uses its left aortic arch to flush blood loaded with
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
from its muscles directly to its stomach; the resulting excess acidity in its blood supply makes it much easier for the stomach lining to secrete more
stomach acidGastric acid, gastric juice, or stomach acid, is a digestive fluid formed within the gastric mucosa, stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together bre ...
to quickly dissolve bulks of swallowed prey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomach stones), which may act as ballast to balance their bodies or assist in crushing food, similar to grit ingested by birds.
Herodotus Herodotus ( ; grc, Ἡρόδοτος, Hēródotos, ; BC) was an ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), ge ...
claimed that Nile crocodiles had a
symbiotic relationship Symbiosis (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...

symbiotic relationship
with certain birds, such as the
Egyptian plover The Egyptian plover (''Pluvianus aegyptius''), also known as the crocodile bird, is a wader Waders or shorebirds are bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by ...

Egyptian plover
, which enter the crocodile's mouth and pick leeches feeding on the crocodile's blood; with no evidence of this interaction actually occurring in any crocodile species, it is most likely mythical or allegorical fiction.


Bite

Since they feed by grabbing and holding onto their prey, they have Evolution, evolved sharp teeth for piercing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. The teeth are not well-suited to tearing flesh off of large prey items as are the dentition and claws of many mammalian carnivores, the hooked bills and talons of Bird of prey, raptorial birds, or the serrated teeth of sharks. However, this is an advantage rather than a disadvantage to the crocodile since the properties of the teeth allow it to hold onto prey with the least possibility of the prey animal escaping. Cutting teeth, combined with the exceptionally high bite, bite force, would pass through flesh easily enough to leave an escape opportunity for prey. The jaws can bite down with immense force, by far the strongest bite of any animal. The force of a large crocodile's bite is more than , which was measured in a
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
, in the field; comparing to for a Rottweiler, for a hyena, for an American alligator, and for the largest confirmed great white shark. A long saltwater crocodile has been confirmed as having the strongest bite, bite force ever recorded for an animal in a laboratory setting. It was able to apply a bite force value of , and thus surpassed the previous record of made by a long American alligator. Taking the measurements of several crocodiles as reference, the bite forces of 6-m individuals were estimated at . The study, led by Dr. Gregory M. Erickson, also shed light on the larger, extinct species of crocodilians. Since crocodile anatomy has changed only slightly over the last 80 million years, current data on modern crocodilians can be used to estimate the bite force of extinct species. An Deinosuchus would apply a force of , nearly twice that of the latest, higher bite force estimations of Tyrannosaurus (). The extraordinary bite of crocodilians is a result of their anatomy. The space for the jaw muscle in the skull is very large, which is easily visible from the outside as a bulge at each side. The muscle is so stiff, it is almost as hard as bone to touch, as if it were the continuum of the skull. Another trait is that most of the muscle in a crocodile's 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 be subdued for study or transport by duct tape, taping their jaws or holding their jaws shut with large rubber bands cut from automobile tire, inner tubes.


Locomotion

Crocodiles can move quickly over short distances, even out of water. The land speed record for a crocodile is measured in a galloping Freshwater crocodile, Australian freshwater crocodile. Maximum speed varies between species. Some species can gallop, including Cuban crocodiles, Johnston's crocodiles, New Guinea crocodiles, Dwarf crocodile, African dwarf crocodiles, and even small Nile crocodiles. The fastest means by which most species can move is a "belly run", in which the body moves in a snake-like (sinusoidal) fashion, limbs splayed out to either side paddling away frantically while the tail whips to and fro. Crocodiles can reach speeds of when they "belly run", and often faster if slipping down muddy riverbanks. When a crocodile walks quickly, it holds its legs in a straighter and more upright position under its body, which is called the "high walk". This walk allows a speed of up to 5 km/h. Crocodiles may possess a homing instinct. In northern Australia, three rogue saltwater crocodiles were relocated by helicopter, but returned to their original locations within three weeks, based on data obtained from tracking devices attached to them.


Longevity

Measuring crocodile age is unreliable, although several techniques are used to derive a reasonable guess. The most common method is to measure lamellar growth rings in bones and teeth—each ring corresponds to a change in growth rate which typically occurs once a year between dry and wet seasons. Bearing these inaccuracies in mind, it can be safely said that all crocodile species have an average lifespan of at least 30–40 years, and in the case of larger species an average of 60–70 years. The oldest crocodiles appear to be the largest species. Saltwater crocodile, ''C. porosus'' is estimated to live around 70 years on average, with limited evidence of some individuals exceeding 100 years. In captivity, some individuals are claimed to have lived for over a century. A male crocodile lived to an estimated age of 110–115 years in a Russian zoo in Yekaterinburg. Named Kolya, he joined the zoo around 1913 to 1915, fully grown, after touring in an animal show, and lived until 1995. A male freshwater crocodile lived to an estimated age of 120–140 years at the Australia Zoo. Known affectionately as "Mr. Freshie", he was rescued around 1970 by Bob Irwin and Steve Irwin, after being shot twice by hunters and losing an eye as a result, and lived until 2010. Crocworld Conservation Centre, in Scottburgh, South Africa, claims to have a male
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
that was born in 1900. Named Henry, the crocodile is said to have lived in Botswana along the Okavango River, according to centre director Martin Rodrigues.


Social behaviour and vocalization

Crocodiles are the most social of reptiles. Even though they do not form social groups, many species congregate in certain sections of
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river
s, tolerating each other at times of feeding and Body temperature, basking. Most species are not highly territorial, with the exception of the saltwater crocodile, which is a highly territory (animal), territorial and aggressive species: a mature, male saltwater crocodile will not tolerate any other males at any time of the year, but most other species are more flexible. There is a certain form of hierarchy in crocodiles: the largest and heaviest males are at the top, having access to the best basking site, while females are priority during a group feeding of a big kill or carcass. A good example of the hierarchy in crocodiles would be the case of the
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
. This species clearly displays all of these behaviours. Studies in this area are not thorough, however, and many species are yet to be studied in greater detail. Mugger crocodiles are also known to show toleration in group feedings and tend to congregate in certain areas. However, males of all species are 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 during various situations and conditions, depending on species, age, size and sex. Depending on the context, some species can communicate over 20 different messages through Animal communication, vocalizations alone. Some of these vocalizations are made during social communication, especially during territory (animal), territorial displays towards the same sex and courtship with the opposite sex; the common concern being reproduction. Therefore most conspecific vocalization is made during the breeding season, with the exception being year-round territorial behaviour in some species and quarrels during feeding. Crocodiles also produce different distress calls and in aggressive displays to their own kind and other animals; notably other predators during Interspecific competition, 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 to excavate the nest. The female then gathers the hatchlings in her mouth and transports them to the water, where they remain in a group for several months, protected by the female * Distress call: A high-pitched call used mostly by younger animals to alert other crocodiles to imminent danger or an animal being attacked. * Threat call: A hissing sound that has also been described as a coughing noise. * Hatching call: Emitted by a female when breeding to alert other crocodiles that she has laid eggs in her nest. * Bellowing: Male crocodiles are especially vociferous. Bellowing choruses occur most often in the spring when breeding groups congregate, but can occur at any time of year. To bellow, males noticeably 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 and nearby objects. These low-frequency vibrations travel great distances through both air and water to advertise the male's presence and are so powerful they result in the water's appearing to "dance".


Reproduction

Crocodiles lay eggs, which are laid in either holes or mound nests, depending on species. A hole nest is usually excavated in sand and a mound nest is usually constructed out of vegetation. Nesting periods range from a few weeks up to six months. Courtship takes place in a series of behavioural interactions that include a variety of snout rubbing and submissive display that can take a long time. Mating always takes place in water, where the pair can be observed mating several times. Females can build or dig several trial nests which appear incomplete and abandoned later. Egg-laying usually takes place at night and about 30–40 minutes. Females are highly protective of their nests and young. The eggs are hard shelled, but translucent at the time of egg-laying. Depending on the species of crocodile, 7 to 95 eggs are laid. Crocodile embryos do not have sex chromosomes, and unlike humans, sex is not determined genetically. Temperature-dependent sex determination, Sex is determined by temperature, where at or less most hatchlings are females and at , offspring are of both sexes. A temperature of gives mostly males whereas above in some species continues to give males, but in other species resulting in females, which are sometimes called high-temperature females. Temperature also affects growth and survival rate of the young, which may explain the
sexual dimorphism Sexual dimorphism is the condition where the sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in ...
in crocodiles. The average incubation period is around 80 days, and also is dependent on temperature and species that usually ranges from 65 to 95 days. The eggshell structure is very conservative through evolution but there are enough changes to tell different species apart by their eggshell microstructure. Scutes may play a role in calcium storage for eggshell formation. At the time of hatching, the young start calling within the eggs. They have an egg-tooth at the tip of their snouts, which is developed from the skin, and that helps them pierce out of the shell. Hearing the calls, the female usually excavates the nest and sometimes takes the unhatched eggs in her mouth, slowly rolling the eggs to help the process. The young is usually carried to the water in the mouth. She would then introduce her hatchlings to the water and even feed them. The mother would then take care of her young for over a year before the next mating season. In the absence of the mother crocodile, the father would act in her place to take care of the young. However, even with a sophisticated Paternal care , parental nurturing, young crocodiles have a very high mortality rate due to their vulnerability to predation. A group of hatchlings is called a pod or Crèche (zoology), crèche and may be protected for months.


Cognition

Crocodiles possess some advanced cognitive abilities. 6 December 2013 9 December 2013 13 October 2014 They can observe and use patterns of prey behaviour, such as when prey come to the river to drink at the same time each day. Vladimir Dinets of the University of Tennessee, observed that crocodiles use Tool use by animals#In reptiles, twigs as bait for birds looking for nesting material. They place sticks on their snouts and partly submerge themselves. When the birds swooped in to get the sticks, the crocodiles then catch the birds. Crocodiles only do this in spring nesting seasons of the birds, when there is high demand for sticks to be used for building nests. Vladimir also discovered other similar observations from various scientists, some dating back to the 19th century. Aside from using sticks, crocodiles are also capable of cooperative hunting. Large numbers of crocodiles swim in circles to trap fish and take turns snatching them. In hunting larger prey, crocodiles swarm in, with one holding the prey down as the others rip it apart. According to a 2015 study, crocodiles engage in all three main types of play behaviour recorded in animals: locomotor play, play with objects and social play. Play with objects is reported most often, but locomotor play such as repeatedly sliding down slopes, and social play such as riding on the backs of other crocodiles is also reported. This behaviour was exhibited with conspecifics and mammals and is apparently not uncommon, though has been difficult to observe and interpret in the past due to obvious dangers of interacting with large carnivores.


Taxonomy and phylogeny

Crocodylidae is cladistically defined as a crown group composed of the last common ancestor of the
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
(''Crocodylus niloticus''), the Dwarf crocodile (''Osteolaemus tetraspis''), and all of its descendants. It contains two subfamily (biology), subfamilies: Crocodylinae and Osteolaeminae. Crocodylinae contains 13-14 living species, as well as 6 extinct species. Osteolaeminae was named by Christopher Brochu in 2003 as a subfamily of Crocodylidae separate from Crocodylinae, and contains the two
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
genus, genera ''
Osteolaemus The dwarf crocodile (''Osteolaemus tetraspis''), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile The mugger crocodile (''Crocodylus palustris''), also called marsh crocod ...
'' and ''Mecistops'', along with several extinct genera. The number of extant species within Osteolaeminae is currently in question. * Subfamily Crocodylinae ** Genus ''
Crocodylus ''Crocodylus'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to ...
'' ***''Crocodylus acutus'', American crocodile ***''Crocodylus halli'', Hall's New Guinea crocodile found South of the New Guinea Highlands ***''Crocodylus intermedius'', Orinoco crocodile ***''Crocodylus johnsoni'',
freshwater crocodile The freshwater crocodile (''Crocodylus johnstoni'' or ''Crocodylus johnsoni''; see below), also known as the Australian freshwater crocodile, Johnstone's crocodile or colloquially as freshie, is a species of crocodile Crocodiles (subfamil ...

freshwater crocodile
, or Johnstone's crocodile ***''Crocodylus mindorensis'', Philippine crocodile ***''Crocodylus moreletii'', Morelet's crocodile or Mexican crocodile ***''Crocodylus niloticus'',
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
or African crocodile (the subspecies found in Madagascar is sometimes called the black crocodile) ***''Crocodylus novaeguineae'', New Guinea crocodile found North of the New Guinea Highlands ***''Crocodylus palustris'', Mugger Crocodile, mugger, marsh or Indian crocodile ***''Crocodylus porosus'',
saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They f ...

saltwater crocodile
or estuarine crocodile ****''Crocodylus raninus'', the Borneo crocodile, is currently considered to be a synonym of ''Crocodylus porosus''; whether or not it is a distinct species remains unclear. ***''Crocodylus rhombifer'', Cuban crocodile ***''Crocodylus siamensis'', Siamese crocodile (may be extinct in the wild) ***''Crocodylus suchus'', West African crocodile, desert or sacred crocodile ***''Crocodylus anthropophagus'' ***''Crocodylus checchiai'' ***''Crocodylus falconensis'' ***''Crocodylus palaeindicus'' ***''Crocodylus thorbjarnarsoni'' ** Genus ''Voay'' ***''Voay robustus'' (formerly ''Crocodylus robustus'') * Subfamily Osteolaeminae ** Genus ''
Osteolaemus The dwarf crocodile (''Osteolaemus tetraspis''), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile The mugger crocodile (''Crocodylus palustris''), also called marsh crocod ...
'' *** ''Osteolaemus tetraspis'',
dwarf crocodile The dwarf crocodile (''Osteolaemus tetraspis''), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile The mugger crocodile (''Crocodylus palustris''), also called marsh crocod ...

dwarf crocodile
(There has been controversy as to whether or not this is actually two species; recent (2010) DNA analysis indicate three distinct species: ''O. tetraspis'', ''O. osborni'' and a third, currently unnamed.) ** Genus ''Mecistops'' ***''Mecistops cataphractus'' West African slender-snouted crocodile *** ''Mecistops leptorhynchus'' Central African slender-snouted crocodile ** Genus ''Brochuchus'' *** ''Brochuchus pigotti'' (formerly ''Crocodylus pigotti'') *** ''Brochuchus parvidens'' ** Genus ''Euthecodon'' *** ''Euthecodon nitriae'' *** ''Euthecodon brumpti'' *** ''Euthecodon arambourgi'' ** Genus ''Rimasuchus'' *** ''Rimasuchus lloydi'' (formerly ''Crocodylus lloydi'')


Phylogeny

Recent molecular studies using DNA sequencing have shown crocodiles to be more closely related to the gavialids rather than to
alligator An alligator is a crocodilia Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago ...

alligator
s, contrary to prior theories based on morphology (biology), morphological studies alone. Below is a cladogram showing the relationships of the major
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
crocodile groups based on molecular studies, excluding separate extinct taxa: A 2018 tip dating study by Lee & Yates simultaneously using morphology (biology), morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodylidae. In 2021, Hekkala ''et al.'' were able to use paleogenomics, extracting DNA from the extinct ''Voay'', to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae. The below cladogram shows the results of the latest study:


Relationship with humans


Danger to humans

The larger species of crocodiles are very dangerous to humans, mainly because of their ability to strike before the person can react. The
saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They f ...

saltwater crocodile
and
Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cl ...

Nile crocodile
are the most dangerous, killing hundreds of people each year in parts of Southeast Asia and Africa. The mugger crocodile and American crocodile are also dangerous to humans.


Crocodile products

Crocodiles are protected in many parts of the world, but are also farmed commercially. Their hides are tanned and used to make leather goods such as shoes and handbags; crocodile meat is also considered a delicacy. The most commonly farmed species are the saltwater and Nile crocodiles, while a hybrid of the saltwater and the rare Siamese crocodile is also bred in Asian farms. Farming has resulted in an increase in the saltwater crocodile population in Australia, as eggs are usually harvested from the wild, so landowners have an incentive to conserve their habitat. Crocodile leather can be made into goods such as wallets, briefcases, purses, handbags, belts, hats, and shoes. Crocodile oil has been used for various purposes. Vietnamese cuisine#Exotic dishes, Crocodiles were eaten by Vietnamese while they were taboo and off limits for Chinese. Vietnamese women who married Chinese men adopted the Chinese taboo. Crocodile meat is consumed in some countries, such as Australia, Ethiopia,
Thailand Thailand ( th, ประเทศไทย), historically known as Siam, () officially the Kingdom of Thailand, is a country in Southeast Asia. It is located at the centre of the Mainland Southeast Asia, Indochinese Peninsula, spanning , wi ...

Thailand
, South Africa, China and also Cuba (in pickled form). It is also occasionally eaten as an "exotic" delicacy in the western world. Cuts of meat include backstrap and tail fillet. Due to high demand for crocodile products, Traffic (conservation programme), TRAFFIC states that 1,418,487 Nile Crocodile skins were exported from Africa between 2006 and 2015.


In religion

Crocodiles have appeared in various forms in religions across the world. Ancient Egypt had Sobek, the crocodile-headed god, with his cult-city Crocodilopolis, as well as Taweret, the goddess of childbirth and fertility, with the back and tail of a crocodile. The Wukari Federation#Religion, Jukun shrine in the Wukari Federation, Nigeria is dedicated to crocodiles in thanks for their aid during migration. In Madagascar various peoples such as the Sakalava people, Sakalava and Antandroy see crocodiles as ancestor spirits and under local ''Fady (taboo), fady'' often offer them food;Campbell, Gwyn (2012). David Griffiths and the Missionary "History of Madagascar". Leiden, The Netherlands: Brill. . in the case of the latter at least a crocodile features prominently as an ancestor deity. Crocodiles appear in different forms in Hinduism. Varuna, a Historical Vedic religion, Vedic and Hindu god, rides a part-crocodile Makara (Hindu mythology), makara; his consort Varuni rides a crocodile. Similarly the goddess personifications of the Ganges, Ganga and Yamuna rivers are often depicted as riding crocodiles. Also in India, in Goa, crocodile worship is practised, including the annual ''Mannge Thapnee'' ceremony. In Latin America, Cipactli was the giant earth crocodile of the Aztec and other Nahua peoples.


Crocodile tears

The term "crocodile tears" (and equivalents in other languages) refers to a false, insincere display of emotion, such as a hypocrite crying fake tears of grief. It is derived from an ancient anecdote that crocodiles weep in order to lure their prey, or that they Crying, cry for the victims they are eating, first told in the ''Bibliotheca (Photius), Bibliotheca'' by Photios I of Constantinople. The story is repeated in bestiaries such as List of medieval bestiaries#DeBestiis, ''De bestiis et aliis rebus''. This tale was first spread widely in English in the stories of the ''Travels of Sir John Mandeville'' in the 14th century, and appears in several of Shakespeare's plays. In fact, crocodiles can and do generate tears, but they do not actually cry.


The Surabaya Shark and Crocodile

The name of Surabaya, Indonesia, is locally believed to be derived from the words "''suro"'' (
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
) and "''boyo"'' (crocodile), two creatures which, in a local mythology, myth, fought each other in order to gain the title of "the strongest and most powerful animal" in the area. It was said that the two powerful animals agreed for a truce and set boundaries; that the shark's domain would be in the sea while the crocodile's domain would be on the land. However one day the shark swam into the river estuary to hunt, this angered the crocodile, who declared it his territory. The Shark argued that the river was a water-realm which meant that it was shark territory, while the crocodile argued that the river flowed deep inland, so it was therefore crocodile territory. A ferocious fight resumed as the two animals bit each other. Finally the shark was badly bitten and fled to the open sea, and the crocodile finally ruled the estuarine area that today is the city. Another source alludes to a Jayabaya prophecy—a 12th-century psychic king of Kediri Kingdom—as he foresaw a fight between a giant white shark and a giant white crocodile taking place in the area, which is sometimes interpreted as a foretelling of the Mongol invasion of Java, a major conflict between the forces of the Kublai Khan, Mongol Empire, Mongol ruler of China, and those of Raden Wijaya's Majapahit in 1293. The two animals are now used as the city's symbol, with the two facing and circling each other, as depicted in a statue appropriately located near the entrance to the Surabaya Zoo, city zoo (see photo on the Surabaya page).


Crocodile (walking)

In the UK, a row of schoolchildren walking in pairs, or two by two is known as 'crocodile'.Angela Brazil


See also

*Alligator meat *''The Crocodile Hunter'' *Crocodilian armor *Game (hunting) *Sewer alligator *Sobek – an ancient Egyptian deity associated with the Nile crocodile


References


Further reading

* Iskandar, DT (2000). ''Turtles and Crocodiles of Insular Southeast Asia and New Guinea''. ITB, Bandung. * Crocodilian Biology Database, FAQ
FLMNH.ufl.edu
"How long do crocodiles live for?" Adam Britton. * Crocodilian Biology Database, FAQ

"How fast can a crocodile run?" Adam Britton.


External links

*
Crocodilian Online



Crocodile Attacks in Australia

BBC news finds powerful agent in crocodile blood

World's most expensive handbag sells in Hong Kong for over US$377,000 – a Hermès white crocodile
(31 May 2017), ''South China Morning Post''
292 New Guinea crocodiles massacred
in West Papua (province), West Papua, Indonesia {{DEFAULTSORT:Crocodile Crocodilians Crocodylidae Reptiles of Asia Reptiles of Africa Crocodiles of Australia Reptiles of North America Reptiles of South America Extant Ypresian first appearances Taxa named by Georges Cuvier