Crocodilians Fossil range: Cretaceous - Recent
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Infraclass: Archosauromorpha Superorder: Crocodylomorpha Order: Crocodilia Owen, 1842
black: range of Crocodilia
Families
Gavialidae Alligatoridae Crocodylidae

Crocodilia is an order of large reptiles that appeared about 84 million years ago in the Late Cretaceous Period (Campanian stage). They are the closest living relatives of birds, as the two groups are the only survivors of the Archosauria.[1] Members of the crocodilian stem group, the clade Crurotarsi, appeared about 220 million years ago in the Triassic Period and exhibited a wide diversity of forms during the Mesozoic Era. The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... Image File history File links Download high resolution version (1050x706, 209 KB) Alligator sinensis, Public domain picture from U.S. Fish and Wildlife Service Source: [1] File links The following pages link to this file: Crocodilia ... Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... Animalia redirects here. ... Typical Classes See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... Clades Subclass Anapsida Subclass Diapsida Infraclass Lepidosauromorpha Infraclass Archosauromorpha Sauropsids are a diverse group of mostly egg-laying vertebrate animals. ... Orders See text Archosauromorpha (Greek for ruling lizard forms) is an Infraclass of diapsid reptiles that first appeared during the late Permian and became more common during the Triassic. ... Groups see taxonomy The Crocodylomorpha are an important group of archosaurs that include the living crocodilians and their extinct relatives. ... Sir Richard Owen KCB (July 20, 1804–December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... Image File history File links Size of this preview: 800 × 370 pixelsFull resolution (1357 × 628 pixel, file size: 18 KB, MIME type: image/png) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Crocodilia ... Binomial name Gavialis gangeticus (Gmelin, 1789) Taxonomy The Gharial (Gavialis gangeticus) is the only surviving member of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... Living Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles, small species of crocodilians and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Crocodylus Osteolaemus Tomistoma A crocodile can be any of the 14 species of large, water-loving reptiles in the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). ... Subclasses Anapsida Diapsida Synonyms Reptilia Laurenti, 1768 Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class Sauropsida. ... The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... The Campanian is a stage on the geologic time scale occuring from 83. ... For other meanings of bird, see bird (disambiguation). ... Groups Pterosauria Crocodylia (crocodiles) Dinosauria    Aves (birds) Archosaurs (Greek for ruling reptiles) are a group of diapsid reptiles that first appeared during the late Permian (roughly 250 million years ago). ... In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. ... A clade is a term belonging to the discipline of cladistics. ... Subtaxa Phytosauridae Prestosuchidae Ornithosuchidae Stagonolepididae Rauisuchidae Poposauridae Crocodylomorpha     Sphenosuchia     Crocodilia Crurotarsi (cross-ankles) is a node-based taxon created by Paul Sereno in 1991 to supplant the old term Pseudosuchia. ... The Triassic is a geologic period that extends from about 251 ± 0. ... The Mesozoic Era is one of three geologic eras of the Phanerozoic eon. ...

The correct vernacular term for this group is "crocodilians", not "crocodiles," although the latter term is sometimes used incorrectly to refer to alligators and caiman, or even their distant prehistoric relatives, "marine crocodiles". Species Alligator mississippiensis Alligator sinensis An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. ... Living Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles, small species of crocodilians and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Paleo Template Project Thalattosuchia is the name given to a clade of marine crocodylians from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. ...

Spelling

The group is often spelled 'Crocodylia' for consistency with the genus Crocodylus Laurenti, 1768. However, Richard Owen used the -i- spelling when he published the name in 1842, so it is generally preferred in the scientific literature. The -i- spelling is also a more accurate Latinization of the Greek κροκόδειλος (krokodeilos, literally "pebble-worm", referring to the shape and texture of the animal). This article needs to be wikified. ... Joseph Nicolai Laurenti (December 4, 1735 - February 17, 1805) was an Austrian naturalist. ... Sir Richard Owen KCB (July 20, 1804–December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome. ...

Description

The basic crocodilian body plan is a very successful one; modern species closely resemble their Cretaceous ancestors of 84 million years ago. Mammals, too, have adapted to this body plan at least once in history. One ancestral whale family, the Ambulocetidae, were aquatic predators living in rivers and lakes, and they filled an ecological niche similar to the crocodilians. This article or section is in need of attention from an expert on the subject. ... The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... Genera Ambulocetus Gandakasia Himalayacetus Ambulocetidae is a family of early cetaceans that still were able to walk on land. ...

Crocodilians have a flexible semi-erect (semi-sprawled) posture. They can walk in low, sprawled "belly walk," or hold their legs more directly underneath them to perform the "high walk."^[1] Most other reptiles can only walk in a sprawled position, and chameleons are the only modern reptiles with a more erect posture than crocodilians.^{[citation needed]} The semi-erect posture makes it possible for some species to gallop on land if necessary.^[1] An Australian species can reach a speed of over 16 km/h while galloping on an irregular forest floor.^{[citation needed]} Crocodilian ancestors, fast-moving terrestrial predators like the rauisuchians, actually had a fully erect posture, indicating that the sprawling and semi-erect posture of crocodilians evolved after they adapted to as semi-aquatic ambush predators. Their the ankle bones, or tarsi are highly modified. Modern crocodilian locomotion is not a primitive trait, but a specialization for their semi-aquatic lifestyle. Genera Bradypodion Calumma Chamaeleo Furcifer Kinyongia Nadzikambia Brookesia Rieppeleon Rhampholeon Chameleons (family Chamaeleonidae) are squamates that belong to one of the best-known lizard families. ... Families Family Prestosuchidae Family Rauisuchidae Family Poposauridae Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters) Triassic archosaurs. ... FIG. 268– Bones of the right foot. ...

Teeth and jaws

All crocodilians have, like Homo sapiens (humans), thecodont dentition (teeth set in bony sockets) but unlike mammals, they replace their teeth throughout life (though not in 'extreme' old-age). Juvenile crocodilians replace teeth with larger ones at a rate as high as 1 new tooth per socket every month. After reaching adult size in a few years, however, tooth replacement rates can slow to two years and even longer. Very old members of some species have been seen in an almost "edentulous" (toothless) state, after teeth have been broken and replacement slowed or ceased. The result of this is that a single crocodile can go through at least 3,000 teeth in its lifetime. Each tooth is hollow, and the new one is growing inside the old. In this way, a new tooth is ready once the old is lost.

From the top: Head of an American alligator (Alligator mississippiensis), a Nile crocodile (Crocodylus niloticus), and an Indian gharial (Gavialis gangeticus).

Crocodilians have a secondary bony palate that enables them to breathe when partially submerged, even if the mouth is full of water. Their internal nostrils open in the back of their throat, where a special part of the tongue called the "palatal valve" closes off their respiratory system when they are underwater. This way they can open their mouths underwater without choking. Most reptiles lack a secondary palate, but some skinks (family Scincidae) have evolved a bony secondary palate too, to varying degrees. Image File history File links Download high resolution version (690x1101, 258 KB) Original caption: Fig 184. ... Image File history File links Download high resolution version (690x1101, 258 KB) Original caption: Fig 184. ... Binomial name Alligator mississippiensis (Daudin, 1801) American Alligator range map The American Alligator (Alligator mississippiensis) is one of the two living species of Alligator, a genus within the family Alligatoridae. ... Binomial name Crocodylus niloticus (Laurenti, 1768) The Nile crocodile is one of the 3 species of crocodiles found in Africa, and the second largest species of crocodile. ... Binomial name Gavialis gangeticus (Gmelin, 1789) Taxonomy The Gharial (Gavialis gangeticus) is the only surviving member of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... The secondary palate exists in species with separate nasal cavities and oral cavities, in order to separate the two. ...

Crocodiles and gharials have modified salivary glands on their tongue (salt glands), which are used for excreting excess salt ions from their body. Alligators and caimans have them too, but here they are non-functioning. This indicates that at some point the common origin of the Crocodylia were adapted to saline/marine environments. This also explains their wide disribution across the continents (i.e. marine dispersal). Species like the saltwater crocodile (C. porosus) can survive protracted periods of time in the sea, and can hunt prey within this environment. Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ... Binomial name Gavialis gangeticus (Gmelin, 1789) The gavial (Gavialis gangeticus) is one of two surviving members of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... “Multivalent” redirects here. ... Species Alligator mississippiensis Alligator sinensis An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. ... Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles closely related to the crocodiles and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ...

Crocodilians are often seen lying with their mouths open, a behavior called gaping. One of its functions is probably to cool them down, but since they also do this at night and when it is raining, it is possible that gaping has a social function too.

Internal organs

Crocodilians lack a vomeronasal organ (yet it is detectable in the embryo) and a urinary bladder. The vomeronasal organ (VNO) or Jacobsons organ is an auxiliary olfactory sense organ in some tetrapods. ...

Like mammals and birds and unlike reptiles, crocodiles have a four-chambered heart; however, unlike mammals, oxygenated and deoxygenated blood can be mixed because of the presence of the left aortic arch. The right ventricle has two arteries leaving it; a pulmonary artery, which goes to the lungs, and the left aortic arch, which goes to the body, or systemic circulation. There is also a hole, the foramen of Panizza, between the left and right aortic arches.^[2] Because the left aortic arch goes directly to the gut, the shunting of oxygen depleted blood which is high in CO₂ may serve to aid in creating stomach acid to assist in digesting bones from its prey.^[3] Their blood has been shown to have strong antibacterial properties.^{[citation needed]} There are very few or no other articles that link to this one. ...

They have alveoli in their lungs and a unique muscular attachment to the liver and viscera that acts as a piston to breathing, separating the thoracic and abdominal cavities (similar to the diaphragm of mammals). Although tegu lizards have a primitive proto-diaphragm, separating the pulmonary cavity from the visceral cavity and allowing greater lung inflation, this has a different evolutionary history. In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. ...

Crocodylians are known to swallow stones, gastroliths ("stomach-stones"), which act as a ballast in addition to aiding post-digestion processing of their prey. The crocodiylian stomach is divided into two chambers, the first one is described as being powerful and muscular, like a bird gizzard. This is where the gastroliths are found. The other stomach has the most acidic digestive system of any animal, and it can digest mostly everything from their prey; bones, feathers and horns.

The gender of the juvenile is determined by the incubation temperature. This means crocodilians do not have genetic sex determination (like us), but a form of environmental sex determination which is based upon temperature embryos undergo early in their development. Look up Genetic in Wiktionary, the free dictionary. ...

Sensory organs

Like all reptiles, crocodilians have a relatively small brain, but it is more advanced than in other reptiles. Among other things it has a true cerebral cortex.

As in many other aquatic or amphibian tetrapods, the eyes, ears, and nostrils are all located on the same plane. They see well during the day and may even have colour vision, plus the eyes have a vertical, cat-like pupil which also gives them excellent night vision. The iris is silvery (light reflecting layer of tapetum behind the retina greatly increases their ability to see in weak light) also makes their eyes glow in the dark. A third transperant eyelid, the nictitating membrane, protects their eyes underwater. However, they cannot focus under water, meaning other senses are more important when submerged under water. Many species of land animals have a nictitating membrane, which can move across the eyeball to give the sensitive eye structures additional protection in particular circumstances. ...

While birds and most reptiles have a ring of bones around each eye which supports the eyeball (the sclerotic ring), the crocodiles lack these bones, just like mammals and snakes. The eardrums are located behind the eyes and are covered by a movable flap of skin. This flap closes, along with the nostrils and eyes, when they dive, preventing water from entering their external head openings. The middle ear cavity has a complex of bony air-filled passages and a branching eustachian tube. There is also a small muscle (which is also seen in gecko) next to or upon the stapes, the stapedius, which probably functions in the same way as the mammalian stapedius muscle does, dampening strong vibrations. Anatomy of the human ear. ... This article describes gecko lizards. ...

The upper and lower jaws are covered with sensory pits, seen as small, black speckles on the skin, the crocodile version of the lateral organ we see in fish and many amphibians. But they have a completely different origin. These pigmented nodules encase bundles of nerve fibers that respond to the slightest disturbance in surface water, detecting vibrations and small pressure changes in water, making it possible for them to detect prey, danger and intruders even in total darkness. These sense organs are known as DPRs (Dermal Pressure Receptors). While alligators and caimans only have them on their jaws, crocodiles have similar organs on almost every scale on their body. The function of the DPRs on the jaws are clear, but it is still not quite clear what the organs on the rest of the body in crocodiles actually do. They are probably doing the same as the organs on their jaws, but it seems like they can do more than that, like assisting in chemical reception or even salinity detection. Species Alligator mississippiensis Alligator sinensis An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. ... Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles closely related to the crocodiles and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ...

Skin and skeleton

West African dwarf crocodile from the forests of West and West Central Africa

The skin is covered with non-overlapping scales composed of the protein keratin (the same protein that forms hoofs, skin, horns, feathers, hair, claws and nails in other tetrapods), which are shed individually. On the head the skin is actually fused to the bones of the skull. There are small plates of bone, called osteoderms or scutes, under the scales. Just like a tree, crocodile osteoderms have annual growth rings, and by counting them it is possible to tell their age. Osteoderms are found especially on the back, and in some species also on the belly. The overlapping rows of scutes cover the crocodile's body from head to tail, forming a tough protective armor. Beneath the scales and osteoderms is another layer of armor, both strong and flexible and built of rows of bony overlapping shingles called osteoscutes, which are embedded in the animal's back tissue. The blood-rich bumpy scales seen on their backs act as solar panels. Image File history File linksMetadata Download high resolution version (2071x1522, 727 KB) West African dwarf crocodile Osteolaemus tetraspis tetraspis at Bristol Zoo, Bristol, England. ... Image File history File linksMetadata Download high resolution version (2071x1522, 727 KB) West African dwarf crocodile Osteolaemus tetraspis tetraspis at Bristol Zoo, Bristol, England. ... Microscopy of keratin filaments inside cells. ... Osteoderms are a bony deposit forming a scale, plate, or other structure in the dermal layers of the skin. ...

Their spool-shaped vertebrae in their ancestors went from being biconcave to having a concave front and a convex back in the modern forms. This made the vertebral column more flexible and strong, a useful adaptation if you are hunting in water.

They possess ribs of dermal origin restricted to the sides of the ventral body wall. The collar bone (clavicle) is absent.

Evolution

Eusuchia, a modern clade which includes the crown group Crocodilia, first appeared in the Lower Cretaceous of Europe. Isisfordia duncani lived approximately 95 to 98 million years ago, during the Cenomanian epoch of the Upper Cretaceous. Isisfordia is the second oldest known eusuchian, and the earliest crocodylomorph yet found in Australia. Eusuchians underwent a mass radiation during the Late Cretaceous and the Paleogene, in which they evolved into numerous forms, such as semi-aquatic dinosaur-eating species (Deinosuchus); hooved, terrestrial carnivores (Pristichampsus), and 'hatchet'-shaped skulled forms (Baru). A clade is a term belonging to the discipline of cladistics. ... A crown group is a living monophyletic group or clade, consisting of the last common ancestor of all living examples, plus all of its descendants. ... The Cenomanian (also known as Woodbinian) is the first stage of the Late Cretaceous Epoch. ... Species (type) Deinosuchus is an extinct genus of alligatorid from the Upper Cretaceous (Campanian) of North America. ... Species (Gray, 1831) (Troxell, 1925) (Li 1984) Pristichampsus is an extinct genus of crocodylian that grew to approximately 3 m (10 ft) in length. ... Barú is a district in the Chiriquí province in Panama. ...

Classification

• Superorder Crocodylomorpha
  • Order Crocodilia
    • Superfamily Gavialoidea
      • Family Gavialidae - Gharials & False Gharials
    • Superfamily Alligatoroidea
      • Family Alligatoridae
        • Subfamily Diplocynodontinae (extinct)
        • Subfamily Alligatorinae - Alligators
        • Subfamily Caimaninae - Caimans
    • Superfamily Crocodyloidea
      • Family Crocodylidae
        • Subfamily Mekosuchinae (extinct)
        • Subfamily Crocodylinae - Crocodiles

Groups see taxonomy The Crocodylomorpha are an important group of archosaurs that include the living crocodilians and their extinct relatives. ... Binomial name Gavialis gangeticus (Gmelin, 1789) Taxonomy The Gharial (Gavialis gangeticus) is the only surviving member of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... Living Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles, small species of crocodilians and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles closely related to the crocodiles and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles closely related to the crocodiles and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Crocodylus Osteolaemus Tomistoma A crocodile can be any of the 14 species of large, water-loving reptiles in the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). ... Genera Australosuchus Baru Kambara Mekosuchus Pallimnarchus Quinkana Trilophosuchus The Mekosuchinae, or mekosuchine crocodiles, were a subfamily of crocodiles from Australia and the South Pacific that have now become extinct. ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ...

Phylogeny

Cladogram after Brochu (1997). Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ...

 Eusuchia ├──Hylaeochampsa └──+──Allodaposuchus └──Crocodilia ├──Gavialoidea │ ├──Eothoracosaurus │ └──+──Thoracosaurus │ └──+──Argochampsa │ ├──Eosuchus │ └──Gavialidae └──+──Borealosuchus └──+──Pristichampsus └──Brevirostres ├──Alligatoroidea │ ├──Leidyosuchus │ ├─?Deinosuchus │ └──Globidonta │ ├──Stangerochampsa │ ├──Brachychampsa │ └──Alligatoridae └──Crocodyloidea ├──Prodiplocynodon └──+──Asiatosuchus └──+──Brachyuranochampsa └──+──Harpacochampsa └──Crocodylidae 

Introduction Allodaposuchus was an ancient crocodilian, living about 100-80 million years ago in Southern Europe. ... Binomial name Gavialis gangeticus (Gmelin, 1789) Taxonomy The Gharial (Gavialis gangeticus) is the only surviving member of the family Gavialidae, a long-established group of crocodile-like reptiles with long, narrow jaws. ... Species (Gray, 1831) (Troxell, 1925) (Li 1984) Pristichampsus is an extinct genus of crocodylian that grew to approximately 3 m (10 ft) in length. ... Species (type) Deinosuchus is an extinct genus of alligatorid from the Upper Cretaceous (Campanian) of North America. ... Living Genera Alligator Caiman Melanosuchus Paleosuchus Alligators and caimans are reptiles, small species of crocodilians and forming the family Alligatoridae (sometimes regarded instead as the subfamily Alligatorinae). ... Genera Crocodylus Osteolaemus Tomistoma A crocodile can be any of the 14 species of large, water-loving reptiles in the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). ...

In popular Culture

• Several science fiction movies have giant crocodilians as their stars, such as Lake Placid, DinoCroc, and the crocodile series.

Lake Placid is a 1999 comedy/horror film, directed by Steve Miner, about a 50-foot long alligator which is released into a lake in Vermont. ... A 10,000 year old dinosaur is asleep in a run-of-the-mill American town when suddenly the monster awakens and has a hankering for human flesh. ...

References

External links

• http://www.il-st-acad-sci.org/kingdom/rept007.html
• http://www.il-st-acad-sci.org/kingdom/rept007a.html
• Before Crocodiles, the Hairless Coyote
• Florida's Museum of Natural History's Crocodilians Natural History & Conservation site
• International Crocodile Rescue
• Mikko's Phylogeny Archive Crocodyliformes