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100-567: Crocodylia ( / k r ɒ k ə ˈ d ɪ l i ə / ) is an order of semiaquatic , predatory reptiles known as crocodilians . They first appeared during the Late Cretaceous and are the closest living relatives of birds . Crocodilians are a type of crocodylomorph pseudosuchian , a subset of archosaurs that appeared about 235 million years ago and were the only survivors of the Triassic–Jurassic extinction event . The order includes

200-456: A cohors (plural cohortes ). Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae ). Such names are known as descriptive family names. In the field of zoology , the Linnaean orders were used more consistently. That is,

300-457: A Latinizing of the Greek κροκόδειλος ( crocodeilos ), which means both lizard and Nile crocodile . Crocodylia, as coined by Wermuth, in regards to the genus Crocodylus appears to be derived from the ancient Greek κρόκη ( kroke )—meaning shingle or pebble—and δρîλος or δρεîλος ( dr(e)ilos ) for "worm". The name may refer to the animal's habit of resting on the pebbled shores of

400-540: A phylogenetic analysis of extant organisms and/or fossils . The last universal common ancestor (LUCA) is the most recent common ancestor of all current life on Earth, estimated to have lived some 3.5 to 3.8 billion years ago (in the Paleoarchean ). The project of a complete description of the phylogenetic relationships among all biological species is dubbed the " tree of life ". This involves inference of ages of divergence for all hypothesized clades ; for example,

500-461: A "first couple". It rather reflects the presence of a single individual with high reproductive success in the past, whose genetic contribution has become pervasive throughout the population over time. It is also incorrect to assume that the MRCA passed all, or indeed any, genetic information to every living person. Through sexual reproduction , an ancestor passes half of his or her genes to each descendant in

600-505: A capital letter. For some groups of organisms, their orders may follow consistent naming schemes . Orders of plants , fungi , and algae use the suffix -ales (e.g. Dictyotales ). Orders of birds and fishes use the Latin suffix -iformes meaning 'having the form of' (e.g. Passeriformes ), but orders of mammals and invertebrates are not so consistent (e.g. Artiodactyla , Actiniaria , Primates ). For some clades covered by

700-440: A crocodilian shut tight. All species have a palatal valve, a membranous flap of skin at the back of the oral cavity that protects the oesophagus and trachea when the animal is underwater. This enables them to open their mouths underwater without drowning. Crocodilians typically remain underwater for fifteen minutes or less at a time, but some can hold their breath for up to two hours under ideal conditions. The maximum diving depth

800-399: A different way from those of other reptiles, a feature they share with some early archosaurs. One of the upper row of ankle bones, the ankle bone , moves with the tibia and fibula , while the heel bone moves with the foot and is where the ankle joint is located. The result is that the legs can be held almost vertically beneath the body when on land, and the foot swings during locomotion as

900-566: A distinct rank of biological classification having its own distinctive name (and not just called a higher genus ( genus summum )) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carl Linnaeus was the first to apply it consistently to the division of all three kingdoms of nature (then minerals , plants , and animals ) in his Systema Naturae (1735, 1st. Ed.). For plants, Linnaeus' orders in

1000-504: A haplogroup is defined by the accumulation of mutations in STR sequences of the Y-Chromosome of that haplogroup only. Y-DNA network analysis of Y-STR haplotypes showing a non-star cluster indicates Y-STR variability due to multiple founding individuals. Analysis yielding a star cluster can be regarded as representing a population descended from a single ancestor. In this case the variability of

1100-399: A higher surface-area-to-volume ratio . The kidneys and excretory system are much the same as in other reptiles, but crocodilians do not have a bladder . In fresh water, the osmolality (the concentration of solutes that contribute to a solution's osmotic pressure ) in the plasma is much higher than it is in the surrounding water. The animals are well-hydrated, and the urine in the cloaca

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1200-472: A largely carnivorous diet. Some species like the gharial are specialized feeders, while others like the saltwater crocodile have generalized diets. Crocodilians are generally solitary and territorial , though they sometimes hunt in groups. During the breeding season, dominant males try to monopolize available females. Females lay their eggs in holes or mounds, and similar to many birds, care for their hatched young. Some species of crocodilians (particularly

1300-483: A left and right aorta which are connected by a hole called the Foramen of Panizza . Like birds and mammals, crocodilians have separate vessels that direct blood flow to the lungs and the rest of the body respectively. They also have unique cog-teeth-like valves that, when interlocked, direct blood to the left aorta and away from the lungs, and then back around the body. This system may allow the animals to remain submerged for

1400-424: A longer period, but this explanation has been questioned. Other possible reasons for the peculiar circulatory system include assistance with thermoregulatory needs, prevention of pulmonary oedema , or faster recovery from metabolic acidosis . Retaining carbon dioxide within the body permits an increase in the rate of gastric acid secretion and thus the efficiency of digestion, and other gastrointestinal organs such as

1500-514: A more solid justification for one spelling over the other was proposed. Prior to 1988, Crocodilia was a group that encompassed the modern-day animals, as well as their more distant relatives now in the larger groups called Crocodylomorpha and Pseudosuchia . Under its current definition as a crown group (as opposed to a stem-based group ), Crocodylia is now restricted to only the last common ancestor of today's crocodilians and all of its descendants (living or extinct ). Crocodilia appears to be

1600-402: A much greater diversity of forms than modern crocodilians. Some became small fast-moving insectivores , others specialist fish-eaters , still others marine and terrestrial carnivores , and a few became herbivores . The earliest stage of crocodilian evolution was the protosuchians in the late Triassic and early Jurassic. They were followed by the mesosuchians , which diversified widely during

1700-594: A non-genetic, mathematical model or computer simulation. In organisms using sexual reproduction , the matrilineal MRCA and patrilineal MRCA are the MRCAs of a given population considering only matrilineal and patrilineal descent, respectively. The MRCA of a population by definition cannot be older than either its matrilineal or its patrilineal MRCA. In the case of Homo sapiens , the matrilineal and patrilineal MRCA are also known as " Mitochondrial Eve " (mt-MRCA) and " Y-chromosomal Adam " (Y-MRCA) respectively. The age of

1800-452: A powerful bite. Like birds, crocodilians possess a four-chambered heart and lungs with unidirectional airflow. Like most other reptiles, they are ectotherms . Crocodilians are found mainly in the warmer and tropical areas of the Americas , Africa , Asia and Oceania . They usually inhabit freshwater habitats , but some can live in saltier environments and even swim out to sea. They have

1900-695: A role in the crushing of food. Digestion takes place more quickly at higher temperatures. When digesting a meal, CO2-rich blood towards the lungs is redirected to the stomach, supplying more acid for the oxyntic glands . Compared to crocodiles, alligators digest more carbohydrates relative to protein. Crocodilians have a very low metabolic rate and consequently, low energy requirements. They can withstand extended fasting, living on stored fat . Even recently hatched crocodiles are able to survive 58 days without food, losing 23% of their bodyweight during this time. Crocodilians are ectotherms , relying mostly on their environment to control their body temperature. The sun's heat

2000-448: A set of individuals can sometimes be determined by referring to an established pedigree . However, in general, it is impossible to identify the exact MRCA of a large set of individuals, but an estimate of the time at which the MRCA lived can often be given. Such time to most recent common ancestor ( TMRCA ) estimates can be given based on DNA test results and established mutation rates as practiced in genetic genealogy, or by reference to

2100-521: A single olfactory chamber and the vomeronasal organ disappears when they reach adulthood. 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 . They appear to have lost their pineal organ , but still show signs of melatonin rhythms. The skin of crocodilians

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2200-523: A single sex chromosome in the male individual and is passed on to male descendants without recombination. It can be used to trace patrilineal inheritance and to find the Y-chromosomal Adam , the most recent common ancestor of all humans via the Y-DNA pathway. Approximate dates for Mitochondrial Eve and Y-chromosomal Adam have been established by researchers using genealogical DNA tests . Mitochondrial Eve

2300-433: A suitable concentration of salt in body fluids. Osmoregulation is related to the quantity of salts and water exchanged with the environment. Intake of water and salts takes place across the lining of the mouth, when water is drunk, incidentally while feeding, and when present in foods. Water is lost during breathing, and both salts and water are lost in the urine and faeces, through the skin, and via salt-excreting glands on

2400-475: Is cladistically defined as the last common ancestor of Gavialis gangeticus (the gharial ), Alligator mississippiensis ( American alligator ), and Crocodylus rhombifer (the Cuban crocodile ) and all of its descendants. The phylogenetic relationships of crocodilians has been the subject of debate and conflicting results. Many studies and their resulting cladograms , or "family trees" of crocodilians, have found

2500-508: Is abundant and dilute, nitrogen being excreted as ammonium bicarbonate . Sodium loss is low and mainly takes place through the skin in freshwater conditions. In seawater, the opposite is true. The osmolality in the plasma is lower than the surrounding water, which is dehydrating for the animal. The cloacal urine is much more concentrated, white, and opaque, with the nitrogenous waste being mostly excreted as insoluble uric acid . Order (biology) What does and does not belong to each order

2600-604: Is assumed to have happened close to the Permian–Triassic extinction event (informally known as the Great Dying). Crocodylomorpha , the group that later give rise to modern crocodilians, emerged in the Late Triassic . While the most basal crocodylomorphs were large, the ones that gave rise to crocodilians were small, slender, and leggy. This evolutionary grade, the so-called " sphenosuchians " first appeared around Carnian of

2700-414: Is clad in non-overlapping scales known as scutes which are covered with in beta-keratin . Many of the scutes are strengthened by bony plates known as osteoderms . They are most numerous on the back and neck of the animal. The belly and underside of the tail possess rows of broad, flat and square-shaped scales. In between crocodilian scales are hinge areas which consist mainly of alpha-keratin . Underneath

2800-419: Is determined by a taxonomist , as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely. The name of an order is usually written with

2900-452: Is diversity in snout and tooth shape, all crocodilian species have essentially the same body morphology. They have solidly built lizard-like bodies with wide, cylindrical torsos, flat heads, long snouts, short necks and tails compressed from side-to-side. Their limbs are reduced in size; the front feet have five mostly non-webbed digits, and the hind feet have four webbed digits and an extra fifth. The pelvis and ribs of crocodilians are modified;

3000-629: Is estimated to have lived about 200,000 years ago. A paper published in March 2013 determined that, with 95% confidence and that provided there are no systematic errors in the study's data, Y-chromosomal Adam lived between 237,000 and 581,000 years ago. The MRCA of all humans alive today would, therefore, need to have lived more recently than either. It is more complicated to infer human ancestry via autosomal chromosomes . Although an autosomal chromosome contains genes that are passed down from parents to children via independent assortment from only one of

3100-566: Is nearly immune to sexual mixing, unlike the nuclear DNA whose chromosomes are shuffled and recombined in Mendelian inheritance . Mitochondrial DNA, therefore, can be used to trace matrilineal inheritance and to find the Mitochondrial Eve (also known as the African Eve ), the most recent common ancestor of all humans via the mitochondrial DNA pathway. Likewise, Y chromosome is present as

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3200-416: Is not fully understood, but it has been suggested that they may be mechanosensory organs. There are prominent paired integumentary glands in skin folds on the throat, and others in the side walls of the cloaca. Various functions for these have been suggested. They may play a part in communication, as indirect evidence suggest that they secrete pheromones used in courtship or nesting. The skin of crocodilians

3300-550: Is permanently erect and relies on cloacal muscles to protrude it out and elastic ligaments and a tendon to pull it back in. The gonads are located near the kidneys . Crocodilians range in size from the Paleosuchus and Osteolaemus species, which reach 1–1.5 m (3 ft 3 in – 4 ft 11 in), to the saltwater crocodile and Nile crocodile, which reach 6 m (20 ft) and weigh up to 1,000 kg (2,200 lb), though some prehistoric species such as

3400-416: Is the main means of warming for any crocodilian, while immersion in water may either raise its temperature via conduction , or cool the animal in hot weather. The main method for regulating its temperature is behavioural. Temperate-living alligators may start the day by basking in the sun on land, and move into the water for the afternoon, with parts of the back breaking the surface so it can still be warmed by

3500-440: Is tough and can withstand damage from conspecifics , and the immune system is effective enough to heal wounds within a few days. In the genus Crocodylus the skin contains chromatophores , allowing them to change color from dark to light and vice versa. The crocodilian has perhaps the most complex vertebrate circulatory system . It has a four-chambered heart and two ventricles , an unusual trait among extant reptiles, and both

3600-492: Is unknown, but crocodiles can dive to at least 20 m (66 ft). Vocalizing is produced by vibrating vocal folds in the larynx . The folds of the American alligator have a complex morphology consisting of epithelium , lamina propria and muscle, and according to Riede et al. (2015), "it is reasonable to expect species-specific morphologies in vocal folds/analogues as far back as basal reptiles". Crocodilian vocal folds lack

3700-462: Is usually maintained between 25 and 35 °C (77 and 95 °F), and mainly stays in the range 30 to 33 °C (86 to 91 °F). Both the American and Chinese alligator can be found in areas that sometimes experience periods of frost in winter. In cold weather, they remain submerged with their tails in deeper, less cold water and their nostrils just projecting through the surface. If ice forms on

3800-542: The European Neolithic . The age of the MRCA of all living humans is unknown. It is necessarily younger than the age of either the matrilinear or the patrilinear MRCA, both of which have an estimated age of between roughly 100,000 and 200,000 years ago. A study by mathematicians Joseph T. Chang, Douglas Rohde and Steve Olson used a theoretical model to calculate that the MRCA may have lived remarkably recently, possibly as recently as 2,000 years ago. It concludes that

3900-520: The International Code of Zoological Nomenclature , several additional classifications are sometimes used, although not all of these are officially recognized. In their 1997 classification of mammals , McKenna and Bell used two extra levels between superorder and order: grandorder and mirorder . Michael Novacek (1986) inserted them at the same position. Michael Benton (2005) inserted them between superorder and magnorder instead. This position

4000-517: The Late Triassic . They ate small, fast prey and survived into the Late Jurassic . As the Triassic ended, crocodylomorphs became the only surviving pseudosuchians. During the early Jurassic period, the dinosaurs became dominant on land, and the crocodylomorphs underwent major adaptive diversifications to fill ecological niches vacated by recently extinguished groups. Mesozoic crocodylomorphs had

4100-698: The Nile . Crocodilians, and birds, are members of the Archosaur clade. Archosaurs are distinguished from other reptiles particularly by two sets of extra openings in the skull: the antorbital fenestra located in front of the animal's eye socket and the mandibular fenestra on the jaw. Archosaurs comprise two main groups: the Pseudosuchia (crocodilians and their relatives), and the Avemetatarsalia ( dinosaurs , pterosaurs , and their relatives). The split between these two

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4200-516: The Nile crocodile ) are known to have attacked humans . Humans are the greatest threat to crocodilian populations through activities that include hunting, poaching, and habitat destruction , but farming of crocodilians has greatly reduced unlawful trading in wild skins. Artistic and literary representations of crocodilians have appeared in human cultures around the world since Ancient Egypt . "Crocodilia" and "Crocodylia" have been used interchangeably for decades starting with Schmidt's redescription of

4300-656: The Santonian - Campanian stages, while definitive longirostres first appeared during the Maastrichtian stage. The earliest known alligatoroids and gavialoids include highly derived forms, which indicates that the time of the actual divergence between the three lineages must have been a pre-Campanian event. Additionally, scientists conclude that environmental factors played a major role in the evolution of crocodilians and their ancestors, with warmer climate being associated with high evolutionary rates and large body sizes. Crocodylia

4400-769: The Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th-century works such as the Prodromus Systematis Naturalis Regni Vegetabilis of Augustin Pyramus de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given

4500-503: The Y-STR sequence, also called the microsatellite variation, can be regarded as a measure of the time passed since the ancestor founded this particular population. The descendants of Genghis Khan or one of his ancestors represents a famous star cluster that can be dated back to the time of Genghis Khan. TMRCA calculations are considered critical evidence when attempting to determine migration dates of various populations as they spread around

4600-405: The cartilaginous processes of the ribs allow the thorax to collapse when submerging and the structure of the pelvis can accommodate large amounts of food, or more air in the lungs. Both sexes have a cloaca , a single chamber and outlet near the tail into which the intestinal , urinary and genital tracts open. It houses the penis in males and the clitoris in females. The crocodilian penis

4700-438: The eardrums are protected by flaps that can be opened or closed by muscles. Crocodilians have a wide hearing range , with sensitivity comparable to most birds and many mammals. Hearing in crocodilians does not degrade as the animal gets older as they can regrow and replace hair cells . The well-developed trigeminal nerve allows them to detect vibrations in the water (such as those made by potential prey). Crocodilians have just

4800-403: The last universal common ancestor (human– bacteria ). It is also possible to consider the ancestry of individual genes (or groups of genes, haplotypes ) instead of an organism as a whole. Coalescent theory describes a stochastic model of how the ancestry of such genetic markers maps to the history of a population. Unlike organisms, a gene is passed down from a generation of organisms to

4900-527: The pancreas , spleen , small intestine , and liver also function more efficiently. When submerged, a crocodilian's heart may beat at only one or two beats a minute, with little blood flow to the muscle. When it rises and takes a breath, its heart rate almost immediately speeds up, and the muscles receive newly oxygenated blood. Unlike many marine mammals , crocodilians have little myoglobin to store oxygen in their muscles. During diving, an increasing concentration of bicarbonate ions causes haemoglobin in

5000-454: The secondary palate was little developed as it consisted only of a maxilla . The mesosuchians saw a fusion of the palatine bones to the secondary palate and a great extension of the nasal passages behind the palatine and in front of the pterygoid bones . This allowed the animal to breathe through its nostrils while its mouth was open underwater. The eusuchians continued this process with the interior nostrils now opening through an aperture in

5100-415: The true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae ), and the gharial and false gharial (family Gavialidae ). Although the term "crocodiles" is sometimes used to refer to all of these, it is less ambiguous to use "crocodilians". Extant crocodilians have long flat heads with long snouts and tails compressed on the sides, with their eyes, ears, and nostrils at

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5200-444: The "short-snouted" families of Crocodylidae and Alligatoridae to be close relatives, with the long-snouted Gavialidae as a divergent branch of the tree. The resulting group of short-snouted species, named Brevirostres , was supported mainly by morphological studies which analyzed skeletal features alone. However, recent molecular studies using DNA sequencing of living crocodilians have rejected this distinct group Brevirostres, with

5300-470: The Americas. European colonization of the Americas and Australia was found by Chang to be too recent to have had a substantial impact on the age of the MRCA. In fact, if the Americas and Australia had never been discovered by Europeans, the MRCA would only be about 2.3% further back in the past than it is. Note that the age of the MRCA of a population does not correspond to a population bottleneck , let alone

5400-580: The Jurassic and the Tertiary. The eusuchians first appeared during the Early Cretaceous , and includes modern crocodilians. Protosuchians were small, mostly terrestrial animals with short snouts and long limbs. They had bony armor in the form of two rows of plates extending from head to tail; this armor would still be found in later species. Their vertebrae were convex on the two main articulating surfaces, and

5500-600: The MRCA of all Carnivora ( cats , dogs , etc) is estimated to have diverged some 42 million years ago ( Miacidae ). The concept of the last common ancestor from the perspective of human evolution is described for a popular audience in The Ancestor's Tale by Richard Dawkins (2004). Dawkins lists "concestors" of the human lineage in order of increasing age, including hominin (human– chimpanzee ), hominine (human– gorilla ), hominid (human– orangutan ), hominoid (human– gibbon ), and so on in 40 stages in total, down to

5600-573: The MRCA of all humans probably lived in East Asia, which would have given them key access to extremely isolated populations in Australia and the Americas. Possible locations for the MRCA include places such as the Chuckchi and Kamchatka Peninsulas that are close to Alaska, places such as Indonesia and Malaysia that are close to Australia or a place such as Taiwan or Japan that is more intermediate to Australia and

5700-543: The ancestry of a set of populations. In this case, populations are defined by the accumulation of mutations on the mtDNA, and special trees are created for the mutations and the order in which they occurred in each population. The tree is formed through the testing of a large number of individuals all over the world for the presence or lack of a certain set of mutations. Once this is done it is possible to determine how many mutations separate one population from another. The number of mutations, together with estimated mutation rate of

5800-425: The animal needs to stop or steer in a different direction, the limbs are splayed out. Swimming is normally achieved with gentle sinuous movements of the tail, but they can move faster when pursuing or being pursued. Crocodilians are less well-adapted for moving on land, and are unusual among vertebrates in having two different means of terrestrial locomotion: the "high walk" and the "low walk". Their ankle joints flex in

5900-401: The ankle rotates. The limbs move much the same as in other quadrupeds , with the left forelimb moving first, followed by the right hindlimb, then right forelimb, and finally left hindlimb, and repeat. The high walk of crocodilians, with the belly and most of the tail held off the ground and the limbs held directly under the bodies, resembles that of mammals and birds. The low walk is similar to

6000-439: The belly outward, and the diaphragmaticus pulls the liver back. When exhaling, the internal intercostal muscles push the ribs inward, while the rectus abdominis pulls the hips and liver forwards and the belly inward. Crocodilians can also use these muscles to adjust the position of their lungs, controlling their buoyancy in the water. An animal sinks when the lungs are pulled towards the tail and floats when they move back towards

6100-403: The blood from the calcium and magnesium in these dermal bones act as a buffer during prolonged submersion when increasing levels of carbon dioxide would otherwise cause acidosis . Some scutes contain a single pore known as an integumentary sense organ. Crocodiles and gharials have these on large parts of their bodies, while alligators and caimans only have them on the head. Their exact function

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6200-603: The blood to release oxygen for the muscles. Crocodilians were traditionally thought to breathe like mammals, with airflow moving in and out tidally, but studies published in 2010 and 2013 conclude that crocodilians breathe more like birds , with airflow moving in a unidirectional loop within the lungs. When a crocodilian inhales, air flows through the trachea and into two primary bronchi , or airways, which split off into narrower secondary passageways. The air continues to move through these, then into even narrower tertiary airways, and then into other secondary airways which were bypassed

6300-486: The crown group crocodilians. The morphology-based phylogenetic analyses based on the new neuroanatomical data obtained from its skull using micro-CT scans suggested that this taxon is a crown group crocodilian and a member of the 'thoracosaurs', recovered as a sister taxon of Thoracosaurus within Gavialoidea, though it is uncertain whether 'thoracosaurs' were true gavialoids. Definitive alligatoroids first appeared during

6400-481: The elasticity of mammalian ones; but the larynx is still capable of complex motor control similar to birds and mammals and can adequately control its fundamental frequency . Crocodilian teeth can only hold onto prey, and food is swallowed unchewed. The stomach consists of a grinding gizzard and a digestive chamber. Indigestible items are regurgitated as pellets. The stomach is more acidic than that of any other vertebrate and contains ridges for gastroliths , which play

6500-591: The eye clean. When a crocodilian leaves the water and dries off, this substance is visible as "tears". While eyesight is fairly good in air, it is significantly weakened underwater. Crocodilians appear to have gone through a "nocturnal bottleneck" early in their history with their eyes losing traits like sclerotic rings , an annular pad of the lens and colored cone oil droplets , giving them dichromatic vision (red-green colorblindness). Since then, some crocodilians appear to have re-evolved full colour vision . The ears are adapted for hearing both in air and underwater, and

6600-411: The first time. The air then flows back into the primary airways and is exhaled. The lungs of crocodilians are attached to the liver and the pelvis by the diaphragmaticus muscle ( analogous of the diaphragm in mammals). During inhalation, the external intercostal muscles expand the ribs, allowing the animal to take in more air, while the ischiopubis muscle causes the hips to swing downwards and push

6700-472: The genealogical MRCA (most recent common ancestor by any line of descent) of all living humans cannot be traced genetically because the DNA of the great majority of ancestors is completely lost after a few hundred years. It is therefore computed based on non-genetic, mathematical models and computer simulations. Since Mitochondrial Eve and Y-chromosomal Adam are traced by single genes via a single ancestral parent line,

6800-495: The genus Borealosuchus of North America, with six species, though its phylogenetic position is not settled. The three primary branches of Crocodilia had diverged by the Late Cretaceous . The possible earliest-known members of the group may be Portugalosuchus and Zholsuchus from the Cenomanian - Turonian stages. The classification of Portugalosuchus has been disputed by some researchers who claimed that it may be outside

6900-438: The group from the formerly defunct term Loricata . Schmidt used the older term "Crocodilia", based on Owen 's original name for the group. Wermuth opted for "Crocodylia" as the proper name, basing it on the type genus Crocodylus ( Laurenti , 1768). Dundee—in a revision of many reptilian and amphibian names—argued strongly for "Crocodylia". However, it was not until the advent of cladistics and phylogenetic nomenclature that

7000-406: The head. This allows them to move through the water without creating disturbances that could alert potential prey. They can also spin and twist by moving their lungs laterally. Swimming and diving crocodilians appear to rely on lung volume more for buoyancy than oxygen storage. Just before diving, the animal exhales to reduce its lung volume and reach negative buoyancy. When diving, the nostrils of

7100-488: The high walk, but without the body being raised, and is quite different from the sprawling walk of salamanders and lizards. The animal can change from one walk to the other instantaneously, but the high walk is the usual means of locomotion on land. The animal may push its body up and use this form immediately, or may take one or two strides of low walk before raising the body higher. Unlike most other land vertebrates, when crocodilians increase their pace of travel they increase

7200-457: The hind limbs launching the body forward and the fore limbs subsequently taking the weight. Next, the hind limbs swing forward as the spine flexes dorso-ventrally , and this sequence of movements is repeated. During terrestrial locomotion, a crocodilian can keep its back and tail straight, since the scales are attached to the vertebrae by muscles. Whether on land or in water, crocodilians can jump or leap by pressing their tails and hind limbs against

7300-526: The human MRCA is unknown. It is no greater than the age of either the Y-MRCA or the mt-MRCA, estimated at around 200,000 years. Unlike in pedigrees of individual humans or domesticated lineages where historical parentage is known, in the inference of relationships among species or higher groups of taxa ( systematics or phylogenetics ), ancestors are not directly observable or recognizable. They are inferences based on patterns of relationship among taxa inferred in

7400-551: The jaws are closed as their teeth fit into grooves along the outside lining of the upper jaw. By contrast the lower teeth of alligators and caimans normally fit into holes along the inside lining of the upper jaw. Thus they are hidden when the jaws are closed. Crocodilians are homodonts , meaning each of their teeth are all of the same type (they do not possess different tooth types, such as canines and molars) and polyphyodonts are able to replace each of their approximately 80 teeth up to 50 times in their 35- to 75-year lifespan. They are

7500-432: The jaws are larger and more powerful than the ones that open them, and a crocodilian's jaws can be held shut by a person fairly easily. Conversely, the jaws are extremely difficult to pry open. The powerful closing muscles attach at the middle of the lower jaw and the jaw hinge attaches behind the atlanto-occipital joint , giving the animal a wide gape. A folded membrane holds the tongue stationary. Crocodilians have some of

7600-420: The late Cretaceous Deinosuchus were even larger at up to about 11 m (36 ft) and 3,450 kg (7,610 lb). They tend to be sexually dimorphic , with males much larger than females. Crocodilians are excellent swimmers. During aquatic locomotion , the muscular tail undulates from side to side to drive the animal through the water while the limbs are held close to the body to reduce drag . When

7700-693: The long-snouted gavialids more closely related to crocodiles than to alligators, with the new grouping of gavialids and crocodiles named Longirostres . Below is a cladogram from 2021 showing the relationships of the major extant crocodilian groups. This analysis was based off mitochondrial DNA , including that of the recently extinct Voay robustus : Caiman [REDACTED] Melanosuchus [REDACTED] Paleosuchus [REDACTED] Alligator [REDACTED] Crocodylus [REDACTED] † Voay Mecistops [REDACTED] Osteolaemus [REDACTED] Gavialis [REDACTED] Tomistoma [REDACTED] Though there

7800-429: The mtDNA in the regions tested, allows scientists to determine the approximate time to MRCA ( TMRCA ) which indicates time passed since the populations last shared the same set of mutations or belonged to the same haplogroup . In the case of Y-Chromosomal DNA, TMRCA is arrived at in a different way. Y-DNA haplogroups are defined by single-nucleotide polymorphism in various regions of the Y-DNA. The time to MRCA within

7900-445: The next generation either as perfect replicas of itself or as slightly mutated descendant genes . While organisms have ancestry graphs and progeny graphs via sexual reproduction , a gene has a single chain of ancestors and a tree of descendants. An organism produced by sexual cross-fertilization ( allogamy ) has at least two ancestors (its immediate parents), but a gene always has one ancestor per generation. Mitochondrial DNA (mtDNA)

8000-431: The next generation; in the absence of pedigree collapse , after just 32 generations the contribution of a single ancestor would be on the order of 2 , a number proportional to less than a single basepair within the human genome . The MRCA is the most recent common ancestor shared by all individuals in the population under consideration. This MRCA may well have contemporaries who are also ancestral to some but not all of

8100-407: The observed divergence is due to migration as evidenced by the archaeological record. However, if the date of genetic divergence occurs at a different time than the archaeological record, then scientists will have to look at alternate archaeological evidence to explain the genetic divergence. The issue is best illustrated in the debate surrounding the demic diffusion versus cultural diffusion during

8200-452: The only non-mammalian vertebrates with tooth sockets . Next to each full-grown tooth there is a small replacement tooth and an odontogenic stem cell in the dental lamina , which can be activated when required. Tooth replacement slows and eventually stops as the animal ages. The eyes, ears and nostrils of crocodilians are at the top of the head. This allows them to stalk their prey with most of their bodies underwater. When in bright light,

8300-698: The orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g. Lepidoptera (moths and butterflies) and Diptera (flies, mosquitoes, midges, and gnats). In virology , the International Committee on Taxonomy of Viruses 's virus classification includes fifteen taxomomic ranks to be applied for viruses , viroids and satellite nucleic acids : realm , subrealm , kingdom , subkingdom, phylum , subphylum , class, subclass, order, suborder, family, subfamily , genus, subgenus , and species. There are currently fourteen viral orders, each ending in

8400-547: The precursor of the currently used International Code of Nomenclature for algae, fungi, and plants . In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905, the word family ( familia ) was assigned to the rank indicated by the French famille , while order ( ordo ) was reserved for a higher rank, for what in the 19th century had often been named

8500-664: The pterygoid bones. The vertebrae of eusuchians had one convex and one concave articulating surface. The oldest known eusuchian is Hylaeochampsa vectiana from the Early Cretaceous of the Isle of Wight in the United Kingdom. It was followed by crocodilians such as the Planocraniidae , the so-called 'hoofed crocodiles', in the Palaeogene . Spanning the Cretaceous and Palaeogene periods is

8600-401: The pupils of a crocodilian contract into narrow slits, whereas in darkness they become large circles. This is typical for animals that hunt at night. Crocodilians also possess a tapetum lucidum which enhances vision in low light. When the animal completely submerges, the nictitating membranes cover its eyes. In addition, glands on the nictitating membrane secrete a salty lubricant that keeps

8700-494: The rank of family (see ordo naturalis , ' natural order '). In French botanical publications, from Michel Adanson 's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles ) was used as a French equivalent for this Latin ordo . This equivalence was explicitly stated in the Alphonse Pyramus de Candolle 's Lois de la nomenclature botanique (1868),

8800-422: The speed at which the lower half of each limb (rather than the whole leg) swings forward, so stride length increases while stride duration decreases. Though typically slow on land, crocodilians can produce brief bursts of speed, and some can run at 12 to 14 km/h (7.5 to 8.7 mph) for short distances. In some small species such as the freshwater crocodile , a running can progress to galloping. This involves

8900-864: The strongest bite forces in the animal kingdom. In a study published in 2003, an American alligator's bite force was measured at up to 2,125 lbf (9.45 kN). In a 2012 study, a saltwater crocodile's bite force was measured even higher, at 3,700 lbf (16 kN). This study also found no correlation between bite force and snout shape. Nevertheless, the gharial's extremely slender jaws are relatively weak and built more for quick jaw closure. The bite force of Deinosuchus may have measured 23,000 lbf (100 kN), even greater than that of theropod dinosaurs like Tyrannosaurus . Crocodilian teeth vary from dull and rounded to sharp and pointy. Broad-snouted species have teeth that vary in size, while those of slender-snouted species are more consistent. In general both rows of teeth are visible on crocodiles and gharials when

9000-445: The substrate and launching themselves into the air. A fast entry into water from a muddy bank can be effected by plunging to the ground, twisting the body from side to side and splaying out the limbs. The snout shape of crocodilians varies between species. Alligators and caimans generally have wider, U-shaped snouts while those of crocodiles are typically narrower and V-shaped. The gharial's are extremely elongated. The muscles that close

9100-425: The suffix -virales . Last common ancestor In biology and genetic genealogy , the most recent common ancestor ( MRCA ), also known as the last common ancestor ( LCA ), of a set of organisms is the most recent individual from which all the organisms of the set are descended . The term is also used in reference to the ancestry of groups of genes ( haplotypes ) rather than organisms. The MRCA of

9200-405: The sun. At night it remains submerged, and its temperature slowly falls. The basking period is longer in winter. Tropical crocodiles bask briefly in the morning but then move into the water for rest of the day. They may also move to land at nightfall, as it is cooler. Gaping with the mouth can provide cooling by evaporation from the mouth lining. By these means, the temperature range of crocodilians

9300-458: The surface, the dermis is thick with collagen . Both the head and jaws lack actual scales and are instead covered in tight keratinised skin that is fused directly to the bones of the skull and which over time develop a pattern of cracks as the skull develops. The skin on the neck and sides is loose. The scutes contain blood vessels and may act to absorb or release heat during thermoregulation . Research also suggests that alkaline ions released into

9400-437: The time to these genetic MRCAs will necessarily be greater than that for the genealogical MRCA. This is because single genes will coalesce more slowly than tracing of conventional human genealogy via both parents. The latter considers only individual humans, without taking into account whether any gene from the computed MRCA actually survives in every single person in the current population. Mitochondrial DNA can be used to trace

9500-411: The tongue, though these are only present in crocodiles and gharials. The skin is a largely effective barrier to both water and ions, and gaping causes water loss by evaporation. Large animals are better able to maintain homeostasis at times of osmotic stress than smaller ones. Newly hatched crocodilians are much less tolerant of exposure to salt water than are older juveniles, presumably because they have

9600-514: The top of the head. Alligators and caimans tend to have broader U-shaped jaws, that when closed, only show the upper teeth, while crocodiles usually have narrower V-shaped jaws with both rows of teeth visible when closed. Gharials have extremely slender and elongated jaws. All crocodilians are good swimmers and can move on land in a "high walk" position, traveling with their legs erect rather than sprawling. Crocodilians have thick skin covered in non-overlapping scales. They have conical, peg-like teeth and

9700-652: The two parents, genetic recombination ( chromosomal crossover ) mixes genes from non-sister chromatids from both parents during meiosis , thus changing the genetic composition of the chromosome. Different types of MRCAs are estimated to have lived at different times in the past. These time to MRCA ( TMRCA ) estimates are also computed differently depending on the type of MRCA being considered. Patrilineal and matrilineal MRCAs (Mitochondrial Eve and Y-chromosomal Adam) are traced by single gene markers, thus their TMRCA are computed based on DNA test results and established mutation rates as practiced in genetic genealogy. The time to

9800-418: The water, they maintain ice-free breathing holes, and there have been occasions when their snouts have become frozen into the ice. Temperature sensing probes implanted in wild American alligators have found that their core body temperatures can descend to around 5 °C (41 °F), but as long as they remain able to breathe they show no ill effects when the weather warms up. All crocodilians need to maintain

9900-446: The world. For example, if a mutation is deemed to have occurred 30,000 years ago, then this mutation should be found amongst all populations that diverged after this date. If archeological evidence indicates cultural spread and formation of regionally isolated populations then this must be reflected in the isolation of subsequent genetic mutations in this region. If genetic divergence and regional divergence coincide it can be concluded that

10000-418: Was adopted by Systema Naturae 2000 and others. In botany , the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. Any number of further ranks can be used as long as they are clearly defined. The superorder rank is commonly used, with the ending -anae that was initiated by Armen Takhtajan 's publications from 1966 onwards. The order as

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