92-422: Madanga ruficollis The madanga or rufous-throated white-eye ( Anthus ruficollis ) is a species of bird that was formerly included in the family Zosteropidae but is now thought to be an atypical member of the family Motacillidae , consisting of the pipits and wagtails. Its close relatives are tree pipits of the genus Anthus , and is endemic to the moist, mountainous, subtropical and tropical forest of
184-460: 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
276-739: A better sense of smell. A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula , and the loss of grasping hands. † Anchiornis † Archaeopteryx † Xiaotingia † Rahonavis † Jeholornis † Jixiangornis † Balaur † Zhongjianornis † Sapeornis † Confuciusornithiformes † Protopteryx † Pengornis Ornithothoraces † Enantiornithes Crocodilia Crocodylia ( / k r ɒ k ə ˈ d ɪ l i ə / )
368-445: 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
460-473: A definition similar to "all theropods closer to birds than to Deinonychus ", with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus . Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and
552-399: 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
644-442: A group called Paraves . Some basal members of Deinonychosauria, such as Microraptor , have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal , have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, studies suggest that
736-401: 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
828-472: 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
920-449: 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
1012-518: 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
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#17328692716451104-403: 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
1196-452: 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
1288-699: 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
1380-525: 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
1472-406: A sister group, the order Crocodilia , contain the only living representatives of the reptile clade Archosauria . During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica . However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and
1564-434: 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
1656-717: A time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction . They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds , parrots, and other species are popular as pets. Guano (bird excrement)
1748-556: 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 the true crocodiles (family Crocodylidae),
1840-606: 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
1932-533: Is called ornithology . Birds are feathered theropod dinosaurs and constitute the only known living dinosaurs . Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians . Birds are descendants of the primitive avialans (whose members include Archaeopteryx ) which first appeared during the Late Jurassic . According to recent estimates, modern birds ( Neornithes ) evolved in
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#17328692716452024-417: 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
2116-456: 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;
2208-429: Is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds
2300-503: Is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs , i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex . The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After
2392-418: 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
2484-554: 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
2576-516: Is synonymous to Avifilopluma. † Scansoriopterygidae † Eosinopteryx † Jinfengopteryx † Aurornis † Dromaeosauridae † Troodontidae Avialae Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs and, more specifically, members of Maniraptora , a group of theropods which includes dromaeosaurids and oviraptorosaurs , among others. As scientists have discovered more theropods closely related to birds,
2668-501: Is 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
2760-416: 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
2852-443: 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
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2944-496: 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
3036-530: Is used by many scientists including adherents to the PhyloCode . Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils , and assigning them, instead, to the broader group Avialae, on the principle that a clade based on extant species should be limited to those extant species and their closest extinct relatives. Gauthier and de Queiroz identified four different definitions for
3128-463: 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
3220-558: The Indonesian island Buru . The bird was initially described from four specimens collected in April 1922 from one area in the western part of the island, near the settlement Wa Fehat, at elevations between 820 m (2,690 ft) and 1,500 m (4,900 ft). These observations were reproduced on two birds in December 1995 at Wakeika, at an elevation of 1,460 m (4,790 ft); changes in
3312-658: The Late Cretaceous and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non- ornithuran dinosaurs. Many social species preserve knowledge across generations ( culture ). Birds are social, communicating with visual signals, calls, and songs , and participating in such behaviour as cooperative breeding and hunting, flocking , and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous , usually for one breeding season at
3404-466: 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
3496-700: 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
3588-516: 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
3680-508: 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
3772-660: The Tiaojishan Formation of China, which has been dated to the late Jurassic period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi , Xiaotingia zhengi , and Aurornis xui . The well-known probable early avialan, Archaeopteryx , dates from slightly later Jurassic rocks (about 155 million years old) from Germany . Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds but were later lost during bird evolution. These features include enlarged claws on
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3864-478: 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 the top of the head. Alligators and caimans tend to have broader U-shaped jaws, that when closed, only show
3956-409: 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
4048-442: 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
4140-476: The laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich . There are over 11,000 living species and they are split into 44 orders . More than half are passerine or "perching" birds. Birds have wings whose development varies according to species;
4232-529: 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
4324-454: 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
4416-581: 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
4508-428: 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
4600-462: The animals to remain submerged for 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
4692-403: 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
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#17328692716454784-428: The appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. The integument evolved into complex, pennaceous feathers . The oldest known paravian (and probably the earliest avialan) fossils come from
4876-443: 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
4968-447: The bird's habitat at Wa Fehat were also noted in 1995. The bird was observed only in a few localities and neither its habitat area nor population is reliably known. The population is estimated at more than several hundred individuals, and the habitat at several hundred km from the available area above 1,200 m (872 km²) and above 1,500 m (382 km²); the birds are believed to disperse over their habitat rather than form groups. Because
5060-509: The birds that descended from them. Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition
5152-404: 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
5244-604: 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
5336-490: 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
5428-665: The earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution , though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. † Coelurus † Ornitholestes † Ornithomimosauria † Alvarezsauridae † Oviraptorosauria Paraves Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used
5520-485: 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
5612-490: The evolution of crocodilians and their ancestors, with warmer climate being associated with high evolutionary rates and large body sizes. Crocodylia 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
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#17328692716455704-596: 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
5796-451: The first avialans were omnivores . The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It
5888-413: 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
5980-443: 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
6072-409: 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
6164-488: 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
6256-459: 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
6348-554: 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
6440-436: 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
6532-425: 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
6624-699: 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
6716-523: The only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds the ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds , have further evolved for swimming. The study of birds
6808-456: 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,
6900-402: The outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle , an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved
6992-528: The previously clear distinction between non-birds and birds has become blurred. By the 2000s, discoveries in the Liaoning Province of northeast China, which demonstrated many small theropod feathered dinosaurs , contributed to this ambiguity. The consensus view in contemporary palaeontology is that the flying theropods, or avialans , are the closest relatives of the deinonychosaurs , which include dromaeosaurids and troodontids . Together, these form
7084-664: 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
7176-401: 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
7268-452: The same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. They assigned other names to the other groups. Lizards & snakes Turtles Crocodiles Birds Under the fourth definition Archaeopteryx , traditionally considered one of
7360-545: The second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering. Avialans diversified into a wide variety of forms during the Cretaceous period. Many groups retained primitive characteristics , such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially
7452-462: The species is restricted to a single island and its habitat is threatened by logging and other human activities, it is listed as endangered by the IUCN since 1996. The madanga most likely eats small invertebrates recovered from bark and lichen. The bird has distinct coloration and body features, namely lack of a white eye-ring; longer toes, wing and tail, and the pointed shape of the rectrices (part of
7544-424: 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
7636-868: 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
7728-585: The subject of debate and conflicting results. Many studies and their resulting cladograms , or "family trees" of crocodilians, have found the "short-snouted" families of Crocodylidae and Alligatoridae to be close relatives, with the long-snouted Gavialidae as a divergent branch of the tree. 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
7820-450: 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
7912-406: 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
8004-463: 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
8096-462: The tail). A 2015 DNA analysis indicates the species is more closely related to the pipits than the white-eyes, and some taxonomic authorities now tend to regard it as being a member of the family Motacillidae within the clade containing pipits in the genus Anthus . Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws,
8188-415: 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
8280-406: 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
8372-419: 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
8464-461: Was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae . Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. Birds are categorised as the biological class Aves in Linnaean taxonomy . Phylogenetic taxonomy places Aves in the clade Theropoda as an infraclass or a subclass, more recently a subclass. Aves and
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