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76-573: The Nightingale Island finch ( Nesospiza questi ) is a species of bird in the family Thraupidae (formerly in Emberizidae ). It is endemic to Nightingale Island of the Tristan da Cunha archipelago , where its natural habitats are temperate shrubland and subantarctic grassland . It is threatened by habitat loss . This article about a tanager is a stub . You can help Misplaced Pages by expanding it . This article about Tristan da Cunha

152-700: 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 Monogamy in animals Monogamy

228-473: 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

304-471: A few hooved animals, some bats , and the Eurasian beaver . This beaver is particularly interesting, as it is practicing monogamy in its reintroduction to certain parts of Europe; however, its American counterpart is not monogamous at all and often partakes in promiscuous behavior. The two species are quite similar in ecology, but American beavers tend to be less aggressive than European beavers. In this instance,

380-420: A greater number of offspring. This eventually leads to large differences in body size between females and males. Polygynous males are often 1.5 to 2.0 times larger in size than females. In monogamous species, on the other hand, females and males have more equal access to mates, so there is little or no sexual dimorphism in body size. From a new biological point of view, monogamy could result from mate guarding and

456-442: 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

532-405: A low to moderate amount of sperm competition. In species where the young are particularly vulnerable and may benefit from protection by both parents, monogamy may be an optimal strategy. Monogamy tends to also occur when populations are small and dispersed. This is not conductive to polygamous behavior as the male would spend far more time searching for another mate. The monogamous behavior allows

608-527: A polygamous mating system. Sexual dimorphism then began to decrease. Studies suggest sexual dimorphism reached modern human levels around the time of Homo erectus 0.5 to 2 million years ago. This line of reasoning suggests human ancestors started out polygamous and began the transition to monogamy somewhere between 0.5 million and 2 million years ago. Attempts to infer the evolution of monogamy based on sexual dimorphism remain controversial for three reasons: Studies of sexual dimorphism raise

684-464: A sexual partner for socially monogamous females in an enforcement pattern. Kleiman also offered a second theory. In obligate monogamy, the driving force behind monogamy is a greater need for paternal investment. This theory assumes that without biparental care fitness level of offspring would be greatly reduced. This paternal care may or may not be equal to that of the maternal care. Related to paternal care, some researchers have argued that infanticide

760-406: 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

836-415: A socially monogamous bird species that usually only have one mate throughout their lives, much like the prairie vole. The female will close herself up in a nest cavity, sealed with a nest plug, for two months. At this time, she will lay eggs and will be cared for by her mate. The males are willing to work to support himself, his mate, and his offspring in order for survival; however, unlike the emperor penguin,

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912-479: A species of animal, however, may potentially operate on a large number of factors throughout that animal's life cycle. For instance, with many species of bear, the female will often drive a male off soon after mating, and will later guard her cubs from him. It is thought that this may be due to the fact that too many bears close to one another may deplete the food available to the relatively small but growing cubs. Monogamy may be social but rarely genetic. For example, in

988-717: 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)

1064-413: Is a stub . You can help Misplaced Pages by expanding it . Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws, 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

1140-604: Is a relatively new concept in salamanders, and has not been seen frequently – it is also concerning that the act of monogamy may inhibit the salamanders reproductive rates and biological success. However, the study which was conducted in cooperation by the University of Louisiana, Lafayette, and the University of Virginia showed that the salamanders are not inhibited by this monogamy if they show alternative strategies with other mates. Azara's night monkeys are another species that proved to be monogamous. In an 18-year study conducted by

1216-413: Is a typical tactic in monogamous species. It is present in many animal species and can sometimes be expressed in lieu of parental care by males. This may be for many reasons, including paternity assurance. While the evolution of monogamy in animals cannot be broadly ascertained, there are several theories as to how monogamy may have evolved. Anisogamy is a form of sexual reproduction which involves

1292-432: Is because males may increase their fitness by mating with many females, whereas females are limited by their own fecundity. Females are therefore typically more likely to be selective in choosing mates. Monogamy is suggested to limit fitness differences, as males and females will mate in pairs. This would seem to be non-beneficial to males, but may not be in all cases. Several behaviors and ecological concerns may have led to

1368-621: Is because resources may be found more easily for the pair than for the individual. The argument for resource availability has been shown in many species, but in several species, once resource availability increases, monogamy is still apparent. With increased resource availability, males may be offsetting the restriction of their fitness through several means. In instances of social monogamy, males may offset any lowered fitness through extra pair coupling . Extra pair coupling refers to male and females mating with several mates but only raising offspring with one mate. The male may not be related to all of

1444-430: Is body size. For example, among mammals, males typically have larger bodies than females. In other orders, however, females have larger bodies than males. Sexual dimorphism in body size has been linked to mating behavior. In polygynous species, males compete for control over sexual access to females. Large males have an advantage in the competition for access to females, and they consequently pass their genes along to

1520-544: Is defined as a pair bond between two adult animals of the same species. This pair may cohabitate in an area or territory for some duration of time, and in some cases may copulate and reproduce with only each other. Monogamy may either be short-term, lasting one to a few seasons or long-term, lasting many seasons and in extreme cases, life-long. Monogamy can be partitioned into two categories, social monogamy and genetic monogamy which may occur together in some combination, or completely independently of one another. As an example, in

1596-567: Is derived from the conflict-centric differential allocation hypothesis, which states that there is a tradeoff between investment and attractiveness. Genetic monogamy refers to a mating system in which fidelity of the bonding pair is exhibited. Though individual pairs may be genetically monogamous, no one species has been identified as fully genetically monogamous. In some species, genetic monogamy has been enforced. Female voles have shown no difference in fecundity with genetic monogamy, but it may be enforced by males in some instances. Mate guarding

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1672-457: Is due to the harshness of the Antarctic weather, predators and the scarcity of food. One parent will protect the chick, while the other finds food. However, these penguins only remain monogamous until the chick is able to go off on their own. After the chick no longer needs their care, approximately 85% of parents will part ways and typically find a new partner every breeding season. Hornbills are

1748-477: Is engaged as a result of sexual conflict . Some researchers have attempted to infer the evolution of human mating systems from the evolution of sexual dimorphism. Several studies have reported a large amount of sexual dimorphism in Australopithecus , an evolutionary ancestor of human beings that lived between 2 and 5 million years ago. These studies raise the possibility that Australopithecus had

1824-429: 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

1900-499: Is in polygamous situations. Therefore, sperm quality for monogamous species has a higher variation and lower quality sperm have been noted in several species. The lack of sperm competition is not advantageous for sperm quality. An example of this is in the Eurasian bullfinch which exhibits relaxed selection and sperm competition. The sperm of these males have a lower velocity than other closely related but polygamous passerine bird species and

1976-417: Is less of a chance for a given male to find multiple females to mate with. In such a case, it becomes more advantageous for a male to remain with a female, rather than seeking out another and risking (a) not finding another female and or (b) not being able to fight off another male from interfering with his offspring by mating with the female or through infanticide . In these situations, male-to-male competition

2052-408: Is more beneficial for their young to be taken care of by both parents. They take turns incubating the eggs, and then supplying their fledglings with food. Black vultures will also attack other vultures that are participating in extra pair copulation , this is an attempt to increase monogamy and decrease promiscuous behavior. Similarly, emperor penguins also stay together to care for their young. This

2128-503: 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

2204-436: Is not needed, there may still be a need for the pair to protect each other. An example of this would be sentinel behavior in avian species. The main advantage of sentinel behavior is that many survival tactics are improved. As stated, the male or female will act as a sentinel and signal to their mate if a predator is present. This can lead to an increase in survivorship, foraging, and incubation of eggs. Male care for offspring

2280-454: Is not seen in all species, such as some primates, in which the female may be more dominant than the male and may not need help to avoid unwanted mating; the pair may still benefit from some form of mate assistance, however, and therefore monogamy may be enforced to ensure the assistance of males. Bi-parental care is not seen in all monogamous species, however, so this may not be the only cause of female enforcement. In species where mate guarding

2356-414: Is one of the main sources of competition females are able to choose sperm from among various male suitors. Typically the sperm of the highest quality are selected. In genetically monogamous species it can be expected that sperm competition is absent or otherwise severely limited. There is no selection for the highest quality sperm amongst the sperm of multiple males, and copulation is more random than it

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2432-400: Is rather rare in some taxa of species. This is because males may increase their fitness by searching for multiple mates. Females are limited in fitness by their fecundity, so multiple mating does not affect their fitness to the same extent. Males have the opportunity to find a new mate earlier than females when there is internal fertilization or the females exhibit the majority of the care for

2508-424: Is reduced and female choice is limited. The end result is that the mate choice is more random than in a more dense population, which has a number of effects including limiting dimorphism and sexual selection . With resource availability limited, mating with multiple mates may be harder because the density of individuals is lowered. The habitat cannot sustain multiple mates, so monogamy may be more prevalent. This

2584-516: 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,

2660-465: Is the true cause of monogamy. This theory has not garnered much support, however, critiqued by several authors including Lukas and Clutton-Brock and Dixson. Monogamous mating may also be caused simply by enforcement through tactics such as mate guarding. In these species, the males will prevent other males from copulating with their chosen female or vice versa. Males will help to fend off other aggressive males, and keep their mate for themselves. This

2736-517: Is thought to be lessened, and typically little to no sexual dimorphism is noted as there is less ornamentation and armor. This is because there is a relaxation of sexual selection. This may have something to do with a feedback loop caused by a low population density. If sexual selection is too strenuous in a population where there is a low density the population will shrink. In the continuing generations sexual selection will become less and less relevant as mating becomes more random. A similar feedback loop

2812-402: Is thought to occur for the sperm quality in genetically monogamous pairs. Once anisogamy has emerged in a species due to gamete dimorphism there is an inherent level of competition. This could be seen as sperm competition in the very least. Sperm competition is defined as a post copulatory mode of sexual selection which causes the diversity of sperm across species. As soon as sperm and egg are

2888-530: 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

2964-660: 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

3040-561: 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 the Late Cretaceous and diversified dramatically around

3116-433: 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; the only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds

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3192-417: The University of Pennsylvania, these monkeys proved to be entirely monogamous, exhibiting no genetic information or visual information that could lead to the assumption that extra pair copulation was occurring. This explained the question as to why the male owl monkey invested so much time in protecting and raising their own offspring. Because monogamy is often referred to as "placing all your eggs in one basket"

3268-480: 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 is called ornithology . Birds are feathered theropod dinosaurs and constitute

3344-478: The amount of abnormalities in sperm structure, length, and count when compared to similar bird families is increased. The evolution of mating systems in animals has received an enormous amount of attention from biologists. This section briefly reviews three main findings about the evolution of monogamy in animals. The amount of social monogamy in animals varies across taxa, with over 90% of birds engaging in social monogamy while only 3–9% of mammals are known to do

3420-428: 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

3496-509: 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

3572-432: The cichlid species Variabilichromis moorii , a monogamous pair will care for eggs and young together, but the eggs may not all be fertilized by the male giving the care. Monogamy in mammals is rather rare, only occurring in 3–9% of these species. A larger percentage of avian species are known to have monogamous relationships (about 90%), but most avian species practice social but not genetic monogamy in contrast to what

3648-410: The cichlid species Variabilichromis moorii , a monogamous pair will care for their eggs and young but the eggs are not all fertilized by the same male. Thierry Lodé argued that monogamy should result from conflict of interest between the sexes called sexual conflict . There are species which have adopted monogamy with great success. For instance, the male prairie vole will mate exclusively with

3724-665: 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

3800-521: The evolution of monogamy as a relevant mating strategy. Partner and resource availability, enforcement, mate assistance, and territory defense may be some of the most prevalent factors affecting animal behavior. First introduced by Kleiman, facultative monogamy occurs when females are widely dispersed. This can either occur because females in a species tend to be solitary or because the distribution of resources available cause females to thrive when separated into distinct territories. In these instances, there

3876-451: 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

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3952-426: The first female he ever mates with. The vole is extremely loyal and will go as far as to even attack other females that may approach him. This type of behavior has been linked to the hormone vasopressin . This hormone is released when a male mates and cares for young. Due to this hormone's rewarding effects, the male experiences a positive feeling when they maintain a monogamous relationship. To further test this theory,

4028-549: The fusion of two unequally-sized gametes. In many animals, there are two sexes: the male, in which the gamete is small, motile, usually plentiful, and less energetically expensive, and the female, in which the gamete is larger, more energetically expensive, made at a lower rate, and largely immobile. Anisogamy is thought to have evolved from isogamy , the fusion of similar gametes, multiple times in many different species. The introduction of anisogamy has caused males and females to tend to have different optimal mating strategies. This

4104-477: The hornbills do not find new partners each season. It is relatively uncommon to find monogamous relationships in fish, amphibians and reptiles; however, the red-backed salamander as well as the Caribbean cleaner goby practice monogamy as well. However, the male Caribbean cleaner goby fish has been found to separate from the female suddenly, leaving her abandoned. In a study conducted by Oregon State University, it

4180-569: The male is not present in these populations, the survivorship of the offspring is drastically lowered and there is a lowering in male fitness. Without monogamy, bi-parental care is less common and there is an increased chance of infanticide . Infanticide with monogamous pairing would lead to a lowered fitness for socially monogamous males and is not seen to a wide extent. Monogamy as a mating system in animals has been thought to lower levels of some pre and post copulatory competition methods. Because of this reduction in competition in some instances

4256-443: The male to have a mate consistently, without having to waste energy searching for other females. Furthermore, there is an apparent connection between the time a male invests in their offspring and their monogamous behavior. A male which is required to care for the offspring to ensure their survival is much more likely to exhibit monogamous behavior over one that does not. The selection factors in favor of different mating strategies for

4332-399: The male wants to ensure his young survive, and thus pass on his genes. The desert grass spider, Agelenopsis aperta , is mostly monogamous as well. Male size is the determining factor in fights over a female, with the larger male emerging as the winner since their size signifies success in future offspring. Other monogamous species include wolves , certain species of fox , otters ,

4408-757: The males and the females. The existence of purely social monogamy is a polygamous or polyandrous social pair with extra pair coupling . Social monogamy has been shown to increase fitness in prairie voles. It has been shown that female prairie voles live longer when paired with males in a social monogamous relationship. This could be because of the shared energy expenditure by the males and females lower each individual's input. In largemouth bass, females are sometimes seen to exhibit cuckoo behavior by laying some of their eggs in another female's nest, thus "stealing" fertilizations from other females. Sexual conflicts that have been proposed to arise from social monogamy include infidelity and parental investment. The proposed conflict

4484-441: The offspring of his main mate, but some offspring are being raised in other broods by other males and females, thereby offsetting any limitation of monogamy. Males are cuckolds, but because they have other female sexual partners, they cuckold other males and increase their own fitness. Males exhibit parental care habits in order to be an acceptable mate to the female. Any males that do not exhibit parental care would not be accepted as

4560-502: The offspring. When males are shown to care for offspring as well as females, it is referred to as bi-parental care. Bi-parental care may occur when there is a lower chance of survival of the offspring without male care. The evolution of this care has been associated with energetically expensive offspring. Bi-parental care is exhibited in many avian species. In these cases, the male has a greater chance to increase his own fitness by seeing that his offspring live long enough to reproduce. If

4636-402: 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

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4712-472: The possibility that early human ancestors were polygamous rather than monogamous. But this line of research remains highly controversial. It may be that early human ancestors showed little sexual dimorphism, and it may be that sexual dimorphism in early human ancestors had no relationship to their mating systems. The relative sizes of male testes often reflect mating systems. In species with promiscuous mating systems, where many males mate with many females,

4788-481: The predominant mating types there is an increase in the need for the male gametes. This is because there will be a large number of unsuccessful sperm which will cost a certain level of expenditure on energy without a benefit from the individual sperm. Sperm in polygamous sexual encounters have evolved for size, speed, structure, and quantity. This competition causes selection for competitive traits which can be pre or post copulatory. In species where cryptic female choice

4864-528: 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

4940-425: The receptors that control vasopressin were placed into another species of vole that is promiscuous. After this addition, the originally unfaithful voles became monogamous with their selected partner. These very same receptors can be found in human brain, and have been found to vary at the individual level—which could explain why some human males tend to be more loyal than others. Black vultures stay together as it

5016-427: The regulation of certain morphological characteristics may be lowered. This would result in a vast variety of morphological and physiological differences such as sexual dimorphism and sperm quality. Sexual dimorphism denotes the differences in males and females of the same species. Even in animals with seemingly no morphological sexual dimorphism visible there is still dimorphism in the gametes. Among mammals, males have

5092-413: The relationship between testis size and mating system. Chimpanzees , which have a promiscuous mating system, have large testes compared to other primates. Gorillas , which have a polygynous mating system, have smaller testes than other primates. Humans , which have a socially monogamous mating system , have moderately sized testes. The moderate amounts of sexual non-monogamy in humans may result in

5168-452: 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

5244-459: The same. This list is not complete. Other factors may also contribute to the evolution of social monogamy. Moreover, different sets of factors may explain the evolution of social monogamy in different species. There is no one-size-fits-all explanation of why different species evolved monogamous mating systems. Sexual dimorphism refers to differences in body characteristics between females and males. A frequently studied type of sexual dimorphism

5320-545: 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

5396-616: The smaller gametes and females have the larger gametes. As soon as the two sexes emerge the dimorphism in the gamete structures and sizes may lead to further dimorphism in the species. Sexual dimorphism is often caused through evolution in response to male male competition and female choice. In polygamous species there is a noted sexual dimorphism. The sexual dimorphism is seen typically in sexual signaling aspects of morphology. Males typically exhibit these dimorphic traits and they are typically traits which help in signaling to females or male male competition. In monogamous species sexual conflict

5472-425: The testes tend to be relatively large. This appears to be the result of sperm competition. Males with large testes produce more sperm and thereby gain an advantage impregnating females. In polygynous species, where one male controls sexual access to females, the testes tend to be small. One male defends exclusive sexual access to a group of females and thereby eliminates sperm competition. Studies of primates support

5548-600: 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

5624-461: 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

5700-484: Was found that this fish practices not true monogamy, but serial monogamy. This essentially means that the goby will have multiple monogamous relationships throughout its life – but only be in one relationship at a time. The red-backed salamander exhibited signs of social monogamy, which is the idea that animals form pairs to mate and raise offspring, but still will partake in extra pair copulation with various males or females in order to increase their biological fitness. This

5776-528: Was previously assumed by researchers. Monogamy is quite rare in fish and amphibians, but not unheard of, appearing in a select few species. Social monogamy refers to the cohabitation of one male and one female. The two individuals may cooperate in search of resources such as food and shelter and/or in caring for young. Paternal care in monogamous species is commonly displayed through carrying, feeding, defending, and socializing offspring. With social monogamy there may not be an expected sexual fidelity between

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