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113-471: Theropsida ( Seeley , 1895) " Pelycosauria " (Cladistically including therapsids) Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota , the other being the more diverse group Sauropsida (which includes all extant reptiles and birds ). Unlike other amniotes, synapsids have

226-409: A Gaussian might describe the frequency with which a species ate prey of a certain size, giving a more detailed niche description than simply specifying some median or average prey size. For such a bell-shaped distribution, the position , width and form of the niche correspond to the mean , standard deviation and the actual distribution itself. One advantage in using statistics is illustrated in

339-431: A secondary palate , separating the mouth and nasal cavity . In early synapsids, a secondary palate began to form on the sides of the maxilla , still leaving the mouth and nostril connected. Eventually, the two sides of the palate began to curve together, forming a U shape instead of a C shape. The palate also began to extend back toward the throat, securing the entire mouth and creating a full palatine bone . The maxilla

452-447: A storage effect . Species can differentiate their niche via a competition-predation trade-off if one species is a better competitor when predators are absent, and the other is better when predators are present. Defenses against predators, such as toxic compounds or hard shells, are often metabolically costly. As a result, species that produce such defenses are often poor competitors when predators are absent. Species can coexist through

565-433: A calcified layer, as most modern reptiles and monotremes do. This may also explain why there is no fossil evidence for synapsid eggs to date. Because they were vulnerable to desiccation, secretions from apocrine -like glands may have helped keep the eggs moist. According to Oftedal, early synapsids may have buried the eggs into moisture laden soil, hydrating them with contact with the moist skin, or may have carried them in

678-664: A cat. Most Jurassic and Cretaceous cynodonts were herbivorous , though some were carnivorous . The family Tritheledontidae , which first appeared near the end of the Triassic, was carnivorous and persisted well into the Middle Jurassic . The other, Tritylodontidae , first appeared at the same time as the tritheledonts, but was herbivorous. This group became extinct at the end of the Early Cretaceous epoch. Dicynodonts are generally thought to have become extinct near

791-727: A certain environment (have overlapping requirement niches) but fundamentally differ the ways that they use (or "impact") that environment. These requirements have repeatedly been violated by nonnative (i.e. introduced and invasive ) species, which often coexist with new species in their nonnative ranges, but do not appear to be constricted these requirements. In other words, contemporary niche theory predicts that species will be unable to invade new environments outside of their requirement (i.e. realized) niche, yet many examples of this are well-documented. Additionally, contemporary niche theory predicts that species will be unable to establish in environments where other species already consume resources in

904-474: A clade containing both the traditional therapsid families and mammals. Although Synapsida and Therapsida include modern mammals, in practical usage, those two terms are used almost exclusively when referring to the more basal members that lie outside of Mammaliaformes . Synapsids evolved a temporal fenestra behind each eye orbit on the lateral surface of the skull. It may have provided new attachment sites for jaw muscles. A similar development took place in

1017-427: A climatic perspective, to explain distribution and abundance. Current predictions on species responses to climate change strongly rely on projecting altered environmental conditions on species distributions. However, it is increasingly acknowledged that climate change also influences species interactions and an Eltonian perspective may be advantageous in explaining these processes. This perspective of niche allows for

1130-482: A competition-predation trade-off if predators are more abundant when the less defended species is common, and less abundant if the well-defended species is common. This effect has been criticized as being weak, because theoretical models suggest that only two species within a community can coexist because of this mechanism. Two ecological paradigms deal with the problem. The first paradigm predominates in what may be called "classical" ecology. It assumes that niche space

1243-412: A fundamental niche of the entire slope of a hillside, but its realized niche is only the top portion of the slope because species Y, which is a better competitor but cannot survive on the top portion of the slope, has excluded it from the lower portion of the slope. With this scenario, competition will continue indefinitely in the middle of the slope between these two species. Because of this, detection of

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1356-480: A given species), 'niche partitioning' (resource differentiation by coexisting species), and 'niche overlap' (overlap of resource use by different species). Statistics were introduced into the Hutchinson niche by Robert MacArthur and Richard Levins using the 'resource-utilization' niche employing histograms to describe the 'frequency of occurrence' as a function of a Hutchinson coordinate. So, for instance,

1469-480: A horny overlay, like those found in modern crocodiles and turtles . These differed in structure from the scales of lizards and snakes , which are an epidermal feature (like mammalian hair or avian feathers). Recently, skin impressions from the genus Ascendonanus suggest that at least varanopsids developed scales similar to those of squamates . It is currently unknown exactly when mammalian characteristics such as body hair and mammary glands first appeared, as

1582-517: A jaw joint in which one of the smaller bones of the lower jaw, the articular, makes a connection with a bone of the cranium called the quadrate bone to form the articular-quadrate jaw joint. In forms transitional to mammals, the jaw joint is composed of a large, lower jaw bone (similar to the dentary found in mammals) that does not connect to the squamosal, but connects to the quadrate with a receding articular bone. Over time, as synapsids became more mammalian and less 'reptilian', they began to develop

1695-490: A moist pouch, similar to that of monotremes ( echidnas carry their eggs and offspring via a temporary pouch), though this would limit the mobility of the parent. The latter may have been the primitive form of egg care in synapsids rather than simply burying the eggs, and the constraint on the parent's mobility would have been solved by having the eggs "parked" in nests during foraging or other activities and periodically be hydrated, allowing higher clutch sizes than could fit inside

1808-465: A niche specific to each species. Species can however share a 'mode of life' or 'autecological strategy' which are broader definitions of ecospace. For example, Australian grasslands species, though different from those of the Great Plains grasslands, exhibit similar modes of life. Once a niche is left vacant, other organisms can fill that position. For example, the niche that was left vacant by

1921-574: A pouch (or pouches) at once, and large eggs, which would be cumbersome to carry in a pouch, would be easier to care for. The basis of Oftedal's speculation is the fact that many species of anurans can carry eggs or tadpoles attached to the skin, or embedded within cutaneous "pouches" and how most salamanders curl around their eggs to keep them moist, both groups also having glandular skin. The glands involved in this mechanism would later evolve into true mammary glands with multiple modes of secretion in association with hair follicles. Comparative analyses of

2034-903: A single temporal fenestra , an opening low in the skull roof behind each eye socket , leaving a bony arch beneath each; this accounts for the name "synapsid". The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period, when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals. The basal amniotes ( reptiliomorphs ) from which synapsids evolved were historically simply called "reptiles". Therefore, stem group synapsids were then described as mammal-like reptiles in classical systematics, and non- therapsid synapsids were also referred to as pelycosaurs or pelycosaur- grade synapsids . These paraphyletic terms have now fallen out of favor and are only used informally (if at all) in modern literature, as it

2147-460: A species not only grows in and responds to an environment, it may also change the environment and its behavior as it grows. The Hutchinsonian niche uses mathematics and statistics to try to explain how species coexist within a given community. The concept of ecological niche is central to ecological biogeography , which focuses on spatial patterns of ecological communities. "Species distributions and their dynamics over time result from properties of

2260-487: A species' density declines, then the food it most depends on will become more abundant (since there are so few individuals to consume it). As a result, the remaining individuals will experience less competition for food. Although "resource" generally refers to food, species can partition other non-consumable objects, such as parts of the habitat. For example, warblers are thought to coexist because they nest in different parts of trees. Species can also partition habitat in

2373-443: A stapes. The malleus is derived from the articular (a lower jaw bone), while the incus is derived from the quadrate (a cranial bone). Mammalian jaw structures are also set apart by the dentary-squamosal jaw joint . In this form of jaw joint, the dentary forms a connection with a depression in the squamosal known as the glenoid cavity . In contrast, all other jawed vertebrates, including reptiles and nonmammalian synapsids, possess

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2486-617: A ton or more in weight (e.g.: Moschops ). After flourishing for many millions of years, these successful animals were all but wiped out by the Permian–Triassic mass extinction about 250 mya, the largest known extinction in Earth's history , possibly related to the Siberian Traps volcanic event. Only a few therapsids went on to be successful in the new early Triassic landscape; they include Lystrosaurus and Cynognathus ,

2599-451: A way that gives them access to different types of resources. As stated in the introduction, anole lizards appear to coexist because each uses different parts of the forests as perch locations. This likely gives them access to different species of insects. Research has determined that plants can recognize each other's root systems and differentiate between a clone, a plant grown from the same mother plants seeds, and other species. Based on

2712-511: Is absent or low, and therefore detection of niche differentiation is difficult or impossible. Below is a list of ways that species can partition their niche. This list is not exhaustive, but illustrates several classic examples. Resource partitioning is the phenomenon where two or more species divides out resources like food, space, resting sites etc. to coexist. For example, some lizard species appear to coexist because they consume insects of differing sizes. Alternatively, species can coexist on

2825-421: Is also closed completely. In fossils of one of the first eutheriodonts , the beginnings of a palate are clearly visible. The later Thrinaxodon has a full and completely closed palate, forming a clear progression. In addition to the glandular skin covered in fur found in most modern mammals, modern and extinct synapsids possess a variety of modified skin coverings, including osteoderms (bony armor embedded in

2938-546: Is believed to have been in species that lived more than 300 million years ago. However, Late Permian coprolites from Russia and possibly South Africa showcase that at least some synapsids did already have pre-mammalian hair in this epoch. These are the oldest impressions of hair-like structures on synapsids. Early synapsids, as far back as their known evolutionary debut in the Late Carboniferous period, may have laid parchment-shelled (leathery) eggs, which lacked

3051-548: Is constrained by different natural enemies, they will be able to coexist. Early work focused on specialist predators; however, more recent studies have shown that predators do not need to be pure specialists, they simply need to affect each prey species differently. The Janzen–Connell hypothesis represents a form of predator partitioning. Conditional differentiation (sometimes called temporal niche partitioning ) occurs when species differ in their competitive abilities based on varying environmental conditions. For example, in

3164-481: Is greater than inter-specific (between species) competition. Since niche differentiation concentrates competition within-species, due to a decrease in between-species competition, the Lotka-Volterra model predicts that niche differentiation of any degree will result in coexistence. In reality, this still leaves the question of how much differentiation is needed for coexistence. A vague answer to this question

3277-486: Is incorrect under the new definition of "reptile", so they are now referred to as stem mammals , proto-mammals , paramammals or pan-mammals . Most lineages of pelycosaur-grade synapsids were replaced by the more advanced therapsids, which evolved from sphenacodontoid pelycosaurs, at the end of the Early Permian during the so-called Olson's Extinction . Synapsids were the largest terrestrial vertebrates in

3390-489: Is largely saturated with individuals and species, leading to strong competition. Niches are restricted because "neighbouring" species, i.e., species with similar ecological characteristics such as similar habitats or food preferences, prevent expansion into other niches or even narrow niches down. This continual struggle for existence is an important assumption of natural selection introduced by Darwin as an explanation for evolution. The other paradigm assumes that niche space

3503-455: Is merely the product of the competitive exclusion principle. Also, because no species is out-competing any other species in the final community, the presence of niche differentiation will be difficult or impossible to detect. Finally, niche differentiation can arise as an evolutionary effect of competition. In this case, two competing species will evolve different patterns of resource use so as to avoid competition. Here too, current competition

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3616-405: Is necessary for ecologists to be able to detect, measure, and quantify the niches of different coexisting and competing species. This is often done through a combination of detailed ecological studies, controlled experiments (to determine the strength of competition), and mathematical models . To understand the mechanisms of niche differentiation and competition, much data must be gathered on how

3729-411: Is now known that all extant reptiles are more closely related to each other and birds than to synapsids, so the word "reptile" has been re-defined to mean only members of Sauropsida or even just an under-clade thereof. In a cladistic sense, synapsids are in fact a monophyletic sister taxon of sauropsids, rather than a part of the sauropsid lineage. Therefore, calling synapsids "mammal-like reptiles"

3842-419: Is that the more similar two species are, the more finely balanced the suitability of their environment must be in order to allow coexistence. There are limits to the amount of niche differentiation required for coexistence, and this can vary with the type of resource, the nature of the environment, and the amount of variation both within and between the species. To answer questions about niche differentiation, it

3955-425: Is the niche that is filled by birds of prey which eat small animals such as shrews and mice. In an oak wood this niche is filled by tawny owls , while in the open grassland it is occupied by kestrels . The existence of this carnivore niche is dependent on the further fact that mice form a definite herbivore niche in many different associations, although the actual species of mice may be quite different. Conceptually,

4068-432: Is to a large degree vacant, i.e., that there are many vacant niches . It is based on many empirical studies and theoretical investigations especially of Kauffman 1993. Causes of vacant niches may be evolutionary contingencies or brief or long-lasting environmental disturbances. Both paradigms agree that species are never "universal" in the sense that they occupy all possible niches; they are always specialized, although

4181-673: The Bashkirian age of the Late Carboniferous . It was one of many types of primitive synapsids that are now informally grouped together as stem mammals or sometimes as protomammals (previously known as pelycosaurs ). The early synapsids spread and diversified, becoming the largest terrestrial animals in the latest Carboniferous and Early Permian periods, ranging up to 6 metres (20 ft) in length. They were sprawling, bulky, possibly cold-blooded, and had small brains. Some, such as Dimetrodon , had large sails that might have helped raise their body temperature . A few relict groups lasted into

4294-559: The Cynodontia are also hypothesized to have had fur or a fur-like covering based on their inferred warm-blooded metabolism. While more direct evidence of fur in early cynodonts has been proposed in the form of small pits on the snout possibly associated with whiskers , such pits are also found in some reptiles that lack whiskers. There is evidence that some other non-mammalian cynodonts more basal than Castorocauda , such as Morganucodon , had Harderian glands , which are associated with

4407-589: The Early Triassic . Synapsid population and diversity were severely reduced by the Capitanian mass extinction event and the Permian–Triassic extinction event , and only two groups of therapsids, the dicynodonts and eutheriodonts (consisting of therocephalians and cynodonts ) are known to have survived into the Triassic . These therapsids rebounded as disaster taxa during the early Mesozoic, with

4520-598: The Olenekian age, an early representative of which was Cynognathus . Unlike the dicynodonts, which were large, the cynodonts became progressively smaller and more mammal-like as the Triassic progressed, though some forms like Trucidocynodon remained large. The first mammaliaforms evolved from the cynodonts during the early Norian age of the Late Triassic, about 225 mya. During the evolutionary succession from early therapsid to cynodont to eucynodont to mammal,

4633-508: The Permian period (299 to 251  mya ), rivalled only by some large pareiasaurian parareptiles such as Scutosaurus . They were the dominant land predators of the late Paleozoic and early Mesozoic , with eupelycosaurs such as Dimetrodon , Titanophoneus and Inostrancevia being the apex predators during the Permian, and theriodonts such as Moschorhinus during

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4746-631: The Saurischia and the Ornithischia , based on the nature of their pelvic bones and joints . He published his results in 1888, from a lecture he had delivered the previous year. Paleontologists of his time had been dividing the Dinosauria in various ways, depending on the structure of their feet and the form of their teeth. Seeley's division, however, has stood the test of time, though the birds have subsequently been found to descend, not from

4859-553: The Sonoran Desert , some annual plants are more successful during wet years, while others are more successful during dry years. As a result, each species will have an advantage in some years, but not others. When environmental conditions are most favorable, individuals will tend to compete most strongly with member of the same species. For example, in a dry year, dry-adapted plants will tend to be most limited by other dry-adapted plants. This can help them to coexist through

4972-683: The Woodwardian Museum . He helped curate the museum's fossil collection and began field studies on the local geology. Seeley graduated from Sidney Sussex College in 1863 and joined St John's in 1868 but never took a degree. He turned down positions both with the British Museum and the Geological Survey of Britain to work on his own. Late in his career he accepted a position as Professor of Geology at King's College, Cambridge and Bedford College (London) (1876). He

5085-404: The canines , molars , and incisors . The trend towards differentiation is found in some labyrinthodonts and early anapsid reptilians in the form of enlargement of the first teeth on the maxilla , forming a sort of protocanines. This trait was subsequently lost in the diapsid line, but developed further in the synapsids. Early synapsids could have two or even three enlarged "canines", but in

5198-443: The diapsids , which evolved two rather than one opening behind each eye. Originally, the openings in the skull left the inner cranium covered only by the jaw muscles, but in higher therapsids and mammals, the sphenoid bone has expanded to close the opening. This has left the lower margin of the opening as an arch extending from the lower edges of the braincase. Synapsids are characterized by having differentiated teeth. These include

5311-476: The therocephalians , which only lasted the first 20 million years of the Triassic period. The second were specialised, beaked herbivores known as dicynodonts (such as the Kannemeyeriidae ), which contained some members that reached large size (up to a tonne or more). And finally there were the increasingly mammal-like carnivorous, herbivorous, and insectivorous cynodonts, including the eucynodonts from

5424-444: The "bird-hipped" Ornithischia, but from the "lizard-hipped" Saurischia. He found the two groups so distinct that he also argued for separate origins: not until the 1980s did new techniques of cladistic analysis show that both groups of dinosaurs really did have common ancestors in the Triassic . Seeley described and named numerous dinosaurs from their fossils in the course of his career. His popular book on pterosaurs , Dragons of

5537-478: The "impact niche" is defined as the combination of effects that a given consumer has on both a). the resources that it uses, and b). the other consumers in the ecosystem. Therefore, the impact niche is equivalent to the Eltonian niche since both concepts are defined by the impact of a given species on its environment. The range of environmental conditions where a species can successfully survive and reproduce (i.e.

5650-708: The 5,500 species of living synapsids, known as the mammals , include both aquatic ( cetaceans ) and flying ( bats ) species, and the largest animal ever known to have existed (the blue whale ). Humans are synapsids, as well. Most mammals are viviparous and give birth to live young rather than laying eggs with the exception being the monotremes . Triassic and Jurassic ancestors of living mammals, along with their close relatives, had high metabolic rates. This meant consuming food (generally thought to be insects) in much greater quantity. To facilitate rapid digestion , these synapsids evolved mastication (chewing) and specialized teeth that aided chewing. Limbs also evolved to move under

5763-714: The Air (1901), found that the development of birds and pterosaurs paralleled each other. His belief that they had a common origin has been proved, for both are archosaurs, just not as close as he thought. He upset Richard Owen 's characterization of the pterosaurs as cold-blooded, sluggish gliders, and recognized them as warm-blooded active fliers. He was elected a Fellow of the Royal Society in June 1879 for his work on reptiles and dinosaurs, and delivered their Croonian Lecture in 1887. ... he will be best remembered, perhaps, for

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5876-495: The Eltonian niche introduces the idea of a species' response to and effect on the environment. Unlike other niche concepts, it emphasizes that a species not only grows in and responds to an environment based on available resources, predators, and climatic conditions, but also changes the availability and behavior of those factors as it grows. In an extreme example, beavers require certain resources in order to survive and reproduce, but also construct dams that alter water flow in

5989-574: The Hutchinsonian definition of a realized niche) is also encompassed under contemporary niche theory, termed the "requirement niche". The requirement niche is bounded by both the availability of resources as well as the effects of coexisting consumers (e.g. competitors and predators). Contemporary niche theory provides three requirements that must be met in order for two species (consumers) to coexist: These requirements are interesting and controversial because they require any two species to share

6102-782: The Royal School of Mines by Thomas Henry Huxley , Edward Forbes , and other notable scientists. In 1855, with the support of his uncle, Seeley began to study law but shortly gave it up to pursue a career as an actuary. In the late 1850s, he studied English and mathematics at the Working Men's College and served as a secretary for the college's museum. He also worked in the library of the British Museum, where Samuel Pickworth Woodward encouraged him to study geology. In 1859, Seeley began studies at Sidney Sussex College, Cambridge , and worked as an assistant for Adam Sedgwick at

6215-460: The biosphere and left vacant niches open to be filled by newly evolved taxa. In non-mammaliaform synapsids, those taxa that gave rise to rapidly diversifying lineages have been both small and large in body size, although after the Late Triassic, progenitors of new synapsid lineages have generally been small, unspecialised generalists. The earliest known synapsid Asaphestera coexisted with the earliest known sauropsid Hylonomus which lived during

6328-784: The body instead of to the side, allowing them to breathe more efficiently during locomotion. This helped make it possible to support their higher metabolic demands. Below is a cladogram of the most commonly accepted phylogeny of synapsids, showing a long stem lineage including Mammalia and successively more basal clades such as Theriodontia, Therapsida and Sphenacodontia: † Caseasauria [REDACTED] † Varanopidae [REDACTED] † Ophiacodontidae [REDACTED] † Edaphosauridae [REDACTED] † Sphenacodontidae [REDACTED] † Biarmosuchia [REDACTED] † Dinocephalia [REDACTED] † Anomodontia [REDACTED] † Gorgonopsia [REDACTED] Harry Seeley Harry Govier Seeley (18 February 1839 – 8 January 1909)

6441-473: The branch within which mammals evolved, and stem mammals, (previously known as pelycosaurs ), comprising the other six more primitive families of synapsids. Stem mammals were all rather lizard-like, with sprawling gait and possibly horny scutes , while therapsids tended to have a more erect pose and possibly hair, at least in some forms. In traditional taxonomy, the Synapsida encompasses two distinct grades :

6554-441: The coordinate system." The niche concept was popularized by the zoologist G. Evelyn Hutchinson in 1957. Hutchinson inquired into the question of why there are so many types of organisms in any one habitat. His work inspired many others to develop models to explain how many and how similar coexisting species could be within a given community, and led to the concepts of 'niche breadth' (the variety of resources or habitats used by

6667-464: The dicynodont Lystrosaurus making up as much as 95% of all land species at one time, but declined again after the Smithian–Spathian boundary event with their dominant niches largely taken over by the rise of archosaurian sauropsids, first by the pseudosuchians and then by the pterosaurs and dinosaurs . The cynodont group Probainognathia , which includes the group Mammaliaformes , were

6780-528: The early synapsids, only two species of small varanopids have been found to possess osteoderms ; fossilized rows of osteoderms indicate bony armour on the neck and back. However, some recent studies have cast doubt on the placement of Varanopidae in Synapsida, while others have countered and lean towards this traditional placement. Skin impressions indicate some early synapsids basal possessed rectangular scutes on their undersides and tails. The pelycosaur scutes probably were nonoverlapping dermal structures with

6893-481: The ecological space occupied by a species) is subtly different from the "niche" as defined by Grinnell (an ecological role, that may or may not be actually filled by a species—see vacant niches ). A niche is a very specific segment of ecospace occupied by a single species. On the presumption that no two species are identical in all respects (called Hardin's 'axiom of inequality' ) and the competitive exclusion principle , some resource or adaptive dimension will provide

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7006-535: The end of the Triassic period, but there was evidence this group survived, in the form of six fragments of fossil bone that were found in Cretaceous rocks of Queensland , Australia. If true, it would mean there is a significant ghost lineage of Dicynodonts in Gondwana . However, these fossils were re-described in 2019 as being Pleistocene in age, and possibly belonging to a diprotodontid marsupial . Today,

7119-801: The environment. As an example of niche partitioning, several anole lizards in the Caribbean islands share common diets—mainly insects. They avoid competition by occupying different physical locations. Although these lizards might occupy different locations, some species can be found inhabiting the same range, with up to 15 in certain areas. For example, some live on the ground while others are arboreal. Species who live in different areas compete less for food and other resources, which minimizes competition between species. However, species who live in similar areas typically compete with each other. The Lotka–Volterra equation states that two competing species can coexist when intra-specific (within species) competition

7232-463: The estimation of the competition coefficients. This postulate, however, can be misguided, as it ignores the impacts that the resources of each category have on the organism and the impacts that the organism has on the resources of each category. For instance, the resource in the overlap region can be non-limiting, in which case there is no competition for this resource despite niche overlap. An organism free of interference from other species could use

7345-472: The evolutionary origin of milk constituents support a scenario in which the secretions from these glands evolved into a complex, nutrient-rich milk long before true mammals arose (with some of the constituents possibly predating the split between the synapsid and sauropsid lines). Cynodonts were almost certainly able to produce this, which allowed a progressive decline of yolk mass and thus egg size, resulting in increasingly altricial hatchlings as milk became

7458-587: The existence of both ecological equivalents and empty niches. An ecological equivalent to an organism is an organism from a different taxonomic group exhibiting similar adaptations in a similar habitat, an example being the different succulents found in American and African deserts, cactus and euphorbia , respectively. As another example, the anole lizards of the Greater Antilles are a rare example of convergent evolution , adaptive radiation , and

7571-482: The existence of ecological equivalents: the anole lizards evolved in similar microhabitats independently of each other and resulted in the same ecomorphs across all four islands. In 1927 Charles Sutherland Elton , a British ecologist , defined a niche as follows: "The 'niche' of an animal means its place in the biotic environment, its relations to food and enemies ." Elton classified niches according to foraging activities ("food habits"): For instance there

7684-472: The exotic or invasive species . The mathematical representation of a species' fundamental niche in ecological space, and its subsequent projection back into geographic space, is the domain of niche modelling . Contemporary niche theory (also called "classic niche theory" in some contexts) is a framework that was originally designed to reconcile different definitions of niches (see Grinnellian, Eltonian, and Hutchinsonian definitions above), and to help explain

7797-427: The extinction of the tarpan has been filled by other animals (in particular a small horse breed, the konik ). Also, when plants and animals are introduced into a new environment, they have the potential to occupy or invade the niche or niches of native organisms, often outcompeting the indigenous species. Introduction of non-indigenous species to non-native habitats by humans often results in biological pollution by

7910-615: The family Kannemeyeriidae) had disappeared by the Rhaetian age, even before the Triassic–Jurassic extinction event that killed off most of the large non-dinosaurian archosaurs . The remaining Mesozoic synapsids were small, ranging from the size of a shrew to the badger-like mammal Repenomamus . During the Jurassic and Cretaceous, the remaining non-mammalian cynodonts were small, such as Tritylodon . No cynodont grew larger than

8023-434: The figure, where it is clear that for the narrower distributions (top) there is no competition for prey between the extreme left and extreme right species, while for the broader distribution (bottom), niche overlap indicates competition can occur between all species. The resource-utilization approach postulates that not only can competition occur, but that it does occur, and that overlap in resource utilization directly enables

8136-636: The fossils only rarely provide direct evidence for soft tissues. An exceptionally well-preserved skull of Estemmenosuchus , a therapsid from the Upper Permian, preserves smooth skin with what appear to be glandular depressions, an animal noted as being semi- aquatic . The oldest known fossil showing unambiguous imprints of hair is the Callovian (late middle Jurassic ) Castorocauda and several contemporary haramiyidans , both non-mammalian mammaliaform (see below, however). More primitive members of

8249-471: The four main subclasses of reptiles . However, this notion was disproved upon closer inspection of skeletal remains, as synapsids are differentiated from reptiles by their distinctive temporal openings. These openings in the skull bones allowed the attachment of larger jaw muscles, hence a more efficient bite. Synapsids were subsequently considered to be a later reptilian lineage that became mammals by gradually evolving increasingly mammalian features, hence

8362-433: The full range of conditions (biotic and abiotic) and resources in which it could survive and reproduce which is called its fundamental niche . However, as a result of pressure from, and interactions with, other organisms (i.e. inter-specific competition) species are usually forced to occupy a niche that is narrower than this, and to which they are mostly highly adapted ; this is termed the realized niche . Hutchinson used

8475-405: The grooming and maintenance of fur. The apparent absence of these glands in non-mammaliaformes may suggest that fur did not originate until that point in synapsid evolution. It is possible that fur and associated features of true warm-bloodedness did not appear until some synapsids became extremely small and nocturnal, necessitating a higher metabolism. The oldest examples of nocturnality in synapsids

8588-401: The idea of competition for resources as the primary mechanism driving ecology, but overemphasis upon this focus has proved to be a handicap for the niche concept. In particular, overemphasis upon a species' dependence upon resources has led to too little emphasis upon the effects of organisms on their environment, for instance, colonization and invasions. The term "adaptive zone" was coined by

8701-457: The idea that the niche of a species is determined by the habitat in which it lives and its accompanying behavioral adaptations . In other words, the niche is the sum of the habitat requirements and behaviors that allow a species to persist and produce offspring. For example, the behavior of the California thrasher is consistent with the chaparral habitat it lives in—it breeds and feeds in

8814-613: The later Permian but, by the middle of the Late Permian, all had either died off or evolved into their successors, the therapsids. The therapsids, a more advanced group of synapsids, appeared during the Middle Permian and included the largest terrestrial animals in the Middle and Late Permian . They included herbivores and carnivores, ranging from small animals the size of a rat (e.g.: Robertia ), to large, bulky herbivores

8927-507: The latter of which appeared later in the Early Triassic. However, they were accompanied by the early archosaurs (soon to give rise to the dinosaurs ). Some of these archosaurs, such as Euparkeria , were small and lightly built, while others, such as Erythrosuchus , were as big as or bigger than the largest therapsids. After the Permian extinction, the synapsids did not count more than three surviving clades. The first comprised

9040-405: The limbs and tail. Their fingers are elongated, similar to those of bats and colugos and likely sharing similar roles both as wing supports and to hang on tree branches. Within true mammals, aerial locomotion first occurs in volaticotherian eutriconodonts . A fossil Volaticotherium has an exquisitely preserved furry patagium with delicate wrinkles and that is very extensive, "sandwiching"

9153-517: The low-slung stem mammals have given rise to the more erect therapsids, who in their turn have given rise to the mammals. In traditional vertebrate classification, the stem mammals and therapsids were both considered orders of the subclass Synapsida. In phylogenetic nomenclature , the terms are used somewhat differently, as the daughter clades are included. Most papers published during the 21st century have treated "Pelycosaur" as an informal grouping of primitive members. Therapsida has remained in use as

9266-452: The lower jaw of modern and prehistoric reptiles consists of a conglomeration of smaller bones (including the dentary, articular , and others). As they evolved in synapsids, these jaw bones were reduced in size and either lost or, in the case of the articular, gradually moved into the ear, forming one of the middle ear bones: while modern mammals possess the malleus , incus and stapes , basal synapsids (like all other tetrapods) possess only

9379-497: The main lower jaw bone, the dentary, replaced the adjacent bones. Thus, the lower jaw gradually became just one large bone, with several of the smaller jaw bones migrating into the inner ear and allowing sophisticated hearing. Whether through climate change, vegetation change, ecological competition, or a combination of factors, most of the remaining large cynodonts (belonging to the Traversodontidae ) and dicynodonts (of

9492-542: The meaning of niche as a recess in a wall for a statue, which itself is probably derived from the Middle French word nicher , meaning to nest . The term was coined by the naturalist Roswell Hill Johnson but Joseph Grinnell was probably the first to use it in a research program in 1917, in his paper "The niche relationships of the California Thrasher". The Grinnellian niche concept embodies

9605-654: The modern cladistic approach to animal relationships, according to which the only valid groups are those that include all of the descendants of a common ancestor: these are known as monophyletic groups, or clades . Additionally, Reptilia (reptiles) has been revised into a monophyletic group and is considered entirely distinct from Synapsida, falling within Sauropsida , the sister group of Synapsida within Amniota. The synapsids are traditionally divided for convenience, into therapsids , an advanced group of synapsids and

9718-483: The name "mammal-like reptiles" (also known as pelycosaurs ). These became the traditional terms for all Paleozoic (early) synapsids. More recent studies have debunked this notion as well, and reptiles are now classified within Sauropsida (sauropsids), the sister group to synapsids, thus making synapsids their own taxonomic group. As a result, the paraphyletic terms "mammal-like reptile" and "pelycosaur" are seen as outdated and disfavored in technical literature, and

9831-475: The narrow extent of focus, data sets characterizing Eltonian niches typically are in the form of detailed field studies of specific individual phenomena, as the dynamics of this class of niche are difficult to measure at a broad geographic scale. However, the Eltonian niche may be useful in the explanation of a species' endurance of global change. Because adjustments in biotic interactions inevitably change abiotic factors, Eltonian niches can be useful in describing

9944-626: The only synapsids to survive beyond the Triassic, and mammals are the only synapsid lineage that have survived past the Jurassic , having lived mostly nocturnally to avoid competition with dinosaurs. After the Cretaceous-Paleogene extinction wiped out all non-avian dinosaurs and pterosaurs, synapsids (as mammals) rose to dominance once again during the Cenozoic . At the turn of the 20th century, synapsids were thought to be one of

10057-444: The other closely related species within the same broad taxonomic class, but there are exceptions. A premier example of a non-standard niche filling species is the flightless, ground-dwelling kiwi bird of New Zealand, which feeds on worms and other ground creatures, and lives its life in a mammal-like niche. Island biogeography can help explain island species and associated unfilled niches. The ecological meaning of niche comes from

10170-402: The other to extinction. This rule also states that two species cannot occupy the same exact niche in a habitat and coexist together, at least in a stable manner. When two species differentiate their niches, they tend to compete less strongly, and are thus more likely to coexist. Species can differentiate their niches in many ways, such as by consuming different foods, or using different areas of

10283-561: The overall response of a species to new environments. The Hutchinsonian niche is an " n-dimensional hypervolume", where the dimensions are environmental conditions and resources , that define the requirements of an individual or a species to practice its way of life, more particularly, for its population to persist. The "hypervolume" defines the multi-dimensional space of resources (e.g., light, nutrients, structure, etc.) available to (and specifically used by) organisms, and "all species other than those under consideration are regarded as part of

10396-441: The paleontologist George Gaylord Simpson to explain how a population could jump from one niche to another that suited it, jump to an 'adaptive zone', made available by virtue of some modification, or possibly a change in the food chain , that made the adaptive zone available to it without a discontinuity in its way of life because the group was 'pre-adapted' to the new ecological opportunity. Hutchinson's "niche" (a description of

10509-410: The past, several species inhabited an area, and all of these species had overlapping fundamental niches. However, through competitive exclusion, the less competitive species were eliminated, leaving only the species that were able to coexist (i.e. the most competitive species whose realized niches did not overlap). Again, this process does not include any evolutionary change of individual species, but it

10622-501: The poorly preserved hands and feet and extending to the base of the tail. Argentoconodon , a close relative, shares a similar femur adapted for flight stresses, indicating a similar lifestyle. Therian mammals would only achieve powered flight and gliding long after these early aeronauts became extinct, with the earliest-known gliding metatherians and bats evolving in the Paleocene . Recently, it has been found that endothermy

10735-454: The presence of niche differentiation (through competition) will be relatively easy. Importantly, there is no evolutionary change of the individual species in this case; rather this is an ecological effect of species Y out-competing species X within the bounds of species Y's fundamental niche. Another way by which niche differentiation can arise is via the previous elimination of species without realized niches. This asserts that at some point in

10848-425: The primary source of nutrition, which is all evidenced by the small body size, the presence of epipubic bones , and limited tooth replacement in advanced cynodonts, as well as in mammaliaforms . Aerial locomotion first began in non-mammalian haramiyidan cynodonts, with Arboroharamiya , Xianshou , Maiopatagium and Vilevolodon bearing exquisitely preserved, fur-covered wing membranes that stretch across

10961-565: The river where the beaver lives. Thus, the beaver affects the biotic and abiotic conditions of other species that live in and near the watershed. In a more subtle case, competitors that consume resources at different rates can lead to cycles in resource density that differ between species. Not only do species grow differently with respect to resource density, but their own population growth can affect resource density over time . Eltonian niches focus on biotic interactions and consumer–resource dynamics (biotic variables) on local scales. Because of

11074-658: The root meristem in that direction, if the interaction is kin. Simonsen discusses how plants accomplish root communication with the addition of beneficial rhizobia and fungal networks and the potential for different genotypes of the kin plants, such as the legume M. Lupulina, and specific strains of nitrogen fixing bacteria and rhizomes can alter relationships between kin and non-kin competition. This means there could be specific subsets of genotypes in kin plants that selects well with specific strains that could outcompete other kin. What might seem like an instance in kin competition could just be different genotypes of organisms at play in

11187-403: The root secretions, also called exudates, plants can make this determination. The communication between plants starts with the secretions from plant roots into the rhizosphere. If another plant that is kin is entering this area the plant will take up exudates. The exudate, being several different compounds, will enter the plants root cell and attach to a receptor for that chemical halting growth of

11300-484: The same resources if each species is limited by different resources, or differently able to capture resources. Different types of phytoplankton can coexist when different species are differently limited by nitrogen, phosphorus, silicon, and light. In the Galapagos Islands , finches with small beaks are more able to consume small seeds, and finches with large beaks are more able to consume large seeds. If

11413-472: The same ways as the incoming species, however examples of this are also numerous. In ecology , niche differentiation (also known as niche segregation , niche separation and niche partitioning ) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive exclusion principle states that if two species with identical niches (ecological roles) compete , then one will inevitably drive

11526-447: The skin), scutes (protective structures of the dermis often with a horny covering), hair or fur, and scale -like structures (often formed from modified hair, as in pangolins and some rodents ). While the skin of reptiles is rather thin, that of mammals has a thick dermal layer. The ancestral skin type of synapsids has been subject to discussion. The type specimen of the oldest known synapsid Asaphestera preserved scales . Among

11639-457: The soil that increase the symbiotic efficiency. Predator partitioning occurs when species are attacked differently by different predators (or natural enemies more generally). For example, trees could differentiate their niche if they are consumed by different species of specialist herbivores , such as herbivorous insects. If a species density declines, so too will the density of its natural enemies, giving it an advantage. Thus, if each species

11752-444: The species, environmental variation..., and interactions between the two—in particular the abilities of some species, especially our own, to modify their environments and alter the range dynamics of many other species." Alteration of an ecological niche by its inhabitants is the topic of niche construction . The majority of species exist in a standard ecological niche, sharing behaviors, adaptations, and functional traits similar to

11865-415: The term stem mammal (or sometimes protomammal or paramammal ) is used instead. Phylogenetically , it is now understood that synapsids comprise an independent branch of the tree of life . The monophyly of Synapsida is not in doubt, and the expressions such as "Synapsida contains the mammals" and "synapsids gave rise to the mammals" both express the same phylogenetic hypothesis. This terminology reflects

11978-434: The therapsids, the pattern had settled to one canine in each upper jaw half. The lower canines developed later. The jaw transition is a good classification tool, as most other fossilized features that make a chronological progression from a reptile-like to a mammalian condition follow the progression of the jaw transition. The mandible , or lower jaw, consists of a single, tooth-bearing bone in mammals (the dentary), whereas

12091-809: The two species interact, how they use their resources, and the type of ecosystem in which they exist, among other factors. In addition, several mathematical models exist to quantify niche breadth, competition, and coexistence (Bastolla et al. 2005). However, regardless of methods used, niches and competition can be distinctly difficult to measure quantitatively, and this makes detection and demonstration of niche differentiation difficult and complex. Over time, two competing species can either coexist, through niche differentiation or other means, or compete until one species becomes locally extinct . Several theories exist for how niche differentiation arises or evolves given these two possible outcomes. Niche differentiation can arise from current competition. For instance, species X has

12204-639: The underbrush and escapes from its predators by shuffling from underbrush to underbrush. Its 'niche' is defined by the felicitous complementing of the thrasher's behavior and physical traits (camouflaging color, short wings, strong legs) with this habitat. Grinnellian niches can be defined by non-interactive (abiotic) variables and environmental conditions on broad scales. Variables of interest in this niche class include average temperature, precipitation, solar radiation, and terrain aspect which have become increasingly accessible across spatial scales. Most literature has focused on Grinnellian niche constructs, often from

12317-442: The underlying processes that affect Lotka-Volterra relationships within an ecosystem. The framework centers around "consumer-resource models" which largely split a given ecosystem into resources (e.g. sunlight or available water in soil) and consumers (e.g. any living thing, including plants and animals), and attempts to define the scope of possible relationships that could exist between the two groups. In contemporary niche theory,

12430-577: The wonderful collections he made in the Karoo Beds of South Africa and the resulting exhibition in the Natural History branch of the British Museum of the remarkable skeleton of Pareiasaurus and numerous other Anomodont reptiles .... - see Alfred Brown Ecological niche A Grinnellian niche is determined by the habitat in which a species lives and its accompanying behavioral adaptations . An Eltonian niche emphasizes that

12543-469: Was a British paleontologist . Seeley was born in London on 18 February 1839, the second son of Richard Hovill Seeley, a goldsmith, and his second wife Mary Govier. When his father was declared bankrupt, Seeley was sent to live with a family of piano makers. Between the ages of eleven and fourteen, he went to a day school and then spent the next two years learning to make pianos. He also attended lectures at

12656-535: Was developed as early as Ophiacodon in the late Carboniferous. The presence of fibrolamellar, a specialised type of bone that can grow quickly while maintaining a stable structure, shows that Ophiacodon would have used its high internal body temperature to fuel a fast growth comparable to modern endotherms. Over the course of synapsid evolution, progenitor taxa at the start of adaptive radiations have tended to be derived carnivores. Synapsid adaptive radiations have generally occurred after extinction events that depleted

12769-544: Was later Lecturer on Geology and Physiology at Dulwich College and Professor of Geology and Mineralogy at King's College London (1896–1905). He died in Kensington, London and was buried in Brookwood Cemetery . He had married in 1872 Eleanora Jane, daughter of William Mitchell of Bath. Their daughter Maude married Arthur Smith Woodward , FRS. Seeley determined that dinosaurs fell into two great groups,

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