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73-627: Eomaia ("dawn mother") is a genus of extinct fossil mammals containing the single species Eomaia scansoria , discovered in rocks that were found in the Yixian Formation , Liaoning Province, China , and dated to the Barremian Age of the Lower Cretaceous about 125  million years ago . The single fossil specimen of this species is 10 centimetres (3.9 in) in length and virtually complete. An estimate of

146-488: A clade termed Australosphenida , a group of mammals from the Jurassic and Cretaceous of Madagascar, South America and Australia, that share tribosphenic molars . However, in a 2022 review of monotreme evolution, it was noted that Teinolophos , the oldest ( Barremian ~ 125 million years ago) and the most primitive monotreme differed substantially from non-monotreme australosphenidans in having five molars as opposed to

219-698: A clade that contains extinct mammals from the Jurassic and Cretaceous of Madagascar, South America, and Australia, but this categorization is disputed and their taxonomy is under debate. All extant species of monotremes are indigenous to Australia and New Guinea , although they were also present during the Late Cretaceous and Paleocene epochs in southern South America, implying that they were also present in Antarctica, though remains have not yet been found there. The name monotreme derives from

292-423: A separate genital tract , whereas most placental mammalian females have separate openings for reproduction (the vagina ), urination (the urethra ), and defecation (the anus ). In monotremes, only semen passes through the penis while urine is excreted through the male's cloaca. The monotreme penis is similar to that of turtles and is covered by a preputial sac. Monotreme eggs are retained for some time within

365-506: A "tribosphenic" form of molars (with the occlusal surface formed by three cusps arranged in a triangle), which is one of the hallmarks of extant mammals. Some recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials, although this hypothesis remains disputed. Tooth loss in modern monotremes might be related to their development of electrolocation . Monotreme jaws are constructed somewhat differently from those of other mammals, and

438-488: A basal eutherian. Metatheria † Sinodelphys † Ambolestes † Acristatherium † Microtherulum † Cokotherium † Juramaia † Eomaia † Prokennalestes † Murtoilestes † Montanalestes † Daulestes † Ukhaatherium † Asioryctes † Kennalestes † Gypsonictops † Cimolestes † Zalambdalestes † Aspanlestes † Protungulatum † Eoungulatum † Leptictis Placentalia Genus The composition of

511-518: A constant body temperature in a variety of circumstances, such as the platypus in icy mountain streams. Early researchers were misled by two factors: firstly, monotremes maintain a lower average temperature than most mammals; secondly, the short-beaked echidna , much easier to study than the reclusive platypus, maintains normal temperature only when active; during cold weather, it conserves energy by "switching off" its temperature regulation. Understanding of this mechanism came when reduced thermal regulation

584-407: A genus is determined by taxonomists . The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful: Moreover, genera should be composed of phylogenetic units of

657-431: A joint between the first metatarsal bone and the medial cuneiform bone in the foot which is offset further back than the joint between the second metatarsal and intermediate cuneiform bones (in metatherians these joints are level with each other), as well as various features of jaws and teeth. However, E. scansoria is not a true placental mammal as it lacks some features that are specific to placentals. These include

730-651: A later homonym of a validly published name is a nomen illegitimum or nom. illeg. ; for a full list refer to the International Code of Nomenclature for algae, fungi, and plants and the work cited above by Hawksworth, 2010. In place of the "valid taxon" in zoology, the nearest equivalent in botany is " correct name " or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split. Prokaryote and virus codes of nomenclature also exist which serve as

803-628: A long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758, and 13 for the bivalve genus Pecten O.F. Müller, 1776. Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example,

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876-437: A much larger study of mammal relationships (including fossil species) was published by O'Leary et al. The study, which examined 4541 anatomical characters of 86 mammal species (including Eomaia scansoria ), found "100% jackknife support that Eomaia falls outside of Eutheria as a stem taxon to Theria", and so could not be considered a placental or a eutherian as previously hypothesized. The results of this study are summarized in

949-409: A reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature". An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for

1022-473: A reptile-like gait, with legs on the sides of, rather than underneath, their bodies. The monotreme leg bears a spur in the ankle region; the spur is not functional in echidnas, but contains a powerful venom in the male platypus. This venom is derived from β-defensins , proteins that are present in mammals that create holes in viral and bacterial pathogens. Some reptile venom is also composed of different types of β-defensins, another trait shared with reptiles. It

1095-475: A substantial reduction at the elevated temperature of 28 °C (82 °F). Monotreme milk contains a highly expressed antibacterial protein not found in other mammals, perhaps to compensate for the more septic manner of milk intake associated with the absence of teats. During the course of evolution the monotremes have lost the gastric glands normally found in mammalian stomachs as an adaptation to their diet. Monotremes synthesize L- ascorbic acid only in

1168-427: A taxon; however, the names published in suppressed works are made unavailable via the relevant Opinion dealing with the work in question. In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name . An invalidly published name is a nomen invalidum or nom. inval. ; a rejected name is a nomen rejiciendum or nom. rej. ;

1241-455: A total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses and prokaryotes, while for others there are compendia with no "official" standing such as Index Fungorum for fungi, Index Nominum Algarum and AlgaeBase for algae, Index Nominum Genericorum and

1314-479: Is a similar pattern of tooth replacement seen in monotremes and marsupials, which originally provided the basis for the competing " Marsupionta " hypothesis in which the divergence between monotremes and marsupials happened later than the divergence between these lineages and the placental mammals. Van Rheede (2005) concluded that the genetic evidence favors the Theria hypothesis, and this hypothesis continues to be

1387-612: Is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants , there are some five thousand such names in use in more than one kingdom. For instance, A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG). The type genus forms

1460-508: Is disputed. Nonetheless, findings on the extinct species Teinolophos confirm that suspended ear bones evolved independently among monotremes and therians. The external opening of the ear still lies at the base of the jaw. The sequencing of the platypus genome has also provided insight into the evolution of a number of monotreme traits, such as venom and electroreception , as well as showing some new unique features, such as monotremes possessing 5 pairs of sex chromosomes and that one of

1533-460: Is somewhat arbitrary. Although all species within a genus are supposed to be "similar", there are no objective criteria for grouping species into genera. There is much debate among zoologists about whether enormous, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance,

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1606-474: Is the type species , and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed. In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with

1679-539: Is the oldest known platypus-like fossil. The durophagous Kollikodon , the pseudotribosphenic Steropodon , and Stirtodon , Dharragarra , Opalios , and Parvopalus occur in the same Cenomanian deposits. Oligo-Miocene fossils of the toothed platypus Obdurodon have also been recovered from Australia, and fossils of a 63 million-year old platypus relative occur in southern Argentina ( Monotrematum ), see fossil monotremes below. The extant platypus genus Ornithorhynchus in also known from Pliocene deposits, and

1752-609: Is the opposite of that hypothesized for Australia's other dominant mammal group, the marsupials , which likely migrated across Antarctica to Australia from South America. In 2024, a prominent assemblage of early monotremes was described from the Cenomanian deposits (100–96.6 Ma) of the Griman Creek Formation in Lightning Ridge, New South Wales. One of these, the fossil jaw fragment of Dharragarra ,

1825-483: Is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups also possess venomous spurs . The key anatomical difference between monotremes and other mammals gives them their name; monotreme means "single opening" in Greek, referring to the single duct (the cloaca ) for their urinary, defecatory, and reproductive systems. Like reptiles, monotremes have a single cloaca. Marsupials have

1898-499: Is thought to provide some insight into the most recent common ancestor of the synapsid lineage leading to mammals and the sauropsid lineage leading to birds and modern reptiles, which are believed to have split about 315 million years ago during the Carboniferous . The presence of vitellogenin genes (a protein necessary for egg yolk formation) is shared with birds; the presence of this symplesiomorphy suggests that

1971-620: The Cretaceous , indicating that monotremes were diversifiying by the early Late Cretaceous. Monotremes have been found in the latest Cretaceous and Paleocene of southern South America, so one hypothesis is that monotremes arose in Australia in the Late Jurassic or Early Cretaceous , and that some migrated across Antarctica to South America , both of which were still united with Australia at that time. This direction of migration

2044-621: The International Code of Zoological Nomenclature ; the earliest such name for any taxon (for example, a genus) should then be selected as the " valid " (i.e., current or accepted) name for the taxon in question. Consequently, there will be more available names than valid names at any point in time; which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to

2117-824: The International Plant Names Index for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus and the Index to Organism Names for zoological names. Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom: The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names;

2190-465: The cynodont therapsids that are closest to mammals. Their function is to stiffen the body during locomotion. This stiffening would be harmful in pregnant placentals, whose abdomens need to expand. The discoverers of Eomaia claimed that, on the basis of 268 characters sampled from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous, Eomaia could be placed at

2263-414: The docodont Castorocauda , discovered in rocks dated to about 164  million years ago , also have traces of fur. Eomaia scansoria possessed several features in common with placental mammals that distinguish them from metatherians , the group that includes modern marsupials. These include an enlarged malleolus ("little hammer") at the bottom of the tibia (the larger of the two shin bones),

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2336-419: The nomenclature codes , which allow each species a single unique name that, for animals (including protists ), plants (also including algae and fungi ) and prokaryotes ( bacteria and archaea ), is Latin and binomial in form; this contrasts with common or vernacular names , which are non-standardized, can be non-unique, and typically also vary by country and language of usage. Except for viruses ,

2409-460: The platypus and the four species of echidnas . Monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts, compared to the more common mammalian types. Although they are different from almost all mammals in that they lay eggs, like all mammals, the female monotremes nurse their young with milk . Monotremes have been considered by some authors to be members of Australosphenida ,

2482-404: The platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms ) . However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym . Since beetles and platypuses are both members of the kingdom Animalia,

2555-457: The Greek words μονός ( monós 'single') and τρῆμα ( trêma 'hole'), referring to the cloaca . Like other mammals, monotremes are endothermic with a high metabolic rate (though not as high as other mammals; see below); have hair on their bodies; produce milk through mammary glands to feed their young; have a single bone in their lower jaw; and have three middle-ear bones. In common with reptiles and marsupials , monotremes lack

2628-531: The X ;chromosomes resembles the Z ;chromosome of birds, suggesting that the two sex chromosomes of marsupial and placental mammals evolved after the split from the monotreme lineage. Additional reconstruction through shared genes in sex chromosomes supports this hypothesis of independent evolution. This feature, along with some other genetic similarities with birds, such as shared genes related to egg-laying,

2701-515: The already eutherian Juramaia is dated to 161–160 million years ago). Teinolophos like modern monotremes displays adaptations to elongation and increased sensory perception in the jaws, related to mechanoreception or electroreception . Molecular clock and fossil dating give a wide range of dates for the split between echidnas and platypuses, with one survey putting the split at 19–48 million years ago, but another putting it at 17–89 million years ago. It has been suggested that both

2774-465: The averages of 35 °C (95 °F) for marsupials and 37 °C (99 °F) for placental mammals . Research suggests this has been a gradual adaptation to the harsh, marginal environmental niches in which the few extant monotreme species have managed to survive, rather than a general characteristic of extinct monotremes. Monotremes may have less developed thermoregulation than other mammals, but recent research shows that they easily maintain

2847-442: The base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis . However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores"). The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of

2920-410: The body weight is 20–25 grams (0.71–0.88 oz). It is exceptionally well-preserved for a 125-million-year-old specimen. Although the fossil's skull is squashed flat, its teeth, tiny foot bones, cartilages and even its fur are visible. The Eomaia fossil shows clear traces of hair. However, this is not the earliest clear evidence of hair in the mammalian lineage, as fossils of Volaticotherium , and

2993-437: The cladogram below.   Monotremata   Henkelotherium guimarotae   Zhangheotherium quinquecuspidens   Eomaia scansoria   Theria The 2013 study by O'Leary et al . is part of a debate about the age of origin of placental mammals (see discussions. ), and in all trees published in that paper Eomaia fell outside Theria (i.e., debates about the findings of O'Leary et al. have not centered on

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3066-520: The common ancestor of monotremes, marsupials, and placental mammals was oviparous , and that this trait was retained in monotremes but lost in all other extant mammal groups. DNA analyses suggest that although this trait is shared and is synapomorphic with birds, platypuses are still mammals and that the common ancestor of extant mammals lactated. The monotremes also have extra bones in the shoulder girdle , including an interclavicle and coracoid , which are not found in other mammals. Monotremes retain

3139-542: The connective structure ( corpus callosum ) which in placental mammals is the primary communication route between the right and left brain hemispheres. The anterior commissure does provide an alternate communication route between the two hemispheres, though, and in monotremes and marsupials it carries all the commissural fibers arising from the neocortex , whereas in placental mammals the anterior commissure carries only some of these fibers. Extant monotremes lack teeth as adults. Fossil forms and modern platypus young have

3212-503: The divergence of the monotreme lineage from the Metatheria ( marsupial ) and Eutheria ( placental ) lineages happened prior to the divergence between marsupials and placental mammals, and this explains why monotremes retain a number of primitive traits presumed to have been present in the synapsid ancestors of later mammals, such as egg-laying. Most morphological evidence supports the Theria hypothesis, but one possible exception

3285-446: The form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as " Canis Linnaeus, 1758" (zoological usage), while Hibiscus , also first established by Linnaeus but in 1753, is simply " Hibiscus L." (botanical usage). Each genus should have a designated type , although in practice there is a backlog of older names without one. In zoology, this

3358-737: The generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, Canis lupus lupus for the Eurasian wolf subspecies, or as a botanical example, Hibiscus arnottianus ssp. immaculatus . Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics . The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example,

3431-424: The jaw opening muscle is different. As in all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in non-mammal cynodonts and other premammalian synapsids ; this feature, too, is now claimed to have evolved independently in monotremes and therians , although, as with the analogous evolution of the tribosphenic molar, this hypothesis

3504-461: The kidneys. Both the platypus and echidna species have spurs on their hind limbs. The echidna spurs are vestigial and have no known function, while the platypus spurs contain venom. Molecular data show that the main component of platypus venom emerged before the divergence of platypus and echidnas, suggesting that the most recent common ancestor of these taxa was also possibly a venomous monotreme. The traditional " Theria hypothesis" states that

3577-633: The largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae). By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species, also including genus names only (no species) for some groups. The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles , which have about 1180 genera,

3650-414: The lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. Monotremata Monotremes ( / ˈ m ɒ n ə t r iː m z / ) are mammals of the order Monotremata . They are the only group of living mammals that lay eggs , rather than bearing live young. The extant monotreme species are

3723-452: The monotremes diverged from the mammalian lineage before the marsupials and placental mammals arose. The only Mesozoic monotremes are Teinolophos (Barremian, 126 Ma), Sundrius and Kryoryctes (Albian, 113–108 Ma), and Dharragarra , Kollikodon , Opalios , Parvopalus , Steropodon , and Stirtodon (all Cenomanian, 100.2–96.6 Ma) from Australian deposits, and Patagorhynchus (Maastrichtian) from Patagonian deposits in

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3796-433: The more widely accepted one. Monotremes are conventionally treated as comprising a single order Monotremata. The entire grouping is also traditionally placed into a subclass Prototheria , which was extended to include several fossil orders, but these are no longer seen as constituting a group allied to monotreme ancestry. A controversial hypothesis now relates the monotremes to a different assemblage of fossil mammals in

3869-403: The most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5–10 species, ~200 have 11–50 species, and only 27 genera have more than 50 species. However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus , contains over 3,000 species. Which species are assigned to a genus

3942-533: The mother and receive nutrients directly from her, generally hatching within 10 days after being laid – much shorter than the incubation period of sauropsid eggs. Much like newborn marsupials (and perhaps all non-placental mammals ), newborn monotremes, called "puggles", are larval- and fetus-like and have relatively well-developed forelimbs that enable them to crawl around. Monotremes lack nipples , so puggles crawl about more frequently than marsupial joeys in search of milk. This difference raises questions about

4015-428: The name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800. However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this

4088-514: The ovum splits into multiple, divisible daughter cells. In contrast, monotreme zygotes, like those of birds and reptiles, undergo meroblastic (partial) division. This means that the cells at the yolk's edge have cytoplasm continuous with that of the egg, allowing the yolk and embryo to exchange waste and nutrients with the surrounding cytoplasm. Monotremes' metabolic rate is remarkably low by mammalian standards. The platypus has an average body temperature of about 31 °C (88 °F) rather than

4161-509: The position of Eomaia ). Meng (2014), who was a co-author on the O'Leary et al. (2013) paper, subsequently referred to Eomaia as a Eutherian but provided no analysis to support this claim. Gheerbrant et al. 2014 mentioned Eomaia in a list of Cretaceous taxa that represented "the primitive eutherian condition" but provided no analytical evidence for this claim; a similar claim was repeated by Sole et al. (2014) again without analytical support. A 2023 cladistical study again recovered Eomaia as

4234-437: The premolar/molar proportion is similar to placentals. Eomaia , like other early mammals and living marsupials, had a narrow pelvic outlet suggesting small undeveloped neonates requiring extensive nurturing. Epipubic bones extend forwards from the pelvis; these are not found in any placental, but are found in all other mammals, including non-placental eutherians, marsupials, monotremes and other Mesozoic mammals as well as in

4307-562: The presence of a malleolus at the bottom of the fibula , the smaller of the two shin bones, a complete mortise and tenon upper ankle joint, where the rearmost bones of the foot fit into a socket formed by the ends of the tibia and fibula, and an atypical ancestral eutherian dental formula of 5.1.5.3 4.1.5.3  × 2 = 54 . Eomaia had five upper and four lower incisors (much more typical for metatherians) and five premolars to three molars. Placental mammals have only up to three incisors on each top and bottom and four premolars to three molars, but

4380-541: The provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. According to "Glossary" section of the zoological Code, suppressed names (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for

4453-420: The root of the eutherian "family tree" along with Murtoilestes and Prokennalestes . This initial classification scheme is summarized below.   Sinodelphys szalayi   Cainozoic metatheria   Juramaia sinensis   Montanalestes keeblerorum   Murtoilestes abramovi   Eomaia scansoria   Prokennalestes trofimovi  Cainozoic placentalia In 2013,

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4526-470: The same kind as other (analogous) genera. The term "genus" comes from Latin genus , a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl Linnaeus popularized its use in his 1753 Species Plantarum , but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". The scientific name (or

4599-408: The scientific epithet) of a genus is also called the generic name ; in modern style guides and science, it is always capitalised. It plays a fundamental role in binomial nomenclature , the system of naming organisms , where it is combined with the scientific name of a species : see Botanical name and Specific name (zoology) . The rules for the scientific names of organisms are laid down in

4672-478: The short-beaked and long-beaked echidna species are derived from a platypus-like ancestor. The precise relationships among extinct groups of mammals and modern groups such as monotremes are uncertain, but cladistic analyses usually put the last common ancestor (LCA) of placentals and monotremes close to the LCA of placentals and multituberculates , whereas some suggest that the LCA of placentals and multituberculates

4745-497: The specific name particular to the wolf. A botanical example would be Hibiscus arnottianus , a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany . When the generic name is already known from context, it may be shortened to its initial letter, for example, C. lupus in place of Canis lupus . Where species are further subdivided,

4818-412: The standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf 's scientific name is Canis lupus , with Canis ( Latin for 'dog') being the generic name shared by the wolf's close relatives and lupus (Latin for 'wolf') being

4891-432: The supposed developmental restrictions on marsupial forelimbs. Rather than through nipples, monotremes lactate from their mammary glands via openings in their skin. All five extant species show prolonged parental care of their young, with low rates of reproduction and relatively long life-spans. Monotremes are also noteworthy in their zygotic development: Most mammalian zygotes go through holoblastic cleavage , where

4964-403: The taxon is termed a synonym ; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names. A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for

5037-511: The three present in non-monotreme australosphenidians. Aptian and Cenomanian monotremes of the family Kollikodontidae (113–96.6 ma) have four molars. This suggests that the monotremes are likely to be unrelated to the australosphenidan tribosphenids. The time when the monotreme line diverged from other mammalian lines is uncertain, but one survey of genetic studies gives an estimate of about 220 million years ago, while others have posited younger estimates of 163 to 186 million years ago (though

5110-576: The values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes. Within Animalia, the largest phylum is Arthropoda , with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up

5183-429: The virus species " Salmonid herpesvirus 1 ", " Salmonid herpesvirus 2 " and " Salmonid herpesvirus 3 " are all within the genus Salmonivirus ; however, the genus to which the species with the formal names " Everglades virus " and " Ross River virus " are assigned is Alphavirus . As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in

5256-517: Was more recent than the LCA of placentals and monotremes. Ornithorhynchus anatinus Tachyglossus aculeatus Z. bartoni Z. attenboroughi Z. bruijnii Ornithorhynchus anatinus Tachyglossus aculeatus Zaglossus bruijnii The first Mesozoic monotreme to be discovered was the Cenomanian (100–96.6 Ma) Steropodon galmani from Lightning Ridge, New South Wales. Biochemical and anatomical evidence suggests that

5329-487: Was observed in the hyraxes , which are placental mammals . The echidna was originally thought to experience no rapid eye movement sleep . However, a more recent study showed that REM sleep accounted for about 15% of sleep time observed on subjects at an environmental temperature of 25 °C (77 °F). Surveying a range of environmental temperatures, the study observed very little REM at reduced temperatures of 15 °C (59 °F) and 20 °C (68 °F), and also

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