Citizendia
Your Ad Here

Monotremes[1]
Fossil range: Early Cretaceous - Recent
Short-beaked Echidna
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
(unranked) Australosphenida
Order: Monotremata
C.L. Bonaparte, 1837
Families

†Kollikodontidae
Ornithorhynchidae
Tachyglossidae
†Steropodontidae

Monotremes (from the Greek monos 'single' + trema 'hole', referring to the cloaca) are mammals that lay eggs (Prototheria) instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Short-beaked Echidna ( Tachyglossus aculeatus) also known as the Spiny Anteater because of its diet of Ants and Termites, is one Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The Australosphenida are a Clade of mammals Today living specimens exist only in Australia and New Guinea with only five surviving species but fossils Charles Lucien (Carlo Jules Laurent Bonaparte 2nd Prince of Canino and Musignano ( May 24, 1803 &ndash July 29, 1857) was a French Kollikodon ritchiei is a Fossil Monotreme Species. It is known only from an opalised Dentary fragment with one Premolar Ornithorhynchidae is one of the two extant families in the order Monotremata, and contains the Platypus and its extinct relatives Echidnas (ɨˈkɪdnə also known as spiny anteaters, are four extant Mammal species belonging to the Tachyglossidae family of the The Steropodontidae was a family of Monotremes that are known from fossils from the Early Cretaceous in Australia. In zoological anatomy a cloaca is the posterior opening that serves as the only such opening for the intestinal and urinary tracts of certain animal species Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Prototheria (ˌproʊtəˈθɪərɪə from Greek prōtos, first + thēr, wild animal is a Taxonomic group or Taxon, to which the order Marsupials are an Infraclass of Mammals characterized by a distinctive pouch (called the marsupium) in which females carry their young through Metatheria is a grouping within the animal class Mammalia First proposed by Thomas Henry Huxley in 1880, it is nearly synonymous with the earlier taxon See also Evolution of mammals Eutheria ("true beast" are a group of Mammals consisting of Placental mammals plus all extinct Mammals See also Evolution of mammals Eutheria ("true beast" are a group of Mammals consisting of Placental mammals plus all extinct Mammals

They are conventionally treated as comprising a single order Monotremata, though a recent classification proposes to divide them into the orders Platypoda (the Platypus along with its fossil relatives) and Tachyglossa (the echidnas). Platypoda is a suborder of the Monotremes it includes three families and a single living species the Platypus. The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. Echidnas (ɨˈkɪdnə also known as spiny anteaters, are four extant Mammal species belonging to the Tachyglossidae family of the Echidnas (ɨˈkɪdnə also known as spiny anteaters, are four extant Mammal species belonging to the Tachyglossidae family of the 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 natural group allied to monotreme ancestry. A controversial hypothesis now relates the monotremes to a different assemblage of fossil mammals in a clade termed Australosphenida. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor The Australosphenida are a Clade of mammals Today living specimens exist only in Australia and New Guinea with only five surviving species but fossils

Monotremes are among the small number of mammalian species known to be capable of electroreception. Electroreception, sometimes written as electroception, is the biological ability to perceive Electrical impulses It is particularly common among aquatic creatures

Contents

General characteristics

Like other mammals, monotremes are warm-blooded 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 Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Hair is a keratinised protein filament that grows through the epidermis from follicles deep within the Dermis. Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. The middle ear is the portion of the ear internal to the Eardrum, and external to the Oval window of the Cochlea.

Monotremes were very poorly understood for many years, and to this day some of the 19th century myths that grew up around them endure. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar It is still sometimes thought, for example, that the monotremes are "inferior" or quasi-reptilian, and that they are a distant ancestor of the "superior" placental mammals. It now seems plain that modern monotremes are the survivors of an early branching of the mammal tree; a later branching is thought to have led to the marsupial and placental groups. Marsupials are an Infraclass of Mammals characterized by a distinctive pouch (called the marsupium) in which females carry their young through See also Evolution of mammals Eutheria ("true beast" are a group of Mammals consisting of Placental mammals plus all extinct Mammals

Similarly, it is still sometimes said that monotremes have less developed internal temperature control mechanisms than other mammals, but more recent research shows that monotremes maintain a constant body temperature in a wide variety of circumstances without difficulty (for example, the Platypus while living in an icy mountain stream). Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different Early researchers were misled by two factors: monotremes maintain a lower average temperature than most mammals (around 32°C [90°F], compared to about 35°C [95°F] for marsupials, and 38°C [100°F] for most placentals); secondly, the Short-beaked Echidna (which is much easier to study than the reclusive Platypus) only maintains normal temperature when it is active: during cold weather, it conserves energy by "switching off" its temperature regulation. The Short-beaked Echidna ( Tachyglossus aculeatus) also known as the Spiny Anteater because of its diet of Ants and Termites, is one Finally, poor thermal regulation has also been observed in the hyraxes, which are placental mammals. A hyrax (from Greek 'shrewmouse' Afrikaans: klipdassie, from Dutch: klipdas 'rockbadger' is any of four Species of fairly

Physiology

A Platypus
A Platypus
A Long-beaked Echidna
A Long-beaked Echidna

The key physiological difference between monotremes and other mammals is the one that gave them their name; Monotreme means 'single opening' in Greek, and comes from the fact that their urinary, defecatory, and reproductive systems all open into a single duct, the cloaca. The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. The long-beaked echidnas make up one of the two genera (Genus Zaglossus) of Echidnas spiny Monotremes that lives in New Guinea In zoological anatomy a cloaca is the posterior opening that serves as the only such opening for the intestinal and urinary tracts of certain animal species This structure is very similar to the one found in reptiles. Monotremes and marsupials have a single cloaca (though marsupials also have a separate genital track) while placental mammal females have separate openings for reproduction, urination and defecation: the vagina, the urethra, and the anus. The vagina (from Latin, literally " Sheath " or " Scabbard " is a fibromuscular tubular tract leading from the Uterus In Anatomy, the urethra (from Greek ουρήθρα - ourethra) is a tube which connects the Urinary bladder to the outside of The anus is an opening at the opposite end of an Animal 's Digestive tract from the Mouth.

Monotremes lay eggs. In most Birds and Reptiles an egg ( Latin ovum) is the Zygote, resulting from Fertilization of the Ovum. However, the egg is retained for some time within the mother, who actively provides the egg with nutrients. Monotremes also lactate, but have no defined nipples, excreting the milk from their mammary glands via openings in their skin. In its most general form a nipple is a Structure from which a fluid emanates Mammary glands are the organs that in Mammals produce Milk for the sustenance of the young All species are long-lived, with low rates of reproduction and relatively prolonged parental care of infants. Infant echidnas are commonly known as puggles; the same term, though not generally accepted, is popularly applied to young platypus as well. [2][3]

Living monotremes lack teeth as adults. Fossil forms and modern platypus young have the "tribosphenic" molars (with the occlusal surface formed by three cusps arranged in a triangle), which are one of the hallmarks of extant mammals. Molars are the rearmost and most complicated kind of Tooth in most Mammals In many mammals they grind food hence the Latin name mola, " Millstone There are numerous commonly used terms of relationship and comparison that refer to different aspects of teeth and are frequently utilized in articles about Dentistry. A cusp is an occlusal or incisal eminence on a tooth Canine teeth otherwise known as cuspids, each possess a single cusp while Premolars However, recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials,[4] although this is not well established. [5] The jaw of monotremes is constructed somewhat differently from those of other mammals, and 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 cynodonts and other pre-mammalian synapsids; however, this feature, too, is now claimed to have evolved independently in monotremes and therians,[6] although, like the analogous evolution of the tribosphenic molar, this is disputed. Cynodonts, or 'dog teeth' are a taxon of Therapsids which includes modern mammals and their extinct close relatives Synapsids ('fused arch' also known as theropsids ('beast face' are a class of Animals that includes Mammals and everything closer to mammals than Theria (ˈθɪərɪə from the Greek θηρίον, wild beast is a subclass of Mammals ref> that give birth to live young without [7][8] The imminent sequencing of the platypus genome should shed light on this and many other questions regarding the evolutionary history of the monotremes. [9]

However, the external opening of the ear still lies at the base of the jaw. The monotremes also have extra bones in the shoulder girdle, including an interclavicle, which are not found in other mammals. Monotremes retain a reptile-like gait, with legs that are on the sides of rather than underneath the body. The monotreme leg bears a spur in the ankle region; the spur is non-functional in echidnas, but contains a powerful venom in the male platypus. The Platypus is one of the few mammals to produce Venom. The male has a pair of spurs on the hind limbs through which it delivers a cocktail of poisons that while excruciatingly

Their metabolic rate is remarkably low by mammalian standards, although the extent to which this is a characteristic of monotremes, as opposed to an adaptation on the part of the small number of surviving species to harsh environmental conditions, is uncertain.

Taxonomy

The only surviving examples of monotremes are all indigenous to Australia and New Guinea, although there is evidence that they were once more widespread. For a topic outline on this subject see List of basic Australia topics. New Guinea, located just north of Australia, is the world's second largest island, having become separated from the Australian mainland when the area now known Fossil and genetic evidence shows that the monotreme line diverged from other mammalian lines about 150 million years ago and that both the short-beaked and long-beaked echidna species are derived from a platypus-like ancestor. The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. Fossils of a jaw fragment 110 million years old were found at Lightning Ridge, New South Wales. Lightning Ridge is a town in north-western New South Wales, Australia, in Walgett Shire, near the southern border of Queensland. These fragments, from species Steropodon galmani, are the oldest known fossils of monotremes. Steropodon galmani was a prehistoric Species of Monotreme, or egg-laying Mammal, that lived during the middle Albian stage Fossils from the genera Kollikodon, Teinolophos, and Obdurodon have also been discovered. Kollikodon ritchiei is a Fossil Monotreme Species. It is known only from an opalised Dentary fragment with one Premolar Teinolophos trusleri was a Prehistoric Species of Monotreme, or egg-laying Mammal. Obdurodon is an extinct Monotreme Genus containing three species In 1991, a fossil tooth of a 61-million-year-old platypus was found in southern Argentina (since named Monotrematum, though it is now considered to be an Obdurodon species). Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. For a topic outline on this subject see List of basic Argentina topics. (See fossil monotremes below. )

Fossil monotremes

Excepting Ornithorhynchus anatinus, all the animals listed in this section are only known from fossils. Ornithorhynchidae is one of the two extant families in the order Monotremata, and contains the Platypus and its extinct relatives The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. The Platypus ( Ornithorhynchus anatinus) is a semi- aquatic Mammal endemic to eastern Australia, including Tasmania. Echidnas (ɨˈkɪdnə also known as spiny anteaters, are four extant Mammal species belonging to the Tachyglossidae family of the The Short-beaked Echidna ( Tachyglossus aculeatus) also known as the Spiny Anteater because of its diet of Ants and Termites, is one The Short-beaked Echidna ( Tachyglossus aculeatus) also known as the Spiny Anteater because of its diet of Ants and Termites, is one The long-beaked echidnas make up one of the two genera (Genus Zaglossus) of Echidnas spiny Monotremes that lives in New Guinea The Western Long-beaked Echidna ( Zaglossus bruijni) is one of the four extant Echidnas and one of three species of Zaglossus that occur in Sir David's Long-beaked Echidna ( Zaglossus attenboroughi) also known as the Attenborough's Long-beaked Echidna or Cyclops Long-beaked Echidna, is one The Eastern Long-beaked Echidna ( Zaglossus bartoni) also known as Barton's Long-beaked Echidna, is one of three species from the genus Zaglossus

Media

An echidna building a defensive burrow on French Island
An echidna building a defensive burrow on French Island

References

  1. ^ Groves, Colin (16 November 2005). French Island National Park is located on French Island in Western Port, Victoria, Australia. Colin Groves is Professor of Biological Anthropology at the Australian National University in Canberra, Australia. Events 534 - A second and final revision of the Codex Justinianus is published Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. in Wilson, D. E. , and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, p. 1-2. ISBN 0-801-88221-4.  
  2. ^ An Echidna Puggle. Fourth Crossing Wildlife. Retrieved on 2007-10-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
  3. ^ Platypus Fact File: Background and Naming. Australian Platypus Conservancy. Retrieved on 2008-03-26. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1026 - Pope John XIX crowns Conrad II as Holy Roman Emperor.
  4. ^ Luo, Z-X; Cifelli, R. L. ; & Kielan-Jaworowska, Z. (2001). "Dual origin of tribosphenic mammals. " 409: 53-57. Nature.  
  5. ^ Weil, A. 2001. Mammalian evolution: Relationships to chew over. Nature 409, 28-31 | doi:10.1038/35051199
  6. ^ Rich, T. H. ; Hopson, J. A. ; Musser, A. M. ; Flannery, T. F. ; & Vickers-Rich, P. (2005). "Independent origins of middle ear bones in monotremes and therians.". Science 307 (5711): 910-914. Science. doi:10.1126/science.1105717. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. 10. 1126/science. 1105717.  
  7. ^ Comment on "Independent Origins of Middle Ear Bones in Monotremes and Therians" (I). Science Magazine. Retrieved on 2007-10-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
  8. ^ Comment on "Independent Origins of Middle Ear Bones in Monotremes and Therians" (II). Science Magazine. Retrieved on 2007-10-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
  9. ^ Platypus (Ornithorhynchus anatinus). Ensembl. Ensembl is a joint scientific project between the European Bioinformatics Institute and the Wellcome Trust Sanger Institute, which was launched in 1999 in response to the imminent Retrieved on 2007-10-21. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg.
General references

External links

Dictionary

monotreme

-noun

  1. (zoology) A mammal that lays eggs and has a single urogenital and digestive orifice. Only the echidnas and platypuses are included in this group.

-adjective

  1. (palynology, of a pollen grain) Having a single trema, or aperture
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic