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A mammal is a vertebrate animal of the class Mammalia. Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 29 orders.
Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of the defining features of marsupials is their unique reproductive strategy, where the young are born in a relatively undeveloped state and then nurtured within a pouch on their mother's abdomen.
Chymosin or rennin is a protease found in rennet. It is an aspartic endopeptidase belonging to MEROPS A1 family. It is produced by newborn ruminant animals in the lining of the abomasum to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption. It is widely used in the production of cheese.
The gastrointestinal tract is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as faeces. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.
Macropodidae is a family of marsupials that includes kangaroos, wallabies, tree-kangaroos, wallaroos, pademelons, quokkas, and several other groups. These genera are allied to the suborder Macropodiformes, containing other macropods, and are native to the Australian continent, New Guinea and nearby islands.
Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again".
The hoatzin or hoactzin is a species of tropical bird found in swamps, riparian forests, and mangroves of the Amazon and the Orinoco basins in South America. It is the only extant species in the genus Opisthocomus which is the only extant genus in the Opisthocomidae family under the order of Opisthocomiformes. Despite being the subject of intense debate by specialists, the taxonomic position of this family is still far from clear.
Trichromacy or trichromatism is the possession of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats.
A cloaca, pl.: cloacae, is the rear orifice that serves as the only opening for the digestive, reproductive, and urinary tracts of many vertebrate animals. All amphibians, reptiles, birds, and a few mammals have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have two or three separate orifices for evacuation and reproduction. Excretory openings with analogous purpose in some invertebrates are also sometimes called cloacae. Mating through the cloaca is called cloacal copulation and cloacal kissing.
A monogastric organism has a simple single-chambered stomach. Examples of monogastric omnivores include humans, pigs, hamsters and rats. Furthermore, there are monogastric carnivores such as cats. A monogastric organism is comparable to ruminant organisms, such as cattle, goats, or sheep. Herbivores with monogastric digestion can digest cellulose in their diets by way of symbiotic gut bacteria. However, their ability to extract energy from cellulose digestion is less efficient than in ruminants.
The Colobinae or leaf-eating monkeys are a subfamily of the Old World monkey family that includes 61 species in 11 genera, including the black-and-white colobus, the large-nosed proboscis monkey, and the gray langurs. Some classifications split the colobine monkeys into two tribes, while others split them into three groups. Both classifications put the three African genera Colobus, Piliocolobus, and Procolobus in one group; these genera are distinct in that they have stub thumbs. The various Asian genera are placed into another one or two groups. Analysis of mtDNA confirms the Asian species form two distinct groups, one of langurs and the other of the "odd-nosed" species, but are inconsistent as to the relationships of the gray langurs; some studies suggest that the gray langurs are not closely related to either of these groups, while others place them firmly within the langur group.
The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants. The omasum comes after the rumen and reticulum and before the abomasum. Different ruminants have different omasum structures and function based on the food that they eat and how they developed through evolution.
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.
Pseudoruminant is a classification of animals based on their digestive tract differing from the ruminants. Hippopotami and camels are ungulate mammals with a three-chambered stomach while equids and rhinoceroses are monogastric herbivores.
A penis is a male sex organ that is used to inseminate female or hermaphrodite animals during copulation. Such organs occur in both vertebrates and invertebrates, but not in all male animals.
In most terrestrial mammals, the scrotum or scrotal sac is a part of the external male genitalia located at the base of the penis. It consists of a sac of skin containing the external spermatic fascia, testicles, epididymides, and vasa deferentia. The scrotum will usually tighten when exposed to cold temperatures.
Monotremes are mammals of the order Monotremata. They are the only known group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are 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.
Hindgut fermentation is a digestive process seen in monogastric herbivores. Cellulose is digested with the aid of symbiotic microbes including bacteria, archaea, and eukaryotes. The microbial fermentation occurs in the digestive organs that follow the small intestine: the cecum and large intestine. Examples of hindgut fermenters include proboscideans and large odd-toed ungulates such as horses and rhinos, as well as small animals such as rodents, rabbits and koalas. In contrast, foregut fermentation is the form of cellulose digestion seen in ruminants such as cattle which have a four-chambered stomach, as well as in sloths, macropodids, some monkeys, and one bird, the hoatzin.
The Jarman–Bell principle is a concept in ecology that the food quality of a herbivore's intake decreases as the size of the herbivore increases, but the amount of such food increases to counteract the low quality foods. It operates by observing the allometric properties of herbivores. The principle was coined by P.J Jarman (1968.) and R.H.V Bell (1971).
References
- ↑ Dehority, Burk A. (1997), Mackie, Roderick I.; White, Bryan A. (eds.), "Foregut Fermentation", Gastrointestinal Microbiology: Volume 1 Gastrointestinal Ecosystems and Fermentations, Boston, MA: Springer US, pp. 39–83, doi:10.1007/978-1-4615-4111-0_3, ISBN 978-1-4615-4111-0 , retrieved 2024-09-15
- ↑ Munn, Adam J.; Snelling, Edward P.; Taggart, David A.; Clauss, Marcus (2022). "Scaling at different ontogenetic stages: Gastrointestinal tract contents of a marsupial foregut fermenter, the western grey kangaroo Macropus fuliginosus melanops". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 264. Elsevier BV: 111100. doi: 10.1016/j.cbpa.2021.111100 . hdl: 2263/82855 . ISSN 1095-6433.
- ↑ "Foregut fermentation in mammals". Map of Life. 2010-07-22. Retrieved 2010-11-11.
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