Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, koalas, opossums and Tasmanian devils; some lesser-known marsupials are the dunnarts and cuscuses. Marsupials represent the clade originating from the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they give birth to undeveloped young that reside in a pouch located on their mothers’ abdomen for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent; the remaining 100 are found in the Americas — in South America, but thirteen in Central America, one in North America, north of Mexico. The word marsupial comes from the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and from the ancient Greek μάρσιππος mársippos, meaning "pouch".
Marsupials are taxonomically identified as members of the mammalian infraclass Marsupialia, first described as a family under the order Pollicata by German zoologist Johann Karl Wilhelm Illiger in his 1811 work Prodromus Systematis Mammalium et Avium. However, James Rennie, author of The Natural History of Monkeys and Lemurs, pointed out that the placement of five different groups of mammals - monkeys, tarsiers, aye-ayes and marsupials - under a single order did not appear to have a strong justification. In 1816, French zoologist George Cuvier classified all marsupials under the order Marsupialia. In 1997, researcher J. A. W. Kirsch and others accorded infraclass rank to Marsupialia. There are two primary divisions: Australian marsupials. Marsupialia is further divided as follows:† - Extinct Superorder Ameridelphia Order Didelphimorphia Family Didelphidae: opossums Order Paucituberculata Family Caenolestidae: shrew opossums Superorder Australidelphia Order Microbiotheria Family Microbiotheriidae: monito del monte Order †Yalkaparidontia Order Dasyuromorphia Family †Thylacinidae: thylacine Family Dasyuridae: antechinuses, dunnarts, Tasmanian devil, relatives Family Myrmecobiidae: numbat Order Notoryctemorphia Family Notoryctidae: marsupial moles Order Peramelemorphia Family Thylacomyidae: bilbies Family †Chaeropodidae: pig-footed bandicoots Family Peramelidae: bandicoots and allies Order Diprotodontia Suborder Vombatiformes Family Vombatidae: wombats Family Phascolarctidae: koalas Family †Diprotodontidae: Giant wombats Family †Palorchestidae: Marsupial tapirs Family †Thylacoleonidae: marsupial lions Suborder Phalangeriformes Family Acrobatidae: feathertail glider and feather-tailed possum Family Burramyidae: pygmy possums Family †Ektopodontidae: sprite possums Family Petauridae: striped possum, Leadbeater's possum, yellow-bellied glider, sugar glider, mahogany glider, squirrel glider Family Phalangeridae: brushtail possums and cuscuses Family Pseudocheiridae: ringtailed possums and relatives Family Tarsipedidae: honey possum Suborder Macropodiformes Family Macropodidae: kangaroos and relatives Family Potoroidae: potoroos, rat kangaroos, bettongs Family Hypsiprymnodontidae: musky rat-kangaroo Comprising over 300 extant species, several attempts have been made to interpret the phylogenetic relationships among the different marsupial orders.
Studies differ on whether Didelphimorphia or Paucituberculata is the sister group to all other marsupials. Though the order Microbiotheria is found in South America, morphological similarities suggest it is related to Australian marsupials. Molecular analyses in 2010 and 2011 identified Microbiotheria as the sister group to all Australian marsupials. However, the relations among the four Australidelphid orders are not as well understood; the cladogram below, depicting the relationships among the various marsupial orders, is based on a 2015 phylogenetic study. DNA evidence supports a South American origin for marsupials, with Australian marsupials arising from a single Gondwanan migration of marsupials from South America to Australia. There are many small arboreal species in each group; the term "opossum" is used to refer to American species, while similar Australian species are properly called "possums". Marsupials have the typical characteristics of mammals—e.g. Mammary glands, three middle ear bones, true hair.
There are, striking differences as well as a number of anatomical features that separate them from Eutherians. In addition to the front pouch, which contains multiple nipples for the protection and sustenance of their young, marsupials have other common structural features. Ossified patellae are absent in most modern marsupials and epipubic bones are present. Marsupials lack a gross communication between the right and left brain hemispheres; the skull has peculiarities in comparison to placental mammals. In general, the skull is small and tight. Holes are located in the front of the orbit; the cheekbone extends further to the rear. The angular extension of the lower jaw is bent toward the center. Another feature is the hard palate which, in contrast to the placental mammals' foramina, always have more openings. The
Placentalia is one of the three extant subdivisions of the class of animals Mammalia. The Placentals are distinguishable from other mammals in that the fetus is carried in the uterus of its mother to a late stage of development, it is somewhat of a misnomer since marsupials nourish their fetuses via a placenta. Placental mammals are anatomically distinguished from other mammals by: a sufficiently wide opening at the bottom of the pelvis to allow the birth of a large baby relative to the size of the mother; the absence of epipubic bones extending forward from the pelvis, which are found in all other mammals. The rearmost bones of the foot fit into a socket formed by the ends of the tibia and fibula, forming a complete mortise and tenon upper ankle joint; the presence of a malleolus at the bottom of the fibula. Analysis of retroposon presence/absence patterns has provided a rapid, unequivocal means for revealing the evolutionary history of organisms: this has resulted in a revision in the classification of placentals.
There are now thought to be three major subdivisions or lineages of placental mammals: Boreoeutheria and Afrotheria, all of which diverged from common ancestors. The orders of placental mammals in the three groups are: Magnorder Afrotheria Superorder Afroinsectiphilia Order Afrosoricida Order Macroscelidea Order Tubulidentata Superorder Paenungulata Order Hyracoidea Mirorder Tethytheria Order Proboscidea Order Sirenia Magnorder Boreoeutheria Superorder Euarchontoglires Grandorder Gliriformes Mirorder Glires Order Lagomorpha Order Rodentia Grandorder Euarchonta Order Scandentia Mirorder Primatomorpha Order Dermoptera Order Primates Superorder Laurasiatheria Order Eulipotyphla Order Chiroptera Order Cetartiodactyla Order Perissodactyla Mirorder Ferae Order Pholidota Order Carnivora Magnorder Xenarthra Order Cingulata Order Pilosa The exact relationships among these three lineages is a subject of debate, three different hypotheses have been proposed with respect to which group is basal or diverged first from other placentals.
These hypotheses are Atlantogenata and Exafroplacentalia. Estimates for the divergence times among these three placental groups range from 105 to 120 million years ago, depending on the type of DNA and varying interpretations of paleogeographic data. Cladogram based on Amrine-Madsen, H. et al. and Asher, R. J. et al. True placental mammals arose from stem-group members of the clade Eutheria, which had existed since at least the Middle Jurassic period, about 170 MYA); these early eutherians were nocturnal insect eaters, with adaptations for life in trees. True placentals may have originated in the Late Cretaceous around 90 MYA, but the earliest undisputed fossils are from the early Paleocene, 66 MYA, following the Cretaceous–Paleogene extinction event; the species Protungulatum donnae was thought to be a stem-ungulate known 1 meter above the Cretaceous-Paleogene boundary in the geological stratum that marks the Cretaceous–Paleogene extinction event and Purgatorius considered a stem-primate, appears no more than 300,000 years after the K-Pg boundary.
The rapid appearance of placentals after the mass extinction at the end of the Cretaceous suggests that the group had originated and undergone an initial diversification in the Late Cretaceous, as suggested by molecular clocks. The lineages leading to Xenarthra and Afrotheria originated around 90 MYA, Boreoeutheria underwent an initial diversification around 70-80 MYA, producing the lineages that would lead to modern primates, insectivores and carnivorans. However, modern members of the placental orders originated in the Paleogene around 66 to 23 MYA, following the Cretaceous–Paleogene extinction event; the evolution of crown orders such modern primates and carnivores appears to be part of an adaptive radiation that took place as mammals evolved to take advantage of ecological niches that were left open when most dinosaurs and other animals disappeared following the Chicxulub asteroid impact. As they occupied new niches, mammals increased in body size, began to take over the large herbivore and large carnivore niches, left open by the decimation of the dinosaurs.
Mammals exploited niches that the dinosaurs had never touched: for example, bats evolved flight and echolocation, allowing them to be effective nocturnal, aerial insectivores.
A hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found through parts of Europe and Africa, in New Zealand by introduction. There are no living species native to the Americas. Hedgehogs share distant ancestry with shrews, with gymnures being the intermediate link, they have changed little over the last 15 million years. Like many of the first mammals, they have adapted to a nocturnal way of life, their spiny protection resembles that of the unrelated porcupines, which are rodents, echidnas, a type of monotreme. The name hedgehog came into use around the year 1450, derived from the Middle English heyghoge, from heyg, because it frequents hedgerows, hoge, from its piglike snout. Other names include urchin and furze-pig. Hedgehogs are recognized by their spines, which are hollow hairs made stiff with keratin, their spines are not poisonous or barbed and unlike the quills of a porcupine, do not detach from their bodies.
However, the immature animal's spines fall out as they are replaced with adult spines. This is called "quilling". Spines can shed when the animal is diseased or under extreme stress. A defense that all species of hedgehogs possess is the ability to roll into a tight ball, causing all of the spines to point outwards; the hedgehog's back contains two large muscles. When the creature is rolled into a ball, the quills on the back protect the tucked face and belly, which are not quilled. Since the effectiveness of this strategy depends on the number of spines, some desert hedgehogs that evolved to carry less weight are more to flee or attack, ramming an intruder with the spines; the various species are prey to different predators: while forest hedgehogs are prey to birds and ferrets, smaller species like the long-eared hedgehog are prey to foxes and mongooses. Hedgehogs are nocturnal, though some species can be active during the day. Hedgehogs sleep for a large portion of the day under bushes, rocks, or most in dens dug in the ground, with varying habits among the species.
All wild hedgehogs can hibernate, though not all do, depending on temperature and abundance of food. Hedgehogs are vocal and communicate through a combination of grunts, snuffles and/or squeals, depending on species. Hedgehogs perform a ritual called anointing; when the animal encounters a new scent, it will lick and bite the source form a scented froth in its mouth and paste it on its spines with its tongue. The purpose of this habit is unknown, but some experts believe anointing camouflages the hedgehog with the new scent of the area and provides a possible poison or source of infection to predators poked by their spines. Anointing is sometimes called anting because of a similar behavior in birds. Like opossums and moles, hedgehogs have some natural immunity against some snake venom through the protein erinacin in the animal's muscular system, although it is available only in small amounts and a viper bite may still be fatal. In addition, hedgehogs are one of four known mammalian groups with mutations that protect against another snake venom, α-neurotoxin.
Pigs, honey badgers and hedgehogs all have mutations in the nicotinic acetylcholine receptor that prevent the snake venom α-neurotoxin from binding, though those mutations developed separately and independently. The olfactory regions have not been studied in the hedgehog. In mammals, the olfactory part of the brain is covered by neopallium; this difficulty is not insurmountable. Tests have suggested. Although traditionally classified in the now abandoned order Insectivora, hedgehogs are omnivorous, they feed on insects, snails and toads, bird eggs, mushrooms, grass roots, berries and watermelons. Berries constitute a major part of an Afghan hedgehog's diet in early spring after hibernation. During hibernation, the body temperature of a hedgehog can decrease to about 2 °C; when the animal awakes from hibernation, the body temperature rises from 2–5 °C back to its normal 30–35 °C body temperature. Depending on the species, the gestation period is 35–58 days; the average litter is 5 -- 6 for smaller ones.
As with many animals, it is not unusual for an adult male hedgehog to kill newborn males. Hedgehogs have a long lifespan for their size. Larger species of hedgehogs live 4–7 years in the wild, smaller species live 2–4 years, compared to a mouse at 2 years and a large rat at 3–5 years. Lack of predators and controlled diet contribute to a longer lifespan in captivity. Hedgehogs are born blind with a protective membrane covering their quills, which dries and shrinks over the next several hours; the quills emerge through the skin after they have been cleaned. Hedgehog bones have been found in the pellets of the European eagle owl. In Britain, the main predator is the badger. European hedgehog populations in the United Kingdom are lower in areas where badgers are numerous, British hedgehog rescue societies will not release hedgehogs into known badger territories. Badgers compete with hedgehogs for food; the most common p
Anatomical terminology is a form of scientific terminology used by anatomists and health professionals such as doctors. Anatomical terminology uses many unique terms and prefixes deriving from Ancient Greek and Latin; these terms can be confusing to those unfamiliar with them, but can be more precise, reducing ambiguity and errors. Since these anatomical terms are not used in everyday conversation, their meanings are less to change, less to be misinterpreted. To illustrate how inexact day-to-day language can be: a scar "above the wrist" could be located on the forearm two or three inches away from the hand or at the base of the hand. By using precise anatomical terminology such ambiguity is eliminated. An international standard for anatomical terminology, Terminologia Anatomica has been created. Anatomical terminology has quite regular morphology, the same prefixes and suffixes are used to add meanings to different roots; the root of a term refers to an organ or tissue. For example, the Latin names of structures such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for "two-headed", brachii as in the brachial region of the arm.
The first word describes what is being spoken about, the second describes it, the third points to location. When describing the position of anatomical structures, structures may be described according to the anatomical landmark they are near; these landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, such as the midclavicular line from the centre of the clavicle. The cephalon or cephalic region refers to the head; this area is further differentiated into the cranium, frons, auris, nasus and mentum. The neck area is called cervical region. Examples of structures named according to this include the frontalis muscle, submental lymph nodes, buccal membrane and orbicularis oculi muscle. Sometimes, unique terminology is used to reduce confusion in different parts of the body. For example, different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals. Here, Rostral refers to proximity to the front of the nose, is used when describing the skull.
Different terminology is used in the arms, in part to reduce ambiguity as to what the "front", "back", "inner" and "outer" surfaces are. For this reason, the terms below are used: Radial referring to the radius bone, seen laterally in the standard anatomical position. Ulnar referring to the ulna bone, medially positioned when in the standard anatomical position. Other terms are used to describe the movement and actions of the hands and feet, other structures such as the eye. International morphological terminology is used by the colleges of medicine and dentistry and other areas of the health sciences, it facilitates communication and exchanges between scientists from different countries of the world and it is used daily in the fields of research and medical care. The international morphological terminology refers to morphological sciences as a biological sciences' branch. In this field, the form and structure are examined as well as the changes or developments in the organism, it is functional.
It covers the gross anatomy and the microscopic of living beings. It involves the anatomy of the adult, it includes comparative anatomy between different species. The vocabulary is extensive and complex, requires a systematic presentation. Within the international field, a group of experts reviews and discusses the morphological terms of the structures of the human body, forming today's Terminology Committee from the International Federation of Associations of Anatomists, it deals with the anatomical and embryologic terminology. In the Latin American field, there are meetings called Iberian Latin American Symposium Terminology, where a group of experts of the Pan American Association of Anatomy that speak Spanish and Portuguese and studies the international morphological terminology; the current international standard for human anatomical terminology is based on the Terminologia Anatomica. It was developed by the Federative Committee on Anatomical Terminology and the International Federation of Associations of Anatomists and was released in 1998.
It supersedes Nomina Anatomica. Terminologia Anatomica contains terminology for about 7500 human gross anatomical structures. For microanatomy, known as histology, a similar standard exists in Terminologia Histologica, for embryology, the study of development, a standard exists in Terminologia Embryologica; these standards specify accepted names that can be used to refer to histological and embryological structures in journal articles and other areas. As of September 2016, two sections of the Terminologia Anatomica, including central nervous system and peripheral nervous system, were merged to form the Terminologia Neuroanatomica; the Terminologia Anatomica has been perceived with a considerable criticism regarding its content including coverage and spelling mistakes and errors. Anatomical terminology is chosen to highlight the relative location of body structures. For instance, an anatomist might describe one band of tissue as "inferior to" another or a physician might describe a tumor as "superficial to" a deeper body structure.
Anatomical terms used to describe location
The cynodonts are therapsids that first appeared in the Late Permian. The group includes modern mammals as well as their extinct close relatives. Nonmammalian cynodonts spread throughout southern Pangea and are represented by fossils from South America, Africa and Antarctica. In the northern continents, fossils have been found in eastern North America as well as in Belgium and northwestern France. Cynodontia is one of the most diverse groups of therapsids. Richard Owen named Cynodontia in 1861. Robert Broom reranked Cynodonia as an infraorder, since retained by others, including Colbert and Kitching, Gauthier et al. and Rubidge and Cristian Sidor. Olson assigned Cynodontia to Theriodonta and Kitching to Theriodontia, Rubridge and Sidor to Eutheriodontia. William King Gregory, Carroll, Gauthier et al. Hopson and Kitching and Botha et al.. Botha et al. seems to have without specifying taxonomic rank. In 2001, James Allen Hopson e.a. defined a clade Cynodontia as the most inclusive group containing Mammalia but excluding Bauria.
Together with the extinct gorgonopsians and the therocephalians, the cynodonts themselves are part of a group of therapsids called theriodonts. The oldest and the most basal cynodont yet found. Other basal cynodonts were a family that includes Procynosuchus and Dvinia. Cynodonts were among the few groups of synapsids that survived the Permian–Triassic extinction event and had a slow recovery after the extinction; the most derived cynodonts are found within the clade Eucynodontia, which contains the members of Mammalia. Representative genera of nonmammalian cynodonts include the large carnivorous cynognathids, the large herbivorous traversodonts, the small mammal-like tritylodontids and ictidosaurs; the presence of respiratory turbinates suggests a rapid metabolism and endothermy. During their evolution, the number of cynodont jaw bones reduced; this move towards a single bone for the mandible paved the way for other bones in the jaw, the articular and angular, to migrate to the cranium, where they function as parts of the mammalian hearing system.
Cynodonts developed a secondary palate in the roof of the mouth. This caused air flow from the nostrils to travel to a position in the back of the mouth instead of directly through it, allowing cynodonts to chew and breathe at the same time; this characteristic is present in all mammals. Early cynodonts have many of the skeletal characteristics of mammals; the teeth were differentiated and the braincase bulged at the back of the head. Outside of some crown-group mammals, all cynodonts laid eggs; the temporal fenestrae were much larger than those of their ancestors, the widening of the zygomatic arch in a more mammal-like skull would have allowed for more robust jaw musculature. They have the secondary palate that other primitive therapsids lacked, except the therocephalians, who were the closest relatives of cynodonts; the dentary was the largest bone in their lower jaw. The cynodonts had some form of warm-blooded metabolism; this has led to many reconstructions of cynodonts as having fur. Being endothermic they may have needed it for thermoregulation, but fossil evidence of their fur has been elusive.
Modern mammals have Harderian glands secreting lipids to coat their fur, but the telltale imprint of this structure is only found from the primitive mammal Morganucodon and onwards. Nonetheless, recent studies on Permian synapsid coprolites show that more basal therapsids had fur, at any rate fur was present in Mammaliaformes such as Castorocauda and Megaconus. Marks in the upper and lower jaw of cynodonts have been interpreted as channels that supplied blood vessels and nerves to whiskers. Whiskers may have evolved in this group. Derived cynodonts developed epipubic bones; these served to strengthen the torso and support abdominal and hindlimb musculature, aiding them in the development of an erect gait, but at the expense of prolonged pregnancy, forcing these animals to give birth to larval young as in modern monotremes and marsupials. Only placentals, Megazostrodon and Erythrotherium, would lose these. A specimen of Kayentatherium does indeed demonstrate that at least tritylodontids had a fundamentally marsupial-like reproductive style, but produced much higher litters at around 38 perinates.
Cynodonts are the only known synapsid lineage to have produced aerial locomotors, with gliding and flying being known in haramiyidans and various mammal groups. Below is a cladogram from Ruta, Botha-Brink and Benton showing one hypothesis of cynodont relationships: Permian–Triassic extinction event Prehistoric mammal Tetrapod Triassic-Jurassic extinction event Hopson, J. A.. W.. "A probainognathian cynodont from South Africa and the phylogeny of non-mammalian cynodonts". Bull. Mus. Comp. Zool. 156: 5–35. Davis, Dwight. "Origin of the Mammalian Feeding Mechanism". Am. Zoologist, 1:229–234. Palaeos cynodonts Phylogeny of Theriodonts and Cynodonts Bennett and Ruben 1986; the Metabolic and Thermoregulatory Status of Therapsids BBC cynodonts
A primate is a eutherian mammal constituting the taxonomic order Primates. Primates arose 85–55 million years ago from small terrestrial mammals, which adapted to living in the trees of tropical forests: many primate characteristics represent adaptations to life in this challenging environment, including large brains, visual acuity, color vision, altered shoulder girdle, dexterous hands. Primates range in size from Madame Berthe's mouse lemur, which weighs 30 g, to the eastern gorilla, weighing over 200 kg. There are 190 -- 448 species of living primates, depending on. New primate species continue to be discovered: over 25 species were described in the first decade of the 2000s, eleven since 2010. Primates are divided into two distinct suborders; the first is the strepsirrhines - lemurs and lorisids. The second is haplorhines - the "dry-nosed" primates - tarsier and ape clades, the last of these including humans. Simians are monkeys and apes, cladistically including: the catarrhines consisting of the Old World monkeys and apes.
Forty million years ago, simians from Africa migrated to South America by drifting on debris, gave rise to the New World monkeys. Twenty five million years ago the remaining Old World simians split into Old World monkeys. Common names for the simians are the baboons, macaques and great apes. Primates have large brains compared to other mammals, as well as an increased reliance on visual acuity at the expense of the sense of smell, the dominant sensory system in most mammals; these features are more developed in monkeys and apes, noticeably less so in lorises and lemurs. Some primates are trichromats, with three independent channels for conveying color information. Except for apes, primates have tails. Most primates have opposable thumbs. Many species are sexually dimorphic. Primates have slower rates of development than other sized mammals, reach maturity and have longer lifespans. Depending on the species, adults may live in solitude, in mated pairs, or in groups of up to hundreds of members; some primates, including gorillas and baboons, are terrestrial rather than arboreal, but all species have adaptations for climbing trees.
Arboreal locomotion techniques used include leaping from tree to tree and swinging between branches of trees. Primates are among the most social of animals, forming pairs or family groups, uni-male harems, multi-male/multi-female groups. Non-human primates have at four types of social systems, many defined by the amount of movement by adolescent females between groups. Most primate species remain at least arboreal: the exceptions are some great apes and humans, who left the trees for the ground and now inhabit every continent. Close interactions between humans and non-human primates can create opportunities for the transmission of zoonotic diseases virus diseases, including herpes, ebola and hepatitis. Thousands of non-human primates are used in research around the world because of their psychological and physiological similarity to humans. About 60% of primate species are threatened with extinction. Common threats include deforestation, forest fragmentation, monkey drives, primate hunting for use in medicines, as pets, for food.
Large-scale tropical forest clearing for agriculture most threatens primates. The English name "primates" is derived from Old French or French primat, from a noun use of Latin primat-, from primus; the name was given by Carl Linnaeus. The relationships among the different groups of primates were not understood until recently, so the used terms are somewhat confused. For example, "ape" has been used either as an alternative for "monkey" or for any tailless human-like primate. Sir Wilfrid Le Gros Clark was one of the primatologists who developed the idea of trends in primate evolution and the methodology of arranging the living members of an order into an "ascending series" leading to humans. Used names for groups of primates such as "prosimians", "monkeys", "lesser apes", "great apes" reflect this methodology. According to our current understanding of the evolutionary history of the primates, several of these groups are paraphyletic: a paraphyletic group is one which does not include all the descendants of the group's common ancestor.
In contrast with Clark's methodology, modern classifications identify only those groupings that are monophyletic. The cladogram below shows one possible classification sequence of the living primates: groups that use common names are shown on the right. All groups with scientific names are monophyletic, the sequence of scientific classification reflects the evolution
Millstones or mill stones are stones used in gristmills, for grinding wheat or other grains. Millstones come in pairs; the base or bedstone is stationary. Above the bedstone is the turning runner stone which does the grinding; the runner stone spins above the stationary bedstone creating the "scissoring" or grinding action of the stones. A runner stone is slightly concave, while the bedstone is convex; this helps to channel the ground flour to the outer edges of the stones. The runner stone is supported by a cross-shaped metal piece fixed to a "mace head" topping the main shaft or spindle leading to the driving mechanism of the mill. Neolithic and Upper Paleolithic people used millstones to grind grains, nuts and other vegetable food products for consumption; these implements are called grinding stones. They used either rotary querns turned by hand; such devices were used to grind pigments and metal ores prior to smelting. In India, grinding stones were used to grind spices; these consist of a stationary stone cylinder upon.
Smaller ones, for household use, were operated by two people. Larger ones, for community or commercial use, used livestock to rotate the upper cylinder; the type of stone most suitable for making millstones is a siliceous rock called burrstone, an open-textured, porous but tough, fine-grained sandstone, or a silicified, fossiliferous limestone. In some sandstones, the cement is calcareous. Millstones used in Britain were of several types: Derbyshire Peak stones of grey Millstone Grit, cut from one piece, used for grinding barley. Derbyshire Peak stones wear and are used to grind animal feed since they leave stone powder in the flour, making it undesirable for human consumption. French burrstones, used for finer grinding. French Burr comes from the Marne Valley in northern France; the millstones are not cut from one piece, but built up from sections of quartz cemented together, backed with plaster and bound with shrink-fit iron bands. Slots in the bands provide attachments for lifting. In southern England the material was imported as pieces of rock, only assembled into complete millstones in local workshops.
It was necessary to balance the completed runner stone with lead weights applied to the lighter side. Composite stones, built up from pieces of emery, were introduced during the nineteenth century. In Europe, a further type of millstone was used; these were uncommon in Britain, but not unknown: Cullen stones, a form of black lava quarried in the Rhine Valley at Mayen near Cologne, Germany. The surface of a millstone is divided by deep grooves called furrows into separate flat areas called lands. Spreading away from the furrows are smaller grooves called feathering or cracking; the grooves help to channel the ground flour out from the stones. The furrows and lands are arranged in repeating patterns called harps. A typical millstone will have eight or ten harps; the pattern of harps is repeated on the face of each stone, when they are laid face to face the patterns mesh in a kind of "scissoring" motion creating the cutting or grinding function of the stones. When in regular use stones need to be dressed periodically, that is, re-cut to keep the cutting surfaces sharp.
Millstones need to be evenly balanced, achieving the correct separation of the stones is crucial to producing good quality flour. The experienced miller will be able to adjust their separation accurately. Grain is fed by gravity from the hopper into the feed-shoe; the shoe is agitated by a shoe handle running against an agitator on the stone spindle, the shaft powering the runner stone. This mechanism regulates the feed of grain to the millstones by making the feed dependent on the speed of the runner stone. From the feed shoe the grain falls through the eye, the central hole, of the runner stone and is taken between the runner and the bed stone to be ground; the flour exits from between the stones from the side. The stone casing prevents the flour from falling on the floor, instead it is taken to the meal spout from where it can be bagged or processed further; the runner stone is supported by a cross-shaped metal piece, on the spindle. The spindle is carried by the tentering gear, a set of beams forming a lever system, or a screw jack, with which the runner stone can be lifted or lowered and the gap between the stones adjusted.
The weight of the runner stone is significant and it is this weight combined with the cutting action from the porous stone and the patterning that causes the milling process. Millstones for some water-powered mills spin at about 125 rpm. In the case of wind-powered mills the turning speed can be irregular. Higher speed means more grain is fed to the stones by the feed-shoe, grain exits the stones more because of their faster turning speed; the miller has to reduce the gap between the stones so more weight of the runner presses down on the grain and the grinding action is increased to prevent the grain being ground too coarsely. It has the added benefit of increasing the load on the mill and so slowing it down. In the reverse case the miller may have to raise the runner stone if the grain is milled too making it unsuitable for baking. In any case the stones should never touch during milling as this would cause them to wear d