Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates. Included in this definition are the living hagfish and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods; because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. The traditional term pisces is considered a typological, but not a phylogenetic classification; the earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era.
Many fish of the Paleozoic developed external armor. The first fish with jaws appeared in the Silurian period, after which many became formidable marine predators rather than just the prey of arthropods. Most fish are ectothermic, allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish can communicate in their underwater environments through the use of acoustic communication. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another; the production of sounds as a means of communication among fish is most used in the context of feeding, aggression or courtship behaviour. The sounds emitted by fish can vary depending on the stimulus involved, they can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.
Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams to the abyssal and hadal depths of the deepest oceans, although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates. Fish are an important resource for humans worldwide as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean, they are caught by recreational fishers, kept as pets, raised by fishkeepers, exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, as the subjects of art and movies. Fish do not represent a monophyletic group, therefore the "evolution of fish" is not studied as a single event. Early fish from the fossil record are represented by a group of small, armored fish known as ostracoderms. Jawless fish lineages are extinct.
An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils; the diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways; the first ancestors of fish may have kept the larval form into adulthood, although the reverse is the case. Fish are a paraphyletic group: that is, any clade containing all fish contains the tetrapods, which are not fish. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications. Traditional classification divides fish into three extant classes, with extinct forms sometimes classified within the tree, sometimes as their own classes: Class Agnatha Subclass Cyclostomata Subclass Ostracodermi † Class Chondrichthyes Subclass Elasmobranchii Subclass Holocephali Class Placodermi † Class Acanthodii † Class Osteichthyes Subclass Actinopterygii Subclass Sarcopterygii The above scheme is the one most encountered in non-specialist and general works.
Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini Class Pteraspidomorphi † Class Thelodonti † Class Anaspida † Class Petromyzontida or Hyperoartia Petromyzontidae Class Conodonta † Class Cephalaspidomorphi † Galeaspida † Pituriaspida † Osteostraci † Infraphylum Gnathostomata Class Placodermi † Class Chondrichthyes Class Acanthodii † Superclass Osteichthy
Armen Leonovich Takhtajan or Takhtajian, was a Soviet-Armenian botanist, one of the most important figures in 20th century plant evolution and systematics and biogeography. His other interests included morphology of flowering plants and the flora of the Caucasus, he was born in Shusha. He was one of the most influential taxonomists of the latter twentieth century. Takhtajan was born in Shusha, Russian Empire, present-day Azerbaijan on 10 June 1910, to a family of Armenian intellectuals, his grandfather Meliksan Takhtadzhyan Petrovich had been born in Trabzon, Ottoman Empire and was educated in Italy, on the island of San Lazzaro degli Armeni, an Armenian enclave, spoke many languages and worked as a journalist. He died in Paris in 1930, his father, Leon Meliksanovich Takhtadzhyan, was born in Batumi and was educated as an agronomist at Leipzig University. Graduating in 1906, he worked on farms in France and the United Kingdom, made a special study of sheep farming, he became proficient in German, English, Russian and Azerbaijani.
Arriving in Shusha in 1908 a centre of sheep farming in the Caucasus, looking for work, Leon was forced to teach German at the local Realschule attached to the Armenian seminary, due to lack of opportunities in his chosen field. There he met and married Gerseliya Sergeevna Gazarbekyan, Armen Takhtajan's mother, a native of Susha, in 1909; the Takhtajans had three children, Armen and Nora. In 1918 the family were forced to flee to northern Armenia because of the pogroms. Throughout his childhood, Armen showed a keen interest in natural history, travelling with his father. Armen attended school in Tbilisi in nearby Georgia at Unified Labor School number 42. There he came under the influence of one of his teachers, Alexander Konstantinovich Makaev, who had taught agriculture at Tbilisi State University, had produced a dictionary of botanical names in Georgian and Latin. Makaev would take Armen on botanical excursions, teaching him to identify plants from Sosnowski and Grossheim's "Determinants of plant life in the vicinity of Tbilisi".
In 1928 he travelled to Leningrad. There he volunteered at the biology school at Leningrad University and attended lectures by Vladimir Leontyevich Komarov on plant morphology. In 1929 he began his studies in biology at Yerevan State University in Yerevan, which he completed in 1931, he returned to Tbilisi, enrolling in the All-Union Institute of Subtropical Crops. In 1932 after completing his course at Tbilisi he worked for a while as a laboratory assistant at Sukhumi, Georgia, at the subtropical branch of the All-Union Institute of Applied Botany and New Crops, before returning to Yerevan. In Yerevan he took a position as researcher at the Natural History Museum of Armenia, at the Herbarium of the Armenian branch of the Institute of Biology, Soviet Academy of Sciences, began teaching at Yerevan University in 1936, while completing his Master's thesis, he died in Saint Petersburg on November 13, 2009, at the age of 99, in 2009, having just completed his most important work, Flowering Plants.
From 1938-48 he headed a Department at the Yerevan State University, from 1944-48 was director of the Botanical Institute of the Academy of Sciences of the Armenian SSR, Professor of the Leningrad State University. Takhtajan was a member of the Russian Academy of Sciences, as well as a foreign associate of the U. S. National Academy of Sciences since 1971, he was the academician of the Academy of Sciences of the Armenian SSR, the president of the Soviet All-Union Botanical Society and the International Association for Plant Taxonomy, member of the Finnish Academy of Science and Literature, the German Academy of Naturalists "Leopoldina" and other scientific societies. While at the Komarov Botanical Institute in Leningrad in 1940, Takhtajan developed his classification scheme for flowering plants, which emphasized phylogenetic relationships between plants, his system did not become known to botanists in the West until after 1950, in the late 1950s he began a correspondence and collaboration with the prominent American botanist Arthur Cronquist, whose plant classification scheme was influenced by his collaboration with Takhtajan and other botanists at Komarov.
He is chiefly famous as the author of works on the origins of flowering plants and paleobotany, developing a new classification system of higher plants. He worked on the "Flora of Armenia" and "Fossil flowering plants of the USSR " books. Takhtajan developed a system of floristic regions. For many years restrictions were placed on his work because of his opposition to the official line on genetics promoted by Lysenko. In 1993 he worked for a while at the New York Botanical Garden; the "Takhtajan system" of flowering plant classification treats flowering plants as a division, with two classes and Liliopsida. These two classes are subdivided into subclasses, superorders and families; the Takhtajan system is similar to the Cronquist system, but with somewhat greater complexity at the higher levels. He favors smaller orders and families, to allow character and evolutionary relationships to be more grasped; the Takhtajan classification system rema
Owls are birds from the order Strigiformes, which includes about 200 species of solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, feathers adapted for silent flight. Exceptions include the gregarious burrowing owl. Owls hunt small mammals and other birds, although a few species specialize in hunting fish, they are found in all regions of the Earth except some remote islands. Owls are divided into two families: the true owl family and the barn-owl family, Tytonidae. Owls possess large, forward-facing eyes and ear-holes, a hawk-like beak, a flat face, a conspicuous circle of feathers, a facial disc, around each eye; the feathers making up this disc can be adjusted to focus sounds from varying distances onto the owls' asymmetrically placed ear cavities. Most birds of prey have eyes on the sides of their heads, but the stereoscopic nature of the owl's forward-facing eyes permits the greater sense of depth perception necessary for low-light hunting.
Although owls have binocular vision, their large eyes are fixed in their sockets—as are those of most other birds—so they must turn their entire heads to change views. As owls are farsighted, they are unable to see anything within a few centimeters of their eyes. Caught prey can be felt by owls with the use of filoplumes—hairlike feathers on the beak and feet that act as "feelers", their far vision in low light, is exceptionally good. Owls can rotate their heads and necks as much as 270°. Owls have 14 neck vertebrae compared to seven in humans, they have adaptations to their circulatory systems, permitting rotation without cutting off blood to the brain: the foramina in their vertebrae through which the vertebral arteries pass are about 10 times the diameter of the artery, instead of about the same size as the artery as in humans. Other anastomoses between the carotid and vertebral arteries support this effect; the smallest owl—weighing as little as 31 g and measuring some 13.5 cm —is the elf owl.
Around the same diminutive length, although heavier, are the lesser known long-whiskered owlet and Tamaulipas pygmy owl. The largest owls are two sized eagle owls; the largest females of these species are 71 cm long, have 54 cm long wings, weigh 4.2 kg. Different species of owls produce different sounds; as noted above, their facial discs help owls to funnel the sound of prey to their ears. In many species, these discs are placed asymmetrically, for better directional location. Owl plumage is cryptic, although several species have facial and head markings, including face masks, ear tufts, brightly coloured irises; these markings are more common in species inhabiting open habitats, are thought to be used in signaling with other owls in low-light conditions. Sexual dimorphism is a physical difference between females of a species. Reverse sexual dimorphism, when females are larger than males, has been observed across multiple owl species; the degree of size dimorphism varies across multiple populations and species, is measured through various traits, such as wing span and body mass.
Overall, female owls tend to be larger than males. The exact explanation for this development in owls is unknown. However, several theories explain the development of sexual dimorphism in owls. One theory suggests that selection has led males to be smaller because it allows them to be efficient foragers; the ability to obtain more food is advantageous during breeding season. In some species, female owls stay at their nest with their eggs while it is the responsibility of the male to bring back food to the nest. However, if food is scarce, the male first feeds himself before feeding the female. Small birds, which are agile, are an important source of food for owls. Male burrowing owls have been observed to have longer wing chords than females, despite being smaller than females. Furthermore, owls have been observed to be the same size as their prey; this has been observed in other predatory birds, which suggests that owls with smaller bodies and long wing chords have been selected for because of the increased agility and speed that allows them to catch their prey.
Another popular theory suggests that females have not been selected to be smaller like male owls because of their sexual roles. In many species, female owls may not leave the nest. Therefore, females may have a larger mass to allow them to go for a longer period of time without starving. For example, one hypothesized sexual role is that larger females are more capable of dismembering prey and feeding it to their young, hence female owls are larger than their male counterparts. A different theory suggests that the size difference between male and females is due to sexual selection: since large females can choose their mate and may violently reject a male's sexual advances, smaller male owls that have the ability to escape unreceptive females are more to have been selected. All owls are carnivorous bi
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
The Primatomorpha are a mirorder of mammals containing two orders: the Dermoptera or colugos and the Primates. The term "Primatomorpha" first appeared in the general scientific literature in 1991 and 1992. Major DNA sequence analyses of predominantly nuclear sequences support the Euarchonta hypothesis, while a major study investigating mitochondrial sequences supports a different tree topology. A study investigating retrotransposon presence/absence data has claimed strong support for Euarchonta; some interpretations of the molecular data link Primates and Dermoptera in a clade known as Primatomorpha, the sister of Scandentia. Primates split from the Dermoptera sister group 79.6 million years ago during the Cretaceous. Other interpretations link the Dermoptera and Scandentia together in a group called Sundatheria as the sister group of the primates; some recent studies place Scandentia as sister of the Glires, invalidating Euarchonta
The Procolophonia are a suborder of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were included as a suborder of the Cotylosauria but are now considered a clade of Parareptilia, they are related to other lizard-like Permian reptiles such as the Millerettidae, Bolosauridae and Lanthanosuchidae, all of which are included under the Anapsida or "Parareptiles". There are two main groups of Procolophonia, the small, lizard-like Procolophonoidea, the Pareiasauroidea, which include the large, armoured Pareiasauridae. According to the traditional classification of Carroll 1988 as well as recent phylogenetic analyses, smaller groups like Rhipaeosauridae and Sclerosauridae are classified with the pareiasaurs and with the procolophonids, respectively; the Nyctiphruretidae was thought to represent the sister taxon of Procolophonia by many studies, however discovered material places it within the group, as the sister taxon of Procolophonoidea. The following cladogram is simplified after the phylogenetic analysis of MacDougall and Reisz and shows the placement of Procolophonia within Parareptilia.
Relationships within bolded terminal clades are not shown. The procolophonians were traditionally thought to be ancestral to the turtles, although experts disagreed over whether turtle ancestors would be found among the Procolophonidae, the Pareiasauridae, or a generic Procolophonian ancestor. Laurin & Reisz, 1995 and Laurin & Gauthier 1996 defined the Procolophonia cladistically as "The most recent common ancestor of pareiasaurs and testudines, all its descendants", listed a number of autapomorphies. However, Rieppel and deBraga 1996 and deBraga & Rieppel, 1997 argued that turtles evolved from Sauropterygians, which would mean that the Parareptilia and Procolophonia constitute wholly extinct clades that are only distantly related to living reptiles; the first genome-wide phylogenetic analysis of turtle relationships was completed by Wang et al.. Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are a sister group of crocodilians and birds.
This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it now possesses an anapsid skull. Notes SourcesCarroll, R. L. Vertebrate Paleontology and Evolution, W. H. Freeman & Co. New York deBraga M. & O. Rieppel. 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society 120: 281-354. Kuhn, O, 1969, part 6 of Handbuch der Palaoherpetologie, Gustav Fischer Verlag, Stuttgart & Portland Laurin, M. & Gauthier, J. A. 1996 Phylogeny and Classification of Amniotes, at the Tree of Life Web Project Laurin, M. & R. R. Reisz. 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113: 165-223. Lee, M. S. Y. 1995. Historical burden in systematics and the interrelationships of'Parareptiles'. Biological Reviews of the Cambridge Philosophical Society 70: 459-547. Lee M. S. Y. 1996. Correlated progression and the origin of turtles. Nature 379: 812-815. Lee, M. S. Y. 1997: Pareiasaur phylogeny and the origin of turtles.
Zoological Journal of the Linnean Society: Vol. 120, pp. 197–280 Rieppel O. & M. deBraga. 1996. Turtles as diapsid reptiles. Nature 384: 453-455. Hallucicrania - Mikko's Phylogeny Archive Basal Anapsids - Palaeos