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Topic Review

Tetrapods (/ˈtɛtrəˌpɒdz/; from grc τετρα- (tetra-) 'four', and πούς (poús) 'foot') are four-limbed vertebrate animals constituting the superclass Tetrapoda (/tɛˈtrɒpədə/). It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including mammals). Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned (sarcopterygian) fish around 390 million years ago in the middle Devonian period; their forms were transitional between lobe-finned fishes and the four-limbed tetrapods. Limbed vertebrates (tetrapods in the broad sense of the word) are first known from Middle Devonian trackways, and body fossils became common near the end of the Late Devonian but these were all aquatic. The first crown-tetrapods (last common ancestors of extant tetrapods capable of terrestrial locomotion) appeared by the very early Carboniferous, 350 million years ago. The specific aquatic ancestors of the tetrapods and the process by which they colonized Earth's land after emerging from water remains unclear. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors. These include the structure of the head for feeding and breathing, limb girdles and digits for locomotion, eyes for seeing, ears for hearing, and the heart and lungs for gas circulation and exchange outside water. The first tetrapods (stem) or "fishapods" were primarily aquatic. Modern amphibians, which evolved from earlier groups, are generally semiaquatic; the first stage of their lives is as fish-like tadpoles, and later stages are partly terrestrial and partly aquatic. However, most tetrapod species today are amniotes, most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous. The key innovation in amniotes over amphibians is the amnion, which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water. (Some amniotes later evolved internal fertilization, although many aquatic species outside the tetrapod tree had evolved such before the tetrapods appeared, e.g. Materpiscis.) Some tetrapods, such as snakes and caecilians, have lost some or all of their limbs through further speciation and evolution; some have only concealed vestigial bones as a remnant of the limbs of their distant ancestors. Others returned to being amphibious or otherwise living partially or fully aquatic lives, the first during the Carboniferous period, others as recently as the Cenozoic. One group of amniotes diverged into the reptiles, which includes lepidosaurs, dinosaurs (which includes birds), crocodilians, turtles, and extinct relatives; while another group of amniotes diverged into the mammals and their extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, pterosaurs from the archosaurs, and bats from among the mammals.

9.6K
04 Nov 2022

Topic Review

List of the Verified Oldest People

This is a list of the 100 verified oldest people, arranged in descending order of each individual's age in years and days. A year typically refers to a calendar year, the time between two dates of the same name. However, years can be of different lengths due to the presence or absence of a leap day within the year, or to the conversion of dates from one calendar to another. The oldest person ever whose age has been verified is Jeanne Calment (1875–1997) of France, who died at the age of 122 years, 164 days. There are six living people on this list, all of whom are women and the oldest of whom is Kane Tanaka of Japan, aged 119 years, 234 days. Since all the people on this list have lived past the age of 110, all of them have been, or still are, supercentenarians.

9.5K
07 Oct 2022

Topic Review

Red algae, or Rhodophyta (/roʊˈdɒfɪtə/, /ˌroʊdəˈfaɪtə/; from grc ῥόδον (rhódon) 'rose', and φυτόν (phutón) 'plant'), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Red algae are abundant in marine habitats but relatively rare in freshwaters. Approximately 5% of red algae species occur in freshwater, environments with greater concentrations found in warmer areas. Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, there are no terrestrial species, which may be due to an evolutionary bottleneck in which the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity. The red algae form a distinct group characterized by having eukaryotic cells without flagella and centrioles, chloroplasts that lack external endoplasmic reticulum and contain unstacked (stroma) thylakoids, and use phycobiliproteins as accessory pigments, which give them their red color. Red algae store sugars as floridean starch, which is a type of starch that consists of highly branched amylopectin without amylose, as food reserves outside their plastids. Most red algae are also multicellular, macroscopic, marine, and reproduce sexually. The red algal life history is typically an alternation of generations that may have three generations rather than two. The coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse (Palmaria palmata) and laver (nori/gim) are a traditional part of European and Asian cuisines and are used to make other products such as agar, carrageenans and other food additives.

8.4K
11 Nov 2022

Topic Review

A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally without tail in Ancient Greek). The oldest fossil "proto-frog" Triadobatrachus is known from the Early Triassic of Madagascar , but molecular clock dating suggests their split from other amphibians may extend further back to the Permian, 265 million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest. Frogs account for around 88% of extant amphibian species. They are also one of the five most diverse vertebrate orders. Warty frog species tend to be called toads, but the distinction between frogs and toads is informal, not from taxonomy or evolutionary history. An adult frog has a stout body, protruding eyes, anteriorly-attached tongue, limbs folded underneath, and no tail (the tail of tailed frogs is an extension of the male cloaca). Frogs have glandular skin, with secretions ranging from distasteful to toxic. Their skin varies in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to show toxicity and ward off predators. Adult frogs live in fresh water and on dry land; some species are adapted for living underground or in trees. Frogs typically lay their eggs in water. The eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. They have highly specialized rasping mouth parts suitable for herbivorous, omnivorous or planktivorous diets. The life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage. Adult frogs generally have a carnivorous diet consisting of small invertebrates, but omnivorous species exist and a few feed on plant matter. Frog skin has a rich microbiome which is important to their health. Frogs are extremely efficient at converting what they eat into body mass. They are an important food source for predators and part of the food web dynamics of many of the world's ecosystems. The skin is semi-permeable, making them susceptible to dehydration, so they either live in moist places or have special adaptations to deal with dry habitats. Frogs produce a wide range of vocalizations, particularly in their breeding season, and exhibit many different kinds of complex behaviors to attract mates, to fend off predators and to generally survive. Frogs are valued as food by humans and also have many cultural roles in literature, symbolism and religion. They are also seen as environmental bellwethers, with declines in frog populations often viewed as early warning signs of environmental damage. Frog populations have declined significantly since the 1950s. More than one third of species are considered to be threatened with extinction and over 120 are believed to have become extinct since the 1980s. The number of malformations among frogs is on the rise and an emerging fungal disease, chytridiomycosis, has spread around the world. Conservation biologists are working to understand the causes of these problems and to resolve them.

8.3K
19 Oct 2022

Topic Review

Evolution of Elephants

Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are an informal grouping within the proboscidean family Elephantidae. Elephantidae is the only surviving family of proboscideans; extinct members include the mastodons. Elephantidae also contains several extinct groups, including the mammoths and straight-tusked elephants. African elephants have larger ears and concave backs, whereas Asian elephants have smaller ears, and convex or level backs. The distinctive features of all elephants include a long proboscis called a trunk, tusks, large ear flaps, massive legs, and tough but sensitive skin. The trunk is used for breathing, bringing food and water to the mouth, and grasping objects. Tusks, which are derived from the incisor teeth, serve both as weapons and as tools for moving objects and digging. The large ear flaps assist in maintaining a constant body temperature as well as in communication. The pillar-like legs carry their great weight. Elephants are scattered throughout sub-Saharan Africa, South Asia, and Southeast Asia and are found in different habitats, including savannahs, forests, deserts, and marshes. They are herbivorous, and they stay near water when it is accessible. They are considered to be keystone species, due to their impact on their environments. Elephants have a fission–fusion society, in which multiple family groups come together to socialise. Females (cows) tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The groups, which do not include bulls, are usually led by the oldest cow, known as the matriarch. Males (bulls) leave their family groups when they reach puberty and may live alone or with other males. Adult bulls mostly interact with family groups when looking for a mate. They enter a state of increased testosterone and aggression known as musth, which helps them gain dominance over other males as well as reproductive success. Calves are the centre of attention in their family groups and rely on their mothers for as long as three years. Elephants can live up to 70 years in the wild. They communicate by touch, sight, smell, and sound; elephants use infrasound, and seismic communication over long distances. Elephant intelligence has been compared with that of primates and cetaceans. They appear to have self-awareness, and appear to show empathy for dying and dead family members. African bush elephants and Asian elephants are listed as endangered and African forest elephants as critically endangered by the International Union for Conservation of Nature (IUCN). One of the biggest threats to elephant populations is the ivory trade, as the animals are poached for their ivory tusks. Other threats to wild elephants include habitat destruction and conflicts with local people. Elephants are used as working animals in Asia. In the past, they were used in war; today, they are often controversially put on display in zoos, or exploited for entertainment in circuses. Elephants are highly recognisable and have been featured in art, folklore, religion, literature, and popular culture.

8.1K
28 Nov 2022

Biography

Eckhart Tolle (/ˈɛkɑːrt ˈtɒlə/ EK-art TOL-ə; German: [ˈɛkhaʁt ˈtɔlə]; born Ulrich Leonard Tölle, February 16, 1948) is a German spiritual teacher and self-help author best known as the author of The Power of Now and A New Earth: Awakening to Your Life's Purpose. After being recommended by Oprah Winfrey, his first book, The Power of Now,[1] reached The New York Times Best Seller l

7.9K
05 Dec 2022

Topic Review

Degeneration Theory

Social degeneration was a widely influential concept at the interface of the social and biological sciences in the 18th and 19th centuries. During the 18th century, scientific thinkers including George Louis Leclerc, comte de Buffon, Johann Friedrich Blumenbach, and Immanuel Kant argued that humans shared a common origin but had degenerated over time due to differences in climate. This theory provided an explanation of where humans came from and why some people appeared different from others. In contrast, degenerationists in the 19th century feared that civilization might be in decline and that the causes of decline lay in biological change. These ideas derived from pre-scientific concepts of heredity ("hereditary taint") with Lamarckian emphasis on biological development through purpose and habit. Degeneration concepts were often associated with authoritarian political attitudes, including militarism and scientific racism, and a preoccupation with eugenics. The theory originated in racial concepts of ethnicity, recorded in the writings of such medical scientists as Johann Blumenbach and Robert Knox. From the 1850s, it became influential in psychiatry through the writings of Bénédict Morel, and in criminology with Cesare Lombroso. By the 1890s, in the work of Max Nordau and others, degeneration became a more general concept in social criticism. It also fed into the ideology of ethnic nationalism, attracting, among others, Maurice Barrès, Charles Maurras and the Action Française. Alexis Carrel, a French Nobel Laureate in Medicine, cited national degeneration as a rationale for a eugenics programme in collaborationist Vichy France. The meaning of degeneration was poorly defined, but can be described as an organism's change from a more complex to a simpler, less differentiated form, and is associated with 19th-century conceptions of biological devolution. In scientific usage, the term was reserved for changes occurring at a histological level – i.e. in body tissues. Although rejected by Charles Darwin, the theory's application to the social sciences was supported by some evolutionary biologists, most notably Ernst Haeckel and Ray Lankester. As the 19th century wore on, the increasing emphasis on degeneration reflected an anxious pessimism about the resilience of European civilization and its possible decline and collapse.

7.7K
21 Oct 2022

Topic Review

An eyelash curler is a hand-operated mechanical device for curling eyelashes for cosmetic purposes. Usually only the upper eyelashes are curled.

7.6K
25 Nov 2022

Topic Review

Dunkleosteus is an extinct genus of large armored, jawed fishes that existed during the Late Devonian period, about 382–358 million years ago. It consists of ten species, some of which are among the largest placoderms to have ever lived: D. terrelli, D. belgicus, D. denisoni, D. marsaisi, D. magnificus, D. missouriensis, D. newberryi, D. amblyodoratus, and D. raveri. The largest and most well known species is D. terrelli, which grew up to 8.79 m (28.8 ft) long and 4 t (4.4 short tons) in weight. Dunkleosteus could quickly open and close its jaw, like modern-day suction feeders, and had a bite force of 6,000 N (612 kgf; 1,349 lbf) at the tip and 7,400 N (755 kgf; 1,664 lbf) at the blade edge. Numerous fossils of the various species have been found in North America, Poland , Belgium, and Morocco.

7.6K
16 Nov 2022

Topic Review

A holobiont is an assemblage of a host and the many other species living in or around it, which together form a discrete ecological unit, though there is controversy over this discreteness. The components of a holobiont are individual species or bionts, while the combined genome of all bionts is the hologenome. The concept of the holobiont was initially defined by Dr. Lynn Margulis in her 1991 book Symbiosis as a Source of Evolutionary Innovation, though the concept has subsequently evolved since the original definition. Holobionts include the host, virome, microbiome, and other members, all of which contribute in some way to the function of the whole. Well-studied holobionts include reef-building corals and humans.

7.2K
14 Oct 2022

Topic Review

The Pinophyta, also known as Coniferophyta or Coniferae, or commonly as conifers, are a division of vascular land plants containing a single extant class, Pinopsida. They are gymnosperms, cone-bearing seed plants. All extant conifers are perennial woody plants with secondary growth. The great majority are trees, though a few are shrubs. Examples include cedars, Douglas firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, redwoods, spruces, and yews. As of 1998, the division Pinophyta was estimated to contain eight families, 68 genera, and 629 living species. Although the total number of species is relatively small, conifers are ecologically important. They are the dominant plants over large areas of land, most notably the taiga of the Northern Hemisphere, but also in similar cool climates in mountains further south. Boreal conifers have many wintertime adaptations. The narrow conical shape of northern conifers, and their downward-drooping limbs, help them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing. While tropical rainforests have more biodiversity and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink. Conifers are of great economic value for softwood lumber and paper production.

7.2K
21 Oct 2022

Topic Review

Tyrannosaurus is a genus of large theropod dinosaur. The species Tyrannosaurus rex (rex meaning "king" in Latin), often called T. rex or colloquially T-Rex, is one of the best represented theropods. Tyrannosaurus lived throughout what is now western North America, on what was then an island continent known as Laramidia. Tyrannosaurus had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the Upper Cretaceous period, 68 to 66 million years ago. It was the last known member of the tyrannosaurids and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event. Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, the forelimbs of Tyrannosaurus were short but unusually powerful for their size, and they had two clawed digits. The most complete specimen measures up to 12.3–12.4 m (40.4–40.7 ft) in length; however, according to most modern estimates, T. rex could grow to lengths of over 12.4 m (40.7 ft), up to 3.66–3.96 m (12–13 ft) tall at the hips, and 8.87 metric tons (9.78 short tons) in body mass. Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it is still among the largest known land predators and is estimated to have exerted the strongest bite force among all terrestrial animals. By far the largest carnivore in its environment, Tyrannosaurus rex was most likely an apex predator, preying upon hadrosaurs, juvenile armored herbivores like ceratopsians and ankylosaurs, and possibly sauropods. Some experts have suggested the dinosaur was primarily a scavenger. The question of whether Tyrannosaurus was an apex predator or a pure scavenger was among the longest debates in paleontology. Most paleontologists today accept that Tyrannosaurus was both an active predator and a scavenger. Specimens of Tyrannosaurus rex include some that are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and biomechanics. The feeding habits, physiology, and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second Tyrannosaurus species, while others maintain Tarbosaurus is a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus. As the archetypal theropod, Tyrannosaurus has been one of the best-known dinosaurs since the early 20th century and has been featured in film, advertising, postal stamps, and many other media.

7.2K
06 Dec 2022

Topic Review

Fruit carving is the art of carving fruit, a very common technique in Europe and Asian countries, and particularly popular in Thailand, China and Japan. There are many fruits that can be used in this process; the most popular one that artists use are watermelons, apples, strawberries, pineapples, and cantaloupes.

7.0K
11 Nov 2022

Topic Review

Cheilitis is a medical condition characterized by inflammation of the lips. The inflammation may include the perioral skin (the skin around the mouth), the vermilion border, or the labial mucosa. The skin and the vermilion border are more commonly involved, as the mucosa is less affected by inflammatory and allergic reactions. Cheilitis is a general term, and there are many recognized types and different causes. According to its onset and course, cheilitis can be either acute or chronic. Most cheilitis is caused by exogenous factors such as dryness (chapping) and acute sun exposure. Allergic tests may identify allergens that cause cheilitis.

7.0K
25 Nov 2022

Biography

Jesse Lee Peterson

Jesse Lee Peterson (born May 22, 1949) is an American conservative pundit, minister, author, and media personality. He is the host of The Jesse Lee Peterson Show—a national radio show which airs on Newsmax TV, and The Fallen State TV web series. He is also president and founder of BOND (Brotherhood Organization of a New Destiny), a religious 501(c)(3) non-profit dedicated to "rebuilding the fa

7.0K
27 Dec 2022

Biography

Sabrina Gonzalez Pasterski

Sabrina Gonzalez Pasterski (born June 3, 1993) is an American theoretical physicist from Chicago who studies high energy physics.[1] She describes herself as "a proud first-generation Cuban-American & Chicago Public Schools alumna."[2] She completed her undergraduate studies at the Massachusetts Institute of Technology (MIT), earned her PhD from Harvard University and is a rising PCTS Postdoctor

7.0K
12 Dec 2022

Topic Review

Dinosaur Behavior

Dinosaur behavior is difficult for paleontologists to study since much of paleontology is dependent solely on the physical remains of ancient life. However, trace fossils and paleopathology can give insight into dinosaur behavior. Interpretations of dinosaur behavior are generally based on the pose of body fossils and their habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches. As such, the current understanding of dinosaur behavior relies on speculation, and will likely remain controversial for the foreseeable future. However, there is general agreement that some behaviors which are common in crocodiles and birds, dinosaurs' closest living relatives, were also common among dinosaurs. Gregarious behavior was common in many dinosaur species. Dinosaurs may have congregated in herds for defense, for migratory purposes, or to provide protection for their young. There is evidence that many types of dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, in a manner similar to modern birds and crocodiles. The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Most dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, in particular, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run, whether diplodocids could create sonic booms via whip-like tail snapping, and whether sauropods could float.

6.9K
31 Oct 2022

Biography

Nikolai Aleksandrovich Kozyrev

Nikolai Alexandrovich Kozyrev (Russian: Никола́й Алекса́ндрович Ко́зырев; 2 September 1908 – 27 February 1983) was a Soviet astronomer/astrophysicist. He was born in St. Petersburg, and by 1928 he had graduated from the Leningrad State University. In 1931 he began working at the Pulkovo Observatory, located to the south of Leningrad. He was considered to be one

6.9K
30 Dec 2022

Biography

Theodor Schwann

Theodor Schwann ([1][2] 7 December 1810 – 11 January 1882) was a Germany physician and physiologist.[3] His most significant contribution to biology is considered to be the extension of cell theory to animals. Other contributions include the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast,[4] and the i

6.8K
18 Nov 2022

Topic Review

Context-Dependent Memory

In psychology, context-dependent memory is the improved recall of specific episodes or information when the context present at encoding and retrieval are the same. In a simpler manner, "when events are represented in memory, contextual information is stored along with memory targets; the context can therefore cue memories containing that contextual information". One particularly common example of context-dependence at work occurs when an individual has lost an item (e.g. lost car keys) in an unknown location. Typically, people try to systematically "retrace their steps" to determine all of the possible places where the item might be located. Based on the role that context plays in determining recall, it is not at all surprising that individuals often quite easily discover the lost item upon returning to the correct context. This concept is heavily related to the encoding specificity principle. This example best describes the concept of context-dependent forgetting. However, the research literature on context-dependent memory describes a number of different types of contextual information that may affect recall such as environmental context-dependent memory, state-dependent learning, cognitive context-dependent memory and mood-congruent memory. Research has also shown that context-dependence may play an important role in numerous situations, such as memory for studied material, or events that have occurred following the consumption of alcohol or other drugs.

6.8K
03 Nov 2022

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