InvertebrateInvertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine), derived from the notochord. This is a grouping including all animals apart from the chordate subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks, annelids, echinoderms and cnidarians. The majority of animal species are invertebrates; one estimate puts the figure at 97%. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata.
Human mitochondrial DNA haplogroupIn human genetics, a human mitochondrial DNA haplogroup is a haplogroup defined by differences in human mitochondrial DNA. Haplogroups are used to represent the major branch points on the mitochondrial phylogenetic tree. Understanding the evolutionary path of the female lineage has helped population geneticists trace the matrilineal inheritance of modern humans back to human origins in Africa and the subsequent spread around the globe. The letter names of the haplogroups (not just mitochondrial DNA haplogroups) run from A to Z.
Arms raceAn arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more states to have superior armed forces, concerning production of weapons, the growth of a military, and the aim of superior military technology. Unlike a sporting race, which constitutes a specific event with winning interpretable as the outcome of a singular project, arms races constitute spiralling systems of on-going and potentially open-ended behavior.
ThylacoleoThylacoleo ("pouch lion") is an extinct genus of carnivorous marsupials that lived in Australia from the late Pliocene to the late Pleistocene (2 million to 46 thousand years ago). Some of these marsupial lions were the largest mammalian predators in Australia of their time, with Thylacoleo carnifex approaching the weight of a lioness. The estimated average weight for the species ranges from . The genus was first published in 1859, erected to describe the type species Thylacoleo carnifex.
MetatheriaMetatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives. There are three extant subclasses of mammals, one being metatherians: monotremes: egg laying mammals like the platypus and the echidna, metatheria: marsupials, which includes three American orders (Didelphimorphia, Paucituberculata and Microbiotheria) and four Australasian orders (Notoryctemorphia, Dasyuromorphia, Peramelemorphia and Diprotodontia), and the eutherians: placental mammals, consisting of four superorders divided into 21 orders.
ExaptationExaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example. Initially they may have evolved for temperature regulation, but later were adapted for flight. When feathers were first used to aid in flight, that was an exaptive use.
CoelacanthCoelacanths (ˈsiːləkænθ ) (order Coelacanthiformes) are an ancient group of lobe-finned fish (Sarcopterygii) in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (which includes amphibians, reptiles, birds and mammals) than to ray-finned fish. Well-represented in both freshwater and marine fossils since the Devonian, they are now represented by only two extant marine species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae), primarily found near the Comoro Islands off the east coast of Africa, and the Indonesian coelacanth (Latimeria menadoensis).
Nuclear arms raceThe nuclear arms race was an arms race competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War. During this same period, in addition to the American and Soviet nuclear stockpiles, other countries developed nuclear weapons, though none engaged in warhead production on nearly the same scale as the two superpowers. The first nuclear weapon was created by the United States of America during the Second World War and was developed to be used against the Axis powers.
TrichromacyTrichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal explanation of trichromacy is that the organism's retina contains three types of color receptors (called cone cells in vertebrates) with different absorption spectra. In actuality the number of such receptor types may be greater than three, since different types may be active at different light intensities.
Carboniferous rainforest collapseThe Carboniferous rainforest collapse (CRC) was a minor extinction event that occurred around 305 million years ago in the Carboniferous period. It altered the vast coal forests that covered the equatorial region of Euramerica (Europe and America). This event may have fragmented the forests into isolated refugia or ecological 'islands', which in turn encouraged dwarfism and, shortly after, extinction of many plant and animal species. Following the event, coal-forming tropical forests continued in large areas of the Earth, but their extent and composition were changed.
