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The smallest order of the class Amphibia, consisting of the wormlike caecilians. The order Apoda is sometimes called Gymnophiona. Its members are known commonly as caecilians, which are wormlike, legless amphibians with indistinct or even hidden…

An order of Paleozoic diapsid reptiles including the families Petrolacosauridae and Araeoscelidae. Members of these families resemble primitive modern lizards, such as the green iguana, in size and most body proportions, but are distinguished by…

An extinct group of mainly Lower Cambrian marine sponges which, although lacking spicules, possessed an intricate, highly porous skeleton of calcite. It was probably a monophyletic group; that is, all representatives were derived from a single…

An order of extinct, free-sporing plants (cryptogams) that lived during the Late Devonian through Early Mississippian. The order includes the genera Archaeopteris (which has been extensively investigated), Actinoxylon, Actinopodium, Svalbardia,…

A genus of fossil birds in the extinct order Archaeopterygiformes, characterized by flight feathers like those of modern birds. Archaeopteryx is generally accepted as the oldest known fossil bird. It represents a unique snapshot of evolution; most…

The most diverse group of early Tertiary mammals are the archaic ungulates (condylarths). Although closely related, they are not a monophyletic group but, along with various extinct and extant mammals, form the taxon Ungulata (Fig. 1). They are…

The establishment of the temporal sequence of prehistoric events. An event can be defined as a duration of time during which certain features came together to form a set, for example, when certain materials were formed into an object (manufacturing…

A diversified group of diapsid reptiles, comprising dinosaurs (and their descendants, birds), crocodylians, pterosaurs (flying reptiles), and various forms closely related to these groups. In the past, the primitive archosaurs from the Triassic…

A heavily armored mammal in the order Cingulata. The order Cingulata (formerly Edentata or Xenarthra) comprises the armadillos, which are divided into two extant families: Chlamyphoridae and Dasypodidae. These creatures are characterized by bony…

The largest phylum in the animal kingdom, including the well-known insects, spiders, ticks, and crustaceans, as well as many smaller, less well-known groups. Members of the phylum Arthropoda, that is, arthropods, are the dominant metazoans…

The only surviving subclass of the echinoderm class Crinoidea. The Articulata include all living members of the echinoderm class Crinoidea and are generally regarded as the post-Paleozoic crinoids. Crinoids are exclusively marine organisms, as are…

An order comprising the even-toed ungulates (hoofed mammals). There are two main radiations: the predominantly omnivorous Bunodontia, including suoids (such as pigs, peccaries, and hippos); and the more herbivorous Selenodontia, including camels and…

A small order of specialized holostean fishes which are first recorded from Middle Jurassic deposits of Europe. Later records indicate that they were a very successful group in terms of geographic range, and probably had a worldwide distribution in…

A relatively small order of extinct South American ungulates in the infraclass Eutheria, known from the late Paleocene to the late Miocene. Members of the order Astrapotheria are customarily divided into two suborders: the late Paleocene–Eocene…

Any member of an adaptively diverse group of extinct hominin species that inhabited Africa between approximately 4.2 million years ago (MYA) and 1.2 MYA. The term australopith is used in preference to the term australopithecine, which is sometimes…

A mathematical model of computing. The versatility of modern computers and their applications to the study of complex and dynamic systems, such as financial markets, cellular growth, and communication networks, raise questions about the ultimate…

The use of computers to automate decision tasks. A decision task is any task requiring the generation or selection of options. There is an increasing demand for autonomous systems that can perform various complex tasks without human control or…

The automatic control of the intermediate frequency in radio, television, or radar receivers, to correct for variations of the frequency of the transmitted carrier or the local oscillator in the receiver. For many reasons the frequency of the…

The automatic maintenance of a nearly constant output signal level of an amplifier circuit in the presence of a variable input signal level by adjusting its gain in inverse proportion to the input signal level. Automatic gain control (AGC) is also…

The class of animals consisting of the birds. Birds (Fig. 1) are vertebrate animals comprising the class Aves. (In some classification schemes, the term Neornithes may also be used when referring to modern birds.) Primarily adapted for flying, the…

The ongoing lower level of species extinction intensity occurring between episodes of mass extinctions. Extinction is a normal part of the history of life. Out of every 100 species that have ever lived on Earth, 99 are no longer in existence.…

An elasmobranch subdivision of cartilaginous fishes known collectively as the rays, skates, or batoids. Batoidea is one of the two subdivisions of the subclass Elasmobranchii (class Chondrichthyes) and consists of 4 extant orders, 17–20 families,…

An order of extinct 10-armed cephalopod mollusks with an internal shell. The order Belemnitida belongs to the subclass Coleoidea in the class Cephalopoda (phylum Mollusca). Constituent members, which are all extinct, are known as belemnites (Fig. 1)…

The collection, storage, and management of huge amounts of digital information. Databases falling into the realm of big data often begin in the hundreds of terabytes but can range up to petabytes (1015) or greater in size.The main characteristics…

Technologies that employ a distinctive, measurable biological or behavioral characteristic that can reliably distinguish one individual from another (biometric) for authentication, identification, and verification of individuals. Biometric…