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An extinct amphibian order of small, mostly aquatic tetrapods found in Carboniferous and Permian rocks in North America, Europe, and North Africa. Nectrideans are usually grouped together with microsaurs and aistopods as lepospondyls; all three have…

One of the two recognized superorders of living birds that comprise the subclass Neornithes of the class Aves. The Neognathae are characterized as flying birds with the absence of teeth in both jaws, fully developed wings, keeled bony sternum,…

An order of coleoid cephalopods, characterized by eight appendages (which encircle the mouth), a saclike body, and an internal shell that is much modified or reduced from that of its ancestors. Members of the order Octopoda (subclass Coleoidea,…

Scientists have identified the earliest known fossil of a modern bird. The fossil remains—comprising an almost-complete skull and a few limb bones embedded in rock—were discovered in a limestone quarry in Belgium. Estimated to be approximately 66.7…

One of two constituent clades of Dinosauria (the other being Saurischia). Ornithischian dinosaurs are characterized by the possession of numerous anatomical features, notably the configuration of the pelvis. In ornithischian hips, the pubis bone…

An extinct order of brachiopods that lived in shallow-shelf seas during the Paleozoic. The order Orthida contains the oldest members of the Rhynchonelliformea and is the stem group for all other brachiopods in this subphylum.Orthids are…

The study of chemical processes used by organisms that lived in the geological past. Most information on the nature of life in the geological past comes from the study of fossils; a record of biochemical processes that occurred can be found in the…

The study of biodiversity throughout geologic time, based on analysis of the fossil record of life preserved on Earth. Assessments of present-day biodiversity are conducted in areas as limited as a tree trunk in a tropical rainforest and as…

The study of fossil plants of the geologic past. A paleobotanist is a plant historian who carefully pieces together the geologic history of the plant kingdom. Other organisms, including fungi and various types of microscopic plankton, are also…

An extinct order of the crustacean class Ostracoda. The order Paleocopa, also called Palaeocopida, is divided into nine superfamilies, one of which, Barychilinacea, is only tentatively assigned to the order. A principal feature of the species in the…

Ecology of prehistoric times, extending from about 10,000 to about 3.5 × 109 years ago. Although the principles of paleoecology are the same as those underlying modern ecology, the two fields actually differ greatly. Paleoecology is a historical…

One of the most remarkable mechanisms by which the remains of extinct organisms are preserved in the fossil record. In petrifactions (though chiefly in the case of plants rather than animals) the original shape and topography of the tissues, and…

Concentrations of appreciable numbers of petrified tree trunks exposed at the earth surface, standing upright in the position of growth, lying prostrate, or both. Petrifaction is a form of mineral emplacement or embedding, by which the organic…

An order of mammals comprising the living pangolins and their poorly known fossil predecessors. All living members of the mammalian order Pholidota, that is, the pangolins (also termed scaly anteaters), belong to the family Manidae and are assigned…

Production of a film of material often on a heated surface and in a vacuum. Physical vapor deposition technology is used in a variety of applications. Coatings are produced from a wide range of materials, including metals, alloys, compound, cermets,…

An order of the plant class Pinopsida (Coniferopsida) within the division Pinophyta (Gymnospermae). All members of the Pinales, often termed conifers, are woody plants. They comprise trees or shrubs, and are often the principal trees of the forests…

Carnivorous mammal members of the Pinnipedia, including seals, sea lions, and the walrus. Pinnipeds belong to the clade or suborder Pinnipedia. Taxonomically, pinnipeds are divided into three families—Odobenidae (walrus; Fig. 1), Otariidae (sea…

One of the major divisions of the seed plants. The most familiar and common representatives of the division Pinophyta are the evergreen, cone-bearing trees of the order Pinales (within the class Pinopsida). Members are known colloquially as…

The single class of the division Pinophyta (Gymnospermae). The class Pinopsida contains both living and fossil taxa. The living representatives of the Pinopsida are woody plants; most are trees with a central axis and excurrent branches. Leaves are…

An order of extinct aquatic diapsid reptiles within the infraclass Sauropterygia, common throughout the world during the Jurassic and Cretaceous periods. These large carnivores are characterized by long, paddle-shaped limbs and short, dorsoventrally…

The Pleistocene or Glacial Epoch is less remarkable for radical evolutionary changes in plant life than for repeated shifts of position because of climatic changes and the resulting ice movements. The influence of these changes is known to have…

A group of diapsid reptiles classified within the Archosauromorpha and recorded from Upper Permian to Lower Jurassic deposits around the world (Australia, Antarctica, India, China, Algeria, South Africa, Israel, Europe including Russia, and North…

An extinct order of the class Lycopsida (clubmosses) of the Devonian Period. Most of these clubmosses are poorly preserved and not well understood; the notable exception is the widespread Leclercqia complexa, which has been largely reconstructed…

An order of fossil plants found in Middle and Upper Devonian rocks. The group is related to Sphenophyllales and includes a single family and two monotypic genera. Pseudobornia ursina is known from Bear Island (north of Norway), Alaska, and Germany.…

A group of extinct seed plants characterized by fernlike leaves that produced naked seeds. The discovery of the seed ferns was a major contribution to the study of plant evolution because it demonstrated the existence of a group of vascular plants…

An extinct order of winged reptiles of the Mesozoic Era, constituting the closest major group to Dinosauria and sharing many features with them. The common ancestor of members of the order Pterosauria (pterosaurs) was a small, bipedal, agile…

An extinct order of primitive, mastodonlike, herbivorous, hoofed mammals restricted to the Eocene and Oligocene deposits of South America. There is only one family (Pyrotheriidae) in the order and four genera (Pyrotherium, Propyrotherium,…

A rigid and wave-resistant marine structure that stands above its surroundings. To navigators, a reef is any rocky structure that poses a threat to navigation. Marine biologists and geologists specify that reefs are constructed by organisms that…

A class of vertebrates composed of turtles, lizards, snakes, crocodilians, amphisbaenians, and tuataras, as well as a variety of extinct forms. The members of the vertebrate class Reptilia are tetrapods, meaning that they possess four limbs or are…

An order of lepidosaurian reptiles represented by one extant species, Sphenodon punctatus, commonly known as the tuatara. The reptilian members of the order Rhynchocephalia are referred to as the tuatara (also tuataras) [Fig. 1]. There is one…

The mammalian order consisting of the rodents, often known as the gnawing mammals. Rodentia is the largest mammalian order. It comprises the most diverse group of mammals in the world, consisting of more than 2000 species and totaling more than 40%…

One of the two principal orders of Paleozoic corals, the other being the Tabulata. Rugose corals first appeared in the Middle Ordovician. The small number of known Cambrian corals include at least one species with superficial similarity, but it is…

One of two major monophyletic clades of Dinosauria, the other being Ornithischia. Saurischian dinosaurs take their name (meaning “lizard hipped”) from the structure of their pelvis. In saurischians, the pubis bone points downward and forward from…

An infraclass of Mesozoic reptiles that are, without exception, adapted to the marine environment. The infraclass includes the nothosaurs, plesiosaurs, and placodonts. These reptiles, along with the ichthyosaurs, played a significant role as…

An order of the subclass Hexacorallia (Zoantharia) which comprises the true or stony corals. Members of the order Scleractinia are solitary (Fig. 1a) or colonial anthozoans which attach to a firm substrate. They are profuse in tropical and…

One of two subdivisions of the subclass Elasmobranchii, consisting of nine extant orders and 34 extant families, collectively known as sharks. The other subdivision, Batoidea, includes the sawfishes, guitarfishes, skates, and rays. In the…

An order of the class Lycopsida (club mosses), regarded as more advanced than the extinct Protolepidodendrales because they produce spores of two sizes, but less advanced than the Lepidodendrales and Isoetales because they lack wood and finite…

An order of the class Cephalopoda (subclass Coleoidea) including the cuttlefishes (Sepia), the bobtail squids (Sepiola), and the ram's-horn squid (Spirula). The group is characterized by an internal shell that is calcareous and broad with closely…

A class of marine planktonic chromists. Their skeletons are composed of hollow, siliceous rods and resemble those of the Radiolaria, with which they have been grouped. They are usually subpyramidal or hemispherical in shape, delicately filigreed,…

An order of herbivorous aquatic placental mammals, commonly known as sea cows. The order Sirenia includes the living manatees (Fig. 1) and dugongs, as well as the exterminated Steller's sea cow (which was hunted to extinction by humans in the late…

A genus of extinct calcareous red algae (Rhodophyta). The extinct algal members of the genus Solenopora (family Solenoporaceae, order Corallinales, division Rhodophyta) are characterized by encrusting, rounded, nodular growth forms ranging in size…

The name originally given by Louis Agassiz in 1840 to a natural (monophyletic) group of echinoids (sea urchins) containing the heart urchins. Members of the order Spatangoida (spatangoids) constitute one of the most diverse sea urchin groups, with…

An extinct group of fossil organisms generally referred to as the Mesozoic stromatoporoids. As originally proposed by Othmar Kühn in 1927, the order included the Mesozoic stromatoporoids (Sphaeractiniidae), the heterastridiids (a group of obscure…

An extinct order of articulate land plants, common during Late Pennsylvanian and Early Permian times. They are typified by Sphenophyllum (see illustration), a small, branching plant, probably of trailing habit. The long, jointed stems rarely…

One of the major divisions (formerly known as Equisetophyta) of vascular plants that includes both living and fossil representatives. The three principal orders are Pseudoborniales (Devonian), Sphenophyllales (Devonian-Triassic), and Equisetales…

Overwhelming fossil evidence of dinosaurs indicates that these reptiles inhabited terrestrial environments and were initially bipedal (two-footed). Then, as dinosaurs evolved, some became quadrupedal, walking on four legs. Other ancient nondinosaur…

An extinct group of genera of Mesozoic fossils. Informally known as the spongiomorphs, they were established as a family of scleractinian corals by Fritz Frech in 1890 on the basis of specimens from the Zlambach beds of late Triassic age in Austria.…

The dominant order of living reptiles, composed of the lizards, snakes, and amphisbaenians. The order Squamata, whose members are known as squamates, is the largest and most diverse order of reptiles. Squamates first appeared in Jurassic times and…

A class of Bryozoa confined to fully marine water. The Stenolaemata include several thousand species distributed among four orders: Cystoporata, Trepostomata, Cryptostomata, and Cyclostomata (=Tubuliporata). The commonly recognized order Fenestrata…

A Paleozoic (Ordovician–Devonian) order of the class Ophiuroidea, consisting of fossil brittle stars. Stenurida (stenurids) have a double row of plates (ambulacra) that abut across the arm axis either directly opposite one another or slightly…