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Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. The time necessary to transform resin…

An organism that has had its genetic material manipulated or altered in a laboratory setting through the use of genetic or genomic engineering techniques. Genetically modified organisms (GMOs) are microorganisms, plants, or animals that have been…

A mammalian order containing the egg-laying platypus and echidnas. Members of the order Monotremata (monotremes) are egg-laying mammals belonging to the subclass Prototheria (in some alternative classifications, the monotremes have been assigned to…

An order of placental mammals containing the largest and most powerful living terrestrial mammals—the elephants. Proboscideans once had a wide distribution, reaching every continent except Australia and Antarctica. Although early forms lacked both…

One of the major classes composing the superclass Tetrapoda of the subphylum Vertebrata, and including frogs, toads, salamanders, and caecilians. Amphibians, that is, members of the class Amphibia, are tetrapod vertebrates. Modern amphibians number…

The group of primates most closely related to humans. The primates included in the ape group are the African great apes, the gorillas (Fig. 1) and chimpanzees; the Asian great apes, the orangutans; and the lesser apes from Asia, the gibbons. Humans…

A class of the asterozoan group of the phylum Echinodermata, often known as sea stars or starfish. Members of the class Asteroidea, that is, asteroids, are notable echinoderms with a star-shaped body plan (Fig. 1). Unlike members of their sister…

One of the main extant classes in the phylum Mollusca. Members of the molluscan class Bivalvia (formerly, Pelecypoda) are known commonly as bivalves and include clams, oysters, mussels, and scallops. All bivalves are aquatic, living at all depths of…

An aquatic mammalian order comprising approximately 90 living species of whales, dolphins, and porpoises and their fossil relatives. Like all other mammals, members of the order Cetacea (cetaceans) nurse their young with milk produced by the mother,…

An order of the class Reptilia, including the turtles, terrapins, and tortoises; also termed Testudines. The order Chelonia (often referred to as Testudines) comprises one of the oldest groups of reptiles on Earth. Members of the Chelonia…

An extremely diverse, species-rich group of arthropods that have inhabited marine environments since the beginning of the Cambrian Period. Crustacea is a notable taxon of invertebrates. Common members of the Crustacea, that is, crustaceans, are…

The term (meaning terrible lizards) assigned to a group of certain large, ancient bipedal and quadrupedal reptiles that lived during the Mesozoic Era. The term Dinosauria [from the Greek deinos (fearful or terrible) and sauros (reptile or lizard)]…

The earliest representatives of people anatomically similar to living humans that evolved from more archaic humans approximately 150,000–300,000 years ago. The general process by which early modern humans (Homo sapiens) emerged from late archaic…

One of two extant orders of brittle stars, comprising the basket stars and snake stars, in the class Ophiuroidea (phylum Echinodermata). The order Euryalida currently includes approximately 190 valid species worldwide, which represents a little less…

An extinct Paleozoic group of aquatic arthropods, belonging to the subphylum Chelicerata and class Merostomata and thus related to the living marine xiphosurans (horseshoe crabs) and terrestrial arachnids (spiders, scorpions). Although most…

The death and disappearance of a species. The fossil record shows that extinctions have been occurring throughout the history of life. Mass extinctions refer to the loss of a large number of species representing broad taxonomic, ecologic, and…

An extinct subclass of stalked or creeping Crinoidea which includes some 50 Paleozoic genera, ranging from Ordovician to Permian times. A flexible tegmen was present with open ambulacral grooves. One of the five oral plates served as a madreporite.…

An order of Granuloreticulosia in the class Rhizopodea. Foraminiferans are dominantly marine protozoa (single-celled animals), with a secreted or agglutinated shell, or test, enclosing the continually changing ameboid body that characterizes this…

Extinct members of the order of mammals to which humans belong. All current classifications divide the living primates (order Primates) into two major groups (suborders) [Fig. 1]: the Strepsirhini (Strepsirrhini) or "lower" primates (lemurs,…

The organic remains, traces, or imprint of seeds and fruits. Seeds, ovules containing a fertilized egg and ready to be shed from the plant, are reproductive organs characteristic of both gymnospermous and angiospermous plants. In angiosperms…

An extinct superfamily of marine organisms in the phylum Protozoa, order Foraminiferida. Fusulinaceans first appeared late in the Mississippian Period, and in the succeeding 100,000,000 years evolved into more than 125 genera and 6000 species before…

A large order of birds containing the gallinaceous, or chickenlike, birds. Members of the order Galliformes are found worldwide, although several of the subgroups have a more limited distribution. Part of the superorder Neognathae, the galliforms…

An order of extinct flightless birds known from Paleocene and Eocene deposits in North America, Europe, and Asia. Members of the order Gastornithiformes (gastornithiforms) are believed to have dispersed across the North Atlantic via a land bridge…

The largest and most varied class in the phylum Mollusca, possibly numbering over 74,000 species and commonly known as snails. Mollusca Functional Morphology The shell is in one piece that, in the majority of forms, grows along a turbinate…

A small order of aquatic birds commonly known as the loons. The order Gaviiformes comprises a single living family, the Gaviidae, with five species restricted to the Northern Hemisphere, and a fossil family, the Colymboididae. Aves Phylogeny and…

An order of gymnosperms in the class Ginkgoopsida with only one extant species, Ginkgo biloba (the maidenhair tree). Ginkgo biloba (Fig. 1), also referred to as the ginkgo tree, is native to China. It is cultivated as a shade tree in cities around…

A class of largely extinct gymnosperms. The class Ginkgoopsida contains one order of seed plants: Ginkgoales. Representatives of the Ginkgoales lived predominantly from the Triassic into the Cretaceous, with one species, Ginkgo biloba, persisting to…

A genus of fossil cyanobacteria. The extinct members of the genus Girvanella are characterized by flexuous, tubular filaments of uniform diameter, composed of thick, calcareous walls (see illustration). The external diameters of these cyanobacteria…

A superclass of the subphylum Vertebrata consisting of animals that possess jaws. The superclass Gnathostomata comprises the jawed vertebrates (subphylum Vertebrata, phylum Chordata). In other words, gnathostomes are animals with jaws, involving a…

A group of marine organisms that were common in the early Paleozoic (the Late Cambrian to Early Devonian periods). Graptolites became extinct in the late Paleozoic Era. They were minute animals that built communal skeletons. Each graptolite colony…

A class of predominantly marine, colonial animals belonging to the phylum Bryozoa. Gymnolaemate zooids (individual colony members) are characterized by their short, wide, vaselike or boxlike zooecia (skeletal outer structures) and circular…

A genus of marine, benthic, green algae (division Chlorophyta) belonging to the family Halimedaceae in the order Bryopsidales. Halimeda plants are attached by a holdfast, generally several centimeters high, and consist of calcareous segments…

A marine bryozoan order in the class Stenolaemata. It is recorded from scattered localities in the Ordovician through Permian systems of the Paleozoic Era but is found prominently in Devonian strata. The colonies comprise tubular zooecia that…

An extinct group of Cretaceous toothed birds. All members were foot-propelled, seagoing birds that could reach the size of a modern Emperor penguin. The largest known hesperornithiform reached a maximum length of over 5 ft (1.5 m). All of the known…

One of the evolutionary lineages of gastropods (class Gastropoda), comprising a very heterogeneous group of snails with forms that resemble typical marine snails with external spiraled shells such as sundial shells (family Architectonicidae), sea…

A small, extinct late Paleozoic order of fossil corals known from Europe, North Africa, Asia, North America, and Australia but limited to the Middle Devonian and to the Late Mississippian. They are found in calcareous shales and in limestones. The…

Extinct, armored, jawless vertebrates with a single pair of external gill openings. Heterostraci first appeared in the Ordovician, according to some authorities, and became common in the Silurian and Devonian. Their bony dermal armor consists mainly…

An order of irregular echinoids (sea urchins) of the superorder Atelostomata (class Echinoidea), with a strongly bilaterally symmetrical test. Members of the Holasteroida have a small, oval mouth (lacking buccal notches) that lies close to the…

An extinct order of primitive irregular sea urchins of the class Echinoidea, which retain a functioning jaw apparatus throughout life. Although the periproct opens on the oral surface in the posterior interambulacrum of members of the Holectypoida,…

An unranked group or infraclass of the fish subclass Neopterygii (class Actinopterygii) consisting of several fossil orders and the extant orders, Lepisosteiformes and Amiiformes. Members of the Holostei (holosteans) are descended from the older…

Enigmatic extinct echinoderms whose members are characterized by a flattened body form and the complete lack of pentameral (five-sided radial) symmetry. Previously considered the fifth subphylum of echinoderms, homalozoans (commonly called carpoids)…

A species of fossil human from the Pleistocene representing a specialized side branch in human evolution in Africa and Eurasia. Homo erectus (Fig. 1) was a common, widespread, and long-surviving ancestor of modern humans (H. sapiens). Fossil remains…

An order of Devonian plants considered by some to be related to the sphenophytes. The small dichotomously forked leaves of Hyeniales tend to be borne in whorls. Some leaves bear terminal sporangia, but these appendages are neither aggregated into a…

An order of mammals closely related to elephants. Hyracoids were a diverse and successful group of mammals in Africa during the Eocene and Oligocene epochs (early part of the Age of Mammals, 55 to 34 million years ago), and they are still…

A supraorder of extinct marine reptiles from the Mesozoic, or the Age of Dinosaurs, belonging to the subclass Diapsida. The group consists of the order Ichthyosauria and several basal forms from the Early Triassic. Diapsida Dinosauria…

A group of extinct flying birds known exclusively from the latest stages of the Cretaceous (80–65 million years ago) in North America. Along with Hesperornithiformes, Ichthyornithiforms are some of the earliest nonmodern bird taxa known to science.…

A class of the phylum Arthropoda, sometimes called the Hexapoda. In fact, Hexapoda is a superclass consisting of both Insecta and the related class Entognatha (Parainsecta) (containing the springtails, telsontails, and proturans). Class Insecta is…

An obsolete order of placental insectivorous mammals, now mostly reassigned to the order Eulipotyphla, including the shrews, moles, hedgehogs, and solenodons. The order Insectivora was formerly thought by taxonomists to be a basal placental order,…

An order in the class Lycopsida that diverged from the Lepidodendrales in the Late Devonian. These two groups have several characters that are not found in other lycopsids, notably a centralized, shootlike rooting structure (rhizomorph) that allows…

The common name for members of the agnathans. The superclass Agnatha (subphylum Vertebrata, phylum Chordata) comprises the jawless vertebrates (agnathans). Members include the cyclostomes (modern lampreys and hagfishes), as well as extinct armored…

An extinct order of the class Lycopsida which, together with Isoetales, forms the monophyletic rhizomorphaleans, the most derived and diverse group of clubmosses. The lepidodendraleans are best known as the scale trees that dominate most…

The dominant group (class) of vertebrates. Members of the class Mammalia (subphylum Vertebrata, phylum Chordata), that is, mammals, have ruled the planet Earth since the extinction of the dinosaurs approximately 65 million years ago. There are…

An order of animals, long considered the only order of the mammalian infraclass Metatheria. Morphology The marsupials are characterized by the presence of a pouch (marsupium) in the female, a skin pocket whose teat-bearing abdominal wall is…

A class of phylum Arthropoda, subphylum Chelicerata. Merostomes are aquatic chelicerates, characterized by abdominal appendages bearing respiratory organs. Most merostomes are extinct; only the horseshoe crabs, comprising four species and three…

An infraclass of therian mammals including a single order, the Marsupialia. The Metatheria are distinguished from the Eutheria (the placental mammals) by numerous characters. The full metatherian dentition is I 5/4 C 1/1 Pm 3/3 M 4/4, for a total of…

The body of knowledge that concerns the fundamental nature, function, development, and use of formal models in science and technology. In its most general sense, a model is a proxy. A model is one entity used to represent some other entity for some…

A class of the phylum Mollusca. Although fossil monoplacophorans had been known since the end of the nineteenth century, it was the discovery of a living species in deep water off Costa Rica in the 1950s that led to universal acceptance of the…

An extinct order in the class Mammalia, subclass Allotheria, comprising a major group of early mammals, ranging from Late Jurassic to Late Eocene (about 155 to 35 million years ago). The group is best known from North America, Mongolia, and Europe.…

Organisms that are classified in the kingdom Fungi and given the class name Myxomycetes, following the rules of botanical nomenclature; or classified in the kingdom Protista at various taxonomic ranks, as class Mycetozoa, following the rules of…

A group of externally shelled cephalopods, represented by the two living genera, Nautilus, known since the 1500s, and the more recently defined Allonautilus, which was seen alive for the first time only in 1986. Allonautilus differs from Nautilus…

A group of late archaic humans (Homo neanderthalensis) from Europe, southwest Asia, and central Asia that immediately preceded the first modern humans in those regions. The closest evolutionary relatives of modern humans are the Neandertals (also…

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,…

The Nobel Prizes for 2020 included the following awards for scientific disciplines. Chemistry The chemistry prize was awarded jointly to Emmanuelle Charpentier of the Max Planck Unit for the Science of Pathogens, Berlin, Germany; and Jennifer A.…

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,…

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…

A highly ambiguous term that designates four different concepts: (1) objective pattern (or natural regularity), (2) formula purporting to represent an objective pattern, (3) law-based rule (or uniform procedure), and (4) principle concerning any of…

The study of matter, energy, and forces. Physical science is generally considered to include astronomy, chemistry, geology, mineralogy, meteorology, and physics. These fields overlap more or less, as illustrated by astrophysics, chemical physics,…

An attempt to explain a certain class of physical phenomena by deducing them as necessary consequences of other phenomena regarded as more primitive or fundamental and less in need of explanation. When formulating a physical theory, any fundamental…

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 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…