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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…

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…

The earliest representatives of modern humans—those belonging to Homo sapiens—evolved from more archaic humans approximately 150,000–300,000 years ago in eastern Africa. During succeeding years, the geographical range of anatomically modern humans…

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…

Life on Earth has been punctuated by a number of catastrophic mass extinctions throughout history. During these events, diverse taxonomic groups collapsed from the relatively rapid and widespread extinction of large numbers of species. Precipitated…

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…

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…