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eukaryote

(Encyclopedia)eukaryote yo͞okârˈē-ōtˌ [key], a cell or organism composed of cells that have a membrane-bound nucleus and organelles (mitochondria, chloroplasts; see cell, in biology) and genetic material orga...

horsetail

(Encyclopedia)horsetail, any plant of the genus Equisetum [Lat.,=horse bristle], the single surviving genus of a large group (Equisetophyta) of primitive vascular plants. Like the ferns and club mosses, relatives o...

Gould, Stephen Jay

(Encyclopedia)Gould, Stephen Jay, 1941–2002, American paleontologist and science writer, b. Queens, New York; grad. Antioch College (B.S., 1963), Columbia Univ. (Ph.D., 1967). With Niles Eldredge, Gould proposed ...

Olduvai Gorge

(Encyclopedia)Olduvai Gorge ōlˈdəwāˌ, –vāˌ [key], a feature of the E African Rift Valley in Tanzania. Erosional processes have exposed geological strata in the gorge dating to the lower Pleistocene epoch, ...

shale

(Encyclopedia)shale, sedimentary rock formed by the consolidation of mud or clay, having the property of splitting into thin layers parallel to its bedding planes. Shale tends to be fissile, i.e., it tends to split...

dragonfly

(Encyclopedia)dragonfly, any insect of the order Odonata, which also includes the damselfly. Members of this order are generally large predatory insects and characteristically have chewing mouthparts and four membr...

lungfish

(Encyclopedia)lungfish, common name for any of a group of fish belonging to the families Ceratodontidae, Lepidosirenidae, and Protopteridae, found in the rivers of Australia, South America, and Africa, respectively...

Caro, Sir Anthony Alfred

(Encyclopedia)Caro, Sir Anthony Alfred, 1924–2014, British sculptor, one of the most important and influential modernist sculptors of the late 20th cent. Educated as an engineer (grad. Cambridge, 1944), he studie...

Tyrannosaurus

(Encyclopedia)Tyrannosaurus tīrănˌōsôrˈəs, tĭr– [key] [Gr.,=tyrant lizard], member of a family, Tyrannosauridae, of bipedal carnivorous saurischian dinosaurs characterized by having strong hind limbs, a m...

human evolution

(Encyclopedia)human evolution, theory of the origins of the human species, Homo sapiens. Modern understanding of human origins is derived largely from the findings of paleontology, anthropology, and genetics, and i...