UCMP Glossary: D
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dacite -- Igneous volcanic rock, less mafic than andesite, typically fine-grained and light in color; rough volcanic equivalent of granodiorite.
decomposer -- An organism that breaks down the tissue and/or structures of dead organisms.
decomposition -- The breakdown of dead organic material by detrivores or saprophytes.
delta -- n. A low, nearly flat accumulation of sediment deposited at the mouth of a river or stream, commonly triangular or fan-shaped; deltaic– adj.
dendrites -- n. Small branching patterns on rocks made of iron and manganese oxides that show the passage of fluids through the rock.
deposition -- Any accumulation of material, by mechanical settling from water or air, chemical precipitation, evaporation from solution, etc.
derived -- Describes a character state that is present in one or more subclades, but not all, of a clade under consideration. A derived character state is inferred to be a modified version of the primitive condition of that character, and to have arisen later in the evolution of the clade. For example, "presence of hair" is a primitive character state for all mammals, whereas the "hairlessness" of whales is a derived state for one subclade within the Mammalia.
detritus -- Accumulated organic debris from dead organisms, often an important source of nutrients in a food web.
detrivore -- Any organism which obtains most of its nutrients from the detritus in an ecosystem.
development -- The process by which a multicellular organism is produced from a single cell.
diagenesis -- All of the changes that occur to a fossil (or more generally any sediment) after initial burial; includes changes that result from chemical, physical as well as biological processes. The study of diagenesis is part of taphonomy.
diapsid -- n. A vertebrate distinguished by a skull with two pairs of openings in the side behind the eyes, e.g., lizards, snakes, crocodiles, dinosaurs, and pterosaurs.
diatomite -- Diatomite, or diatomaceous earth, is a siliceous sedimaentary rock formed from the accumulations of diatoms or other nanoplankton.
dikaryotic -- Having two different and distinct nuclei per cell; found in the fungi. A dikaryotic individual is called a dikaryon.
dinosteranes/dinosteroids -- chemicals found in dinoflagellates, which have been useful in documenting their existence early in the fossil record.
diorite -- Igneous plutonic rock, less mafic than gabbro, but more mafic than granite and granodiorite; rough plutonic equivalent of andesite.
dip -- The angle that a bedding plane or fault makes with the horizontal when measured perpendicular to the strike of the bedding plane or fault.
diploid -- Having two different sets of chromosomes in the same nucleus of each cell. Most metazoans and plants are diploid. Compare with haploid.
diploid life cycle -- Occurs when the only multicellular stage in an organism's life cycle is diploid.
disease -- Organisms suffer from disease when their normal function is impaired by some genetic disorder, or more often from the activity of a parasite or other organism living within them. Many diseases are caused by viruses, bacteria, or fungi.
dispersal -- The scattering of organisms of a species, often following a major reproductive event. Spores and larvae are commonly dispersed into the environment. Pollen or gametes may also be dispersed, but in this case the intent is to target another individual so that reproduction may occur. Organisms may disperse as spores, seeds, eggs, larvae, or adults.
diversity -- Term used to describe numbers of taxa, or variation in morphology.
DNA -- "deoxyribonucleic acid". The nucleic acid which carries the genetic code of an organism. It is the primary component of chromosomes. MORE?
dolomite -- A carbonate sedimentary rock composed of more than 50 percent of the mineral calcium-magnesium carbonate (CaMg(CO3)2).
dormancy -- A period of suspended growth and metabolic activity. Many plants, seeds, spores, and some invertebrates become dormant during unfavorable conditions.
double membrane -- In mitochondria and plastids, there is a two-layered membrane which surrounds the organelle. This is believed to be the result of endosymbiosis, with the outer membrane coming from the eukaryotic cell, and the inner membrane belonging to the original prokaryote which was "swallowed".
drill core -- n. A column of material (e.g., mud, ice, rock) removed from the earth by drilling. Often used as a tool for exploration of natural resources.
drumlin -- n. Elongated mound of glacial sediment deposited parallel to ice flow.
