Glossary Database

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

 Glossary Term: 

Definition:

 Paedomorphosis  Condition in which a larva becomes sexually mature without attaining the adult body form. Paedomorphosis may be achieved by neotony or by progenesis(Pough 1996).
 Pahoehoe flow  A lava flow with a billowy or ropy surface. Contrast with aa flow.
 Palatal complex  Bones and soft tissue that make up the palate.
 Paleocurrent  An ancient current, which existed in the geologic past, with a direction of flow that can be inferred from cross-bedding, ripple marks, and other sedimentary structures.
 Paleogeography  The study of geography in the geologic past, including the patterns of Earth's surface, the distribution of land and ocean, and ancient mountains and other landforms.
 Paleomagnetism  The study of ancient magnetic fields, as preserved in the magnetic properties of rocks. It includes studies of changes in the position of the magnetic poles and reversals of the magnetic poles in the geologic past.
 Paleontology  The study of ancient life.
 Paleowind  An ancient wind, existing in the geologic past, the direction of which can be inferred from patterns of ancient ash falls, orientation of cross-bedding, and growth rates of colonial corals.
 Paleozoic  The geologic era from 570-225 million years ago. View timeline of geologic events.
 Palpus (pl. Palpi)  One of a pair of appendages on the front of a butterfly's head which protect the feeding apparatus, the proboscis.
 Pangaea  A former continent from which the present continents originated by plate movement from the Mesozoic Era to the present.
 papilla  Any small, soft rounded protuberance on the skin.
 Parabola  A curve formed by the intersection of a cone with a plane parallel to its side.
 Parabolic dune  A dune shaped like a parabola with the concave side toward the wind.
 Parallel  Extending in the same direction and at a constant distance apart, so as to never meet. A parallel line, surface, etc. Also used to refer to lines of latitude which circle the earth and are all parallel to the equator and each other.
 Parasitic  To obtain nutrients necessary for life from another living organism. For example, a mosquito is a parasite of warm-blooded animals, including humans.
 Parasphenoid teeth  In amphibians, teeth actually borne by the parasphenoid bone itself (Peters 1964).
 Parent isotope (or parent element)  The radioactive isotope from which a daughter isotope is produced because of radioactive decay. For example, radium is the parent isotope of radon.
 Parent material  Inorganic, mineral base from which the soil is formed; usually consisting of regolith.
 Parent rock  The original rock that a sediment or soil may have eroded or weathered from.
 Parietal eye  A sensory structure capable of light reception, located on the dorsal side of the diencephalon, and opening to the outside through the parietal foramen (Peters 1964).
 Parity  the condition or fact of having borne offspring (Morris 1992).
 Parotoid gland  Large, swollen, glandular area lying behind the eye on the head, and extending in some species well onto the neck, in some species of anurans. Prominently developed in bufonid (toad) species, in many of which the glandular secretions are potent poisons (Peters 1964).
 parr marks  Vertical dark bands found in the young of many salmonids; may persist in the adult in a few species.
 Parthenogenic  Having unisexual reproduction in which young are produced by unfertilized females (Morris 1992).
 Partial melting  The process by which minerals with low melting points liquefy within a rock body as a result of an increase in temperature or a decrease in pressure (or both) while other minerals in the rock are still solid. If the liquid (magma) is removed before other components of the parent rock have melted, the composition of the magma can be quite different from that of the parent rock. Partial melting is believed to be important in the generation of basaltic magma from peridotite at spreading centers and in the generation of granitic magma from basaltic crust at subduction zones.
 Parturition  the act or process of giving birth (Morris 1992).
 Passive margin (plate tectonics)  A lithospheric plate margin at which crust is neither created nor destroyed. Passive plate margins generally are marked by transform faults.
 Patagium  1. in birds, a feathered web of skin that spans the angle in front of the elbow. 2. a fold of skin in flying squirrels, flying lizards, and other arboreal gliding animals that encloses the limbs on both sides from neck to tail, enabling the animal to glide (Morris 1992).
 Patrol  A strategy of mate location used by male butterflies, consisting of constant flight.
 Peat  An accumulation of partly carbonized plant material containing approximately 60% carbon and 30% oxygen. It is considered an early stage, or rank, in the development of coal.
 Pebble  A rock fragment with a diameter between 2 mm (about the size of a match head) and 64 mm (about the size of a tennis ball).
 pectoral fin  Paired fins on the breast.
 Pediment  A gently sloping erosion surface formed at the base of a receding mountain front or cliff. It cuts across bedrock and can be covered with a veneer of sediment. Pediments characteristically form in arid and semi-arid climates.
 Pelage  the fur or other soft surface covering of a mammal (Morris 1992).
 Pelagic  The water of the ocean as an environment.
 Pelagic sediment  Deep-sea sediment composed of fine-grained detritus that slowly settles from surface waters. Common constituents are clay, radiolarian ooze, and foraminiferal ooze.
 Pelt  the hide or skin of an animal (Stein 1966).
 pelvic fins  Ventral paired fins on the lower side which are either ventral to the pectoral fins or between them and the anal fin.
 Peneplain  An extensive erosion surface worn down almost to sea level. Subsequent tectonic activity can lift a peneplain to higher elevations.
 Peninsula  An elongate body of land extending into a body of water.
 Penultimate phalange  Next to last digit (Guralnik 1970).
 Perch  A strategy of mate location used by male butterflies, consisting of waiting in a constant location for females to pass by.
 Perched aquifer  Geologic formation (usually a clay lens) within the vadose zone that intercepts water and creates a small, localized aquifer above the upper surface of a local zone of saturation that lies above the regional water table.
 Perennial  happening throughout the year or over a period of many years (Morris 1992).
 Perennial stream  A stream that runs all year.
 Peridotite  A dark-colored ultramafic, intrusive, igneous rock of coarse-grained texture, largely composed of olivine; peridotite may also contain other mafic minerals such as pyroxenes, amphiboles or micas.
 Period  A division of geologic time smaller than an era and larger than an epoch. Example: Cretaceous Period. View timeline of geologic events.
 Periodic table  A table that lists the elements in order of increasing atomic number.
 Permafrost  Permanently frozen ground.
 Permanent stream  A stream or reach of a stream that flows continuously throughout the year. Synonymous with perennial stream. Compare to ephemeral stream.
 Permeability  The ability of a material to transmit fluids.
 Permeable  A rock, sediment, or soil that allows fluids (such as gas, oil, or water), to pass through it.
 Perpendicular  A line or plane at a right angle to a given line or surface.
 Petiole  The stalk of a leaf, attaching it to the stem.
 Petrographic  Pertaining to petrography.
 Petrography  The description and systematic classification of rocks.
 Phalanges  The bones of the fingers or toes (Morris 1992).
 Phalanx  Any one of the bones in the fingers or toes (Peters 1964).
 Phaneritic  A coarse grained texture in igneous rocks in which the mineral grains are easily visible without magnification. A phaneritic texture results from slow cooling of a magma.
 Phaneritic texture  The texture of igneous rocks in which the interlocking crystals are large enough to be seen without magnification.
 Phanerozoic  The eon that follows the Proterozoic Eon. That part of geologic time represented by rocks in which the evidence of life is abundant.
 pharyngeal teeth  Bony projections found on, and embedded in, the tissues of the 5th gill arch.
 Phenocryst (volcanology)  A crystal that is significantly larger than the crystals surrounding it. Phenocrysts form during an early phase in the cooling of magma, and are crystals of minerals that crystallize at higher temperatures than the groundmass.
 Pheromone  A scent chemical used for communication. For example, male butterflies emit pheromones to attract female butterflies of the same species. Some caterpillars can emit a chemical which mimics an ant alarm pheromone.
 Philopatric  Of or relating to species or groups that remain in or habitually return to their native regions or territories (Morris 1992).
 Photoperiod  the amount of time per day that an organism is exposed to light (Morris 1992).
 Phreatic zone (groundwater)  Zone of saturation. All pore spaces that can be filled with water (or a gas or other fluid), are.
 Phyllite  A metamorphic rock intermediate in grade between slate and mica schist.
 Physiographic map  A map showing surface features of the Earth.
 Physiography  The study of the surface features and land forms of the Earth.
 phytoplankton  Microscopic free-floating plants.
 Pillar  A land form shaped like a pillar.
 Pillow lava  An ellipsoidal mass of igneous rock formed by extrusion of lava underwater.
 Pinnacle  A tall, tower-shaped or spire-shaped pillar of rock.
 piscivorous  Fish-eating.
 Placer  A mineral deposit formed by the sorting or washing action of water. Placers are usually deposits of heavy minerals, such as gold.
 Plagioclase  A group of triclinic feldspar minerals with the general formula (Na,Ca)Al(Si,Al)Si2O8 ; plagioclases are one of the most common rock-forming minerals.
 Plain  An extensive region of level or rolling, almost treeless country; a prairie.
 Planetary differentiation  The processes by which the materials in a planetary body are separated according to density, so that the originally homogeneous body is converted into a zoned or layered (shelled) body with a dense core, a mantle, and a crust.
 Plankton  1.) Collective term for very small plants and animals that drift near the surface of water. Phytoplankton include bacteria, algae (including diatoms), and fungi. The small animals are called zooplankton, the small plants are called phytoplankton. 2.) All free-floating plants and animals (usually microscopic), alive or dead.
 Plastic  See ductile.
 Plastic deformation  A permanent change in a substance's shape or volume that does not involve failure by fracture or rupture.
 Plastron  The ventral part of the turtle shell, consisting of a series of paired bones, overlain by series of laminae alternating with bones (Peters 1964).
 Plate (tectonics)  A broad segment of the lithosphere (including the rigid upper mantle, plus oceanic and continental crust) that floats on the underlying asthenosphere and moves independently of other plates.
 Plate tectonics  The theory of global dynamics in which the lithosphere is believed to be broken into individual plates that move in response to convection in the upper mantle. The margins of the plates are sites of considerable geologic activity.
 Plateau  1. An extensive upland region. 2. A relatively elevated area of comperitively flat land.
 Plateau basalt  Basalt extruded in extensive, nearly horizontal layers, which, after uplift, tend to erode into great plateaus. Synonymous with flood basalt.
 Platform reef  An organic reef with a flat upper surface developed on submerged segments of a continental platform.
 Playa  A depression in the center of a desert basin, the site of occasional temporary lakes.
 Playa lake  A shallow temporary lake formed in a desert basin after rain.
 Pleistocene  The epoch of geologic time from the end of the Pliocene Epoch of the Tertiary Period (about 2 million years ago) to the beginning of the Holocene Epoch of the Quaternary Period (about 10,000 years ago). The major event during the Pleistocene was the expansion of continental glaciers in the Northern Hemisphere. Synonymous with glacial epoch, ice age.
 Pleistocene Age  The geologic epoch of the Quartenary period extending from the end of the Pliocene to the beginning of the Holocene, and the rocks formed during that time (Morris 1992).
 Pliocene Epoch  A time span during the Tertiary Period, from roughly 2 to 5 million years ago.
 Plucking (glacial geology)  The process of glacial erosion by which large rock fragments are loosened by ice wedging, become frozen to the bottom surface of the glacier, and are torn out of the bedrock and transported by the glacier as it moves. The process involves the freezing of subglacial meltwater that seeps into fractures and bedding planes in the rock.
 Plumage  the feather covering of birds, sometimes colored for purposes of camouflage, courtship display, etc., and divided in certain stages of a bird's growth to indicate age or maturity, such as natal plumage, juvenile plumage, first winter plumage, first nuptial plumage, and the like (Morris 1992).
 Plume  See mantle plume.
 Plumes  The conspicuous feather or feathers of a bird (Morris 1992)
 Plunge  The inclination, with respect to the horizontal plane, of any linear structural element of a rock. The plunge of a fold is the inclination of the axis of the fold.
 Plunging fold  A fold with its axis inclined from the horizontal.
 Pluton  Igneous rock formed beneath Earth's surface.
 Pluvial lake  A lake that was created under former climatic conditions, at a time when rainfall in the region was more abundant than it is now. Pluvial lakes were common in and regions during the Pleistocene.
 Point bar  A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander bend.
 Polar climate  The climate that prevails at Earth's poles, with temperatures commonly below freezing and with low precipitation.
 Polar wandering  The apparent movement of the magnetic poles with respect to the continents.
 Polarity epoch  A relatively long period of time during which the Earth's magnetic field is oriented in either the normal direction or the reverse direction.
 Polarity event  A relatively brief interval of time within a polarity epoch; during a polarity event, the polarity of the Earth's magnetic field is reversed with respect to the prevailing polarity of the epoch.
 Pole of rotation  A pole of the imaginary axis about which a tectonic plate rotates.
 Polyandrous  when one female mates with two or more males
 Polychaets  A class of mostly marine worms in the Phylum Annelida, with anterior tentacles and palps and most segments bearing parapodia with bristles; free-swimming or sessile in tubes or burrows; often brightly colored, most 5-10 cm in length (Morris 1992)
 Polyestrus  having more than one estrus cycle in a year. Many small mammals that have multiple litters each year are polyestrus.
 Polygynous  of or relating to polygyny (Morris 1992). Polygyny
 Polyhedra  An object with many sides.
 Polymorphism  The ability of a chemical compound to crystallize with more than one kind of crystal structure. For example Al2SiO, may crystallize as three different minerals, depending on the prevailing temperature and pressure.
 Pore fluid  A fluid, such as groundwater or liquid rock material resulting from partial melting, that occupies pore spaces of a rock.
 Pore space  The spaces within a rock body that are unoccupied by solid material. Pore spaces include spaces between grains, fractures, vesicles, and voids formed by dissolution.
 Pores  See pore space.
 Porosity  The percentage of the total volume of a rock or sediment that consists of pore space.
 Porphyritic texture  The texture of igneous rocks in which some crystals are distinctly larger than others.
 Porphyry copper  Deposits of copper disseminated throughout a porphyritic granitic rock.
 Pothole  A hole formed in a stream bed by sand and gravel swirled around in one spot by eddies.
 Precambrian  The division of geologic time from the formation of Earth (about 4.5 billion years ago) to the beginning of the Cambrian Period of the Paleozoic Era (about 600 million years ago). Also, the rocks formed during that time. Precambrian time constitutes about 90% of Earth's history.
 Precipitate (chemical)  A solid that settles to the bottom of the container during a chemical reaction.
 Precipitation  any form of water particles, such as frozen water in snow or ice crystals, or liquid water in raindrops or drizzle (Morris 1992).
 Precipitation (H2O)  Particles of liquid or frozen water that fall from the atmosphere and may reach the ground.
 Precocial  being born in a relatively advanced state of development and some what capable of being independent shortly after birth. An example would be hares as compared to rabbits.
 Precocious  appearing, developing, or maturing earlier than is usual (Morris 1992).
 Predator Mutualism  two or more species of predators working together to capture prey
 Pre-Imbrian period  The earliest period of lunar history, extending from the formation of the moon (about 4.5 billion years ago) to the formation of the multi-ring basins (about 3.9 billion years ago).
 premaxilla, premaxillary  A small paired bone forming the anterior part of the upper jaw.
 preopercle  A sickle-shaped bone located behind and below the eye.
 Preservation  A management program which prohibits harvest or angling in order to preserve and rebuild theviability of a wild population. May be applied to an individual species or to water areas which are important spawningor nursery areas.
 Pressure  The force per unit of area exerted upon something, such as on a surface.
 Pressure ridge  An elongate uplift of the congealing crust of a lava flow, resulting from the pressure of underlying and still fluid lava.
 prevomer  A flat, usually median, bone found in the roof of the mouth, separating the nasal chambers.
 prickles  small projections from the skin of some fishes that feel rough to touch.
 Primary coast  A coast shaped by sub-aerial erosion, deposition, volcanism, or tectonic activity.
 Primary Productivity  the productive capabilities of self-feeding organisms (Morris 1992).
 Primary sedimentary structure  A structure of sedimentary rocks (such as cross-bedding, ripple marks, or mud cracks) that originates contemporaneously with the deposition of the sediment (in contrast to a secondary structure, such as a joint or fault, which originates after the rock has been formed).
 Primary wave  See P wave.
 Proboscis  A biological term typically used to describe a long, flexible feeding structure. In butterflies, it is the long, coiled tube through which they feed.
 Progenesis  Accelerated development of reproductive organs relative to somatic tissue, leading to paedomorphosis (Pough 1996).
 Prograding  The outward extension of a shoreline into the sea or a lake due to sedimentation.
 Proleg  A false leg, used in locomotion, found on the abdominal segment of a caterpillar. A caterpillar has five pairs of prolegs. Caterpillars, like other insects, have only six true legs, and these arise from the thorax (or thoracic segments).
 Promiscuous  a mating behavior in which the male and female do not form lasting pair bonds; one male may mate with several females, or one female with several males (Morris 1992).
 Promontory  A peak of high land that juts out into a body of water.
 Prostration  extreme physical weakness or exhaustion (Stein 1966).
 Proterozoic  The more recent of the two divisions of the Precambrian. View timeline of geologic events.
 Proton  A positively charged nuclear particle. Protons comprise about half of the mass of an atom.
 protractile  Capable of being extended. The upper jaw is protractile if it is separated by a continuous groove from the face.
 protrusible  Capable of being thrust out or downward.
 Pterygoid bones  In the skull of most lower vertebrates, four large, medially situated bones of the palatal complex that is located on the lower surface of the palatal cartilage (Morris 1992).
 Pubescence  Soft, fine hair or hair-like structures.
 Puddling  A behavior of some butterflies in which they congregate at puddles, moist soil, or dung to obtain moisture and salts.
 Pumice  A rock consisting of frothy natural glass.
 Pupa (pl. Pupae)  The resting stage between juvenile and adult forms of an insect; in butterflies, the pupa is encased by a chrysalis. Typically this stage (the pupal stage) is immobile and does not feed; internally, however, complete reconstruction is taking place.
 Pupate  To become a pupa.
 Put-and-Take Trout  A management program using intensive stocking of catchable size (larger than 8 inches) hatchery rainbow trout to provide high consumptive catch rates. Applied to small lakes, ponds, and reservoirs and certain streams or stream reaches with good access and moderate to high fishing pressure. Used where long-term survival and growth is limited due to water area characteristics or harvest rates. Other species, including some naturally-produced trout, may be present.
 P-Wave   A seismic wave that involved particle motion in the direction of propagation; the p stands for primary because this wave arrives first.
 Pyroclastic (pyroclastic flow)  Pertaining to fragmental rock material formed by volcanic explosions.
 Pyroclastic texture  The rock texture of igneous rocks consisting of fragments of ash, rock, and glass produced by volcanic explosions.
 Pyroxene  A group of rock-forming silicate minerals composed of single chains of silicon-oxygen tetrahedra. Compare with amphibole, which is composed of double chains.