plain: Large area of extremely
flat ocean floor lying near a continent and generally over
4 km in depth.
Now extinct, earliest group of fish with jaws, ranging from
the Silurian to the Permian.
Organic-walled microfossils common throughout the Proterozoic
and early Paleozoic
Any heritable characteristic of an organism that improves
its ability to survive and reproduce in its environment. Also
used to describe the process of genetic change within a population,
as influenced by natural selection. Alternatively,
some heritable feature of an individual's phenotype
that improves its chances of survival and reproduction in
the existing environment.
radiation (also "radiation", for short): The diversification,
over evolutionary time, of a species or group of species into
several different species or subspecies that are typically
adapted to different ecological niches (for example, Darwin's
finches). The term can also be applied to larger groups of
organisms, as in "the adaptive radiation of mammals."
For example, trilobites underwent a massive radiation during
the Cambrian, and insects during the Cretaceous.
triphosphate: Adenosine-5'-triphosphate (ATP) transports
chemical energy within cells for metabolism. It
is produced by photophosphorylation and cellular respiration
and used by enzymes and structural proteins in many cellular
A jawless, heavily armored fish that appeared in the Devonian.
Photosynthetic, almost exclusively aquatic, nonvascular plants
that appeared in the Precambrian and that range in size from
simple unicellular forms to giant kelps.
allele: One of the alternative forms
of a gene. For example, if a gene determines the color of
eyes, one allele of that gene may produce brown eyes and another
allele produce blue eyes. In a diploid cell there are usually
two alleles of any one gene (one from each parent). Within
a population there may be many different alleles of a gene;
each has a unique nucleotide sequence.
that occurs when two or more populations of a species are
geographically isolated from one another sufficiently that
they do not interbreed.
Living in separate places. Compare with sympatry.
specimen designated from the type series that is the opposite
sex of the holotype.
acid: The unit molecular building
block of proteins, which are chains of amino acids in a certain
sequence. There are 20 main amino acids in the proteins of
living things, and the properties of a protein are determined
by its particular amino acid sequence.
acid sequence: A series of
amino acids, the building blocks of proteins, usually coded
for by DNA. Exceptions are those coded for by the RNA of certain
viruses, such as HIV.
Cephlapods that evolved from nautiloids and are generally
spiral-shaped shell with numerous chambers.
A transitional group of vertebrates between fish and reptiles,
capable of living on land, but returning to the water to reproduce.
( Devonian to Holocene)
Generally, a lack of oxygen, usually in refernce to a
environment. Anoxic sea water refers to water depleted of
oxygen that can occur with restricted water exchange.
cases, oxygen is prevented from reaching the deeper parts
of the sea area by a physical barrier (sill) as well as
pronounced density stratification. Anoxic conditions will
occur if the rate of oxidation of organic matter by bacteria
is greater than the supply of oxygen. When oxygen is depleted,
bacteria first turn to the second-best electron acceptor,
which in sea water is nitrate. Denitrification occurs, and
the nitrate will be consumed rather rapidly. After reducing
some other minor elements, the bacteria will turn to reducing
sulphate. If anoxic sea water becomes reoxygenized, sulphides
will be oxidized to sulphate according to: HS + 2O2 > HSO4.
conical, calcareous, Cambrian fossils with a long history
of phylogenetic uncertainty and changing interpretations.
There is now a strong consensus that archaeocyaths are sponges.
Autotrophs: can use carbon dioxide (CO2) and water to form
oxygen and complex organic compounds, mainly through the
process of photosynthesis.
plane: A surface separating layers of sedimentary rocks and
deposits. A bedding plane marks termination of one deposit
and beginning of another of different character, such as a
surface separating a sandstone bed from an overlying mudstone
bed. Rocks tend to breaks or separate along bedding planes.
term used to designate aquatic organisms that are bottom dwelling.
symmetry: The condition, found in many organisms, where one
half of the body or structure is the mirror image of the other.
A clade of animals whode members share: bilateral symmetry,
are triploblastic (three tissue layers: ectoderm, mesoderm,
endoderm), and with HOX genes in one
or more clusters with the genes within a cluster arranged
in the same order as the body parts they affect.
species concept: The concept of species, according to which
a species is a set of organisms that can interbreed among
each other. Compare with cladistic species concept, ecological
species concept, phenetic species concept, and recognition
The formation of minerals by organisms. Biominerlization is
a widespread phenomenon within nature whereby organisms form
complex and genetically determined mineral structures for
a myriad of reasons such as stiffening of soft tissues as
in insect exoskeletons, mammal endoskeletons, and the formation
of animal teeth for chewing food. In the process, minerals
nucleate and grow on purely organic templates.
The branch of geology concerned with the separation and differentiation
of rock units by means of the study of the fossils they contain.
A mollusk having two shells hinged together, as the oyster,
clam, or mussel; or any animal with two halves to its shell
such as an ostracode or brachiopod.
very generally, an extraterrestrial body of indeterminant
composition, in the 1-10-km size range, that impacts the earth
at velocities faster than a bullet (20-70 km/sec = Mach 75),
explodes upon impact, and creates a large crater.
fishes: Fish of the class Osteichthyes,
characterized by a skeleton composed of bone in addition to
cartilage, gill covers, and an air bladder.
Bryophytes comprise the mosses (Class Musci), as well as liverworts
(Class Hepaticae) and hornworts (Class Anthocerotae). They
are believed to have been the first true plants,
evolving from charophytes almost 500 million years ago. Unlike
other plants, bryophytes do not have true organs, such as
leaves, stems, or roots. In place of roots, most bryophytes
have thin, hairy tubes called rhizoids that provide anchorage
and nutrient uptake from the soil. The bryophyte life cycle
is unique in having a dominant gametophyte generation. The
actual green plant in mosses and worts is the gametophyte
plant, while the sporophyte consists of simply an enclosed
sporangium, typically atop a stalk.
Of, containing, or like calcite (calcium carbonate).
A common compound (CaCO3) in rock formation and the main component
of limestone. Calcite can be many colors and effervesces (bubbles)
in hydrochloric acid
rock: A rock consisting primarily of a carbonate mineral such
as calcite or dolomite, the chief minerals in limestone and
(formally Homalozoa): Extinct subphylum (Phylum
whose members have no trace of radial symmetry. The theca
is depressed and asymmetrical. Homalozoa are known from Middle
Cambrian to Middle Devonian rocks.
the destructive metabolism of larger organic molecules into
smaller constituents, usually with the release of energy (usually
A variety of limestone made up in part of biochemically derived
calcite, in form of skeletons or skeletal fragments of microscopic
oceanic plants and animals mixed with fine-grained calcite
deposits of biochemical or inorganic-chemical origin.
A cryptocrystalline form of quartz, microscopically granular.
Occurs as nodules and as thin, continuous layers. Duller,
less waxy luster than chalcedony. Occurs in limestone, dolostone,
choanoflagellates: A group of sigle-celled and colonial
flagellate eukaryotes, generally accepted as the closest
of the animals (metazoa).
animal with a notochord, a cartilaginous rod extending the
length of its body, dorsal hollow nerve cord (a fluid-filled
tube running the length of the body), gill slits or pouches,
and a tail at some stage during its life cycle.
A structure in the cell nucleus that carries DNA.
At certain times in the cell cycle, chromosomes are visible
as string-like entities. Chromosomes consist of the DNA with
various proteins, particularly histones, bound to it.
A set of species descended from a common ancestral species.
Synonym of monophyletic group.
Phylogenetic classification. The members of a group in a cladistic
classification share a more recent common ancestor with one
another than with the members of any other group. A group
at any level in the classificatory hierarchy, such as a family,
is formed by combining a subgroup at the next lowest level
(the genus, in this case) with the subgroup or subgroups with
which it shares its most recent common ancestor. Compare with
evolutionary classification and phenetic classification.
species concept: The
concept of species, according to which a species is a lineage
of populations between two phylogenetic branch points (or
speciation events). Compare with biological species concept,
ecological species concept, phenetic species concept, and
recognition species concept.
A branching diagram that illustrates hypotheses about the
evolutionary relationships among groups of organisms. Cladograms
can be considered as a special type of phylogenetic tree that
concentrates on the order in which different groups branched
off from their common ancestors. A cladogram branches like
a family tree, with the most closely related species on adjacent
Refers to rock or sediments made up primarily of broken fragments
of pre-existing rocks or minerals.
structures of varying shape and size that are made of calcite,
are secreted by calcareous nannoplankton, and are found in
marine deposits from the Triassic period to the Recent. Coccoliths
range in size from one to thirty-five microns.
A triplet of bases (or nucleotides) in the DNA coding for
one amino acid. The relation between codons and amino acids
is given by the genetic code. The triplet of bases that is
complementary to a condon is called an anticodon; conventionally,
the triplet in the mRNA is called the codon and the triplet
in the tRNA is called the anticodon.
body cavity within which internal organs can develop, which
is completely lined with tissue of mesodermal origin.
A compact mass of mineral matter, usually spherical or disk-like
in shape and embedded in a host rock of different composition.
They form by precipitation of mineral matter about a nucleus
such as a leaf, trilobite exoskelton or a piece of shell of
crust: Solid, outer layers
of the earth, including the rocks of the continents. The part
of the crust that directly underlies the continents and continental
shelves. Averages about 35 km in thickness, but may be over
70 km thick under largest mountain ranges.
drift: The theory that horizontal
movement of the earth's surface causes slow, relative movements
of the continents toward or away from one another.
continental shelf: That portion of the continental margin
that extends as a gently sloping surface from the shoreline
seaward to a marked change in slope at the top of the continental
slope . Seaward depth averages about 130 m.
slope: That portion of the continental margin that lies between
the continental shelf and the continental rise. It is relatively
steep, i.e., 3o - 6o degrees. The continental slope is underlain
by crustal rocks of the continent.
rise: That portion of the continental margin that lies between
the abyssal plain and the continental slope. The continental
rise is underlain by crustal rocks of the ocean basin.
coprolite: The fossilized waste (dung;
fecies; poop) matter of animals.
A part of the earth's crust that has attained stability and
has been little deformed for a prolonged period.
group: A designation in phylogenetics denoting
a agreggation of species comprising all living representatives,
if any are extant, plus all their ancestors back to their
most recent common ancestor, as well as all of that ancestor's
descendants. In simpler terms, it is a clade comprising
a species together with all its descendants. Related stem
group members are excluded from the crown group.
The region of a eukaryotic cell outside the nucleus.
evolution: Evolution by the
process of natural selection acting on random variation.
Clade of Bilateran animals that share multiple HOX
genes for the posterior. Means "second mouth",
so called because the mouth develops from the second opening
into the embryonic gut. The first opening (the blastopore)
forms the future anus only, and the mouth forms later. The
body cavity (coelom) develops from buds off the gut. Deuterostomes
belong to a larger group within the Animalia called the Bilateria,
because they are bilaterally symmetrical with a left and a
right side to their bodies. Some d euterostomes such as echinoderms
like starfish exhibit radially symmetry. They are nonetheless
in the group because during embryonic starfish develop, they
begin bilaterally, but switch to radial symmetry during development.
The physical, chemical or biological alteration of sediments
into sedimentary rock at relatively
low temperatures and pressures that can result in changes
to the rock's original mineralogy and texture. After deposition,
sediments are compacted as they are buried beneath successive
layers of sediment and cemented by minerals that precipitate
from solution. Grains of sediment, rock fragments and fossils
can be replaced by other minerals during diagenesis. Porosity
usually decreases during diagenesis, except in rare cases
such as dissolution of minerals and dolomitization.
Having two sets of genes and two sets of chromosomes (one
from the mother, one from the father). Many common species,
including humans, are diploid. Compare with haploid and polyploid.
(or genetic diversity): A measure of the possible choices
of different information at a gene. For example, whether it
codes for brown or blue eyes.
A nucleic acid that constitutes the genetic material of
cellular organisms and the DNA viruses; DNA replicates and
controls through messenger RNA the inheritable characteristics
of all organisms. A molecule of DNA is made up of two parallel
twisted chains of alternating units of phosphoric acid
deoxyribose, linked by crosspieces of the purine bases and
the pyrimidine bases, resulting in a right-handed helical
structure, that carries genetic information encoded in the
sequence of the bases.
base sequence: A chain of repeating
units of deoxyribonucleotides (adenine, guanine, cytosice,
thymine) arranged in a particular pattern.
(genetic): An allele (A) is dominant if the phenotype of the
heterozygote (Aa) is the same as the homozygote (AA). The
allele (a) does not influence the heterozygote's phenotype
and is called recessive. An allele may be partly, rather than
fully, dominant; in that case, the heterozygous phenotype
is nearer to, rather than identical with, the homozygote of
the dominant allele.
species concept: A
concept of species, according to which a species is a set
of organisms adapted to a particular, discrete set of resources
(or "niche") in the environment. Compare with biological
species concept, cladistic species concept, phenetic species
concept, and recognition species concept.
The relationship between organisms which live one within another
(symbiont within host) in a mutually beneficial relationship.
This process is believed to have accurred in the the evolution
of eukaryotes from prokaryotes involved
the symbiotic union of several previously independent ancestors.
According to the theory, these ancestors included a host cell,
an ancestor of mitochondria, an ancestor of chloroplasts,
and, more controversially, a prokaryote that brought with
it the structures that today provide cellular motion.
Clade of animals that: grow by periodically moulting - shedding
their skin or exoskeleton (timed by steroid hormone signals);
share a unique pattern of HOX genes,
lack cilia; have separate sexes that copulate to achieve egg
variance: Within a population,
the measure of how much of the variation of a particular phenotype
is due to environmental factors (as opposed to variations
in genotype - see genetic variance). An example might be the
height of a plant as determined by such factors as nutrition
or damage during development.
Any organism made up of eukaryotic cells. Eukaryotes are generally
larger and have more DNA than prokaryotes
(whose cells do not have a nucleus to contain their DNA).
Almost all multicellular organisms are eukaryotes.
The primary clade of Kindom
Animalia that can be considered a subkingdom. The cells
of Eumetazoans truly co-operate to form unmistakable tissues
and organs. Nutrients and signals (e.g., hormones) flow efficiently
betwwen cells, such that only specialized cells are involved
in the acquisition of food.
The nucleotide sequences of some genes consist of parts that
code for amino acids, with other parts that do not code for
amino acids interspersed among them. The coding parts, which
are translated, are called exons; the interspersed non-coding
parts are called introns.
in contrast to an endoskeleton, is an external anatomical
feature that supports and protects an animal's body. Many
invertebrate animals such as insects, spiders, crustaceans
and shellfish have exoskeletons. Lobsters, for example, have
tough outer shell systems which provide rigidity and shape
to their bodies. An exoskeleton may interfere with an animal's
growth. To overcome this, arthropods go through a process
called moulting in which they shed their exoskeleton and replace
it with a new, larger one.
metamorphic: A set of metamorphic
mineral assemblages, repeatedly associated in space and time,
such that there is a constant and therefore predictable relationship
between mineral composition and chemical composition. That
relationship is a consequence of conditions of temperature
and pressure under which the assemblages are stable.
The category of taxonomic classification
between order and genus (see taxon). Organisms within a family
share a close similarity; for example, the cat family, Felidae,
which includes lions and domestic cats.
The success of an individual (or allele or genotype in a population)
in surviving and reproducing, measured by that individual's
(or allele's or genotype's) genetic contribution to the next
generation and subsequent generations.
A group of organisms comprising the kingdom Fungi, which includes
molds and mushrooms. They can exist either as single cells
or make up a multicellular body called a mycelium. Fungi lack
chlorophyll and secrete digestive enzymes that decompose other
Haploid reproductive cells that combine at fertilization to
form the zygote, called sperm (or pollen) in males and eggs
A sequence of nucleotides coding for a protein (or, in some
cases, part of a protein); a unit of heredity.
expression: The degree to which
a gene is active in a certain tissue of the body, measured
by the amount of mRNA in the tissue.
Related to genes. A gene is a sequence of nucleotides coding
for a protein (or, in some cases, part of a protein); a unit
The study of genes and their relationship to characteristics
code: The code relating nucleotide
triplets in the mRNA (or DNA) to amino acids in the proteins.
drift: Changes in the frequencies
of alleles in a population that
occur by chance, rather than because of natural
variance: Within a population,
the measure of how much of the variation of a particular phenotype
is due to genotypic variation (as
opposed to environmental factors - see environmental variance).
An example might be the height of a tree as determined by
genes inherited from the parents.
The full set of DNA in a cell or organism.
The science dealing with analysis of the full range of genes
in an organism.
The set of two genes possessed by an individual
at a given locus. More generally, the genetic profile of an
(plural genera): The second-to-lowest category in taxonomic
classification. The phrase "species
name" generally refers to the genus and species together,
as in the Latin name for humans, Homo sapiens. See taxon.
The formation of large sheets of ice across land. Glaciation
of the continents marks the beginning of ice ages, when the
makeup of Earth and organisms on it changes dramatically.
Gondwana: The southern portion of the
late Paleozoic supercontinent
known as Pangea. It means, literally "Land of the Gonds"
(a people of the Indian subcontinent).
The condition of having only one set of genes or chromosomes.
In normally diploid organisms such as humans, only the gametes
The resistance of a mineral to scratching.
Comprise organisms that are not self-sustaining; that is,
they derive energy from the oxidation of organic compounds
either by consumption or absorption of other organisms.
An individual having two different alleles at a genetic locus.
Compare with homozygote.
specimen that serves as the standard bearer of a species or
Extinct subphylum (Phylum
Enchinodermata) whose members have no trace of radial
symmetry. The theca is depressed and asymmetrical. Homalozoa
are known from Middle Cambrian to Middle Devonian rocks.
genes (Hox cluster): Genes (transcription
factors) paramount in development and found to be highly conserved
in evolution. Occuring in clusters they act as master switches
for other genes in that express and time developmental processes.
The genomes of all animals
that have been sequenced have at least one Hox cluster that
show strong homology to the genes in Drosophila (the friut
fly). For example, mice and humans have 4 Hox clusters (a
total of 39 genes in humans) located on four different chromosomes.
sedis, meaning "of uncertain
position (seat)", is a term used to define a taxonomic
group where its broader (phylogenetic)
relationships are unknown or undefined
trace fossils that are seen as preserved tracks or other signs
of the behaviors of animals in the substrate. Ichnofossils
can provide insights on the behavior of an extinct animal.
Very rarely is the animal itself found in direct association
with the ichnofossil it created.
The nucleotide sequences of some genes consist of parts that
code for amino acids, and other parts
that do not code for amino acids interspersed among them.
The interspersed non-coding parts, which are not translated,
are called introns; the coding parts are called exons.
Animalia: Comprises the
animals. These are multicellular organisms with cells that
lack a cell wall. Many are capable of movement, or movement
of some of their body parts, at some time of their life. Animals
are heterotrophic, that is, they
cannot obtain energy from non-living forms and must eat other
organisms, or their products, to obtain energy.
Fungii: Comprise mushrooms, yeasts,
and other fungi. These are eukaryotic
multicellular organisms that are typically non-moving, have
a cell surrounded by a cell wall, and are heterotrophic, that
is, they cannot use energy from non-living forms and must
consume other organisms, or their products, to obtain energy.
Many are decomposers, that is, they obtain energy by breaking
down molecules in dead, decaying organisms.
Monera: Comprise bacteria and
cyanobacteria. These are unicellular organisms that are prokaryotic,
that is, do not have a nucleus surrounded by a nuclear membrane.
The bacteria are mostly heterotrophic, that is, they cannot
obtain energy from non-living forms and must eat other organisms,
or their products, to obtain energy. The cyanobacteria are
autotrophic, that is, they can convert energy from non-living
forms into biologically useful energy (stored in the chemical
bonds of biological molecules); cyanobacteria, like plants,
accomplish this through the process of photosynthesis.
Plantae: Comprise the plants.
These are eukaryotic multicellular
organisms with cells surrounded by a cell wall made of the
carbohydrate cellulose. Plants are typically non-mobile. They
are autotrophic, that is, they can convert energy from non-living
forms into biologically useful energy (stored in the chemical
bonds of biological molecules); plants accomplish this through
the process of photosynthesis,
synthesis of energy-containing biological compounds by trapping
Protista: Comprise unicellular
organisms that are eukaryotic, that
is, have a nucleus separated from the cytoplasm of the cell
by a nuclear membrane. Some are plant-like in that they are
autotrophic, while others are animal-like in that they are
The northern portion of the late Paleozoic supercontinent
is a sedimentary rock composed largely of the mineral calcite
(calcium carbonate: CaCO3). Limestones often contain varying
amounts of silica in the form of chert or flint, as well as
varying amounts of clay, silt and sand as disseminations,
nodules, or layers within the rock. The primary source of
the calcite in limestone is most commonly marine organisms.
(from the Greek word lithos meaning 'rock' and the Latin-derived
suffix -ific) is the process whereby sediments compact under
pressure, expel connate fluids, and gradually become solid
rock. Essentially, lithification is a process of porosity
destruction through compaction and cementation. Lithification
includes all the processes which convert unconsolidated sediments
into sedimentary rocks. Petrification, though often used as
a synonym, is more specifically used to describe the replacement
of organic material by minerals in the formation of fossils.
lithosphere: the outer skin of the
earth, composed of the crust and the uppermost mantle.
A clade of animals that share a cluster of HOX
genes quite different from those found in the ecdysozoans
(and deuterostomes). They share similar sequences in their
18S rRNA genes. The phylogeny of this clade that includes
brachiopods, mulluscs, bryozoa, and many other groups is the
subject of many competing hypothses.
The zone of the earth below the crust and above the core.
marine sediment made of sand, clay, and glauconite in different
The solid matter in which a fossil or crystal is embedded.
Also, a binding substance (e.g., cement in concrete).
RNA (mRNA): The molecule transcribed
by DNA that then carries genetic information
from a gene to the site in the cell where the information
determines the order of amino acids in the synthesis of a
all the multicellular, eukaryotic organisms comrising Kingdom
Animalia (the animals).
monophyletic: A group composed
of a collection of organisms, including the most recent common
ancestor of all those organisms and all the descendants of
that most recent common ancestor. A monophyletic taxon is
also called a clade.
selection: The differential survival and reproduction of classes
of organisms that differ from one another in on or more usually
heritable characteristics. Through this process, the forms
of organisms in a population that are best adapted to their
local environment increase in frequency relative to less well-adapted
forms over a number of generations. This difference in survival
and reproduction is not due to chance.
(also ontogenesis or morphogenesis): describes the origin
and the development of an organism from the fertilized egg
to its mature form. Ontogeny is studied in developmental biology.
a large and believed monophyletic
group of eukaryotes, including both the animals and fungi,
and some protists that have the common characteristic of flagellate
cells to propel themselves.
Any individual living thing.
Primitive jawless fishes, covered by bony armor, that lived
in the Cambrian through Devonian periods.
The act of oxidizing or state of being oxidized. Chemically
it consists in the increase of positive charges on an atom
or the loss of negative charges. Most biological oxidations
are accomplished by the removal of a pair of hydrogen atoms
(dehydrogenation) from a molecule. Such oxidations must be
accompanied by reduction of an acceptor molecule.
living in the open ocean.
The biological study of fossils.
Study of the Earth's past magnetism as it is recorded in the
A scientist who studies fossils to better understand life
in prehistoric times.
The scientific study of fossils.
A supercontinent that existed from about 300 to 200 million
years ago, and included most of the continental crust of the
in which the new species forms from a population contiguous
with the ancestral species' geographic range.
group: A set of species containing
an ancestral species together with some, but not all, of its
descendants. The species included in the group are those that
have continued to resemble the ancestor; the excluded species
have evolved rapidly and no longer resemble their ancestor.
All of the specimens in the type series of a species
or subspecies other than the holotype.
speciation: A synonym of
A form of allopatric speciation in which the new species is
formed from a small population isolated at the edge of the
ancestral population's geographic range. Also called peripatric
Petrifaction or petrification is the process by which organic
material is converted into stone or a similar substance. It
is approximately synonymous with fossilization. Petrified
wood is the most well known result of this process.
The application of genomic information to clinical trials
to determine which patients, based on their genetic make-up,
are most likely to benefit from a certain drug or which are
likely to suffer adverse effects.
photosynthesis: The fundamental
biological process by which green plants make organic compounds
such as carbohydrates from atmospheric carbon dioxide and
water using light energy from the Sun. The process has two
main phases: the light-dependent light reaction responsible
for the initial capture of energy, and the light-independent
dark reaction in which this energy is stored in the chemical
bonds of organic molecules. Since virtually all other forms
of life are directly or indirectly dependent on green plants
for food, photosynthesis is the basis for almost all life
species concept: A concept
of species according to which a species
is a set of organisms that are phenotypically similar to one
another. Compare with biological species concept, cladistic
species concept, ecological species concept, and recognition
The physical or functional characteristics of an organism,
produced by the interaction of genotype and environment during
growth and development.
variance: Variance of the phenotype
due to genotypic and environmental
factors combined. Phenotypic variance = genetic variance +
The study of ancestral relations among species, often illustrated
with a "tree of life" branching diagram, which is
also known as a phylogenetic tree. Phylogenetics is the study
of evolutionary relationships and relatedness among various
groups of organisms as applied to the level of domains, phyla,
orders, etc. Phylogeny (or phylogenesis) traces the origin
and evolution of a set of organisms, usually a set of species.
A major task of systematics is to determine the ancestral
relationships among both extant and extinct known species.
(plural phyla): One of the highest levels of taxonomic classification.
See taxon. More
Pathway: The sequence of biochemical interactions among proteins
that regulates the function of living cells.
Microscopic aquatic organisms that, like plants, use photosynthesis
to capture and harness solar energy.
Originating in various ways or from various sources.
tectonics: The theory that the surface of the earth is made
of a number of plates, which have moved throughout geological
time resulting in the present-day positions of the continents.
Plate tectonics explains the locations of mountain building
as well as earthquakes and volcanoes. The rigid plates consist
of continental and oceanic crust together with the upper mantle,
which "float" on the semi-molten layer of the mantle
beneath them, and move relative to each other across the earth.
Six major plates (Eurasian, American, African, Pacific, Indian,
and Antarctic) are recognized, together with a number of smaller
ones. The plate margins coincide with zones of seismic and
A condition in which a population possesses more than one
allele at a locus. Sometimes it is defined
as the condition of having more than one allele with a frequency
of more than five percent in the population.
group: A set of species descended
from more than one common ancestor. The ultimate common ancestor
of all species in the group is not a member of the polyphyletic
group, usually because the common ancestor lacks the characteristics
of the group.
An individual containing more than two sets of genes and chromosomes.
A group of organisms, usually a group of sexual organisms
that interbreed and share a gene pool, and are normally relatively
isolated from other groups of the same species.
isolation: A form of reproductive isolation in which a zygote
is successfully formed but then either fails to develop or
develops into a sterile adult. Donkeys and horses are postzygotically
isolated from one another; a male donkey and a female horse
can mate to produce a mule, but the mule is sterile.
isolation: A form of reproductive
isolation in which the two species never reach the stage of
successful mating, and thus no zygote is formed. Examples
would be species that have different breeding seasons or courtship
displays, and which therefore never recognize one another
as potential mates.
array: Used in microarray technology
- a silicon or glass chip to which small pieces of DNA,
or probes, have been attached, with each probe representing
a sequence of bases unique to a known gene or gene fragment.
Also known as a microarray or DNA chip.
A cell without a distinct nucleus. Bacteria and some other
simple organisms are prokaryotic. Compare with eukaryote.
All prokaryotes form a paraphyletic
The earliest stage recognized in larval trilobite (Trilobita)
development. The larva is small, often spiny, and grows through
successive moult stages. Initially it is a small disc but
size and segmentation increase with each successive moult.
A molecule made up of a sequence of amino
acids (there are 23 different amino acids). Many of the
important molecules in a living thing -- for example, all
enzymes -- are proteins.
An organism that belongs to the kingdom Protista,
which includes forms with both plant and animal affinities,
i.e., protozoans, bacteria, and some algae, fungi, and viruses.
symmetry: The arrangement of
parts in an organ or organism such that cutting through the
centre of the structure in any direction produces two halves
that are mirror images of each other. The stems and roots
of plants usually show radial symmetry, while all animals
belonging to the Cnidaria (e.g. jellyfish) and Echinodermata
(e.g. starfish) are radially symmetrical - and typically sessile
- in their adult form. The term actinomorphy is used to describe
radial symmetry in flowers.
Proteins that can bind to other specific molecules. Usually
on the surface of a cell, receptors often bind to antibodies
An allele (A) is recessive if the phenotype
of the heterozygote (Aa) is the same as the homozygote (aa)
for the alternative allele (a) and different from the homozygote
for the recessive (AA). The allele (a) controls the heterozygote's
phenotype and is called dominant. An allele may be partly,
rather than fully, recessive; in that case, the heterozygous
phenotype is nearer to, rather than identical with, the homozygote
for the dominant allele.
species concept: A
concept of species according to which a species is a set of
organisms that recognize one another as potential mates; they
have a shared mate recognition system. Compare with biological
species concept, cladistic species concept, ecological species
concept, and phenetic species concept.
fauna: A group of animal species that is found in a particular
environment. As the environment recurs, so does the fauna.
isolation: Two populations
or individuals of opposite sex are considered reproductively
isolated from one another if they cannot together produce
fertile offspring. See prezygotic isolation and postzygotic
oceanic: A major submarine mountain range.
system: The oceanic ridges formed where tectonic plates are
separating and a new crust is being created; also, their on-land
counterparts such as the East African Rift.
zone: A zone of volcanic features associated with underlying
dikes. The location of the rift is marked by cracks, faults,
The regions of mountain-building earthquakes and volcanoes
which surround the Pacific Ocean.
a linear, usually single-stranded polymer of ribonucleotides,
each containing the sugar ribose in association with a phosphate
group and one of four nitrogenous bases: adenine, guanine,
cytosine, or uracil. RNA is found in all living cells; in
prokaryotic and eukaryotic cells, it encodes the information
needed to synthesize proteins (i.e., it copies instructions
that it receives from DNA); in certain viruses, it serves
as the genome. (An abbreviation for ribonucleic acid.)
A clastic sedimentary rock in which the particles are dominantly
of sand size, from 0.062 mm to 2 mm in diameter.
attached or stationary, as opposed to free-living or motile.
spreading: The mechanism by which new seafloor crust is created
at oceanic ridges and slowly spreads away as plates are separating.
A submarine volcano.
facies: An accumulation of deposits that exhibits specific
characteristics and grades laterally into other sedimentary
accumulations that were formed at the same time but exhibit
rock: Rock formed from the accumulation
of sediment, which may consist of fragments and mineral grains
of varying sizes from pre-existing rocks, remains or products
of animals and plants, the products of chemical action, or
mixtures of these.
The order of the chemical bases -adenine (A), thymine (T),
cytosine (C), and guanine (G)-in a gene. The base sequence
determines the order of amino acids making up the protein
encoded by the gene.
Shale is a fine-grained sedimentary rock whose original constituents
were clays or muds. It is characterized by thin laminae breaking
with an irregular curving fracture parallel to in situ
A chemical combination of silicon and oxygen.
nucleotide polymorphism (SNP): A site on the DNA at which
the base sequence differs among individuals. (The abbreviation
is pronounced "snip.")
Sirenia: mammal herbivors adapted to aquatic coastal environments
such that arms are modified into paddles, have no legs, are
fat, and have highly modified skulls with greatly reduced
dentition. Their nipples are under their arms (e.g. the extant
Changes in related organisms to the point where they are different
enough to be considered separate species. This occurs when
populations of one species are separated and adapt to their
new environment or conditions (physiological, geographic,
An important classificatory category, which can be variously
defined by the biological species concept, cladistic species
concept, ecological species concept, phenetic species concept,
and recognition species concept. The biological species concept,
according to which a species is a set of interbreeding organisms,
is the most widely used definition, at least by biologists
who study vertebrates. A particular species is referred to
by a Linnaean binomial, such as Homo sapiens for human beings.
gravity: The ratio of the density of a material to the density
a paraphyletic grouping of organisms comprising the total
group (pan-group) less
members of the crown group, and consequently
excluding all extant members of the pan-group. By this definition,
a stem group contains only the primitive relatives of members
of the crown groups, all the way back to and excluding the
crown group’s last common ancestor as well as the crown
groups nearest extant relatives. By definition then, all
members of a stem group are, in fact, extinct.
The study of rock strata, especially of their distribution,
deposition, and age.
The succession and age relation of layered rocks.
Morphologically circumscribed accretionary growth structures
with primary lamination that is, or may be, biogenic.
In geology, engineering, and surveying, subsidence describes
the motion of a surface (usually, the Earth's surface) as
it shifts downward relative to a reference point such as sea-level.
The opposite of subsidence is uplift, which results in an
increase in elevation.
(plural taxa): Any named taxonomic group, such as the family
Felidae, or the genus Homo, or the species Homo sapiens. Also,
a formally recognized group, as distinct from any other group
(such as the group of herbivores, or the group of tree-climbers).
The theory and practice of biological classification.
An attribute or character of an individual within a species
for which heritable differences can be defined.
The process by which messenger RNA is read from the DNA forming
set of activated genes associated with specific tissue, which
will vary over time.
RNA (tRNA): A type of RNA that brings the
amino acids to the ribosomes to make proteins. There are 20
kinds of transfer RNA molecules, one for each of the 20 main
amino acids. A transfer RNA molecule has an amino acid attached
to it, and contains the anticodon corresponding to that amino
acid in another part of its structure. In protein synthesis,
each codon in the messenger RNA combines with the appropriate
tRNA's anticodon, and the amino acids are arranged in order
to make the protein.
The group (specifically, a subphylum) of animals, descended
from a common ancestor, that share the derived character of
an internal skeleton made of bone or cartilage.
A measure of resistance to flow in a liquid (water has low
viscosity while honey has a higher viscosity.)
The cell formed by the fertilization of male and female gametes.