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acronomic adj. describes an animal that dwells in
high places (treetops, cliffs, etc.)
accretion
n. an object grown by the process of externally layering
material one layer on top of another. Caliche and pearls are
examples of accretions --accrete v.
altricial adj. describes organisms that are
born relatively undeveloped, requiring significant parental care for
survival. Humans are an example of an altricial organism
anchor taxa adj. describes the taxa used to
define a phylogenetic taxon or clade
apomorph n.
1. evolutionarily advanced ('derived') character state. The long
neck of the giraffe is apomorphic; the short neck of its ancestor is
plesiomorphic 2. in cladistics, a character state present
throughout a clade but not present in any close outgroup of the
clade --apomorphy n. --apomorphic adj.
arboreal adj. describes an organism that
spends most of its life in trees, off the ground
Archosauria n. ("ruling lizards") clade of
animals, partly distinguished by an antorbital fenestra, that
includes the Crocodylia, Pterosauria, Dinosauria, and several other
closely related groups of animals --archosaur adj.
autapomorph n. 1. apomorph character state
that is unique to a particular species or lineage in the group under
consideration 2. in cladistics, an apomorphy that
distinguishes a single clade --autapomorphy n.
--autapomorphic adj.
caliche
n. nodules of calcium carbonate (CaCO3) formed in soil. Caliche forms due to the
rise and fall of mineral-rich groundwater during wet and dry
seasons. When the water rises it deposits calcium carbonate into the
soil which accretes into caliche nodules. The length of time it
takes for certain size nodules to grow, and at what distance from
the surface, is well known. In paleontology caliche is therefore an
excellent indicator of how long a layer of soil existed before it
changed due to erosion or deposition (Horner, John. 1988. Digging
Dinosaurs. New York: Workman Publishing.)
character
n. any well-defined feature, whether anatomical,
behavioral, biochemical, or genomic, of an organism
character state n. a changeable attribute of a
character; the state that a character is in. The most basic
character state is either absent or present.
clade
n. a hypothetical species of animal and all its
descendants; a monophyletic taxon. Clades should not be mistaken for
actual "family trees" as clades are hypothetical groupings whereas
"family trees" are real groupings. Clades replace the old system of
Linnean rankings such as Class, Order, etc. An animal is a member of
every clade that its ancestors are, thus making a bird a reptile (it
is descended from a member of clade Reptilia) and a human a mammal
(it is descended from a member of clade Mammalia). Clades carry both
a definition, based on ancestry, and a diagnosis, based on
synapomorphies. For example, the node-based clade Dinosauria is
defined as the most recent common ancestor of "birds" and
Triceratops (Holtz and Padian 1995) and all its descendants,
and diagnosed by at least three sacral vertebrae, a partially to
fully open acetabulum, and other synapomorphies. It should be noted
that diagnoses of clades can change while definitions do not
cladistics n. (also known as phylogenetic
systematics and Hennigian systematics) the whole field of
phylogenetic reconstruction, approximation, description, and
analysis using the principle of shared derived characters for
determining relationships. Organisms are classified by analyzing the
distribution of their characters and character states, determining
which characters are synapomorphies, plesiomorphies, or homoplasies,
and then grouping the organisms into clades using the
synapomorphies. Although there were German and South American
antecedents to cladistics dating back a century, cladistics as
practiced today stems from the work of Willi Hennig in the 1950s and
1960s
cladogram n. a diagram (usually a graph)
depicting the results of a cladistic analysis and displaying the
clades into which the analyzed organisms have been classified
coenose n. an assemblage of fossils
common ancestor n. 1. the hypothetical single
species of organisms that two or more different species of organisms
evolved from 2. in cladistics, a species that evolves into a
clade
convergent adj. describes characters
that are similar in structure and function but have arisen
separately rather than from a common ancestor. Convergence is common
in groups that become adapted to a similar habitat or way of life;
the similar body shapes of the North American Gray Wolf and the
Tasmanian Wolf, each evolving from different ancestors (the former
is a placental mammal, the latter is a marsupial mammal), resulted
from secondary adaptation to similar habitats --convergence
v.
crown clade n. a clade whose
definition is restricted to the most recent common ancestor of all
living members of the clade and all its descendants. For example,
the most recent common ancestor of all modern birds and all its
descendants is the crown clade Neornithes. Note that all crown
clades are node-based clades, but not all node-based clades are
crown clades
cursorial adj. describes an
animal built for rapid terrestrial locomotion
derived adj. describes a character or
group of characters that has changed from its primitive state;
advanced. The anatomy of a bird's forelimb (wing) is derived
relative to the anatomy of a reptilian forelimb
derived
characteristic n. evolutionarily advanced character state
(synonym of apomorph)
descendant adj.
describes a species or taxon that has evolved from another species
or from within a taxon
Diapsida n. ("two
holes") clade of animals, partly distinguished by two temporal
fenestrae, that includes the Archosauromporpha, Lepidosauromorpha,
and several other closely related groups of animals --diapsid
adj.
dinosaur adj. 1. in proper
usage, describes any member of clade Dinosauria 2. in common
usage, describes any member of clade Dinosauria that is not a "bird"
Dinosauria n. ("fearfully great lizards")
clade of animals, partly distinguished by a largely to fully open
acetabulum, that first evolved in the latter third of the Triassic
and was the dominant land animal from the early Jurassic to the end
of the Cretaceous. Holtz and Padian (1995) define Dinosauria as the
most recent common ancestor of Triceratops and modern birds,
and all its descendants. Dinosaurs were wholly terrestrial, with no
known aquatic species. Only one major clade of dinosaurs, Aves
("birds"), survives today
directional selection
n. natural selection where species survive by evolving
new characters or modifying old characters. Genotypes that produce
new characteristics have great reproductive success, and
consequently the gene frequencies for these characters shift.
Directional selection results in evolutionary changes; it is,
however, a relatively short-lived process, because once a new
adaptive state is reached the population then enters stabilizing
selection
disruptive selection n. natural
selection where subpopulations of a single species within the same
habitat exhibit different adaptations. Disruptive selection occurs
when a habitat contains distinctly different types of soil
conditions, food sources, or other factors, and developing
subpopulations adapt to particular features of the area. Disruptive
selection results in evolutionary changes and new species; once this
occurs, however, the subpopulations enter into stabilizing selection
evolution v. changes in the character
states of organisms, species, and clades through time
exaptation v. (formerly preadaptation)
adoption of a character that had one use in an ancestral form into a
new, different use in a descendant form. For example, three bones in
the jaws of the ancestors of mammals were exapted into the hammer,
stirrup and anvil, the bones of the middle ear --exaptation
adj.
exclusive anchor taxon adj.
describes the anchor taxon not included in the taxon being defined.
For example, in the stem-based clade definition of Carnosauria,
Allosaurus and all taxa sharing a more recent common ancestor
with Allosaurus than with "birds," "birds" is the exclusive
anchor taxon
extant adj. describes types or
species of animals that are currently living. Not extinct
faculative biped adj. describes an
animal that walks or otherwise moves about on its two hindlimbs, but
can and does spend some time locomoting on all four limbs
faculative quadruped adj. describes an animal
that walks or otherwise moves about on all four limbs, but can and
does spend some time locomoting on only its hindlimbs
genotype n. a specific combination of
genes that determine a character. For example; in humans each
character is determined by the combination of two genes specific to
that character. Let B and b represent the two genes that determine
height (a capital letter denotes a dominant gene, a lowercase letter
denotes a recessive gene). Each human will have one of the height
genotypes BB, Bb or bb. If two humans produce an offspring, the
offspring will receive one of its height genes from the mother and
the other from the father. If the father has the height genotype BB
and the mother bb, then the offspring will have the height genotype
Bb (B from the father, b from the mother). Parents with height
genotypes BB and BB can only produce offspring with height genotype
BB (similarly bb and bb can only produce bb). BB and Bb can produce
offspring with genotypes BB or Bb; Bb and Bb can produce offspring
with genotypes BB, Bb or bb. In mixed genotypes (in our example Bb)
the dominant gene determines the character (if B is tall and b is
short, the offspring with genotype Bb will be tall)
graviportal adj. describes an animal built for
slow terrestrial locomotion as a result of its comparatively heavy
body weight
homology n. a similar
character state present in two or more species of organisms that is
derived from a single character in their common ancestor
--homologous adj.
homoplasy n. a
character state present in two or more species of organisms that is
not present in their common ancestor 2. in cladistics, a
character present in at least two clades that is absent in the
common ancestor of the two clades
ichnocoenose
adj. an assemblage of trace fossils, such as an area
containing dinosaur trackways
inclusive anchor taxon
adj. describes the anchor taxon included in the taxon
being defined. For example, in the stem-based clade definition of
Carnosauria, Allosaurus and all taxa sharing a more recent
common ancestor with Allosaurus than with "birds,"
Allosaurus is the inclusive anchor taxon
K-selection n. natural selection
typically occurring in populations near the carrying capacity (K) of
the environment. This tends to result in a species which survives by
producing few young with substantial resource investment by the
parents, who typically care for the young until they reach maturity
--K-selected adj.
Lagerstatte
deposit n. a deposit that preserves an extensive
cross-section of the biota that once lived at that locality.
Lagerstatte deposits can be Konzentrat-lagerstatte, deposits with
very high numbers of fossils, or Preservat-lagerstatte where the
fossils are preserved in exceptional detail, including preservation
of soft body parts. The Cleveland-Lloyd deposit is a
Konzentrat-lagerstatte deposit. The Solnhofen limestone of Bavaria,
Germany, the volcanic deposit of Liaoning, China and the Burgess
Shale of Canada are all Preservat-lagerstatte deposits
lacustrine adj. describes anything
characteristic of lakes. In geology it describes deposits formed by
lakes or preserving lake environments. Lacustrine deposits can be
limestone, shale, mudstone or saline deposits. The lithographic
limestones of Las Hoyas, Cuenca, Spain and the volcanic ash deposits
of Liaoning, China, are lacustrine deposits.
"mammal-like" reptile adj. term once
used to describe those animals that were thought to have been
reptiles yet thought to have exhibited mammal-like characteristics
during life, such as homeothermy. This term has fallen into disfavor
as the clade Reptilia has been greatly refined and now excludes
those animals formerly called "mammal-like" reptiles. These animals
are now referred to the clades Synapsida and Therapsida, with the
latter often called "proto-mammals." The Therapsids were the direct
ancestors of the true mammals, while Synapsids were the direct
ancestors of the Therapsids.
Maniraptora n.
("hand robbers") a clade of animals defined as birds and all taxa
closer to birds than to Ornithomimus. It should be noted that
this is not a grouping of dinosaurs that may include birds, it is a
grouping of birds that may include certain dinosaurs. If it would be
discovered that birds are not dinosaurs but crocodiles, for example,
the group would be nested in the crocodilia, retain its name, and be
a bird group that no longer includes any dinosaurs but may include
certain crocodiles
matrix n. a substance in
which rocks, minerals, fossils or other similar materials are
embedded. In paleontology, matrix is the rock in which a given
fossil is embedded
mediportal adj. describes
an animal built primarily for slow terrestrial locomotion as a
result of its comparatively heavy body weight, but with a few
adaptations for speed, such among the rhinoceratidae
monophyletic adj. describes a taxon or clade
that contains all the descendant organisms or taxa of its common
ancestor
monospecific adj. describes a
grouping, assemblage, collection, etc., that is comprised of only
one species
monotreme n. member of a lineage
of egg-laying mammals. The platypus and echidna are the only
surviving members of this lineage
multituberculate
n. member of a diverse lineage of rodent-like non-therian
mammals that were common from the late Jurassic to the early Eocene.
Monotremes may be their closest living relatives
natural selection n. the process in
evolution by which those individuals of a species with characters
that help them to become adapted to their specific environment tend
to transmit their characters, while those less able to become
adapted tend to die out
node-based clade n. a
clade defined as the most recent common ancestor of two or more taxa
and all its descendants. For example, the node-based clade
Allosauroidea is defined as the most recent common ancestor of
Allosaurus and Sinraptor and all its descendants
nodule n. a small, rounded lump of mineral,
usually harder than the surrounding rock
non-avian dinosaur adj. describes any member
of clade Dinosauria that is not a bird --dinosaur (common
usage) syn.
obligate biped
adj. describes an animal whose anatomy requires it to use
only its two hindlimbs in walking or similar locomotion. A bird is
an example of an obligate biped
obligate quadruped
adj. describes an animal whose anatomy requires it to use
all four limbs in walking or similar locomotion. An elephant is an
example of an obligate quadruped
Ornithischia
n. ("bird hips") formerly the major grouping of dinosaurs
that is comprised of the beaked dinosaurs. Padian and May (1993)
formally defined Ornithischia as Triceratops and and all taxa
closer to Triceratops than to Saurischia. Dropped by this
author in favor of Predentata --ornithischian adj.
outgroup n. in cladistics, a clade considered
primitive to a group of organisms in a cladistic analysis of that
group
Ornithopoda n. ("bird feet") clade
comprised of three-toed predentatans --ornithipod adj.
organism n. an individual member of a species;
a single biological entity
paraphyletic
adj. describes a taxon or clade that does not contain all
the descendant species or taxa of their common ancestor
parallelism n. an evolutionary pattern that
results in the formation of homologous character states. The similar
body forms of Old World Monkeys and New World Monkeys are due to
their having a common ancestor; their similar body forms are due to
parallel evolution rather than convergence
parsimony,
principle of n. a scientific rule that states that if
there exists two answers to a problem or a question, and if, for one
answer to be true, well-established laws of logic and science must
be re-written, ignored, or suspended in order to allow it to be
true, and for the other answer to be true no such accommodation need
be made, then the simpler of the two answers (the second) is much
more likely to be correct. In cladistics, the phylogenetic
reconstruction that requires fewer changes (evolutionary steps) is
more parsimonious than one that requires more steps. What
constitutes a parsimonious solution can sometimes be open to
interpretation --parsimonious adj.
phylogeny n. the evolutionary development and
history of a species or higher taxonomic grouping of organisms. The
phylogeny of an organism is sometimes called a "family tree."
Cladistics is used to construct hypothetical phylogenies, called
clades --phylogenetic adj.
phylogenetic
taxonomy n. the branch of cladistics concerned with the
verbal representation (rather than the reconstruction or estimation)
of phylogenetic relationships. It was developed by Kevin de Queiroz
and Jacques Gauthier in a series of papers in the early 1990s.
plesiomorph n. evolutionarily primitive
character state. The long neck of the giraffe is apomorphic; the
short neck of its ancestor is plesiomorphic; a character present
throughout a taxon because it is present in an outgroup of the taxon
--plesiomorphy n. --plesiomorphic adj.
polyphyletic adj. describes a taxon or clade
that does not include the common ancestor of the taxon's or clade's
species. Polypheletic groups are often of different species of
animals that do not share a recent common ancestor. An example of
this is the Pachydermata, an early grouping no longer used, that
united rhinos, hippos and elephants. All of these animals evolved
their similar forms from different ancestors, rather than from the
same shared ancestor, thus making the Pachydermata polypheletic
precocial adj. describes organisms that are
born capable of surviving with little or no parental care. Sea
turtles are an example of a precocial organism
Predentata
n. ("predentary-boned (dinosaurs)") major grouping of
dinosaurs that is comprised of the beaked dinosaurs. Formerly called
the Ornithischia, the name was dropped by this author in favor of
Predentata as this new name is based on a character that
predentatans share with no other dinosaurs, a predentary bone.
Padian and May (1993) formally defined Ornithischia, now Predentata,
as Triceratops and and all taxa closer to Triceratops
than to Saurischia --predentatan adj.
primitive adj. describes a character state in
the common ancestor of a clade. A five-digit forefoot is the
primitive forefoot state in amniotes.
Pterosauria
n. ("winged lizards") clade of animals, partly
distinguished by a greatly elongated fourth finger that supported a
membranous wing, that first evolved in the latter third of the
Triassic and survived until the end of the Cretaceous. Pterosaurs
were not dinosaurs, but were closely related to both dinosaurs and
crocodiles --pterosaur adj.
r-selection n. natural selection
typically occurring in situations that favor a high reproductive
rate (r). This tends to result in a species which survives by
producing many young with minimal individual resource investment by
the parents, who typically abandon their eggs or newborns
--r-selected adj.
Reptilia n.
all descendants of the most recent common ancestor of turtles,
lepidosaurs (tuataras and squamates), and archosaurs (crocodilians
and birds). In the past, animal groups were defined by physical
traits such as hair, scales or whether they were "warm-" or
"cold-blooded." Animals are now grouped by ancestry thus making
birds reptiles, or more formally members of the clade Reptilia,
despite the fact that they carry few of the traits that defined the
Class Reptilia of the old Linnean system of taxonomy. Because birds
in particular do not share the characteristics that many people
today think all reptiles should have, many scientists favor dropping
the name "Reptilia" and adjective "reptile" completely
Saurischia n. ("lizard hips") major grouping
of dinosaurs that is comprised of theropods and sauropods. Gauthier
(1986) formally defined Saurischia as birds and all taxa closer to
birds than to Ornithischia (Predentata) --saurischian
adj.
Sauropoda n. ("lizard feet")
clade comprised of quadrupedal, plant eating saurischians
--sauropod adj.
scansorial adj.
describes an animal with unspecialized limbs allowing it to grasp
and climb as well as walk and run
species n.
1. a freely interbreeding population of organisms. The organisms
in a species usually share a large number of characters. 2.
generally the lowest level in a taxonomy
stabilizing
selection n. natural selection where species survive by
maintaining existing characters. Individuals that exhibit extreme
variations of any critical characters are eliminated, and the
population tends to become narrow in the expression of adapted
traits. Stabilizing selection does not result in evolutionary
changes; rather, the existing state of adaptation is maintained
stem-based clade n. a clade defined as one
taxon and all taxa sharing a more recent common ancestor with that
taxon than with another. For example, the stem-based clade
Carnosauria is defined as Allosaurus and all taxa sharing a
more recent common ancestor with Allosaurus than with
"birds." Despite appearances, stem-based clades, like node-based
clades, include the actual common ancestor of the taxa in the clade;
the common ancestor of the taxa in the clade is considered to be
ancestral to itself. For example, the actual species from which the
entire Carnosauria evolved, which we will call the ur-carnosaur,
shares a more recent common ancestor with Allosaurus than it
does with "birds," thus making it a carnosaur. That common ancestor
of Allosaurs and the ur-carnosaur is the ur-carnosaur itself
synapomorph n. 1. apomorphic features
possessed by two or more taxa in common. If the two groups share a
character state that is not the primitive one, it is plausible that
they are related in an evolutionary sense, and only synapomorph
character states can be used as evidence that taxa are related.
Phylogenic trees are built up by discovering groups united by
synapomorphies. 2. in cladistics, an apomorphy that occurs in
two related clades and thereby supports grouping of the two clades
into a single larger clade --synapomorphy n.
--synapomorphic adj.
taxon n.,
pl. taxa 1. a group of organisms of any
taxonomic rank, e.g. family, genus or species 2. a group of
organisms or other taxa sharing a single common ancestor
taxonomy n. 1. the method of classifying
things into groups 2. in biology, the classification of
living organisms into taxa. A biological taxonomy is cladistic if
all the taxa are clades.
terrestrial adj.
living on land
thanatocoenose n. an assemblage
of fossils that formed at the actual place of death
therian mammal n. mammal within the
marsupial+placental clade
Theropoda n. ("beast
feet") major grouping of dinosaurs that is comprised of carnivorous
dinosaurs and birds --theropod adj.
total
group n. a stem-based clade defined using two crown
clades. For example, the total group Crocodylotarsi is defined as
the crown clade Crocodylia and all taxa sharing a more recent common
ancestor with the Crocodylia than the crown clade Neornithes
volant adj. describes an animal
capable of flight
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