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DINOSAUR GLOSSARY

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