Organismal groups that appear in this glossary are cladistically defined as either stem-based or node-based taxa and diagnosed on the basis of their shared derived characters (synapomorphies). See de Queiroz and Gauthier 1990 for the rationale for this decision. Also included in some of these entries is a reference to a recent comprehensive study of the taxon.
Acromion: A bony spine or process on the outer side of the scapula, to which some of the shoulder musculature is attached. This feature is very prominent in nodosaurid ankylosaurs.
Actinistia: The fleshy-finned fish, cladistically defined as the common ancestor of Miguashaia and Latimeria, and all the descendants of this common ancestor. This clade can be diagnosed by modifications of the appendicular fin skeleton, among other features. The most famous actinistian is the living coelacanth, Latimeria. See also “Coelacanth.”
Albian: The interval of geologic time from approximately 112 to 99 million years ago.
Allopatry: When two species do not occur together, but exclude each other geographically.
Alpine Tethyan Sea: An oceanic basin, located where the western Alps presently are, that opened in the Early Jurassic (following the opening of the Atlantic Ocean) and closed during the Tertiary.
Altriciality: The kind of vertebrate ontogeny that is characterized by a short gestation and the birth of relatively underdeveloped, helpless young.
Alvarezsauridae: A node-based taxon defined as the most recent ancestor of Mononykus and Alvarezsaurus, and all the descendants of this ancestor. This clade is diagnosed by laterally compressed synsacral vertebrae, extreme modification of the forelimbs, and the absence of distal fusion in the pubis and ischium, among other characters. The phylogenetic position of alvarezsaurids is quite controversial. These theropods have been placed on either side of Archaeopteryx, making them either a true avialan clade or a very close outgroup. On the other hand, alvarezsaurids have been identified as the sister group to ornithomimosaurs. Other alvarezsaurids include Shuvuuia, Mononykus, and Patagonykus (Chiappe et al. 2002).
Ammonites: An extinct group of marine cephalopods whose closest living relative is the modern pearly nautilus. Their shells generally are in the form of flat spirals, although others uncoil to produce a straight conical shell. Known worldwide from the Silurian to the end of the Cretaceous, ammonites were among the top predatory invertebrates of their time.
Ankylosauria: The “armored” dinosaurs, a stem-based taxon defined as all eurypodan thyreophorans closer to Ankylosaurus than Stegosaurus. This clade can be diagnosed by numerous features of the skull, vertebral column, pelvis, and armor. Other ankylosaurs include Edmontonia, Ankylosaurus, and Pinacosaurus (Vickaryous et al. 2004).
Ankylosauridae: A stem-based taxon defined as those ankylosaurs more closely related to Ankylosaurus than to Edmontonia, and diagnosed by having a pyramidal squamosal boss, raised nuchal sculpturing, a premaxillary palate that is wider than long, a premaxillary notch, a deltoid quadratojugal boss, a postocular shelf, and a tail club, among other features. Other ankylosaurids include Gobisaurus, Saichania, and Euoplocephalus (Vickaryous et al. 2004).
Apparent polar wandering: The apparent migration, over Earth’s surface, of Earth’s magnetic poles through geologic time. Known from the direction of magnetization of many rocks, apparent polar wandering attests to the movement of continental landmasses and makes it possible to infer the relative movement of various continental blocks over different intervals of geologic time.
Aptian: The interval of geologic time from approximately 121 to 112 million years ago.
Apulia: A region in southeastern Italy, on the Adriatic coast and the Gulf of Taranto. In terms of plate tectonics, it is a microcontinental plate that once formed the promontory of northern Africa, but it detached to eventually suture with several other microcontinents and the Eurasian plate to form Italy, the inner region of Transylvania, and the Banat. See also “Moesia” and “Rhodope.”
Aves: The monophyletic clade of all living birds; crown-group birds.
Avetheropoda: A node-based taxon consisting of Allosaurus fragilis, Passer domesticus (the living English sparrow), their most recent common ancestor, and all of its descendants, diagnosed by broad contact between the quadratojugal and the squamosal, palatine recesses, laterally displaced zygapophyses of the cervical vertebrae, a large and narrow iliac preacetabular fossa, an obturator process that is separated from the pubic plate, and the development of an accessory trochanter on the proximal lateral surface of the femur, among other characters. Other avetheropods include Sinraptor, Carcharodonto-saurus, Archaeopteryx, and modern birds (Holtz and Osmólska 2004).
Avialae: A stem group encompassing living birds and all maniraptorans closer to them than to Deinonychus, a dromaeosaurid. This clade is diagnosed by many features, among them long, narrow, and pointed premaxillae; a quadrate that articulates with the prootic and the squamosal; unserrated teeth that are reduced in size and number; a pronounced acromion process on the scapula; a coracoid with a pronounced sternal process; forelimbs that are nearly as long as or longer than the hind limbs; forearms approximately as long as or longer than the humerus; and modifications of the foot, among other characters. This clade includes Archaeopteryx, Hesperornis, and Aves (Padian et al. 2004).
Azhdarchidae: A stem-based taxon defined as all pterosaurs more closely related to Quetzalcoatlus than to Tapejara, diagnosed by an elongation of the middle cervical vertebrae and the reduction or loss of the neural spines on these cervicals. In addition to Quetzalcoatlus, Azhdarchidae presently includes Azhdarcho (Kellner 2003).
Biogenic Law: Haeckel’s term for his principle that ontogeny recapitulates phylogeny.
Biogeography: The study of the geographic distribution of life.
Biological constraints: The limits or boundary conditions on biological traits whose success or failure depends on alternatives in other organisms with which a species competes. These biological constraints are historical and developmental in their essence, since the ultimate arbiter is competitive advantage, and thus survival is imparted by design.
Biological determinism: A theory that claims that the traits of organisms are entirely determined by the interaction of genetic variation and the overarching control of natural selection.
Bioturbation: The biological activities that occur at or near the sedimental surface that cause the sediment to become mixed. Examples of these activities include burrowing and boring.
Campanian: The interval of geologic time from approximately 83.5 to 71.3 million years ago.
Casichelydia: A stem-based taxon defined as all testudines closer to Crysemys picta (the living painted turtle) than to Proganochelys. This clade is diagnosed by the loss of the lacrimal bone and duct, and a modification of the palate and braincase. Other casicheyids include Kayentachelys and two living turtles, the yellow-spotted Amazon River turtle (Podocnemis unifilis) and the eastern box turtle (Terrapene carolina) (Gaffney and Meylan 1988).
Cenomanian: The interval of geologic time from approximately 99 to 93.5 million years ago.
Ceratopsia: A stem clade defined as all of Marginocephalia closer to Triceratops than to Pachycephalosaurus, which is diagnosed by a high external naris separated from the ventral border of the premaxilla by a flat area, a rostral bone, an enlarged premaxilla, well-developed lateral flaring of the jugal, wide dorsoventral length of the infraorbital ramus of the jugal, and contact of the palatal extensions of the maxillae rostral to the choana. Other ceratopsians include Psittacosaurus, Protoceratops, and Styracosaurus (You and Dodson 2004).
Ceratosauria: A stem-based taxon defined as those theropods more closely related to Ceratosaurus nasicornis than to birds. This clade can be diagnosed by modifications of the vertebral column and pelvis, among others. Other ceratosaurians include Coelophysis, Syntarsus, and Carnotaurus. There is some question about the monophyly of this group (Tykoski and Rowe 2004).
Cimmerian block: An elongate and narrow continental block that, when it began its northern motion approximately 280 million years ago, extended from modern-day Gibraltar to the eastern margin of Australia, where it formed the southern margin of the Paleotethyan Ocean. The Cimmerian block docked with the Eurasian continental landmass, thereby creating the largest extent of the Neotethyan Ocean, about 200 million years ago.
Clade: A group of biological taxa that includes all the descendants of a single common ancestor.
Cladistics: A system of biological taxonomy that defines taxa by shared unique characteristics not found in ancestral groups and uses inferred evolutionary relationships to arrange taxa in a branching hierarchy, such that all members of a given taxon have the same ancestors. See also “Phylogenetic systematics.”
Cladogram: A branching diagrammatic tree used in cladistic classification to illustrate phylogenetic relationships.
Coelacanth: Usually refers to the living form, Latimeria, and its two species (L. chalumnae and L. menadoensis), as well as their closest (but extinct) relatives. See also “Actinistia.”
Coevolution: Evolution involving successive changes in two or more ecologically interdependent species that affect their interactions.
Comparative anatomy: The study of the anatomy of several groups of organisms.
Cope’s Rule: The tendency for size increases to occur in evolutionary lineages.
Court Jester hypothesis: A model of extinction in which changes in the physical environment are the initiators of major changes in organisms.
Crocodylia: A node-based (crown-group) taxon defined as the common ancestor of the living Alligator mississippiensis and the living Gavialis gangeticus, and all the descendants of this common ancestor. This clade is diagnosed by the construction of the skull roof and the mandible. Modern crocodilians include alligators, crocodiles, gavials, and caimans, among others (Buscalioni et al. 2001).
Crown group: The clade made up of all living members of the group, the ancestor of that clade, and all the descendants of that ancestor. Examples include Mammalia, Aves, and Archosauria.
Cryptodira: The hidden-necked turtles, a node-based taxon defined as the common ancestor of Kayentachelys and Crysemys picta (the living painted turtle), and all the descendants of this common ancestor. This clade can be diagnosed by several features of the palate, the jaw system, and the skull roof, as well as the turtle’s unique way of folding its neck. Other cryptodires include Meiolania, living soft-shelled freshwater turtles, and the modern Galápagos giant tortoise (Geochelone nigra) (Gaffney and Meylan 1988).
Dacians: The people who inhabited the region known as Dacia (in what is now Romania, Moldova, and parts of Serbia, Bulgaria, Hungary, and Ukraine) between the second century BCE and the second century CE, when they were conquered by the Romans.
Definition: A statement about the membership of a clade, based on common ancestry.
Dental battery: Upper and lower dentition, composed of abundant (up to 60 tooth positions), closely packed cheek teeth and consisting of one to three functional teeth and up to five replacement teeth per tooth position. Dental batteries are known in hadrosaurid dinosaurs.
Diagnosis: The list of features that are synapomorphies, delimiting the taxon that has been defined.
Diastema: A space between teeth in a jaw, usually referring to the gap between the front of the jaws and the cheek teeth (as seen in hadrosaurids), or the gap between the incisors and premolars (in horses).
Dinosauria: A node-based taxon consisting of Triceratops, Neornithes, their most recent common ancestor, and all their descendants. It is diagnosed by the loss of the postfrontal, elongated deltopectoral crest on the humerus; a brevis shelf on the ventral surface of the postacetabular part of ilium; an extensively perforated acetabulum; a tibia with a transversely expanded, subrectangular distal end, as well as a caudolateral flange and a depression for the astragalus; and an ascending astragalar process on the cranial face of the tibia (Benton 2004).
Dromaeosauridae: A node-based taxon defined as all the descendants of the most recent common ancestor of Microraptor zhaoianus, Sinornithosaurus milleni, and Velociraptor mongoliensis. This clade can be diagnosed by features of the skull roof, the vertebrae, and a sickle-shaped claw on the second digit of the foot, among others. Other dromaeosaurids include Saurornitholestes and Deinonychus (Norell and Makovicky 2004).
Dsungaripteroidea: A node-based pterosaur taxon defined as the most recent common ancestor of Nyctosaurus and Quetzalcoatlus, and all of its descendants, diagnosed by edentulous jaws, a notarium, and a pneumatic foramen on the proximal humerus, among other features. Other dsungaripteroids include Pteranodon, Noripterus, and Anhanguera (Kellner 2003).
Euhadrosauria: The true hadrosaurids, a node-based taxon defined as the common ancestor of Edmontosaurus and Corythosaurus, and all the descendants of this common ancestor. The clade is diagnosed by modifications of the jaws. Other euhadrosaurs include Gryposaurus, Parasaurolophus, and Charonosaurus (Horner et al. 2004).
Eusuchia: The true suchians, a node-based taxon defined as the common ancestor of Hylaeochampsa and Alligator, and all the descendants of this common ancestor. This clade can be diagnosed by modifications of the palate and the vertebrae. Other eusuchians include Alligator, Caiman, and Gavialis (Buscalioni et al. 2001).
Foraminifera: A group of large, chiefly marine protozoans—usually having calcareous shells that often are perforated with minute holes for the protrusion of slender pseudopodia—that form the bulk of chalk and nummulitic limestone.
Founder effect: The principle that the founders of a new, isolated population carry a gene pool that is not representative of that of the population as a whole.
Functional morphology: The study of how biological structures work, which, in paleontology, entails the use of analogies with mechanical and extant animal models.
Ghost lineage: The lineage of an organism for which there is no physical record, but whose existence can be inferred by phylogeny calibrated by stratigraphy. The length of time incorporated into a ghost lineage is known as its ghost lineage duration (GLD).
Gondwana: The region consisting of the once-connected Indian subcontinent and the landmasses of the Southern Hemisphere.
Hadrosauridae: The duck-billed dinosaurs, a node-based taxon defined as the common ancestor of Telmatosaurus and Corythosaurus, and all the descendants of this common ancestor. This clade can be diagnosed by numerous features involving dentition, the skull and palate, the vertebral column, and the appendicular skeleton. Other hadrosaurids include Gryposaurus, Edmontosaurus, and Parasaurolophus (Horner et al. 2004).
Hadrosaurinae: The non-lambeosaurine euhadrosaurians, a stem-based taxon defined as all euhadrosaurs more closely related to Edmontosaurus than to Corythosaurus. This clade can be diagnosed on the basis of modifications of the nasal region of the skull. Other hadrosaurines include Gryposaurus, Maiasaura, and Saurolophus (Horner et al. 2004).
Hadrosauroidea: A stem-based taxon defined as all iguanodontians more closely related to Corythosaurus than to Iguanodon. This clade is diagnosed by modifications of the facial skeleton, the tail vertebrae, the pelvis, and the hind foot. Other hadrosauroids include Shuangmiaosaurus, Altirhinus, and Eolambia (You et al. 2003).
Heterochrony: Evolutionary differences in the features of organisms due to ontogenetic changes in the relative rates or timing of the development of organismal traits. When a descendant is ontogenetically less well developed than its ancestor, the resulting morphology is termed paedomorphic. When its development goes beyond that of its ancestor, the resulting morphology is called peramorphic. See also “Paedomorphosis” and “Peramorphosis.”
Hierarchy: In evolutionary biology, the ordering of organisms by a pattern of common descent; clades within clades.
Histology: The study of tissue structure or organization.
Historical contingency: The conditions by which the details of evolutionary history are unpredictable, that is, determined by chance events and/or by improbable events with large consequences.
Homology: A similarity between two organisms, due to the inheritance of the same feature from a common ancestor.
Homoplasy: A similarity between two organisms, due to separate and independent inheritances from different ancestors. Evolutionary convergence is one kind of homoplasy.
Iguanodontia: A stem-based taxon defined as all euornithopods closer to Edmontosaurus than to Thescelosaurus. This clade can be diagnosed by numerous modifications of the snout, the sternum, the pelvis, and the manus. Other iguanodontians include Dryosaurus, Ouranosaurus, and hadrosaurids (Norman 2004).
Insularity: As used in this volume, the state or condition of being cut off or isolated from other organisms.
Island Rule: The common pattern of a dwarfing of mammals evolving on islands.
K selection / strategy: Selection on individuals in populations at or near the carrying capacity of their environments, usually favoring the production of a few, slowly developing young that are well adjusted in form and function to their (usually stable) environment. K-selected individuals are good competitors in conditions of density-dependent mortality.
Lambeosaurinae: The hollow-crested hadrosaurids, a stem-based taxon defined as all euhadrosaurs more closely related to Corythosaurus than to Edmontosaurus. This clade can be diagnosed by modifications of the jaw system and the skull roof. Other lambeosaurines include Lambeosaurus, Corythosaurus, and Tsintaosaurus (Horner et al. 2004).
Laurasia: The region consisting of the once-connected landmasses of the Northern Hemisphere, except for the Indian subcontinent.
Laws of physics: From an evolutionary perspective, the universal/ahistorical laws that dictate the general configuration of biological forms. These laws arise from the physical tenets of geometry, scaling laws, and packing principles.
Life-history strategies: Selected sets of adaptations to local environments, involving such quantitative aspects of life history as fecundity, the timing of maturation, and the frequency of reproduction. Responses to r and K selection represent two different life-history strategies.
Lithosphere: The solid, outer part of Earth’s core, composed of rock essentially like that exposed at the surface and usually considered to be about 80 km thick.
Living fossil: An organism that has remained essentially unchanged from much earlier geologic times and whose close relatives are usually extinct. Living fossils are descendants of extinct organisms greatly removed in time from their sister group (i.e., having a large GLD) and with very little character transformation over that GLD.
Lycian Sea: A small oceanic basin, located along the southwestern coast of Anatolia in northern Turkey. The Lycian Sea opened in the late Early Cretaceous as a second basin adjoining that of the Vardar Sea, and it persisted into the Tertiary.
Maastrichtian: The interval of geologic time from approximately 71.3 to 65 million years ago.
Maniraptora: A stem-based clade consisting of Passer domesticus (the living English sparrow) and all taxa closer to it than to Ornithomimus velox. This clade is diagnosed by the presence of ossified sternal plates, changes in the elbow, a semilunate carpal, modification of the hand, changes in the pelvis (including the rearward rotation of the pubis), and broad pennaceous feathers on the forelimb and tail, among other characters. Other maniraptorans include troodontids, oviraptorosaurs, and dromaeosaurids (Holtz and Osmólska 2004).
Marsupialia: A node-based (crown-group) taxon defined as the most recent common ancestor of the modern American opossum (Didelphis virginiana) and the modern wombat (Lasiorhinus latifrons). This clade is diagnosed by modifications of the ear and the braincase; the number of incisors, premolars, and molars; and, of course, by their reproductive biology (paired female internal genitalia, a very short gestation period, and early development in a pouch). The stem-based taxon that contains Marsupialia is known as Metatheria.
Megaloolithidae: One of the categories in the classification of fossil eggs, in which the shell is formed from shell units of tabular calcite crystals arranged in a radiating pattern (dinosauroid-spherulitic basic type). Each shell unit forms an external bump or node (tubospherulitic structural morphotype).
Moesia: An ancient country and then a Roman province in southeastern Europe, presently represented by Serbia and Bulgaria (south of the Danube from the Drina to the Black Sea). In terms of plate tectonics, it is the microcontinental plate of the central Peri-Tethyan region that was the first to collide and then suture with the Eurasian continental plate. See also “Apulia” and “Rhodope.”
Monophyly: The condition of having evolved from a single common ancestral form.
Monotremata: A node-based (crown-group) clade defined as the most recent common ancestor of the modern echidna (Tachyglossus) and the modern platypus (Ornithorhynchus), and all the descendants of this ancestor. This clade is diagnosed by a reduced or absent jugal, a slender dentary with only a vestige of the coronoid process, the absence of auditory bullae, and complex modifications of the shoulder girdle, among other features. The stem-based clade that contains Monotremata is known as Prototheria.
Morphospace: A multidimensional space comprising the set of all theoretically possible morphologies, based on geometric or growth parameters of particular groups of organisms.
Multituberculata: A node-based taxon, now extinct, defined as the most recent common ancestor of Zofiabaatar and Kogaionon, and all the descendants of this common ancestor. This clade can be diagnosed by modifications of the teeth, the skull, and the pelvis. Multituberculates were the most diverse and widespread of all mammals at the end of the Mesozoic and into the Tertiary (Kielan-Jaworowska et al. 2004).
Neo-Lamarckism: A late nineteenth- and early twentieth-century theory of evolutionary transformation, named after Jean-Baptiste de Monet de Lamarck (1744-1829), a French naturalist. This theory postulates that adaptations arise as characters are acquired by active organic responses to the environment, which are then passed on to offspring through heredity.
Neotethyan Ocean: The ocean that developed south of the northward-moving Cimmerian block sometime during the Permian. Similar to the earlier Tethyan Ocean, this younger ocean once again separated Laurasia and Gondwana and opened to the east. The Neotethyan Ocean was present throughout the Mesozoic.
Neoteny: The retention of juvenile features in adults, due to a slowing down of growth rates.
Nodosauridae: A stem-based clade defined as all ankylosaurs more closely related to Edmontonia than to Ankylosaurus. This clade can be diagnosed by features of the skull, the shoulder and pelvic girdles, and armor. Other nodosaurids include Animatarx, Struthiosaurus, and Sauropelta (Vickaryous et al. 2004).
Notarium: The fusion of the first six to eight dorsal vertebrae, a condition found only in some pterosaurs and many birds.
Ontogeny: The life course of the development of an individual organism; the history of an individual, both embryonic and postnatal.
Optimization: Establishing the most parsimonious sequences of character transformation on an existing cladogram.
Ornithischia: The bird-hipped dinosaurs, a stem-based taxon defined as all dinosaurs that are closer to Triceratops than they are to Saurischia. This clade can be diagnosed by the predentary bone capping the front of the lower jaws and a rearwardly rotated pubic bone, among other features (Benton 2004).
Ornithocheiridae: A poorly defined and diagnosed group of pterodactyloid pterosaurs, now regarded as a “wastebasket” taxon.
Ornithomimosauria: The ostrich-mimicking theropods, a node-based taxon consisting of the last common ancestor of the clade defined by Ornithomimus edmontonicus and Pelecanimimus polyodon, and all of its descendants. This clade is diagnosed by an inflated cultriform process forming a bulbous, hollow structure; a premaxilla with a long, tapering, subnarial ramus that separates the maxilla and the nasal for a distance, caudal to the naris; an elongated and subtriangular dentary; and a tightly bound distal radius and ulna, among numerous other characters. Other ornithomimosaurs include Garudimimus, Struthiomimus, and Gallimimus (Makovicky et al. 2004).
Ornithopoda: A stem-based taxon defined as all genasaurians (ornithischians with cheeks) more closely related to Parasaurolophus walkeri than to Triceratops horridus. This clade can be diagnosed by modifications of features of the jaw system and the back of the skull. Other ornithopods include Hypsilophodon, Tenontosaurus, and Iguanodon (Butler et al. 2008; Norman et al. 2004).
Oviraptoridae: A stem-based taxon consisting of the most inclusive oviraptorosaurian clade, containing Oviraptor philoceratops but not Caenagnathus collinsi, diagnosed by a narrow snout; a pneumatized premaxilla; a skull roof and quadrate, fused nasals; large and subquadrate infratemporal fenestra; and many other (principally cranial) modifications. Other oviratptorids include Citipati, Ingenia, and Conchoraptor (Osmólska et al. 2004).
Oviraptorosauria: A stem-based taxon defined as all maniraptorans closer to Oviraptor philoceratops than to Passer domesticus (the living English sparrow), diagnosed by a crenulated ventral margin of the premaxilla, a parietal that is at least as long as the frontal, an ascending process of the quadratojugal bordering more than three-quarters of the infratemporal fenestra, a U-shaped mandibular symphysis, an edentulous dentary, and a cranial process on the pubic foot that is longer than the caudal process. Other oviraptorosaurs include Incisivosaurus, Chirostenotes, and Khaan (Osmólska et al. 2004).
Pachycephalosauria: A stem-based clade defined as all taxa more closely related to Pachycephalosaurus wyomingensis than to Triceratops horridus, diagnosed by a thickened skull roof, the exclusion of the frontal from the orbital margin, tubercles on the caudolateral margin of the squamosal, a caudal basket of fusiform ossified tendons, a medial process on the iliac blade, and a pubis that is nearly excluded from the acetabulum, among other features. Other pachycephalosaurs include Wannanosaurus, Homalocephale, and Stygimoloch (Vickaryous et al. 2004).
Paedomorphosis: The retention of ancestral juvenile characters by later ontogenetic stages of descendants. Paedomorphosis is produced by neoteny (the deceleration of growth rate in descendants), progenesis (the early termination of the development of a feature in descendants), and postdisplacement (the late onset of the development of a feature in descendants). See also “Heterochrony” and “Peramorphosis.”
Paleobiology: The branch of paleontology concerned with the biology of fossil organisms. This discipline originated with the work of Vladimir Kovalevsky (1842-1883); was taken up as a distinct discipline in the early twentieth century in the studies of Dollo, Abel, Nopcsa, Wiman, Versluys, and others; and was reintroduced as a major research field in the 1970s.
Paleogeography: The geographic disposition of continents and oceans over geologic time.
Paleosol: A fossil soil; a soil formed during an earlier period of pedogenesis.
Paleotethyan Ocean: A mainly Paleozoic ocean (Silurian-Jurassic) that separated the Laurasian and Gondwanan regions of Pangaea, opening to the east. Beginning in the Permian, the Cimmerian block moved northward, diminishing the size of the Paleotethyan Ocean, until the latter disappeared in the Early Jurassic, replaced by the Neotethyan Ocean.
Pangaea: A region believed to have been the once-connected landmasses of the Southern Hemisphere and the Northern Hemisphere, dating from the Mississippian-Pennsylvanian boundary (323 million years ago) to the transition between the Triassic and the Jurassic (206 million years ago).
Parapatry: The condition in which diverging populations occupy distinct but contiguous areas.
Paris Basin: The depositional basin surrounding the area of Paris, France, that preserves sedimentary rocks of Mesozoic and Tertiary age.
Parsimony: The principle of parsimony (also known as “Ockham’s Razor”) requires ad hoc assumptions to be minimized as far as possible in scientific explanations of natural phenomena. For cladistics, this means that, from the millions of theoretically possible cladograms, those should be preferred that minimize the number of necessary assumptions of nonhomology (homoplasies).
Peramorphosis: The extension of descendant ontogeny beyond that of the ancestral condition. Peramorphosis is produced by acceleration (an increase in the growth rate in descendants), hypermorphosis (the late termination of the development of a feature in descendants), and predisplacement (the early onset of the development of a feature in descendants). See also “Heterochrony” and “Paedomorphosis.”
Peripatry: Occurring at the periphery.
Phylogenetic systematics: A methodology, described by Willi Hennig, for the reconstruction of phylogenetic trees and the discovery of monophyletic groups by the exclusive use of shared (homologous) derived character states. See also “Cladistics.”
Phylogeny: The evolutionary history of the relationships of species within a clade.
Pindos Sea: A small oceanic basin, extending across present-day northern Greece, that opened in the Late Triassic and closed during the Late Cretaceous.
Placentalia: A node-based taxon defined as the most recent common ancestor of the modern two-toed tree sloth (Cholepus didactylus) and humans (Homo sapiens), and all of the descendants of this ancestor. This clade is diagnosed by a prolonged intrauterine gestation, the loss of epipubic bones, and changes in dentition, among other features. The stem-based clade that contains Placentalia is known as Eutheria.
Plate tectonics: The theory in geology in which Earth’s lithosphere is divided into a small number of plates that float on, and travel independently over, the mantle. Much of Earth’s seismic activity occurs at the boundaries of these plates.
Pleurodira: The side-necked turtles, a node-based taxon defined by the common ancestor of Proterochersis and Podocnemidae, and all the descendants of this common ancestor. This clade can be diagnosed by a unique pulley arrangement of the jaw musculature, a suturing of the pelvis into the shell, and particular aspects of the jaw system. Other pleurodires include the extinct Stupendemys, the living yellow-spotted Amazon River turtle (Podocnemis unifilis), and the living mata mata (Chelus fimbriatus) (Gaffney and Meylan 1988).
Polish Trough: The depositional basin that extends from what is now the North Sea to the Black Sea.
Precociality: The kind of vertebrate ontogeny that is characterized by the birth of relatively mature, independent young.
Predentary: The single bone that caps the front of the paired mandibles, found solely in Ornithischia.
Pterodactyloidea: A node-based taxon defined as the most recent common ancestor of Pterodactylus and Quetzalcoatlus, and all of its descendants. This clade can be diagnosed by modifications of the facial skeleton, the vertebral column, the hand, and the foot. Other pterydactyloids include Pteranodon, Ornithocheirus, and Azhdarcho (Kellner 2003).
Pterosauria: The flying reptiles, a node-based taxon defined as the most recent common ancestor of Eudimorphodon and Quetzalcoatlus, and all the descendants of this common ancestor. This clade can be diagnosed by numerous features, including an enlargement and modification of the skull, a modification of the vertebral column, and an elongation and modification of the forelimb, among other characters. Other pterosaurs include Dimorphodon, Rhamphorhynchus, and Anhanguera (Kellner 2003).
r selection/strategy: Selection on individuals in populations well below the carrying capacity of their environments, usually favoring the early and rapid production of large numbers of quickly developing young. r selection generally operates in ecological situations favoring a rapid increase in population size—either because environments fluctuate so severely and unpredictably that organisms do best by making as many offspring as quickly as possible; or because ephemeral, superabundant resources can best be utilized to build up the population size before the inevitable exhaustion of these resources.
Red Queen hypothesis: The theory that describes how the coevolution of competing species creates a dynamic equilibrium in which the probability of extinction remains fairly constant over time. As one species evolves improvements that make it more competitive, its competitors experience selection pressures that force them to evolve in order to keep pace with it.
Regression: In a geologic context, the retreat of the sea from land areas.
Rhabdodontidae: A node-based taxon defined as the common ancestor of Rhabdodon priscus and Zalmoxes robustus, and all the descendants of this common ancestor. The clade is diagnosed by abundant sharp ridges on the dentary and the maxillary tooth crowns, the straight dorsal margin of the ilium, and a distinctly bowed femur, among other features (Weishampel et al. 2003).
Rhamphotheca: The cornified beak of birds, ornithischians, and turtles, consisting of the keratinized covering of the tips of the upper and lower jaws.
Rhodope: Mountains in southern Bulgaria and northeastern Greece. In terms of plate tectonics, it is the microcontinental plate sandwiched between Moesia and Eurasia to the east and north and Apulia to the west. After the collision of Moesia with Eurasia, Rhodope then collided with Moesia, and it was subsequently struck by Apulia. Full suturing of these three microcontinents with Eurasia took place in the mid-Tertiary. See also “Apulia” and “Moesia.”
Rudists: Sedentary clams (Bivalvia; Rudistacea) that have a superficially coral-like form and lifestyle, including their habit of gregarious reef building.
Santonian: The interval of geologic time from approximately 85.8 to 83.5 million years ago.
Saurischia: The lizard-hipped dinosaurs, a stem-based clade defined as all dinosaurs closer to birds than they are to Ornithischia. This clade can be diagnosed by modifications of the skull, the pelvis, and the hind limb (Benton 2004).
Sauropoda: The gigantic, long-necked, long-tailed dinosaurs, a stem-based clade defined as all sauropodomorphs more closely related to Saltasaurus than to Plateosaurus. Features diagnosing this clade include an extensive modification of the neural arch and the spine of the cervical vertebrae, relatively short forelimbs, changes in the forefoot, a compressed distal end of the ischial shaft, several modifications of the size and shape of the femur, and alterations of the hind foot, among other features. Other sauropods include Apatosaurus, Diplodocus, and Brachiosaurus (Upchurch et al. 2004).
Selmacryptodira: A stem-based taxon defined as all cryptodires more closely related to Crysemys picta (the living painted turtle) than to Kayentachelys. This clade is diagnosed by palatal, middle ear, and braincase features, and by the loss of palatal teeth (Gaffney and Meylan 1988).
Severin Ocean: A small oceanic basin, located in southwestern Romania, that opened in the Late Jurassic and closed during the Late Cretaceous.
Skeletochronology: The use of bone histology to calibrate growth stages and determine growth rates.
Speciation: The process of biological species formation, usually regarded as the splitting of one species lineage into two lineages.
Stegosauria: A stem-based clade defined as all taxa more closely related to Stegosaurus than to Ankylosauria, diagnosed by a flattened dorsal surface of the parietals, dorsal neural arches that are at least 1.5 times as high as the dorsal centra, a prominent triceps tubercle and a descending ridge caudolateral to the deltopectoral crest on the humerus, fusion of the wrist bones in adults, numerous modifications of the hind foot, parasagittal rows of plates or spines, and the loss of ossified epaxial tendons, among other features. Other stegosaurs include Huayangosaurus, Hesperosaurus, and Dacentrurus (Galton and Upchurch 2004).
Stratigraphy: The part of geology that deals with the origin, composition, distribution, and succession of strata.
Sympatry: Occurring in the same geographic region.
Taphonomy: The study of the processes (i.e., burial, decay, and preservation) that affect animal and plant remains as they become fossilized.
Taxon (pl. taxa): A taxonomic group or entity.
Tectonics: A branch of geology concerned with the structure of Earth’s crust.
Testudines: All turtles. This node-based (crown-group) taxon is defined as the most recent common ancestor of Proganochelys and Crysemys picta (the living painted turtle), and all the descendants of this ancestor. The clade is diagnosed by a bony shell consisting of a carapace and a plastron, edentulous jaws covered with a rhamphotheca, and the loss of several skull-roof bones, among other features (Gaffney and Meylan 1988).
Tetanurae: A stem-based clade that includes Passer domesticus (the living English sparrow) and all taxa sharing a more recent common ancestor with it than with Ceratosaurus nasicornis. This clade can be diagnosed by an axially reduced and rodlike neural spine on the second cervical vertebra (axis), a prominent acromion on the scapula, modifications of the hand and the wrist, and changes in femoral morphology, among other features. Other tetanurans include Megalosaurus, Allosaurus, Tyrannosaurus, dromaeosaurids, troodontids, and birds (Holtz et al. 2004).
Tethyan Ocean: The sea believed to have extended into eastern Pangaea, and later to have separated Laurasia to the north from Gondwana to the south. The Mediterranean is a remnant of it.
Tetrapoda: The vertebrates with legs, cladistically defined as the common ancestor of Amphibia and Amniota (mammals, turtles, lizards and snakes, crocodilians, and birds), and all the descendants of this common ancestor. This clade can be diagnosed by a host of modifications in the braincase, the ear, the pelvis, and the limb skeleton.
Theoretical morphology: The field of evolutionary biology that involves the mathematical simulation of organic morphogenesis and an analysis of the possible spectrum of organic form via hypothetical morphospace construction.
Theria: A node-based taxon defined as the most recent common ancestor of the modern American opossum (Didelphis americana) and humans (Homo sapiens), and all the descendants of this ancestor. This clade is diagnosed by the presence of a suprascapular fossa on the scapula, the absence of shelled eggs for reproduction, mammary glands, and a coiling of the cochlea in the inner ear, among other characters (Novacek et al. 1988).
Therizinosauroidea: A node-based taxon defined as the least inclusive clade containing Therizinosaurus and Beipiaosaurus, diagnosed by a toothless premaxilla with a sharp, ventrally projecting rim; a greatly elongated external naris; a palate with greatly elongated vomers and rostrally reduced pterygoids; a greatly enlarged and pneumatized basicranium; laterally compressed, symmetrical maxillary and dentary teeth with coarse serrations and cylindrical roots; modifications of the wrist and the hand; a deep and long preacetabular process of the ilium that flares outward at a right angle to the sagittal plane; and short and broad metatarsals, among other features. Other therizinosauroids include Alxasaurus, Segnosaurus, and Nothronychus (Clark et al. 2004).
Theropoda: The predatory dinosaurs, a stem-based clade defined as all saurischians more closely related to Passer domesticus (the living English sparrow) than to Cetiosaurus oxoniensis. Diagnosing this clade are modifications of the palate to accommodate cranial air sinuses, a reduction in the overlap of the dentary and postdentary bones in the mandible to form an intramandibular joint, considerable pneumatization of the vertebral column and the long bones, and a substantial transformation of the hand (a greatly reduced digit V, closely appressed proximal shafts of metacarpals I-III, and deep extensor pits on metacarpals I-III), among other features. Included among the theropods are Ceratosaurus, Allosaurus, Velociraptor, and birds. Tetanurae, Avetheropoda, and Maniraptora are sequential, less inclusive clades within Theropoda (Holtz and Osmólska 2004).
Tibiotarsus (pl. tibiotarsi): A long bone in the leg of a bird, formed by the fusion of the tibia with the proximal bones of the tarsus (the ankle bones).
Titanosauria: A stem-based taxon defined as those sauropods more closely related to Saltasaurus than to Brachiosaurus, diagnosed by a prominent caudolateral expansion of the caudal end of the sternal plate and an extremely robust radius and ulna. Other titanosaurs include Argentinosaurus, Rapetosaurus, and Opisthocoelicaudia (Upchurch et al. 2004).
Transgression: In a geologic context, the spread of the sea over land areas.
Troodontidae: A stem-based taxon defined as all taxa closer to Troodon formosus than to Velociraptor mongoliensis. This clade is diagnosed by a neurovascular groove on the outer face of the dentary, a caudal pneumatic foramen in the quadrate, the loss of the basisphenoid recess on the basicranium, a large number of teeth, a sulcus on the dorsal midline of the distal caudal vertebrae, and an asymmetrical ankle and foot, among other features. Other troodontids include Byronosaurus and Saurornithoides (Makovicky and Norell 2004).
Trophic: Of or relating to nutrition.
Typostrophy: The theory that the pathway of evolution within a taxon goes through stages analogous to the ontogenetic stages of organisms. Thus, there is the origin of a taxon (birth), diversification (growth), degeneration (senescence), and extinction (death).
Tyrannosauroidea: A stem-based taxon defined as the clade of theropods sharing a more recent common ancestor with Tyrannosaurus rex than with Ornithomimus velox, Deinonychus antirrhopus, or Allosaurus fragilis. This clade is diagnosed by characteristics of the lower jaw and by pelvic modifications, among other features. Other tyrannosauroids include Eotyrannus, Gorgosaurus, and Daspletosaurus (Holtz 2004).
Vardar Sea: A small oceanic basin, located in present-day Macedonia, that probably opened sometime in the Middle Jurassic and closed in the latest Cretaceous or early Tertiary.
Zero-sum game: A game in which the reward for winning is fixed and can only be won by one of the two players; that is, there can be only one winner and one loser.