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 ag
o).
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, compositio
n, 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.
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