advanced mesotarsal (am) ankle The ankle of pterosaurs, dinosaurs, and birds, in which the only hinge is between the astragalus and calcaneum and the rest of the foot. The astragalus is much larger than the calcaneum, and both bones are rigidly attached to each other and to the tibia.
aetosaur A heavily armored, plant-eating archosaur with a crocodile-normal (CN) ankle.
alveolar lung Lungs made of millions of tiny, very vascularized, spherical alveoli; the lungs of mammals.
ammonoid Any of a group of extinct invertebrates, most of which have coiled shells, that were close relatives of living octopuses, squids, and Nautilus.
amniotic egg An egg in which the developing embryo is almost totally surrounded by a liquid-filled cavity enclosed by the amnion, which is a membrane continuous with the skin of the embryo.
amphicoelous A vertebra with sockets (cavities) in the centrum both anteriorly and posteriorly.
anapsid A reptile with a skull that lacks upper and lower temporal fenestrae.
angiosperm A vascular plant in which the seed is covered by an ovary; a flowering plant.
archosaurs Reptiles that include crocodilians, pterosaurs, and dinosaurs. A variety of skeletal evolutionary novelties distinguish the archosaurs from the other diapsids, the lepidosaurs.
binomen The two-word name of a species in the Linnaean hierarchy; for example, Tyrannosau- rex.
biological classification The grouping of organisms into categories (taxa).
biostratigraphy The study of the distribution of fossils in layered rocks (strata).
biped An animal that walks on its hind limbs.
body fossil Fossil of a body part, usually skeletal, of an organism.
bone microstructure The microscopic arrangement of the inorganic matrix and organic component of bone.
calcium phosphate The organic mineral matrix of bone.
Cenozoic Era The past 66 million years of earth history; the geological time interval after dinosaur extinction.
clade A branch or cluster of branches with a common stem on a phylogeny. A synonym of monophyletic group.
cladistic phylogeny A phylogeny based on shared evolutionary novelties.
cladogram A diagram of a cladistic phylogeny.
clutch A nest of eggs.
cold-blooded A popular term referring to an animal that receives most, or all, of its body heat from external sources, usually the sun; a virtual synonym of ectothermic.
compact bone The dense, tightly woven exterior layer of most vertebrate bones.
connotation The meaning suggested by a word other than what it explicitly names or describes. See also denotation.
convergence The evolution of similar features in two distinct clades.
coprolite Fossilized feces.
Cretaceous Period The last period of the Mesozoic Era, approximately 65 to 145 million years ago.
crocodile-normal (cn) ankle The ankle of crocodiles and many archosaurs, in which the ankle twists while the animal walks.
cross-sectional area The area of the surface at right angles to the axis (of a bone).
deltaic Having to do with a delta, a triangular body of sediment formed where a river enters a large, quiet body of water, either a sea or lake.
denotation The direct, specific meaning of a word, in contrast to its connotation.
dental battery A large number of teeth cemented to each other to form an extensive shearing and grinding surface.
dermal bones Bones in the integument of a tetrapod.
determinate growth The pattern of growth of endothermic animals that stop growing at maturity.
diapsid A reptile with two temporal fenestrae on each side of its skull.
dimensionless speed The actual speed of an animal divided by some dimension of its body size.
dinosaur An archosaurian reptile having an upright posture and an advanced mesotarsal (AM) ankle.
dinosaur fauna All dinosaurs that lived during a specific interval of geologic time.
dinosaur track (footprint) A fossilized dinosaur footprint.
divergence The evolutionary splitting of one clade into two.
ectotherm An animal that receives most, or all, of its body heat from external sources, usually from the sun. The popular term cold-blooded is a virtual synonym of ectothermic.
ejecta Rock material thrown from an impact crater.
endocast A natural or human-made cast (replica) of the brain cavity; short for “endocranial cast.”
endotherm An animal that generates most, or all, of its body heat internally. The popular terms hot-blooded and warm-blooded are virtual synonyms of endothermic.
eolian Having to do with wind.
epicontinental sea Marine waters on top of continental crust.
equable Marked by a lack of variation or change (roughly uniform).
evolution The origin and change of organisms over time.
evolutionary novelty A feature unique to a group of animals that may indicate they have a close common ancestry.
extinction The disappearance of a species or of a larger clade of animals or plants.
extramophological variation Features of a trace fossil due to factors other than the anatomy (morphology) of the trace maker.
facultative biped An animal that is normally a quadruped but that occasionally walks bipedally.
facultative quadruped An animal that is normally a biped but that occasionally walks quadrupedally.
family The category in the Linnaean hierarchy above genus; a group of genera with a shared evolutionary ancestry.
feeding range The vertical height above the ground at which a plant eater forages.
flood plain A plain built by stream deposits adjacent to river channels.
fluvial Having to do with rivers.
footprint (track) See dinosaur track (footprint).
foraminifera Microscopic single-celled animals that have a hard shell and live in the sea.
fossil Any evidence of past life. Dinosaur fossils include bones and teeth, footprints, coprolites, gastroliths, tooth marks, eggs, and skin impressions.
four-chambered heart A vertebrate heart that separates blood containing oxygen from blood lacking it; characteristic of endotherms.
frill A posterior-projecting shelf of bone at the back of the skull usually composed of the parietals and squamosals.
function The specific contribution of a body part to the biology and behavior of an organism.
furcula The “wishbone” of birds; fused clavicles (collarbones).
gastralia Rib-like bones covering the stomach region.
gastrolith A “fossilized” gizzard or stomach stone.
gastromyth Supposed gastrolith that is actually just a polished stone.
genus (plural: genera) The category in the Linnaean hierarchy above species; a group of species with a shared evolutionary ancestry.
gigantotherm A large animal with a nearly constant body temperature due to its large size. A synonym of inertial homeotherm.
Gondwana The southern supercontinent of the Paleozoic and Mesozoic composed of Africa, Australia, Antarctica, South America, India, and Madagascar.
grade A set of clades that do not have a close common ancestor.
graviportal A quadrupedal animal with pillar-like legs and massive shoulder and hip girdles designed to bear great weight during slow and powerful locomotion.
greenhouse A warm, equable, and humid climate.
gymnosperm A vascular plant with a “naked” seed not enclosed in an ovary.
herd A group of wild animals usually led by a dominant individual.
heterotherm An animal whose body temperature varies considerably daily, seasonally, or throughout its life.
homeotherm An animal that maintains a nearly constant body temperature.
hot-blooded A somewhat sensational synonym of warm-blooded. See also endotherm.
ichthyosaur Any of a group of Mesozoic reptiles that converged remarkably on a fish-like appearance and lived in the sea.
igneous rock A rock that has cooled from a molten state.
indeterminate growth The pattern of growth of most ectothermic animals in which growth continues, although at a decreasing pace, throughout life.
inertial homeotherm A synonym of gigantotherm.
inoceramid A type of thin-shelled, plate-like clam of the Cretaceous Period.
iridium A platinum-group metal rare on earth but more abundant in meteorites and asteroids.
Jurassic Period The middle interval of the Mesozoic Era, about 145 to 201 million years ago.
lacustrine Having to do with lakes.
Laurussia The northern supercontinent of the Paleozoic and Mesozoic composed of North America and most of Eurasia.
lepidosaur Any of a group of diapsid reptiles that includes lizards, snakes, and their close relatives.
Linnaean hierarchy The categorical system used by biologists and paleontologists to classify organisms; named after Carolus Linnaeus.
locomotion The movement of an animal.
Maastrichtian The last time interval of the Cretaceous Period, about 66 to 70 million years ago.
macroevolution Evolution above the species level. The origination and evolution of taxa larger than species.
marine Having to do with the seas or oceans.
marsupial A mammal in which the young typically are born very immature and initially live in a pouch (marsupium) on the mother’s abdomen.
mass death assemblage A large accumulation of fossils of a single species of organism, often thought to be the result of a single catastrophe.
Mesozoic Era The interval of geological time 66 to 251 million years ago, when dinosaurs lived.
metabolism The chemical processes that provide energy to and repair the cells of an organism.
metamorphic rock A rock that has been altered by great heat and/or pressure.
microevolution Evolution at the species level. The evolution of populations of organisms that results in the origination of new species.
mineralization The replacement of organic or inorganic matter by minerals such as silica, calcite, or iron during the process of fossilization.
missing link A fossil that fills a significant gap in our knowledge of the evolution of a group of organisms. Typically, missing links bridge the evolutionary gap between two major groups of organisms.
monophyletic group A taxon that includes all taxa derived from a single ancestor. A synonym of clade.
monsoon A period of high winds and rainfall.
mosasaur Any of a group of extinct, giant marine lizards of the Cretaceous Period.
natural selection The process by which an organism that is better adapted to an environment more successfully reproduces than less-adapted organisms.
nest A bed or receptacle prepared by an animal for its eggs and young.
numerical time scale A classification of geologic time based on numbers (usually millions) of years.
opisthocoelous The condition of a vertebra with a socket (cavity) in the centrum facing posteriorly.
origination The appearance of a new type of organism.
pace (step) angle The angle between a line drawn from the posterior margin of one hind footprint to an equivalent point on the next hind footprint on the opposite side, and a second line drawn to the equivalent point on the next hind footprint of the same side as the first.
pace length The distance between the posterior margins of two successive footprints of the hind limbs on opposite sides of the body measured parallel to the direction of travel.
paleontologist A scientist who studies fossils and the history of life.
paleontology The scientific study of fossils and the history of life.
Paleozoic Era The interval of geological time 251 to 541 million years ago, before dinosaurs lived.
Pangea The supercontinent of the Paleozoic and Mesozoic comprising all of the present continents before breakup.
Panthalassa The single, gigantic ocean that existed when Pangea was assembled.
paraphyletic group A taxon that does not include all of its descendants.
phylogenetic relationships The relationships of taxa to each other.
phylogenetic tree A diagram that depicts the phylogenetic relationships of a group of taxa and has geologic time as its vertical axis.
phylogeny The history of how a group of organisms evolved.
phytosaurs A Late Triassic group of quadrupedal, meat-eating, crocodilian-like archosaurs having crocodile-normal (CN) ankles.
placental Describes a type of mammal in which the young develop in a placenta and are born relatively mature compared to newborn marsupials.
plesiosaur Any of a group of extinct, long-necked marine reptiles of the late Triassic, Jurassic, and Cretaceous.
pneumatic Having to do with air; a pneumatic bone is hollow and perforated so air can pass into it.
pneumatic ducts Openings (perforations) in the long bones of birds for the passage of air.
polyphyletic group A group of organisms from which its common ancestor is excluded.
postcrania The bones of the skeleton other than those of the skull and lower jaw.
predator–prey ratio The biomass of predators divided by the biomass of prey.
principle of biostratigraphic correlation The generalization that rocks containing the same kinds of fossils are of the same age.
principle of priority The rule that states that the first name of a taxon properly introduced has priority over (is used instead of) names later introduced for the same taxon.
principle of superposition The generalization that in layered rocks (strata), the older rocks are at the bottom, and the younger rocks are on top.
procoelous A vertebra with a socket (cavity) in the centrum facing anteriorly.
pterosaur A flying archosaur of the Late Triassic through to the Late Cretaceous; not a dinosaur.
quadruped An animal that habitually walks on four limbs.
radioactive clock A means of measuring geologic time by the radioactive decay of unstable atoms.
ratites Some of the flightless birds, including living ostriches and emus.
rauisuchians A group of Triassic meat-eating archosaurs having crocodile-normal (CN) ankles.
relative time scale A way to measure geologic time by determining if one event is older than or younger than another by assigning each event to a named interval of geologic time.
reptile A tetrapod that lays an amniotic egg and has scaly skin.
resonating chamber An air space that intensifies sound waves that enter it.
respiratory turbinates Small bones in the nasal passages of mammals and birds that increase the surface area over which blood and moist tissues are exposed to the air.
reworked A fossil is said to have been reworked if, after initial fossilization in the rock, it was exhumed and redeposited in an overlying, younger layer of rock.
rudist Extinct, reef-building clams of the Cretaceous Period.
sedimentary (depositional) environment The place where and particular conditions under which a sedimentary rock was formed.
sedimentary rock A rock formed by the accumulation and cementation of mineral grains or by chemical precipitation.
selenium A nonmetallic, often poisonous, element.
septate lung A tetrapod lung that is like one huge alveolus and has vascularized septa that penetrate it from its perimeter
sexual dimorphism Anatomical differences between the male and female of a single species.
“shocked quartz” A type of quartz grain with a laminar deformation known to be generated only by high-speed shock in laboratories, at nuclear test sites, and near impact craters.
soft-tissue anatomy That part of a vertebrate that is not skeleton, such as muscles, nerves, the circulatory system, and internal organs.
species (plural: species) The lowest grouping in the Linnaean hierarchy; a group of populations with a shared evolutionary ancestry.
sprawling posture The posture in which the limbs are held out to the side of the body so that the upper segments are horizontal to, or nearly horizontal to, the substratum.
strata (singular: stratum) Layers of sedimentary rock.
stratigraphy The scientific study of layered rocks (strata).
stratophenetic phylogeny A phylogeny that relies on the relative geologic age and overall similarity of taxa to identify ancestors and descendants.
stratum (plural: strata) A single bed or layer of sedimentary rock.
stride The distance between the posterior margins of two successive hind footprints on the same side of the body in the direction of travel.
substratum The ground surface.
supernova The complete obliteration of a star in an explosion.
surface-area-to-volume relationship The observation that volume increases as the cube of a linear dimension, whereas surface area increases only as the square of a linear dimension. Animals of large volumes have relatively less surface area than animals of smaller volume.
taphonomy The scientific study of the processes by which a fossil assemblage is formed and the losses of information these processes produce.
temnospondyl A type of extinct amphibian of the Paleozoic and Mesozoic.
temporal fenestra An opening for the passage and attachment of muscles in the skull of a reptile behind its eyes.
Tethys Sea The seaway between Laurussia and Gondwana during the Mesozoic.
trace fossils Fossils that are not part of the actual body of an animal. Dinosaur trace fossils ainclude footprints, eggs, gastroliths, tooth marks, and coprolites.
trackway A series of footprints made by a single animal.
Triassic Period The oldest period of the Mesozoic Era, 201 to 251 million years ago.
upright posture The posture in which the limbs are held vertically underneath the body so that they are vertical to, or nearly vertical to, the substratum.
warm-blooded A popular term virtually synonymous with endothermic. See also hot-blooded.