Introduction to the Study of Dinosaurs

Anthony J. Martin


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Clade of amniotes characterized by hair and mammary glands, among other traits. Descended from synapsid ancestors during the Late Triassic.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanuare, Avetheropoda, and Coelurosauria.
Relatively more dense and thickest layer of the earth, immediately below the crust, and forming the lower part of the lithosphere and all of the asthenosphere.
Hand, associated with the forelimbs. Contrast with pes.
Clade of ornithischian dinosaurs, considered a sister clade to Ornithopoda. Characterized by an abbreviated posterior portion of the premaxillary as it contributes to the palate and a shortened pubis accompanied by widely spaced hip sockets. Includes clades Pachycephalosauria and Ceratopsia.
Middle part of an organism, especially definable in those organisms with bilateral symmetry, but also can refer to the middle portion of a body part.
Splitting of diploid cells into haploid cells, which produces gametes.
Clade of saurischian dinosaurs, placed with clades Theropoda and Tetanurae. Considered as an outgroup of the latter.
Mesozoic Era
Division of geologic time scale that is defined as lasting from about 245 to 65 million years ago, consisting of the Triassic, Jurassic, and Cretaceous Periods.
Metamorphic Rock
Rock formed from heat and pressure that changes the original minerals or texture of a previous rock, such as another metamorphic rock, igneous rock, or sedimentary rock.
Solid, naturally occurring, inorganic substance with a definite chemical composition and an ordered internal arrangement of atoms expressed as a crystal habit.
Splitting of diploid cells to form more diploid cells.
Impression made as a result of a body or body part contacting with a substrate. Can be either external or internal. Contrast with cast.
Group of organisms with a common ancestor.
Study of form in an organism, but also refers to the overall shapes of an organism and products of its behavior, i.e., track morphology and egg morphology.
Morrison Formation
Well-known Upper Jurassic rock unit made famous for its abundant dinosaur body fossils and some trace fossils. Named after its type area in Morrison, Colorado.
Mode of preservation that involves desiccation (dehydration) of a body.
Form of commensalism, where two of or more species benefit from associating with one another.


Natural Selection
Hypothesis that is part of the theory of biological evolution. States that species have genetic variation within their populations. These variations may constitute adaptations with relation to intraspecific competition or environmental factors, and those better adapted individuals survive long enough to reproduce, thus selectively passing on their inheritable traits. Older version called Darwinism, new version called Neo-Darwinism.
Decomposition of a body after it dies. Important process in taphonomy.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia and Ceratopsia.
Term used to describe newer version of Darwinism, which includes concepts of modern genetics.
Clade of avians represented by modern birds, originated in the Cretaceous Period. Can be divided into carinates (flighted birds) and ratites (flightless birds).
Biogenic structure that typically (but not always) contains a clutch. Best represented by an arrangement of eggs or eggshells in definite patterns, but can also be denoted as a semicircular depression with a raised rim that was originally used to hold eggs or young (mound nest), or a hollow, subsurface chamber for holding eggs (hole nest).
Node-based Clade
Clade that has all of the descendants of the most recent common ancestor for two groups, where the common ancestor forms the node. Nodosauridae Clade of ornithischian dinosaurs, placed with clades Thyreophora and Ankylosauria. Had laterally placed nares, and lacked horns and tail club. Nucleic Acids Biomolecules such as RNA and DNA that are chains of nucleotides.


Closing of an animal’s mouth so that the teeth from the upper and lower jaws come together on a surface (occlusal surface).
Omnivory; (Omnivorous)
Eating of both plants and animals.
Growth history (development) of an organism during its lifetime.
Idea that may or may not be based on factual information, but more on how a person feels.
Original Horizontality
Basic geologic principle that sediments are originally deposited in more-or-less horizontal layers.
Clade placed with the Dinosauria that is one of the two defining all dinosaurs. Characterized by a hip arrangement that has the pubis together with the ischium and pointing posteriorly.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, Maniraptiformes, and Arctometatarsalia. Also known as the “ostrich dinosaurs.”
Clade of ornithischian dinosaurs, characterized by a minimum of the following traits: offset tooth row, where the maxillary teeth are more dorsal than those in the premaxillary, (but teeth in the latter might be missing altogether), occlusal surface more dorsal than jaw joint, crescent-shaped paraoccipital process, and premaxilla with an elongate process that touches either, (or both,) the prefrontal or lachrymal.
Bony outgrowth of skin. Typical trait in titanosaurids and thyreophorans.
In female birds and reptiles, the passageway between uterus and cloaca, colloquially called a “birth canal.” Paired in some crocodilians.
Amniote that reproduces by laying an enclosed egg on land.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, and Maniraptoriformes.


Pace Angulation
In a trackway, angle described by the pace of one side in comparison to the overall stride.
Pace Length
In a trackway, the distance between two successive tracks made by appendages from opposite sides, such as right-left or left-right.
Clade of ornithischian dinosaurs, placed with clade Marginocephalia. Characterized by fusing together the frontals and parietals into a thick deposit of bone, thus the popular nickname of “bonehead” dinosaurs.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia and Pachycephalosauria. Also known as the “dome-headed” dinosaurs.
Study of how maps can be used to describe the geographic distribution of organisms during the geologic past.
Study of interrelationships between ancient organisms and their original environments.
Study of ancient life. Can include invertebrate paleontology (animals without backbones), vertebrate paleontology (animals with backbones), micropaleontology (one-celled organisms), and paleobotany (plants).
Study of sickness, injuries, and other abnormalities in the health of ancient organisms.
A group of related organisms but excluding some of their descendants that might be much different. (See monophyletic.)
Form of symbiosis where one organism is living at the expense of another host organism. Parasitic organisms can be either endoparasites (within the host) or ectoparasites (outside the host).
Naming of either trace fossils or some body fossils, (such as eggs,) similar to that for biological species, using binomial nomenclature to identify a specific morphology.
Filling of pores in a fossil by minerals precipitated from solution. Common mode of preservation for petrified wood and bones.
Foot, associated with the hindlimbs. Contrast with manus.
Negative logarithm of the hydrogen ion concentration in a solution, measured on a scale from 1 (most acidic) to 14 (most basic).
Phalangeal Formula
Count of phalanges associated with each digit in a manus or pes.
Phalanges (plural of phalanx)
Distal bones associated with the digits of either a manus or pes.
Phylogenetic Classification
System used for classifying organisms on the basis of their inferred phylogeny. Also known as cladistics.
Evolutionary history of an organism.
Piscivory; (Piscivorous)
Fish-eating habit. Proposed as a hypothetical feeding strategy for some theropods, such as spinosaurs.
Locomotion that involves contact of the digits and more proximal bones of the limb, such as tarsals and metatarsals. Also known as “flat-footed.” (Contrast with digitigrade.)
Plate Tectonics, (Theory of )
Generally accepted explanation for observed earthquakes, volcanoes, and some other geologic phenomena that occur in definite places on the earth.
Character in an ancestor that is also observable in a descendant. Considered as a primitive trait, such as ziphodont teeth.
Cavities within vertebrae of some dinosaurs, such as ceratosaurs.
Pneumatic (Bones)
Air-filled or otherwise less dense bones. Typical trait of both avian and non-avian theropods.
Group of organisms that had separate ancestors.
Group of organisms interbreeding with one another, presumably representing a species.
Anatomical reference to the rear of an animal or any part.
Behavioral reference to juveniles capable of moving and fending for themselves soon after birth, with little or no parental care.
Pressure-release Structure
Deformity associated with a track caused by the application or release of pressure by a foot.
Clade of saurischian dinosaurs, placed with clade Sauropodomorpha, characterized by a minimum of the following traits: atlas and a total of 10 cervical vertebrae, 15 dorsal, three sacral (attached to the pelvic bones), and nearly 50 caudal vertebrae, phalangeal formula on pes of 2-3-4-5-1, with small unguals, and phalanx on digit V seemingly vestigial, phalangeal formula on manus of 2-3- 4-3-2, with unguals present on digits I through III, enlarged ungual on digit I, which is deviated from the rest of the manus.
Combination of any 20 amino acids into a compound that facilitates biochemical reactions or provides structural support for an organism. Examples are albumin, collagen, hemoglobin, and osteocalcin.
Uncertainly assigned as a clade of ornithischian dinosaurs, placed with clades Marginocephalia, Ceratopsia, and Neoceratopsia, among the most primitive of neoceratopsians.
Anatomical reference to a body part that is close to an organism’s midline. Contrast with distal.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia and Ceratopsia, considered as the oldest clade of ceratopsians.
One of the hip bones, anterior and medial with relative to the ischium and ilium.


Using four legs for locomotion.
Quantum Mechanics, (Theory of)
Generally accepted explanation for observed behavior of atomic and subatomic particles.


Process where a body part of an organism is replaced by a material with a different composition from the original material.
Reproductive Isolation
Separateness of a species from another, represented by an inability to reproduce with one another to produce viable offspring.
Reptilia; (Reptiles)
General term for a polyphyletic group of amniotes that includes modern snakes, lizards, crocodillans, and turtles. Sometimes synonymized with clade Eureptilia, but the latter excludes clade Anapsida, which includes turtles.
Resonating Chambers
Tube-like structures that connected with nasal cavities in some hadrosaurids. Hypothetically used for changing sounds produced by moving air through the skull.
Respiratory Turbinates
Spaces within nasal cavities that accommodate folded bony or cartilaginous structures, often lined with mucous membranes. Considered as an indicator of endothermy.
RNA Ribonucleic acid.
Ruminant Herbivore that uses a multi-chambered stomach for the digestion of its food, which is physically mashed into a compacted mass called a bolus, (or cud).