Introduction to the Study of Dinosaurs

Anthony J. Martin


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Body parts referring to the hip region, such as sacral vertebrae.
Clade placed with the clade Dinosauria that is one of the two defining all dinosaurs. Characterized by a hip arrangement that has the pubis pointing anterior and separate from the ischium.
Clade of saurischian dinosaurs, placed with clade Sauropodomorpha, characterized by a minimum of the following traits: 12 or more cervical vertebrae, neural arches and other processes smaller but forming better support for musculature as struts, sacrum with four or more vertebrae, large and separate pelvic bones, including an ilium with an expanded anterior end, minimum of 45 to more than 80 caudal vertebrae.
Clade of saurischian dinosaurs, characterized by a minimum of the following traits: distal part of the tibia covered by an ascending process of the astralagus, short hindlimbs in comparison to the torso length, thin and flat (spatula-like) teeth with bladed and serrated crowns, minimum of 10 cervical vertebrae that are typically elongated and a total of 25 presacral vertebrae, and large digit I on the manus, pes with five digits and unguals on digits I–III, manus with five digits with smaller phalanges on digits II–V, ungual on digit I of manus. Includes clades Prosauropoda and Sauropoda.
Unconsolidated material, typically formed as a result of weathering from a previously existing rock.
Sedimentary Environment
Place where sediments are deposited.
Sedimentary Rock
Rock formed through consolidation of sediment, forming either chemical or clastic sedimentary rocks.
Study of sediments, specifically how they are formed, transported, buried, and altered with burial.
Semi-erect Posture
Body alignment used by an animal that is in between and an upright and sprawling posture, with its legs directly underneath its torso.
Square-, triangular-, oval-, or rectangular-shaped denticles on carinae separated by narrow indentations (cellae) along a tooth surface.
Sexual Selection
Choosing of mates on the basis of attractive traits possessed by that mate. An important part of natural selection.
Sister Group
Taxon that had the same “parent,” or ancestral group, as another taxon and split from that ancestral group, e.g., Sauropodomorpha is a sister group to Theropoda because they both have a saurischian ancestor.
Site Fidelity
Habitual (annual) visitation and inhabitation of an area by a species of animal, typically for breeding and brooding purposes.
Evolution of one species into another species. Has been observed in some organisms, thus is part of factual basis of the theory of biological evolution.
Species (Biological Concept)
Population of organisms that can interbreed and produce offspring that can also reproduce with one another. A closed gene pool.
Species (Name)
Taxon for biological species based on binomial nomenclature, italicized and using genus and trivial name; e.g., Triceratops horridus, Tyrannosaurus rex.
Male gamete containing a haploid complement of chromosomes. Although outnumbered by millions of its compatriots, one will combine with female gamete (egg) to form a zygote. (Everyone should know this, but if not, this textbook was worth writing in order to pass on that knowledge alone.)
Sprawling Posture
Body alignment used by an animal that has its legs lateral to (outside of ) the plane of its torso.
Stable Isotope
Variation of an element based on differing numbers of neutrons, which affect its mass (isotope) that does not undergo radioactive decay. Ratios of stable isotopes are used for interpreting temperatures in ancient ecosystems.
Clade of ornithischian dinosaurs, placed with the clade Thyreophora, characterized by osteoderms evident as spikes on the shoulder regions (parascapular spines) and dermal armor restricted to two rows of vertically oriented plates, parallel to but also lateral to the axial skeleton (parasagittal plates) or spikes.
Stem-based Clade
Clade that has a shared common ancestor more recent than that of another group.
Width of a trackway, measured across the diameter of the trackway.
Study of rock layers, (particularly sedimentary rocks:), how they were formed, and mapping of their geometry (areal distribution and thickness).
Stride Length
In a trackway, the distance between two successive steps made by the same foot.
Superposition, (Principle of )
Basic geologic principle that originally horizontal layers have the oldest layers on the bottom and youngest layers on the top of a sequence, i.e., whatever is on the top is younger and vice versa.
Two or more organisms of different species living together or interacting in a way that one or all are dependent on the relationship for survival. Parasitism is a form of symbiosis, as is mutualism.
Character, shared between two or more groups of organisms, that was derived from earlier characters. Evolutionarily derived (“new” or “novel”) anatomical trait. Used in cladistic (phylogenetic) classification system.
Clade of amniotes characterized by single temporal foramen on each side of the skull. Clade Mammalia is placed with this clade.
Different species name assigned to an organism that has already been given a species name (a common problem in naming of dinosaur species).


Study of all processes that affect an organism after it dies, (such as scavenging, tissue degradation, transport of a body, and burial) and its fossilization potential. Also can be applied to the preservation of trace fossils.
Classification system in which names are applied to organisms or groups of organisms with regard to defining features; name given is a taxon. System applied to naming traces of behavior by organisms or their eggs is parataxonomy.
Clade of saurischian dinosaurs, placed with clade Theropoda, characterized by a minimum of the following traits: dentition in the maxilla only anterior to the orbital, antorbital and maxillary fenestrae, accompanied by increased pneumaticity of the skull, manus with digits I through III but digit III is absent in some cases, tibia that overlapped a reduced fibula, development of a large notch on the ischium, well-developed stiffening of the caudal vertebrae by processes (zygopophyses) that extended anterior and posterior from the neural arches.
Hypothesis, or set of related hypotheses, that withstood repeated testing to the point of widespread acceptance by the scientific community.
Assemblage of organisms in the fossil record that may be composed of only allochthonous species or a mixture of allochthonous and autochthonous species. Also known as a “death assemblage.”
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, and Maniraptiformes. Considered as the most unusual of theropods, especially in their dentition. They possibly were insectivorous, omnivorous, or herbivorous.
Study of heat and its relationship to work.
Clade of saurischian dinosaurs, has minimum of following traits: lachrymal bone prominently exposed on dorsal surface of skull, minimum of five sacral vertebrae, manus with claws (unguals) and reduction or loss of digits IV and V, slightly curved femur, which is also more than twice as long as the humerus, pes with digits II through IV, digit I separate from pes, pes length greater than width, bilaterally symmetrical from digit III, and a well-defined processes on cervical and caudal vertebrae. Generally known as “carnivorous dinosaurs” but probably with some exceptions.
Any body part referring to the thorax (torso), such as thoracic vertebrae.
Clade of ornithischian dinosaurs, characterized by dermal armor, typically present as osteoderms in rows parallel to the midline of the body and a well-developed postorbital process associated with the jugal and a palpebral (supraorbital bone). Includes clades Stegosauria and Ankylosauridae.
Clade of saurischian dinosaurs, placed with clades Sauropodomorpha and Sauropoda, distinguished by dermal armor (osteoderms) and procoelous caudal vertebrae.
Bone-like projection from the jaw of a chordate used primarily for grasping, biting, or chewing food. If found in the fossil record is considered as a body fossil.
Trace left on a substrate, either as a puncture or scrape mark, that represents behavior by an animal using its teeth. If found in the fossil record is considered as a trace fossil.
Topographic Map
Graphical, two-dimensional representation of differences in elevation in a specific area as well as its surface features, such as forested areas, roads, and cities.
Trace Element
Element that is normally in very small amounts in the earth’s crust or in a body.
Trace Fossil
Any indirect evidence of ancient life as represented by the effects of behavior. Includes tracks, trails, burrows, toothmarks, gastroliths, coprolites, and nests.
Trace left by appendage of an animal, typically as a result of its locomotion. If found in the fossil record is considered as a type of trace fossil. A series of two or more successive tracks made by the same foot is a trackway.
Path worn by repeated movement of animals along a route, typically the result of numerous trackways.
Triassic Period
Time interval in the geologic time scale spanning from about 245 to 206 million years ago. Dinosaurs had evolved from archosaur ancestors by the latter part of this period, including the clades Theropoda and Sauropodomorpha. Tridactyl Three-toed track or foot, often affiliated with either theropods or most ornithopods, (especially hadrosaurids).
Trivial Name
Second part of a species name (in binomial nomenclature) that must always be used in combination with and preceded by a genus name. Is always lowercase and italicized.
Clade of saurischian dinosaurs, placed with clades placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, Maniraptoriformes, and Arctometatarsalia.
Type Specimen
Individual organism or parts of an organism used to define a species. Tyrannosauridae Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, Maniraptoriformes, and Arctometatarsalia.


Track preserved below the actual surface on which an animal walked as a result of compression of underlying layers.
Nail or hoof, located at the distal ends of phalanges.
Upright posture
Body alignment used by an animal that stands and walks with its legs directly underneath its torso.


Bottom side of a horizontally oriented organism or a body part; contrast with dorsal.
Vertebrata, (Vertebrates)
Clade with synapomorphy of a series of bones (vertebrae) forming the main axial elements in the dorsal part of the skeleton. Placed with clade Chordata.
Vertebrae (plural of Vertebra)
Repeated and interconnected bones that formed the main axial elements in the dorsal part of a skeleton. Can be classified as cervical, dorsal, sacral, and caudal, in order from cranially to caudally, and with each composed of a centrum, neural arch, and nerve canal.
Amniote that reproduces by giving “live birth,” where its juveniles are retained in its body just before birth, rather than being born from cleidoic eggs.


Popularized description of endothermy.


Yolk Sac
Food supply in a cleidoic egg.


Curved and serrated teeth; considered as a plesiomorphic trait in dinosaurs and present in most theropods.
Processes emanating from the caudal vertebrae that, when welldeveloped, helped to stiffen the tail.
Female gamete (egg) that has combined its haploid complement of chromosomes with that of a male gamete (sperm); a fertilized egg.