Introduction to the Study of Dinosaurs

Anthony J. Martin


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Opening (hole) on each side of a pelvis that allows for the insertion of a ball-like proximal end of each femur. A distinguishing character of a dinosaur.
Physical attribute of an organism that can help it to survive at least long enough to successfully reproduce.
Physics of air flow. Important for interpreting sedimentary environments and taphonomy.
Sac that develops between the eggshell and amnion for respiration of the embryo in a cleidoic egg.
In taphonomy, refers to a body that has been moved (perhaps very far) from where it originally died.
Study of size and how it changes with growth of an organism in various dimensions.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, and Carnosauria.
Behavioral reference to state of juveniles not capable of moving and fending for themselves soon after birth, requiring much parental care. (Contrast with precocial.)
Amino acid
Organic compound that forms the basis for much soft tissue in an animal and helps to facilitate biochemical reactions. Must have a carboxyl group (COOH) and amino group (NH2), in which the carboxyl performs as an acid and the amino as a base.
Fluid-filled sac surrounding a developing embryo, characteristic of amniotes.
Clade of tetrapods that reproduce through by enclosed eggs with an amnion. Members are amniotes.
Paraphyletic group of chordates and tetrapods (formerly Class Amphibia under gradistic classification) that normally are dependent on water bodies for reproduction. Contrast with amniotes.
Juxtaposition of items or situations that belong to different and separate time periods, such as Stegosaurus (of the Jurassic Period) with Tyrannosaurus (of the Cretaceous Period).
Clade of ornithischian dinosaurs, placed with clade Thyreophora, that includes clades Ankylosauridae and Nodosauridae.
Clade of ornithischian dinosaurs, placed with the clades Thyreophora and Ankylosauria, that shares common ancestor with clade Nodosauridae.
Reference to the front part of an animal or front surface of a part.
Anatomical reference to the appendages (limbs) of an animal.
Arboreal hypothesis
Explanation of origin of flight in theropods from treedwelling species. Also known as the “trees down” hypothesis.
Study of human artifacts and other traces of human behavior. Someone who studies artifacts is an archaeologist.
Clade of diapsids, characterized by a minimum of the following traits: openings anterior to the orbits (antorbital fenestrae), teeth with serrations compressed laterally and none on the palate, dentary fenestrae, differently shaped calcaneum, and elongated ilium and pubis. Part of lineage of dinosaurs.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Coelurosauria, and Maniraptoriformes. Named for how the middle metatarsal is “pinched” between metatarsals on either side of it. Includes clades Troodontidae, Ornithomimosauria, and Tyrannosauridae.
Hot, plastically flowing, and partially molten portion of the upper part of the mantle that theoretically interacts with the lithosphere to cause plate tectonic movement.
In taphonomy, refers to a body that is in the same place where it originally died.
Clade of saurischian dinosaur, placed with the clades Theropoda, Tetanurae, and Avetheropoda, Coelurosauria, Maniraptoriformes, Maniraptora, and Avialae. Colloquially known as birds.
Clade of saurischian dinosaurs, placed with clades Theropoda and Tetanurae. Includes clades Carnosauria, Sinraptoridae, Allosauridae, and Coelurosauria.
Anatomical reference to the axis of an animal, such as its vertebrae.


Binomial Nomenclature
In Linnaean classification, method that names a species through combined use of a genus and trivial name, e.g., Stegosaurus stenops.
Assemblage of organisms in the fossil record that is autochthonous and thus represents the living community.
Study of chemical processes caused by organisms in geologic media and how elements are cycled.
Biologic Succession, (Principle of)
Observation that fossil assemblages may change in a vertical sequence of rocks (succeed one another). Explained through extinctions and evolution that happened through over time.
Biological Evolution, (Theory of)
Generally accepted explanation for observations of organisms that are (or were) modified through descent.
Study of how living systems, such as animal bodies, perform work.
Study of life through measurements and statistical methods.
Process for formation of hard parts (shells, bones, teeth) in organisms.
Combinations of elements that only could have been formed only by organisms. Examples include nucleic acids, lipids (fatty molecules), carbohydrates (also known as sugars), and proteins.
Processes that affect an organism between its death and final burial; an important part of taphonomy.
Process in which an organism causes mixing of a sediment. Product of bioturbation is a bioturbate texture.
Using of two legs for locomotion.
General term applied to members of clade Aves, which includes Archaeopteryx and all of its descendants.
Body Fossil
Any direct evidence of ancient life as represented by bodily remains. Includes actual or altered body parts (such as bone), impressions of any body part (skin, muscles, feathers), and eggs (which are body parts of embryos). Bone Biomineralized skeletal tissue in vertebrates composed of dahllite but often in combination with softer organic tissue in varying proportions. Can be either cancellous (“spongy” or low-density) or compact (high-density).
Clade of saurischian dinosaurs, placed with clades Sauropodomorpha and Sauropoda, which had more rounded skulls more rounded than diplodocids and nares were positioned more anteriorly (and below) the orbitals.
Behavior where eggs or juveniles are provided with care by the parents, such as through protection or insulation.


Clade of saurischian dinosaurs, placed with clades Sauropodomorpha and Sauropoda. They have more rounded skulls than diplodocids, spoonlike teeth, and smaller numbers of their cervical, dorsal, and caudal vertebrae.
Fossilization process where volatile elements, such as carbon, nitrogen, and oxygen, depart from an organism’s body and leave a carbon impression. Common mode of preservation for soft tissues in both plants and animals. Carina, (of Tooth) Narrow, blade-like or ridge-like part of a tooth that may have serrations or other denticles.
Carina, (of Sternum)
Bladed middle part of the sternum to which large flight muscles are attached in avians. Also known as the keel.
Carnivory; (Carnivorous)
Meat eating, but more generally the eating of any animal, whether through predation or scavenging.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanuare, and Avetheropoda. Previously was a general category for all large meateating dinosaurs.
Mass of protein collagen arranged as parallel, linear fibers, forming a part of a flexible, non-ossified connective tissue in a chordate.
Positive (convex) feature made from what was originally a negative (concave) feature, such as for preservation of dinosaur skin and tracks.
Anatomical position referring to the tail of an animal, such as caudal vertebrae.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia, Ceratopsia, and Neoceratopsia, characterized by short squamosals.
Node-based clade of ornithischian dinosaurs. Includes sister clades of Marginocephalia and Ornithopoda.
Clade of ornithischian dinosaurs, placed with clade Marginocephalia, characterized by a minimum of the following traits: rostral bone anterior to the maxilla that paired with a predentary to form a sharp beak, frill formed by the parietals that hung past the rest of the skull, cheeks that extend laterally and posteriorly, and a palate positioned high in the skull. Includes sister clades of Psittacosauridae and Neoceratopsia.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia, Ceratopsia, and Neoceratopsia.
Clade of saurischian dinosaurs, placed with clade Theropoda, characterized by a minimum of the following traits: fusion of bones in ankle and feet, sacrum fused to ilium and ribs, two fenestrae on the pubis, four digits, but with digit IV reduced so that digits I through III were the most functional, and two pairs of cavities (pleurocoels) in the cervical vertebrae.
Any body part with reference to the neck, such as cervical vertebrae.
Trait or characteristic of an organism’s anatomy distinctive enough to use for classification, such as in cladistics.
Clade of ornithischian dinosaurs, placed with clades Marginocephalia, Ceratopsia, and Neoceratopsia, characterized by long squamosals.
Clade of animal distinguished by a notochord, dorsal nerve cord, and pharyngeal gill slits. Placed with this clade is the clade Vertebrata.
Packet of genetic material in a cell, contains DNA.
Group of organisms defined on the basis of common ancestry as indicated by shared, derived characters (synapomorphies).
Classification system that places organisms into clades based on shared derived traits (synapomorphies). (See also phylogenetic classification.)
Diagram showing relatedness of clades to one another; serves as a visual display of a hypothesis on evolutionary relationships between clades.
Cleidoic Egg
Enclosed structure in combination with an embryo that provides a food supply (through a yolk sac) and a membrane for respiration, temperature maintenance, and waste disposal.
Organ in some birds that serves a dual purpose as the end orifice for the alimentary canal and oviduct.
One or more eggs laid in a single egg-laying episode by a mother.
Clade of saurischian dinosaurs, dinosaurs placed with clades Theropoda and Ceratosauria. One of the first theropod clades in the Late Triassic.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, and Avetheropoda. Includes other clades far too numerous to mention here, but with all of its members are united by possession of a semilunate carpal.
Popularized description of ectothermy.
Shape Overall geometric outline of a track. Useful for identifying a track made in substrates other than sand or mud, and a common mode of preservation for undertracks.
Continental Drift, (Hypothesis of )
First substantial hypothesis, stated originally by Alfred Wegener, explaining the geographic distribution of similar fossils, rocks, and rock structures in widely separated continents that also have closely fitting coastlines. Seminal hypothesis for later development of the theory of plate tectonics.
Trace fossil representing the end product of digestion by an animal. Fossilized equivalent of feces.
Anatomical position referring to the head of an animal, such as cranial bones.
Cretaceous Period
Time interval in the geologic time scale spanning from about 140 to 65 million years ago. Last period of the Mesozoic Era.
Cretaceous-Tertiary (K-T)
Boundary Division between Cretaceous and Tertiary Periods (from about 65 million years ago) marking a mass extinction that resulted in the end of the non-avian dinosaurs and many of their contemporary species.
Muscular organ anterior to the stomach and gizzard in the alimentary canal of some certain herbivorous animals, such as some birds, and presumed to have existed in some herbivorous dinosaurs.
Solid and less-dense upper part of the lithosphere.
Cursorial Hypothesis
Explanation of the origin of flight in theropods from ground-dwelling species. Also known as the “ground up” hypothesis.


Mineral composed primarily of calcium phosphate and described by approximately the same formula as the mineral apatite, Ca10(PO4)6(OH, CO3, F)2. Forms the main framework of hard parts (bones and teeth) in chordates.
Term used to describe older version of hypothesis of natural selection, as co-authored by Charles Darwin and Alfred Wallace.
Clade of amniotes with paired temporal fenestrae on each side of the skull. Part of lineage for dinosaurs.
Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, Maniraptiformes, and Maniraptora.
Dental Battery
Assemblage of interlocking teeth that form broad grinding or shearing surfaces for chewing of plant material. Typical in hadrosaurids and ceratopsians.
Sum of an animal’s teeth in its jawbones.
Biological, chemical, and physical processes in a sediment or sedimentary rock that occur after those sediments have been deposited. Important factor in taphonomy.
Locomotion that involves contact only through the digits. (Contrast with plantigrade.)
(1) A reptile- or bird-like animal with an upright posture that spent most (perhaps all) of its life on land and lived only during the Mesozoic Period. (2) An animal that had a minimum of the following synapomorphies: three or more sacral vertebrae, shoulder girdle with backward-facing (caudally pointing) glenoid, asymmetrical manus with less than or equal to three phalanges on digit IV, acetabulum with open medial wall, tibia with cnemial crest, astragalus with a long ascending process that fits into the anterior part of the tibia, sigmoidally shaped third metatarsal, postfrontal absent, humerus with long deltopectoral crest, and femur with ball-like head on proximal end. (3) The closest common ancestor to Triceratops and modern birds.
Clade of archosaurs characterized by certain synapomorphies. (See dinosaur.) Term originally coined by Sir Richard Owen.
Clade of saurischian dinosaurs, placed with clades Sauropodomorpha and Sauropoda, distinguished by more cervical and caudal vertebrae than other sauropods, teeth restricted to the anterior portion of the skull, and nares dorsal to the orbitals.
Number of chromosomes that results from the uniting of two haploid gametes.
Deoxyribonucleic acid.
Reference referring to the top surface of a horizontally oriented animal. Dromaeosauridae Clade of saurischian dinosaurs, placed with clades Theropoda, Tetanurae, Avetheropoda, Coelurosauria, Maniraptoriformes, Maniraptora, and Deinonychosauria.


Ecological Community
Collective group of organisms in an ecosystem.
Study of interrelationships between organisms and their environments.
Environment where organisms are interacting with both one another and abiotic (non-biological) factors.
Animal that is dependent on the ambient temperature outside of its body for maintaining internal body temperature. (Contrast with endotherm.)
Egg (Cleidoic)
Permeable structure enclosing and interacting with an embryo. Is a body part of the embryo, hence its fossil equivalent is a body fossil.
Egg (Gamete)
Sex cell with only a haploid set of chromosomes supplied by the female of a species.
Eggshell Types
Categories of morphologically distinctive mineralized remains of cleidoic eggs. Examples include geckoid, testuoid, crocodiloid, dinosauroid spherulitic, dinosauroid prismatic, and ornithoid.
Eisospherite Layer
Inner, organic shell membrane of an egg.
In geometry, a body where all plane sections are either circles or ellipses. Used to describe geometry of most dinosaur eggs.
Stage of development in ontogeny of an organism between a zygote (fertilized egg) and juvenile. In amniotes, associated with an amnion and (in cases of oviparous amniotes) an egg.
Clade of toothed avians that went extinct by the end of the Cretaceous Period.
Encephalization Quotient (EQ)
Ratio of cerebral cortex mass:totalbrain mass. Used as measure of relative “braininess” of an animal.
Animal that is dependent on its body for maintaining internal temperature rather than the ambient temperature outside of its body. (Contrast with ectotherm).
Study of insects.
Set of principles of conduct or behavior in human society and how that behavior affects people’s relationships with one another.
Clade of ornithischian dinosaurs, placed with clade Ornithopoda, includes clades Hypsilophodontidae and Iguanodontia.
Change in a population between generations, or descent with modification. See also biological evolution, (theory of).
Exospherite Layer
Crystalline (mineralized) exterior of an egg.
Permanent cessation of propagation of a species, which can be either local or global. Occurs when the last individual of a species is prevented from reproducing. Extinction, (Mass) Near-simultaneous extinction of many different (unrelated) species.