Glossary of Terms

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alveolus (alveoli, plural) The depressions or sockets in the tooth-bearing skeletal elements such as maxillae and dentaries into which the roots of the teeth are inserted. Especially well developed in mammals and crocodilians.

amniote A member of the taxonomic group Amniota, such as reptiles, mammals, and birds, characterized by possession of the amnion, a specialized embryonic membrane.

arboreal Descriptive term for an animal that primarily lives in trees.

astragalus (also talus) Bone that articulates with the tibia and fibula to form the ankle joint.

atlas The first or anteriormost vertebra of a tetrapod, the one that articulates with the skull.

auditory bulla (auditory bullae, plural) The bone that encloses the inner ear region of the mammalian skull and is found on the ventral surface of the posterior region of the skull. Typically fragile and thus rarely preserved in fossils; but inflated and composed of very solid bone in whales. For that reason, whale auditory bullae are commonly recovered as fossils. Alternatively called the tympanic bulla.

autochthonous In paleontology, used to describe a taxon or clade that evolved frim its common ancestor in its present geographic region.

axis (axes, plural) The second vertebra in a tetrapod, it follows the atlas.


basicranium The posterior and ventral portion of the skull comprised of the basioccipital, basisphenoid, petrosal, and auditory bulla, and portions of the squamosal and pterygoid bones. The evolutionary relationships of mammals can often be deduced by careful study of the arrangement of these bones and the foramina through which pass blood vessels and nerves.

basicranial Of or relating to the basicranium.

bilophodont Descriptive term for a tooth in which the crown is primarily comprised of two transverse ridges, for example, the lower molars of tapirs. Usually used only in conjunction with mammalian teeth.

brachyodont (brachydont, alt. sp.) Descriptive term for a tooth in which the crown is relatively short, especially one in which the crown is shorter than the roots; or an animal with such teeth. Usually used only in conjunction with mammalian teeth.

bone 1. Any single component of the vertebrate skeletal system, regardless of its compositio For example, the maxilla, humerus, and ribs are all bones. 2. A particular type of vertebrate skeletal tissue comprised of a mixture of inorganic hydroxyapatite crystals and proteins.

browser An animal whose diet is entirely or mostly made up of the leaves and stems of shrubs, bushes, and trees. Their food is often referred to as browse.

bunodont Descriptive term for a tooth in which the crown is comprised of low, rounded, isolated cusps or cones that are not connected by ridges or lophs. Usually used only in conjunction with mammalian teeth.


calcaneum Bone forming the heel and often the largest of the tarsal bones. Articulates primarily with the cuboid and astragalus bones of the foot and ankle.

canine The usually large, pointed, single-rooted tooth between the incisor and premolar series in the mammalian dentition.

caniniform Any tooth having the sharp, conical appearance of a canine; usually used to describe an incisor or premolar that functionally resembles a typical canine.

carapace The bony dorsal shell of a turtle or cingulate edentate (armadillos).

carnassial The specialized blade-like cheek teeth of carnivorous mammals, used to cut meat. Usually consists of a pair of teeth (one upper, one lower), and best developed in the families Felidae and Nimravidae. The carnassial pair in the mammalian order Carnivora consists of the fourth upper premolar and the first lower molar.

carnivore 1. Any animal whose diet principally includes vertebrate flesh and tissues. 2. Common name for a member of the mammalian order Carnivora, regardless of diet. To avoid ambiguity, the term “carnivoran” is sometimes used instead in this context.

carpal Any one of the skeletal elements making up the wrist, such as the unciform or trapezoid. Distally the carpals articulate with the metacarpals, proximally with the radius and ulna. Collectively they are referred to as the carpus.

cartilage A flexible, organic vertebrate tissue found in the skeletal system. Softer than bone, it is found in places of the skeleton where flexibility is a greater asset than strength, such as on movable joint surfaces, the external ears, and the tip of the nose. Because of its ability to reshape itself (unlike bone), the skeletons of fetal and very young juveniles consist primarily of cartilage, which is gradually replace by bone tissue as the animal matures. Some animals, such as sharks, retain an internal skeleton made of cartilage as adults. Unless it contains calcium-rich minerals, cartilage rarely preserves in the fossil record.

caudal Of or relating to the tail; especially one of the vertebrae of the tail.

cement A relatively soft, fibrous tissue of the vertebrate skeletal system. It surrounds the roots in the alveoli of mammals and some reptiles, adhering the tooth to the bone. Also found on the crown of the tooth in some hypsodont or hypselodont mammals where it surrounds the enamel and fills in deep valleys and depressions, thus providing structural support.

centrum (centra, plural) The spool-shaped or cylindrical body of a vertebra.

cervical Of or relating to the neck; especially one of the vertebrae of the neck.

cf. An abbreviation of the Latin word confer meaning "compare." When placed in front of the scientific name of a taxon, it means that there is some uncertainty about the identification. It may mean that the fossil(s) are to incomplete to be identified with certainty, or that the available specimens are not adequate to distinguish between two or more similar species.

cheek tooth Any mammalian tooth found posterior to the canine, i.e., a premolar or molar.

chordate Any member of the Chordata, a taxon of animals distinguished from other animals by having a notochord, pharyngeal gill slits, a dorsal main nerve chord, V-shaped segmented muscles, and a post-anal tail. Vertebrates are the best known group of chordates, but the taxon also includes several marine groups most notably the tunicates and the cephalochordates. Some of the chordate character states are found in vertebrates only during embryonic development and are either lost or highly modified in adults.

cingulum (cingula, plural) A ridge or shelf found on the cheek teeth of some mammals, located on the outer margin of the tooth. Cusps protruding from the cingulum are referred to as styles (or stylids on lower teeth), such as a parastyle or metastyle. In certain mammalian groups, the cusp referred to as the hypocone originally evolved on the posterolingual region of the cingulum.

clade A group of organisms believed to have evolved from a common ancestor. A clade often refers to any taxonomic level up to the genus level where members within that group are evolutionarily distinguishable from other clades of a similar taxonomic rank. On a cladogram, a clade is represented by all branches following a node.

cladistics A method in classification that defines taxa based on shared characteristics and arranges them using inferred evolutionary relationships so that all members of a given taxon share a closest common ancestor.

cladogram A branching diagram showing the phylogenetic relationships between species, genera, or other taxa.

collagen The major type of protein found in vertebrate bone and other hard skeletal tissues.

cone The major cusps or hill-like structures found on mammalian teeth. A prefix is added to indicated a specific cone, such as metacone or paracone. The term conid is used with lower teeth.

conspecific con- meaning 'with' and -specific, the adjective form of 'species'. Of or relating to a single species. For example, if two specimens are identified as belonging to the same species, they would be described as conspecific; two members of a single species population are also conspecifics. Note that conspecific is an adjective, verb, and noun depending on its context.

contemporary Existing or occurring in the same time period. Contemporaneous (adjective form)

convergent evolution The independent evolution of similar features in species of different lineages.

co-occurrence To appear together simultaneously or nearly simultaneously.

coprolite Fossilized feces or dung.

crown The portion of a tooth that usually extends beyond the gums, and is usually covered with enamel.

cursorial Descriptive term for an animal well adapted for running, usually at high speed or over long distances; or for any anatomical feature found in such an animal, such as long, slender limb bones.


deciduous An anatomical structure, such as a tooth or antler, that is shed or dropped off the body. Especially refers to the deciduous tooth series of juvenile mammals, which consists of a set of incisors, canine, and premolars that erupt early in life (sometimes prior to birth) and which are usually shed sequentially as the animal approaches maturity and replaced by members of the adult or permanent tooth series.

dental arcade The shape made by the rows of teeth in the upper jaw.

dental formula The number of teeth a mammal has of each kind of tooth along one side of the sagittal axis (central line of symmetry). The formula denotes incisors, canines, premolars, and molars in that order. Dental formulas can be written in several ways where the top numbers represent the upper teeth and the bottom numbers represent the lower teeth, e.g. 2/2-1/1-2/2-3/3 in humans, where we have 2 sets of incisors, 1 set of canines, 2 sets of premolars, and 3 sets of molars. In some mammals, the number of upper and lower teeth may differ, hence the need to denote top and bottom number of sets.

dentine (dentin, alt. sp.) A hard vertebrate tissue similar in composition to bone but found only in teeth and dermal tissue. Dentine exists in a number of varieties with differing internal structures and hardnesses.

dentition A collective term for the teeth of an individual vertebrate or those of a taxonomic group of vertebrates.

derived Refers to a feature or suite of features that evolved more recently compared to other conditions of the feature(s) in question. Older forms are considered more primitive.

derived character state When comparisons are made between differing character states found on two taxa, if one has evolved from (or is thought to have evolved from) the other, then the former is considered the derived character state.

dermal Of or relating to the skin.

describe The process by which species are formally defined and given a scientific name. Involves a systematic comparison of specimens of the same and different species and a description detailed enough that others can identify the species as well.

development Refers to the process by which organisms and their specific features are formed during gestation and the organism's lifetime before reaching maturity.

diagenesis The physical and chemical changes that occur when sediment is converted to sedimentary rock.

diaphysis The shaft of a mammalian limb bone, the portion that excludes the epiphyses.

diastema (diastemata, plural) The gap between consecutive teeth found in some mammals, especially herbivorous groups such as rodents and ungulates.

digitigrade The condition of supporting the body weight and walking on the digits or phalanges, as opposed to the metapodials (plantigrade). Dogs and birds are examples of digitigrade animals.

diphyodont Any animal that replaces its first set of teeth with a second set of teeth it retains throughout the rest of its life.

dispersal The action or process of distributing across a wider area or region.

diurnal Used to describe organisms whose behaviors take place during the day time and sleep at night.

durophagy The eating behavior of animals that eat hard-shelled organisms or those with exoskeletons, such as mollusks or crabs. Durophagous (adjective form)


ecology The relationship between organisms to each other and to the physical environment.

edentulous Lacking teeth.

element Part of the skeleton; refers to one or more bones or teeth, e.g., a humerus or metacarpal.

enamel The hardest vertebrate tissue, composed primarily of the mineral hydroxyapatite. A shiny, glossy substance, it forms the outer covering of the teeth in tetrapods and some fishes.

enameloid A variety of very hard dentine that compositionally resembles true enamel and is found on the teeth and scales of some fish. Can only be distinguished from true enamel microscopically.

endemic Prevalent in or limited to a certain region.

epiphysis (epiphyses, plural) Separate centers of bone development found at the ends of some bones in juvenile mammals and a few other vertebrates.

epoch One of the formal units of the geologic time scale, epochs are subdivisions of periods. The term is capitalized when it follows the formal name of such a time unit, for example, the Miocene Epoch.

era One of the formal units of the geologic time scale, eras are made up of two or more contiguous periods. The term is capitalized when it follows the formal name of such a time unit, for example, the Cenozoic Era.

estuarine Of or pertaining to an estuary. An estuary is a body of water where freshwater from rivers and/or streams flows into the ocean and mixes with the seawater. It is considered the transitionary environment between land and sea and is intermediate in salinity between the freshwater of rivers and the seawater of the ocean.

evolution The process of morphologic and genetic change in biologic organisms over time that occurs because of natural selection and genetic drift.

extant Describes a species or taxon that still exists and has living members; the opposite of extinct.


family The basic rank in the taxonomic hierarchy above the genus and below the order. The formal name of a family must end in the suffix “-idae” which is preceded by the root form of the generic name of the type genus of the family. A common name for most family names can be made by changing the terminal “ae” to an “s” and starting it with a lower case letter. For example, Felidae is the formal scientific name of a mammalian family, while felids is its informal equivalent. The species making up a family can be further subdivided into subfamilies, tribes, and subtribes. The well-known ranks, in order of most broadly classified to most specific, are life, domain, kingdom, phylum, class, order, family, genus, and species.

feral A once captive or domesticated species of animal or plant that is now living and breeding in the wild, usually in a region where it is not a native species. For example, the feral burros and horses living in the American Southwest.

fluvial Of or pertaining to a river.

foramen (foramina, plural) A small hole or opening in a bone, usually for the passage of a nerve or blood vessel.

formation The basic unit of rock in the geologic discipline of stratigraphy, it consists of one or more beds of same type of rock (limestone, sandstone, etc. [or alternately a distinctive combination of rock types]) with a lateral extent of at least several miles. Formal names of formations are capitalized and based on geographic names. Examples from Florida are the Anastasia Formation and the Suwannee Limestone.

fossa (fossae, plural) A prominent depression or concavity in a bone, often to house a muscle or gland.

fossil record The total number of fossils discovered and the information inferred from them.

fossorial Descriptive term for an animal well adapted for digging; or for any anatomical feature found in such an animal


generalization The combination of morphological or behavioral features that allow an organism to exist in a wider spectrum of environments or exhibit a wider range of behaviors, depending on its environment. Organisms of this nature are called generalists. Compare to specialists.

generic Of or relating to a genus.

genus (genera, plural) The basic taxonomic rank immediately above the species level. A genus consists of a group of species more closely related to each other than any is to a species not included in the genus, but a genus may contain only a single species. A formal genus name is capitalized and written in italics, for example, Canis or Triceratops. Species making up a genus may be grouped into two or more subgenera. In that case, one of the subgenera will have the same name as the genus, while the other subgenera will have different names. The subgeneric names are formally written like generic names but follow the generic name and are enclosed in parentheses. For example, Hespertestudo (Hesperotestudo) and Hesperotestudo (Caudochelys) are two subgenera of tortoises found as fossils in Florida. A formal species name is made up by the genus and species name, such as Smilodon gracilis where Smilodon is the genus name and gracilis the species designation. Note that without the genus name, the second component of a formal species name is meaningless. For example, the species designation gracilis applies to more than 50 species of animals, plants, and bacteria. 

granivore An herbivorous animal whose diet is entirely or mostly made up of seeds. granivorous (adjective form)

grazer A herbivorous animal (usually a mammal) whose diet is entirely or mostly made up of grasses.

group 1. A basic unit of rock in the geologic discipline of stratigraphy consisting of two or more contiguous formations. A group is therefore typically a larger and more widespread stratigraphic unit than a formatio An example from Florida is the Hawthorn Group. 2. An informal assemblage of species, more or less synonymous with the term taxon.


herbivore An animal whose diet is entirely or mostly made up of plant matter of any type. herbivorous (adjective form)

heterodont An animal whose teeth have different shapes and functions. The opposite of homodont. Although most common in mammals, some sharks, fish and reptiles are also heterodont.

holotype The single specimen upon which the scientific name of a species is based, and was explicitly designated as such in the original published description. All other specimens are only referred to the species.

homodont An animal whose teeth all have the same general appearance and function.

homonymy In biological taxonomy, when two different taxonomic groups have identically spelled scientific names. In such cases, the name that was published after the other one is invalid and must be replaced.

hypercarnivory An animal whose diet consists of more than 70% of meat.

hypselodont Descriptive term for a tooth with a high-crowned, ever-growing crown lacking roots; or an animal with such teeth. Usually used only in conjunction with mammalian teeth. Found in xenarthrans, rabbits, some rodents, and a few ungulates.

hypsodont Descriptive term for a tooth with a relatively tall or high crown, especially one in which the crown is taller than the roots; or an animal with such teeth. Usually used only in conjunction with mammalian teeth.


incisor One of the anterior-most teeth in the mammalian dentition, usually single-rooted and with either a chisel-shaped or conical crown.

incisiform Descriptive term for a tooth having the appearance of a typical mammalian incisor; especially in reference to the lower canine in some artiodactyls.

index fossil Term used in biochronology to describe a species or genus whose chronologic range is restricted to a particular biochronologic  unit. For example, the horse species Neohipparion eurystyle is an index fossil for the Hemphillian land mammal age, as it occurs only in Hemphillian fossils sites and does not occur at sites of any other age.

intermediate feeder An herbivorous animal that exhibits adaptations for both grazing and browsing. Also called a mixed-feeder.

interspecific Relating to characteristics or features found in two or more species.

intraspecific Relating to characteristics or features found within a single species.


keratin Hard, organic dermal tissue that makes up fingernails and the sheaths of horns; on occasion it preserves in fossils. keratinous (adjective form)


labial Refers to the external or lateral side of a tooth, towards the lips or cheek. An alternate, synonymous term is “buccal.”

land mammal ages Refers to the North American land mammal ages (NALMA), a timescale established for prehistoric fauna in North America using geographic place names for where the initial fossils were collected.

life history The series of changes undergone by an organism during its lifetime, the phases of which are typically marked by biological phenomena, such as reaching sexual maturity.

lingual Refers to the internal side of a tooth, towards the tongue. The opposite of the labial side.

locomotion The ability to move from one place to another. Different forms of locomotion produce different morphologies, which is of interest to morphologists. locomotive (adjective form)

lophodont Describes tooth in which the cusps or cones on the crown are connected by ridges (that are called lophs). Usually used only in conjunction with mammalian teeth.


mandibular symphysis A vertical ridge that marks the fusion of the right and left parts of the mandible.

marine Of or pertaining to the ocean or saltwater environments.

matrix Samples of fossil-bearing sediment to be processed by screen-washing.

member A basic unit of rock in the geologic discipline of stratigraphy consisting of a portion of a formation. The subdivision of a formation into two or more members is optional. As an example, in southern Florida the Arcadia Formation includes beds placed in the Tampa Member and the Nocatee Member.

mesic A descriptive term for a region or habitat with ample rainfall and vegetation.

metapodial The set of bones in the limbs of tetrapods found between the carpals or tarsals and the phalanges. The metapodials of the hand or forelimb are called metacarpals and those of the hind limb are called metatarsals. In the limbs of birds, the metacarpals and some of the carpals have fused to form a single bone called the carpometacarpus, while the fusion of the metatarsals and some of the tarsals forms a single bone called the tarsometatarsus.

microwear Microscopic patterns of damage on the surface of teeth or bone.

mineral The inorganic, crystalline compounds that make up rocks. Common examples are quartz, calcite, gypsum, and feldspar. The mineral found in the vertebrate skeletal system is hydroxyapatite, a phosphatic mineral that is synthesized by special bone-producing cells.

mixed-feeder A herbivorous animal (usually a mammal) whose diet is made up of both grasses and leaves.

molar One of the posterior-most series of mammalian teeth, usually with more than one root and a complicated occlusal surface with numerous cusps and cones. By definition, a molar does not have a deciduous precursor.

molariform Descriptive term for a tooth having the appearance of a typical mammalian molar; especially in reference to the posterior premolars in many herbivorous groups.

monogamy Not to be confused with the sociocultural definition of monogamy, it typically refers to the behavior exhibited by animals that pair-bond for a period of time, sometimes for life, but copulations outside of the pair-bonded unit is observed frequently in nature in numerous species of animals, ranging from birds to primates. It is a strategy used by animals who exhibit biparental care. Ecologists today prefer to use the term "pair-bonding" instead of monogamy because of the confusion coming from its vernacular meaning.

monophyletic A taxonomic group that includes the closest common ancestor of the group and all of its descendants.

morphology The form of a skeleton or its parts and its structure.


neoteny The retention of juvenile features in an adult animal.

neotype A specimen formally designated in a published study to replace a missing or destroyed holotype. After a neotype has been designated, it has the same importance and duties as a holotype.

node The point at which branches of a phylogenetic tree diverge; representative of a common ancestor between diverged branches.


occlusal Relating to or involving the surface of teeth where they touch each other as in chewing or biting down.

occlusion The relationship between the upper and lower teeth when they contact.

omnivory Animals that eat both plant and animal material exhibit omnivory. They are called omnivores.

ontogenesis The development of an individual or anatomical or behavioral feature from its earliest stages to maturity. Ontogenetic (adjective form). Ontogeny is the study of ontogenesis.

orbit The depression or deep concavity in the skull which houses the eye.

order Taxonomic rank used in classification of organisms. Members within a particular order are evolutionarily more closely related to each other than they are to any other order within their class. The well-known ranks, in order of most broadly classified to most specific, are life, domain, kingdom, phylum, class, order, family, genus, and species.

osteoderm A piece of bone found in the skin of some vertebrates (also informally called a scute). Especially well developed in crocodilians, tortoises, and armadillos.

osteological Of or relating to bone.

otolith Small, oval structures made of calcium carbonate that grow in the inner ear region of some fishes. Fossil otoliths are typically only studied by specialists.


paleoecology The inferred relationship between past organisms to each other and to their past physical environment.

paleoenvironment Environment of the past.

parallelism The independent acquisition of the same derived character state in two or more taxonomic groups not through a common ancestor. Also sometimes referred to as “convergence” or parallel evolution.

paraphyletic A taxonomic group that includes the closest common ancestor of the group, but not all of the descendants of that species. Paraphyletic groups are not considered valid by some scientists.

paratype One or more referred specimens specifically designated in the original description of a new species that provide additional information beyond that provided by the holotype.

parsimony In systematics, the acceptance of one possible phylogenetic arrangement in deference to other arrangements because it requires the fewest number of character state reversals and parallelisms. parsimonious (adjective form).

pathology An individual or anatomical part of an individual with an unusual morphology caused by illness, injury, malnurishment, or genetic defect. pathological (adjective form).

pectoral Relating to the anterior paired lateral fin in chondrichthyan and osteichthyan fish, the forelimb in tetrapods, or the region where the forelimb attaches to the torso.

pectoral girdle The bone(s) in the shoulder region in tetrapods that articulate with the proximal end of the humerus, and serve to structurally anchor the forelimb to the torso and as attachment sites for many of the muscles that move the forelimb. Individual elements of the pectoral girdle include the scapula, coracoid, and clavicle.

pelage The hair, fur, or wool of a mammal.

pelvic girdle The bone(s) in tetrapods that articulate with the proximal end of the femur, and serve to structurally anchor the hind limb to the torso and as attachment sites for many of the muscles that move the hind limb. Individual elements of the pelvic girdle are the ilium, ischium, and pubis; in adult mammals these three elements are fused together to form a single bone called the pelvis or innominate.

period One of the formal units of the geologic time scale, a subdivision of time between the ranks of era and epoch. The term is capitalized when it follows the formal name of such a time unit, for example, the Cretaceous Period.

petrosal The mammalian skull bone that houses the inner ear. Detailed analysis of these and other features of the ear region of the skull often reveal important evolutionary information. Alternatively called the periotic.

phalanx (phalanges, plural) One of the bones in the digits (fingers and toes) of a tetrapod.

phenetic (taximetrics, also) The classification of organisms based on overall similarity in morphology, regardless of phylogeny or evolutionary relation.

phylogeny The pattern of ancestor-descendant relationships among a group of biologic species that is deduced by the study of character states.

piscivory An animal whose diet primarily cosists of fish. Piscivorous (adjective form)

plantigrade The condition of supporting the body weight and walking on the metapodials, as opposed to the phalanges (digitigrade, op cite). Humans and bears are examples.

plastron The ventral portion of the shell of a turtle.

polygyny Comes from poly- meaning 'many' and -gyn meaning 'female'. Refers to social systems where one or few males control reproductive access to most or all females within a social unit. Sexual dimorphism is characteristic of species that exhibit polygynous behavior because of increased competition between males for mating access to females.

polyphyletic A taxonomic group that does not include the closest common ancestor of the group. Polyphyletic groups are not considered valid by scientists.

polyphyodont Any animal whose teeth are continuously replaced.

postcranial Of or related to that portion of the skeletal system other than the skull and jaws.

prehensile Capable of grasping, such as a prehensile tail in some species of New World monkeys.

premolar One of the mammalian teeth found posterior to the canine and anterior to the molars, usually with more than one root. They vary in morphology from simple to complicated and molariform depending on the type of mammal. Premolars usually have a deciduous precursor, but in some cases the deciduous premolar is retained in the adult.

preorbital Anatomically located anterior to the orbit.

preparation In paleontology commonly referred to as prep work or prepping, it is the process by which the surrounding rock or sediment is systematically removed from fossils, broken parts are glued back together, and weak areas are strengtheded with consolidents. Most fossils require some degree of preparation for future analysis and use in studies, and long-term storage or display. A person trained in these activities is called a preparator.

primitive Refers to a feature or suite of features that exhibit an older condition than seen in more recent representatives of a particular lineage. Those exhibiting more recent conditions of a feature are considered derived.

primitive character state When comparisons are made between two differing character states, if one has evolved from (or is thought to have evolved from) the other, then the latter is consider the primitive character state.

prospect Search for potentially fossiliferous deposits in a particular area.


ramus (rami, plural) One side of a mammalian mandible. Technically “mandible” refers to the combined right and left rami, but is often used informally to indicate only one side.

reworked Descriptive term for a fossil that eroded out of the sediments or rock enclosing it, and was subsequently deposited in younger sediments. By this manner, fossils of different ages can be found in the same rock unit. Reworked fossils can often be recognized by their worn appearance.

root The basal portion of a tooth (as opposed to the enamel-covered crown) where it attaches to the jaw.

rostrum (rostra, plural) The anterior portion of the skull, usually consisting of the maxillary, premaxillary, and nasal bones. rostral Of or relating to the rostrum.


sacral Of or relating to the vertebra or vertebrae that articulate with the pelvis. In some vertebrates, these vertebrae are fused to form a sacrum.

salinity The saltiness or dissolved salt content of a body of water.

sample A part or quantity used to represent the whole.

scansorial Descriptive term for an animal well adapted for climbing; or for any anatomical feature found in such an animal.

scavenger An animal that feeds on decaying carcasses, dead plant material, or garbage.

screen-wash The process of separating fossils from sediment by the use of running water and one or more sets of boxes with bottoms made of different size screens. Sedimentary particles smaller than the screen openings wash through, leaving a residue of concentrated grains and fossils that is sorted after it has dried. Screen-washing is a widely used method to collect fossils of small rodents, birds, lizards, snakes, salamanders, frogs, and fish.

selenodont A special type of lophodont tooth in which the cusps or cones are connected by crescentic ridges. Characteristic of ruminant and tylopod artiodactyls such as bison and deer.

serrated Having a notched or jagged edge similar to the cutting edge of a saw. In paleontology the term is most often used to describe teeth. For example, the canine teeth of some saber-toothed cats had serrated edges, as do the teeth of some species of sharks.

sesamoid A bone that forms in a joint capusule or tendon near a joint. The patella (or kneecap) is typically the largest sesamoid found in the body. In many medium- to large-sized mammals, there are well-formed sesamoids found in the joints between the metapodials and the proximal-most phalanges.

sexual dimorphism The condition when the two sexes of a species differ in size or morphology of one or more characters.

sister taxon (sister taxa, plural) A species or group that shares its most common ancestor with one or more other species or groups (e.g., sister clade, sister family, etc.). Sister taxa are more closely related to each other than to any other taxon.

specialization The presence of morphological or behavioral features that have a highly specific and narrow-ranged function. The term specialized is often used in a relative sense to describe groups or species where one is more specialized than the other, but both can be specialized when compared to an outgroup that is more generalized. Organisms who are specialized are called specialists and exhibit specializations as well.

species The lowest commonly used rank in the taxonomic hierarchy. A species is a group of morphologically similar individuals with one or more diagnostic character states that distinguish them from all other species. Some taxonomists define a species as a group of interbreeding individuals, although this is difficult to test in modern animals and impossible in fossils. A formal species name consists of two words written in italics, for example, Homo sapiens or Tyrannosaurus rex. Note that without the genus name, the second component of a formal species name is meaningless. For example, the species designation gracilis, as in Smilodon gracilis, applies to more than 50 species of animals, plants, and bacteria.

stable isotopes Isotopes that do not decay into other elements over time. Isotopes of an element have the same number of protons, which gives them their identity as that element, but vary in their number of neutrons. Unlike stable isotopes, radioactive isotopes are unstable and will decay into other elements over time. Stable isotope analysis use stable isotopes to learn about the chemical (elemental) make up of the past, such as in determining diets, environments (different plants produce different isotopic signatures), and climate.

stratigraphy Refers to the study of the order and relative position of strata and their relationship to the geologic time scale. Stratigraphic (adjective form).

stratum (strata, plural) A layer or series of layers of rock in the ground that denotes a period in time when sediment was being deposited.

subfamily Taxonomic rank of classification that denotes a level below family but falls above the genus level. Used when genera within a family can be further divided into subfamilies based on morphological or molecular similarities that groups them phylogenetically from one another. The well-known ranks, in order of most broadly classified to most specific, are life, domain, kingdom, phylum, class, order, family, genus, and species.

subfossil A fossil less than 10,000 years old.

subspecies The lowest formal taxonomic rank, subdivisions of a species, used to separate different populations within a species usually on criteria such as color patterns or size. A formal subspecies name consists of three words written in italics, for example, Lynx rufus koakudsi. Subspecies are infrequently used in vertebrate paleontology but may be more commonly used among ecologists who want to differentiate a particular population within a species from another population within that same species.

supraorbital Anatomically located dorsal to the orbit.

symphysis (symphyses, plural) Immovable (or nearly so) joint where the right and left sides of a skeletal element fuse together. Examples are the mandibular symphysis and the pelvic symphysis.

synonymy In biological taxonomy, when a single taxonomic group has two or more scientific names. When species names are synonymized, all specimens under multiple names are henceforth referred to by the original scientific name given to the first described fossil. The original name is called the senior synonym, while all other names given after the first name are called junior synonyms.

systematics The scientific study of the phylogeny of biological organisms and the methods used to reconstruct their evolutionary relationships.


tarsal Any one of the skeletal elements making up the ankle, such as the cuboid or astragalus. Distally the tarsal bones articulate with the metatarsals, proximally with the tibia and fibula. Collectively they are referred to as the tarsus.

taxon (taxa, plural) Any group of biologic organisms that together make up one of the scientific hierarchies of classification. For example, the genus Canis, the family Bovidae, and the class Actinopterygii are all taxa.

taxonomy The scientific study of classifying and naming biologic organisms.

tetrapod Common name applied to the taxon Tetrapoda, which includes amphibians, reptiles, birds, and mammals. Most tetrapods live on land, although some are secondarily aquatic.

thoracic Of or relating to the chest region (the thorax); especially one of the vertebrae in a mammal that articulates with a rib.

trace fossil A fossil that consists of something made by ancient organism while it was alive. Fossilized footprints, burrows, nests, stomach stones, and coprolites are examples of trace fossils.

tribe A taxonomic rank that is above genus but below family and subfamily and is sometimes subdivided into subtribes.

trilophodont A tooth primarily composed of three transverse ridges. Usually used only in conjunction with mammalian teeth, especially proboscideans.

trophic level any of several hierarchical levels in a food chain where members of each trophic level serve the same function in that food chain.

type genus The genus which defines a biological family and is the root of the family name in taxonomy.

type locality The fossil site or locality where the holotype specimen of a species was collected.

type species The type of a genus or subgenus, and under modern rules of scientific names must be explicitly designated at the time a new genus or subgenus is formally named. If a scientist determines that the species placed in a single genus actually belong in two or more genera, then the group of species which includes the type species will remain in the original genus; the other species are assigned to a different genus.

type specimen A formally selected specimen intended to serve as the prinicipal reference for a particular species. Used to help identify that species in the fossil record. See also holotype.


ungual Of, or relating to a hoof, claw, or nail.

ungulate A hoofed mammal.

unguligrade An extreme form of digitigrade posture where the body weight is supported by only the distal-most phalanx of one or a few digits. Fairly common in artiodactyls such as bison and deer, but otherwise rare among other mammals.


variation The differences in size, color, morphology, behavior, and other biological characteristics between two or more individuals.

vertebrate Common name for a member of the monophyletic taxon Vertebrata, a group which includes the jawless fishes, bony fishes, sharks and rays, and tetrapods. Among animals, vertebrates uniquely possess a brain which coordinates the nerves and senses of the body and which is protected and supported by a chondrocranium. Almost all vertebrates have a series of bones known as vertebrae (hence the name) and the capacity to produce calcium phosphate crystals.

volant Descriptive term for an organism that is capable of powered flight, such as most birds and bats.


xeric Used to describe a dry habitat characterized by low levels of rainfall, such as an arid or semiarid region.