mm in diameter).A horizon mixed zone of mineral and organic matter at the top of a soil profile. Commonly referred to as topsoil.
acidic chemical condition in soils denoted by higher concentrations of hydrogen protons than base cations, such as sodium, calcium, and potassium.
alfisol soil order in semiarid to humid areas, typically under a hardwood forest cover. It has a clay-enriched subsoil and a relatively high native fertility. “Alf” refers to aluminum (Al) and iron (Fe).
alkaline chemical condition in soils in which base cations, such as sodium, calcium, and potassium, are more abundant than hydrogen protons.
anoxic environment lacking oxygen.
anterior near or toward the front of something (such as the body)
antorbital vacuities openings in front of the orbit within a skull.
aperture opening of a snail shell.
apomorphy in cladistics, a derived character state, or one that evolved later. Any feature novel to a species and its descendants. See synapomorphy.
aragonite form of calcium carbonate that makes up mother-of-pearl shells.
arboreal living in or often found in trees.
argillan film of clay on the surfaces of peds that form by the translocation of clays downward in a soil profile.
argillic horizon pedogenic horizon (Bt) that is enriched in clays that have been translocated downward.
aridisol soil most commonly found in association with arid environments, such as deserts; often have accumulations of carbonate or gypsum in their profiles.
articulation degree of connectivity between various bones in a fossil deposit. Articulated bones retain their original life position on the organism, and disarticulated bones are free-floating but generally in the same area as other bones.
avulsion process by which a river changes its overall course of flow by breaching the natural levee that contains it.
B horizon primary horizon of accumulation (illuvial horizon) in a soil profile. The type of materials that concentrate in the B horizon reflect dominant climatic conditions.
bed load portion of sediment transported by a river that is in contact with the stream bed as it moves.
benthic foraminifera microscopic single-celled organisms that precipitate a calcite shell (test) and live on the seafloor.
bentonite particular type of swelling clay (smectite) named for Benton, Wyoming.
bicipital groove groove on the anterior border of the proximal humerus between the medial and lateral tuberosities.
bioapatite apatite is a group of phosphate minerals, calcium apatite is the mineral that forms bone. The individual crystals are held together by collagen, which decays upon death and burial.
biochronology correlation of rock units based solely on the presence of fossils, either individual taxa or an assemblage.
biomineralization process by which living organisms produce minerals, often to harden or stiffen existing tissues; an extremely widespread phenomenon, it occurs in all six taxonomic kingdoms, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates.
biostratigraphic unit rock units defined solely by their fossil content. Biostratigraphic units are not required to adhere to lithologic boundaries.
biostratigraphy branch of stratigraphy focusing on correlating and assigning relative ages of rock strata by using the fossil assemblages within the strata.
bone bed accumulation of fossil bone that has a higher-than-normal concentration within a given area relative to the volume of sediment.
brachyodont having teeth with low crowns, well-developed roots, and only narrow canals in the roots, typically found in browsing mammals.
bunodont mammal with cheek teeth with low, rounded cusps on the occlusal surface of the crown, typical of omnivores.
C horizon bottom of a soil profile; has little to no modification from its original parent material state.
C3, C4 vegetation particular photosynthetic pathways utilized by certain types of plants. C3 plants include most shrubs and trees, whereas C4 plants are dominated by grasses. These differences in photosynthetic pathways, which are a response to general climatic conditions (such as moisture availability) can be preserved in the rock record as distinct ranges of carbon isotopic values of preserved organic matter. Measurement of the amount of carbon 13 in tooth enamel can provide information about an extinct animal’s diet.
caldera cauldronlike volcanic feature usually formed by the collapse of land after a huge volcanic eruption.
cambic horizon beginning stages of subsurface accumulation of translocated materials to form a B horizon. The cambic horizon (Bw) is sufficiently different from either the A or C horizon but has not reached a diagnostic stage of accumulation.
caniniform of or bearing similarity to the shape and appearance of a canine tooth.
cannon bone bone in hoofed mammals that extends from the hock to the fetlock; especially the enlarged metacarpal or metatarsal of the third digit of a horse. The term may also be applied to the fused third and fourth metatarsals in some artiodactyls.
carbonate primarily composed of the carbonate ion, CO2; can refer both to carbonate minerals and carbonate rock (which is made of chiefly carbonate minerals)
carina angular lateral margin of a snail shell.
carnassials teeth in mammalian carnivores with sharp edges for cutting flesh, formed by the fourth upper premolar and first lower molar teeth in modern carnivores, but may be formed by other premolars and molars in primitive carnivorous mammals like the hyaenodonts.
catena laterally linked set of soils across a landscape, the result of laterally changing CLORPT conditions. See CLORPT.
caudal of the tail region.
cementation hardening and welding of clastic sediments (those formed from preexisting rock fragments) by grain compaction and the precipitation of secondary minerals in the pore spaces between individual particles.
centrocrista tooth crest that connects the paracone and metacone (more lingually).
cephalic relating to the head or the head end of the body.
cervical neck region of an animal. In a turtle shell, it refers to the portion relating to, involving, or situated near the anterior portion of the shell.
channel belt broad band of individual channel deposits formed from a stream or river that is in a relatively stable position for a long period of time, typically decades to centuries.
chemical weathering chemical breakdown of geologic materials, commonly by dissolution, oxidation, or hydrolysis.
cingulum portion of the teeth occurring on the lingual or palatal aspects that forms a convex protuberance at the cervical third of the anatomic crown. It represents the lingual or palatal developmental lobe of these teeth.
cladistics method of classification of animals and plants according to the proportion of measurable characteristics they have in common. It is assumed that the higher the number of characteristics shared by two organisms, the more recently they diverged from a common ancestor.
clay smallest particle size class (4 µm or less) commonly described by geologists; special class of minerals (phyllosilicates) defined by sheetlike arrangement of their atomic structure. Particular clay minerals in the White River Group include smectite, kaolinite, and illite.
claystone clastic sedimentary rock composed of more than two-thirds clay-size particles (grains less than mm in diameter).
claystone breccia fragments of clay eroded from their source, transported, and redeposited into a new layer. A claystone breccia is commonly created by lateral migration of river cutbanks into their floodplain.
CLORPT five factors of soil formation: climate, organisms, relief, parent material, and time. See catena.
concretions bodies of specific minerals in soils and rock bodies that form by precipitation from fluids. Common varieties include calcium carbonate and iron oxide.
condyle articular prominence of a bone.
continental shelf large, flat expanse of ocean floor that stretches from the beach out to the shelf-slope break.
coprolite fossilized feces. The shape of the coprolite and materials inside of it can provide clues to the animal and its diet.
costal relating to, involving, or situated near a rib.
crevasse splay thin sheet of sand deposited in a proximal floodplain position by breaching the natural levee along a river.
cumulic soil soil characterized by a gradual buildup of sediment that is incorporated into the active soil. Cumulic profiles are overthickened compared to normal soils and tend to form at the base of slopes or in places where eolian additions to the soil are common.
cursorial adapted specifically to run.
dahllite original form of bioapatite in vertebrate bones. Dahllite recrystallizes into francolite upon fossilization.
detrital zircon sediment grains of the mineral zircon (ZrSiO4) that are typically derived from multiple source rocks. Zircons are resistant to weathering and contain uranium, which allows them to be radiometrically dated.
dextral coiling coiling in a snail shell in which the coil is to the right. In dextral shells, the aperture opens to the right of the spire axis when the apex of the spire is held vertically. See sinistral coiling.
diachronous “over time”; commonly used to refer to a rock unit that has different ages across a large area.
diapophyses part of the transverse process of a thoracic vertebra that articulates with its corresponding rib.
diastema space or gap between two teeth. Many species of mammals have a diastema as a normal feature, most commonly between the incisors and molars.
diatoms microscopic single-celled plants that precipitate opaline silica shells (tests) and live in fresh- and ocean waters.
digitigrade standing or walking on the toes (digits). See plantigrade and unguligrade.
discoidal shells coiled snail shells only slightly elongated along the axis of coiling. The resulting shell is very flat and wide, like a disk that is also called a low-spired shell.
distal location farther away from a point of reference; in vertebrates, this is usually from the midline of the body.
drab-haloed root trace greenish traces of former roots in paleosols created by the anaerobic decay of plant matter.
dung ball mass of feces rolled into a ball by a dung beetle and buried in the ground to serve as a food source for developing beetles inside the mass. Dung balls are a common trace fossil in certain layers of strata in the Badlands.
durophagous ability to break and eat the hard parts of organisms, such as bone crushing in hyenas or the ability to break the shells of snails.
E horizon soil horizon characterized by high rates of eluviation (loss) of clays and elements to lower parts of the soil profile. These horizons, also referred to as albic horizons, are commonly white in soil profiles when very well developed.
ectepicondylar process on the distal humerus (upper arm bone) or femur (upper leg bone) on the lateral side just above the articular surface. It is associated with attachment of the extensor muscles of the lower forelimb.
ectoloph one of the principal crests of a lophodont molar extending from the paracone to the metacone. See lophodont, metaloph, and protoloph.
ejecta material created by the impact of an extraterrestrial object, including glass spherules and shocked quartz.
eluviation process by which materials are removed from the upper part of a soil profile and translocated downward to accumulate in the B horizon. See horizonation and illuviation.
endothermy ability to maintain the body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat.
entepicondyle on the distal humerus or femur, a process above the medial condyle for the attachment of muscles, that faces posteriorly (for sprawling tetrapods) or medially (for erect tetrapods).
entisol soil that does not show any profile development other than a horizon. An entisol has no diagnostic horizons and is basically unaltered from its parent material, which can be unconsolidated sediment or rock.
entocondylar medial condyle of a bone on the side next to the body.
entoconid in mammalian dentition, a major cusp on the lingual side of the talonid.
eolian pertaining to wind activity. In geology, eolian refers to features formed by the wind. Also spelled aeolian or æolian.
epiclastic sediment derived from local sources, in contrast to those derived from distant volcanoes.
epipubic bones pair of bones projecting forward from the pelvic bones of modern marsupials and of some fossil mammals.
euhedral crystals mineral with well-formed crystal faces.
exodaenodonty cusp of tooth is more pronounced than surrounding cusps.
fenestra relatively large opening through bone; literally “window.”
fissiped having the toes separated from one another, as in the feet of certain carnivorous mammals.
floodplain flat area on either side of a river channel that is covered during flooding. The floodplain is built by the deposition of fine-grained sediments that settle out of the floodwaters.
fluvial processes, sedimentary deposits, and landforms associated with rivers and streams.
fontanel opening or gap in the skull.
forbes herbaceous flowering plant that is not a graminoid (grasses, sedges, and rushes); used in biology and in vegetation ecology, especially in relation to grasslands and understory.
formation widespread, lithologically distinct rock unit sufficiently thick to be easily mapped in the field. The formation is the fundamental unit of lithostratigraphy.
fossa depression in a bone, often a point of muscle attachment; fossettes and fossetids are smaller depressions or fossas.
fossilization process by which skeletal materials are preserved in the rock record. Bone fossilization includes recrystallization of bioapatite and incorporation of mineral materials.
fossorial animal adapted to digging and life underground such as a badger or mole. It is an adjective used to describe the habit of living underground even if even if the physical adaptions are minimal; most bees and many wasps are thus called fossorial, and many rodents are considered fossorial. Some organisms are fossorial to aid in temperature regulation, while others utilize the underground habitat for protection from predators or for food storage.
francolite recrystallized version of dahllite found in fossil bone. Recrystallization is accompanied by the inclusion of rare and trace elements into the bone.
geochronology science of dating and correlating distinct periods of geologic time in the rock record.
glaebule three-dimensional body of mineralized material in soils that forms by precipitation. The most common types are calcium carbonate and iron oxide.
Global Stratotype Section and Point (GSSP) precise stratigraphic point used as the global standard for the boundary between two units of geologic time.
globose conic conical snail shell with highly inflated whorls.
group stratigraphic unit composed of two or more formations.
herbivore animal that eats plants.
hermaphroditism process of self-fertilization in some types of organisms.
high-spired shells coiled shells in snail shells that are elongated along the axis of coiling. The resulting shell is very tall in comparison to its width.
horizonation process by which soils are differentiated into distinct horizons by physical, chemical, and biological processes, resulting in either the gain or loss of particular soil materials within each horizon. See eluviation and illuviation.
hydrolysis process by which water interacts with a mineral, leading to the replacement of hydrogen from the water with assorted cations on the mineral surface. Over time, this will change the original mineral structure to a clay.
hydromorphy influence of water on the development of a soil profile.
hydroxyapatite inorganic calcium phosphate mineral of bone and teeth, imparting rigidity to these structures (also hydroxylapatite).
hypercarnivore animal with a diet of more than 70 percent meat, with the balance consisting of nonanimal foods such as fungi, fruits, and plants.
hypocarnivore animal that consumes less than 30 percent meat for its diet, the majority of which consists of nonvertebrate foods that may include fungi and fruits.
hypoconulid in mammalian dentition, the buccal main cusp of the talonid on the lower molars.
hypotarsus in birds, a ridge or process located on the posterior side of the tarsometatarsus, near the proximal end.
hypselenodont high-crowned teeth with open roots and are ever-growing teeth.
hypsibrachydont teeth containing both low-crowned and high-crowned cusps.
hypsodont having teeth with high crowns. Hypsodont dentition is associated with a diet of abrasive foods.
hystricomorphous in which the deep masseter passes through the infraorbital foramen to attach to the side of the snout in front of the eye, as in porcupines. See myomorphous, protrogomorphous, and sciuromorphous.
illuviation process by which materials removed from the upper part of a soil profile (eluviation) collect in the B horizon. See eluviation and horizonation.
impactite defined body of material, such as an ejecta blanket, produced by the impact of an extraterrestrial bolide.
inceptisol soil with a defined cambic (Bw) horizon between an A and C horizon.
inflated whorls spiral whorls of a snail shell that are expanded, thus looking as if they have been inflated.
insectivore animal that feeds on insects.
intercotylar prominence ridge or process in birds located on the proximal end of the tarsometatarsus next to the hypotarsus.
iridium element in low abundance in crustal materials but relatively enriched in certain extraterrestrial objects. Iridium is commonly used as evidence of bolide impacts in the rock record.
isotopes elements with the same number of protons but different numbers of neutrons, which creates different atomic masses. For example, the 12C, 13C, and 14C isotopes of carbon have six, seven, and eight neutrons, respectively.
kaolinite (kaolin) aluminum-rich type of clay mineral that forms under well-drained and acidic soil conditions.
lacustrine processes and features associated with lakes.
land mammal ages biochronologic units of the late Cretaceous and Cenozoic defined by mammalian faunas. See NALMA.
lanthanides group of elements on the periodic table, also referred to as rare earth elements, which range from atomic number 57 to 71 and include scandium (21) and yttrium (39).
Laramide Orogeny period of mountain building during the late Cretaceous and into the Paleogene that generated the Rocky Mountains and several isolated mountain features, such as the Black Hills of South Dakota and Wyoming.
lateral accretion process by which rivers meander via lateral construction of point bars as the meander loop excavates the opposite bank.
Laurentide ice sheet large continental glacier of North America, centered in eastern Canada, during the late Pleistocene.
levee natural buildup of sediment from floods deposited adjacent to a river channel.
lithology description of the physical characteristics of a rock unit, such as composition, color, texture, and grain size.
loess silt-size sediments formed from the deposition of wind-transported dust.
loessite siltstone formed from the lithification of eolian dust deposits (loess).
lophodont tooth form with increasing specialization for grazing, resulting in fusion of cusps into ridges (lophs). Lower molars typically have two transverse lophs, the protoloph and the metaloph. In the upper molars, these ridges are fused with a longitudinal ridge (ectoloph). See ectoloph, metaloph, and protoloph.
magnetostratigraphy science of measuring and correlating magnetic signatures in the rock record.
marker bed rock strata readily distinguishable by its physical characteristics and traceable over large distances.
master horizon primary soil horizons (e.g., A, B, C) that can be subdivided with subordinate descriptors of soil features.
meander loop bend in a river characterized by erosion on the outside of the meander (cutbank) and deposition on the inside of the loop (point bar).
member rock unit that is a subdivision of a formation.
mesaxonic having the axis of the foot passing through the third digit of the hand or foot.
metaloph crest of tooth attaching the paracone to the hypocone. See ectoloph, lophodont, and protoloph.
metapodial term used to include both the metacarpals and metatarsals, often applied when a specific identification of these bones is not possible.
micrite limestone composed of microcrystalline calcite (crystals less than 4 μm in diameter) formed by recrystallization of lime mud.
mollisol soil commonly found associated with grasslands; must have a mollic epipedon, a 20 cm thick accumulation of base-rich organic matter at the top of the soil.
monophyletic group of organisms descended from a common evolutionary ancestor or ancestral group, especially one not shared with any other group. See paraphyletic.
monotypic taxonomic group containing only one immediately subordinate taxon. For example, a monotypic genus has only one species.
mudstone rock that includes subequal amounts of clay and silt that is lithified.
myomorphous in which the middle masseter is attached in front of the eye and the deep masseter passes up into the orbital area and through the infraorbital foramen, as in rats and mice. See hystricomorphous, protrogomorphous, and sciuromorphous.
NALMA (North American land mammal age) intervals of time defined by distinct mammalian faunas found in North America. See land mammal ages.
neural portion of a turtle shell relating to the bones on the midline of the carapace formed from the vertebrae.
nodules accumulations of mineralized soil or rock, most commonly calcium carbonate or iron oxide. In petrology or mineralogy, it is a secondary structure, generally spherical or irregularly rounded in shape. Nodules are typically solid replacement bodies of chert or iron oxides formed during diagenesis of a sedimentary rock.
nomen vanum literally “vain name”; available taxonomic names consisting of unjustified but intentional emendations of previously published names. They have status in nomenclature, with their own authorship and date.
normal magnetic polarity direction of Earth’s magnetic field that humans have always known, i.e., the current north–south direction shown by a compass needle.
nuchal scute located on the anterior margin of the carapace of a turtle shell above the neck.
O horizon organic horizon at the top of the soil profile, also known as leaf litter.
omnivore animal that eats both plant and animal materials.
oncolite sedimentary structure similar to stromatolites, but instead of forming columns, they form approximately spherical structures resulting from layers deposited by the growth of cyanobacteria. The oncoids form around a central nucleus, such as a shell particle, and the calcium carbonate structure is precipitated by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but they are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter.
ontogeny origin and development of an individual organism from embryo to adult.
orogeny forces and events resulting in large structural deformation of the Earth’s lithosphere (crust and uppermost mantle) as a result of the movement of the Earth’s tectonic plates.
overbank deposit alluvial geological deposit consisting of sediment that has been deposited on the floodplain of a river or stream by floodwaters that have broken through or overtopped the river’s banks.
oxbow lake meander loop of a river that has been isolated by cutting through a thin neck of floodplain material.
oxidation chemical process by which an element gives up an electron, thus increasing the amount of positive charge for any given ion.
paleobotany study of ancient plants, including their taxonomy, evolution, and paleoecology.
paleocatena laterally linked set of paleosols across a paleolandscape that were the result of laterally changing paleo-CLORPT conditions. See CLORPT.
paleoclimatology study of ancient climate patterns and trends preserved in various archives of the rock and fossil record.
paleoecology study of ecological relationships and interactions of ancient plants and animals.
paleoenvironmental analysis study of ancient environments, as recorded by sediments, sedimentary structures, and fossils in the rock record.
paleomagnetism study of the geologic record of the Earth’s magnetic field as preserved by magnetic minerals in rocks. These minerals record changes in the direction and intensity of the Earth’s magnetic field over time.
paleopedology study of ancient soils in the rock record.
paleosol fossil soil, formed when a soil becomes preserved by burial underneath either sediments or rocks; soils that are outside the range of active pedogenesis because of burial.
paleotopography geometry of ancient land surfaces preserved in the geologic record.
paleovalley ancient valley, typically recognized by its deeply eroded bottom contact and its thick fill from river deposits.
parabolic dune eolian dune with long ridges that point upwind and connect with a tightly curved ridge on the downwind end.
paracone one of the major cusps of a tribosphenic upper molar, typically in the anterobuccal corner.
paraphyletic group of organisms descended from a common evolutionary ancestor or ancestral group, but not including all the descendant groups. See monophyletic.
paraxonic having the axis of the foot between the third and fourth digits.
parent material original substrate material on which a soil develops. This material is typically unconsolidated sediment.
pedogenesis sum of all physical, chemical, and biological processes that modify original materials to form a soil.
pedogenic processes that lead to the formation of soil.
peds three-dimensional units of soil material that range in size and shape from small granular shapes to large columnar and prismatic shapes. Peds form by the segregation of soil material due to rooting, shrink and swell processes, and translocation of clays onto ped surfaces.
pentadactyl having five digits on the manus/pes.
perennial streams stream or river channel that has continuous water flow throughout the year.
periglacial cold environmental conditions along the margins of glaciers.
permineralization process by which pores within a skeletal material are filled with mineral material. The most common examples are petrified (silicified) wood and fossilized bone. See petrified wood.
petrified wood wood that has been fossilized by the filling of pores or replacement of organic material with minerals, typically silicate minerals. See permineralization.
pH measurement on a scale of 0 to 14 of the acidity (low pH) or alkalinity (high pH) of a solution. A neutral pH is 7.
phreatic water groundwater below the water table in the saturated zone where all available pore space is filled with water.
physical weathering process by which geologic materials are broken down into smaller sizes and shapes.
piscivore animal that eats fish.
planktonic foraminifera floating microscopic single-celled marine organisms that precipitate a calcareous shell (test).
plantigrade standing or walking with the podials and metatarsals flat on the ground. See digitigrade and unguligrade.
pleurodont having the teeth attached by their sides to the inner side of the jaw, as in some lizards.
pneumatized presence of air spaces within bones.
postcranial bones of the skeleton that are behind the skull.
posterior further back in position; of or nearer the rear or hind end, especially of the body or a part of it.
postmortem after death.
potassium feldspar aluminosilicate mineral that contains potassium; the most common constituent of granite. K-feldspar is one of the most common minerals in continental crustal rocks.
potato-ball concretions masses of calcium carbonate that are more resistant to erosion than the surrounding rock matrix.
procoelous vertebrae vertebrae whose anterior surface is concave and posterior surface is convex.
prosobranch snail that respires using a gill.
protocone central of the three cusps of a primitive upper molar that in higher forms is the principal anterior and internal cusp.
protoloph anterior cross-crest of a tooth, as that of a tapir or rhinoceros. See ectoloph, lophodont, and metaloph.
protrogomorphous in which the middle and deep layers of the masseter muscle attach to the zygomatic arch, as in rodent teeth and jaws in primitive forms. See hystricomorphous, myomorphous, and sciuromorphous.
proximal location closer to a common point of reference; in vertebrates, this is usually from the midline of the body.
pulmonate lung-bearing organism, typically referring to types of aquatic and land snails.
radiometric dating technique used to obtain numeric dates for some types of rocks, usually on the basis of a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, often referred to as the parent and daughter element. Also called radioisotopic dating.
rare earth element (REE) one of a set of 17 chemical elements in the periodic table, specifically the 15 lanthanides plus scandium and yttrium, taken up during diagenesis. They can be used to determine the provenance and depositional environments of vertebrate fossils. Also called rare earth metal.
reduction chemical process by which an element takes up an electron, thus reducing the amount of positive charge for any given ion.
reversed magnetic polarity direction of the Earth’s magnetic field in which the current north and south magnetic poles are reversed.
rhizolith root coated by the precipitation of minerals, most commonly calcium carbonate or iron oxide, which can eventually can kill the root.
riparian area along a river that supports a distinctly different ecosystem as a result of the proximity to the river, such as a line of trees along a river that is flowing across a prairie.
saltation sediment grains, typically sand, that bounce along the ground or substrate during windstorms or during water transport.
sandstone sedimentary rock primarily composed of sand particles ranging from 1/16 to 2 mm in diameter.
sandstone blankets thick accumulations of stacked sandstone sheets.
sandstone ribbons long, linear bodies of sandstone that are narrow laterally but extend for long distances along a linear trend. These ribbons have lenticular cross sections with a width-to-thickness ratio of less than 15. See sandstone sheets.
sandstone sheets laterally extensive but relatively thin sandstone bodies. The width-to-thickness ratio of these sheets is greater than 15. See sandstone ribbons.
scandium one of the rare earth elements (atomic number 21) incorporated into bone during the fossilization process. See lanthanides.
sciuromorphous in which the middle masseter attaches in front of the eye, as in squirrels. See hystricomorphous, myomorphous, and protrogomorphous.
sedimentology study of modern sediments such as sand, mud, and clay, and the processes that result in their deposition, as well as their equivalents in the rock record.
shell microsculpture very fine ornamentation that can only be seen with magnification on the surface of a snail shell. It can include small granulations or thin spiral grooves.
shocked minerals minerals in rock deformed by the pressures associated with bolide impacts. Shocked minerals display planar deformation features that represent deformation along defined atomic planes in the mineral structure.
siliciclastic clastic noncarbonate rock almost exclusively bearing silicon minerals, either as forms of quartz or other silicates.
siltstone clastic sedimentary rock composed of more than two-thirds silt-size particles, defined as grains 2 to 62 µm in size.
sinistral coiling coiling in a snail shell in which the coil is to the left. In sinistral shells, the aperture opens to the left of the spire axis when the apex of the spire is held vertically. See dextral coiling.
slickensides set of parallel striations on the surface of peds indicating swelling of soil materials. Also used for grooves developed between two sliding blocks of rock in a fault zone.
smectite particular type of clay mineral that expands upon addition of water. Some varieties of smectite can expand up to 50 percent of their original volume. These clays return to their original size upon drying.
soil fabric preferred alignment of soil materials created by pedogenic modification of parent materials.
soil order first level of classification in USDA soil taxonomy. Twelve soil orders are currently recognized. (See Table 3.1.)
soil profile two-dimensional exposure showing the vertical association of soil horizons.
soil structures three-dimensional bodies of soil material, such as peds and glaebules.
soil taxonomy philosophy and methodology of soil classification and identification. USDA soil taxonomy is broken down into seven levels of classification and currently recognizes over 18,000 different soils in the United States.
spherule type of impact ejecta formed by the vaporization of target rock and impactor, followed by subsequent cooling and condensation in the atmosphere to form glasslike beads that then fall back to earth.
spiral fracture particular style of break in fresh bone caused by carnivore or scavenger activity. Spiral fractures run along the length of the bone and curve around the radius of the bone shaft.
squamate scaled reptile.
steinkern internal mold of a shell, often the only indication of the animal after the shell has weathered away (German for “stone kernel”).
stratigraphy study of the distribution of rocks in space and time. Stratigraphy is typically used with sedimentary rocks.
stromatolite interlayered mass of photosynthetic cyanobacteria and clay that forms through the periodic addition of a thin layer of mud and clay to the surface of the cyanobacteria mat.
subduction process that takes place at the convergent boundaries of two tectonic plates when one moves under the other and sinks into the mantle.
subfossorial adapted for digging; often seen in the hands, feet, and bone structure of some rodents, such as prairie dogs. An animal is said to be subfossorial if it shows limited adaptations to a fossorial lifestyle.
supratendinal bridge any bony bridge over a tendon, in particular the bridge over the extensor canal at the distal end of the tibiotarsus of certain birds.
suspended load sediment suspended in a water body, primarily because of the small size of the particles. See turbidity.
symphysis type of joint in which the apposed boney surfaces are firmly united by a plate of fibrocartilage. In vertebrates, the two main symphyses are the mandibular and pubic.
synapomorphy in cladistics, a trait shared by two or more taxa and inferred to have been present in their most recent common ancestor, whose own ancestor in turn is inferred to not possess the trait. See apomorphy.
talonid crushing surface of a tribosphenic molar.
taphonomy collective study of the mode of death, postmortem modification, and burial of an animal to form a fossil.
taxonomy practice and study of classification of things or concepts, including the principles that underlie such classification.
terrestrial environments of deposition on land, including lakes, rivers, dunes, and glaciers.
test microscopic shell of single-celled marine organisms, such as foraminifera.
time averaging means by which fossil bones of different stratigraphic ages can be grouped together by surficial processes, such as the incision and lateral migration of a river.
translocation process by which soil materials, either as suspended or dissolved solids, can be moved through a soil profile to accumulate at a new level.
trigonid shearing end of a molar.
tritubercular having or designating teeth with three cusps or tubercles; tricuspid.
trochlea spool-shaped area of bone providing a smooth articular area for rotation on another bone. For example, the trochlea on the distal humerus articulates with the proximal ulna.
tufa porous variety of limestone, formed by the precipitation of carbonate minerals from ambient-temperature water bodies.
tuff type of rock that is a lithified volcanic ash originally ejected from vents during a volcanic eruption.
turbidity amount of sediment suspended in a water body. See suspended load.
ultisol soil most commonly found in association with forests in the southeast part of the United States. Ultisols are noted for high concentrations of translocated kaolinite clay in their B horizon and a low amount of base ions.
unconformity large gap of geologic time in the rock record that forms as a result of nondeposition and erosion.
unguligrade standing or walking only on the distalmost tips of the digits, as horses and cattle. See digitigrade and plantigrade.
urostyle long unsegmented bone that represents a number of fused caudal vertebrae and forms the posterior part of the vertebral column of frogs and toads.
vadose water zone of groundwater above the water table with pore spaces filled by variable amounts of air and water; also known as unsaturated zone.
vertical accretion aggradational growth of floodplain materials by settling of sediments onto a preexisting land surface during periods of flooding.
volant capable of flight.
volcaniclasts sediment particles derived from volcanic sources.
yttrium one of the rare earth elements (atomic number 39) incorporated into bone during the fossilization process. See lanthanides.
zalambdodont having teeth with two ridges that meet at an angle, forming the shape of the Greek letter lambda.
