Glossary

A short list of terms that may be helpful as you investigate this site

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Accessions:  This word is used by museum professionals to refer to new objects added to a museum’s permanent collections, whether purchased, donated, or collected.  The process of accessioning each group of newly acquired objects involves assigning it a unique registration number and recording information about what it consists of and how it was acquired.

Age: The age of a specimen can be stated in two ways.   Relative age places the specimen in order with respect to other fossil specimens, rocks or geologic events, but does not provide an actual number or years.    Absolute age is a measurement in years.  (Texas Geologic History)

Amethyst: Purple quartz (Si0₂)

Ammonoid: Any cephalopod of the subclass Ammonoidea, including ammonites, ceratites, and goniatites.  (Ammonoids)

Ammonites: An ammonoid of the order Ammonitida, in which the suture pattern is complex (both the lobes and the saddles are intricately folded).  They range in age from the Ordovician to the Cretaceous.  (Ammonoids)

Aragonite: A orthorhombic form of  calcium carbonate (CaCO₃), less stable than the rhombohedral form (calcite).

Basalt: A fine-grained igneous rock, usually volcanic (extrusive).

Benthic: Relating to or occurring in the depths of the ocean.  Usually used to refer to organisms that live on the ocean floor.

Bivalve: A mollusc of the class Bivalvia (Pelecypoda). Includes clams, mussels, oysters, and scallops.  (Bivalves)

Building stone: A rock which has been hewn for building purposes.

Calcified demosponge: Demosponges are sponges (Phylum Porifera) that have skeletons composed of spongin, or a mixture of spongin and siliceous spicules.  Calcified demosponges (also called sclerosponges, contain a massive basal layer of aragonite or calcite below the spongin layer. This basal layer enables fossilization to occur even though the spongin layer quickly disintegrates into spicular remnants upon death.

Calcite: Rhombohedral form of calcium carbonate, CaCO₃. Effervesces in dilute HCl.

Cast: Lithified sediment (rock) infilling a natural mold, and providing a replica of the original organism.  A similar process is also used to create man-made casts of fragile or rare specimens for display, research, or exchange with other museums.

Cephalopod: A mollusc of the class Cephalopoda, which includes squids, cuttlefish, octopi, nautiloids, and ammonoids.

Chaetetids: Unusual sponges of the Paleozoic era, resembling tabulate corals in certain structural aspects and originally placed within the Phylum Cnidaria. The chaetetid sponge contained spicules and is thought to have been related to calcified demosponges (sclerosponges).  They were important ‘reef’ builders in the later Paleozoic.  (Unusual sponges)

Cinnabar: A mineral composed of mercury sulfide (HgS), which is the most important ore of mercury. It is often found near volcanic rocks and hot springs. Cinnabar crystals usually are rhombohedral, vermilion red in color (if pure), and produce a red streak.

Cnidaria: A phylum, encompassing corals, sea anemones, jelly fish, and colonial hydroids.  These groups used to be included with the ctenophores (comb-jellies) in Phylum Coelenterata, but cnidarians and ctenophores are now regarded as distinct phyla.  Cnidarians are the simplest true metazoans, although they have more organized cells than do poriferans (sponges).

Coelenterata: A phylum, encompassing corals, sea anemones, jelly fish, colonial hydroids, and ctenophores (comb jellies).  It is more common to split  the corals, sea anemones, jelly fish, and colonial hydroids into the phylum Cnidaria.

Cratinaster: Cratinaster mccarteri is the famous starfish species on the large Cretaceous slab currently on display at TMM. You may know it better as Austinaster mccarteriAdkins; unfortunately, this species  had already been described and assigned a name before Adkins named his specimen, and so this ‘local’ name is incorrect!  (Starfish and sea urchins)

Cretaceous: The last period of the Mesozoic era, after the Jurassic period of the Mesozoic era and before the Tertiary period of the Cenozoic era. Covers the time from about 135 million years ago to about 65 million years ago.  (Texas Geologic History)

Crinoids: A member of the Phylum Echinodermata and in the Class Crinoidea. Consists of a globular body (calyx) from which extend flexible arms (brachia), and often rests on a flexible stalk.  Both arms and stalk are jointed. Crinoids were very important in the Paleozoic era, with many genera having stalks.  Most modern genera of crinoids do not have stalks.

Cruziana: A trace fossil with distinctive paired chevron markings, thought to be the track left by a trilobite.  (Tracks and trails)

Diatoms: Microscopic, unicellular (single celled), golden-brown algae.  They are found practically everywhere, including marine, brackish, fresh water, soil, and ice environments. They are characterized by a ‘pill box’ style skeleton (frustule) composed of opaline silica. The opaline silica is unstable and begins to convert to cristobalite as the diatom-bearing sediment is buried and temperatures rise. The frustule is dissolved and the record of the organism is lost.

Diploria: A genus of coral that first appeared in the Late Cretaceous, and is still extant (Phylum Cnidaria, Class Anthozoa, Order Scleractinia, Family Faviidae). Component of modern reefs in the Caribbean and Florida.

Echinodermata: The Phylum Echinodermata includes five Subphyla, of which three are mentioned here:  Echinozoa includes the sea urchins, sea cucumbers, and extinct edrioasteroids.  Asterozoa includes the starfish and brittle stars.  Crinozoa includes the crinoids. Other classifications of this important phylum have been proposed based upon cladistic analysis.  One characteristic aspect of the echinoderms is their pentameral (five-rayed) symmetry.  They have internal ‘mesodermal’ skeletons of calcite plates.  (Starfish and sea urchins)

Echinoids: A general term used for any member of the Subphylum Echinozoa.

Exogyra: Common oyster genus in the Cretaceous rocks of central Texas.  (Bivalves)

Exoskeleton: An external supportive covering of an animal, which may be composed of any or a variety of different materials.  Exoskeletons are most often found in animals that lack an internal skeleton.

Favia: Coral genus found in the Cretaceous of central Texas.   May have formed very small reef structures around the Pilot Knob volcano.

Flower Garden Banks: Modern coral reef in the Gulf of Mexico, now a National Marine Sanctuary.  These beautiful reefs are the most northerly in the Gulf, and owe their existence to a salt dome which elevated the seafloor into a depth at which reef organisms could thrive.

Foraminifera: Protozoans with a wide variety of test (‘skeleton’) compositions and morphologies. They range in age from the Cambrian to the Recent, and are highly abundant in sediments. They are an important fossil for the study of biostratigraphy and paleoenvironmental reconstruction.

Fossil: A remnant, impression, or trace of an animal or plant of past geological ages that has been preserved in the earth’s crust.  (Introduction to paleontology)

Fusulinids: Foraminifers of the Suborder Fusulina, Family Fusulinidae, having a distinctive multichambered calcite test (‘skeleton’), resembling a rice grain. They ranged from the Ordovician period in the Paleozoic era to the Triassic period in the Mesozoic era.  They are most important as ‘index’ fossils during the Pennsylvanian and Permian periods.

Gastropod: A mollusc of the class Gastropoda. Most gastropods (snails) have a single, non-chambered, calcareous shell which often spirals. They range from the Cambrian period to the Recent.  (Snails)

Genus: Intermediate between Family and Species in the Linnaen taxonomic hierarchy.

Halimeda: A genus of green algae with internal calcareous secretions.   Upon death the alga disintegrates and the calcareous grains become an important component of  beach sands, such as those in the Caribbean.  (Algae)

HCl: Hydrochloric acid.  A dilute form of this acid will react with the mineral Calcite (Calcium carbonate) to create a distinct effervescence.

Ichnofossil: A trace fossil, evidence of an organism or of its activities (e.g.: burrows or tracks) but with no remnant of the original organism remaining.  Sometimes it is impossible to determine which organism was responsible for a particular ichnofossil.  In other cases several organisms may create the same ichnofossil.   Distinctive ichnofossils may be given scientific names (referred to as form genera) for purposes of identification.  (Tracks and trails)

Igneous: Igneous rocks are formed by the solidification of molten magma. If the cooling takes place deep within the earth the rocks are coarse-grained, and are often termed intrusive or plutonic.  If the cooling takes place at the surface the rocks are fine-grained and are often termed extrusive or volcanic.

Intertidal: The zone of the shoreline that lies between high tide and low tide.

Invertebrate paleontology: The study of fossils of organisms that do not have backbones. Includes organism such as clams, snails, starfish, sponges, and corals.  (Introduction to paleontology)

Iron pyrite: The mineral iron pyrite, FeS₂, can occur in igneous, metamorphic and sedimentary rocks. It is often found in fossil shells, and can become a problem in museum collections because it may react with oxygen and water to form compounds that may destroy the specimen.

Jurassic: A period in the Mesozoic following the Triassic period and prior to the Cretaceous period. It covers a time span from about 190 million years to about 135  million years before present.  (Texas Geologic History)

Lithified: Sediment is said to be lithified if it has become hardened into solid rock.   The process includes some combination of compaction, cementation, or crystallization. Sediments can become lithified very soon after they are deposited, they may take millions of years, or they may never truly be lithified.

Loriolia: A genus of regular echinoid, common in the Glen Rose Formation. (Starfish and sea urchins)

Macraster: A genus of irregular echinoid, common in the Lower Cretaceous rocks of Texas. (Starfish and sea urchins)

Metamorphic:  Metamorphic rocks are those rocks that have undergone change after original lithification has occurred. Increases in heat, pressure and fluids penetrating the rocks cause chemical, mineral and structural changes resulting in the formation of different type of rock. An example is limestone, a sedimentary rock, becoming marble, a metamorphic rock.

Metazoa: A group that encompasses all animals having a body comprised of cells differentiated into tissues, and having organs, usually including a digestive cavity lined with specialized cells.  See also:  Protozoa.

Micropaleontology: The study of microfossils – extremely small fossils which require the use of a microscope.  (Introduction to paleontology)

Mineral: A naturally occurring, inorganic, crystalline element or compound with defined chemical composition.

Mold: An impression of an organism made in the sediment surrounding that organism, which is lithified and becomes a fossil itself.  The term ‘mold’ can also refer to a man-made form (usually made of latex or silicone) that is used to create a copy (cast) of a specimen that is too fragile to be handled, or for exchange with another museum.  (Molds and casts)

Mollusca: Phylum Mollusca includes the major classes Bivalvia, Gastropoda, and Cephalopoda. The invertebrate mollusc organism has an unsegmented body with a calcareous exoskeleton.

Montastrea: Genus of scleractinian coral known from the Upper Jurassic to the Recent.

Nautiloid: A cephalopod with a centrally located siphuncle and less complex sutures than ammonoids. They range from the Late Cambrian to the Recent.  (Nautiloids)

Opal: An unstable form of silica, Si0₂.nH₂0. The largest source is the siliceous tests of silica-secreting organisms such as the frustules of diatoms.

Operculum: A lid or covering flap found in several different groups of invertebrates.  Most often used to cover an opening in the animal’s exoskeleton.

Ophiomorpha: Burrow structures with nodular walls, probably formed by decapods (such as  mud shrimps, Callianassa sp.). This kind of fossil is known as a trace fossil, or ichnofossil.  (Tracks and trails)

Oysters: The best known of the group of bivalves that attach themselves by cementing their shells to the substrate (which can be a hard surface of any type, rock or shell). They are in the Order Pteroida, Suborder Ostreina.  Oysters are one of the most successful bivalves, and are abundant in the Mesozoic and Cenozoic eras. Many examples from the Cretaceous of central Texas are preserved in life position.  (Bivalves)

Paleobotany: The study of fossil plants.  Fossil plants are rarely found as one entire unit; the seed may be many miles away from its source, so too the leaf, and stems can be found in disparate environments far from the source plant. This pattern of fossilization can make it hard to be sure whether a particular leaf or seed came from the same plant or two different ones.  This has led to the use of form genera (scientific name referring to ichnofossils, or parts of fossil organisms, that can’t reliably be assigned to a specific taxon) to identify individual plant parts by shape and structure, rather than taxonomic affinity.  One plant may be composed of several different form genera, and one form genus may be found on several different plants.

Pentameral: Pentameral symmetry is five-rayed symmetry, which is a characteristic pattern seen in many echinoderms (sea urchins, starfish).

Period: A geologic time unit shorter than an era and longer than an epoch. It is the most important unit of the geological time scale.  (Texas Geologic History)

Permission: With very rare exceptions, fossils belong to the owner of the land on which they are found.  It is imperative that permission be gained from the landowner prior to any fossil collecting, even if the specimens are lying loose on the surface.

Phylum: A major level in the Linnaen taxonomic hierarchy, below that of Kingdom but higher than Class.

Pilot Knob: A Cretaceous aged submarine volcano to the south of Austin, Texas.  One of a small chain of similar volcanoes stretching as far as Uvalde County.

Porifera: Phylum Porifera (sponges) are multicellular organisms, but are not true metazoans. They have only a few cell types and these are not really organized into tissues. They are usually sessile (non-mobile), benthic (live on the sea floor) animals, and obtain food by filtering it out of the water around them. Most sponges have some sort of skeleton composed of spongin fibers, and/or spicules of calcium carbonate or silica.

Protozoa: A group that encompasses all animals that are acellular (no cell structure) or unicellular (only one cell).  Protozoans are extremely varied in morphology and physiology, and often have complex life cycles.  They occur in almost every type of habitat.  See also:  Metazoa

Provenance: The place of origin of a fossil. A fossil is only of true value if the precise stratigraphic and geographic location from which it was collected is recorded.

Radiolitid: A large, extinct, cemented, rudist (Phylum Mollusca, Subclass Heterodonta, Order Hippuritoida) with thick walls.

React: One example of chemical reactions that may harm fossils is the changes that can occur in iron pyrite (FeS₂).  The sulfide component oxidizes to FeSO₄ in the presence of oxygen, which leads to the production of sulfuric acid (H₂ SO₄) if water (H₂O) is available.  A simplified reaction is shown below:

4FeS₂ + 13O₂ + 2H₂O -> 4FeSO₄ + 2H₂ SO₄+ 2SO₂

This reaction is more commonly observed where the pyrite occurs in microcrystals. The resulting ‘decay’ is marked by yellow-white efflorescences, cracking of the specimen, sulfurous odor, and scorched boxes or labels where they come in contact with the reacting specimen.

Rock: A lithified combination of one or more minerals, or lithified undifferentiated material (e.g. obsidian), or lithified organic matter (e.g. coal)

Rudists: Unusually shaped form of extinct mollusc bivalve (Subclass Heterodonta), in which one or both valves became extended, and either highly coiled or cone-shaped. The organisms cemented to the substrate, and were responsible for reef build-ups in shallow tropical seas of the Late Jurassic and Cretaceous periods of the Mesozoic era.

Sclerosponge: Another name for calcified demosponges.

Seasonality: A measure of the differences between summer and winter temperatures and precipitation.  These differences may be reflected in fossils as growth rings or other structural or biochemical changes.

Sediment: Particulate matter transported and deposited by wind, water or ice, inorganic or organic precipitates from solution, deposited in layers.

Sedimentary: Relating to rocks composed of sediment, or structures within such rocks.

Septa: The internal walls between chambers of cephalopod shells.

Siphuncle: A tube connecting the chambers of nautiloids and ammonoids which allows the organisms to control the fluid content of each chamber, and thus its buoyancy.

Species: Groups of plant or animal organisms that can interbreed and produce fertile offspring. In the taxonomic hierarchy, ‘species’ joins with the higher level ‘genus’ to give the binomial term ‘Genus species’.

Sphalerite: A mineral composed of zinc sulfide (ZnS).  The most important ore mineral of zinc.

Spicule: One of the minute, usually hard, calcareous or siliceous bodies that support the soft tissue of various invertebrates.

Spirobranchus: Also know as Christmas-tree worms, found on brain coral.

Spongin: A scleroprotein that is the chief constituent of flexible fibers in sponge skeletons.

Stable isotopes: Isotopes are different types of atoms of the same chemical element. Stable isotopes are those that are not radioactive. The stable isotopes of oxygen, carbon and nitrogen are often used to investigate ecology and environmental characteristics of their habitats.

Steinkern: Lithified sediment infill of an organism – a natural cast. Often found as the ‘fossil’ of Cretaceous gastropods (snails) in central Texas, and of Tertiary gastropods in west Texas.

Suture: A useful feature for identification purposes that is found in fossils of invertebrate organisms whose shells are chambered. The dividing walls (septa) between their internal chambers leave a distinctive pattern on their external shell.  You might visualize this by thinking how the walls of the rooms in your house could leave an indication of the shape of those rooms on the ceiling.  These suture patterns are used extensively to identify fossil cephalopods.

Symbionts: An organism which lives together in more or less intimate association with another, dissimilar organism in a mutually beneficial relationship.   An organism which maintained a similar, but non-beneficial relationship would be called a parasite.

Taphonomy: The study of the death, burial, and fossilization process of organisms.

Taxonomy: The orderly classification of plants and animals based on their presumed natural relationships.  Taxonomic classification schemes generally are hierarchical, with groups at the lowest level containing organisms that are considered to be fundamentally identical, and groups at each successively higher level of the hierarchy relating groups at the next lowest level.  The taxonomic hierarchy first proposed by Linnaeus is used to classify specimens in the NPL collection:

	Kingdom
		Phylum
			Class
				Order
					Family
						Genus
							Species

A species name must always be used together with its associated genus name, in the form ‘Genus species’ (called a binomial, and traditionally italicized or underlined).  Genus names may be used on their own if the species is unknown or has not been designated (“Genus sp.”), and higher order (family through phylum) names can be used alone to designate all members of a group.

A number of other classification schemes have been proposed over the years.  One of the best known and widely used is cladistic analysis, in which specimens are related to each other by their shared derived characters.

Tertiary: The first period of the Cenozoic era, following the Cretaceous period of the Mesozoic era, and preceding the Quaternary period of the Cenozoic era. It has an approximate time span from 65 million years ago to 2 million years ago. It is divided into five smaller divisions (epochs), which are, oldest to youngest: Paleocene, Eocene, Oligocene, Miocene, and Pliocene.  (Texas Geologic History)

Trace fossil: See Ichnofossil

Trilobite: Extinct marine arthropods, ranging from the Cambrian to Permian periods. Distinctive three-section body plan with a chitinous exoskeleton.

Turridae: A family of high-spired gastropods (snails).

Type specimen:  The single specimen on which the first published description of that species is based, considered to be the best available example of that species’ morphology.  It is an important specimen and is used for all later reference to that particular species.  Several modifying terms may be applied to the type designation.  For example, the holotypeis the original specimen used as the type of the new species, and a neotype is a new type that may be designated if the holotype has been lost.

Unionid: Non-marine bivalve, for example, the genus Unio.

Valve: One of the two, usually articulated, pieces that form the shell of a bivalve mollusc. The term is also applied to shells of brachiopods and other invertebrates with paired shells.

Well cuttings: Fragments of rock that are cut by drill bits during the process of well drilling.  They can provide a good record of the different rock layers cut through by the drilling operation.

Zooxanthellae: Symbiotic algae that live in the tissues of hermatypic corals, thus truly ‘endosymbiotic’. They are dinoflagellates of the genus Zooxanthella