Glossary

This glossary provides explanations of the more important technical and arcane terms used in the introductions to the chapters and in the 'Highlights' and 'Conclusions'. These explanations do not pretend to be scientific definitions but are intended to help the general reader. Detailed stratigraphical terms are omitted as they are given context within the tables and figures. Systematic names for groups of organisms are given with the formal version followed by the informal plural suffix in brackets. This is followed by a vernacular translation of the Greek or Latin roots of the terms.

Acanthodii (-ians): 'spiny', a member of the extinct class of Palaeozoic (Silurian–Permian) primitive jawed fish, the so-called 'spiny sharks' with spine supported fins and a covering of small scales, which occupied both marine and fresh waters.

Acanthomorpha (-phs): 'spine form', a group of advanced spiny neoteleosts with true dorsal and anal fin spines.

Acanthopterygii (-ians): 'spiny fin', an advanced group of neoteleosts with spiny fins, ranging from the Upper Cretaceous(?) to the present, including living perch, mackerel, plaice etc.

Achanolepid (-ids): one of five types of thelodont scale, very small with no pulp cavity, a bulging base and crown made up of dentine-type tissue; regarded as the most primitive type.

Acme: 'prime', the high point attained by an organism or group of organisms, as measured by some aspect of phylogenetic success, e.g. number of species; in palaeontology this depends on relative abundance of preserved fossils in a body of strata.

Actinopterygii (-ians): 'ray fin', (one of) the largest and most diverse of extant vertebrate groups, including many extinct forms and most living bony fishes; characterized by a hypermineralized cap to the teeth, and only one dorsal fin, although it may be subdivided; they also have ganoid scales, reduced pelvic girdles and usually paired fins with broad bases.

Actualism: a methodological approach to the interpretation of geological phenomena, based purely on an understanding of present processes on Earth.

Aeolian: 'of Aeolus, god of winds', sediments carried and deposited by the wind.

Agnatha (-ns): 'without jaws', a class of primitive jawless vertebrates, including a large number of extinct marine and freshwater groups but now reduced to two — the hagfish and lampreys.

Albanerpetontidae (-ids): 'alba reptile', an extinct and enigmatic group of freshwater salamanders.

Ammocoete larva: 'sand bed-mask', larval form of the lampreys.

Ammonitina (-ites): 'horn of (Ammon) Jupiter', an advanced group of ammonoids, characterized by the complexity of the sutures between septal chamber walls and the outer wall of the shell.

Ammonoidea (-oids): 'horn of (Ammon) Jupiter', members of an extinct group of marine cephalopods, whose nearest living relative is the Nautilus, and are generally characterized by a coiled shell, regularly partitioned into chambers (Devonian-end Cretaceous).

Amniota (-otes): 'foetal membrane', a group of craniates including reptiles, birds and mammals having an amnion (foetal membrane) around the embryo.

Amphibia (-ians): 'both life', a class of amniote tetrapod vertebrates with larval gills but adult lungs and a skin usually without scales; includes both living Lissamphibia — frogs, salamanders, etc.- and a large number of extinct fossil groups, whose characterization as amphibians is often problematic especially amongst early representatives.

Anaerobic: literally 'without air' or oxygen.

Anaspida (-ids): 'without shield', a group of extinct small agnathans with fusiform bodies and heads and bodies covered by small bony scales.

Angiospermae (-erms): 'vessel seed', a major division of the plant kingdom, commonly referred to as the flowering plants, with seeds developed in a closed 'vessel', the ovary.

Anoxic: literally 'without oxygen', synonymous with anaerobic.

Anthracosauria (-aurs): 'charcoal lizards', a group of 'labyrinthodont' fish-eating tetrapods (early Carboniferous to Permian in age), some of which were terrestrial but others were aquatic; they may include the ancestors of the reptiles and are often referred to as reptilomorphs.

Antiarchi (-archs): 'against first', an extinct group of Devonian placoderms, whose bodies are covered in bony plates, with two median dorsal plates and in which the paired pectoral fins are replaced by long, jointed bony appendages.

Anura (-ans): 'without tail', a major group of living amphibians including the frogs and toads.

Arachnida (-ids): 'spider form', a large group of carnivorous chelicerate arthropods, mainly terrestrial, including the scorpions and spiders.

Arenite (-aceous): 'sand', a clastic sediment made of sand-sized particles.

Argillite (-aceous): 'clay', a fine-grained sediment made of silt, or clay-sized particles.

Arthrodira (-ires): 'jointed neck', a group of placoderm fishes (Devonian to Carboniferous), characterized by bony shields covering the head and thorax, which are articulated by a joint.

Aspidin: 'shield', an acellular bone-like material found in the bony plates and scales of some extinct jawless fish.

Aspidorhynchidae (-ids): 'shield snout', an extinct group of basal teleosts with long bodies and long pointed snouts.

Astraspida (-s): 'star shield', a group of extinct early agnathans, characterized by thick enameloid caps to the tubercles of the skin scales; the head armour is made of loosely linked polygonal plates.

Autostylic: 'self pillar', a means of jaw suspension whereby the mandibular arch is self-supporting and articulates directly with the skull.

Avalonia: 'Avalon Peninsula, Newfoundland', an early Palaeozoic crustal plate consisting of Newfoundland, England, Wales, south-east Ireland and part of western Europe, which was brought together with Laurentia at the end of the Silurian.

Baltica: 'Baltic', an early Palaeozoic crustal plate consisting of much of present day north-western Europe, including Scandinavia, European Russia and central Europe; the plate formed the south-eastern continental margin of the Iapetus Ocean and collided with Laurentia to form the Caledonian mountain belt when the ocean was subduct-ed.

Batoidea (-oids): 'thorn bush', a group of neoselachian elasmobranch fishes (Jurassic-extant), such as the skates and rays, with dorso-ventrally flattened bodies, enlargened pectoral fins for locomotion and a reduced tail and other fins.

Belemnite: 'javelin form', a member of an extinct group of cephalopod marine molluscs related to the squids, having an internal solid calcium carbonate 'bullet-shaped' and posterior skeletal element (predominantly Jurassic-Cretaceous but with problematic earlier Carboniferous and Triassic forms and a later questionable Tertiary form).

Benthic: 'depths', living on or in the substrate.

Benthosuchidae (-ids): 'deep lizard', an extinct group of Triassic stereospondyls which may be paraphyletic and thus not a valid entity.

Biocoenose: 'life in common', a living community of organisms occupying a particular biotope.

Biostratigraphy: 'life layer writing', the subdivision and correlation of sedimentary strata based on their fossil content.

Biota: 'life', the flora and fauna of a particular place.

Biotope: 'life place', habitats within which the environmental conditions are relatively uniform and similar assemblages of inhabitants recur.

Bioturbation: 'life disorder', any physical disturbance of the substrate, such as burrows and feeding traces, by the organisms living on or in it. These traces are often preserved in ancient sediments.

Biozone: a stratigraphically restricted unit of sedimentary rocks defined by its fossil content, most usefully by species of narrowly defined temporal range, and named after a single characteristic species.

Bloom: a seasonal and often dramatic increase in numbers of phytoplankton due to simultaneous reproduction.

Bone-bed: a stratigraphically restricted sedimentary accumulation and concentration of bones, or other vertebrate remains such as teeth or scales, often worn by transport and associated with fluviatile deposition, especially channel lag deposits or marine near-shore conglomerates. Bone beds may reflect a lack of other coarse grained sediment or a mass or catastrophic extinction event and occasionally are an economic source of phosphates. They represent an important source of palaeontological and geological information.

Bowfms: common name for the amiiforms, an extant group of primitive neopterygians, characterized by the living Arnia.

Brachiopoda (-ods): 'arm footed' a phylum of bivalved and lophophorate shellfish, superficially similar to the bivalved molluscs but distinguished by a different anatomy. Particularly common in the Palaeozoic seas but replaced by the molluscs as the dominant shellfish since Mesozoic times.

Bradydonti (-onts): 'slow toothed', a group of holocephalan fishes.

Breccia: a fragmental elastic sediment, characterized by angular grains.

Caecilia (-ians): 'blind', a group of limbless burrowing amphibians.

Calcrete: a deposit of a semi-arid region cemented by calcium carbonate, often referring to a superficial terrestrial soil.

Caledonides: 'of Caledonia', the Palaeozoic mountain chain extending in a northeast--south-west direction in Spitsbergen, eastern Greenland, Scandinavia, Scotland, northern Ireland, the Lake District of England, Wales and continued in Eastern Canada, which resulted from the closure of the Iapetus ocean.

Capitosauridae (-ids): 'head lizard', a member of a group of temnospondyl labyrinthodont amphibians with flattened skulls, some of which were 'crocodile-like' and reached considerable size (Triassic).

Cartilage (-inous): 'gristly', a strong elastic connective tissue, which is an important skeletal material in the vertebrates and the sole skeletal material in the chondrichthyan fishes.

Caturidae (-ids): 'of Caturus',a small group of extinct amiiform halecomorph neopterygians.

Cenozoic: 'recent life', the division of geological time which succeeds the Mesozoic and is characterized by the radiation of the mammals, flowering plants, insects, etc.

Cephalaspida (-ids): 'head-shield', an extinct group of osteostracan agnathans characterized by a solid bony head-shield and broad cornual processes.

Cephalochordata (-ates): 'head string', a group of primitive chordates, commonly called the lancelets and are thought to typify an ancestral form for the vertebrates; metamerically segmented, with an axial stiffening rod, the notochord, persisting in the adult and a perforated pharynx for feeding and respiration.

Ceratodidae (-ids): 'horn', an extant group of freshwater lungfishes.

Ceratodontidae (-ids): 'horn teeth', a group of extinct freshwater and marine lungfishes.

Chimaeridae (-aeras): 'monster shape', extant group of durophagous holocephalans with tooth plates, holostylic jaw suspension, an articulated dorsal spine, pelvic claspers and long narrowing tail (hence common name — rat-fish).

Chondrichthyes (-yans): 'cartilage fish', a major group of fish, commonly called the cartilaginous fishes, which have a cartilaginous endoskeleton, no lungs or air bladder and a spiral valve in the gut; typified at present by the sharks and rays.

Chondrostei (-ians): 'cartilage bone', a group of primitive actinopterygians with a heterocereal tail and a spiracle, typified at present by the sturgeons and paddlefish.

Chordata (-ates): 'string', major group of coelomate animals, characterized by a notochord and perforated pharynx at some stage in the life history and a dorsal hollow nerve cord.

Chronostratigraphy (-ical): 'time layer writing', the subdivision of geological time into a hierarchy of sequential units to which the layers (strata) of sedimentary rocks are allocated.

Cladistic analysis: 'branch analysis', an attempt to characterize natural groupings of organisms by means of a search for shared derived characters.

Cladodont: 'branch tooth', teeth with a prominent central cusp and smaller lateral cusps.

Cladogram: 'branch picture', a branched treelike classification diagram produced by cladistic analysis.

Clastic: 'broken in pieces', fragmental sediment composed mainly of particles derived from pre-existing rocks or minerals, including organic remains (designated as bioclastic).

Cleithrum: 'bar', the clavicular elements of some fish.

Climatiidae (-lids): 'Climatius shape', a group of extinct acanthodians with two dorsal fins and a row of spines between the pectoral and pelvic fins.

Clupeocephala (-ans): 'herring head', an extinct group of Jurassic advanced teleosts derived from the elopocephalans and characterized by tooth plates fused with endoskeletal gill-arch elements.

Clupeomorpha(-orphs): 'herring form', a group of primitive teleosts ranging from the Jurassic to the present and including the living salmon and herring.

Coccolith (-iths): 'berry stone', a member of a palaeontologically important group of unicellular flagellate and planktic marine microorganisms producing a calcium carbonate skeleton made up of a series of plates. The Cretaceous chalk limestone is often largely made up of coccolith skeletons (Upper Triassic-Recent).

Coccosteidae (-ids): 'berry bone', an extinct group of arthrodire gnathostomes with an embayment in the central plate for the pre-orbital plate.

Coelacanth: 'hollow spine', a group of sarcopterygians, the actinistians with a reduced air bladder and no choana, characterized by the 'living fossil' coelacanth Latimeria.

Coelolepida (-ids): 'hollow scale', synonymous with thelodont, a group of extinct jawless ostracoderms, characterized by a covering of small shagreen-like scales, which can be used to identify them and are of considerable use in biostratigraphy.

Conchostraca (-ans): 'shelled shell', members of a group of freshwater crustaceans (the clam shrimps) in which the body is contained within a chitinous bivalved shell (Devonian-Recent).

Conodonta (-onts): 'cone teeth', an extinct group of small eel-like marine coelomates, characterized by assemblages of paired teeth made of bone-like material; recently considered to be chordates or possibly primitive agnathan vertebrates. The teeth have considerable use in biostratigraphy.

Coprolite: 'dung stone', petrified or fossil faecal material which may contain identifiable food remains and occasionally abundant enough to be a source of phosphate.

Coquina: 'of shells', a limestone deposit largely made of shells or their fragments.

Cornstone: a concretionary limestone deposit, characteristic of arid terrestrial environments.

Cornua(-ates): 'horn', a horn or horn-like projection.

Cosmine: 'order', a kind of dentine found in the cosmoid scales, which have an outer layer of enamel, then cosmine and an inner layer of bone; found in crossopterygians and early lungfish.

Craniata (-ates): 'skull', synonymous with Vertebrata, a major subdivision of the chordates, in which there is a high degree of cephalisation, producing a brain enclosed in a protective 'skull' and an endoskeleton consisting of a backbone, paired girdles and attached locomotory appendages.

Creatine: 'flesh', a biochemical found in all vertebrate muscle.

Crinoidea (-oids): 'lily form', a group of echinoderms, characterized by roots, stems, cups and arms made of jointed plates of calcium carbonate, hence the common name — 'sea lily'; the carbonate skeleton is readily fossilized and they were particularly common from the Middle Palaeozoic to Mesozoic but less so in more recent times.

Crossopterygia (-ians): 'tassle finned' an old classificatory term for a mainly extinct group of sarcopterygian fish which includes the living coelacanth.

Cryogenic: 'frost kin', produced by freezing.

Cryptozoic: 'hidden life', synonymous with Archean, the earliest phase of Earth history prior to 2600 Ma ago, during which life originated and from which only a few primitive organisms have been fossilized.

Ctenacanthiformes (-orms): 'comb thorn form', an extinct group of elasmobranch sharks, with flexible jaw systems and enhanced sensory apparatus, from which the neoselachians may have originated.

Cyathaspida (-ids): 'cup shield', an extinct group of heterostracans, characterized by a fusiform dorsal head-shield in a single plate, ornamented with longitudinal parallel dentine ridges and the body scales are relatively large.

Cycloid: 'circle form', scales with an evenly curved free edge.

Cyclostomata (-omes): 'circle mouth', a grouping of living agnathans without bone or paired fins, the hagfish and lampreys, on the basis of a number of shared characters such as the structure of the 'tongue'.

Cyclothem: 'circle laid down', a succession of sedimentary layers, representing a sequence of depositional events which tend to be repeated.

Denticle: 'little tooth', small tooth-like processes and scales.

Dentine: 'tooth', a hard material resembling bone, which makes up the greater part of teeth.

Dermal bone: 'skin bone', bony elements which develop within the skin and may be thickened into tough 'leathery armour-like' plates of varying size.

Diachronous: 'through time', relating to sedimentary or stratigraphical units where the environmental or facies boundaries cut across the time boundaries in the succession of deposition. Diachronism reflects the migration of a geological event through time so that the sediment produced by that event is not everywhere the same age.

Diastrophism: 'through turning point', large-scale movement and deformation of the Earth's crust.

Dinoflagellate: 'rotating whip', a member of a large and diverse group of aquatic unicellular micro-organisms, loosely placed with the algae, which swim by means of flagellae and some of which are covered with cellulose plates that can be preserved in the fossil record (Mid-Triassic-Recent).

Diphycercal: 'two-fold tail', a tail fin in which the vertebral column runs straight through to the tip and divides the fin into two symmetrical lobes.

Dipnoi (-oans): 'two times to breathe', a group of primitive bony fishes with both gills and lungs for breathing, hence the common name — lungfish.

Dipteridae (-ids): 'of Dipterus,'similar to the lungfish Dipterus.

Discoglossidae (-ids): 'round flat tongue', a member of a group of primitive frogs (anurans) with a long fossil record (Upper Jurassic-Recent) and both aquatic and terrestrial representatives.

Disconformity: 'asunder with form', a break in time, during which no sediment is deposited or the sediment that is deposited is subsequently eroded before the succession of strata continues without angular discordance.

Dolomite: a carbonate mineral containing a significant amount of magnesium carbonate, forming extensive deposits, often as a result of secondary, post-depositional chemical changes to limestones.

Durophagous: 'hard to eat', consuming prey with hard parts, which need to be crushed, such as shellfish and crustaceans.

Ecostratigraphy: 'household layers, writing of', the study of the changing relationships between organisms, their evolution and their environments through time.

Elasmobranchii (-anchs): 'to draw out gills', a group of chondrichthyans with placoid scales, a spiracle and no operculum over the gills, such as the sharks, skates and rays; many forms have the two dorsal fins armed with large spines, which are amongst the few features that are fossilized.

Elopocephala (-ans): 'fish head', an extant group of advanced teleosts which gave rise to the clupeocephalans.

Elopomorpha (-orphs): 'fish form', a primitive group of teleosts, which includes the eels. Embolomeri (-eres): 'wedge part', in earlier classifications — an extinct group of primitive labyrinthodonts', originally thought to be characterized by a particular vertebral structure.

Entopterygoid (-oids): 'within wing form', a dorsal membrane bone behind the palatine in some fishes.

Epeiric: 'mainland', produced by large-scale uplift or subsidence of crustal rocks without the severe deformation associated with orogeny.

Epicontinental: 'upon continent', located on a continent or the surrounding continental shelf.

Epilimnion: 'upon lake', the upper layer of warm water, formed in summer, within a thermally stratified lake.

Eriptychiformes (-orms): 'very folded form', a poorly known extinct group of tesselated heterostracans.

Erratic: 'mistake', a rock which seems out of place within the sedimentary environment within which it is found, especially glacial erratics which have been carried great distances by glaciers or icebergs before being dumped wherever the ice melts.

Eugenodontiformes (-orms): 'well-born tooth form' an extinct group of cladoselachian elasmobranchs, some of which were large shark-like forms, characterized by a median series of large teeth on the lower jaw, which is scrolled into a tooth spiral in some, lacking anal and pelvic fins.

Euramerica: 'Europe-America', continental mass of north-western Europe and North America, formed when the Iapetus Ocean was subducted during the Caledonian orogeny; also used to denote a biogeographical province.

Eurypterida (-ids): 'of Eurypterus, broad fern', an extinct group of large aquatic arthropods which superficially resemble scorpions.

Euteleosta (-osts): 'wide finished', the largest group of teleosts, which includes over 17 000 species, belonging to three main groupings ranging from pike to goldfish and salmon.

Evaporite: sediments and minerals grown from a saline solution by evaporation of the solvent — normally water, which may be marine or continental in origin. A wide range of mineral salts may be precipitated depending on the original composition of the solvent, e.g. carbonates, sulphates and chlorides, and mixed with other types of sediment, often finely laminated.

Fish: the common and convenient name for a wide range of aquatic vertebrates, which used to be united under the old classificatory term Pisces.

Fissure-filling: cavities, often formed by solution of limestone host rock, infilled with relatively younger deposits, which may be of particular interest when they contain fossils, especially microvertebrates that are not preserved elsewhere.

Flash flood: an infrequent and ephemeral flood, characteriztic of semi-arid regions and often associated with storms. The water may evaporate and dump its sediment load before discharging into the sea.

Flint: a hard, glassy and non-crystalline mineral form of silicon dioxide (quartz), frequently found in carbonate sediments, where it has developed from dissolved silica derived from sponges.

Flood basalts: widespread layers of basaltic lava, generally derived from the relatively quiet fissure-type eruption of free-running basic lavas.

Foraminifera (-ans): 'carrying an opening a member of a group of small unicellular aquatic organisms which secrete a coiled shell of various materials; often very abundant in marine waters with representatives that are benthic and planktic (Cambrian-Recent).

Gadiiformes (-orms): 'Gadus or cod shape' a group of neoteleosts with an air bladder and soft jointed fins, which includes cod, hake, mackerel and whiting.

Galeaspida (-ids): 'helmet shield', an extinct group of agnathans endemic to China and the surrounding region, characterized by their broad bony headshields, with a large median dorsal opening which connects with the oralo-branchial cavity.

Galeomorphii (-orphs): 'of Galus form', the largest group of neoselachians, including the dogfishes and modern sharks.

Ganoid: 'sheen', rhombic scales with outer layers of ganoine, cosmine below and then lamellar bone.

Ganoidei (-oids): 'sheen form', a group of primitive actinopterygians with ganoid scales.

Ganoine: 'sheen', enamel-like material on the outside of ganoid scales, which are rhomboid in shape and have layers of ganoine, cosmine and lamellar bone; found in primitive actinopterygians.

Gar: 'spear', common name for the lepisosteids, a primitive group of neopterygians, characterized by the living pike-like Lepisosteus.

Genotype: 'race image', type species of a genus.

Geochronometry (-etric): 'earth time measure', the method of measuring geological time in years before present, commonly using the known decay rates of the daughter isotopes of radioactive minerals; mainly derived from igneous rocks.

Glauconite: 'sea stone', containing the diagenetic (growing in place) mineral glauconite, a complex green-coloured hydrous potassium iron silicate which is sufficiently common in some shallow-water marine sediments to give them an overall green coloration e.g. Cretaceous greensands.

Gnathostomata (-omes): 'jaw mouth', a group of vertebrates with jaws, derived from the anterior gill-arches, and a considerable degree of cephalization.

Gondwanaland: a grouping of the major southern continental plates of Africa, Australasia, Antarctica, South America, India, several smaller plates and fragments of what are now parts of Mediterranean Europe, which formed a massive southern supercontinent in upper Palaeozoic times.

Goniatite: 'angle-like', an extinct group of upper Palaeozoic ammonoid cephalopods with coiled shells.

Graben: a linear block of crust downthrown between two parallel faults.

Graptolithina (-lites): 'writing stone', an extinct group of marine colonial hemichor-dates, which secreted a proteinaceous skeleton in the form of an interconnected series of cups to house and protect the zooids.

Gymnophiona (-ones): 'naked snake-like', synonymous with caecilians and apodans, a group of limbless burrowing amphibians, with an absent or reduced larval stage, a stoutly built skull, small calcareous denticics in the skin and an elongate trunk with up to 200 vertebrae.

Gymnospermae (-erms): 'naked seed', members of a major division of the plant kingdom, consisting of woody plants with alternation of generations and seeds produced on the surface of the sporophylls and not enclosed in an ovary, e.g. seed ferns and conifers (late Devonian–Recent).

Hagfish: common name for the living myxinoids, a marine group of the surviving agnathans.

Halite: 'salt-like', common salt, NaCl, a naturally occurring mineral particularly associated with evaporite deposits from sea water.

Hardground: a sediment surface preserved within a sequence of strata, which has hardened through early diagenetic processes and whose ecology has changed as it came to be occupied by different organisms.

Hemicyclaspida (-ids): 'half round shield', an extinct group of ateleaspid osteostracans distinguished by a distinct cornual angle and a rounded rostral angle to the headshield.

Hercynian: ( = Variscan) an upper Palaeozoic phase of mountain building following sub-duction of a WSW–ENE oriented ocean, from south-west England through Scania, central and southern Europe and the Iberian Peninsula.

Heterocercal: 'other tail', where the vertebral column terminates in the upper lobe of the tail, whose lobe is usually larger than the lower lobe.

Heterostraci (-acans): 'other shell', an extinct group of agnathans, with extensive head armour of large plates and a pair of common branchial openings on either side.

Histology: 'tissue discourse', the detailed study of plant and animal tissues.

Holocephali (-ans): 'whole head', a group of mainly fossil cartilaginous fish with holostylic jaws, gills covered by an opercu-lum, narrowing whip-like tail and crushing teeth; includes the surviving chimaeras.

Holoptychidae (-ids): 'whole plate', an extinct group of porolepiform sarcopterygians with scales and dermal bones covered with dentine and cosmine.

Holostei (-eans): 'whole bone', a grouping of largely fossil actinopterygians, intermediate between the palaeoniscids and teleosts, which includes many Mesozoic taxa and the surviving bow fin and gar pike.

Holostylic: 'whole pillar', a type of jaw suspension in which the palatoquadrate bone is fused directly to the cranium, as found in the holocephalans.

Holotype: 'whole pattern', the single specimen selected to characterize a species. Homocercal: 'same tail', where the vertebral axis ends near the middle of the base and there are similar-sized upper and lower lobes.

Horsetail: common name for the sphenopsid pteridophytes with jointed stems and leaves in whorls; abundant in the upper Palaeozoic and surviving to the present day.

Horst: an upfaulted block of crustal rocks, often on either side of a graben.

Hybodont: 'hump tooth', a grouping of extinct elasmobranchs, characterized by their elongate and low hybodont teeth, ornamented with sinuous ridges and pierced by numerous nutrient canals, with placoid scales and calcified pleural ribs.

Hypersaline: 'above salt', when the salinity of water exceeds 40 parts per thousand; a condition which can only be tolerated by those halophilic organisms adapted to the conditions; the mean salinity of sea water is 35 parts per thousand.

Hypochordal: 'under cord', where the vertebral column descends into the lower lobe of the tail, which is generally larger than the upper one.

Hypolimnion: 'under lake', the layer of water below the thermocline in a lake.

Iapetus: a 'proto-Atlantic' ocean, which separated the Lower Palaeozoic crustal plates of Laurentia and Baltica and divided the present British Isles until the ocean floor was finally subducted in Ordovician-Silurian times.

Ichnofossil: 'track fauna', an assemblage of trace fossils that records life in sediments disturbed by the activity of organisms, e.g. worm burrows or foot prints (see bioturbation).

Ichthyodectidae (-ids): 'fish acceptable', an extinct group of important large predatory teleosts of the Jurassic and Cretaceous.

Ichthyology: 'fish discourse', the study of fishes.

Ichthyostegidae (-ids): 'fish roof', an extinct group of primitive tetrapods, which retain many fish-like characteristics such as a laterally flattened tail and lateral line system, which evolved from the rhipidistians.

Index fossil: a particular fossil species which characterizes a named biozone within a biostratigraphical subdivision.

Inoceramid (-ids): 'strong clay pot', a member of a large group of extinct pterioid marine bivalves, which have been used for biostratigraphical subdivision (Triassic-end Cretaceous).

Intraclast (conglomerate): 'within fragments', a carbonate fragment derived by erosion from local contemporaneous strata within the same depositional basin.

Ischnacanthidae (-ids): 'hip thorn', a extinct group of acanthodians, often with large teeth, two dorsal fins and no spines between the pelvic and pectoral fins.

Kaolinite: a mud rock consisting mainly of the potassium-rich clay mineral kaolin from which china clay is made.

Katoporid (-ids): one of five thelodont scales with a large open pulp cavity with extensions into dentine tubules.

Kerogen: a naturally occurring organic material which yields petroleum-like hydrocarbons on heating and distillation.

Labyrinthine: 'labyrinth', having an infolded structure such as the dentine of labyrinthodont teeth'.

Labyrinthodont: 'labyrinth tooth', traditionally one of three groups of stem tetrapods that included the first land vertebrates, and which are characterized by teeth with compex infolding of the dentine, large body size and compound vertebrae; no longer a valid entity as it is not monophyletic (late Devonian-Triassic).

Lag (deposit): a layer of larger or denser clasts, such as pebbles or bones, which have accumulated in the bottom of a channel during deposition.

Lagerstatten (fossil): a rock containing well-preserved fossils that are worth exploiting for their intrinsic interest; their nature implies some unusual circumstances of preservation.

Laminites: thin layers of generally fine-grained sediment, reflecting rapidly fluctuating, often seasonal, changes in sediment supply or environmental conditions; characteristic of lakes and other shallow basins of deposition where there is a restricted bottom fauna.

Lamprey: 'Lampetra', common name for one of the surviving agnathan groups, the petromyzontids.

Laurasia: 'St Lawrence-Asia' the northern supercontinental mass formed in the early Mesozoic by the rifting of Pangaea with the opening of the Tethys and Atlantic Oceans; comprised of the amalgamated plates of North America, Greenland, Europe and Asia.

Laurentia: 'St Lawrence', North American crustal plate in lower Palaeozoic times, prior to the subduction of the Iapetus Ocean; comprised mainly of the ancient Precambrian core of the Canadian Shield and Greenland plus Scotland and north-west Ireland.

Laurussia: 'St Lawrence–Russia', the amalgamated plates of North America and Russia, following the subduction of the Iapetus Ocean.

Lectotype: 'chosen pattern', a specimen chosen from available syntypes to be the designated type of the species.

Lepospondyli (-yles): 'husk vertebrae', a traditional grouping of basal tetrapods, characterized by small size, simple tooth structure and spool-shaped vertebrae, which are formed as single structures, such as is found in the urodeles and apodans; cladistic analysis has shown that the group is not mono-phyletic, thereby undermining its validity.

Leptolepidae (-ids): 'slender scale', a group of halecostome neopterygians which show some early teleost characters, such as no enamel layer on the skull bones and a vertically keeled rostrum.

Lingulida (-ids): 'tongue', a group of extant brachiopod shellfish, which were much more abundant in the Palaeozoic than at present.

Lissamphibia (-ians): 'smooth both lives', a grouping which includes all the living and diverse amphibians with reduced or absent scales and skin respiration, i.e. anurans (frogs and toads), urodeles (newts and salamanders) and apodans (the limbless caecilians).

Lithostratigraphy: 'rock layer writing', the organisation and division of strata into units and their correlation based entirely upon their lithological (rock compositional) characteristics.

Littoral: 'seashore', the zone between high and low water marks on a shoreline.

Loganellida (-ids): 'Logan (Water)', a group of thelodont agnathans with a characteristic form of scale.

Lungfish: see Dipnoi.

Maceration: 'softening', the process of softening or isolating tissue and separating cells.

Mastodonsauridae (-ids): 'breast tooth lizard', an extinct group of freshwater Triassic stereospondyls.

Maxilla: 'jaw', part of the upper jaw behind the premaxilla.

Mesoderm: 'middle skin', the embryonic cell layer between the ectoderm and endoderm.

Mesosauridae (-ids): 'middle lizard', an extinct group of small Upper Palaeozoic fish-eating reptiles with elongate bodies, necks and long narrow jaws; they were the first known marine amniotes.

Mesozoic: 'middle life', the middle division of geological time with abundant life, after the Palaeozoic, before the Cenozoic and containing the Triassic, Jurassic and Cretaceous periods.

Metamorphosis: 'change of form', a significant change of structure and form undergone by an organism between the embryonic and adult stage, such as is found in insects and amphibians with a tadpole larva preceding the adult tetrapod.

Micrite: the fine-grained microcrystalline carbonate matrix of limestones, much of which is chemically precipitated as a lime mud but which may also include a significant proportion of organic-derived mud.

Microvertebrate: often referred to as Ichthy-oliths', literally the small fossil remains of vertebrates, such as scales, teeth and bones, which may be barely visible with the unaided eye when disarticulated. They can be separated from many kinds of rock matrix by careful acid preparation and are then available for microscopic study. Although they have been known for over 150 years, their potential for revealing so much about the palaeontology of vertebrates and their use in biostratigraphy, has only been realized in the last decade Or so.

Miospore (-ores): 'less seed', a fossil plant spore less than 0.22 mm in diameter, for which the parent plant is often unknown.

Molasse: a terrestrial clastic deposit, generally of poorly sorted, immature sediment associated with the uplift and rapid erosion of newly formed mountain belts; often accumulating to considerable thickness in marginal or intermontane basins.

Monophyletic: a natural taxonomic group that includes all descendants of a single common ancestor, e.g. the Aniniota which include the reptiles, birds and mammals.

Myriacanthoidea (-oids): 'numberless spines' an extinct group of Palaeozoic holocephalians with loss of mandibular plates.

Myxinoidea (-oids): 'Myxine — slime form', an extant group of marine agnathans, commonly referred to as the hagfish.

Nasohypophysial: 'nose under growth', a keyhole-shaped opening on the dorsal surface of the head in lampreys and the extinct osteostracans, which combines a single nasal opening with a blind hypophysial tube, allowing water to enter and leave the olfactory organ.

Nautiloidea (-oids): 'nautilus form', an almost extinct group of cephalopods with straight or coiled conical shells, which were more abundant in the Palaeozoic but survive in only one genus, Nautilus.

Nekton: 'swimming', those organisms which actively swim in water.

Neocatastrophism: the doctrine that the most important driving forces in Earth history and the evolution of life have not been those of gradual change, but a variety of catastrophic events, both internal and extra-terrestrial.

Neopterygii (-ians): 'new fin', a group of Recent actinopterygians characterized by an equal number of fin rays of the dorsal and anal fins and the reduction or loss of the clavicle; includes the ginglymods, halecomorphs and teleosts.

Neoselachii (-ians): 'new sharks', a modern-type group which includes all extant elasmobranchs, characterized by enameloid on the teeth and scales and a septate notochordal canal.

Neoteleosti (-osts): 'new bone', an extant group of advanced bony fishes (teleosts).

Neotype: 'new pattern', a new or replacement type specimen taken from the original type locality.

Neural crest: 'nerve crest', an ectodermal thickening of a dorsal groove, which gives rise in embryological development of the living agnathans and cephalochordates to the central nervous system.

Neurocranium: 'nerve skull', the cartilaginous or bony encasement to the brain and special sense organs.

Nodule: 'knob', a spherical or elliptical mineral concretion, generally grown post-depositionally within a sediment, as the result of the concentration of a particular mineral around a nucleus.

Nomen nudum: 'name naked', in taxonomy, an invalid name because the organism to which it is attached was inadequately described or illustrated.

Notochord: 'back cord', a stiff flexible rod of large vacuolated cells which acts as an anteri or—posterior axis between the gut and dorsal nerve cord in chordates.

Old Red Sandstone: a classic term still applied to the terrestrial, largely elastic facies of the Devonian in Britain, characterized by conglomerates and red sandstones.

Oolitic: 'egg stone', a sedimentary rock, usually a limestone made up of small (1–10 mm) ovoid accretionary bodies cemented together. The ovoids resemble fish eggs but are formed by the precipitation of layers of calcium carbonate concentrically arranged around a nucleus, e.g. a sand grain, as it is rolled around on the sea floor by waves and currents, especially in shallow tropical and subtropical seas.

Orobranchial: 'mouth gills', in association with the mouth and gills as in orobranchial cavity.

Orogeny: 'mountain genesis' a process of mountain building during which the rocks and sediments of a particular area of a conti-nent(s) are deformed and uplifted to form mountain belts. Although these processes take a long time, they can be distinguished as recognizable and discrete phases in Earth history and are named accordingly, e.g. Variscan orogeny.

Ossiferous: 'bone make', made up from bones or their fragments.

Osteichthyes (-yans): 'bone fish', all fishes whose endoskeletons are made from bone, usually having an air bladder and operculum covering the gills.

Osteoglossomorpha (-orphs): 'bone tongue form', an extant group of freshwater teleosts.

Osteolepiformes (-orms): 'bone scale form', an extinct group of rhipidistian sarcopterygians with labyrinthine teeth, long considered to be ancestral to the tetrapods because of the endoskeletal structure of the paired fins.

Osteostraci (-ans): 'bone shell', an extinct group of agnathans with both exoskeleton and endoskeleton of bone, characterized by median and lateral depressions on the surface of the dorsal head-shield, which has a 'horseshoe' shape and a pair of pectoral flap-shaped fins; also, generally there is a peculiar horizontal fin below the main tail fin.

Ostracoda (-ods): 'shell-like', members of a group of small crustaceans having a bivalved shell around the body. Throughout their long geological history (Cambrian–Recent) they have diversified into a wide range of aquatic ecological niches both on land and at sea.

Ostracoderma (-erms): 'shell skin', all those jawless craniates with an exoskelton of dermal bone, i.e. the fossil agnathans.

Otolith: 'ear stone', a calcareous structure found in the otocyst capsule and used to maintain orientation in relation to gravity and balance; they are often the only structures to be fossilized from many teleosts, and individual otoliths can be identified specifically.

Pachycormidae (-ids): 'thick trunk shape', a group of Mesozoic basal teleosts, characterized by a mobile premaxilla and long swordfish-like jaws.

Palaeocurrent: a flow direction deduced form sedimentary structures associated with an ancient depositional or erosive event.

Palaeoecology: 'ancient household discourse', the study of the relationship between organisms and their environments in the past.

Palaeokarst: 'ancient karst', fossil solutional features associated with buried limestone topography.

Palaeonisciformes (-orms): 'Palaeoniscus —ancient small form', a group of almost extinct early actinopterygians, typically carnivorous in habit with markedly heterocercal tails; traditionally regarded as chondrostean grade but more recently as neopterygians, including the living sturgeons and paddlefish.

Palaeoslope: 'ancient slope', the orientation of an original inclined surface as determined from an ancient depositional or erosive event.

Palaeosol: 'ancient soil', a 'fossil' soil deposit characterizing a terrestrial environment.

Palaeozoic: 'ancient life', the first major division of geological time which is characterized by abundant life and which is preceded by the Proterozoic and succeeded by the Mesozoic; divided into six or seven periods from the Cambrian to the Permian.

Palatine: 'palate', in the region of the palate or roof of the mouth.

Palinspastic: 'again draw', restored to an original condition, or in the case of a map to represent original conditions or features.

Palynology: 'pollen discourse', the study of plant spores and pollen and their distribution, which has proved to be of considerable biostratigraphical use.

Palynomorph: 'pollen form', a microscopic, resistant, walled organic body found in paly-nological preparations, including both plant-derived bodies such as spores and pollen and also other acid-resistant remains such as acritarchs and chitinozoans.

Palynozone: 'pollen zone', a biostratigraphical subdivision characterized by an assemblage of pollen 'species'.

Panderichthyida (-ids): 'Pander's fish', an extinct group of thin streamlined rhipidisteans with long, dorso-ventrally flattened skulls and only paired pelvic and pectoral fins, without the midline paired fins of their relatives; they are now considered to be very close to the early tetrapods.

Pangaea: 'the whole Gaea', a supercontinent formed by ocean-floor subduction, plate collision and assembly of all continents in the late Permian.

Paraphyletic: 'beside tribe', arising from a single common ancestor but not including all descendants, e.g. Class Reptilia which does not include the descendant birds and mammals.

Paratypes: 'beside pattern', a specimen or specimens in the same series or collection from which the holotype has been selected.

Pedocal: 'ground calcium', an arid or semi-arid soil-type deposit, characterized by the presence of calcium carbonate, e.g. the 'Psammosteus Limestone'.

Peneplain: 'almost plain', a landscape surface with greatly reduced features as a result of prolonged weathering and erosion.

Perichondral bone: 'around cartilage — bone', ossification of cartilage from the outside.

Perleidiformes (-orms): 'Perleidus-form',an extinct group of basal actinopterygians, of 'chondrostean' grade, with ganoid scales, nearly symmetrical tail fins and small slender bodies, best known from the Triassic.

Petalodont: 'leaf tooth', an extinct group of Upper Palaeozoic holocephalans, known only from fossils of their leaf-shaped teeth.

Petromyzontiformes (-orms): 'Petromyzon —rock suck form', an extant group of freshwater agnathans, commonly called lampreys, with a semi-parasitic mode of life, elongate eel-like bodies, no body armour or paired fins.

Pharyngeal: 'gullet', a structure or tissue associated with the gullet.

Pholidophoridae (-ids): 'bearing scales' an extinct group of Mesozoic neopterygian halecostomes, which show some characteristics of the primitive teleosts, such as cycloid scales and the loss of enamel from most skull bones.

Phosphate: a phosphorus salt associated with mineral phosphate in bone.

Phylogeny: 'race descent', the evolutionary relationships and history of a species or group of organisms.

Phytoplankton: 'plant wandering', free-living plants within an aquatic environment, often microscopic and with limited powers of locomotion, so mainly dispersed by wind and tide.

Pineal: 'of the pine', cone shaped, as in pineal gland — which is often externally visible in lower vertebrates and may have endocrine functions and be sensitive to light.

Pituaraspida (-ids): 'phlegm broad', a small group of poorly preserved agnathans only known from a few Devonian sandstone impressions in Australia.

Placodermi (-erms): 'plate skin', an extinct group of primitive Palaeozoic jawed fishes, with a dermal armour in two parts, one covering the head, the other the trunk, which are sometimes articulated, e.g. the arthrodires.

Placoid scale: 'plate form — scale', scales which are structured and formed similar to teeth and are characteristically found covering the elasmobranchs as shagreen.

Planktonic: 'wandering', belonging to the plankton; those generally small organisms which drift in water bodies and have limited powers of locomotion.

Playa: the flat dry bottom of a desert basin, often the bed of an ephemeral lake and underlain by evaporites.

Pleuracanth: 'side thorn', a small extinct group of Palaeozoic freshwater elasmobranch sharks.

Point-bar: a low bank of sediment on the inside bend of a river channel, consisting of material derived from the eroded outside bank.

Precambrian: 'before Cambrian', the first major division of geological time which includes the first 4 billion or so years of Earth history before abundant metazoan life capable of secreting skeletons had evolved; the top of the Precambrian is defined by the base of the Cambrian Period in the Palaeozoic Era.

Prokaryote: 'before nucleus', organisms such as blue-green algae and bacteria whose chromosomes are not surrounded by a nuclear membrane.

Proterozoic: 'former life', the younger subdivision of Precambrian time from 2.5 Ga ago until the beginning of the Cambrian at the base of the Palaeozoic; when primitive life had evolved and has been preserved as rare fossils of prokaryotes and soft-bodied metazoans in the youngest rocks of the division.

Protobranch: 'first gills', a member of a 'primitive' group of marine bivalve molluscs with a very long fossil record (Lower Cambrian-Recent) that commonly occupy mud substrates and feed by extracting organic material from the mud, e.g. the nuculids.

Protochordata (-ates): 'first string', a group of primitive chordates, which have 'tadpole-like' larvae with a perforated pharynx, notochord, hollow dorsal nerve cord and post-anal tail.

Protopteraspidae (-ids): 'first Pteraspis — wing shield', one of a number of extinct pteraspid groups, which retains some features of the cyathaspids, from which the pteraspids are thought to have originated; characterized by the supra-orbital canal passing through the pineal plate.

Psammosteiformes (-orms): 'sand bone form', an extinct group of large pteraspidi-form heterostracans with a secondary tuberculate ornamentation to the dermal armour and two orbital plates.

Pteraspida (-ids): 'of Pteraspis — wing shield', an extinct group Palaeozoic heterostra-cans, which had head-shields made of several large and independent bony plates, ornamented with concentric ridges.

Pycnodontiformes (-orms): 'dense tooth', a large extinct group of marine neopterygians, mostly deep-bodied forms, characterized by symmetrical (homocercal) tail fins.

Pyrite: 'fire stone', an iron sulphide mineral common within sediments, resulting from the biochemical action of bacteria within anaerobic environments.

Pyroclastic: 'fire fragments', the fragmentation of igneous rock materials during volcanic eruption, ranging from large rock bombs to pulverized rock dust and ash.

Radio-isotope: 'ray — equal place', the isotopes of radioactive elements which have the same atomic number but different atomic weights.

Raffish: see chimaeras.

Red beds: sedimentary deposits that are predominantly red in colour, generally as a result of abundant iron oxides, which often reflect deposition in an oxidizing situation, e.g. in an arid terrestrial environment and may be associated with evaporites.

Regression: referring to the retreat of the sea from land areas as a result of a fall in sea level or elevation of the landmass.

Reptilia (-iles): 'creeping animals', members of a large class of amniote vertebrates, having a long fossil history extending back to the Carboniferous, with a dry, waterproof horny skin of scales, plates or scutes, functional lungs, a four-chambered heart and laying eggs fertilized inside the female's body.

Reptilomorph (-orphs): 'creeping animal form', term applied to many early fossil tetrapods which are difficult to characterize as either reptile or amphibian.

Rhipidistia 'fan', an extinct group of Upper Palaeozoic 'lobe-finned' sarcopterygian fish which are considered ancestral to the tetrapods.

Rhizodontidae (-ids): 'root teeth', a poorly known extinct group of very large 'rhipidisteans' with thin and loosely attached skull bones, characterized by dermal fin rays with a long unsegmented portion, covered by rounded scales; the folded teeth are poly-plocodont like those of osteolepiforms and tetrapods.

Rhizodontiformes (-orms): 'root tooth form' an extinct group of poorly known, large sarcopterygians, probably effective predators, with thin and loosely attached skull bones and dermal fin rays with a long unsegmented portion.

Rhythmic sequence: a regularly banded vertical sequence of sediments, reflecting rhythmic changes in the supply of sediment often related to seasonal changes e.g. the varved couplets of silt and clay in glacial lakes.

Rötliegendes: 'red layers', a German stratigraphical term applied to the largely continental deposits of Lower to Middle Permian times, which are often reddened with iron oxide minerals.

Rudist: 'rough', a member of an unusual and varied group of extinct marine cemented bivalve molluscs (also known as hippuritoids), which flourished in the shallow tropical seas of the Tethyan area and in places formed reef-like clusters. Some had thick cone-shaped shells up to 1 m long, whilst others had coiled 'snail-like' shells (Upper Jurassic–end Cretaceous).

Sabkha: a halite-encrusted surface of salt flats, which are often developed just inland parallel to dry hot tropical coastlines, where periodic flooding by the sea is evaporated with precipitation of various evaporite minerals and laminae of dried algae.

Sacculus: 'small bag', lower part of the ear vestibule, which contain the otoliths of some teleosts.

Sapropel: 'rotten mud', anaerobic mud often enriched in bacteria.

Sarcopterygii (-ians): 'fleshy or lobe fin', a group of bony fishes, characterized by paired 'fleshy fins' and internal nostrils in some groups; includes the crossopterygians and dipnoans.

Scale: 'husk', a flat, plate-like protective structure for the skin, generally small and in rows to allow flexibility; may be either dermal or epidermal in origin.

Scapherpetontidae (-ids): 'boat reptile form', an extinct group of neotonous salamanders.

Sclerite: 'hard', an exoskeletal element in the form of spines or plates, often mineralized.

Scolenaspidea (-ids): 'worm broad form', one of five extinct groups of cornuate osteostracans, abundant in the Lower Devonian of Britain, Spitsbergen, North America and Podolia.

Scorpionid (-ids): 'scorpion', a group of arachnids which includes the scorpions.

Sea-squirt: common name for the hemichordate ascidians, marine organisms with a free-swimming larva and a sessile benthic adult.

Selachii (-ians): 'shark', a grouping of elasmobranch fishes, which includes fossil and living sharks and dogfish and ranges from the Devonian to the present; see Neoselachii.

Semicircular canals: the ducts of the ear labyrinth.

Semionotidae (-ids): 'Semionotus — half-pointed dorsal fin shape', an extant and ancient group of basal neopterygians, with median neural spines, which includes the gar pikes and originated in Permian times.

Serpulid (-ids): 'small snake', a small tubular fossil, mineralized with calcium carbonate and generally regarded as related to the living polychaete worms, which have similar form and encrusting habits.

Shagreen: common name for shark skin with its covering of many small overlapping dermal denticles.

Siliciclastic: 'hard stone fragments', a fragmental deposit, consisting mainly of grains of silica minerals, especially quartz.

Somite (-ites): 'body', the body compartments of metamerically segmented animals.

Sphenopsida (-ids): 'wedge shape', commonly referred to as 'horsetails', a group of pteridophyte plants with jointed stems and leaves arranged in whorls; of considerable importance in the Upper Palaeozoic, when some grew to tree size, but now much smaller and fewer in kind.

Squamata (-ates): 'scaly', a member of a large group of lepidosaur reptiles that includes the lizards and snakes and whose inter-relationships are not clear (Upper Jurassic-Recent).

Squamation: 'scale', the arrangement of dermal scales.

Squamosal: 'scale nature', a membrane bone forming part of the side wall of the vertebrate skull.

SSSI: Site of Special Scientific Interest.

Stegocephalia (-ians): 'roof head', an extinct group of amphibians with salamander-like body form.

Stem group: in cladistics, an extinct and presumed ancestral group, defined on the absence of features of the presumed descendants.

Stereospondyli (-yles): 'solid vertebrae', an extinct group of labyrinthodont amphibians having fused vertebrae.

Stratotype: 'layer pattern', a sequence of strata at a particular location, which has been internationally recognized as the definitive section for a particular chronostratigraphical subdivision of geological time.

Strike: the trend of a geological surface measured at right angles to the direction of slope.

Stromatolite: 'bedded stone', layered structures built up by mats of blue-green algae, which trap fine sediment as they grow; typically found in shallow tropical seas and extend back as fossils for some 30 Ga.

Subduction: 'under lead', the descent of large slabs of relatively dense ocean floor crust below less dense continental crust rocks, as the result of the collision of two crustal plates, with the release of vast amounts of energy in the form of earthquakes and often accompanied by vulcanicity.

Sulphate: a chemical compound containing sulphur and oxygen, which forms common sedimentary minerals with a variety of other elements, epecially in evaporite deposits.

Suture: 'seam', the line of collision between two crustal plates following the subduction of any intervening crust.

Symmoriiformes (-orms): 'in proportion form', an extinct group of shark-like elasmobranchs, characterized by a very long rod in the pectoral fins and a peculiar arrow-shaped element in the dorsal fin supports.

Synapomorphy: 'joined together shape', a shared derived character(s) which defines a sister-group in cladistic analysis.

Syntype: 'with pattern', any one of a series of specimens which characterize a species when there are no designated holotype and paratypes.

Taphonomy: 'burial cutting', the study of the processes of death, decay and burial by which organisms become selected and recruited to the fossil record.

Tectonism: 'builder', the processes of crustal deformation, often associated with plate tectonics and mountain building.

Teleostei (-osts): 'end bone', an extant and major group of advanced neopterygians, which includes the majority of living bony fishes; characterized by an air bladder, loss of enamel layer on skull bones, homocercal tail and thin bony cycloid scales.

Temnospondyli (-yles): 'cut vertebra', an extinct group of Upper Palaeozoic labyrinthodonts, with flattened skulls.

Terrane: 'earth', a small crustal plate or fragment of a larger plate, with distinctive characteristics, which can be displaced considerable distances from its original site and added to another plate during plate tectonic movement.

Tethys: 'Tethys, a mythical titaness and wife of Oceanus', an east-west-extending major ocean, which separated the southern supercontinent of Gondwanaland from Laurasia in Mesozoic times; subducted to form the Alpine-Himalaya mountain belt.

Tetrapoda (-ods): 'four footed', developmentally four-footed vertebrates including amphibians, reptiles and mammals.

Thanatocoenose: 'death common', an assemblage of fossil organisms which have been brought together by the processes of sedimentation, following their death, so that the assemblage may contain organisms that did not originally live near one another.

Thelodonta (-onts): 'teat teeth', an extinct group of agnathans, characterized by their shark-like dermal denticles, which are commonly fossilized as separate elements within the sediment.

Thermocline: 'heat swerve', a layer of water with fluctuating temperatures, which forms in summer and separates the epilimnion above from the hypolimnion below.

Theromorpha (-orphs): 'summer form', an extinct group of Upper Palaeozoic primitive mammal-like reptiles with a sprawling gait, including a group with heat exchange 'sailfins'.

Thyestida (-ids): 'pestle', an extinct group of cornuate osteostracans with an infra-orbital sensory line passing medially to the lateral fields.

Transgression: 'across walk', referring to the encroachment of the sea across a landscape as a result of either a rise in sea level or subsidence of the land.

Tremataspida (-ids): 'hole shield', an extinct group of cornuate osteostracans within the thyestids, which have lost their paired fins and cornual processes and have a 'tadpole-shaped' head.

Trophic pyramid: 'food pyramid', a layered subdivision of the food chain with the broad base of numerous primary producers at the base rising to the relatively few top carnivores at the apex of the 'pyramid'.

Tuff: volcanic ash, comprising rock and crystal fragments from an explosive eruption.

Turbidite: the deposit of a gravity-controlled turbidity current.

Unconformity: a break in the relationship between successive rocks in a sequence as a result of a variety of causes, from a lack of deposition to an intervening phase of tectonism and erosion; consequently the missing time interval may also vary enormously.

Urochordata (-ates): 'tail cord', a group of protochordates in which the chordate features are often only expressed in the larval stages; see sea-squirts.

Uronemidae (-ids): 'tail thread', one of five extinct groups of Carboniferous dipnoans.

Variscan: 'land of the Varisci or Vogtland', synonymous with Hercynian.

Varved: a laminite deposit in which the layers of sediment are graded and generally result from a seasonal influx of sediment-laden water into a low-energy water body such as a lake or lagoon.

Vascular (plant): 'small vessel', the major group of tracheophyte plants, in which there are special cells for the transmission of fluids.

Vertebrata (-ates): 'back bone', synonymous with Craniata, those metamerically segmented chordates in which the notochord is replaced by a backbone as part of an endoskeleton of cartilage or bone and with a high degree of cephalization.

Viviparous: 'live bearing', producing live young, as in the mammals, rather than eggs.

Xenacanthiformes (-orms): 'strange spine', an extinct group of shark-like elasmobranchs with a long dorsal spine on the head and diplodont teeth with a divergent crown and small median cusps.

Zechstein: a European stratigraphical name for Upper Permian deposits, including carbonates and evaporites of a shallow sea in northern Germany and the North Sea area.

Zone: a division of geological or stratigraphical time defined by fossil content, see biozone.

References