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Glossary

Alluvial fan:An outspread mass of alluvium deposited by flowing water where it debouches from a steep, narrow canyon onto a plain or valley floor. Viewing from above the deposits are generally fan-shaped. They are generally associated with arid regions.

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Ammonites: Extinct marine invertebrates.  They show a characteristic coiled shell, which led to the theory that the earliest discoveries were coiled snake fossils dating back to when snakes were driven from Ireland. The ammonites nearest relatives are nautiloids, which live in our seas.
 
Ammonite Picture

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Archosaur: The ruling reptiles. This very diverse group all shared one feature a diapsid skull. The evolution of the Archosaurs would change life on land for more than 200 million years, as this is the group which gave rise to the dinosaurs, the flying pterosaurs, the crocodiles and the birds. The group is characterised by flattened rather than rounded teeth, and an additional knob like muscle attachment on the femur, the feet had also been improved with a more flexible ankle joint.

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Bed: In geology the term bed refers to a individual layer of the rock, which is distinguishable from the beds above and below it.

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Biostratigraphy:The differentiation of rock units by means of the fossils they contain.

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Calcareous: Containing calcium carbonate

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Catastrophism:A hypothesis that preferred recurrent, violent, worldwide events as the reason for the sudden disappearance of some species and the abrupt rise of new ones.

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Clastic:Pertaining to the fragments (clasts) of which a clastic rock is composed. The clasts are derived from a parent rock and are then deposited by mechanical transport e.g. sandstone, shale, conglomerate.

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Conodonts: Conodont fossils are small and tooth like, found mainly in rocks of 570-245 million years old. In some places they are so abundant that they are used for dating rocks. The 'conodont animal is a 40mm long worm shaped animal with the teeth shaped structures in the head region.

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Cynodonts: The most successful group of therapsid reptiles, and were also known as the dog teeth.  They were not only the longest lived but also they are the direct ancestors of today's most successful group the mammals (so in effect our direct ancestors. They are found from the Late Permian to about the middle Jurassic.  Thrinaxodonis an example of a cynodont.

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Desiccation crack:A crack in fine sediment produced by water loss or drying.

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Diapsid: Arose in the Late Carboniferous period and become the dominant fauna in the Jurassic and Cretaceous periods. characterised by in addition to the temporal fenestra, they also showed an anorbital fenestra.  The function of the fenestra is unknown but obviously the removal of bone from the skull would have lightened it. The openings would also have provided areas for muscle attachment providing their owners with jaws that could open wider and close with more force.

The diapsids are not only an ancient group, dying out with the dinosaurs, they are important in evolutionary terms as most modern reptiles ( lizards, snakes, and modern crocodiles) also belong to the diapsid group.
 
The Skull of Herrerasaurus. 
 
 
 
 

 


 

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Ecosystem:  a community of plants and/ or animals interacting, and interdependent with each other and the physical environment in which they live.

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Ectothermic: Organisms which receive their heat energy from outside their bodies, i.e. form the sun. Modern examples include Lizards, Snakes (reptiles).

Endothermy: Organisms which generate their own body heat from internal metabolic reactions, rather than receiving it from an external source (see Ectothermic). Feature shown by all mammals (warm blooded).

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Euryapsid: a group which has one upper temporal fenestra, similar to that in modern reptiles. This group seems to have evolved from the diapsid ancestors.  The group contains the extinct marine reptiles the ichthyosaurs and the placodonts, as well as the nothosaurs and plesiosaurs.

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Eustatic:Pertaining to worldwide changes in sea level, as distinct from local changes.

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Fossils:Ancient or extinct, prehistoric remains that were buried by natural processes and subsequently permanently preserved.

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Geological time scale:an arbitrary chronological arrangement of geological events, such as mountain-building activity, usually presented in a chart like from with the oldest event and time unit at the bottom and the youngest at the top.

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Georges Cuvier:a French biologist, supported the doctrine, explaining most extinctions and landscape changes as consequences of the biblical deluge.

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Gradualism:A theory through which earth processes including evolution take place gradually and at a steady rate with no need for any catastrophic influences. This theory stated that mass extinctions were actually evolutionary advances and replacements, this has now been replaced by the punctuated equilibrium model (of Gould and Eldridge) where a steady state is the norm.

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Halite Pseudomorph:A mineral takes the outer form of cubic halite crystals.This may occur in different ways:

a) by replacement

b) the halite may be dissolved, leaving a cavity in which the new mineralis deposited (infiltration)
c) a coating of the new mineral may be deposited on the halite.

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Hypersaline: water with a high concentration of dissolved mineral salts present, can be found in places such as sabkhas, playas etc in arid environments.

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Inertial Homeothermy: A mechanism proposed as to how cold blooded animals could maintain a constant body temperature. When an animal becomes larger its, surface area to body ratio becomes smaller.  This means it will have less surface area from which to lose heat, i.e. can maintain a constant body temperature without having to generate heat internally, as it will not cool down much at night. This is one theory why dinosaurs became so big.

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Lithology:The description of the characteristics of rocks, as seen in hand-specimens and outcrops on the basis of colour, grain size and the composition.

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Lystrosaurus: Could well be described as a reptilian hippo, thought to wallow in the shallows and feed on weeds growing by the sides of it's watering holes. Though new work seems to show that it fed on more resistant vegetation, and was able to burrow. Both habits would be consistent with an animal adapting to a new more arid environment, which is something which Lystrosaurus did to great effect in the early Triassic.  Lystrosaurus averaged about 1m in length. (Palmer 1999)

Lystrosaurus

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Mammal Like Reptiles: The mammal like reptiles appeared in the Late Carboniferous period, they were well adapted land animals. It is believed that some could regulate their body temperature by means of a sail on their backs (a feature which became common in the Permian). In the Permian period the mammal like reptiles reached their peak (they are also known as therapsids) and were the dominant group until their decline in the Mid to Late Triassic, but not before they gave rise to the first mammal.
 
Thrinaxodon an advanced mammal like reptile. It walked with it's legs beneath it's body, which allowed it to become a fast moving predator. It's teeth and jaws were powerful.  It is thought that the rib cage was closed by a muscle diaphragm which allowed the lungs to expand and contract for efficient breathing. We have however no way of telling if fur was present .

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Marl:Friable mixture of subequal amounts of micrite and clay minerals

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Norian: A subdivision of the Triassic Period, see timeline

Palaeozioic:  An era extending from about 590 to 250 million years ago, see geological timescale

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Pyroclastic Flows:   flows of superheated volcanic ash, debris, and gas. Flow is controlled by gravity and are generally topographically confined to valleys, though there are documented exceptions to this, when flows have 'swapped' valleys.

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Regression:The retreat of sea from land areas.

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Rhynchosaurs: A Heavy barrel shaped group of reptiles which thrived throughout the Middle to Late Triassic, were part of the early ruling reptile (archosaur) group. They probably arose from early diapsids in the Late Permian, and share some primitive thecodontian features.  The earliest rhynchosaurs are small lizard like animals from the Lystrosaurus zone (see ecology of Triassic). The most ecologically important animals in this group arose in the Mid Triassic where they can be classed as medium to large herbivores.  These animals had triangular shaped skulls with bony "tusks".  Due to their size and weight they are not thought to have been able to eat material higher up than one meter above the ground, this may have contributed to their extinction in the Middle Norian, as seed ferns were beginning to be replaced by conifers.

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Sir Charles Lyell: British geologist who was mainly responsible for the acceptance that rocks etc are formed by slow processes such as heat and erosion. This theory was popularised in his publications The Principles Of Geology. This work had a great influence on Charles Darwin and in turn, Lyell became one of the earliest supporters of Darwin’s theory of evolution by natural selection.

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Strata: the rocks belonging to a particular bedding sequence or outcrop which contains something of interest for example fossils, or radioactive isotopes.

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Stratigraphy:The branch of geology concerned with all characteristics and attributes of rocks as they are in strata, and the interpretation of strata in terms of derivation and geological background.

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Synapsid: The group synapsid contains all the animals that have ever had the synapsid skull, this includes the therapsids ( the reptilian ancestors of mammals) and the mammals ( see mammal like reptiles). The group was common in the Permian period, but massively hit by the end Permian mass extinction, after an initial resurgence in the Early Triassic, they were replaced by Diapsids. Synapsids are characterised by having only one opening in the Skull called the Temporal fenestra.
 
synap.jpg (29450 bytes)
CLICK THE PICTURE FOR AN ENLARGED PICTURE

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Thecodonts: Small agile reptiles with long tails and short forelimbs, many were bipedal (they walked on two legs). This allowed the forelimbs to be freed for other tasks, such as catching prey or becoming modified for flight.  One of the most distinguishing features about the group was that they had their teeth set in sockets. The thecodonts are thought to be the group which gave rise to the dinosaurs, flying reptiles (pterosaurs), armored carnivores and crocodile like aquatic reptiles (phytosaurs)

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Transgression:The incursion of the sea over land areas, or a change that converts initially shallow-water conditions to deep-water conditions.

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Variscan orogeny:The Upper Palaeozoic orogenic period of central Europe during the Carboniferous and Permian periods. (also referred to as the Hercynian orogeny)

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