Palaeontology and evolution


Classification of organisms

Linnaean system used 









Genera are capitalised, species is lowercase 

sp. is written for unknown species 

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Theories of evolution

Phyletic gradualism 

One species slowly changes into another by natural selection 

Punctuated equilibrium

A species remains in stasis, genetic pressure builds up within a population until every species thereafter has a morphological change 


Small scale over a small time period e.g. Micraster (sea urchin) 


Large scale over long time period e.g. Horse 

Was a small browser, became an ungulate so taller, larger teeth 

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Bias in the fossil record

Bias towards hard-bodied marine organisms that lived in a calm environment 

Marine vs terrestrial: Burial not quick enough on land, scavengers, erosion, fast decomposition

Soft vs hard bodied: Soft-bodied eaten by scavengers, decay too quick 

Large vs small size: Larger easier to find, less likely to be damaged 

Age: Younger less likley to be damaged 

Human bias: Easy to miss, only collected if recognised as a fossil, motivation of finder 

Life position - way a fossil would have orientated during life 

Life assemblage - was buried in life position 

Death assemblage - was during burial e.g. by current 

Derived fossil - Fossil in sedimentary rock younger than the original rock it was deposited in

Relic - fossil distorted due to movement e.g. folding 

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Environments and likelihood of preservation

Highland - Erosion is dominant so no fossils

Lowland - Still erosion but few fossils restricted to rivers, deltas, lakes etc. 

Shallow marine - Good chance but scavengers destroy remains before they're fossilised 

Deep sea - Floaters/swimmers, fine sediment (low energy), lack of scavengers and anoxia (fewer decomposers) means fossilisation is good 

Carbon and silica compensation depth 

Boundary below which they dissolve 

The CCD is higher but both vary globally due to temperature 

CCD: High temperature - lower CCD

SCD: High temperature - higher SCD 

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Taphonomy - The science of fossilisation 

Life assemblage -> necrolysis -> death assemblage -> biostratinomy -> initial fossil assemblage -> diagenesis -> final fossil assemblage 

Unaltered - Amber, tar, skeletal remains 

Carbonisation - Heated, volatiles lost, carbon left and creates a film 

Permineralisation - Percolation of groundwater, minerals deposited in pore spaces 

Recrystallisation - Crystals to become stable (increase in temp.) Aragonite replaces with calcite

Replacement - Molecule-by-molecule one mineral replaced with another via percolation; slower the process, the more detailed 

Moulds - External: impression organism made on bed; internal: shell is hollow and infilled

Casts: External mould is filled with sediment 

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Bivalve morphology and mode of life


Are equivalve, inequilateral 

Shells made of calcite or aragonite and can have ribs, spines, and growth lines

Umbo - rounded part of the bivalve

Pallial sinus - where foot used to be, if a burrower                                   

Adductor scar - where muscles used to be

Hinge - contain teeth and sockets 

Mode of life 

Epifaunal/cementers - rough outer shell to cope with high energy, entire pallial line 

Burrowers - smooth shell so streamlined - easier to find food, pallial sinus and siphons (larger sinus -> larger siphon needed)

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Brachiopod morphology and mode of life


Are inequivalve, equilateral and shells made of calcite 

Can be articulated or inarticulated (valves move by adductor and diductor muscles in former)

Pedicle valve - larger valve, contains foramen (where pedicle was attached) 

Brachial valve - smaller valve - ventral margin marks boundary between the two

Lophophores used to filter feed

No ligaments, teeth fit into sockets

Mode of life

Epifaunal - larger, rough shell (high energy) 

Infaunal - long foramen, more rectangular (streamlined) 

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Coral morphology and mode of life


Corallum - hard calcitic skeleton

Septae - vertical divisions 

Tabulae - horizontal divisions 

Rugae - large 3D ridges on coral 

Mode of life

Shallow marine:

Tropical - temperature >21C

Clear water in photic zone 

High enough energy for organic matter to wash in 

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Cephalopod morphology and mode of life


Septae - thin walls that separate the chambers 

Suture lines - show the intersection with the septae and outer shell

Whorl - one rotation of a shell

Protoconch - initial chamber where cephalopod grows from

Mode of life


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Cephalopod evolution

Cephalopod - nautiloid, goniatite, ceratite, ammonite 

Ammonoid - goniatite, ceratite, ammonite 

Nautiloid - Simple saddle, simple load 

Goniatite - Rounded saddle, angular lobes 

Ceratite - Rounded saddle, complex lobes

Ammonite - Complex saddle, complex lobes 

Enabled them to reach greater depths and get more food 


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Graptolite morphology and mode of life


Rhabdosome - whole structure made of scleroprotein 

Thecae - hold the soft bodied polyps zoozanthelae 

Thecae attached to stipes and stipes hold the central nervous system 

Mode of life

Nektonic - swimmers 

Made of protein therefore buoyant 

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Graptolite evolution

Dendroid - barely evolved 

Graptoloid - rapid evolution - loss of stipes, more complex thecae 

Dichograptus - 8 thecae 

Tetragraptus - 4 thecae 

Didymograptus - 2 thecae (pendant, horizontal, reclined, scandent) 

Climacograptus - 1 theca 

Monograptus - 1 theca 

Good zone fossils

Globally widespread - in shale, easy to identify, abudant, evolved rapdily 

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Trilobite morphology and mode of life


Cephalon, thorax, pygidium - head, body, tail

Genal spine - covers head 

Glabella - inbetween eyes, inflates with methane for movement 

Occipital ring - central lobe, bottom of cephalon 

Eyes - compound (contain calcite so double refraction) 

Mode of life

Infaunal - no eyes, streamlined

Benthic - large eyes, spines for defence 

Nektonic - spinose, buoyant, inflated glabella 

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Dinosaur morphology and mode of life



Mode of life 

Herbivores: Small heads, long necks, hollow bones, large torso, stout legs, quadrupedal 

Carnivores: Forward-facing eyes, large skulls, strong jaw and teeth, bipedal, sharp claws

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Dinosaur evolution

Archosaurs evolved into dinosaurs 

Dinosaurs split into Ornithschian (bird-hipped) and Saurischian (reptile-hipped) 

Ornithischians were herbivores 

Saurichia into sauropoda and theropods

Sauropods: herbivores with leaf-shaped crowns, stout legs, and long necks 

Theropods: Carnivores with a long tail to give a low centre of gravity, strong jaws, and 3-clawed toes to run fast 

Theropods evolved into Aves (birds) 

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Age ranges

Bivalves - E. Cambrian - Present 

Brachiopod - E.Cambrian - Present 

Nautilus - M.Ordovician - Present 

Goniatite - M. Devonian- P-T

Ceratite - M. Permian - L. Triassic 

Ammonite - L. Triassic - K-T

Rugose - M. Ordovician - PT

Tabulate - M.Ordovician - P-T 

Scleractinian - E. Triassic - Present 

Trlibotes - E. Cambrian - P-T

Dictyonema - L. Cambrian - E. Carboniferous 

Graptloids - Cambrian - Silurian 

Archosaurs - L. Permian/E.Triassic - present 

Dinosaurs - M-Triassic - K-T 

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