F3 Palaeontology

• Fossils are remains of once living organisms. They are greater than 10,000 years old and have undergone the process of fossilization.
• • Body fossils preserve elements of the body
  • Trace fossils keep physical evidence of the existence of organisms through their traces.
• Factors affecting preservation

  • Original fossil composition
  • Energy levels
  • Transport distance
  • Rapidity of burial
  • Amount of oxygen
  • Size of sediment
  • Diagenesis
  • Compaction
• • Petrification - mineral replacement occurs. Original material dissolved atom by atom and substituted by another mineral present in groundwater.
  • Calcification - a type of petrification. Aragonite turns to calcite (more stable). They are polymorphs.
  • Silicification - a type of petrification. Percolating groundwater rich in Si02 causes Sio2 to crystallise out of solution and Sio2 fills void or pores in fossil.
  • Pyritization - a type of petrification. Replacement by iron pyrite. Anaerobic environment. Sulphur bacteria reduces Sulphur to form bisulphate. Reacts with Fe to form iron pyrite.
• Carbonisation - During burial pressure is increased because of overlying pressure. Volatiles driven off and Carbon content relatively increased. Leaves a layer of carbon.
• Molds and casts- shell is dissolved. Void is left which is precise shape of original fossil. Minerals precipitate from pore water in the void.
• • Tracks - set of discrete footprints left behind by animals found on surface of bedding plains. Typically soft fine grained sediment.
  • Trails - continuous traces formed by a whole part/body.
  • Burrows - dwelling, moving, feeding. Soft sand or mud.
  • Coprolites - animal faeces. Need to be covered quickly to prevent breakup by currents or bacteria
• Why is the fossil record incomplete?

  • Transport distance
  • Dissolution
  • Weathering and erosion
  • Decay
  • Scavenging/predation
  • Metamorphism
  • Bias towards marine organisms
  • Destruction of oceanic crust by subduction
  • Sampling
  • Entirely soft bodied animals, rare animals, short stratigraphic ranges have a lower chance of preservation
• • Life is anything that is capable of replication and undergoes the process of Darwinian evolution
  • Dalmanites myops - binomial name
  • Genus, species
  • Taxonomy is the science of naming and describing organisms
• • Order of classification
  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• History of lineages as they change through time. Different species arise from previous forms via descent, and all organisms are connected by the passage of genes along the branches of the tree
• • Class - Trilobita.
  • Phylum - arthropoda.
  • Arthropods are invertebrates with a segmented body and a chitinous hard exoskeleton.
  • Trilobites are extinct. Marine arthropods.
  • Stratigraphic range - base of Cambrian to Permian
  • Geographically widespread, occurring in a variety of environments with a variety of life modes.
  • Closest living relative is thought to be a horseshoe crab.
• Trilobite morphology

  • Composition of skeleton - skeleton is made of chitin hardened by calcium salts. Exoskeleton cannot expand and therefore must have moulted - process known as ecdysis. For one trilobite - many fossilised moults as well as one entire body fossil preserved.
  • Body divisions - trilobite refers to the well defined LATERAL lobes. They also have a well-defined head shield (cephalon), main body segments (thorax) and tail shield (pygidium).
• • Trilobite morphologyCephalon structures - Glabella is the strongly convex area in the centre of the cephalon. The cheeks lie on either side of the glabella and sometimes in front of it as well. The compound eyes comprise many lenses, giving good vision. Not all trilobites had eyes. Genal spines are long spiney extensions of the genal angle found in many trilobites.
• Pelagic planktonic - floating in the water column

  • Eyes - None
  • Spines - None
  • Glabella - Normal
  • Thoracic segments - Few
  • Pleura - Normal
  • Axis - Normal
  • Shape - Normal
• Pelagic nektonic - swimming in the water column

  • Eyes - Facing down or forward on stalks
  • Spines - Large genal spines and head and tail spines present to spread weight in water.
  • Glabella - Inflated for buoyancy
  • Thoracic segments - many segments to articulate through water or sediment
  • Pleura - separated to allow water to flow through for swimming
  • Axis - Normal
  • Shape - streamline to glide through water.
• Benthonic epifaunal - walking on the seafloor

  • Eyes - Side of head to see around seafloor
  • Spines - Large genal spines and head and tail spines present to spread weight in water.
  • Glabella - Normal
  • Thoracic segments - many to contain legs for walking
  • Pleura - normal; not separated
  • Axis - Normal
  • Shape - Normal
• Benthonic infaunal - burrowing

  • Eyes - Projecting above head on stalks if present. Sometimes reduced or not present.
  • Spines - no spines, smooth
  • Glabella - normal
  • Thoracic segments - Many segments to allow to move through sediment
  • Pleura - Normal
  • Axis - wide containing muscles that allow the animal to move through sediment
  • Shape - streamline to glide through sediment
• Morphology

  Factors affecting morphology include

  • Environmental conditions
  • Mode of life
  • Competition
  • Prey-predator relationships
  • Genetics + time
• Issues with reconstructing the behaviour of trilobites:

  • No living forms so cannot be directly observed
  • Inferred from fossil record, preservation may be poor affecting interpretation
  • Often not presented in siteu.
• Brachiopods

  • Phylum - brachiopoda
  • Extant sessile marine animals. Defined by the presence of a lophophore (used to filter feed) and a pedicle.
  • Appeared in early Cambrian. Common in Paleozoic. Early cambrian - recent
  • They have a bilateral symmetry - plane of symmetry is parallel to the length. passes through the middle of both valves.
• Brachiopod morphology

  • The umbo are the points on both valves where the animal started its life
  • Growth lines represent each growth phase and run parallel to the outside of the shell
  • Ribs strengthen the shell and run perpendicular to the outside of the shell
  • The foramen is the opening for the pedicle
  • The hinge line is the point of contact between both valves
  • The pedicle is a fleshy stalk that allows attachment to rock
  • Adductor muscles close the shell. Diductor muscles open the shell.
• Bivalves

  • Phylum - mollusca
  • Class - bivalvia
  • Large class of extant molluscs that have a hard calcareous shell made of two parts called valves. The soft parts are inside the shell. Occur in a range of environments today though early forms were marine only.
  • Long lifespan - worlds oldest animal was a bivalve.
  • Cambrian - recent
• Mode of life

  Epifaunal - attached to seafloor

  Mytilus type

  • Streamlined, airtight shell to protect against waves.
  • Large adductor muscle to hold valves tightly together

  Oyster type

  • Cemented to rock
  • Strong thick shell to protect against high energy currents and atmosphere
  • One large muscle
  • Irregular surface like substrate

  Gryphea type

  • Large surface area in contact with substrate
  • Strong, thick, heavy shell to protect in high energy environments
• Mode of life

  Nektonic - swimming in the water column

  Scallop type

  • Ribs to divert water flow
  • Thick growth lines for strength
  • Large muscle scar
  • Ears to direct water flow
  • Thin shell - light
• Mode of life

  Infaunal - burrowing

  Cockle type

  • Small pallial sinus
  • Compact so small foot
  • Ribbed - survives in high energy intertidal zone. Suggests it is regularly uncovered
  • All these features suggest a shallow burrower

  Deep infaunal

  • Streamlined shell to glide through sediment
  • Large pallial sinus - houses the muscles that attach to the siphon
  • Large foot
  • Thin shell, no ribs
  • May have gape for foot and siphon
• Cephalopods (Ammonoids)

  • Class - cephalopoda
  • Extant class of marine molluscs characterised by a prominent head and a set arms or tentacles modified from a molluscan foot.
  • Most intelligent of the invertebrates containing a complex central nervous system
• Subclass Ammonoidea

  • Extinct group of cephalopods
  • Devonian - Cretaceous stratigraphic range
  • Marine and nektonic
  • Their buoyancy was maintained by gas chambers in the shell
  • Chambers divided by walls called septa which strengthened the shell against water pressure
  • Where the septa meets the outside of the shell is called the suture line
• Ammonoid evolution

  • Goniatites (Devonian-Permian) were the earliest of the ammonoids
  • Ceratites (Triassic) were the second
  • Ammonites (Jurassic - Cretaceous) were the last.
  • The suture lines became increasingly complex with the most simple ones being goniatitic and the most complex being ammonitic.
  • ALL ornamented ammonoids are ammonites.
• Ammonoids as zone fossils

  • Zone fossils are used for dating rock to high resolution
  • Useful characteristics include:
  • Short stratigraphic range
  • Geographically widespread (marine organisms usually are)
  • Occurs in a variety of rock types and lithologies (pelagic)
  • High preservation potential
  • Abundant
  • Easily identifiable
  • Ammonoids are useful as zone fossils due to this!
• Graptolites

  • Phylum: hemichordata
  • Class: graptolithina
  • Graptolites are an extinct group of marine invertebrates
  • Marine, colonial organisms made up of individual zooids which all inhabit the same exoskeleton
  • Late Cambrian - Carboniferous
  • Graptoloids - one or a few stipes and theca of a variety of types
• Graptoloid Morphology

  • Pendant - thecae point inward, stipe curves downwards
  • Horizontal - stipes in horizontal plane
  • Reclined - stipes curve upwards from the sicula. Thecae point outward
  • Scandent - describes straight stipes with thecae facing outward
• Coral

  • Class - Anthozoa
  • Extant group of marine invertebrates
  • Live in compact colonies or as solitary individuals
  • Important reef builders that live in tropical oceans
  • Associated with ecosystems of high biodiversity
  • Benthic epifaunal sessile in adult form, mobile in juvenile form
• • Tabulate - Ordovician-Permian
  • No dissepiments
  • Septa sometimes present but poor
  • Compound only
  • Corallite mm, forms a mass up to 2m
  • Mural pores. Walls between corallites are pierced by pores known as mural pores which allowed transfer of nutrients between polyps.
• • Rugose - Ordovician - Permian
  • Contain dissepiments
  • May contain columella
  • Compound or solitary
  • Corallite mm to >20cm
  • Bilateral symmetry
• • Sclerectinian - Triassic - Recent
  • Dissepiments (sometimes) & septa present
  • Made of aragonite
  • Radial symmetry
• Coral reefs as palaeoenvironmental indicators

  • High temperature (23-29 degrees C)
  • Shallow depth ( around 15m). Water depth is important as light is filtered out at depth
  • Marine environment with salinity of 30-40 parts per thousand
  • Oxygen levels - well oxygenated waters
  • Clear waters - sunlight for symbiotic algae to survive
  • High energy levels to incorporate more oxygen into the water and to circulate nutrients
  • Solitary coral do NOT require as specific environmental factors to survive so they are not useful palaeoenvironmental indicators.
• Plants

  • Kingdom - Plantae
  • Extant eukaryotes
  • Use photosynthesis to make their own food
  • Ordovician - recent
  • Excellent palaeoenvironmental indicators
• • Plants

  Usually preserved as compression fossils

  • Commonly preserved in mudstone, siltstone and fine grained sandstone
  • Plant fossils preserved by silicification may show excellent microscopic detail of tissues
• • Vascular plants appeared on land in the silurian
  • Seeds and large leaves developed in the late Devonian and Carboniferous
  • Flowering plants did not appear until the Cretaceous
  • Grass thought to appear around 55 Ma in the Eocene however recent evidence from dinosaur coprolites suggest grass appeared in the late Cretaceous