Give an account of the taphonomy of an organism. What factors contribute to its preservation?
1. Biostratinomy - before final burial
* Organism dies
* Before burial, soft parts decompose (bacteria). Hard parts abraded/bioeroded
* Preservation: fast burial under sediment, escape TAZ
* More likely in sea (net accumulation of sed) benthic (less travel before burial)
* Sedimentary reworking - return to TAZ
* Too deep, caco3 dissolves (CCD)
* Exceptional preservation: fast anoxic, eg storm, peat bog
2. Diagenesis - after final burial
* Hard parts lithified with sed
* Aragonite not stable, recrystallise to calcite, replaced by pyrite, lost giving mould/cast
* Soft parts: permineralisation (minerals grow in structure before destruction)
* Coal/oil/gas: chemical fossils
What makes a good index fossil?
- Morphologically distinctive
- Easily preserved
- Abundant
- Geographically widespread
- Facies independent
- Short stratigraphic range
- Pelagic - less tied to local env
- Microfossil - small size less vulnerable, superabundant
What are the three types of fossil, and what do they show?
- Body fossils - intact remains of living organisms
- Trace fossils - records of organism behaviour
- Chemical fossils - geochemical signatures
What are five ways in which the ecological habit of an extinct organism is determined?
- Phylogenetic inference: similar organisms have similar lifestyles
- Functional morphology: form is related to function
- Recurrent fossil associations: reveals behaviour such as symbiosis/parasitism
- Trace fossils: provide a direct record of ancient behaviour
- Geochemical signatures: evidence of metabolic activity
Corals
* Taxonomy
* Location
* Mode of life
* Groups
* Fossil record
- Cnidaria
- Marine, warm shallow seas
- Sessile epifaunal benthic
- Suspension feeders
- Symbiosis with zooxanthellae
- Aragonitic (Triassic-now), calcitic (Ord-Perm)
- Morphological groups: rugose, tabulate, scleractinian
- Range: Ord-Perm (rugose and tabulate), Triassic-now (scleractinian)
Foraminifera
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
What is special about coccolithophores relative to other plankton?
They photosynthesise
What was the effect of the appearance of marine carbonate producers?
Created a major long-term carbon sink in sediment on the ocean floor
Nautiloids
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Cephalopod molluscs
* Shell had chambers separated by septa, meet shell at straight/weakly curved suture
* Chambers joined by siphuncle through centre of septa
* Marine, nektonic
* Buoyancy control by adjusting liquid/gas content of chamber
* Jet propelled, carnivorous
* Aragonitic shells (unstable, erode)
* Straight or coiled
* Range: Ord-Perm (straight), Ord-now (coiled)
Ammonoids
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Cephalopod molluscs
* Siphuncle joins chambers at the edge of each septum
* Sutures have different patterns depending on type
* Marine, nektonic
* Liquid/gas content buoyancy control
* Jet propelled
* Carnivorous
* Aragonitic
* Range: Dev-Perm (goniatite), Triassic (ceratite), Jur-Cret (ammonite)
Belemnites
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Coleoid cephalopods
* Bullet-shaped cylinder
* Posterior pointed, anterior has cavity
* Radially oriented needles of calcite
* Skeleton of a squid
* Marine, nektonic
* Jet propelled, carnivorous
* Range: very common Jur-Cret, present since Carb
Trilobites
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Arthropoda
* Segmented body: head, thorax and tail
* Marine, vagrant, epifaunal/semi-infaunal
* Tracks can be trace fossils
* Deposit (eat decomposing stuff) feeders or scavengers
* Moults
* Calcitic
* Range: very common Camb-Sil, gone by Perm
Graptolites
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
- Stick-like or branch, sometimes sawtooth
- Marine, pelagic, dendroids benthic
- Suspension feeders
- Organic skeleton, preserved as films
- Range: common Ord-Sil, present Camb-Carb
Bivalves
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Molluscs
* Two hinged valves (L and R)
* Sometimes symmetric about shell join
* Usually marine, benthic
* Can be epi/infaunal, sessile/vagrant
* Suspension feeders
* Calcitic/aragonitic
* Range: present since Ord, increasing since Triassic
Brachiopods
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Brachiopods
* Two shells (dorsal and ventral)
* Symmetrical about shell mid-line
* Marine
* Benthic, epifaunal, sessile
* Calcitic
* Range: very common Ord-Perm, common Triassic-Cret
Give an account of pre-Cambrian life, and evidence for it
What is the composition of hard parts?
- Biominerals
- Calcite (stable), aragonite (unstable)
- SiO2 (unstable)
- Calcium phosphate (stable)
- Magnetite (rare)
What are the five types of skeletal construction?
- Addition: adding bits on
- Accretion: adding to localised growth fronts
- Moulting: shedding and replacing
- Remodelling: vertebrate bone is living tissue
- Agglutination: gluing sediment together
Gastropods
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Molluscs
* Coiled shell, may be planispiral
* Marine/non-marine/land
* Benthic, vagrant, epifaunal
* Carnivorous or deposit feeders
* Aragonitic
* Range: common Carb-Perm, increasingly common since Jur
Echinoids
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
Echinoderms
* Pentaradial symmetry
* Calcitic tests made of plates with external spines
* Marine, benthic, vagrant, epifaunal (irregular are infaunal)
* Varied feeding
* Range: very common since Jur
Crinoids
* Taxonomy
* Location
* Mode of life
* Groups, if any
* Fossil record
- Cylindrical stem
Terms
* Epifaunal/infaunal
* Sessile/vagrant
* Benthic/planktic/nektonic
- Epifaunal live on sediment surface, infaunal bury into sediment
- Sessile are fixed, vagrant can move around
- Benthic live on the sea floor, planktic float around the water column, nektonic are larger and can propel themselves
Labelled diagram of bivalve outer surface
Labelled diagram of bivalve inner surface
