Palaeobiology (Lectures 25-35) Flashcards
What are the three types of fossils?
Body fossils
Trace fossils
Chemical fossils
What are body fossils?
How are they represented?
Morphologically intact remains of once-living organisms
Represented primarily by biomineralized hard parts
Give examples of biominerals
Calcium phosphate
Calcium carbonate
Silica
What do trace fossils show?
Record behaviour of once-living organisms
What are considered trace fossils?
Tracks of an animal Hard-substrate bioerosion Plant generated disturbance Fossilized faecal pellets (coprolites) Soft-sediment burrows
What are chemical fossils?
What can be chemical fossils?
Any geochemical signatures
Fossil DNA/lipid biomarker molecules/stable isotope fractionation
What can chemical disequilibrium imply with respect to chemical fossils?
Presence of underlying biological processes
What is biostratigraphy?
A relative time scale based on appearance/disappearance of fossil forms
Outline the two types of the biomineral calcium carbonate
Trigonal and thermodynamically stable calcite
Orthorhombic and unstable aragonite
Biomineral calcium phosphate often seen as?
Compare it to calcite
Hydroxyapatite: a constituent of vertebrate bones and teeth
Harder than calcite
Dissolves less at lower pH than calcite
Where is the biomineral silicon dioxide found?
What is a main property?
The hard part in sponges, radiolarians and diatoms, and many land plants
Susceptible to dissolution/alteration
Where is the biomineral magnetite found?
In the teeth of certain molluscs
In magnetotactic bacteria to keep positioned
What is accretionary skeletal construction?
Examples
Continual addition of new material on one or more localized growth fronts
Examples: bivalves, brachiopods and trees
What opportunities are presented by examining an accretionary skeleton?
Tracking climate and environment through time
What is addition skeletal construction?
Add more bits to the skeletons as organisms grow
How do echinoderms construct their skeleton?
Combine addition of new ossicles with the accretion of old ones
What is moulting/ecdysis skeletal construction?
Examples
Secrete a jointed exoskeleton that is cast off and replaced during development
Examples: trilobites, insects, crustaceans
What is remodelling skeletal construction?
Vertebrate bone is a living cellular tissue
It can remodel during growth and can destroy evidence of pre-existing states
What is agglutination skeletal construction?
Collect sedimentary grains and glue them together
Starting from the oldest, what is the order of the periods that should be learned?
Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene Quaternary
What are the eras that need to be learnt, starting from the oldest?
Paleozoic
Mesozoic
Cenozoic
What are the four eons, starting from the oldest?
Hadean
Archean
Proterozoic
Phanerozoic
Standard taxon ranks
Domain Kingdom Phylum Class Order Family Genus species
What are the three great Domains?
Bacteria
Archaea
Eukaryota
How do prokaryotes rapidly evolve?
Horizontal gene transfer
How are eukaryotic cells different to prokaryotic cells?
Central nucleus
Intracellular organelles: mitachondria, chloroplasts
Dynamic cytoskeleton
Name the three kingdoms of macroscopic eukaryotes
Animals - Metazoa
Plants - Embryophyta
Fungi - Fungi
What do nested evolutionary groups share?
A last common ancestor (LCA)
What is a crown group?
A modern phylum including the LCA of the phylum and all the descendants
What is a stem-group?
Extinct intermediate forms that lead back to a deeper LCA shared with the most closely related phylum
How are birds and crocodiles related to LCA and stem-group?
Birds are crocodiles closest living relative
Both part of Archosauria
Dinosaurs are stem-group birds
Define taphonomy
What is it often divided into?
The study of what happens to mortal remains, from the point of death through to fossil signal recovery
Biostratinomy and diagenesis
Define biostratinomy
The processes acting on a carcass from death through to final burial
Such as decay, transport, disarticulation, erosion etc
Define diagenesis
What does it do?
Processes after final burial (mostly geochemical)
Converts biological remains into fossils
Which two factors are fundamental to how a carcass will pass through the biostratinomic phase?
Skeletal type
Biomineralization
Define palaeoecology
Where and how the original organism made a living
Define bioerosion
Breakage, boring and erosion of substrate via biological agents
What is the region where fossilisation cannot take place?
Taphonomically active zone
What is the best way to minimise the effects of bioerosion on a fossil?
Rapid and final burial
Which minerals are prone to early dissolution during diagenesis?
Aragonite
Opaline silica
Under the right conditions, how can metastable mineral fossils be preserved?
Altered to a more stable phase through: recrystallisation, mineral replacement, or complete dissolution producing moulds/casts
What is one of the most common diagenetic pathways that can lead to the exceptional preservation of soft parts?
Permineralisation
Infilling of internal spaces with secondary minerals prior to degradational collapse
What kind of environment would silica, carbonate and pyrite imply if a fossil was permineralised by them?
Silica: terrestrial hot springs or localised acid volcanism
Carbonate: seawater
Pyrite: localised anaerobic degradation by sulfate-reducing bacteria in a marine context
How can soft-bodied organisms fossilise by another means than mineralisation?
Conditions for this?
Carbonaceous compression fossils
Low/no oxygen, low pH, low T
Coalification conditions
Coalification process
Coalification pathway
Ever wet, low pH, bog-like conditions
Plant material accumulates to form peat
With deep burial and diagenesis
Peat -> lignite -> bituminous coal -> anthracite -> graphite
Define ecology
The study of what organisms do - how they make a living and how they engage with their environment
What feedback effects can ecology have?
Biogeochemical cycles
Evolutionary process
Phylogenetic inference works on what assumption?
Closely related things are likely to have similar lifestyles
What is functional morphology based on?
Form relates to function
What is the difference between autotrophs and heterotrophs?
Autotrophs: organisms producing their own food
Heterotrophs: consume other organisms for a living
How can autotrophs be further distinguished?
Photoautotrophs: using sunlight as the energy source
Chemoautotrophs: using chemical energy
Define stenohaline
Intolerance of slight fluctuations from normal salinity
What is the opposite of stenohaline?
Euryhaline
What is the difference between benthic and pelagic?
Benthic = bottom-dwelling Pelagic = water-column-dwelling
How can benthic organisms be further distinguished?
Epifaunal (living above sediment-water interface) vs infaunal (living below sediment-water interface)
OR
Vagrant (capable of movement) vs sessile
What are the two basic habits of pelagic organisms?
Plankton - things that float
Nekton - things that swim
What are the three groups of unicellular phytoplankton responsible for half of Earth’s primary productivity?
Siliceous diatoms
Calcareous coccolithophores
Non-biomineralising dinoflagellates
Besides unicellular phytoplankton, which other marine organisms have a large effect on Earth’s primary productivity?
Heterotrophic zooplankton:
Calcareous planktic foraminifera
Siliceous radiolarians
Define ecosystem engineers
Organisms that contribute significantly to physical environments through their presence or their activities
Define bioturbation
The disturbance of sediment by living organisms
The majority of carbonate precipitation in the oceans is mediated by what?
Biomineralizing organisms
Mostly corals, forams and coccolithophores
Outline the higher-order taxonomy for modern corals
Domain Eukaryotes Kingdom Metazoa Phylum Cnidaria Class Anthozoa Order Scleractinia
Outline scleractinians
Strictly marine, benthic and epifaunal
All fundamentally predatory
Some corals are known for having what relationship?
Endosymbiotic association with photosynthesising dinoflagellates (called zooxanthellae)
What is the benefit of corals hosting zooxanthellae?
Thrive in low nutrient (oligotrophic) water
Photosynthetic activity enhances the capacity for biomineralisation
Zooxanthellate corals are responsible for 25% of what?
Global carbonate burial
What are the two extinct Palaeozoic groups of corals?
Rugosa
Tabulates
Why do scleractinian corals excel at forming reefs?
They can cement themselves to hard substrates
Zooxanthellate corals and calcifying red algae combine in certain conditions, and they add wave resistance
What can be the reasons for a failed reef?
What is the response to these events?
Excessive nutrient input
Disturbance to overheating, predation and disease
Coral bleaching (loss of zooxanthellae) followed by death
What are foraminiferas?
What do they contribute to?
What can they host, and what for?
Group of single-celled heterotrophic eukaryotes
Contribute to 25% of marine carbonate production
Many host photoendosymbionts that increase calcite biomineralisation
What are the three types of benthic forams?
What does the ratio of these types offer a rough measure of?
Hyaline, porcellaneous and agglutinating
Palaeoenvironment
When did benthic and planktic forams appear respectively?
Benthic: Cambrian
Planktic: Jurassic
How do coccolithophores contribute to total buried carbonate?
What are coccolithophores?
When did coccolithophores first appear?
Calcitic coccoliths constitute 25%
Photosynthetic, one of three principal groups of eukaryotic phytoplankton
Triassic
What are coccolithophores and planktic forams responsible for?
Formation of almost all off-shore and deep-sea calcareous ooze (precursor to chalk)
Why do planktic forams and coccolithophores preserve better than scleractinian corals?
Forams and coccolithophores biomineralise in calcite
Scleractinians are aragonitic (which is only metastable)
Why does calcite dissolve at depth?
Lower temperatures
Increased pressure
What is the Calcite Compensation Depth (CCD)?
The level at which oceanic calcite dissolves more rapidly than its delivery
What is the equation for calcite precipitation?
2 x CO2 + H2O + CaSiO3 -> CaCO3 + CO2 + H2O + SiO2
How are calcium and bicarbonate ions delivered to the oceans?
CO2 mediated weathering of CaSiO3 rocks
What is the lysocline?
The depth at which significant dissolution of CaCO3 begins
What are photosynthesising land plants responsible for?
Half of Earth’s primary productivity
Over 80% of standing biomass
What are embryophytes (land plants) characterised by?
A two-part life cycle: alternating between a haploid (one set of chromosomes) and diploid (two sets of chromosomes) phase
Differentiated tissues: including female and male reproductive organs
Female retention of a fertilised embryo during early development
Define angiosperms
Flowering plants
What have most embryophytes covered their diploid phase with?
Why?
What does this then require?
A waxy cuticle
To prevent water loss
Stomata for gas exchange for photosynthesis
Except for bryophytes, what do all embryophytes have, and what is it for?
What are vascular land plants known as?
A vascular system for water transport (xylem) and nutrients (phloem)
Tracheophytes
What is the xylem composed of?
How is water transported through the system?
Tracheids
Capillary action and stomatal transpiration
What are the two different ways of plant dispersal?
Diploid seeds
Haploid spores
What are the modern spore-bearing plants?
Bryophytes
Ferns, horsetails and lycopods
What is the advantage of a seed habit?
How does it work?
What are seed-bearing plants called?
No need for open water
Fertilisation is done within a growing pollen tube
Spermatophytes
What was the most successful way for plants to grow large and increase water transport capacity?
When did this first appear?
Production of secondary xylem (wood)
Early Devonian for wood, mid-late Devonian for large trees and forests
How do trees grow vertically and laterally?
Vertically: apical meristems
Laterally: lateral meristems
What effect did the rapid colonisation of land by plants have on the carbon cycle?
Increased chemical weathering of silicate rocks
Increased burial of terrestrially derived organic carbon
Generated massive amounts of oxygen
How do land plants affect the temperature of the Earth?
Absorb substantial sunlight
Lower planetary albedo (amount of light reflected back into space)
Colder climate without vegetation
How do land plants affect the hydrological cycle?
Vascular conduction and stomatal transpiration pumps major amounts of water into the atmosphere
A major decrease in precipitation without vegetation
Where and when were coal swamps?
What comprised coal swamps?
Late Carboniferous
Ever-wet, tropical and low-latitude setting
Giant horsetails, tree ferns and arborescent lycopods
How were Carboniferous coal swamps cyclical?
Fluctuated between terrestrial and shallow marine conditions
Driven by glacioeustatic sea-level changes
Define biostratigraphy
Correlation based on their fossil constituents
What is the principle of faunal succession?
Fossil biotas always occurred in the same sequence
In what two ways can geological time be measured?
Geochronology - days, years, millennia
Chronostratigraphy - the material accumulated during that time
What are the different units for geochronology and chronostratigraphy?
Geochronology: eon, era, period, epoch, age
Chronostratigraphy: eonothem, erathem, system, series, stage
What are the types of biozones in biostratigraphy?
Taxon range zone - the known stratigraphic and geographic range of occurrence of a taxon
Assemblage zone - taxon range zone equivalent for three or more forms
Interval biozone - the interval between the beginning of a lower biozone and the beginning of an upper one
Abundance/acme zone - marks a local abundance horizon
What are the requirements for an index fossil?
Morphologically distinctive
Easily preserved
Abundant
Facies independent (environmentally insensitive)
Geographically widespread
Short stratigraphic ranges (high evolution rate)
Why are cephalopod molluscs good index fossils for Palaeozoic through Mesozoic strata?
Goniatites: mid-Devonian - end Permian
Ceratites: Triassic
Ammonites: Mesozoic
Recognised by their suture pattern
What are belemnites?
When are they good index fossils for?
Internal calcitic guards of Mesozoic squid
Jurassic and Cretaceous
When are graptolites good index fossils for?
Early Palaeozoic up until mid-Devonian
What is one of the principle challenges in deriving a global biostratigraphy?
Bio-provinciality: the tendency of most organisms to live in more or less localised geographic areas
Give a modern example of how geographic isolation affects organism assemblage
Modern marsupials are mostly limited to Australia
They used to have a larger Gondwanan distribution
How can trilobites be used to show the effect of plate-tectonics on biogeographic partitioning?
Closing of the Iapetus Ocean in the early Palaeozoic
Endemic trilobites and graptolites of Laurentia and Avalonia became more similar
What are the simple premises that Darwinian natural selection is based on?
Superfecundity
Variation
Heritability
Time
Define superfecundity
How does it relate to natural selection?
All natural populations of organisms have the capacity to increase in number exponentially
Populations tend to remain the same size and resources tend to remain the same size too
More offspring are produced than can be supported so there is competition between individuals, there is a struggle for existence
How does variation relate to natural selection?
Wide range of variation in the biological attributes of individual organisms, some contribute to success or failure in the struggle for existence
Members of a population with successful attributes tend to reproduce more often and successfully than those without (differential reproductive success)
How does heritability relate to natural selection?
Much of the variation in populations is heritable and passed on to subsequent generations
Individuals that survive to reproductive age will pass on their characteristics
Descendant populations differ from ancestral ones
Heritable change accumulates through generations: ipso facto evolution
How does time relate to natural selection?
Long time for evolution to take place
Hence observed diversity and adaptations
What is selection a product of?
The ecological interplay between organism and environment
What is stabilising selection?
What pattern will be produced on an evolutionary time scale?
Surviving offspring emerging from the centre of the total distribution
Statis - extended intervals showing no evolutionary change
What is directional selection?
What pattern will be produced on an evolutionary time scale?
Surviving offspring emerging from one side of the distribution
Anagenesis - unidirectional, gradual change in form but no increase in diversity
What is disruptive selection?
What pattern will be produced on an evolutionary time scale?
Surviving offspring emerging from the extremes of the distribution
Cladogenesis - separation of a single lineage into two, leading to an increase in total diversity
What are the two ways cladogenesis can occur?
Which is more common?
Sympatric speciation - behavioural differentiation within a common geographic range
Allopatric speciation - imposed externally through physical partitioning of the original population
Allopatric is more common
What is peripatric speciation?
When allopatric speciation occurs in small peripheral populations around the main geographic range
What does the fossil record fail to document regarding evolution?
Phyletic gradualism - slow incremental change through time
If phyletic gradualism is not seen in the fossil record, what is?
Punctuated equilibrium - a pattern of one discrete species for a long time followed by the abrupt appearance of a closely related species, and no intermediate form
What does the presence of punctuated equilibrium suggest regarding how evolution takes place?
Long term stasis with little/no continuous evolutionary change
Evolution is related to speciation events
How would evolution only taking place by speciation events explain the lack of intermediate forms in the fossil record?
Relatively rapid change in small peripheral populations - too small and too fast to be captured by the fossil record
Major evolutionary transitions are often associated with what?
Give an example
Adaptive radiations - rapid evolutionary diversification events occurring within a single lineage (not always an immediate response)
Cambrian explosion
What is the main difficulty in reconstructing phylogenies (evolutionary relationships) from fossil data?
Distinguishing characters that are similar due to shared ancestry from those that are similar due to shared function or habit
If two characters are similar due to shared ancestry, they are said to be what?
How do homologous features come about?
Homologous
Divergent evolution from a last common ancestor
How do analogous features come about?
A product of shared habits or convergent evolution
Which transition were lobe-finned fishes preadapted for?
Fish-tetrapod transition in the late Devonian
What evolution in derived tetrapods allowed their land invasion to be independent of water availability?
Amniotic egg
What are the two lineages of the amniotes?
Reptiles/sauropsids
Synapsids (leading to mammals)
When did synapsids first appear, and then dominate?
Late Carboniferous
Permian
When did mammals come about?
Mesozoic
What are the two definitions of macroevolution?
Recognition of long term patterns
Non-Lyellian view: some things seen in the fossil record are distinct from day-to-day uniformitarian processes added up over time
How is a mass extinction defined?
A geographically widespread event that leads to a loss of at least 75% of initial diversity?
When did the 5 major mass extinctions take place in the Phanerozoic?
End-Ordovician Late Devonian End Permian End Triassic End Cretaceous
How can the triggers of a mass extinction be found?
How can the kill mechanism be found?
Sedimentological and geochemical evidence
Comparing the ecological habits of the victims with those of the survivors
When was the end Ordovician mass extinction?
What caused it?
Which organisms were hit hard?
444 Ma
Major glaciation event on Gondwana lowered sea levels and reduced shallow-shelf habit, worsened by global cooling and marine eutrophication
Trilobites, graptolites and brachiopods
When was the late-Devonian mass extinction?
How does it differ to others?
Which organisms were hit hard?
What may have caused it?
360 Ma
More drawn out and limited to marine organisms
Reef-builders, trilobites and brachiopods
Embryophytes massively fertilised downstream oceans resulting in algae-choked ‘dead zones’ in coastal seas
Intervals of marine anoxia in the late-Devonian
When was the end Permian mass extinction?
What was lost?
What was the trigger?
Which organisms were hit hard?
251.9 Ma, end of the Palaeozoic era
Over 90% of marine species, and some terrestrial
Siberian traps (4M km^3 of extruded basalt) a large igneous province dated to the same time
Passed through petroleum-bearing strata and sedimentary sulfates so released volatiles into the air
Estimated 30,000 GT of CO2
Global warming, acid rain, ocean fertilisation, ocean acidification
Brachiopods, bryozoans, crinoids and forams, 70% of terrestrial vertebrates went extinct
When was the end-Triassic extinction?
What was the trigger?
201 Ma
Exceptionally large LIP: Central Atlantic Magmatic Province (CAMP) when Pangaea broke up generated 3M km^3 of extrusive rock
When was the end-Cretaceous mass extinction?
What was the trigger?
What coincides with the trigger?
What is the theory behind the two events?
66 Ma
150km diameter meteorite Chicxulub crater in Yucatan peninsula of Mexico
Deccan Traps in India: 1M km^3 basalt
The incident in Mexico may have triggered the flood basalts in India
The nature and extent of the Chicxulub impact has come from the identification of what?
Globally distributed iridium layer at the Cretaceous-Paleogene boundary
Locally distributed shocked quartz and impact spherules
Which organisms were hit hard in the end-Cretaceous mass extinction?
Pelagic organisms: coccolithophores and planktic forams
Cephalopods and marine reptiles
Large animals: only crocodiles and turtles were the ones above 25kg known to have survived
Non-avian dinosaurs wiped out
What happened after the end-Cretaceous mass extinction?
A significant gap in the surviving ecosystems
Mammals rapidly radiated
What are stromatolites?
Lithified sedimentary structures
Trace fossils of microbes forming mat-like populations
What behaviour do stromatolites document?
Trap, bind and influence sediment accumulation in a cyclical accretionary fashion
Most Proterozoic stromatolites are thought to have been built by what?
What do they perform?
Cyanobacteria
Oxygenic photosynthesis
What is the oxygenic photosynthesis reaction?
What is the inverse called?
What does it do?
6 CO2 + 6 H2O <=> C6H12O6 + 6 O2
Aerobic heterotrophy
Uses oxygen to consume biomass
What is the process of anoxygenic photosynthesis?
What is the inverse process?
What does the inverse?
H2S can then react with what and form what?
CO2 + H2S <=> CH2O (sugars) + SO4(2-)
Anaerobic heterotrophy
Sulphate reducing bacteria
Iron to form pyrite
What is the process of fermentation?
What is it also called?
What performs it?
C6H12O6 -> 3 CO2 + 3 CH4
Methanogenesis
Methanogenic archaea
Metabolic pathways by bacteria are accompanied by what?
Kinetic isotope effects
What is used as a kinetic isotope effect for photosynthesis?
The enzyme responsible for C fixation is RuBisCO
Isotopic fractionation of 25‰ between C-12 and C-13
What is the oldest well preserved sedimentary rocks on Earth?
What is shown here that proves life existed then?
In the early Archaean (3.5 Ga) Warrawoona Supergroup in Western Australia
Clear RuBisCO isotopic fractionation between carbonate and organic-carbon constituents
How can sulfur metabolisms be tracked by isotopic fractionation?
Stable isotopes of S-32 and S-34
Show activities of anoxic sulfate-reducing bacteria
When is it estimated that oxygenic photosynthesis first evolved?
How was this discovered?
What is this event called?
2.4 Ga
Mass Independent Fractionation of Sulfur (MIF-S) that only occurs in the absence of the ozone disappears at this time
Great Oxidation Event (GOE)
What does the GOE coincide with?
First widespread glaciation
First appearance of sedimentary red beds
Enormous deposits of banded iron formation
Major fluctuations in δC-13 signatures
