Palaeontology Flashcards
The fossil record:
FIRST EVIDENCE OF ORGANIC LIFE
- 1 GA
- Zircon crystals with with high 12C ratio in carbon class
- Jack Hills, Australia
- life prefers lighter C - 7 GA
- BIFS
- Isua, Greenland
- require oxygen, produced in photosynthesis
Stromatolites
- rock like structures formed by bacteria
The fossil record:
BODY FOSSILS
- 43 GA
- Strelley Pool Chert
- Australia
- contains ‘petrified’ sulphur-reducing bacteria
The fossil record:
EUKARYOTES
1600 MA
Small carbonaceous fossils with a distinct morphology
The fossil record:
FIRST SEXUALLY PRODUCING ORGANISM
1050 MA
- Bangiomorpha Pubescens
- Arctic Canada
The fossil record:
FIRST BIOMARKERS
750 MA
24-isopropylcholestone
- produced by sponges
- ALSO produced by seaweed; weakens claim as a biomarker
The fossil record:
FIRST ANIMALS
555 MA
Sponges
- Australia and Russia
- macroscopic scale (cm) mouldic preservations
TRANSFORMED THE OCEANS BY FILTERING OUT AND ALLOWING BIODIVERSITY
The fossil record:
FIRST SKELETONS
545 MA
Small Shelly Fossils (SSFs) called Cloudina
The fossil record:
FIRST FORESTS
400 MA
Devonian trees
Unusual preservation methods and examples
Amber preservation
- insects
- 140 Ma to recent
- tree resin
Ice preservation
- mammoths
- 10Ka
- oldest ice 1.2 Ma
Why is the fossil record biased?
DECAY
SCARCITY
SEDIMENTATION
ECOLOGY
CHEMISTRY
DIAGENESIS
METAMORPHISM
OUTCROP
COLLECTION
Preservation potential; decay
Reduces available info e.g. colour/soft tissue
Preservation potential; scarcity
If more common, fossilisation more likely e.g. humans/ants, not pandas
Preservation potential; sedimentation
Land erosion dominated
Ocean sedimentation dominated = more appropriate for fossilisation
Preservation potential; ecology
High energy environments e.g. foreshore will destroy fossils
Low energy environments e.g. estuarine muds will encourage
Preservation potential; chemistry
Acidic/anoxic
Anoxic environments will preserve soft parts because there are no break-down organisms
Preservation potential; diagenesis
Two scenarios:
- Decreases preservation potential because mud is squeezed through the shell and dissolves/displaces the fossil
- Increases preservation potential because a mineral e.g. pyrite forms on the outside of the shell like a protective layer
Preservation potential; metamorphism
Unrecognisable
Preservation potential; outcrop
May/may not be visible
e.g. in Permean times there are few marine fossils, however there are also few marine rocks known
Preservation potential; collection
E.g. China only recently discovered feathered dinos
Darwin’s theory of evolution
Natural selection
Opposed by CATASTROPHISM, Cumber 1976
Darwin’s obstacles
- Absence of intermediate forms
2. Cambrian explosion
Absence of intermediate forms
Primitive and complex organisms with no fossil link
Both alive at the same time = don’t evolved from one another
= 3rd unknown in the past which is ancestral to both
- more simple than either i.e. not an intermediate
- not hard/fast split, many dead ends along the way
The tree of life
Thins out very quickly
- not all fossils have direct ancestors that survive to this day
Further back in time = fewer fossils are members of current living taxa; more are extinct
“The tree of life is dominated by dead ends”
Possible reasons for the Cambrian Explosion
ENVIRONMENTAL CHANGE
- not possible
- looked at different locations around the world and found this was not the case
TAPHANOMIC EVENT
- = missing fossils due to preservation issues
- shell dissolution etc
- BUT this was because the only fossils available in Darwin’s time for SSFs
- NOW lots of other fossilisation modes available
- weakens argument as they show same Cambrian explosion
So now we believe it was ?due to a small atmospheric rise in oxygen
- Ediacaran atmosphere lacked O2 (sea floor sediment evidence)
- 15-40% of present level
N.B. ENOUGH FOR SPONGES…
Did life drive change? “POSITIVE FEEDBACK”
Sponges, once evolved, could pump and mix O2 to deeper waters
Small increase in O2 lead to the gradual emergence of predators = diversification for survival e.g. Cloudina grew hard, mineralised exoskeletons
Other types of fossilisation
Small carbonaceous fossils
Exceptional fossilisation
Burgess-Shale
Ediacara-type
Small carbonaceous fossils
NOT mineralised
Same taxa as SSFs
Simple in Ediacaran to diverse/complex in Cambrian
Exceptional fossilisation
Preserve cellular-level detail of microscopic fossils
Fossil Lagerstätten:
- Concentration (large no.s)
- Conservation (amazing detail)
e.g. phosphatisation
Burgess-Shale
Soft tissue present in a white clay mineral
Shallow marine organisms swept into deep sea settings by turbidity currents
Ediacaran = seaweed-grade organisms Cambrian = animals
Ediacara-type preservation
Microbial mats of blue-green algae (in O2-starved areas) overgrew soft-bodied organisms on a soft muddy seabed
Influx of sand then produced casts/moulds
e.g. Dickinsonia
N.B. Not photosynthetic organisms
- disappeared when sponges came in
- ?they cleaned the water of nutrients
Moving onto land:
PALAEOSOILS
2760MA
Rich in organic matter
Moving onto land:
Fossil evidence of life outside oceans
1060MA
Microfossils in Nonesuch Shale, N USA
Moving onto land:
INCREASE IN LAND WEATHERING
850MA
Evidence = change in carbon isotope signatures
Due to microbes
N.B. INDIRECT EVIDENCE
Moving onto land:
TRACE FOSSILS (AND MORE SOIL)
510MA
Climactichnites found in tidal/beach settings - refuge concept?
Also soils depleted in phosphorous due to the presence of fungus
Moving onto land:
FIRST DIRECT EVIDENCE OF LIFE ON LAND
460 MA
Trilete spores with trilete mark retained
- suggests hardened in terrestrial environment to protect from desiccation
- made of sporopollenin (tough biopolymer) = :) fossilisation
Moving onto land:
FIRST FOSSILS OF TERRESTRIAL ORGANISMS
444MA
Tortotubus = underground fungus network - infiltrated regolith - increase soil stability - increase bedrock weathering N.B. Since funghi decompose things, there must have been something for them to decompose?
Moving onto land:
FIRST LAND PLANTS
432 MA
Cooksonia
= a TRACHEOPHYTE
- vascular tissue = transports water through stems
- impermeable cuticle layer which closes during desiccation and stomata allow CO2 in/out
- tough vessels (water pressure) = can grow upwards
Moving onto land:
TRACE FOSSILS OF LAND DWELLING ORGANISMS
428MA
Pneumodesmus = terrestrial millipedes
Challenges getting onto land
Osmosis/gas exchange
- most marine organisms in osmosis with nutrients in sea water
Pressure difference
Desiccation
Gravity/movement
UV radiation
- at depth = shielded
Reproduction
- many expelled into the water
Food
N.B. Could have provided a refuge away from predators e.g. Crabs lay eggs on the beach in moonlight
How did afforestation/land plants change the atmosphere?
- Caused in increase in O2 due to oxygenic photosynthesis
- = reached 13% of atmosphere = FIRE Wildfire = charcoal plants
(By Devonian land plants were firmly established and in the early Silurian effects were detected in sedimentary systems)
- more clay/soil production
- less runoff
- less sediment erodibility
- less feldspar abundance in sedimentary deposits (converted to quartz/clay in weathering)
- braided rivers with unconsolidated banks»_space;> meandering rivers with lateral accretion sets and root traces in bank deposits
- more stable groundwater sources = trunks reinforced by sturdy lignin molecules
Devonian forests; impact
1st source of coal deposits
- lignin»_space;> kerogen/coal due to rapid burial in O2-poor sediments
- transferred carbon from the atmosphere to the stratigraphic record
N.B. WE ARE QUICKLY REVERSING THIS TRANSFER TODAY
Arctic Ocean Background
Linked to N Atlantic by Fram Strait - opened 17.5MA
49MA low sea levels cut off Arctic Ocean entirely
CO2 was high ~3500ppm
10-15 degreesC average annual temps at the poles
Warm/salt-free freshwater inputs (rain/melting winter snow)
= LOW DENSITY NEPHELOID LAYER
Effect of a nepheloid layer in the Arctic Ocean
Inhibits mixing as water is not dense enough to maintain convection
= stratified
- deep waters = cold, dense, saline and ANOXIC
“The Azolla event”
Azolla = freshwater fern
= ‘superplant’ with ASEXUAL REPRODUCTION
- “can double its biomass every 2-3 days in 20-hour warm days of Arctic summer”
Top layer of Arctic = freshwater and rich in nutrients due to continental weathering
= built up
Sank to anoxic deep water = didn’t decay
= sequestered 10,000 x more carbon than we have in our atmosphere today
= 3900-650ppm
CRETACEOUS GREENHOUSE WITH EXTENSIVE FLOODING OF CONTINENTAL SURFACES»_space;> PRESENT ICEHOUSE WORLD
Evidence of Azolla
Glacial dropstones after azolla event
8m thick organic-rich sediments
- laminations of 100% azolla
- grew in situ
Evolution of powered flight
Evolved 4 times (or 3 within vertebrates)
Insects - 396 MA
Pterodactyl - 250MA
Birds - 150MA
Bats - 50MA
Wings are homologous as appendages but not as wings
= convergently derived homoplasies
K-Pg mass extinction:
- incumbent species died creating gaps for birds
- adaptive radiation; origin of flight made new niches available and led to an immediate diversification of birds
Homoplasy =
Character shared by a set of species but not in their common ancestor i.e. originated independently
Archaetopteryx
Oldest bird 160MA
Intermediate between birds and dinosaurs - therapods
Types of dinosaur
SAUROPODS
- long tails/necks
- veggie
ORNITHISCIANS
e.g. stegosaurus/triceratops
THERAPODS
e.g. T-Rex/velociraptor
Evidence for birds evolving from dinosaurs
ANATOMY
RESPIRATORY SYSTEM PREFERENCES
GENETIC SEQUENCES
FEATHERS
Evidence for birds evolving from dinosaurs:
ANATOMY
Arm joints
- fold up into chest
Skulls
- large brain chamber and eye sockets
- for coordination and senses
Furcula
- “wishbone”
- strengthens ribcage
Tail
- birds have squashed vertebrae
- reduced therapy feature
Bones between ribs
- strengthen for e.g. water diving
- increases respiratory efficiency
Enlarged sternum
- greater respiratory capacity
Evidence for birds evolving from dinosaurs:
RESPIRATORY SYSTEM PNEUMATICS
Flexible bellow-like reservoirs = pump air through inflexible lungs
CAUDAL air sac = fresh air
CRANIAL air sac = stale air
= access to oxygen when breathing in AND out
= more efficient
Blood flow opposes air flow
As with some therapies, birds have hollow bones = more space for air
Evidence for birds evolving from dinosaurs:
GENETIC SEQUENCES
Protein collagen can preternaturally survive for at least 200 million years = original genetic sequencing reconstruction possible
Antibodies that bind to chicken collagen also respond to T-Rex collagen (although ?contamination issues)
Ornithischian protein sequences contain some crocodile characteristics and bird characteristics
Evidence for birds evolving from dinosaurs:
FEATHERS
Jurassic dinosaurs had small ‘bristle’ feathers for insulation/camouflage
e.g. Therapod: Sinosauropteryx
Ornithischian: Kulindadromeus
Found in amber fossils
EXAPTATION CONCEPT
Exaptation =
Process by which features acquire functions for which they were not originally adapted or selected
Original uses of wings
Ornithomimus - mating
- bright colours preserved by melanosomes e.g. Anchiornis
- Wing Assisted Incline Running, not flying
Oviraptor - keep eggs warm
Permo-triassic mass extinction
Largest of all time
17% marine orders extinct
52% marine families extinct
At least 75% of species extinct
- pre 45,000-240,000
- post 1800-9600
~251MA
Two pulses:
- Latest Permian 252.28+/- 0.08 Myr
- Earliest Triassic 252.10+/- 0.06 Myr
Who suffered in the Permo-Triassic extinction?
Corals (tabulate/rugose)
Trilobites
Brachiopods
Crinoids
Bryozoans
Insects
Tetrapods
Plants
Kill mechanisms in the Permo-Triassic extinction
High temperature
High CO2 levels
Anoxia
Extinction =
Process of becoming extinct; of a species/family/larger group to have no living members
Kill mechanisms; high temperature
Warm surface water inhibited circulation = deep waters nutrient rich
Evidence of continental weathering from High 87Strontium:86Strontium
Tropical rainfall and runoff killed plants
Nutrient rich runoff = eutrophication
Kill mechanisms; high CO2 (RAPID!)
Ocean acidification due to CO2 dissolution = carbonic acid
Hypercapnia (200ppm greater than ambient CO2 for several weeks) decreased growth/survival/reproduction
Those with ‘passive’ calcareous skeleton formation didn’t survive:
- 86% of genera with carbonate skeletons without physiological buffering went extinct
- 54% of those with potential physiological buffering
- 4.7% with little/no carbonate shell e.g. conodants/fish/polychaete worms
ALSO those with:
- low metabolic rate
- limited circulatory systems
- simple respiratory structures (CO2 inhibits the Bohr effect in ammonoids - 79% of these went extinct)
Kill mechanisms; anoxia (evidence and causes)
Evidence:
- demise of burrowing
- organic/pyrite-rich horizons at P/Tr boundary in rocks
Causes:
- decrease in the intake of O2 by the oceans
- high respiration rates using O2 by organisms/decay
Clathrates =
Methane hydrates
“Methane ice:
- narrow temperature/pressure stability fields
- small changes = major releases = high levels of LIGHT C I.E. 12C into the oceans
Causes of a high 12C:13C/extinction:
METHANOSARCINA
IMPACTOR
VOLCANISM
Causes of a high 12C:13C/extinction:
METHANOSARCINA
Bacterium which makes organic matter into methane
Then, higher temps = CO2
BUT
- molecular clocks not very accurate
- nickel-based bacterium; why so much Ni?
- scale difficult to constrain
Causes of a high 12C:13C/extinction:
IMPACTOR
Iridium-rich layer near P-Tr boundary Only major source is extra-terrestrial BUT - not significant amounts - 1m BELOW boundary layer - no evidence of a crater
6-15cm thick claystone breccias could have been ejected during the impact
BUT
- could just be reworked soils
Glassy spherules of ‘shocked’ quartz veins
BUT
- rarer/smaller than at K-Pg extinction
- could be mountain formation/volcano heat causing ash particles to melt
Causes of a high 12C:13C/extinction:
VOLCANISM
Siberian traps = large igneous province of 1-4 million km3 of lava
Enough for
- poisonous gas/acid rain/CO2 = mutant spores due to halogen gases attacking the ozone layer
- lava to melt permafrost and sublimate frozen clathrates
- lava to encounter coal deposits and start sooty fires
Evidence of high levels of mercury in shallow (associated with biomass/soil) AND DEEP waters = mercury poisoning
The Fossil Record: summary
4.1Ga/3.7Ga
Evidence of organic life
3.43Ga
Strelley
1600Ma
SCFs
1050Ma
Sexually reproducing
750Ma
Biomarkers
555Ma
Sponges
545Ma
SSFs
400Ma
Forests
Life on land: Summary
2760Ma
Palaeosoils
1060Ma
Nonesuch shales
850Ma
Weathering
510Ma
Soil and climactichnites
460Ma
Trilete
444Ma
Tortotubus
434Ma
Cooksonia
428Ma
Pneumodesmus
