Palaeobiology Yr 2 Flashcards
What are some important points from Charles Darwin stated in the Origin of species:
(1809 - 1882)
- Heritable variation is generated by RANDOM processes (mutation and recombination) it is not direted
- variation therefore proceeds selection
- natural selection is non-random, it is the non random survival of random variants
- natural selection is not entirely predictable or deterministic
- changes aren’t inexorable (limited by physics, a cheetah can’t run 200mph)
Can natural selection be proven?
In the modern day, sickle cell anaemia
- blood cells are sickle shaped (1/3 carry gene in sub sahara)
- life expectancy for men:42 women: 48
- We are only evolving due to resistance to bugs, like prostitutes in Nairobi becoming HIV resistant
- Peppered moth
- Dog breeds
- Lab experiments on fruit flies
What is artificial selection?
Human induced selection process, Russian geneticist, Dimitry Belyaev, delibrelately bred silver foxes for their tamness
- 20yrs later they behaved like border collies
- They seeked company, had floppy ears, wagged their tail
- year round breeding
- However their fur changed to spotty/blotchy, this is a Pleiotropy
- there is more than one way of making a change/affecting attribute
What is sexual selection?
- Many features in nature are highly costly or deleterious to survival
- sexual selection is a specialized form of Natural selection, there are 2 types
- Intrasexual
- Intersexual
- This lead to evolution of behaviour and anatomical features
What is meant by Intrasexual selection?
male v.s male for the attention of the female (fight)
What is meant by intersexual selection?
males compete for the attention of the female
What is a species?
a species consists of all individuals that naturally breed together and produce viable offspring
- some birds may look identical but have a different song so can’t breed
Genotypes and Phenotypes:
Genotype: Genetic composition and Phenotype: External appearance
- but the relationship between DNA and morphology, ecology, physiology and behaviour complex
- Frogs have very similar morphologies, plancental mammals do not (phenotype)
- But genotypes don’t reflect this:
- DNA of two subspecies of clawed toad are greater than those between humans and New world monkeys
Microevolution:
Evolution at or below the species level
Macroevolution:
Evolution above the species level
- origins and fates of major novelties (limbs, wings)
- diversity patterns over long time scales
- impact of continental drift, climate and physical factors on evolution
What are the two types of speciation:
- Allopatric
- Sympatic
Allopatric speciation:
An original population are separated by a barrier, therefore, reproductive isolation (Ernst Mayr 1940).
- Symmetrical model (geographic barrier for B and C) = 2 new species
- Asymmetric model (isolation from A making B with no gene flow) = 1 new species
- Cichlids in lake victoria show both
- lake is 100,000yrs old
- endemic cichlids between 200-500 species (probs 450), all evolved in the last 100,000 yrs, (FOUNDER EFFECT: smaller group show rapid evolution)
- isolation by drying, fish choosing not to migrate, sexual (female may chose a coloured fin over another)
Sympatric speciation:
new species evolve from an original population, it undergoes genetic polymorphism inducing reproductive isolation while inhabiting the same geographic region
- common in plants
- contoversial examples
- Orcas in NE Pacific
- resident orcas, big pods daughters and offspring stay with mother
- transident orcas, small pods (eat dolphins and whales, dangerous for residents)
- not bred in 1000’s of years
Phyletic gradualism:
Evolution takes place in lineages and speciation is a side effect of that.
- common in asexual microorganisms in open ocean
- most evolution takes place within species lineages
Punctuated equilibrium:
evolutionary stasis except in periods of speciation, 1972 Eldridge and Gould
- sexual organisms
- within species lineages there is stasis
- most evolution is concentrated in the speciation events
- stasis is most common in the fossil record
How do you test punctuated equilibrium:
- Abundant specimens
- Fossils with living representatives, species can be clearly identified
- Information on geographical variation, rapid speciation events could be distinguished from migration
- Good stratigraphic control
- Example: Fine scale evolution in fresh water snails and bivalves, Lake Turkana, Kenya
Give an example of gradual speciation:
Radiolarians; phyletic gradualism of planktonic diatoms.
- Rhizosolenia today there are 2 species over their 3.4Ma existance they have diverged over 500000ya (3.2-2.7)
What did Steven stanley come up with?
“Species selection”
- 1975
- It occurs at the same time as but separate from natural selection
- Some parts of the tree of life diversify slowly, others rapidly.
How do you work out the original function of structures?
- comparison with modern analogues
- could use phylogentic bracketing
- most useful when fossil belongs to modern group
- Elephant more useful than a crocodile or a bird for sauropods
- biomechanical testing
- paradigm approach
- circumstantial evidence
- rocks, trace fossils, fossils (e.g. those showing predation) - empirical evidence
Describe biomechanical mechanical modelling:
- interpret movements (feeding, locomotion)
- use 3D models or computer modelling (finite elements analysis)
- stress and strain calculations estimate leg muscle volume
- larger dinosaurs exceeded the maximum aerobic capabilities of modern exotherms, herefore, functionally endothermic
- Seilachers Triangle for the consideration of form
- Phylogentic factor
- Functional/Adaptation
- Fabricational
Describe circumstantial/empirical evidence:
- rocks give evidence of ancient climate
- fossils indicate prey and predator relationships
- T-rex has ornithischian dinosaur bones in gut, shows fast digestion pathway, teeth of prey show what kind of plants they ate
- trace fossils are used to look at locomotion modes of the maker
- manipulating bones you can work out if an animal stood upright
- footprints show where feet fell, what pattern of movement
- End Permian mass extinction, shift from sprawing to upright
Desribe comparison with modern analogues
- function and behaviour of fossil bat inferred with living ones
- rhino and elephant have similar functional morphology to dinosaurs so they are better than burds or crocodiles
- EPB and development of parsimony principle
- osteological correlation of unpreserved features can be identified
- allow inferences about presence of unpreserved features e.g. T-rex eyeball has certain properties, birds and crocodiles share common eye characteristics
Phylogenetic Factor:
- constraints imposed by the evolutionary history of an organism
- genetic heritage
- Evolution is a tinkerer, making a new object using only parts from an old one, but keeps the old one working until completely replaced.
- Mosaic evolution
- vestigal structures
- atavisms
Mosaic evolution:
changes in different features that occur at different times/rates evolving lineage
- human eye and octopus eyes are very similar but didn’t evolve the same way
- vertebrates photo-receptor points away from light
- cephalopods photo-receptor points towards light
Vestigal structure:
reduced or degenerate remnants of a functional feature in ancestors
- Whales have hind legs
- Snakes have vestigal lung, back legs (evolved from lizards in the early cretaceous
Reasons:
- organs less useful
- inrease fitness
- preadaptation (Ostrich wings became vestigal for flight but important for feeding and behaviour)
Atavisms:
reappearance of a characteristic typical of remote ancestor that were absent for a long time
- reversion to a previous evolutionary state
- structures have not been lost, switch mechanism is suppressed until a mutation resurrects it
- polydactyl horses, occasionally extra toes appear
- human tail bone
- illustrate hidden potential for morphological change that all organisms possess
Functional factor:
- demands that require an organism to keep functioning until it has produced progeny
- machinery to cope with demands of survival and reproduction in the prevailing environment
- Bivalve may need a thicker shell to aid from predation, but it must maintain viable integration of whole organism
- needs stronger muscles to keep shell closed, stronger foot to move around, needs to eat more, more active, needs to improve gills
- Bivalve may need a thicker shell to aid from predation, but it must maintain viable integration of whole organism
Fabricational factor:
- you must be able to make it! A shell must be able to secrete it to use it (no diamond encrusted shells)
- becareful of fabricational noise (features with no functional significance; incidental biproducts due to the way a feature is made)
Life habitats of living bivalves:
- Byssally attached
Mytilus - epifaunal, wedge shaped, often flat ventral surface - Cemented (hard substrate)
- Reclining (soft substrate)
Gryphaea - most evolved from cemented or byssally attached forms - Swimming
Chlamys varia/opercularis - large umbonal angle (C.Op) means more lift:drag ratio = more efficient swimmer - Burrowing (soft substrate)
shallow - rounded often heavily ribbed, strong hinge teeth
deep - elongate, shell gape, thin, smooth shell - Boring (hard substrate)
Pholas (stone), Teredo (wood) - similar morphology to deep burrowers, shell edges have stout spines - Nestling (hard substrate)
What is a radiation
A rapid expansion of a clade
- Sometimes called adaptive radiation (bad terminology)
- Made of Process = hypothesis (adaptive) and Pattern = observation (radiation)
- Example is placental mammals after K/T within 10Ma 20 major clades (bats, whales, horses, rodents)
The initial appearance of a new taxa:
is often followed by a period of rapid evolution
- new form spreads into new areas and adapts to new environmental pressures
- triggered by the introduction of a new morphological innovation or opening of new ecospace
Whats a great example of paired replacement by competition
Bivalves and brachiopods
Bivalves:
- upper and middle Cambrian: no species known
- lower Cambrian: Fordilla and Pojetaia
- Arenig radiation (Ordovician) all major groups appear
- After P/T early Mesozoic radiation: Siphon formation
- radiated owing to aquisition of key adaptive morphological features: siphons, tight seal, foot for mobility
Describe the early Mesozoic radiation:
- majority of Palaeozoic bivalves were epifaunal or primitive infaunal
- Fueled by the Mesozoic revolution
- breakthrough of Hetrodont
- mantle fusion formed siphons, go deeper in sediment and invade littoral zone
Mesozoic revolution:
A lot of predators around, increasing pressure) - more durophagy
What are the 2 types of replacement:
Active replacement
- double wedge: competition from B causes extinction of A
Opportunistic replacement
- mass extinction killed A, B took over
Gould and Calloway 1980
- took brachiopod and bivalve data (number of genera) through time
- P/T extinction event 75-95% species
Describe Opportunistic replacement:
- exansion in 1 group not met by decline in the other group
- the P/T effects the brachiopods more than the bivalves
- Change in dominancy arises as a result of one instance = P/T, bivalves increased and brachiopods hold their own
- Early triassic bivalves are ahead and they stay ahead
What is the coupled logic equation?
Used by Sepkoski in 1996 it takes into acount:
- group diversity
- diversification rate
- equilibrium density
- crowding effects
Its more sophisticated however it is a model and makes assumptions and can not account for everything (long term environmental changes)
Describe active replacement:
Sepkoski looked at residuals and not just best fit line for bivalves and brachiopod numbers through time
- By the end ordovician bivalves were on the rise and brachiopods were levelling out
- Immediately before the extinction brachiopods were losing diversity as a result of competitive replacement
Reasons for variation in fossil populations within a single species:
Factors within interbreeding populations (can eventually lead to geographic sub-speciation)
- Ontogeny: size/shape change during growth
- Conditions of life i.e. low nutrition = slow growth, distortion due to crowding/pathological variants
- genetic variation e.g. rib number, sexual dimorphism
Reasons for fossil variation
All help build a picture of species and its range of morphological variation; Qualitative - human eye picks out differences; Quantify - better, esp. if data handled mathematically.
- Taphanomic sorting - sedimentological/diagentic factors impose variables for preservation
- Fossils from a single bed often contain main populations = time averaging
- Collection bias
What is a reef:
- wave resistant carbonate frame work
Describe the earliest reefs:
Early Cambrian
- Intertidal stromatolites
- migrating ooid shoals
- 3-10m scale reefs made from archaeocyathids (extinct phyllum) and calcimicrobes that trap mud. Reef formers are filter feeders in eutrophic water
- extinction in U.Cambrian = no reefs
When was the first golden age for reefs
Mid devonian
- equable climate
- colonial calcitic organisms encouraged by predator evolution and rise in land plants (sequester more nutrients = more oligotrophy in oceans)
- symbiosis between reef formers and algae
- very diverse system
- Devonian great barrier reef
Describe the Devonian great barrier reef
350km long in the Canning basin inbetween Gondwana margin and Antartica
- tabulates
- rugose
- sponge
- stromatoporoids
Palaeozoic reef builders:
- mainly stromatoporids (extinct)
- calcareous algae
- sometimes tabulates
- more rarely rugose
How did P/T mass exinction effect reef systems
- decimated reef and palaeozoic corals
- 8-10Ma after P/T
- appearance of scleractinians
- evolved from anemone-like ancestors “naked coral hypothesis”
- small and non reef-building
- Late Triassic biotic turnover and adaptive radiation
- Coral reef framework, coral-zooxanthellae symbiosis
Cretaceous reefs:
- Scleractinians (coral type fossil) present but didn’t form large frameworks
- Reefs made of Rudist bivalves (filter feeders)
- warm seas, perhaps too many nutrients
- K/T extinction
When was the second golden age?
Tertiary - Quaternary
- productivity very high = upto 1000 x greater than surrounding ocean
- diversity very high ~1/4 marine species
- Oligotrophic waters (much like rainforests in poor soil)
Describe symbiosis:
- symbiosis means living together so that could be mutualistic, commensal or parasitic
- The reef recovery time gap (8-20Ma) after a mass extinction might reflect time needed for symbiosis to return
What do corals gain from symbiosis:
- symbionts recycle nutrients
- O2 from photosynthesis
- C and N
- accelerated growth rate 5 times faster in daytime
What do algae gain from symbiosis:
- safe habitat
- nutrients waste P and N
- constant supply of CO2
What are Ahematypic corals?
Corals that lack algal symbionts are commonly solitary or uniserial compounds with large poorly integrated corrallites
Scleratinians:
- 6 different clades are symbionts - contain dinoflagellates
- multiple clade in one coral
- depending on light/depth coral may actively expel them for better ones
- We can track environmental/evolutionary changes
- Radiated during Mesozoic, with zooxanthellate forms dominating reefs, Triassic to recent
- Arose numerous times from anemones with scleractinian type polyps “naked coral hypothesis”
- Solitary or colonial, Aragonite capped with coral tissue, symbiotic algae within
- Hermatypic and cold water forms; reefs, banks
- Good stability
Why are corals so successful?
- zooxanthellae allow for greater growth rates
- more efficient predators (esp. fish) eat coral competitors
- new herbivours (gastropods) eat algae providing antifouling (ability to prevent biofouling, a build up of algae)
- Widespread oligotrophy, helped by diatoms locking in nutrients
What are the current threats to coral?
- Natural: storms, predator explosions, El Nino (5-7yrs climate pertebation)
- New/enhanced: fishing - dynamite, siltation, diving (tourism), UV light thinned Ozone, climate change bleaching, eutrophication.
Modern reefs:
- 0.1% of planetary area but about 1/4 of species (~50,000 described, ~30000 undescribed)
- 95% damaged
- In Indo Pacific 85% lost large fish
- no lobsters 81% worldwide
- In 40yrs 70% of reefs worldwide will be lost 200,000 species lost
Sponges (Porifera):
- They are parazoan that lack a gut
- Ediacaran - The first were a cluster of flagellate cells
- Almost entirely filter feeding members of the sessile benthos
- 2 types of reef builders, sponge silica spicules, calcareous basal skeleton
- Cambrian = wide cosmopolitan distribution
- Ordovician = Demosponge decline due to stromatoporoids + rugose + tabulate corals incoming
- Hexactinellids = siliceous sponge
- Calcarea = calcareous sponge
- Demospongea = common sponge
Calcareous skeleton developed numerous times across the phyllum that are independantly in different clades
- All 3 type were responsible for reef building from carboniferous to the Jurassic
What is a parazoan?
A metazoan that lacks cellular and organ complexity/variation
Stromatoporoids:
A grade of organism within Porifera with a secondary calcareous skeleton
- important in reefs during the mid Palaeozoic and mid Mesozoic
- Silurian reefs in Gotland (Kershaw 1990) provided habitats for over 30 epibiont species + borers and encrusting
- First cryptic habitats for Phanerozoic biota
- Largely extinct in the Devonian, some living sponges are stromatoporoids
Archaeocyaths (ancient cups):
- Cambrian organisms of sponge grade, mainly solitary but developed a branching, modular growth mode
- Often built reefs in turbulent and unstable environments
- Carbonate substrates, growth on modular organisation meant secure attachment on soft substrate, grow to large size improving regeneration (Wood et al 1992)
- Reef type structures already present in late precambrian, hosting large robust colonial organisms
Cnidarians:
- The simplest of the higher metazoans with radial diploblastic body plan and stinging cells or cnidoblasts
- Phyllum includes sea anemones, jelly fish and hydra, together with corals
3 main classes (Ediacaran to recent)- Hydrozoan
- Scyphozoan
- Anthozoan
What are Hydrozoans?
A class that includes:
- freshwater colonial and fire corals
- Most kinds of jelly fish
What are Scyphozoans?
A class that includes:
- Free swimming jellies or medusae in open ocean
e. g. moon jellyfish
What are Anthozoans?
A class that includes:
- Sea anemones, sea fans, sea pens, sea pansies
- soft and stony corals
- sessile, colonial mainly
- Subclass Zoantharia
- Orders: Rugosa, Tabulata, Scleractinia
What confirms symbiosis in late Triassic?
- stable isotope and organic matrix analysis
Zooxanthellae are endosymbionts this means:
they live together in the tentacles and mouth of some Cnidarian, where they recycle nutrients, increase rate of skeleton deposition and convery organic C and N
Rugosa:
- Colonial and solitary (fasciculate; massive)
- Ordovician to Permian
- Shallow water limestones; reef formers
- Calcite
- Poor stability
Tabulata:
- Only colonial (compound)
- Ordovician to Permian
- Shallow water limestones; reef formers
- Calcite
- Poor stability
Reef development through time:
Has waxed and waned, dominated at different times by different groups.
- coloniality within the metazoans has evolved many times, 1 suggestion is a precambrian colonial organism was the source for bilaterals.
Three main types of structure occur in tropical water:
- Fringing reef (directly adjacent to land area) - most common but sensitive to human impact
- Barrier reef (have an intervening lagoon)
- Atoll (surround a deep circular lagoon) - conducive to volcanic island formation
Why were Palaeozoic corals not the best reef builders?
- They preferred a hard substrate, due to lack of structure
- Calcareous algae and stromatoporoids were more important
What is a concentration deposit?
(Koncentrat)
- High abundance mot necessarily high quality preservation
- community ecology or behaviour e.g. cave deposits
- Sedimentary artefact produced by time averaging, winnowing ect.
What is a Conservation deposit?
Often fossils are rare high quality preservation of tissues and structures, not normally forund in the fossil record
Articulated skeletons:
can contain mineralized parts e.g. Jurassic Crinoids and bivalves attached to a log
- If 260M people each with 206 bones only 50 bones left preserved
What is soft part preservation:
- non biomineralized (cartilage, keratin, chitin)
- real soft tissue (worms rarely preserved)
- Can find worm neurons, organs and internal parts as well as external, gastric content under microscope, proboscis
What do soft bodies tell us?
- Animal affinities
- Biology
- Evolution
- Community diversity
What does soft body preservation tell us about an organism’s affinities?
- Animals have hard parts that tell us little about their underlying soft parts
- Conodonts
- teeth made of apatite
- used for dating rocks they are so common
- preservation of a notochord suggests its one of our earliest relatives
What does soft body preservation tell us about an organism’s biology?
- 425Ma Ostrocod preservation, the first example of sexual diamorphism, exceptional preservation in nodule, Herefordshire Lagerstatte. (Siveter, 2003)
- computer tomography
What does soft body preservation tell us about an organisms evolution?
The Jurassic solnhofen limestone, Arcyopterix 150Ma
- Shows all bones and feathers
- reconstruct colours - melanosomes are organelles that contain and manufacture melanin, darker hair is oval and ginger is circle.
- They are found in early cretaceous Jehol biota, China (Microraptor, Anchiornis)
- pterosaurs had fur, microraptor was a four winged dromaesaurid, from Liaoning China, 120Ma (E.Cret) (Xu, 2003)
What does soft body preservation tell us about community diversity?
Using the Cambrian as an example:
- Normal cambrian fossil community: decay processes have taken place, only hard parts remain
- The burgess shale fossil community 86% of forms are soft bodied, they would not normally be preserved
Needs for preservation:
- Die in an area of deposition
- Be buried quickly in an inhospitable sediment = no bioturbation
- Hypersaline - Solnhofen beds
- Anoxic -Jurassic Ammonites and marine reptiles
- Avoid bacteria decay, mineralisation can replace organic matter during decay
- plants and animal tissue decay in a sequence that depends on their volatile content, the process of decay can only be altered by mineralisation
The process of fossilisation is a race:
between rate of decay and pre burial mineralisation, the point of intersection determines the quality of preservation
- Early mineralisation may be achieved in pyrite, phosphate and carbonate
What controls the pre burial mineralisation type:
Pyrite = rapid burial, low organic content, presence of sulphates
Phosphate: Low rate of burial, high organic content
soft part Carbonate: rapid burial, high organic content, low salinity - at high salinity carbon is layed down as calcite
What are the 3 post burial minerals:
- CaCO3
- Apatite
- Silica
Often each relates to a type of organism or tissue, e.g. Apatite is common in worms and conodonts
What is an abruption deposit:
when sediment buries an organism virtually instantly
- delta fronts/rapid migrating river channels
What is a stagnation deposit:
Anoxic conditions in stagnant or hypersaline water reduces microbial decay
What is the Gunflint chert in Canada:
- show benthic algal mats and planktonic forms
- most photsynthetic, some used iron for motabolism
Precambrian Lagerstatte:
- Doustantuo Formation 600Ma China
- Ediacara Hills 565Ma S.Australia
Cambrian Lagerstatte:
- Mautianshan shales 525Ma Chengjiang china
- Burgess shale 505Ma Mistaken point, British Columbia
- Marella, 15,000 specemins
- Annelids, priapulid, Cnidarian
- most common fossil was most common fossil, rangeomorph
Ordovician Lagerstatte:
- Soom shale 435Ma S.Africa
- Famous for conodonts, Promissum pulchrum
- Beechers trilobite bed in N.York state
Silurian Lagerstatte:
- Ludlow bone bed 420Ma Shropshire
- Herefordshire
Devonian Lagerstatte:
- Rhynie chert 400Ma Scotland
- Earliest vascular plants, arthropods around hot springs, plants with no leaves - no herbivores
- Hunsruck Slate 390Ma Germany
- Marine life: Echinoderms, fish, arthropods in pyrite
- Giboa 380Ma New York
- Similar to Rhynie Chert but flattened in shales
Carboniferous Lagerstatte:
Mazon Creek 300Ma Illonois
- Ironstone nodules containing arthropods, plants, sharks, molluscs, crustaceans, gastropods like the Tully monster
Triassic Lagerstatte:
Petrified forest Arizona
- logs of conifers, Coelophysis, Placerias
Jurassic Lagerstatte:
- Morrison Formation Western USA
- Classic concentration deposit, large bones (Diplodocus, Stegosaurus, Apatosaurus)
- Holdzmaden 160Ma Germany
- Marine reptiles, Ichthyosaurs giving birth, ammonites, fish, belemnoids
- Solnhofen 149Ma Germany
- Horseshoe crabs, dragonflys, pterosaurs, Archaeopteryx
Cretaceous Lagerstatte:
- Crato 117Ma NE.Brazil
- Resembles Solnhofen, with fish Dastilbe
- Santana 100Ma NE.Brazil
- Phosphatic nodules with fish, pterosaurs (Anhanguera) and rare dinosaurs
Eocene Lagerstatte:
Messel Oil Shale 49Ma Hessen Germany
- Propalaeotherium, bats, Leptictidium, Messel birds
- Subtropical forest
Miocene -Oligocene Lagerstatte:
Dominican amber 30-10Ma Dominican republic
- amber acts as an antiseptic, desiccating insects
Quaternary Lagerstatte:
- Frozen mammoth 23,000ya Siberia
- Rancho La Brea tar pits 20000ya
- no internal organs just pickled skin and hair
What is the Cambrian Explosion?
Earthis 4.6Ga
- The earliest life is controversial besides the earliest fossils 3.2Ga - Stromatolites
- Oldest Eukaryotes 1.9Ga
- Metazoans first appeared as fossils 600-550Ma
- Most appear rapidly at the base of the Cambrian
- Is it a real biological radiation or a change in preservability
Describe the transition of the fossil record from the Vendian to the Cambrian
Vendian ¦ Cambrian
—- Doushantuo
Ediacaran ————–
Trace Fossils ———————————————–
Cnidaria —-
Porifera —-
—- Small shelly
———– Molluscs
———– Brachiopods
———– Arthropods
———– Echinoderms
Neoproterozoic Trace fossils:
- elongate sinuous groves/furrows
- > 1Ga
- Is this evidence of bilatarian (have to have bilateral symmetry to move)
- Controversial evidence that this was created by a giant protist
What evidence of life of metazoans recorded?
Doushantuo embryo’s
- Multiple localities around the world
- tiny spheres = embryos in early cleavage states
- a stem group metazoan (now extinct)
- some people think they are fungi or rangeomorphs
- Dated ~580Ma or 580-550Ma
Meiofauna (Fortey, 2004) - crustaceons and worms etc, living within sand grains - they aren’t preserved but part of slow fuse theory
Ediacara:
- Found on every continent
- oldest = 565Ma
- > 100 species
- affinities much debated
- ancestors to cambrian organisms or a failed evolutionary branch
- Not symmetrical
- Is Kimberella a Mollusc?
- then there must have been a divergence in time for bilateral life forms
- we don’t have any evidence just impressions in ash
What group of organisms dominated from the Precambrian to Cambrian boundary?
SSF - Small Shelly fauna
- assemblages best in lower cambrian
- 1st major appearance of hard skeletal material
- Some elements are considered to be the sclerites of larger animals, multiplated worms possibly, others
seem to be the tiny shells of individual animals. Many components of the small shelly fauna cannot be allied with any modern group, and like the Ediacara, could represent anatomies that arose early and disappeared quickly
- biological relationships hard to address
Burgess shale type faunas:
- soft part and hard preservation
- Chengjiang Moutianshan shales 525Ma
- Sirius Passet Greenland 518Ma
- Burgess Shale 505Ma
> 30 localities for lower-mid cambrian
What triggered the Cambrian explosion:
- Environmental changes
- lots of O2 needed for complex larger life
- difficult to determine O2 levels, as soon as rock is heated it changes composition
- lots of O2 needed for complex larger life
- Developmental changes
- HOX genes are master control genes
- these are similar across all animal groups
- So developmental in 1 HOX gene in an ancestral metazoan could produce RAPID EVOLUTION + LARGE RANGE OF BODY PLANS
- Ecological changes
- Arms race, evidence of predation in Precambrian e.g. drills in SSF shells, spiny acritarchs
- evolution of eyes meant new aaptations needed to avoid predators (armour/spines)
- maybe linked with mass extinction of ediacara, followed by adaptive radiation
In the Cambrian explosion new body plans coincide with:
appearance of bilateria (Conway Morris, 1998, 2006)
- Theres the standard view as the fossil record shows
- Alternative is that some animals diverged 800Ma before Cambrian (Wray et al, 1996), suggested by the molecular clock
- mobile bilatarian evidence 555Ma, also sugested by new molecular clock data (Peterson et al, 2004,2005)
What are Coelosclerites:
organisms from the Tommotian
- didn’t grow but secreted mineralized material from organic matter in the center
- important for understanding origin of biomineralisation (Bengton, 2005)
What is meant by the term Fitness landscapes
(Marshall, 2006) - Principal of Frustration
- the multiplication of attempted solutions to new opportunities, such as to protect from predators new morphological features arise but this makes the organism perform less optimal.
What are some of the arguments for when a fossil is verified into a fossil group?
- When is the timing established of extant body plans
- How far back do you go?
- could extend phylogentic bracket (Fortey et al 1996)
- Possibility of apomorphic character states being plesiomorphic and then lost later in the sister group, to the group that now posses them (Budd and Jenson, 2000)
- How far back do you go?
Why is O2 increase not a strong candidate for fueling the Cambrian explosion?
There was an increase for 40Ma till 516Ma it can not be the sole benefactor even though it would greatly benefit and allow the development of some ecologies (Budd, 2008)
Requirements for a classified mass extinction:
- many species become extinct ~ >30%, must be higher than he background rate
- across a broad range of ecologies
- worldwide
- occur within a relatively short amount of time
Patter and timing for P/T extinction:
- best record from microfossils (foraminifera)
- any gaps in data (a hiatus around the P/T boundary) will make a gradual event appear sudden
- Signor Lipps effect - A sudden event may appear gradual as likely the very last species of a fossil isn’t found
The presence of Pangaea at the end Permian:
reduced continental she;f with high CO2 and the hot arid continent, there were only 2 oceans.
- small extinction 260Ma - Guadolupian
P/T Extinction effects:
- greatest one in history
- earth bound causes
- 50% families wiped out
- 80 - 96% species wiped out
- All reef/corals
- All fussulinids
- 97% Ammonoids
- 94% other forams
- 85% Articlate brachiopods and gastropods
- 59% bivalves
- 63% terrestrial tetrapods
- took until Cretaceous for diversity to recover
Describe the isotope data for P/T extinction:
- 13C prolonged negative shift, a sharp shift near the boundary (Foster et al 2017)
- therefore light 12C is released into atmosphere
- productivity collapse
- basalt intruded into carbon rich rock
- gas hydrate (main theory)
- therefore light 12C is released into atmosphere
- 18O shows a 6 degree increase in atmospheric temperature
- 34S show widespread precipitation and burial of pyrite (anoxic conditions)
- 87Sr/86Sr meant a major increase in rate of continental weathering (acid rain)
Where did the negative shift in carbon come from at the P/T boundary?
- productivity collapse (probably not enough)
- basalt intruded into carbon rich rocks
- gas hydrates
- At the bottom of the ocean or locked up in ice, methane hydrate etc is stable. Until pressure is applied or the ice melts due to warming. Causing an increasing sea level in turn creating a run away greenhouse effect
- long ‘mean lifetime’ of atmospheric CO2, compared
with the eruption flux and duration, meant that significant accumulation could occur over periods
of 10^5ya (Saunders and Reichow, 2009)
Describe the sedimentology for the P/T boundary
In the Triassic - black shales with pyrite
Permian upto boundary - carbonate shelly, then bioturbated
- Golden spike Meishan China
- Peak eruption of siberian trapps 250Ma
- before peak extinction
- U/Pb zircons
- 40Ar/39Ar
After the P/T extinction:
- very low diversity faunas, following P/T there was a time gap before radiation
- remarkable cosmopolitanism
- 7-8Ma for many benthic fauna to recover
- Marine nekton and terrestrial fauna recover quicker
- size reduction in surviving taxa (Twitchett et al, 2015)
- Most marine cordates survived (conodonts,most fish)
- Early Triassic coal gap (extinction of peat forming plants (Retallack et al 1996)
- Plankton suck out CO2 fromatmosphere but temp increase causes their deathand ocean can hold only so much CO2 = stagnation
- Compromise of the carbon sequestration systems (by curtailment of photosynthesis, destruction
of biomass, and warming and acidification of the oceans) probably led to rapid atmospheric
CO2 build-up, warming, and shallow-water anoxia, leading ultimately to mass extinction. (Saunders and Reichow, 2009)
Describe the Siberian Trapp eruption:
- 1.6Mkm^2 = area extent, 2Mkm^3, 400 -3000m thick
- If that much basalt was dumped on the UK = 12km thick
- Huge outpourings of CO2 and SO2 (short term) creating acid rain and starting a positive feedback loop with gas hydrate melting = CH4 = more CO2 = increase in global temperature leading to terrestrial extinction and reduced O2 circulation.
- Sulphate aerosols triggered short term volcanic winters (Saunders and Reichow, 2009)
- Reduced O2 circulation causes reduced upwelling, and thus productivity collapse, as well as ocean anoxia, both of which cause extinction rates to increase.
- 18,000Gt of C over 1Ma: 0.018Gt per year
- long ‘mean lifetime’ of atmospheric CO2, compared
with the eruption flux and duration, meant that significant accumulation could occur over periods
of 10^5ya (Saunders and Reichow, 2009)
Dating the P/T
- Boundary in Meishan China, ash layers bracket boundary, bed 28 = 249.25Ma
- peak extinction base of bed 25, 249.83 +/- 0.15Ma
- Peak eruption = 250Ma
Describe the pattern and timing of K/T:
Gradual, step wise or catastophic?
- many taxa unresolved, the Signor-Lipps effect is a major issue here, there is a research bias (Hudson, 1998) towards exciting topics such as dinosaur extinction and meteor impact
Ecological time:
- 9 months: Dust cloud begins to clear
- 10yrs: severe cooling ends
- 1000yrs: continental vegetation recovers
Geologically measurable:
- ~2Ma (probs less) Plankton systems recover
- 3Ma Back to normal
Marine extinctions in the K/T:
- Planktonic forams
- dramatic turn around
- most believe its sudden
- little affected at high latitude
- Benthic forams
- mixed views
- Calcareous microplankton/nano
- sudden at the boundary
- Ammonites, belemnoids, inoceramids, rudists
- gradual decline
- Maastrichtian rapid decline
Terrestrial extinction at K/T:
- Dinosaurs (rubbish at telling if its gradual or rapid)
- prove very bad data
- arguably gradual then rapid
- Mammals
- rapid overturn, no mass extinction
- Plants
- NW USA + NE Asia = 75% species loss
- little loss in the southern hemisphere
- Abrupt shift in pollen ratios (Alvarez, et al, 1980) show a shift from angiosperms, followed by 1cm Ir layer, to fern spores (first to recover after ash fall)
Geochemistry of K/T:
- Ir anomaly in boundary (Alverez, et al, 1980)
- world wide
- on land and sea
- upto 450ppb (background 0.3)
- 13C shift at boundary
- destruction of plankton
- 87Sr/86Sr rises through K and peaks at K/T boundary
- increased continental weathering
- regression/acid rain?
- Famous O2 and C isotope data from Tunisia
- initial recovery after the K/T boundary event about 300,000–400,000 years after the K/T boundary. The prolonged low productivity episode after the K/T crisis and the pre-K/T boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single K/T boundary bolide impact (Keller and Lindinger, 1989)
P/T volcanics:
- Deccan trapps began erupting 2Ma before
- could produce Ir anomaly but then meteor theory came about
- Aerosols + CO2 caused temperature increase
- effects coincide with P/T extinctions
- The temporal match between ejected Deccan eruption layer at the time of K/T and onset extinction and agreement of ecological patterns in fossil record conclude Chixulub impact triggered the mass extinction (Schulte, et al, 2010)
What percentage of families survived the K/T
75%
- killing models for Deccan trapps and impact combined could explain the reason for the both gradual sea level + climate change and final dissapearance of species in the fossil record, but its hard to tell (Benton and Harper, 2016)
