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