Lecture 7 - evolutionary patters from the fossil record Flashcards
what was darwins opinion of the fossil record?
- didnt fit his theory of evolution
- suggests the rock record is really incomplete and we will never see evolution in action therefore its basically useless
what are modern paelontologists view on the fossil records?
- aware that it is incomplete and biased
- applied a variety of metric to look at the biodiversity of fossils through time compared to rock volume
- if we understand how incomplete and how bias the fossil record is we can counter it so it can be used for something meaningful
what did Darwin identify as a positive of the fossil record but also a problem with it?
shows us extinction and speciation has occurred but it cant tell you anything about the tempo and mode of evolution i.e proves evolution but can inform us on how it works
what happened to change the worlds view on evolution?
mendels work was rediscovered and neodarwinism evolved to tell us how evolution worked - then punctuated equilibrium theory was proposed and the fossil record was proven useful
what 7 evolutionary patterns can be inferred from the fossil record?
1) biodiversity
2) morphological disparity
3) origination patterns
4) extinction patterns
5) taxonomic duration
6) rates of evolution
7) fossils and biogeographic patterns
describe morphological disparity and how it can be measured
can get a group of 100 species all not that different or a group of 10 species all extremely different
- use landmark analysis e.g. size of eyes and plot how different they are in a group through time (trilobites have been demonstrated to become more disparate through time in terms of eye size)
- can then be compared with biodiversity to give a strong idea of how life changes through time
- can also score characters by how difficult they are to build - add them up and plot them
describe origination patterns and how to measure them
- look at if new species are appearing regularly through time or if there is periods of time with more and less speciation
- look at different groups (e.g. if they are all speciating rapidly around the same time suggests it could be an external factor causing it)
- look at number of species through time over a broad area
what is the issue with looking at number of species through time over a broad area?
if you do it over one area of the world origination patterns can be confused with immigration and emigration
what is important to consider when looking at extinction patterns?
- need to differentiate between background extinction, pulses of extinction (extinction events) and mass extinctions
what are the 5 big mass extinctions?
1) end ordovician
2) end Devonian
3) end permian
4) end triassic
5) KT
describe the end ordovician mass extinction
short glaciation event - difficult to explain why it happened
describe the end devonian mass extinction?
due to aquatic anoxia in the oceans - black shales everywhere full of iron pyrite - possibly related to spread of forests on land pushing nutrients into the ocean blanketing everything with mud and killing it
describe the end perminan mass extinction
- biggest extinction of them all - 90% of life wiped out
- due to atmospheric pollution and heating due to emplacement of Siberian traps LIP - fracture in the continent and lava pours out releasing masses of CO2 and methane (poisons atmosphere)
- ocean reached temp over 40 degrees where metabolism doesn’t work
describe the end triassic mass extinction
same as the end permian but due to emplacement of the central America LIP
describe the KT mass extinction
bolide impact causing a nuclear winter
why are extinction events difficult to study?
- need long continuous stratigraphic sections over the mass extinction event in a variety of habitats e.g. marine and terrestrial
- signor lipps effect can muddy the waters
what does the signor - lipps effect state
states that since the fossil record is never complete, neither the first or the last organism in a given taxon will be recorded as a fossil
why do mass extinctions vary in magnitude?
what is affected varies due to the nature of the causal mechanism (but may be stochastic luck)
describe recovery after a mass extinction
recovery can be rapid due to adaptive radiation into the created vacuum
- can be protracted (lilliput effect) - all survivor taxa get smaller
how does the fossil record allow you to address taxonomic duration?
- fossil record allows you to address questions that cannot be addressed by studying the modern world
- can study survivorship curves in different time periods - probability of survivorship is independent of age
how can you analyse rates of evolution?
- rigorous phylogenetic analysis through cladistics
- taxonomy should mirror phylogeny and phylogeny should mirror evolutionary relationships
- can plot the occurrence of taxa through time and then analyse the characters to see how the speed of evolution has changed through time
how can you measure fossils and biogeographic patterns?
- can be done within a phylogenetic framework
- can look at how certain groups diversified in different areas of the world as continents changed etc
What do patterns of evolution help us to understand?
the journey of time and the debate of phyletic gradualism vs punctuated equilibrium - both extremes neither has to be right of wrong could be a combination of both
what are the two theories of what drives evolution?
1) court jester - environment is driving changes
2) red queen - interactions between species
- debate over which - probably combination of both
what does the term species sorting mean?
fledgling species are more likely to survive if they are ecologically different from their parent species
what does the term species selection mean?
the differential rates of appearance and extinction of species within lineages
what does the term habitat tracking mean?
ecological communities follow habitats as they move during environmental change
what did Gould claim about evolution?
it was tiered
describe goulds tiers of evolution?
first tier - microevolutionary processes e.g. competition -> evolutionary events in their ecological moment
second tier - punctuated events - > trends with lineages over geological time
third tier - mass extinctions -> mass extinction
what do gradualists tend to believe about evolution?
tend to think microevolution is scaled up to macroevolution and there is no tiering at all
according to cladistics birds are reptiles, wjay defines a bird?
1) feathers
2) carpometacarpus
3) unique foot structure
4) pygostyle
5) hollow bones with pneumatic foramen
6) sternum and keel
7) furcula - wish bone
8) high EQ with advanced vision
what is the archaeopteryx?
missing link between birds and reptiles - a bird with flight feathers and furcular but also teeth, tail and claws
what did cladistic analysis reveal about the archaeopteryx?
shows it to be a sister group to the theropods
- theropods needed to be light and active so started to evolve hollow bones etc- slow development of characters that birds posses
what does the new evidence of feathered dinosaurs from china mean?
flight can evolve in dromosaurial dinosaurs via the arboreal or cursorial hypothesis
