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Evolving lineages in the fossil record
Like all sources of data, the fossil record has
inherent strengths and limitations
“…so must the number of intermediate varieties,
which have formerly existed, be truly enormous. Why
then is not every geological formation and every
stratum full of such intermediate links?…The
explanation lies, as I believe, in the extreme
imperfection of the geological record”
Darwin, 1859
Imperfection of the fossil record
Many time periods represented by few sedimentary
layers
Many lineages represented over long time periods with
no fossils in between
Many extinct species of large organisms represented
by only a few fossils
New taxa continue to be discovered
Geologic column
younger
older
index fossils define strata
extinction events mark boundaries
Evidence for an asteroid impact at the end-Cretaceous
is now overwhelming
The asteroid impact had profound effects on both
marine and terrestrial ecosystems
Extinctions of marine invertebrates at K-T were
selective; genera with broad geographic ranges
survived better
cenozoic
mesozoic
paleozoic
proterozoic
archaean
hadean
Millions of years ago
1
10
100
1000
10000
cenozoic
mesozoic
paleozoic
proterozoic
archaean
hadean
Millions of years ago
0
1000
2000
3000
4000
5000
Paleontological vocabulary
Species - reproductively isolated population
- morphologically distinguishable form
Speciation - splitting of 1 lineage into reproductively
isolated gene pools
Chronospecies - does not imply speciation
Extinction - termination of a lineage
Pseudoextinction - species names disappear because
lineage has changed form
Evolution in the fossil record - sticklebacks
Speciation - typically allopatric
-need to be sympatric, synchronic
Phylogeny & the fossil record
Strong correspondence between phylogenetic
branching and appearance in the fossil record
Archaeopteryx
Evolutionary trends
Neo-Lamarckian theories
Inherent drive
Directional mutation
Directional natural selection
Irreversibility
Irish elk
Evolutionary trends
Neo-Lamarckian theories
Inherent drive
Directional mutation
Directional natural selection
Irreversibility
Evolutionary trends
Parallel trends
-same structural features evolve in parallel in
related lineages
Cope’s rule
-trend toward larger body size in many groups
Iterative evolution
-same trend repeated in sequential radiations
Evolutionary trends
Clade - monophyletic
group
Grade - group of
organisms that have
achieved a certain
level of structural
organization
Rate of evolution
Taxonomic frequency rate
-rate at which new taxa replace previous ones
Phylogenetic rate
-rate of change of single characters within a lineage
-measured in standard deviations or darwins
Rate of evolution
Taxonomic frequency rate
-rate at which new taxa replace previous ones
Phylogenetic rate
-rate of change of single characters within a lineage
-measured in standard deviations or darwins
Rate of evolution - darwins
-change by a factor of 2.718 per million years
-rapid rates masked if:
rate fluctuates
direction of evolution changes