Evolving lineages in the fossil record
Jan 13, 2016
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
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
Imperfection of the fossil record
younger
older
index fossils define strata
extinction events mark boundaries
Geologic column
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
110100100010000
hadeanarchaean
proterozoic
paleozoicm
esozoic
cenozoic
Millions of years ago
010002000300040005000
hadean
archaean
proterozoic
paleozoicm
esozoiccenozoic
Millions of years ago
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
Strong correspondence between phylogenetic branching and appearance in the fossil record
Phylogeny & 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
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
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 fluctuatesdirection of evolution changes