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