Quantifying Evidence of the Cambrian ExplosionCrazy CreaturesEnormous TimescalesA Macro-Evo/Eco PerspectiveDating Genes and FossilsMolecular ClocksCambrian Explosion like Mammalian Speciation?ConclusionsReferencesQuantifying Evidence of Quantifying Evidence of the Cambrian Explosionthe Cambrian ExplosionEric DuchonEric DuchonMay 5, 2008May 5, 2008Crazy CreaturesCrazy Creatures•Proliferation of metazoans•Many animal taxa first seen in Cambrian fossils•Live in a shallow sea•Globally distributed population?Enormous TimescalesEnormous Timescales• Long period of high stability, low evolutionary rates• How is this multitude of forms generated?– Environmental perturbations of glaciers, phosphorus, molybdenum & oxygen?• Similar to radiation of mammals in the Tertiary?A MacroA Macro--EvoEvo/Eco Perspective/Eco Perspective• Little speciation or evolution in Precambrian– Stasis from simple 2 trophic level ecosystem?• Stable with respect to perturbations via simple system and global distribution?• Ediacaran – Eumetazoa and a dynamic food web– Drives evolution at a faster rate through more dynamic interactions• Cambrian – Geographic niches and species specialization encourage fast evolution via ecosystem interactionsDating Genes and FossilsDating Genes and Fossils• Animal fossils first seen at Cambrian• Thin lines – inferred rapid speciation• Dashed lines –estimated clade dates using molecular clocks• Unclear how to fill in pre-fossil phylogenyMolecular ClocksMolecular Clocks• Comparative studies with few genetic markers date animal clading from 1 to 10 bya• New study uses fifty genetic groups– Many clade relationships still unresolvable• A resolution limit for this technique exists?– Works great for uniformly evolved fungi– Equally poorly for time-modeled mammalsCambrian Explosion like Cambrian Explosion like Mammalian Speciation?Mammalian Speciation?Cambrian Phylogeny with 4 out of 14 nodes well-resolvedTime-evolved model of Mammalian cladesConclusionsConclusions• Is there a fundamental shift in evolutionary rates and mechanisms from the Precambrian to Cambrian Eras?• Long branches after a clade limit the resolution of molecular clock techniquesReferencesReferences• Rokas, Krueger, Carroll. “Animal Evolution and the Molecular Signature of Radiations Compressed in Time. Science, Vol 310, December 2005.• Jermiin, Poladian, Charleston. “Is the ‘Big Bang’ in Animal Evolution Real? Science, Vol 310, December 2005.• Butterfield. “Macroevolution and Macroecology Through Deep Time.”Paleontology, Vol 50, Part 1, 2007.• Dunne, Williams, Martinez, Wood, Erwin. “Compilation and Network Analyses of Cambrian Food Webs.” PLoS Biology, Vol. 6, April 2008.• Scott, Lyons, Bekker, Shen, Poulton, Chu, Anbar. “Tracing the Stepwise Oxygenation of the Proterozoic Ocean.” Nature, March 27,
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