b. By Proterozoic, - protected from solar radiation if about 10 M below surface of water - dominated by

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1 I. Diversification of Life A. Review 1. Hadean Eon a. b. 2. Archaean Eon a. Earliest fossils of b. Establishment of three major domains B. Proterozoic Eon (2.5 bya mya) 1. Emergence of the a. Rock cycles begin to leave b. Most Archaean Deposits more c. Prolonged period of continental growth 2. Developed assembly of land masses - major continents by late Proterozoic a. - Greenland, N. America, England, Siberia, initially S. America b. - Africa, India, Antarctica, Australia - eventually included 3. Early Biosphere a. Archaean Atmosphere measured to contain primarily b. By Proterozoic, - protected from solar radiation if about 10 M below surface of water - dominated by c. Conversion from primordial heterotrophs to autotrophs was key to atmosphere - trace amounts of O2 released via - microbial autotrophs, cyanobacteria, d. Poisonous Oxygen - Initial insurgence of atmospheric O2 detectable as early as 2.2 bya - Early on Earth dominated by Prokaryotic life - increase in O2 - many early dominant forms i. Retreat to specialized environments 4. Diversification of Form Began with the a. resting stage of b. Earliest fossil record dates to about - acritarch fossils abundant by 800 mya c. Rapid divergence into variety of early Eukaryote lineages

2 5. a. Earliest evidence of b. Found initially in Ediacara Hills in Australia - more than 20 sites with Ediacaran fauna now known c. rocks dated to about 620 mya mya d. Variety of forms found from - soft-bodied - most resemble sponges, jellyfish, sea pens, comb-jellies i. - some may be worms (extremely rare) i. e. Dramatic increase in - occurs as get nearer the - reflects new modes of locomotion - reflect insurgence of f. Gap in the fossil record - sediments during interval appear to be - Predator dominance theory i. Rise of hunters * Ediacaran fauna unable to protect against new mobile predators * II. The Phanerozic Eon A. The Cambrian Explosion 1. Cambrian Period 2. Cambrian deposits suddenly full of diversity a. - Most famous fossil bed - British Columbia - discovered in 1909 by Charles Walcott b., from China - discovered more recently 3. Represents a. known major recognizable body plans found b. most forms - some Poriferan (sponge) and Cnidarian (e.g. sea pens, jellyfish) forms persist c. includes some body plans unknown from previous fossils or from extant taxa - grouped in the

3 d. Marrella - Cambrian shrimp-like crusteacean e. Leanchoilia, arthropod (crusteacean/scorpion/insect-like animal) f. Nectocaris: a probable arrow worm 4. How are fossils reconstructed? a. via comparison of extant species - some are very similar i. e.g. Aysheaia * ii. * - some unlike known taxa but have recognizable components i. e.g. Opabinia - some have proven difficult due to limited remains i. e.g. Anomalocaris - some just plain difficult i. e.g. Wiwaxia * Originally completely confounded * Recent theories suggesting mollusk * More recently assigned to ii. Hallucenagenia

4 5. (1980s & 1990s) a. estimates of the timing of the origin of lineages - estimates for earliest divergence times b. search for earlier fossils c. 6. Conditions causing Cambrian Diversification a. - allowed development of multicellular structures - allowed increase in - allowed increase in b. Increased - allowed - predation created selection gradient for - increase in hard body parts allowed for dramatic increase in 7. a. Major diversification of body plans associated with changes at genetic level - all multicellular organisms have system of organizing cells in space and time during development i.cells differentiate according to ii. Cells differentiate - how control of cell signaling acts as mechanism for evolution is among least well known areas b. What are Homeotic Loci? - genes that carry information for i. Typically refer to Homeotic genes in general as - Found in all animal phyla studied c. Hox loci are organized in gene complexes - occur together in

5 d. Correlation between - 3 end genes expresse d in - 5 end genes expresse d in - Deletion experiments demonstrate association of genes with segment specific expression e. All Hox genes contain bp sequence - Homeotic genes act as i.bind DNA of other loci f. Changes in Hox clusters led to major diversification - Hox gene homologs - Hox genes found even in jellyfish and sponges - likely that Hox genes - Can Map Hox gene condition to phylogeny of animals i.allows ii. Other genes likely arose - Can associate shifts in major taxa with i. Specific clusters associate with ii. e.g. addition of Abd-b g. Why don t we get new maj or mutant body plans continuing to show up? - It worked early when environment was wide open - ecological condition favor evolution of larger and more diverse body plans i. Favored use of ii. more efficient and complex * - eventually niche space becomes i. Competition for ii. Mutations seen as deleterious