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 - 543 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
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 - 550 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
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
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
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 - 180 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