The Cambrian and Beyond
A. Types of Fossils
1. Compression & Impression fossils 2. Permineralized fossils 3. Casts & Molds 4. Unaltered remains – mummy
B. Sorting out the Fossil Record: Strengths & Weaknesses
1. Lowland and shallow marine bias 2. Hard part bias 3. Age bias 4. Goal is to recognize the constraints and still be creative
C. Cambrian Explosion Revisited – The Metazoan Body Plan
1. All animal phyla appeared in ~40 million years! 2. Symmetry – Diploblasts and Triplotblasts (Radial and Bilateral) a. Ecto/Endo vs Ecto/Endo/Mesoderm 3. Coelom or fluid filled cavity via mesoderm lined peritoneum a. Coelomates, pseudocoelomates, acoelomates 4. Protostomes (Ecdysozoans & Lophotrochozoans) and deuterostomes a. both have bilateral symmetry, true coeloms, 3 tissue types b. spiral cleavage vs. radial cleavage c. gastrulation – first the mouth or second the mouth 5. Notochords....
D. Ediacaran & Burgess Shale Faunas
1. Ediacaran – Soft bodies forms, many trace type fossils 2. Burgess Shale – Wide variety of body plans evolved, only a subset remained, fewer yet exist today.
Lecture 12.1 E. Phylogeny of Metazoans: New Ways to Make a Living
1. Environmental forcing functions, e.g., Oxygen Story 2. Genetic forcing functions, e.g., HOM/Hox genes
F. Macroevolutionary Patterns: Evolution’s Greatest Hits!
1. Adaptive radiations correlated with adaptive innovations giving rise to a number of descendant species that occupy a large range of niches. a. Lacking competitors over superior adaptations
2. Major Examples: ! Cambrian Explosion for animals ! Twice with land plants, Silurian/Devonian and Cretaceous
1. Darwin: aware of the problem, but wrote off as patchy record due to incompleteness of the fossil record.
2. Eldredge & Gould: New Theory describing process & pattern a. Dominant pattern of rapid morphological change followed by stasis in a lineage b. Predictive capability? Tough requirements:
! Known phylogeny, so direction of descent is known ! Ancestors must overlap with descendants in fossil record otherwise might be anagenesis (morph change w/o spp)
c. Don’t forget about cryptic spp (diff spp. w/o morph change) d. Stasis is data?
3. Stasis & speciation in Bryozoans revisited...
4. Habitat Tracking or Dynamic Stasis – Limulus crabs & Bivalves
Lecture 12.2 Mass Extinctions &Their Consequences
A. Background vs. Global Mass Extinction Events
1. Background Rates = 96% of all extinctions 2. Self-similar fluctuations using statistics 3. Phanerozoic average @ 26 Ma (if random) 4. Geographic range & larval life styles regarding specificity
B. The BIG FIVE of the Phanerozoic
1. Terminal Ordovician ca. 440 Ma 2. Late Devonian ca. 365 Ma 3. Permo-Triassic Boundary ca. 250 Ma 4. Terminal Triassic ca. 215 Ma 5. K/T Boundary ca. 65 Ma
C. The Permo-Triassic Boundary: The Mother of all Mass Extinctions
1. Came close to losing all multicellular life 2. Considered one of the four major advancements a. Origin of life b. Origin of multicellular life (Eukarya) c. Cambrian Explosion d. P/T Boundary Mass Extinction Event
3. Box score of exterminations: 96% of all spp. & 50% of all families a. 8 of 27 insects b. 21 of 27 reptiles c. 6 of 9 amphibians d. 70% of marine invertebrate genera including corals e. 1 major order of forams (the only time this happened!)
Lecture 12.3 4. Selectivity of the P/T
a. 35% cosmopolitan genera vs. 93% endemic genera went extinct (same pattern as background) b. END of the Trilobites as opposed to other marine arthropods
D. Multiple Causation Hypothesis aka “World-went-to-hell” hypothesis
1. Researchers tend to search for a single unified cause.....climate change, sea level change, oceanic anoxia, flood basalts, acid rain, etc. 2. As much as 5 Ma separation period 3. Bolide impact hypothesis?
E. K/T boundary – Impact extinction
1. 60 to 80% kill of all spp. a. END of the Ammonites as opposed to other marine mollusks b. Sea Urchins were selectively hit too c. Bivalves were less selectively hit, broad range survival
F. The Human Meteor
1. Pleistocene Megafauna of N. America vs. African Megafauna 2. Polynesian Birds are dropping like flies 3. Recovery & Replacement a. Lazarus taxa hiding out in refugia 4. Fortuitous Contingency of Magnetars 1998 & 1999!
Lecture 12.4