BISC 102 Lecture Notes - Lecture 5: Burgess Shale, Anaerobic Respiration, Simple Living

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Animals (Not just mammals): Multicellular, eukaryotes, chemoheterotroph that
ingest/digest food: a monophyletic group
It obtains both energy and carbon by eating organic material
Sponges are most simple living animal
Endosymbiosis: Many corals and anemones incorporate living algae in tissues as
symbionts. Lichens too
2008 Discovery of East Coast USA: (solar powered sea slug). Uses chloroplasts taken
from its algal food source. Chloroplasts are divorced from free living ancestors
Timeline/O2 Curve:
Biological change was slow from the first 3.5 billion years
Biological change is more dramatic in last billion years (Ediacaran Biota) (565-544 mya)
Cambrian “Explosion”: Sudden and dramatic appearance of diverse and complex marine
animals (phyla) in the fossil record (but not familiar mammals, birds, insects, plants)
Many hypotheses for why animals diversity happened
1) Increased Oxygen
Aerobic respiration more efficient than anaerobic respiration and fermentation
(more ATP per glucose)
Evolution of increased metabolic efficiency allowed for larger and active
2) Predation
Cambrian Fauna
Body plans that allow motility (swimming/burrowing)
Defensive structures (ex. shells/spines)
Appendages for sensing prey and escaping (ex. eyes/antennas)
3) New niches/co-evolution
Evidence of animals burrowing under, living on, and swimming above sea
Species evolved in response to abiotic environment as well as other
organisms (ex. symbionts, food, parasites)
4) New genes produce new body plans
Evolution of Hox genes that play regulatory role in body development
Hox genes are master regulatory genes that turn other genes on/off
Small genetic changes can cause morphological responses
Long Fuse: Perhaps animals diversified gradually before the Cambrian but were suddenly
preserved in the fossil record during the Cambrian
Molecular clocks suggest most animal phyla diverged >600 mnya
Molecular clocks are used to estimate divergence dates (but mostly complicated)
Cambrian Fauna:
Marked the appearance of:
Most modern animals Phyla (Echinodermata, Arthropoda, Mollusca)
BIlateral symmetry
Diverse animal body plans (many extinct)
Present in several key fossils bed
Burgess Shale (BC)
Located near Field, BC
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