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Lecture 10

BIOLOGY 1M03 Lecture Notes - Lecture 10: Burgess Shale, Ediacara Hills, Cambrian Explosion

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Jon Stone

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BIOLOGY 1M03- Chapter 27: Phylogenies and the History of Life Part 3
The Edicaran Fossils
The Ediacara Hills and associated formation in Australia, which date to 544-565 Ma,
contain fossils that researchers have interpreted as sponges, jellyfish, comb jellies, and
traces from other animals (e.g., burrows and tracks)
These were soft-bodied animals that burrowed in sediments, sat immobile on the sea
floor, or floated in the water
The Burgess Shale Fossils
The Burgess Shale formation in British Columbia, Canada, which dates to 515-525 Ma,
contain fossils that researchers have interpreted as representing almost every major
living animal group
These fossils indicate a tremendous increase in size and morphological complexity,
accompanied by diversification in how animals lived
This diversification filled many ecological niches still found in marine habitats today
What Triggered the Cambrian Explosion?
Increased oxygen levels
Novel niches
New genes (i.e., Hoxgenes)
Encode transcription factor protein product
Contain 60-amino-acid DNA-idig seuee hoeoo
Ehiit olieait i epessio
Many researchers predicted a strong association among the order in which animal
lineages appeared during evolutionary history, Hox genes present in each lineage, and
morphological complexity and body size
The logi ehid this e gees, e odies hpothesis was that existing homeotic
genes could have been duplicated before and during the Cambrian explosion, producing
new body plans and appendages
Data from animals generally support this hypothesis
The following conclusions can be inferred from the data:
o Hox clusters appear to have expanded during evolution
o Hox genes appear to have been duplicated, because the genes within clusters
are similar in structure and nucleotide sequence.
o Hox clusters were duplicated several times in the lineage leading to vertebrates.
o These changes in concert with changes in gene expression and function have
been important in elaborating animal body plans
27.4 Mass Extinction
A mass extinction is the rapid extermination over many lineages,. defined as a period
heei ≥% speies ae iped out ithi  illio eas
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