The Cambrian Explosion

The Cambrian Explosion

Kingdom Animalia eukaryotic,

multicellular, heterotrophic feed by ingestion Animal Evolution Non-molting vs. Molting

Embryonic Mouth Formation Body Symmetry Organs vs. non-organs or Tissues vs. non-tissues

Kingdom Animalia Most animals have: Sense organs Nervous system Muscles Digestive tract

Sex organs Brief History of the World 1) Hadean Eon4.63.8 BYA -Earth & Moon formed as solid bodies 2) Archean Eon3.82.6 BYA

-Origin of Life -Origin of Prokaryotes -Fermentation -Photosynthesis Brief History of the World 3) Proterozoic Eon2.60.57 BYA

-Continental Drift begins -O2 Revolution -Krebs Cycle -Origin of Eukaryotes -Cryogenian period snowball earth 720635 MYA -Ediacaran Periodfirst multicellular animals

Precambrian (Ediacaran) Fossils 635-541 MYA All soft bodiedpoor fossil record Brief History of the World 4) Phanerozoic Eon0.54Today

Cambrian Explosion -First skeletal remains -Origin of most major multicellular phyla THE CAMBRIAN EXPLOSION

(490-543 MYA) ~ 35 animal phyla originated in ~ 50 million yrs Early Cambrian Fossils

New Cambrian fossil Nature Feb.24, 2011 Two Major Questions Why and when did multicellularity arise? What caused the Cambrian Explosion?

Multicellularity (>700 MYA) Advantages of Large size Cell specialization (Division of labor)

Humans Birds Amphibians Dinosaurs Fish

Cephalopods Echinoderms Arthropods Jellyfish Sponges Science Nov. 6, 2015

Multicellularity (>700 MYA) Multicellularity originated When unicellular organisms stayed together after cell division Originated many times

What Caused the Cambrian Explosion? What Caused the Cambrian Explosion? 1)There was a real explosion.

(i.e. In a few million years all major phyla evolved from protozoans) Why? What Caused the Cambrian Explosion?

2) Major forms were already present. They were small and without skeletons. Did not fossilize well. Then at the Cambrian they increased in size and developed skeletons. --DNA evidence supports this view

What Caused the Cambrian Explosion? What could have prompted increase in animal diversity, increased size and skeletal development? Three explanations:

Environmental Developmental Ecological What Caused the Cambrian Explosion? Environment:

1) Sea chemistry change. Shift towards high calcium carbonate and high pH would encourage biomineralization calcium based skeletons. Nature 6/4/2017 2) Oxygen revolution (Large size and active metabolism requires

large amounts of oxygen to generate large amounts of ATP via the mitochondria.) Oxygen Revolution What Caused the Cambrian Explosion?

Development: Genetic modifications might have caused major change in development into embryo thus to adults. Horizontal gene transfer of genes coding for biomineralization occurred from bacteria to sponges occurred allowed skeletal development.

What Caused the Cambrian Explosion? Ecological: Arms race between predator and prey led to diversity of attack (e.g. teeth and rapid swimming ) and defense strategies like burrowing and exoskeletons = co-evolution

Lets Look at the Burgess Shale Great Cambrian Fossils THE BURGESS SHALE GREAT CAMBRIAN FOSSILS


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