Miss Grant
Kaimuki Christian School
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About 3 billion years after the first
prokaryotic cells evolved, organisms
remained single-celled
Scientists think multicellular eukaryotes
evolved from choanoflagellates (single-celled
eukaryotes that typically live in colonies)
Oldest evidence of multicellular life: 600
million year old fossils (eggs, embryos, trace
fossils)
Evidence shows the first animals began
evolving long before the Cambrian Explosion
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Ediacara Hills of Australia: where some of the
most important fossils explaining early
animal life came from
2 major Cambrian Fossil sites: Chengjiang,
China and the Burgess Shale of Canada
Fossils show that over 10-15 million years
animals evolved complex body plans
Cambrian animals evolved shells, skeletons,
and other hard body parts
Why do you think we have more fossils from
the Cambrian era than the pre-Cambrian era?
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Most abundant animals on Earth
Live in nearly every ecosystem
Present in nearly every food web
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The cladogram shows the proposed
evolutionary relationships among major
groups of modern invertebrates
Indicates sequence in which characteristics
evolved
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Porifera- sponges
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Cnidarians- jellyfish sea fans,
sea anemones, hydras, corals
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Arthropoda- spiders,
centipedes, insects,
crustaceans
Nematoda- nematodes
(round worms)
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Platyhelminthes- flatworms
Annelida- annelids
(earthworms, parasites,
leeches)
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Mollusca- snails, slugs, clams,
squid, octopi
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Echinodermata- sea stars, sea
urchins, sand dollars