o Cell junctions, Nerve & Muscle cells.
o Sexually reproduce with life cycle of
Embryonic stages. o Developmental
o Gametes alone represent haploid stage of life cycle.
Section 20.2 – Animal diversification began more than half a BYA.
(Billion years ago)
Oldest accepted animals are known/found to be 575-550
MYA. (Ediacaran period) o Discovered in 1940’s in
o Similar found in Asia, Africa & North America.
o Impressions of soft body animal’s 1cm-1m in length.
Invertebrates (Sponges, Cnidarians) do not appear to be closely related to any living organism.
Animal diversification rapidly accelerated from 535-525 MYA.
Cambrian animals had hard body parts such has shells & spikes.
(Related to existing animal groups)
o 1/3 of species found in Burgess Shale are Arthropods
(Crab, shrimp, insects) o Member of our phylum, Chordata.
(Hallucigenia & Anomalocaris).
What created Cambrian Explosion Hypothesis:
Increase complex predator-prey relationship
Increase in atmospheric o