1. Cambrian Explosion
Evolutionary Diversification mya

2. Cambrian
Explosion:
All major
body plans
first made
an appearance
in the fossil
record during
a 40 my period

5. Ediacaran Fuanas entirely soft-bodied organisms from 565 mya
Brachina delicata
Spriggina floundersi
(sponges, jellyfish, comb jellies)

6. New Fossil Finds are Pushing Back Estimates of Divergence Times
Fossil embryos
suggest precambrian
diversification of
bilateralians
(Xiao et al. 1998)
Possible flatworm or arthropod zygotes and embryos

7. Burgess Shale Faunas 520 mya
(trilobites, segmented worms, molluscs, chordates)

8. New Fossil Finds are Pushing Back Estimates Of Animal Divergence Times
(Shu et al.
1999)
530 my Cambrian vertebrate: Haikouichthys eraicunensis

9. Small subunit RNA
most basal
earliest fossils

10. Cambrian: Diversification of Animal
Body Plans
Symmetry
a. Radial or asymmetrical:
Diploblast (endoderm and ectoderm)
b. Bilateral:
Triploblast (endo, ecto, and mesoderm)
Coelomate
i. Protostomes
ii.Deuterostomes
Also: segmented body plans, shells,
exoskeletons, appendages, notochords

11. Was the Cambrian Explosion Explosive?
Molecular clock estimates suggest my divergence
times for the major animal groups (Wray et al., 1996).
i.e.
Major animal lineages were established pre - Cambrian.
if so
There should be fossil evidence!

12. What Caused the Cambrian Explosion?
Environmental change: Higher oxygen
may have allowed for larger, energetically
costly morphologies.
Diversification of phytoplankton may have
spurred the evolution of herbivores and
predators.
Genetic changes?
Cloudina

13. Stasis Is Evolution Too!
Darwin’s View
Punctuated Equilibrium
(Gould and Eldridge, 1972)

14. Jackson and Cheetham, 1994

15. Why Does Stasis Occur?
not for lack of
genetic variation
dynamic stasis
in pliocene bivalves

16. Extinction
Mass extinctions account for
4% of all extinctions
The big 5 of the
phanerozoic.

17. Iridium concentration
in clay layer at
KT Boundary
Other evidence:
Chicxulub crater
Microtektites
Soot deposits
Evidence of
tsunami

18. Habitat Destruction Human Population by 2050 = 13 billion
Current extinctions are occurring at times
the normal or background rate.
May et al. 1995, Pimm et al., 1995
Human Population by 2050 = 13 billion