Ediacarans, Ediacarans, Small Shells Small Shells

and the Dawn and the Dawn of the of the

PhanerozoicPhanerozoic

Edicaran BiotaEdicaran Biota• First fossils of multicellular organisms• Some controversy

– Multicellular life?– Colonies of single cells?

• Definitely not single cells• Signs of tissue differentiation• Advanced symmetry

Ediacaran (Vendozoan)BiotaEdiacaran (Vendozoan)Biota

Taphonomy of theTaphonomy of theEdicaran BiotaEdicaran Biota

• Soft/firm bodied?• Molds and casts in coarse sandstone• Facies preference?• Taphonomic bias?

Radial and Bilateral Radial and Bilateral SymmetrySymmetry

Radial SymmetryRadial Symmetry

Bilateral Symmetry and Bilateral Symmetry and Differentiated StructuresDifferentiated Structures

Symmetry and DiversitySymmetry and Diversity

Filter Feeders?Filter Feeders?

Differentiated Structures, Differentiated Structures, But Which End Was Up?But Which End Was Up?

Significant Diversity or Significant Diversity or Variations on a Single Theme?Variations on a Single Theme?

Dawn of the Phanerozoic: Small Dawn of the Phanerozoic: Small Shelly Fauna and TrilobitesShelly Fauna and Trilobites

What Do We Choose as the What Do We Choose as the Start of the Cambrian?Start of the Cambrian?

• Extinction of the Ediacarans?• First appearance of the ”small shelly fauna”?

– Late Proterozoic• First trilobites? – Part of “Cambrian Explosion”

– Lower, but not lowest Cambrian• First trace fossils of trilobites?• First evidence of mobility (burrows)?• First burrows chosen