Ediacarans, Small Shells and the Dawn of the Phanerozoic

Ediacarans,
Small Shells
and the Dawn
of the
Phanerozoic
Edicaran 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)Biota
Taphonomy of the
Edicaran Biota
• Soft/firm bodied?
• Molds and casts in coarse sandstone
• Facies preference?
• Taphonomic bias?
Radial and Bilateral
Symmetry
Radial Symmetry
Bilateral Symmetry and
Differentiated Structures
Symmetry and Diversity
Filter Feeders?
Differentiated Structures,
But Which End Was Up?
Significant Diversity or
Variations on a Single Theme?
Dawn of the Phanerozoic: Small
Shelly Fauna and Trilobites
What Do We Choose as the
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