Cambrian diversification

Above the Ediacaran / Cambrian boundary

• A series of three events marks the life evolution just above the Ediacaran /Cambrian boundary

• They happened in the WHAT

• Overall, resulted in a major WHAT of life forms

Above the Ediacaran / Cambrian boundary

• A series of three events marks the life evolution just above the Ediacaran /Cambrian boundary

• They happened in the LOWER CAMBRIAN

• Overall, resulted in a major DIVERSIFICATION of life forms

Evolution of the first shelly fauna and the oldest reef builders

• Abundant WHAT fossils start occurring in the fossil record during the WHAT stage

• They are also known as “WHAT”

Evolution of the first shelly fauna and the oldest reef builders

• Abundant SHELLY fossils start occurring in the fossil record during the TOMMOTIAN stage

• They are also known as “Tommotian fauna”

What are the Tommotians

• small-sized WHAT, which commonly are less than WHAT millimetres in maximum dimensions

• Most of them are WHAT, but some can be recognized as WHAT

• The mineralogical/chemical compositions show that the WHAT and WHAT ones dominated

What are the Tommotians

• small-sized SHELLS, which commonly are less than 5 millimetres in maximum dimensions

• Most of them are ENIGMATICAL, but some can be recognized as MOLLUSCS

• The mineralogical/chemical compositions show that the CALCITE and SILICEOUS ones dominated

Changes produced by tommotians

• At the time of the evolution of the tommotians, the Earth was a “WHAT world.”

• Some of the tommotians were WHAT, and just like today, it seems they used to feed on WHAT

• A significant numerical reduction of the WHAT is encountered after the evolution of the tommotians

Changes produced by tommotians

• At the time of the evolution of the tommotians, the Earth was a “STROMATOLITE world.”

• Some of the tommotians were GASTROPODS, and just like today, it seems they used to feed on STROMATOLITES

• A significant numerical reduction of the STROMATOLITES is encountered after the evolution of the tommotians

The first true reef builders

• Stromatolite reduction resulted in the occurrence of new empty WHAT, and under these circumstances we witness the evolution of the first (oldest) WHAT

The first true reef builders

• Stromatolite reduction resulted in the occurrence of new empty ECOLOGICAL NICHES, and under these circumstances we witness the evolution of the first (oldest) REEF BUILDERS

The first true reef builders

• They were WHAT known as WHAT (class WHAT)

The first true reef builders

• They were CALCAREOUS SPONGES known as ARCHAEOCYATHIDS (class ARCHAEOCYTHA)

Archaeocyathids - mode of living

• Cup-like WHAT, which were of small dimensions, in general, up to a few WHAT in height

Archaeocyathids - mode of living

• Cup-like CALCAREOUS SPONGES, which were of small dimensions, in general, up to a few CENTIMETERS in height

Archaeocyathids - mode of living

• Lived attached to the WHAT with a WHAT-like structure

Archaeocyathids - mode of living

• Lived attached to the SEA FLOOR with a ROOT-like structure

Archaeocyathids - mode of living

• WHAT organisms and exclusively WHAT; never colonizes waters of low WHAT

Archaeocyathids - mode of living

• SOLITARY organisms and exclusively MARINE; never colonizes waters of low SALINITY

Archaeocyathids - distribution

• Evolved in the WHAT times and remain abundent for the rest of the WHAT

• Very rare in the WHAT

• Only one report from the WHAT

Archaeocyathids - distribution

• Evolved in the LATE TOMMOTIAN times and remain abundent for the rest of the EARLY CAMBRIAN

• Very rare in the MIDDLE CAMBRIAN

• Only one report from the LATE CAMBRIAN

Archaeocyathids : Key morphological features

• WHAT wall

• WHAT wall

• WHAT

• WHAT

Archaeocyathids : Key morphological features

• OUTER wall

• INNER wall

• SEPTA (sing = septum)

• INVERVALLUM

Atdabanian diversification

• Mostly associated with the evolution of WHAT

• Other groups were in the process of WHAT

Atdabanian diversification

• Mostly associated with the evolution of TRILOBITES

• Other groups were in the process of DIVERSIFICATION (e.g., brachiopods, echinoderms, other arthropod groups,
  poriferans).

Trilobites - Key morphological terms

• WHAT

• WHAT

• WHAT

• WHAT

Trilobites - Key morphological terms

• Cephalon

• Thorax

• Pygidium

• Axial and lateral pleural zones

Cambrian diversification

Herein, it is detailed with two cases of exceptional fossil preservation

• WHAT

• WHAT

Cambrian diversification

Herein, it is detailed with two cases of exceptional fossil preservation

• Burgess Shale

• Chengjiang fauna

Burgess Shale (BC canada)

• WHAT diversification and experimentation

Burgess Shale (BC canada)

• INVERTEBRATE diversification and experimentation

Chengjiang fauna (Yunnan china)

• Evolution and diversification of WHAT and WHAT

Chengjiang fauna (Yunnan china)

• Evolution and diversification of CHORDATES and VERTEBRATES

Burgess shale

• age: WHAT

• Sedimentation at the WHAT; submarine landslides triggered by WHAT led to the rapid burial of (mostly) WHAT

• WHAT conditions at certain stratigraphical levels prevented the occurrence of WHAT

Burgess shale

• age: MIDDLE CAMBRIAN

• Sedimentation at the SLOPE BASE; submarine landslides triggered by EARTHQUAKES led to the rapid burial of (mostly) INVERTEBRATES

• ANOXIC conditions at certain stratigraphical levels prevented the occurrence of SCAVENGERS

Chengjiang fauna

• age: WHAT

• Sedimentation onto the WHAT in relatively WHAT conditions

• Document the evolution of the earliest WHAT and WHAT in a highly diverse WHAT and WHAT assemblage

Chengjiang fauna

• age: EARLY CAMBRIAN

• Sedimentation onto the SHELF in relatively QUIET conditions

• Document the evolution of the earliest CHORDATES and VERTEBRATES in a highly diverse ANIMAL and ALGAL assemblage