The Cambrian fauna

1. Sepkoski’s Curves

2. The Cambrian fauna

3. Small shelly fossils

4. Archaeocyathids

5. Trilobites

6. Burgess Shale

7. Ecological overview

1. Sepkoski’s Curves

Family diversity

End Permian extinctionOrdovician radiation

Cambrian fauna

Diversity = evolution - extinction

An analysis of shallow marine diversity through time

2. Cambrian fauna

Mud-eating trilobites and hyolithids

Low tiering aboveor below sea floor

Simple brachiopods

3. Small shelly fossils

550

510

520

530

540

Precambrian

Cambrian

Ma

Include diverse shapes and compositions

Sometimes whole shells,eg primitive molluscs

Sometimes parts of larger, cataphract organisms, eg Wiwaxia

4. Archaeocyathids

Cup-like forms, usually about 10 cm in height

Could be solitary or colonial

Probably sponges

Calcareous skeleton

Filter feeders

550

510

520

530

540

Precambrian

Cambrian

Ma

Intervallum

Pore-bearing outer wall

Sole

Inner wall

5. Trilobites

C.

Hypostome,mouth locatedat rear. InCalymene thehypostomewas fixed tothe front ofthe cephalon.

Leg/gill pairs. One pair for eachsegment in the thorax, probablythree under the cephalon andseveral vestigial ones under thepygidium.

Central groove between legs.Food was probably manipulatedby the legs into this groove andthen moved to the mouth. Thefirst leg segments are serratedto provide gripping and tearingfunctions.

Antennae

Pygidium

Thorax

Pygidium

Arthropods with diverse habits and modes of life

Highly developed senses and head

Segmented body and tail

Trilobite diversity through time

Cephalon

6. Burgess Shale

Middle Cambrian Canadian Rockies

Arthropods dominate fauna

Preserved at base of a steep marine palaeoslope.Most of fauna has been transported off a reef

Abundant infauna including predatory worms

7. Ecological overview

1. Cambrian sees massive increase in diversity due to introduction of hard parts

2. Diversity plateaus at about 100 families

3. Dominated by mud-grubbers and food chains based on them

4. Low faunal tiering may have inhibited diversity, but archaeocyathids were reef builders

5. Faunal interpretations based on Burgess Shale suggest greater complexity.

6. Declined gradually though Ordovician and were badly affected by end Ordovician mass extinction