The Cambrian fauna 1. Sepkoski’s Curves 2. The Cambrian fauna 3. Small shelly fossils

1. 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

2. 1. Sepkoski’s Curves An analysis of shallow marine diversity through time Family diversity Cambrian fauna End Permian extinction Ordovician radiation Diversity = evolution - extinction

3. 2. Cambrian fauna Mud-eating trilobites and hyolithids Simple brachiopods Low tiering above or below sea floor

4. 3. Small shelly fossils Ma 510 Include diverse shapes and compositions Sometimes whole shells, eg primitive molluscs Sometimes parts of larger, cataphract organisms, eg Wiwaxia 520 530 540 Cambrian Precambrian 550

5. 4. Archaeocyathids Ma 510 Intervallum Pore-bearing outer wall Inner wall 520 Sole Cup-like forms, usually about 10 cm in height Could be solitary or colonial Probably sponges Calcareous skeleton Filter feeders 530 540 Cambrian Precambrian 550

6. 5. Trilobites Arthropods with diverse habits and modes of life Highly developed senses and head Trilobite diversity through time Segmented body and tail Cephalon

7. 6. Burgess Shale Middle Cambrian Canadian Rockies Preserved at base of a steep marine palaeoslope. Most of fauna has been transported off a reef Arthropods dominate fauna Abundant infauna including predatory worms

8. 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