Paleozoic Life

Invertebrates

• Major invertebrate phyla evolved in the Cambrian

• Trace fossils common• Echinoderms diverse• Trilobites, inarticulate

brachiopods, archaeocyathids –major skeletonized animals

Paleozoic Life – Introduction

• Tectonics important role on evolution– Opening and closing of ocean basins– Transgressions and regressions of epeiric seas

– Change positions of continents• Evolution– Skeletonized animals appear (PreЄ- Є boundary)– Marine invertebrates diversify – Vertebrates also evolved– Organisms move from water to land

• Major Extinctions (end of Paleozoic)– Marine invertebrate community– Many amphibians and reptiles on land

The First Shelled Fossils

• Mineralized skeleton appeared abruptly – Why?

– Cambrian organisms complex Multi-celled organism must’ve had pre-Є history Lacked hard parts; did not leave a fossil record

– Ediacaran Fauna (570-670 Ma)

– Skeletons of chitin, silica, & CaCO3

1st multi-celled organism

Early Cambrian Emergence of Shelly Fauna

• Low diversity

• Composed of CaCO3 & Ca3(PO4)2

• Fauna had fully developed features

– Anatomies indicate extended evolution

– Extended from Cambrian to Ordovician

Early CambrianShelly Fauna Abrupt Appearance

• Possible explanations

– Changes in ocean chemistry Deficient in Ca &

PO43- = no hard parts

Rejected; numerous carbonate rxs and phosphate deposits

– Invertebrates need to eliminate mineral matter

CambrianSkeleton Advantages

• Protect against UV radiation

– Move into shallower H2O

• Prevent dry out

• Protect against predators

• Skeleton for support; increase size

• Attachment site for muscles Injured Trilobite

Middle CambrianShelly Fauna

• Many invertebrate groups evolved– Brachiopods (still around)– Archeocyathids– Trilobites

• Cambrian Marine Community

Middle CambrianMarine Community

• Brachiopod– Primitive type

Inarticulate (chitin phosphate)

– Present type

Articulate

Hinged by muscles

• Archeocyathids

• Trilobites most common

– Benthonic, sessile, suspension feeder

– Made reef structure

– Benthonic, mobile, sed dep feeder, crawled or swam

• Echinoderms

Middle CambrianBurgess Shale

• Sauk Transgression

– Black, anoxic seds• Soft-bodied

organisms preserved– Fossils classified into

existing phyla– Most fossil in mid-Є,

but fewer species– Strange fossils– No living counterparts

– extinct?– Reassigned to known

phyla

Middle CambrianBurgess Shale

Cambrian Worm Cambrian WormCambrian Arthropod

Ordovician

• Major transgression warm water

• Reef Builders

• More abundant

– Increased diversity Epifaunal, benthonic,

sessile, susp feeders Articulated brachs

Bryozoans Tabulate/Rugose

corals Stromatoporids

Conodont - tooth like CaPO43-

Graptolite - plankton Acritarchs

Graptolites

Graptolites

End of Ordovician

• Mass Extinction– 100’s of families did not make it to Silurian

– 50% of brachiopods and bryozoans died

– Maybe glaciation in Gondwana

Silurian & Devonian

• Rediversification

• Major reef building

• Common guide fossils

– After Ordovician extinction

– Tabulate/rugose corals

– Stromatoporids

– Euryterids

– Ammonites

End of Devonian

• Mass Extinction (L. Frasnian – Famennian)– Lose most reefs– Decline of many organisms

Brachiopods, ammonites, acritarchs, gastropods, bryozoans

– Mostly tropical groups; not polar• Possible Causes

– Global cooling; Iapetus closing

Carboniferous & Permian• Rediversification

– After Devonian extinction

– Small, patchy reefs

– Brachiopods & ammonites

• Permian life restricted

Crinoids, blastoids, brachs, bryozoas

– Seas regressed

– Fusilinids diverse Mississippian AmmonoidPermian Fusilinid

End of Permian

• Mass Extinction– 50% marine families

90% marine invertebrates

– Regression

• Possible Causes

Less living area

– Pangaea forms Continental suturing

– Decreased S ‰ Arid climate Evaporite formation

Other Permian Extinction Possibilites• Climate Change

– Warming at close of Permian– More CO2 in atmosphere

• More volcanism

– Changes in ocean ciruculation brings CO2 to surface/atmosphere

• Meteorite Impact