Life in the Paleozoic Era

Chapter 13 Section 2

The Cambrian Period

• The Cambrian Explosion: a span of about 15 million years when many new types of invertebrates evolved.

• Fossils of life from the Cambrian period are found in a rock formation from the Canadian Rockies called the Burgess Shale

Charles Doolittle Walcott and the Discoveryof the Burgess Shale (1909)

Although the fossils are located high up in the Canadian Rockies today, 505 million years ago the area was covered by the sea. The Burgess Shale animals were preserved in a series of mudslides that instantly buried their thriving late Cambrian reef community. The amazing range of fossilized organisms that Walcott and his colleagues discovered at the Burgess Shale give us one of the best picture we have of what is known as the Cambrian Explosion—the burst of diversification and proliferation of animals that gave rise to the lineages of life as we know it today. In the Burgess Shale were found the first examples we have of trilobites, brachiopods, echinoderms, and others, including curious oddities that come from extinct lines.

• Hallucigenia

Marrella splendensCredit: Photo by Chip Clark, Smithsonian Institution.

The Cambrian Period

• Animals from the Cambrian Explosion include:• The 1st vertebrates• Mollusks with hard shells• Arthropods including the trilobite– 600 different types of trilobites lived during this

time• Early reefs that were made of remains of

sponges and mats of cyanobacteria. No coral yet!

Haikouichthys

The earliest known chordate- dating from the Cambrian- and possibly ancestor of all vertebrates on earth.

The Cambrian Period

• All life existed in the oceans at this time!

Pikia Pikia-chu

The Ordovician Period

• The diversity of ocean life increased including:• The 1st corals• Trilobites still alive, brachiopods became more

common• Jawless fishes evolved. They had large bony

plates covering their bodies. They would be the ancestors of later vertebrates

Bryozoans Brachiopods

Heterostraci

The Ordovician Period

• The first plants made it on to land at this time. They were small, non-vascular plants similar to liverworts. They reproduced with spores instead of seeds. These plants helped to add more oxygen to the earth’s atmosphere

Ordovician plants

The Ordovician Period

• The Ordovician ended with a mass extinction possibly caused by an ice age or by volcanoes.

The Silurian Period

• Reef-building corals evolved• The first fish with Jaws evolved from jawless

fishes that had survived the end-Ordovician extinction

• More diversity appeared in jawless fish• New arthropods like eurypterids evolved

Eurypterids

Agnathans

Birkenia – one of the first fish with jaws

The Silurian Period

• The 1st vascular plants on land• Trace fossils suggest that arthropods may have

moved on to land at this time.

The Devonian Period

• New life forms in the ocean included:• Bony fishes – jaws and skeletons• Sharks• Reefs continued to form in tropical seas

The Devonian Period

• On land, The 1st forests grew and were inhabited by wingless insects, spiders, and centipedes

• Amphibians evolved – most had both lungs and gills and lived in shallow pools near coastlines– Acanthostega and Tiktaalik are examples of early

amphibians

Tiktaalik

Acanthostega

The Devonian Period

• The Devonian period ended with 2 mass extinctions that killed off many species including jawless fishes and armored fishes

The Carboniferous Period

• The first reptiles evolved during the Carboniferous. These reptiles were able to move away from water because of the amniotic egg.

• Insects were dominant on land and much larger than today

1st Reptiles

The Carboniferous Period

• Vast swamps, called coal swamp forests, developed in tropical areas. These swamps would later form the coal deposits we use for energy today.

• Plants that make seeds also evolved during the Carboniferous

Carboniferous centipedes

The Permian Period

• Life on land and in the oceans became more diverse

• Conifer trees became more abundant• New insects, amphibians, and reptiles evolved

Helicoprion

The Permian Period

• Reptiles with mammal-like legs, skulls, and jawbones evolved during this time

• The dimetrodon had a large sail on its back which may have helped regulate body temperature

Mammal – Like Reptiles

The Permian Period

• The End-Permian Extinction occurred 250 million years ago.

• 96% of all species went extinct• Trilobites died out• Only a few mammal-like reptiles survived