Chapter Study Questions 1. Know what constituted the \"Cambrian explosion of lif

Question

Chapter Study Questions

1.

Know what constituted the "Cambrian explosion of life" and be able to describe the

fossil record of the Early Cambrian fauna.

2.

Understand how life evolved during the Middle and Late Cambrian Periods.

3.

Be able to describe the Tommotian and Burgess Shale fauna.

4.

Know what major forms of life expanded in the Early Ordovician Period.

5.

Know what constituted the great Ordovician r

adiation of life and be able to describe

the fossil record of the Middle and Late Ordovician fauna.

6.

Understand how ecological tiering became more prevalent in Ordovician

communities.

7.

What unique properties do both bryozoans and rugose coral possess

that allowed

them to dominate Ordovician reef communities?

8.

What evidence exists from the fossil record that predation became a particularly

powerful selective pressure in evolution of marine life?

9.

Know what evidence suggests the appearance of the first

land plants.

10.

Know the evidence for the brevity of the period of glaciation at the end of the

Ordovician Period.

11.

Be able to describe the characteristics of the mass extinctions that ended the

Ordovician Period.

12.

Understand the events of the Taconic

orogeny on the eastern margin of Laurentia.

13.

What evidence exists that terranes were accreted to the NE margin of the continent

during Ordovician time?

14.

Know the patterns of deposition in western Laurentia near the end of Ordovician

time.

15.

Be able

to describe the depositional environment, diversity of life preserved, and

uniqueness of preservation in the fossils of the Burgess Shale and Chengjian biotas.

16.

Be familiar with now extinct organisms from the Early Paleozoic, such as the

archaeocyathi

ds, helicoplacoids,

anomalocariids

, lobopodians

and hyolithids

– and

suggest some affinities with extant group

Explanation / Answer

1. The Cambrian explosion is the morphological imbalance and evolutionary stasis displayed by Cambrian fauna. Representatives of several phyla are exclusively soft-bodied fossils were appeared. The lower Cambrian sediments near Chengjiang, China have preserved soft tissues. Large and soft-bodied organismslike the Ediacaran fauna (565 to 548 Ma) is a distinctive group which have been discovered from around the world. During the Vendian period (650-544 Ma) they had global distribution. They are only fossil markings and not truly fossilised organisms.

2. The Cambrian Period is the first geological time period of the Paleozoic Era(500-570my). It is marked a dramatic burst of evolutionary changes in life on Earth, known as the "Cambrian Explosion." The animals that evolved during this period were the chordates: animals with a dorsal nerve cord; hard-bodied brachiopods, which resembled clams; and arthropods — ancestors of spiders, insects and crustaceans. Trilobites become the most dominate organism of the Cambrian period. In the Burgess Shale 12 pieces were there.

3. Tommotian Fauna is the first organism to have mineralized body parts. It was appear at the beginning of the Cambrian period. They appear in the rock record with considerable diversity. Charles Walcott discovered an outcrop of shale that contained perhaps the most important fossils ever found i.e the Burgess Shale. The fossils were from the time of Cambrian explosion.

4. Ordovician period is from Paleozoic Era(430-500 My). The major life from that period were Trilobites and Graptolites. The rocks of the Ordovician period contain abundant remains of past life. The first fish appeared in that period.

5. The Ordovician radiation may have been an event independent of the Cambrian radiation and thus requiring a different set of explanations. This event is unique in homotypic, ecologic and biogeographic aspects. The Ordovician radiation represents an acceleration of diversification following the initially slow growth of the Paleozoic Fauna in the Cambrian.

6. The ecological tiering levels reached 1 m depth in the Ordovician period.

7. The Ordovician radiation included groups as phylogenetically disparate as corals, and bryozoan. These are the only phylum to have originated in the post-Cambrian.

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