Chapter 16 - History of Life

Notes for Understanding Evolution - Chapter 16

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Notes for Chapter 16: History of Life

Please browse these links for an overview of the history of life, emphasizing land vertebrates.

Introduction

I. Geological Ages

Note: Some of the dates listed in Table 16.1 (p. 175) are out-dated. In particular, scientists have been able to more accurately date the base of the Cambrian Period based on recent study of Siberian fossil deposits, and the Cambrian is now known to have begun about 543 MYBP, not 600 MYBP as listed in the text. Click here for a current division of the latest Precambrian, when multicellular animals first make their appearance as fossils, and here for a better breakdown of the Cambrian Period early in the Paleozoic Era, when more familar animals with skeletons first become abundant. See here for many links on the early evolution of animals (including some broken links), and here is a good article with images on what is currently known about the "Cambrian Explosion." It is important to realize that we are getting a much more complete view of the earliest appearance of animals with bilateral symmetry, based on what we now know about fossils of the latest Precambrian through to the about 520 MYBP Burgess Shale fauna, when almost all of the major animal groups still alive today had already become established.

RQUE16.1: Using the 12 hour clock analogy, where do the Burgess Shale animals fit in relative to other important milestones we have discussed, such as the first land animals, the first mammals, and the first humans?

II. Fossil Record of Plants

There are some links to ancient land plants here, and some links to the significance in the coevolution of land plants and their animal pollinators here.

RQUE16.2: What adaptations are especially important in the history of land plants?

III. Fossil Record of Animals

RQUE16.3: Why is the Burgess Shale fossil site of interest? These are not the earliest fossil animals known, so what is the significance of this fossil rich locality? What are some alternative ideas about what might have led to such a dramatic diversification of different kinds of animals.

IV. Convergence

See here for some links on Australian mammals.

RQUE16.4: How do Australian mammals illustrate the principle of convergence? What general biogeographic principles does this phenomenon suggest? (Hint: Think about ecological opportunities and the animals that fill them in different places, at different times.)

V. The Plains-Dwelling Mammals

See here for a brief description of the history of the Cenozoic Era or here for a more extensive discussion of important events influencing the biogeography of animals. This site is especially good for the last event.

RQUE16.5: Probably the two biggest North American events in the relatively recent past happened about 3 MYBP and about 10,000 YBP (0.01 MYBP). Describe what happened at each of these times, and how this influenced the diversity of mammals in N. and S. America.

VI. Extinction and Evolutionary Stability

See here or here for some links on extinction events.

RQUE16.6: What role have mass extinctions played in the history of animals? When were major extiction events and what important lineages went completely extinct (careful - remember what I said about birds)?

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