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Ch. 30 - An Introduction to Animals
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoFreeman 8th EditionCh. 30 - An Introduction to AnimalsProblema 3
Capitolo 30, Problema 3

True or false?
New major animal body plans have continued to evolve since the Cambrian about 550 million years ago.

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1
Understand the concept of 'animal body plans': Animal body plans refer to the basic structural and functional design of an organism, including its symmetry, segmentation, and limb arrangement.
Review the Cambrian Explosion: The Cambrian Explosion was a period approximately 541 million years ago when most major animal phyla appeared in the fossil record. It is known for the rapid diversification of life forms.
Consider the evolutionary process: Evolution is a continuous process, but the emergence of entirely new major body plans is rare. Most changes involve modifications of existing plans rather than the creation of new ones.
Examine the fossil record: The fossil record provides evidence of the diversity and changes in life forms over time. It can help determine if new major body plans have appeared since the Cambrian period.
Evaluate scientific consensus: Scientists generally agree that while evolution continues to modify existing body plans, the appearance of entirely new major body plans has not been observed since the Cambrian Explosion.

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Cambrian Explosion

The Cambrian Explosion refers to a period approximately 541 million years ago when most major animal phyla appeared in the fossil record. This event is characterized by a rapid diversification of life forms, leading to the establishment of complex body plans. Understanding this period is crucial for assessing the evolution of animal body plans.
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05:10
Cambrian Explosion

Animal Body Plans

Animal body plans are the structural and functional designs of organisms, including symmetry, segmentation, and limb arrangement. These plans are established during embryonic development and are crucial for understanding evolutionary biology, as they determine the basic layout of an organism's anatomy.
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Body Axes

Evolutionary Stasis

Evolutionary stasis refers to periods in which little evolutionary change occurs in organisms' body plans. After the Cambrian Explosion, many animal body plans have remained relatively unchanged, suggesting a stasis in major evolutionary innovations. This concept helps explain why new major body plans have not emerged since the Cambrian period.
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History of Evolutionary Theory Example 1
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Domanda del libro di testo

To estimate the relative abundance of the major phyla, calculate how many named species of arthropods, mollusks, and nematode worms exist per named species of chordate (the phylum containing vertebrates, including humans; see Table 30.1).

Do you think these calculations are likely to be underestimates or overestimates? Why?

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Domanda del libro di testo

Which of these characteristics does not apply to cnidarians?

a. Are diploblastic

b. Possess a gastrovascular cavity with one opening

c. Undergo metamorphosis

d. Have a central nervous system

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Domanda del libro di testo

Why is it ecologically significant that animals are heterotrophic and multicellular?

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