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Ch. 25 - Phylogenies and the History of Life
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All textbooksFreeman 8th EditionCh. 25 - Phylogenies and the History of LifeProblem 15

Chapter 24, Problem 15

Which traits do not correlate strongly with diversification rate within phyla, but are likely to have been important in the original diversification of animal phyla during the Cambrian? Select True or False for each trait. T/F presence of a head T/F mobile lifestyle T/F terrestrial lifestyle T/F bilateral symmetry

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Hi everyone here's our next question. A major part of the fossil records is made up of calcium carbonate and calcium phosphate. Coming from the animals blank that had evolved during the Cambrian period. So let's look through our answer choices here. Choice A says external skeletons. Well that is our correct answer choice. Um During the Cambrian period in the early Cambrian animals evolved oops external skeletons both to protect and support their bodily tissues. And these external skeletons were composed of calcium carbonate and calcium phosphate. And the structures of these external skeletons, shelves, tubes and spines do compose the major part of the fossil record. So external skeletons is our choice here. But let's just look through the other answer choices. Choice B. Says digestive system. Well the digestive system is obviously soft tissue doesn't contain calcium. So it's not found in fossil records. I accepted very very circumstances where you had you know odd sort of preservation of something but definitely not the major part of the fossil record. So choice be not our answer choice. C skull the skull is bone. It does contain calcium phosphate. Uh So we do find plenty of fossil skulls but not the major part of the fossil records. They're just kind of a small percent. So not our answer here. And choice D. D. N. A. Um D. N. A. Is not going to contain calcium. So not going to be a candidate here. Um Sometimes you find small amounts of DNA left in bone or teeth but again not made up of calcium carbonate and calcium phosphate, definitely not a major part of the fossil record. So the major part of the fossil records made up of calcium carbonate and calcium phosphate coming from animals choice. A external skeletons evolved during the Cambrian period. See you in the next video.
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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? Based on your reading of this chapter, propose at least five traits that you think might have been most important in triggering diversification within phyla (examples: origin of hearing, origin of internal fertilization).

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? Jezkova and Wiens used a type of graph called a linear regression to find correlations between variables such as the proportion of species per phylum with legs (on the y-axis) and the diversification rate per phylum (on the x-axis). Sketch a graph to show what a strong positive correlation between these two variables would look like and what the absence of a correlation would look like.

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? A sample of Jekova and Wiens' results is shown here. The R2 value represents the strength of the correlation (where 0.00 is lowest and 1.00 is highest). The P value represents the statistical significance. Which five traits look most important?

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Textbook Question

The vast majority of animals that ever existed are now extinct, but Tereza Jezkova and John Wiens wondered which variables were most important in driving the diversification of species that exist today. Why are there so many species in some phyla, such as Cnidaria (see photo), but so few in others, such as Ctenophora? The researchers know that correlation does not equal causation. However, can the absence of a correlation enable you to reject a hypothesis of causation? How would the R2 values be different in a scenario where a single trait was important to diversification in many phyla versus a scenario where different traits were important to diversification in different phyla?

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