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Ch. 34 - The Origin and Evolution of Vertebrates
Campbell - Campbell Biology 12th Edition
Urry12th EditionCampbell BiologyISBN: 9785794169850Not the one you use?Change textbook
Chapter 34, Problem 4

In Figure 34.25, which of the following is the sister taxon to the archosaurs?
a. Synapsids
b. Crocodilians
c. Turtles
d. Lepidosaurs

Verified step by step guidance
1
Understand the concept of a sister taxon: In phylogenetics, a sister taxon refers to the closest relative or group to another taxon in a phylogenetic tree. They share a common ancestor that is not shared with any other group.
Review the phylogenetic tree in Figure 34.25: Locate the archosaurs on the tree. Archosaurs typically include birds and crocodilians.
Identify the branching point: Look for the node where the archosaurs branch off from other groups. This node will help you determine which group is the sister taxon.
Compare the options: Examine each of the given options (synapsids, crocodilians, turtles, lepidosaurs) and see which one shares the most recent common ancestor with archosaurs.
Select the correct sister taxon: Based on the tree structure, choose the group that is directly connected to the archosaurs at the branching point, indicating they are sister taxa.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phylogenetic Trees

Phylogenetic trees are diagrams that depict the evolutionary relationships among various biological species based on similarities and differences in their physical or genetic characteristics. Each branch point represents a divergence from a common ancestor, and sister taxa are groups that share an immediate common ancestor.
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Building Phylogenetic Trees Example 2

Archosaurs

Archosaurs are a group of diapsid reptiles that include birds, crocodilians, and extinct dinosaurs. They are characterized by specific skull and limb features. Understanding their evolutionary relationships helps in identifying their sister taxa, which are groups that diverged from the same ancestral node.

Sister Taxa

Sister taxa are two groups or species that are each other's closest relatives, sharing a most recent common ancestor. In phylogenetic trees, they are depicted as branches that split from the same node, indicating a close evolutionary relationship. Identifying sister taxa involves analyzing shared traits and genetic data.
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Parts of a Phylogenetic Tree
Related Practice
Textbook Question

Vertebrates and tunicates share

a. Jaws adapted for feeding

b. A high degree of cephalization

c. An endoskeleton that includes a skull

d. A notochord and a dorsal, hollow nerve cord

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Textbook Question

Living vertebrates can be divided into two major clades. Select the appropriate pair.

a. The chordates and the tetrapods

b. The urochordates and the cephalochordates

c. The cyclostomes and the gnathostome

d. The marsupials and the eutherians

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Textbook Question

Unlike eutherians, both monotremes and marsupials

a. Lack nipples

b. Have some embryonic development outside the uterus

c. Lay eggs

d. Are found in Australia and Africa

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Textbook Question

As hominins diverged from other primates, which of the following appeared first?

a. Reduced jawbones

b. An enlarged brain

c. The making of stone tools

d. Bipedal locomotion

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Textbook Question

Which of the following could be considered the most recent common ancestor of living tetrapods?

a. A sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates

b. An armored, jawed placoderm with two pairs of appendages

c. An early ray-finned fish that developed bony skeletal supports in its paired fins

d. A salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes

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Textbook Question

Living members of a vertebrate lineage can be very different from early members of the lineage, and evolutionary reversals (character losses) are common. Give examples that illustrate these observations, and explain their evolutionary causes.

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