Multiple Choice
The last common ancestor of all animals was probably a _____.
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21. Evolution
Introduction to Evolution and Natural Selection
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What do all craniates have that earlier chordates did not have?
A
A post-anal tail
B
Pharyngeal slits
C
A notochord
D
A distinct skull enclosing the brain
Verified step by step guidance1
Step 1: Begin by understanding the term 'craniates.' Craniates are a subgroup of chordates that possess a distinct skull, which encloses and protects the brain. This is a defining feature that sets them apart from earlier chordates.
Step 2: Review the features of earlier chordates. Earlier chordates, such as lancelets and tunicates, have characteristics like a notochord, pharyngeal slits, and a post-anal tail, but they lack a distinct skull.
Step 3: Compare the features of craniates and earlier chordates. While both groups share common chordate traits (e.g., notochord, pharyngeal slits, post-anal tail), craniates uniquely possess a skull, which is a significant evolutionary advancement.
Step 4: Understand the evolutionary significance of the skull. The development of a skull in craniates provides protection for the brain and sensory organs, allowing for more complex behaviors and adaptations.
Step 5: Conclude that the correct answer is 'A distinct skull enclosing the brain,' as this is the key feature that distinguishes craniates from earlier chordates.
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