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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Vertebrates evolved from primitive chordates. This occurred about 550 million years ago. The earliest vertebrates may have been jawless fish, like the hagfish in Figure below . Vertebrates evolved a backbone to replace the notochord after the embryo stage. They also evolved a cranium , or bony skull, to enclose and protect the brain. Answer: chordates
Output:
Vertebrates evolved from primitive forms of which creature?