Question

The ancestors of modern-day fish were vertebrate chordates. Vertebrate chordates are believed to have evolved from invertebrate chordates, which were similar to modern-day tunicates.

What change must have occurred during the evolution from invertebrate chordates to vertebrate chordates?

A.
A backbone evolved to enclose the spinal cord, which develops from the dorsal nerve cord.
B.
An endoskeleton evolved to enclose the dorsal nerve cord, which develops from the notochord.
C.
An endoskeleton evolved to enclose the spinal cord, which develops from the notochord.
D.
A backbone evolved to enclose the notochord, which develops from the spinal cord.

Answer 1

Its actually A. A backbone evolved to enclose the spinal cord, which develops from the dorsal nerve cord.

Step-by-step explanation:

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Vertebrates are chordates, but unlike invertebrate chordates, they have a backbone. Additionally, the dorsal nerve cord in vertebrates develops into a spinal cord. The front end of the dorsal nerve cord develops a brain.