The ancestors of modern-day fish were vertebrate chordates

Last updated: 7/9/2022

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