Question

At one time, chondrichthyes were thought to have split off from other vertebrates before the evolution of bone. now we have concluded that the chondrichthyes split off after the evolution of bone had started. this change demonstrates ________. at one time, chondrichthyes were thought to have split off from other vertebrates before the evolution of bone. now we have concluded that the chondrichthyes split off after the evolution of bone had started. this change demonstrates ________. cartilage contributes to keeping sharks light so they do not sink evolution is one-way and straight line characteristics can be lost in evolution hagfishes and lampreys have ancestors with bone

Answer 1

This change demonstrates that some characteristics can be lost in evolution.
In the case of Chondrichthyes, boneless fish like sharks and rays, the skeleton made out of bones that were present in the common ancestor of them and other vertebrates was slowly changed for cartilage which enabled these fishes to move agiler in the water.