Links between major classes of vertebrates have been established primarily by who?

Links between major classes of vertebrates have been established primarily by scientists and researchers in the fields of Paleontology, comparative anatomy, and molecular Biology. Notable figures include Charles Darwin, who proposed evolutionary relationships, and more recently, researchers using genetic and fossil evidence to illustrate connections. The use of phylogenetic trees and cladistics has also played a significant role in understanding these relationships. Overall, it's a cumulative effort from many scientists over time.