Figure 1
From: Diversity and repertoire of IgW and IgM VH families in the newborn nurse shark
Phylogenetic tree. Cartilaginous fish, which includes the Holocephali ratfish and Elasmobranch sharks, skates and rays, shared a common ancestry with the ray-finned and lobe-finned bony fishes 460 million years ago (MYA). Cartilaginous fish have been identified as the earliest extant vertebrate group with major components of the adaptive immune system, i.e., Ig, TCR and MHC.