Whale sharks are the largest living non-mammalian vertebrate known in the world as its scientific name Rhincodon typus indicates typus means typical and rhinos and kodon refers to the cartilaginous plates which serve as filter-feeders. While they often get their name as a type of whale due to their size the name shark comes from their classification due to having a cartilaginous skeleton, five to seven-gill slits on the sides of their head, and pectoral fins that aren't fused to their heads. Their cartilaginous skeletons mean there is only the skull that fossilizes.