The whale shark, \(Rhincodon\) \(typus\), is the largest fish in the world, often reaching lengths comparable to a school bus. Its common name, a combination of “whale” and “shark,” frequently causes confusion regarding its true biological identity. Despite its immense size and gentle, filter-feeding nature, the animal is fundamentally a shark, not a whale, and therefore is a fish, not a mammal. The scientific classification is based on specific physical characteristics that unequivocally place this giant within the evolutionary lineage of sharks.
Defining Characteristics of Sharks
Sharks are grouped into the class \(Chondrichthyes\), which includes all cartilaginous fishes, separating them from bony fishes. Unlike the skeletons of mammals and most other fish, a shark’s endoskeleton is composed almost entirely of flexible, calcified cartilage. This material is significantly less dense than bone, providing a lighter frame that aids in buoyancy. Sharks breathe using multiple external gill openings, typically five to seven pairs, that are not covered by a protective bony plate called an operculum. The exterior of a shark is also covered by dermal denticles, which are tiny, tooth-like structures that give the skin a rough, sandpaper texture.
Whale Shark Anatomy Confirming Classification
The whale shark possesses all the distinct anatomical features required for classification as a true shark. Like all members of the class \(Chondrichthyes\), the whale shark has a skeleton made of cartilage. This classification is further supported by the presence of five large, prominent gill slits located on the sides of its broad head. These gill slits contain specialized filter pads that function as a massive sieve, allowing the shark to process large volumes of water while retaining small prey. The whale shark also exhibits the cold-blooded metabolism common to all fish, and its body is equipped with two distinct dorsal fins and thick skin covered in placoid scales.
The ‘Whale’ Part of the Name
The “whale” part of the name is a reference to its colossal size and unique feeding strategy. Reaching lengths of up to 60 feet and weighing over 40,000 pounds, the whale shark rivals the size of many actual whale species. Early observers named the animal by drawing parallels between the world’s largest fish and the world’s largest mammals. The shared trait that cemented this comparison is filter feeding, as the whale shark, like baleen whales, consumes massive quantities of plankton by straining water through its mouth. The biological differences are profound: whales are mammals with bone skeletons and lungs, while the whale shark is a fish with a cartilaginous skeleton and gills.