While often grouped together in popular imagination, stingrays are not sharks. Despite their distinct appearances, these marine creatures share a deep evolutionary connection, stemming from a common lineage of ancient fish. Understanding their shared ancestry and unique characteristics helps clarify their relationship within the aquatic world.
A Shared Ancient Lineage
Stingrays and sharks belong to the Class Chondrichthyes, a group of jawed fish known for their skeletons primarily composed of cartilage instead of bone. Within Chondrichthyes, both sharks and stingrays are further categorized into the Subclass Elasmobranchii. This subclass also includes skates and sawfish.
The term “Elasmobranchii” itself refers to their broad, flattened gills. Members of this subclass possess five to seven pairs of gill slits that open individually to the exterior, a distinguishing feature. This shared anatomical foundation underscores why they are considered close relatives, despite their divergent evolutionary paths over millions of years.
Distinctive Features
Despite their shared lineage, sharks and stingrays exhibit clear physical differences. Sharks possess a streamlined, torpedo-shaped body, which is efficient for fast swimming through open water. In contrast, stingrays have a flattened, disc-like body, which allows them to camouflage themselves on the seafloor.
Their fins differ; sharks have distinct pectoral fins, used for steering and lift. Stingrays, however, have enlarged pectoral fins that are fused to their head, forming broad “wings” for movement. Shark mouths are positioned at the front or slightly underneath their heads, with gill slits located along their sides. Stingrays, adapted for bottom feeding, have both their mouths and gill slits positioned on their underside.
Another distinction lies in their tails. Sharks have caudal (tail) fins that provide thrust for propulsion. Stingrays possess a whip-like tail, equipped with a venomous barb for defense, and they primarily rely on their pectoral fins for movement rather than their tails. These adaptations reflect their differing preferred habitats, with sharks being pelagic, while stingrays are benthic.
Beyond the Basics: Other Common Traits
Beyond their cartilaginous skeletons, sharks and stingrays share several other biological features. Both possess a unique skin texture due to placoid scales, often referred to as dermal denticles. These small, tooth-like structures offer protection and reduce drag during movement through water.
Both also exhibit specialized sensory organs called Ampullae of Lorenzini, which are a network of jelly-filled pores around their snouts. These electroreceptors allow them to detect faint electrical fields, aiding in hunting prey and navigation, even when visibility is poor. Additionally, neither sharks nor stingrays possess a swim bladder, a gas-filled organ for buoyancy control. Instead, they maintain buoyancy through oil-rich livers and by continuous swimming to generate hydrodynamic lift.