Stingrays are not sharks, though often mistaken for them. While both groups inhabit marine environments and share some biological characteristics, they represent distinct evolutionary paths within a broader category of fish. This confusion stems from shared ancestry, but distinct differences in anatomy, behavior, and lifestyle set them apart.
Shared Evolutionary Roots
Stingrays and sharks belong to the class Chondrichthyes, a group of jawed fish distinguished by skeletons composed primarily of cartilage rather than bone. They are classified alongside chimaeras. Beyond this class, both sharks and rays are further grouped into the subclass Elasmobranchii, which also includes skates and sawfish. This shared lineage indicates a common ancestor millions of years ago.
The evolutionary split between sharks and rays is estimated to have occurred approximately 200 million years ago. Rays are believed to have evolved from ancient shark-like ancestors that adapted to a bottom-dwelling lifestyle. This divergence led to distinct body plans and ecological niches. Despite their outward differences, their cartilaginous skeletons and other shared features underscore their deep evolutionary connection.
Key Distinctions
Sharks and rays exhibit fundamental anatomical differences. Sharks typically possess a streamlined, torpedo-shaped body. Their gill slits are positioned laterally. Sharks primarily use their powerful caudal (tail) fin for propulsion. Their pectoral fins aid in steering and lift.
Rays, in contrast, have a flattened, disc-like body, with their large, wing-like pectoral fins broadly fused to their heads, forming a continuous disc. Their five pairs of gill slits are located on their ventral (underside) surface. Most rays propel themselves by undulating their pectoral fins. While many stingrays have a long, slender, whip-like tail that often contains venomous, serrated barbs, not all rays possess this feature.
Ecological roles also differ. Many ray species are benthic, meaning they live and feed on the ocean floor, preying on shellfish, crustaceans, and mollusks. They often use spiracles, small openings behind their eyes, to draw in water for respiration when buried in the sand. Sharks, while diverse in habitat, include many active predators that hunt in the open water.
Varieties of Rays
Stingrays represent one group within the diverse ray species. All rays fall under the superorder Batoidea, which encompasses over 600 species characterized by their flattened bodies and enlarged pectoral fins. This superorder is further divided into various orders, including Myliobatiformes, which contains true stingrays, eagle rays, and manta rays, and Rajiformes, which includes skates.
Skates are distinct from stingrays, featuring shorter, thicker tails that lack a venomous barb. Instead, skates often have thorny projections on their backs and tails for protection and reproduce by laying eggs encased in capsules known as “mermaid’s purses.” Manta rays are the largest rays, known for their wing-like fins and filter-feeding behavior, consuming plankton and small fish. They also lack a stinging barb.
Electric rays, belonging to the order Torpediniformes, possess specialized organs capable of generating powerful electric shocks for defense and to stun prey. Other ray types, such as eagle rays and cownose rays, exhibit unique adaptations like plate-like teeth for crushing hard-shelled prey.