While the classic image of a shark is a streamlined, torpedo-like form, not all sharks conform to this design. The diversity within the cartilaginous fish class (Chondrichthyes) includes a lineage of shark that has developed a body plan so dramatically flattened that it is often mistaken for a ray. This visual confusion highlights the powerful influence of lifestyle on physical evolution.
The Specific Shark Family Resembling Rays
The shark that most strikingly resembles a stingray belongs to the order Squatiniformes, commonly known as Angel Sharks. These animals are the sole members of the family Squatinidae, comprising over 20 known species globally. They inhabit the sandy and muddy bottoms of temperate and tropical seas worldwide, from shallow coastal waters down to depths of 1,300 meters. Angel Sharks are masters of camouflage, using their flattened body as an adaptation to their role as ambush predators. Their physical appearance features a broad, flattened anterior body that tapers to a muscular tail, and their enlarged pectoral and pelvic fins allow them to bury themselves just beneath the sediment.
The eyes and prominent spiracles, which are respiratory openings, are located on the dorsal surface of the flattened head. This positioning allows the shark to keep watch for prey and draw in water for respiration while remaining hidden in the substrate. When a small fish or crustacean ventures too close, the Angel Shark rapidly snaps its extensible jaws upward to capture the meal.
Shared Adaptations: Why They Look Alike
The visual similarity between Angel Sharks and true rays is a textbook example of convergent evolution. This occurs when unrelated organisms develop similar traits due to adapting to similar environments. Both groups occupy the benthic zone—the bottom of the ocean—which requires a specific set of physical tools for survival.
The flattened, or dorsoventrally compressed, body shape is a key adaptation to this bottom-dwelling lifestyle. This morphology provides a significant advantage for remaining inconspicuous on the seafloor, helping both rays and Angel Sharks effectively ambush prey. The broad, expanded pectoral and pelvic fins allow the animal to rest securely on the substrate.
Fossil evidence indicates that the distinctively flattened shape of the Angel Shark was established early in its evolutionary history, dating back approximately 160 million years. The specialized fins are also used for quick, powerful bursts of movement to launch upward from the sand when attacking prey.
Defining Features: Shark vs. Ray Anatomy
Despite their striking visual resemblance, the Angel Shark is scientifically distinct from true rays. The differences are rooted in comparative anatomy, starting with the placement of the gill slits, which extract oxygen from the water. Rays, which belong to the superorder Batoidea, have five pairs of gill slits located entirely on the ventral, or underside, surface of their bodies.
In contrast, Angel Sharks, like all other sharks, have their five gill slits positioned on the sides of their head, just in front of their large pectoral fins. Although the Angel Shark’s head is flattened, the lateral placement of these respiratory openings maintains its classification as a shark. This anatomical difference is a fundamental marker that separates the two groups.
A second defining feature is the attachment of the pectoral fins to the head. In all true rays, the enlarged pectoral fins are fused directly to the side of the head, creating the characteristic disk-like outline. Angel Sharks, however, have pectoral fins that are separated from the head by a distinct gap. Furthermore, rays possess a mouth located on the underside of the body, whereas Angel Sharks retain a sub-terminal mouth positioned near the front of the head.