Are Stingrays Related to Sharks? Rays and Their Cousins

How are stingrays and sharks related?

Fish with skeletons made of cartilage form the class Chondrichthyes, which means “cartilage fish”. This class has two main branches. The smaller one holds the chimaeras, also called ghost sharks or ratfish, deep-sea fish with smooth skin and a single gill opening on each side. The larger branch is the subclass Elasmobranchii, which holds the sharks on one side and the rays on the other.

The ray side, called Batoidea or Batomorphi, includes stingrays, skates, electric rays, guitarfishes, wedgefishes and sawfishes. It is actually the bigger of the two groups. A 2021 global assessment covered about 610 species of rays, about 540 sharks and about 50 chimaeras. You can read more about shark diversity in how many species of shark are there?

The oldest known ray fossils, from Germany, are about 185 million years old, so rays and sharks have been evolving separately for at least that long.

What do stingrays and sharks have in common?

Stingrays and sharks share a long list of features that set them apart from bony fish such as tuna or salmon:

• A skeleton of cartilage, strengthened by tiny tiles of calcium salts, as explained in do sharks have bones?
• Skin covered in dermal denticles, small tooth-like scales; a stingray’s barb is a giant modified denticle
• Teeth that are shed and replaced throughout life
• Five to seven pairs of separate gill slits, with no bony gill cover
• No swim bladder; an oily liver helps with buoyancy instead
• Ampullae of Lorenzini, jelly-filled pores that sense the weak electric fields of prey
• Internal fertilization, with males using a pair of claspers on the pelvic fins

Both groups also grow slowly, mature late and produce few young. Many give birth to live pups, while others lay eggs in tough cases. Skates, for example, lay the leathery egg cases known as mermaid’s purses, while stingrays such as the southern stingray give birth to live young.

How can you tell a ray from a shark?

The single most reliable clue is the position of the gill slits. In rays, they lie on the underside of the body. In sharks, they are on the sides of the head, even in the flattest sharks.

Because their mouths are underneath and often buried in sand, many rays breathe in through the spiracles on top of the head instead of through the mouth. Rays also lack an anal fin, which many sharks have.

Are rays just flattened sharks?

In the 1990s, some scientists thought so. Based on skeleton features, they proposed that rays had evolved from inside the shark group, as close relatives of the flat angel sharks and the sawsharks.

DNA studies published since the early 2000s have rejected this idea. They show that sharks and rays are two separate lineages that share a common ancestor. The flat body of angel sharks and wobbegongs evolved independently, as an adaptation to lying in wait on the bottom, and these sharks still have gill slits on the sides and pectoral fins that are not joined to the head.

Guitarfish, wedgefish and sawfish: rays that look like sharks

Some rays look surprisingly like sharks. Guitarfishes, wedgefishes and the bowmouth guitarfish, also called the shark ray, have long, thick tails with shark-like dorsal and tail fins, and they swim mainly by beating the tail. Only their flattened heads and the gill slits on their undersides show that they are rays.

Sawfishes are rays too, despite their shark-like bodies and long, toothed snouts. They are easy to confuse with sawsharks, which are true sharks. Sawsharks have gill slits on the sides of the head, a pair of long whiskers called barbels halfway along the saw, and saw teeth of alternating sizes. All five sawfish species are threatened, and the smalltooth sawfish, which survives mainly in southwest Florida and the Bahamas, is listed as Critically Endangered.

Where do manta rays fit in?

Manta rays belong to the order Myliobatiformes, the stingrays and their relatives, together with eagle rays and cownose rays. They evolved from bottom-dwelling stingrays and became open-ocean filter feeders. The giant manta ray is a cousin of sharks in the same way as a stingray, with a cartilage skeleton and denticle-covered skin. The differences between mantas and stingrays are covered in manta ray vs stingray.

Sharks and rays face the same threats

Sharing so much biology, sharks and rays also share the same weakness: they breed too slowly to cope with heavy fishing. The 2021 global assessment found that more than one-third of all sharks and rays are threatened with extinction, with overfishing as the main cause. Among the most threatened families are the wedgefishes and giant guitarfishes, sometimes called rhino rays, which are caught for their meat and highly valued fins.