Head to head
Shark vs Ray
A common question is whether a ray is a kind of shark. The answer is close to yes. Sharks and rays are the two main groups of cartilaginous fish, they share a long list of features, and rays evolved from within the shark lineage, essentially as sharks that flattened out and moved onto the sea floor.
| Shark | Ray | |
|---|---|---|
| Group | Cartilaginous fish; the shark branch | Cartilaginous fish; a branch that arose within the sharks |
| Body shape | Rounded and streamlined | Flattened from top to bottom |
| Gill slits | On the sides of the head | On the underside |
| Pectoral fins | Separate from the head | Enlarged and fused to the head as a disc or wings |
| How it swims | Sweeps the tail | Ripples or flaps the disc |
| Lifestyle | Mostly active open-water hunters | Mostly bottom-dwelling shellfish crushers |
| Shared traits | Cartilage skeleton, denticle skin, electric sense, replaceable teeth | The same list |
| More endangered | About a third of species threatened | A higher share threatened than sharks |
Shark vs Ray: common questions
Is a ray a type of shark?
Effectively, yes, in evolutionary terms. All rays descend from a common ancestor they share with modern sharks, and that ancestor sits inside the shark part of the family tree, so the rays are a specialised group that branched off the sharks rather than a separate line. Biologists group sharks and rays together as the elasmobranchs, the cartilaginous fish minus the chimaeras. In everyday language people keep the words shark and ray separate because the two look and live so differently, but a ray is not fundamentally a different kind of animal from a shark. The clearest way to picture it is a shark that became flattened, moved its gills to its belly, and turned its pectoral fins into wings.
How do rays breathe if their gills are on the bottom?
Through a pair of openings on top of the head called spiracles. In a fast-swimming shark, water for the gills is simply forced in through the mouth as the animal moves. A ray spends much of its time lying still on, or buried in, the sea floor, so drawing water in through a mouth pressed against the sand would fill the gills with sediment. Instead the ray takes water in through the spiracles, which sit just behind the eyes on the upper surface, and passes it down over the gills and out through the slits underneath. Sharks have spiracles too, but they are small or absent in the active species and well developed mainly in the bottom-dwelling sharks.
Which is more dangerous to people, a shark or a ray?
Both risks are small, and they are different in kind. A handful of large sharks, chiefly the great white, tiger, and bull sharks, are involved in the rare serious bites on humans, of which there are roughly 70 to 100 worldwide in a year with fewer than ten deaths. Rays do not bite people, but many stingrays carry a venomous barbed spine on the tail that they use purely in defence if trodden on or grabbed, causing a very painful wound that occasionally, as in the death of Steve Irwin in 2006, proves fatal when it strikes a vital area. In practice, both are best treated with simple caution, keeping a respectful distance from sharks and shuffling the feet in shallow sandy water so a hidden ray can move away.