Strange Sharks

Top predators often get a bad rap. We understandably fear things that might pose a threat to us or our livelihoods, but tend to over-react to those threats (e.g. driving wolves extinct in Yellowstone). One particular type of predator has gained an especially bad reputation – sharks.

  Great white shark at Guadalupe Island, Mexico, by  Kyle McBurnie .

Great white shark at Guadalupe Island, Mexico, by Kyle McBurnie.

While sharks can of course be dangerous, they don’t really deserve to be quite so vilified. Yes, sharks have bitten and very occasionally killed people, but those “attacks” are usually due to the shark’s curiosity. They bite things to learn about them, much in the same way that dogs sniff things or babies put everything in their mouths. It’s just that a shark’s mouth tends to be on the pointy side.

We humans, on the other hand, have killed far more sharks than they’ve killed us. Sometimes it’s accidental, like if they’re bycatch in commercial fishing operations, but more often it’s deliberate. Shark fin soup is a popular dish in China, shark oil and cartilage are used for (ineffective) medicine, and many people hunt sharks just for fun. We excuse the killing by villainizing sharks in the extreme, starting with Jaws and continuing with sensationalist reporting of (extremely rare) shark attacks and things like Shark Week on the Discovery Channel.

We admittedly know very little about the ocean and the life it holds. Scientists estimate that we’ve only discovered about 10-15% of marine species. But here’s some of what we do know about sharks:

Shark skin is made up of tiny tooth-like scales called denticles. Image by Sue Lindsay via Australian Museum.

  • They belong to a class of fish called Chondrichthyes, or cartilaginous fish – their skeletons are made entirely out of cartilage, not bone (rays, skates, and sawfish are also cartilaginous).
  • They’re ancient – the oldest known records of sharks date back more than 420 million years.
  • There are more than 500 shark species, which range in size from the tiny dwarf lantern shark (about 6 in/15 cm long) to the enormous whale shark, the world’s largest fish (40 ft/12 m long).
  • They have amazing senses of smell and hearing, and have special organs called the ampullae of Lorenzini that detect the electromagnetic fields of other animals. They also have a lateral line system that allows them to feel vibrations in the water (i.e. those caused by panicking prey).
  • Their teeth (which are arranged in several rows) constantly grow, fall out, and replace themselves. 
  • Water must be constantly flowing past their gills in order for to breathe. This means that many species have to keep moving constantly, even while asleep.
  • Contrary to popular belief, sharks are not immune to cancer, and their fins and cartilage hold no medicinal value.  

We’re all familiar with a few shark species – the great white, the hammerhead, the mako – but from here on out, let’s focus on some of the weird, lesser-known ones:

 
  Juvenile goblin shark from near western Tasmania. Image from Julian K. Finn via  Museum Victoria .

Juvenile goblin shark from near western Tasmania. Image from Julian K. Finn via Museum Victoria.

This nosey fellow is a goblin shark, a pink-skinned medium-sized shark with a truly bizarre jaw. When it’s swimming around, the jaw is in more-or-less the same configuration as other sharks. When it hunts for prey along the sea floor, it picks up electrical signals with a particularly sensitive set of ampullae of Lorenzini (hence the extra-long snout). When it detects an animal, its jaws shoot forward to grab the food and then rapidly retract, as can be seen in this (somewhat creepy) video.

 
  Not a sea serpent, but a frilled shark. Image by  Ibolya .

Not a sea serpent, but a frilled shark. Image by Ibolya.

It may look like an eel crossed with a dragon, but this is actually a frilled shark, one of the most primitive and ancient shark species (they co-existed with the megalodon, discussed later in this post). They live in deep water, and their teeth (of which there are over 300) have multiple points and are aimed inwards, which allows them to hook and trap prey.

 
  A preserved specimen of a cookiecutter shark. Image by Jennifer Strotmen via  Smithsonian Ocean .

A preserved specimen of a cookiecutter shark. Image by Jennifer Strotmen via Smithsonian Ocean.

The cookiecutter shark – a cute name for a not-so-cute animal – is so named for the distinctive round marks and holes left behind when it attacks something. It’s on the small side, so it doesn’t usually eat entire large animals, but instead prefers to take out small chunks, making it a sort of parasite. Several sharks are known to be bioluminescent, but the cookiecutter has a stronger and longer-lasting glow than any other shark species.  

 
  The megamouth is extremely well-named. Image by Richard Ellis via  Mental Floss .

The megamouth is extremely well-named. Image by Richard Ellis via Mental Floss.

On the opposite side of the jaw spectrum we find the megamouth shark, one of three shark species that filter feed on plankton and jellyfish (like the whale shark and basking shark). They can grow up to 16 ft/5 m long, and as their name implies, their mouths can open up to over 4 ft/1.3 m wide. Not much else is known about them, since they’re deep-water sharks and fewer than 100 specimens have ever been observed or caught since its discovery in 1976.

 

An early guess at the appearance of a helicoprion. Image by Alexander Karpinsky, 1899.

A more recent guess at the appearance of a helicoprion. Image by Dmitry Bogdanov, 2008.

While we’re on the subject of weird mouths, check out this guy. Those are artists’ representations of what the helicoprion, a shark-like fish that lived during the early Permian age (about 290 million years ago), might have looked like. Scientists have unearthed several fossils that at first glance appear to be ammonites, but on closer inspection turned out to be “tooth whorls” – spirals of ancient shark teeth. It’s thought that the whorl of teeth formed a structure similar to a circular saw. As you might expect, this jaw design didn’t really catch on.

 
  Modern divers are probably pretty glad that the megalodon isn't around anymore. Image from  PADI .

Modern divers are probably pretty glad that the megalodon isn't around anymore. Image from PADI.

As long as we’re talking about ancient extinct sharks, I’ve got to mention the megalodon, the one of the largest predators to have ever lived. Megalodons probably looked fairly similar to today’s great whites, but were much, much bigger. We can speculate size based on fossil jaws and teeth; they could reach at least 59 ft/18 m in length. And scientists estimate that they could exert a whopping 182,201 newtons of bite force. They died out about 2.6 million years ago, probably as a result of oceans cooling due to an ice age.  


You can help shark conservation efforts by supporting Oceana, the Marine Conservation Institute, or Sea Shepherd.