The first fish-like animal appeared roughly 530 million years ago during the famous Cambrian Explosion. Since then, fish have got bigger, deadlier, and notably toothier says Will Newton.
There are many large, deadly fish living today - take the great white shark, for example, perhaps the most feared underwater predator.
However, a lot of the largest and deadliest fish lived during prehistory and a long, long time before the great white shark assumed its ‘most feared’ title.
These prehistoric giants were the apex predators of their day and would have, quite literally, eaten great white sharks for breakfast. Here are 10 monstrous fish you’ll be glad are no longer around today…
The deadliest prehistoric fish
Titanichthys
The clue is in the name when it comes to this particular fish - a 7m-long behemoth that would have rivalled today’s orcas in terms of size.
Unlike most of the other fish on this list, Titanichthys wasn’t a ‘superpredator’. It was a giant of its time, no doubt, but its jaws were ill-equipped for biting, crushing, and dismembering prey - the techniques typically employed by other predatory fish.
Instead, Titanichthys employed a method of feeding known as ‘filter feeding’, whereby it opened its cavernous mouth and hoovered up schools of small fish and krill-like zooplankton before swallowing them whole. Its mouth was covered in a series of small plates that helped it filter out these tiny animals, trapping them while allowing water to escape as it closed its jaws.
Titanichthys belongs to a group of heavily armoured fish known as the placoderms, a group characterised by the bony plates that cover their heads and upper bodies. It lived in shallow seas during the Late Devonian and ultimately faced extinction 359 million years ago, along with the rest of the placoderms and many other diverse groups of fish in the second of Earth’s ‘Big Five’ mass extinctions.
Megalodon
There are few prehistoric fish more famous (or infamous, rather) than megalodon. This extinct shark has become somewhat of a cultural icon, appearing as the antagonist in the sci-fi hit ‘The Meg’ and inspiring a wave of conspiracy theories as to how it still lurks in the depths of the Mariana Trench.
At nearly 20m in length, megalodon is more than three times the size of an average great white shark - its closest living relative. Its jaws were also significantly stronger, with some studies estimating megalodon had a bite force of 40,000 PSI, which is more than 10x that of a great white’s!
It’s thought megalodon’s diet changed as it grew. The juveniles fed primarily on fish, while the adults - based on deep, megalodon-tooth-shaped gashes discovered on a number of different bones - feasted on dolphins, whales, seals, turtles, and other sharks.
This indiscriminate hunter lived from the Early Miocene (23 million years ago) to the Early Pliocene (3.6 million years ago) and inhabited seas all over the world, from Europe to Australia. The cause of its extinction is somewhat of a mystery, though some suggest competition with its cousins, great white sharks and tiger sharks, may have been a contributing factor.
Rhizodus
Some 335 million years ago, in the freshwater lakes, rivers, and large swamps that covered parts of what is now Eurasia and North America, there lived a 5m-long ambush predator known as Rhizodus, or ‘root tooth’.
Rhizodus gets its name from the two, 22cm-long fangs that protrude from the front of its mouth and give it the look of an aquatic saber tooth tiger. It used these fangs to catch and puncture the bodies of its prey, lunging at them from the shallows just like today’s crocodiles do.
Based on interpretations of how it hunted, Rhizodus is believed to have preyed upon everything from other fish that also lived in the shallows, to large amphibians that hopped along the shores of the waterways where it lived.
Rhizodus was, by definition, a fish, but it belonged to an interesting group known as the tetrapodomorphs. This is the group that contains trailblazing fish like Tiktaalik - a limbed, half-fish, half-tetrapod that was one of the first of its kind to crawl out of the water. Tiktaalik and others of its kin spawned a terrestrial dynasty that would go on to include amphibians, reptiles, birds, and mammals.
Helicoprion
There’s no chance that a prehistoric shark best known as the ‘buzzsaw shark’ would miss out on being included on this particular list.
Helicoprion, owing to its nickname, had some of the most peculiar mouth anatomy of any animal ever, with a whorl of teeth resembling a buzzsaw set vertically into its jaws. It’s thought Helicoprion used this ‘buzzsaw’ to deshell hard-shelled cephalopods, such as ammonoids and nautiloids, in order to get at the soft meat hidden inside.
Other studies that have examined the biomechanics of Helicoprion’s strange jaws have suggested that it may have even had a bite strong enough to cut straight through the spines of unarmoured bony fish and other types of sharks.
There are a handful of named Helicoprion species, but the largest remains ever found - a 56cm tooth whorl that would have belonged to an individual over 7.6m in length - come from a so-far unnamed species. This giant, enigmatic species was discovered in Idaho, US.
Helicoprion lived during the Early Permian (290-270 million years ago) and, based on its global distribution of fossils, likely inhabited seas all over the world. Their strange tooth whorls make up the majority of these fossils and they’ve been found everywhere from the US to China, Norway to Australia.
Dunkleosteus
This prehistoric predator, affectionately known as ‘the Dunk’, lived during the Late Devonian (382-359 million years ago) and belongs to the same group of heavily armoured fish as Titanichthys - the placoderms.
Dunkleosteus is widely considered the largest placoderm, with some suggesting it may have exceeded lengths of 10m. However, these estimates have been questioned in recent years and lengths of ~4m are now better supported. Still, Dunkleosteus was a giant of its day and equipped with some of the strongest jaws of any animal living or extinct, terrestrial or aquatic, it’s no surprise that it was the apex predator in the warm, shallow seas that it lived in.
Dunkleosteus didn’t have ‘teeth’ in a conventional sense; instead it had two pairs of long, bony blades that protruded from its upper jaws and its lower jaws. These blades were capable of biting down at a force of 80,000 PSI, which is strong enough to puncture steel.
Using its powerful jaws, Dunkleosteus was able to open its mouth in just 20 milliseconds and, in doing so, create a vacuum that would have sucked in its prey. Its mouth would have then clamped shut, its blades sinking straight through the shell, bony plates, or fleshy skin of its prey. Nothing was off the menu for Dunkleosteus, even other Dunkleosteus.
Tiktaalik
As mentioned above, Tiktaalik was a trailblazer that paved the way for all vertebrates that live on land today, including us. However, it was also a predator that, 375 million years ago, terrorised a lot of the animals that lived in and around the shallow, freshwater swamps that once covered parts of northern Canada.
Tiktaalik is often referred to as a ‘fishapod’ - an animal that blurs the lines between ‘fish’ and ‘tetrapod’. In life, it would have looked quite similar to today’s crocodiles, with a flat, pointed snout, upward-pointing eyes, paddle-shaped limbs, and an elongated, streamlined body. Based on fossils, it’s estimated Tiktaalik grew to lengths of almost 3m.
These adaptations would have made Tiktaalik a deadly shallow-water predator, able to lie in wait in just inches of water before lunging at the small fish that dared to enter its domain. Using its specialised, limb-like fins, Tiktaalik may have also crawled on land for short periods and hunted some of the invertebrates that lived along the shores of its habitat, such as spiders, scorpions, and insects.
Tiktaalik may be a fish, but as a member of the group known as the tetrapodomorphs it’s actually more closely related to you reading this article that it is to a goldfish.
Ptychodus
Like Helicoprion, Ptychodus is another prehistoric shark known for its strange mouth. Instead of having a buzzsaw set into its jaws, Ptychodus’ jaws were lined with knobbly plates covered in hundreds of rounded teeth, each one topped with a series of laminar folds.
These specialised teeth allowed Ptychodus to crush and grind down the shells of a variety of hard-shelled animals. Some early studies of Ptychodus interpreted it as a predator that fed primarily on bottom-dwelling prey, such as bivalves and crustaceans. However, a recent study has suggested that, based on its large body size, it probably hunted in the open ocean and dined on ammonites and marine turtles.
Ptychodus lived during the Cretaceous (105-75 million years ago) and is widely regarded as one of, if not the largest shark of its day, with the largest individuals estimated to have grown up to 10m in length.
Fossils of Ptychodus have been found worldwide, suggesting it had a near-global distribution. These fossils indicate that Ptychodus grew slowly and matured very late. It’s unclear exactly how long individuals lived, but some may have made it well into their 100s.
Leedsichthys
Dwarfing today’s largest fish - the 12m-long whale shark - by several metres, Leedsichthys is often referred to as the largest fish of all time. While it may currently hold this particular title, the size of Leedsichthys has been debated for decades.
In the early 20th century, just a few years after its discovery, Leedsichthys was estimated to have reached lengths of ~9m, but by the end of the 20th century these estimates had more than tripled. Since then, and thanks to the discovery of some more fossils, estimates of 16.5m have now been widely agreed upon. This might not be quite as large as the more speculative estimates of the largest megalodon (around 20m), but it’s thought Leedsichthys were larger on average.
Like today’s giant fish, Leedsichthys was a filter feeder that used thousands of pipecleaner-like structures attached to its gill arches to extract zooplankton and other small animals from the water column.
Leedsichthys occupied a similar niche to today’s whale sharks, basking sharks, and baleen whales. However, unlike these giant filter feeders, Leedsichthys had several natural predators that would have, even during its adult years, posed a significant threat. The largest of these predators were the pliosaurs; they shared the open oceans with Leedsichthys during the Middle to Late Jurassic (165-148 million years ago).
Mawsonia
For nearly 100 years, the group of fish to which Mawsonia belongs - the coelacanths - were thought to be long extinct and relics of a bygone underwater era. However, in 1938 a living species was found just off the coast of South Africa and the group was officially declared ‘un-extinct’.
Mawsonia, meanwhile, is confirmed to have faced extinction in the Cretaceous (~94 million years ago), during a time when coelacanths were particularly diverse. It’s known by several species, but the aptly named Mawsonia gigas is by far the largest, with the largest individuals thought to have exceeded lengths of 5m.
While 5m doesn’t sound that large, especially when compared with the other fish on this list, it’s worth noting that Mawsonia lived in freshwater and brackish environments, the kind that typically don’t support giant fish.
Mawsonia was likely the apex predator in its environment, but exactly how it fed is a mystery. It has been suggested that it used the small, rounded knobs of bone that line its mouth to crush hard-shelled animals. It may have also swallowed its prey whole using a method known as suction feeding.
Megapiranha
Yes, this may be the name of a 2010 mockbuster, but it was also a real-life species of fish that lived during the Late Miocene (10-8 million years ago) in Argentina.
Megapiranha was originally thought to have reached lengths of 130cm and weights of 73kg, which would have made it larger than the largest carp ever caught and just a tad smaller than the average human. However, more recent estimates place its length at 70cm and its weight at 10kg - still, that’s roughly 10x the size of a modern piranha!
Like their living relatives, Megapiranha likely lived in large schools that hunted en masse. The jaws of these freshwater killing machines were incredibly powerful and magnitudes stronger than those of modern piranhas. A 2012 study found that, pound for pound, Megapiranha had a bite force stronger than that of a T.rex - the animal with the strongest bite force ever reconstructed.
It’s thought Megapiranha used its ‘mega’ bite to crush the shells of turtles, the plates of armoured catfish, and even the bones of large mammals that were foolish enough to stray into the rivers where it lived.