Mosasaurus, Pliosaurus, And Predator X: Which Ancient Marine Predator Was The Deadliest?

We’d live in a yachtless world if these things were alive today.


Rachael Funnell


Rachael Funnell

Writer & Senior Digital Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Writer & Senior Digital Producer

a mosasaurus with its mouth open

Mosasaurus Vs Pliosaurus: who's your money on?

Image credit: Dotted Yeti /

Ancient marine predators were some of the biggest animals the world’s ever seen, as well as the deadliest. While humans haven’t yet found evidence of an animal that was bigger than the extant blue whale, sea monsters of the Jurassic and Cretaceous ate prey significantly larger than krill, and we have the fossil teeth to prove it.

Predator X was the name given to a mysterious marine reptile (not a dinosaur) excavated in Norway in 2009 that was estimated to have a bite force four times stronger than that of Tyrannosaurus rex, reports National Geographic. It wasn’t until 2012 that its identity was revealed as Pliosaurus funkei.


What was Pliosaurus?

Pliosaurus is a genus that breaks down into the Ancient Greek for “more” and “lizard”. It was named by English palaeontologist Richard Owen in 1841, and he was kind of onto something, as you really got a lot of bang for your buck with these giant-headed marine predators. The genus represents just one of several groups within the Pliosauridae family that lived during the Jurassic and Early Cretaceous periods.

One such sea monster was Lorrainosaurus, excavated in France. As one of the oldest “megapredatory” pliosaurs dating back 170 million years, its discovery demonstrated when these marine predators evolved away from the smaller size of their plesiosaur relatives into the “sea murderers” after which their clade, Thalassophonea, was named.

a pliosaurus vs human size comparison
Pliosaurus funkei making humans look a bit ridiculous.
Image credit: By ДиБгд - Own work, CC BY-SA 4.0 via Wikimedia

Lorrainosaurus was one of the first truly huge pliosaurs,” said Sven Sachs, a researcher at the Natural History Museum in Bielefeld, reports Discover. “It gave rise to a dynasty of marine reptile mega-predators that ruled the oceans for around 80 million years.”

Jurassic Park/World fans will no doubt be more familiar with a different marine predator: mosasaur. So how did these two hunters match up, and did they ever cross paths?

Pliosaurus Vs Mosasaurus

Unfortunately, the world never got the Pliosaurus Vs Mosasaurus showdown we all would’ve loved to see (and likely never will unless we innovate the tech to bring back ancient animals). Mosasaurs emerged during the Late Cretaceous meaning they missed the pliosaur party by a few tens of million years. However, we can make some educated guesses as to how a fight might’ve gone down were they both plopped in the same pond.

In terms of length, Mosasaurus hoffmanni had Pliosaurus funkei beaten at 17 meters (56 feet) long, while our Predator X was a poxy 12 meters (40 feet). However, mosasaurs were typically slimmer with elongated skulls, while pliosaurs had big stocky heads. This gave them a bite force capable of chomping through giant prey like ichthyosaurs with their huge teeth, while mosasaurs tended to snatch and swallow their prey whole using pointy teeth. 

So, if we’re going off chomp factor, our money’s on the pliosaurs, but if we’re working from how many teeth? It’s a close one to call. 


And while we're pitting ancient beasties against one another, how about Megalodon Vs Mosasaurus?


  • tag
  • animals,

  • mosasaur,

  • extinct,

  • Palaeontology,

  • pliosaur