The Largest Sea Snake Ever: Discover an Ancient 40-Foot-Long Giant

Written by Brandi Allred
Updated: June 9, 2022
Image Credit Nobu Tamura ( / Creative Commons
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Key Points

  • 50 million years ago, an ocean existed in the deserts Nigeria, Mali and Algeria, the Trans-Saharan Seaway
  • Palaeophis colossaeus fossils were analyzed in 1999 and it was determined to be the largest sea snake to exist, calling the Trans-Saharan Seaway its home.
  • Colossaeus grew up to 40 ft long because of isolation from other serpent species and predators.

Back in 1999, a team of international scientists began work in the Sahara desert in northern Africa. They were looking for evidence of something not seen in the arid lands of Nigeria, Mali, and Algeria in over 50 million years: an ocean. This ancient ocean was home to more than fish; it was the personal hunting ground of the largest sea snake ever, Palaeophis colossaeus. 

Using fossil analysis, scientists have discovered that the ancient Trans-Saharan Seaway was home to even more gigantic species. And they think they know why so many monster creatures inhabited this strange, ancient ocean. 

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Let’s take a closer look at the largest sea snake ever, and discover how it got so big. To do that, we’ll need to know more about colossaeus’s home, what it might have eaten, and how it would have killed its prey. 

How Big Was the Largest Sea Snake Ever?

Palaeophis collossaeus could grow up to 40 feet long.

Nobu Tamura ( / Creative Commons – License

Palaeophis collossaeus could grow up to 40 feet long.

Snakes were bigger in the past, or, at least, some snakes were bigger. This is especially true for the species known as palaeophis collossaeus, an ancient type of sea snake. Under normal conditions, these snakes grew to around 30 feet long. That’s still bigger than any snake alive today! But, in the Trans-Saharan Seaway, collosaeus grew even larger.

According to the scientists that authored the study, “The Trans-Saharan Seaway exhibited intermittent isolation from major seas. This environmental variable may have created aquatic centers of endemism, stimulating selection for gigantism as previously observed for species on terrestrial islands.” 

In layman’s terms, scientists believe that the periodic isolation of the creatures living in the Seaway paved the way for them to grow to gigantic proportions. For collosaeus, this meant growing up to 40 feet long, making it one of the largest snakes ever. 

Where Did Collosaeus Live?

The Sahara desert, which was once an ocean, is now filled with sand.

Anton Petrus/

If you walk around the Sahara desert today, you would never know that it used to be home to an ancient, 165-foot-deep ocean channel. But, the locals will tell you that finding fossilized marine shells is not uncommon. That’s because, between 50-100 million years ago, a great seaway bisected the land from north to south and covered the entire northern boundary of the Sahara.

Within this Seaway, large predators like giant catfish, sharks, and ancient crocodiles, hunted. The largest sea snake ever had plenty of hunting grounds to choose from; the ocean supported deltas, shoals, and lagoons of all kinds. Scientists believe that collosaeus was entirely (or almost entirely) aquatic and would have spent its life in the 1,800 square miles Trans-Sahara Seaway. 

But, the water isn’t the only thing that was different in the ancient Sahara. According to the story in the rocks, the lands surrounding this ocean channel were filled with verdant forests. These lush woodlands may have given way to mangrove swamps leading to the open ocean—the perfect place for the largest sea snake ever to hunt.

What Did the Largest Sea Snake Ever Eat?

Redtail catfish in the aquarium. The fish is a long-whiskered catfish.
The largest extant snakes can eat prey as large as catfish.


Collosaeus measured around 40 feet long, long enough to prey on large creatures. But, scientists aren’t sure whether the structure of its skull allowed it to consume creatures bigger than its own head, as many of today’s snakes do. Why aren’t scientists able to tell? Because the only fossilized remains of the largest sea snake ever don’t include skull bones. However, scientists hypothesize that collosaeus would have been similar to today’s boas, which can eat prey many times the size of their heads.

So, if the largest sea snake ever could eat giant foods, just what did it eat? Well, in a land of gargantuan swimmers, there were plenty of choices. Collosaeus lived alongside the largest ever catfish in Africa, which would have made an excellent meal. These giant snakes also would have eaten large sharks, bony fish, ancient crocodiles, and big turtles.

For the largest sea snake ever, very few creatures would have been off the menu.

How Did Collosaeus Hunt?

If collosaeus was big enough to eat giant catfish and sharks, just how did it hunt? Scientists can’t be sure, but there are two definite possibilities. The first is that the largest sea snake ever was venomous. A venomous giant snake would have bitten and envenomated its prey, then waited for it to die before swallowing it whole.

The other option is that collosaeus constricted its prey, like modern-day boa constrictors. If this were the case, then this giant sea snake would have wrapped itself around the bodies of its prey and literally squeezed the life out of them.

What is certain about collosaeus is that its heavy, narrow-body was designed for swimming. So, however they hunted, they likely hunted in the water. Their size, coupled with their carnivorous diet, would have made them an apex predator in the waters of the Trans-Saharan Seaway.

Which Was Bigger: Titanoboa, or Collosaeus?

titanoboa size
The largest snake ever found is the titanoboa, which lived in ancient South America.

Michael Rosskothen/

Collosaeus may be the largest sea snake ever, but is it the largest snake to ever live? Even with its tremendous length of up to 40 feet, collosaeus still doesn’t beat out the largest snake ever, titanoboa

Titanoboas are thought to have stretched up to 50 feet long, making it bigger than the monstrous collosaeus’s of the Trans-Saharan Seaway. Like the largest sea snake ever, the titanoboa lived millions of years ago and would have preyed on giant-sized prey.

So, collosaeus may be the largest sea snake ever, but it’s still only the second largest snake to ever live.

Other Colossal Creatures of the Eocene

If you’re curious about other megafauna living at the same time these sea snakes did, here are a few:

  • Chalicotherium – unclassifiable
  • Moropus – unclassifiable
  • Coryphodon – half-ton herbivore
  • Hyaenodon – considered ancestral to dogs
  • Andrewsarchus – terrestrial carnivorous mammal

Up Next…

If ancient creatures were to make a comeback, we would all be in big trouble. Find out more about the giant, scary animals of the past in these articles:

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