Discover the Largest River Monster to Ever Exist

Written by Emmanuel Kingsley
Updated: August 31, 2023
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The Earth’s giant monsters have mostly been believed to live underground or at the bottom of the ocean. However, fossils of a large river monster species have been found in 10 states in America and northern Mexico.

This extinct giant named Deinosuchus, the ‘terrible crocodile’ was believed to have been the largest predator in North America millions of years ago.

The Deinosuchus, or “terrible crocodile,” was the largest semi-aquatic river predator that ever existed.

Let’s find out how big the largest river monster truly was.   

Deinosuchus: The Largest River Monster to Ever Exist

Largest Crocodiles Ever Deinosuchus

There are four named species of Deinosuchus; D. hatcheri, D. rugosus, D. schwimmeri, and D. riograndensis.

©Daderot / CC0 1.0 – License

Deinosuchus existed 82 to 73 million years ago in a time known as the ‘Cretaceous Period’ wherein many extinct giant creatures, including the dinosaurs, existed.

Description and Size


Deinosuchus grew up to 36.09 feet and weighed as much as 15,432.4 pounds.

©Herschel Hoffmeyer/

According to the West Australian Museum, these behemoth reptiles grew up to 36.09 feet long and weighed as much as 15,432.4 pounds, making them the largest semi-aquatic predators in their ecosystem. Deinosuchus was endemic to North America.  

These ancient reptiles had a relatively similar appearance to modern alligators, having broad snouts and at least 22 teeth in their upper and lower jaws, respectively. However, in contrast to alligators, Deinosuchus had heavy and deeply pitted plates covering their backs and two holes in front of the nares, which are not seen in alligators, and they were much heavier.

What Did Deinosuchus Eat?

Crocodile Bite Force - Deinosuchus Attacking a Dinosaur

Deinosuchus ate sea turtles, dinosaurs, and possibly everything else on the menu.


Deinosuchus had very strong teeth, which were as long as bananas, and possessed a bite force between 18,000 and 102,803 Newton. According to Science Daily, Deinosuchus’ bite marks were found on discovered dinosaur bones and sea turtle shells. This evidence means that these river monsters would have fed on dinosaurs, sea turtles, large fish, and possibly everything else on the menu in their habitats.   

What Was The Lifespan of Deinosuchus?


Deinosuchus lived for up to 50 years.

©Andrey Atuchin / CC BY-SA 4.0 – License

According to Wingham Wildlife Park, Deinosuchus lived for up to 50 years, the same as a modern-day alligator.

Where Did the Deinosuchus Live?

Acrocanthosaurus and Sarcosuchus

Deinosuchus lived on both sides of the Western Interior Seaway, an inland sea in North America.

©Michael Rosskothen/

During the Cretaceous Period, the Deinosuchus species lived on both sides of the Western Interior Seaway. This seaway was an inland sea in North America about 100 million years ago that connected the Gulf of Mexico to the Arctic Ocean through America and Canada. According to reports, the Western Interior Seaway divided the continent into two landmasses: Laramidia and Appalachia.

Deinosuchus that lived in Appalachia, the eastern region, were smaller in size and were opportunistic apex predators. In Laramidia, the Deinosuchus species were much bigger, reaching their largest sizes there, but they were less populated than in the eastern region.

Deinosuchus Versus the Largest River Monsters Today


Deinosuchus was bigger than any river animal today.

©Herschel Hoffmeyer/

Since the extinction of the Deinosuchus species, other giant animals have appeared in the rivers and lakes around the world. Let’s see how modern-day river monsters compare to the largest ever.

Lake Sturgeon

lake sturgeon in dark water

The largest lake


ever caught weighed 300 pounds and was 8 feet.

©Galina Savina/

The lake sturgeon is the largest Great Lake fish. The record for the largest lake sturgeon ever caught weighed 300 pounds and was 8 feet long. It was caught in Lake Michigan. This large fish often grows up to 6 feet and weighs about 200 pounds on average.

Despite the incredible size of the lake sturgeon, it would have ended up on the menu list of the Deinosuchus if the river monster still lived. However, lake sturgeons would have outlived Deinosuchus since they can grow as old as 100 years, according to the Michigan Department of Natural Resources.

Beluga Sturgeon

The Beluga Sturgeon or European sturgeon (Huso huso)

The largest Beluga sturgeon ever caught measured 23.62 feet and 3,463.43 pounds.

©Miroslav Halama/

The Beluga sturgeon is one of the largest fish worldwide. These freshwater fish are one of the only sturgeons that feed on other fishes. According to Oceana, these large predatory fish can grow up to 24 feet and weigh as much as 3,500 pounds. The largest Beluga sturgeon ever caught measured about 23.62 feet long and weighed 3,463 pounds.

These large fish are found outside North America, thus, they would never have encountered the Deinosuchus. They are considered critically endangered.  

Mekong Giant Stingray

Mekong giant freshwater stingray (Urogymnus polylepis)

The biggest Mekong giant stingray captured measured 13 feet and 661 pounds.

©Danny Ye/

Mekong giant stingrays are the largest stingrays in the world. These unique fish species are known for their flat body shape and stingers. The biggest stingray captured measured 13 feet long and weighed about 661 pounds, which is as big as a grizzly bear. According to The New York Times, this giant stingray was found in the Mekong River in Cambodia on June 13, 2022.

Despite the Mekong giant stingray’s giant size, 30-mile-per-hour speed, and venomous tail, the large stingray would have had a hard time against the Deinosuchus.    

Amazon River Dolphins

Amazon River Dolphin

According to the Guinness World Records, Amazon river dolphins can grow up to 9 feet.


Amazon river dolphins are one of the largest freshwater mammals in the world. Though they are smaller than saltwater dolphins, they can weigh between 220 to 440 pounds. According to the Guinness World Records, these pink mammals can grow up to 9 feet long. Amazon River Dolphins live for 12 to 18 years, less than the lifespan of Deinosuchus. If the two species are put together in the same river, the river dolphin’s best bet is to put some distance between the two species. Deinosuchus was a very large reptile and did not have great speed.  

Alligator Gar

An Alligator gar, Atractosteus spatula, while swimming in a huge aquarium

The largest alligator gar on record was measured to be 8 feet 5 inches long and weighed about 327 pounds.

©Bill Roque/

The alligator gar looks like a crossbreed between a fish and an alligator. These large fish are the largest gar species in North America, growing up to 10 feet long and weighing 350 pounds. The largest alligator gar on record was caught in the Mississippi River, measuring 8 feet 5 inches long and weighing about 327 pounds. These alligator-like fish are big but would have been tasty snacks for the Deinosuchus.

Fossils and Discoveries

There have been many discoveries of the different fossil remains of the great Deinosuchus. In 1858, geologist Ebenezer Emmons believed two large teeth found in North Carolina belonged to a giant crocodile which was the first impression of Deinosuchus.

Since then, other remains have been found all over the United States and Mexico and have created assumptions about the river monster until it was officially classified as Deinosuchus.  

Two years ago in 2020, Deinosuchus schwimmeri was officially named and cemented as the largest river monster ever. One of the most notable discoveries was in New Mexico in a release by the National Library of Medicine in 2021. Two other Deinosuchus remains were also found in Mississippi and Alabama.

The photo featured at the top of this post is © Sammy33/


  1. State of Michigan, Available here:
  2. Western Australian Museum, Available here:
  3. National Library of Medicine, Available here:
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