9 Ancient Dinosaurs That Were Like Giant Alligators

Written by Austin S.
Updated: September 7, 2022
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Crocodiles and alligators are massive animals even by today’s standards. Alligators belong to an animal group known as “ruling reptiles.” The name of this animal group is Archosaurs. The archosaurs genus is an animal group that giant reptiles evolved from. This genus is the same to which dinosaurs belong.

Alligators are reptiles that can grow up to 15 feet in length. They can weigh up to 600 lb. With these features, combined with their bite force of about 2,900 lb, we get a picture of a reptilian monster. Modern-day alligators and crocodiles are no match for the ancient dinosaurs they evolved from. 

Ancient alligators lived between 25 to 250 million years ago. These giant reptiles evolved before and also lived with dinosaurs. Their complex genetics has allowed them to survive the meteor strike and evolve into the crocodiles and alligators we have today.

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What Were the Giant Alligators Like?

Ancient dinosaurs were massive reptiles. They evolved about 250 million years ago in the Triassic period. The Triassic period belongs to the Mesozoic era. This era features three periods. They are:

  • Triassic period
  • Jurassic period
  • Cretaceous period

Dinosaurs evolved during the Jurassic period and lived with the ancient alligators. These periods feature the evolution of giant creatures on Earth. Ancient alligators can measure up to 41 feet and weigh up to 17,000 lb. This size dwarfs that of modern-day alligators. 

Ancient alligators were prime predators. They had massive skulls and teeth the size of a banana. Alligators and crocodiles of today look much like their ancient self. The monstrous size they evolved from is the only apparent difference. The bite of a modern crocodile is one of the strongest today. This hints at the amount of power ancient alligators had in their snouts.

Ancient Dinosaurs That Were Like Giant Alligators

The size of each alligator varies. Some were smaller compared to the massive ones that even hunted dinosaurs. This list discusses X ancient dinosaurs that were like giant alligators. They include:


Deinosuchus is an ancient crocodile that existed between 80 to 70 million years ago. The Deinosuchus name adopts ‘dino’ to indicate its monstrosity. Deinosuchus means ‘terrible crocodile’ in greek. This crocodile can weigh between 5 to 10 tons. They can measure up to 35 feet. Its skull alone can measure up to 6 feet with a snout filled with huge sharp teeth. 

Deinosuchus was a carnivorous animal. Its diet includes fish, carrion, and land animals like dinosaurs. Deinosuchus bite marks are present in fossils of some dinosaurs. They had a bite force between 10,000 to 15,000 lb. With their long and strong snout, huge prey like dinosaurs is ripped into smaller bits. 

These ancient crocodiles lived in the waters of North America. The first complete construction of a Deinosuchus fossil was done in 1904. A complex fossil history caused some fossils to be wrongly identified until then. William Jacob Holland reassessed the fossils and constructed the genus.


The Deinosuchus lived between 70 to 80 million years ago and could weigh between 5 to 10 tons.

©Herschel Hoffmeyer/Shutterstock.com


Sarcosuchus is the largest crocodile in history. It’s popularly called ‘supercroc’ due to its monstrous size. 

Sarcosuchus means ‘flesh crocodile’ in greek. They could grow up to 41 feet with a head-to-tail measurement. They could grow bigger because they dont stop growing till death. Sarcosuchus weigh as much as dinosaurs at over  80,000 lb. The osteoderms that form armour for crocs cover Sarcosuchus all over. Unlike today’s crocodiles that have limited armour protection. 

Sarcosuchus lived around 100 million years ago. They lived in North Africa and West Africa. At the time, the northern region was tropical. It featured vegetation and rivers that have now dried out to a desert. 

Sarcosuchus enjoyed constant heat in this region. Food was plenty as there were plenty of dinosaurs and other animals for prey in this region. Traces of their existence were also present in rivers across South America.

Like most marine reptiles, Sarcosuchus fed on fish and small marine animals. As they attain their full size, they become a match for any animal in the region. They had around 100 teeth for tearing into any kind of prey they encountered. 

Dinosaurs were part of the prey that they killed. Sarcosuchus could compare with the largest dinosaurs in size. They were also big and strong enough to drag unsuspecting dinosaurs into the river. There is speculation that they mainly feed on fish while they go for bigger prey as they grow.


Sarcosuchus means ‘flesh crocodile’ in Greek.

©Michael Rosskothen/Shutterstock.com


Purussaurus lived around 8 million years ago. It evolved from a giant caiman native to ancient South America. Similarly, Purussaurus fossils were present in South America amazons. 

Purussaurus got its name from the Purus river. It can measure up to 41 feet long and weigh around 18,000 lb. This monster reptile had a bite force of about 15,000 lb. They were one of the largest reptile species in history. 

The skull of this reptile can measure up to 5 feet, only a foot shy of the ‘supercroc’. They had razor teeth for fleshy prey. Purussaurus was a carnivore that preyed on fish and land animals. 

Further examination suggests that they also lived on vegetation around and carrion. Purussaurus are unique in the reptile genus due to their speed. They can attain speed up to 16 mph when swimming. Its large tail helps it swim effectively. It could also use its tail to ward off animals with powerful swipes.

Purussaurus skull

The skull of the Purussaurus measured up to 5 feet in length.

©di Lissandro/Shutterstock.com


Darkosaurus means ‘tearing lizard’ in greek. The tearing lizard lived in the Eurasian seas and the American waters. They can measure up to 15 feet in length and weigh between 1500 to 2000 lb. 

These marine reptiles evolved through the late Jurassic period. They existed between 150 to 130 million years ago. Unlike other ancient crocodiles, they had heads like dinosaurs. They also had flippers, like turtles. These flippers indicate that they were not suited for movement on land. 

The diet of Darkosaurus includes squids and fish. They also preyed on other reptiles in their environment. They were not fast swimmers but were fast enough to chase and catch prey. Their skull features scattered teeth like a dinosaur’s.


Mosasaurus got its name from the Meuse river. ‘Mosa’ means the Meuse River in Latin while ‘Sauros’ means lizard in greek. It existed between 70 to 65 million years ago. 

This period was the late Cretaceous epoch. Mosasaurus had the head of an alligator and a fin on its tail. Their flippers also indicate an entire marine lifestyle. This reptile looks more evolved for marine life. It could grow to about 50 feet and weigh up to 30,000 lb. This reptile lived on fish, shellfish and squid. They went extinct about 65 million years ago.


The flippers on a Mosasaurus indicate a marine lifestyle.

©Daniel Eskridge/Shutterstock.com


Desmatosuchus means ‘link crocodile’ in greek. It lived about 230 million years ago in North American forests. It can measure up to 15 feet in length and weigh about 1000 lb. Desmatosuchus had a crocodile’s posture and armoured skin. They were herbivores and lived on plants. These lizards belong to the Archosaur family. 

This lizard evolved a defence mechanism as it was not capable of preying on other animals. Their defence mechanism was their spiked shoulders. There’s the hypothesis that they were hunted by other lizards of the time. Their fossils are also present at other predatory archosaur fossil sites.


The Desmatosuchus

was an herbivore.



Baurusuchus lived in the forests of South America. They lived during the late Cretaceous period between 95 to 85 million years ago. Baurusuchus means ‘Bauru crocodile’ in greek. They had long legs and walked on all four like dogs. Baurusuchus can measure up to 12 feet and weigh about 500 lb. They had big and powerful skulls with nostrils. The nostrils indicate that they were land reptiles. They were carnivores and lived on other land animals. 


Aegisuchus means ‘shield crocodile’ in greek. It lived in the North African waters. Aegisuchus lived between 100 to 95 million years ago during the Mid Cretaceous period. These massive reptiles were unique with their broad and flat snouts. They can measure up to 70 feet in length and weigh up to 20,000 lb. Their skulls can measure up to 8 feet long. 

Aegisuchus’s eyes are on top of their head. Their skull structure suggests that they lurk just below the water surface. They were carnivores that fed on fish, land animals, and smaller dinosaurs.


Angistorhinus is a reptile that lived between 230 and 220 million years ago. This period was the late Triassic period. They can measure up to 20 feet in length and weigh up to 1100 lb. They were carnivores that lived on small animals in their environment. Angistorhinus Lived in swamps across North America. 

How did they go extinct?

The reptiles we have discussed lived in different periods of time. Some of them existed with dinosaurs meaning that they also perished when the meteors hit. The ones that survived continued to evolve into the crocodiles and alligators we have today. 


Dinosaurs are terrifying creatures. However, they existed with other reptiles that were more monstrous. Imagine Godzilla being real. That’s how enormous some of these reptiles were. Dinosaurs and ancient crocodiles evolved from the same ancient species. They existed in the same era when reptiles reigned. 

Evolution has changed these beasts into the scary reptiles we have today. However, crocodiles and alligators of today still have the genes for growing into massive sizes. Just not back to the dinosaur age.

The photo featured at the top of this post is © Kate33/Shutterstock.com

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About the Author

Growing up in rural New England on a small scale farm gave me a lifelong passion for animals. I love learning about new wild animal species, habitats, animal evolutions, dogs, cats, and more. I've always been surrounded by pets and believe the best dog and best cat products are important to keeping our animals happy and healthy. It's my mission to help you learn more about wild animals, and how to care for your pets better with carefully reviewed products.

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