The “Monster of Aramberri” Was a 50 Foot Gigantic Predator

Written by Kyle Glatz
Updated: March 17, 2023
Share on:


Listen to Article

When scientists find a fossil, they take time to officially describe it, present their findings to their peers, and record the creature’s genus and species. Sometimes this process takes a while. In the interim, fossilized ancient animals can be granted some interesting nicknames. For example, the Monster of Aramberri refers to an enormous marine reptile.

This gigantic predator was discovered decades ago, yet it has not yet been provided a name. Learn what else makes this creature so unusual!

What Was the Monster of Aramberri?


Pilosaurs had shorter necks compared to other plesiosaurs.

4,303 People Couldn't Ace This Quiz

Think You Can?

©Mario Lanzas, CC BY-SA 4.0, via Wikimedia Commons – License

The so-called Monster of Aramberri was a large pliosaur. This large reptile was a member of the Plesiosauria order. This order consisted of marine reptiles, and some of them, like this monster, grew very large. While some pliosaurs were as few as 12 feet long, the Monster of Aramberri was about 50 feet long.

Scientists believe that this creature measured anywhere between 33 and 50 feet long and weighed about 17 tons or 34,000 pounds. Some new estimates concerning the creature say that it may have been smaller than previously thought, about 36 feet long.

The creature resembles many other pliosaurs in terms of its morphology. They had somewhat shorter necks than other members of Plesiosauria, but they still had long heads and powerful jaws with cone-shaped teeth somewhat like modern crocodiles.

Also, they had large flippers to propel them through water, with larger rear flippers than front flippers. Scientists have little information about the lifestyle of the Monster of Aramberri. Still, they know that other pliosaurs were generalists that ate a variety of other marine animals, even fish up to half their size!

Was the Monster of Aramberri a Dinosaur?

Dimetrodon skeleton

Dimetrodon may look like a dinosaur, but it was not.

©Nick Fox/

The clade name Pliosauridae to which the monstrous pliosaur belongs is somewhat confusing. After all, the “-saur” suffix is frequently attached to members of Dinosauria. Yet, the Monster of Aramberri was not a dinosaur. In fact, the Plesiosaur order indicates that they are “near to” the lizards, or dinosaurs, that were alive at the time.

Several major differences exist between dinosaurs and plesiosaurs. The most significant differences are that the latter were marine animals that lived in water. Few dinosaurs spent much time in the water. Scientists believe that Spinosaurus was an exception, spending at least some of its time hunting in and around the water.  

Also, dinosaurs had anatomical qualities that allowed them to walk upright. Meanwhile, other reptiles at the time, including the marine reptiles and Dimetrodon, had a sprawling stance.

Although it was a massive reptile, the Monster of Aramberri was a completely different creature than a dinosaur.  

Where Were Fossils of This Reptile Found?

The original fossils of this reptile were discovered by a student in 1985. During that year, a student from Universidad Autónoma de Nuevo León, a public university in Nuevo León, Mexico, was performing some geological work in La Caja Formation located in Aramberri, Nuevo León, Mexico. Several fragments of the creature were discovered, and initial estimates claimed that the reptile was about 45 feet long.

Scientists were not able to discern much about the pliosaur’s identity other than it was a plesiosaur. Initially, scientists claimed it was Liopleurodon ferox, but that turned out to be incorrect. The creature may belong to Kronosaurus, but its identity is still unknown.

After the fossils were sent to many other places around the world, including Germany, they were returned to Mexico in 2012. Currently, they reside at Facultad de Ciencias de la Tierra at Universidad Autónoma de Nuevo León. The so-called Monster of Aramberri still does not have an identity over 30 years after its discovery.

When Did the Monster of Aramberri Live?


Plesiosaurs were abundant during the Jurassic Period, and some lived well into the Cretaceous.

©Daniel Eskridge/

Scientists have not released much information about the life of the pliosaur in question. However, the creature was discovered in La Caja Formation, an area found in the northeastern and central portions of Mexico.

The fossils in this area date back to a time between the Kimmeridgian and the lower Berriasian times. The Kimmeridgian age was a stage of the Late Jurassic era from roughly 157.3 to 152.1 million years ago. Meanwhile, the Berriasian was a stage of the Cretaceous that occurred from 145 million to 139.8 million years ago.

That means this pliosaur lived at some point between those eras. Yet, future finds could greatly expand the known time that it roamed the seas. However, very little specific information has been revealed about the Monster of Aramberri. Aside from not knowing to which family this reptile belongs, scientists can only narrow down the reptile’s existence to a period of about 18 million years or so.

Scientists would need other fossils of the same creature to develop a complete understanding of when the animal lived. That may be somewhat difficult considering that scientists don’t even know what specific reptile they’re dealing with yet.

Again, future discoveries could change all of this, narrowing or broadening the timeline in which the reptile lived while also granting some certainty on its size, location, and more.

Why Did Plesiosaurs Go Extinct?

The Elasmosaurus is a long necked plesiosaur

An Elasmosaurus, a long necked plesiosaur featuring a streamlined body with legs shaped like paddles to move their huge bodies around.

©Daniel Eskridge/

Plesiosaurs, including the pliosaurs, lived in the ancient seas for millions of years before going extinct. Scientists don’t know why pliosaurs went extinct, and the same applies to the Monster of Aramberri. Yet, they believe that Plesiosaurs went extinct at the end of the Cretaceous Period due to the same event that killed off the dinosaurs.

The Cretaceous-Paleogene extinction event occurred when a large asteroid impacted the Yucatan Peninsula, causing massive devastation and killing off all terrestrial dinosaurs as a result of the changes in the environment. The impact would have also wiped out significant portions of marine life by killing off many creatures directly and altering the food chain.

Plesiosaurs most likely went extinct as a result of the asteroid impact or possibly ongoing volcanism at the Deccan Traps.

The Monster of Aramberri remains a mystery. While scientists know this creature was a pliosaur, they haven’t discovered much more about the reptile. Without other discoveries, we may never know anything else about this gigantic marine animal.  

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

Share on:
About the Author

Kyle Glatz is a writer at A-Z-Animals where his primary focus is on geography and mammals. Kyle has been writing for researching and writing about animals and numerous other topics for 10 years, and he holds a Bachelor's Degree in English and Education from Rowan University. A resident of New Jersey, Kyle enjoys reading, writing, and playing video games.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.