The Sahara desert, with its endless stretches of sand and searing heat, may not be the first place you’d expect to find a prehistoric sea monster. But that’s exactly where National Geographic grantee Federico Fanti and his team of paleontologists made an astonishing discovery: the remains of a massive marine crocodile named Machimosaurus rex.

With estimated lengths of up to 30 feet (9.14 meters) and razor-sharp teeth, M. rex was a true apex predator of the Late Jurassic seas. Fanti and his colleagues pieced together the crocodile’s fossilized bones, unlocking clues about its anatomy, behavior, and evolutionary history. This groundbreaking research sheds new light on the ancient ecosystems of North Africa and the fascinating creatures that roamed them millions of years ago.

National Geographic grantee Federico Fanti and his research team have unearthed a sea-dwelling crocodylomorph (a teleosaurid) skeleton in southern Tunisia, in the Sahara desert: Machimosaurus rex. It is the world’s largest marine crocodyliform and was previously unknown to science. Its length is estimated at more than 30 feet (9.14 meters) [Notte: later, this size was downgraded]. The giant probably weighed at least three tons.

The fossil dates back 130 million years ago. The head of the crocodile alone is over 5 feet long. The discovery proves that this animal lived 25 million years past the hypothesized global extinction at the end of the Jurassic period.

Machimosaurus rex: a giant Cretaceous crocodile

Machimosaurus rex: National Geographic grantee Federico Fanti and his research team discovered a giant Cretaceous crocodile skeleton in southern Tunisia. The fossil dates back 130 million years ago. The head of the crocodile alone is over 5 feet long. The discovery proves that this animal lived 25 million years past the hypothesized global extinction.

The teleosaurids were marine crocodyliforms similar to the modern gharial (Gavialis gangeticus, the fish-eating crocodile) that lived from the Early Jurassic to the Early Cretaceous. They had long snouts, which allowed them to swim in the ocean, indicative of piscivory (fish-eating).

So, other than its massive size, the Machimosaurus rex would have looked much like a modern-day gharial (the gharial is one of the longest of all living crocodilians, measuring up to 6.25 meters /20.5 feet, though it should be noted that this is an extreme upper limit, as the average adult gharial is only 3.5 to 4.5 meters / 11 to 15 feet in size).

The head of the Machimosaurus rex fossil
The head of the Machimosaurus rex fossil. The full-grown adults are estimated at more than 30 feet (9.14 meters) long.
Machimosaurus rex vs human size comparison
Machimosaurus rex size compared to an average-sized scuba diver. Although the recovered fossil remains are fragmentary, enough remained in the 120-million-year-old rock to identify the reptile as the largest known member of a particular lineage of crocodiles that spent their lives almost entirely at sea.

Federico Fanti, the head of the research team, says: “Machimosaurus rex had stocky, relatively short and rounded teeth and a massive skull capable of a remarkable bite force.” It was preying mainly on fish, but capable of hunting a variety of prey, including large marine turtles.

The biggest freshwater crocodilian ever, Aegisuchus, lived during the Late Cretaceous (100.5-66 million years ago) and grew 15 to 21 meters (49 to 69 feet).

Machimosaurus rex
The rendering of Machimosaurus rex by Davide Bonadonna of National Geographic.

Update: a new estimate of Machimosaurus rex’s size

More recent estimates put Machimosaurus rex along with Machimosaurus hugii (another Machimosaurus species known from the Kimmeridgian of Portugal, Spain, Tunisia, and Switzerland) at about 6.9-7.2 meters (22.6-23.6 feet) long (skull length 155 cm or 61 inches).

Still larger than all modern crocodiles, but not as large as previously thought.

Quote from a recent study on the Palaeontologia Electronica website:

“Known to have evolved a wide range of body lengths (2-5 meters based on complete skeletons), there is currently no way of reliably estimating the size of incomplete specimens. This is surprising, as some teleosaurids have been considered very large (9-10 meters in total length), thus making Teleosauridae the largest-bodied clade during the first 100 million years of crocodylomorph evolution.”

“Our examination and regression analyses of the best-preserved teleosaurid skeletons demonstrate that: they were smaller than previously thought, with no known specimen exceeding 7.2 meters in length; and that they had proportionally large skulls, and proportionally short femora when compared to body length. Therefore, while many teleosaurid species evolved a cranial length of ≥1 meter, these taxa would not necessarily have been larger than species living today. We advise caution when estimating body length for extinct taxa, especially for those outsides of the crown group.”


M. Özgür Nevres

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