The Terror From the Cretaceous Lagoon

Lurking within humid waters all over the world, one of nature’s most successful lineages of killers thrives: the crocodiles. Regularly portrayed as living fossils, the history of crocodilians is one of nature’s greatest success stories. Crocodiles are part of the family known as the Pseudosuchians, a group that first appeared in earth’s history during the Triassic period alongside their Dinosaurian cousins. The fossils of early Pseudosuchians are extremely strange and diverse, with members including everything from the massive land carnivores known as the Rauisuchians to the Aetosaurs, herbivorous goliaths with appearances akin to armoured dinosaurs. Throughout the Mesozoic era, these strange forbearers to modern crocodiles were slowly replaced by more advanced species. By the end of the Cretaceous period, the first true crocodiles and alligators began emerging across the world, setting the stage for their modern ancestors to take over the waterways of the present, inspiring fear in all those who dare step foot in the waters they call home.

Sadly, most Pseudosuchians went extinct during the Mesozoic era; only crocodiles, alligators, the South American caimans and the strange (but near-extinct) gharial remain today. While these ferocious animals are some of the largest predatory animals alive today, crocodiles in the past were entirely different monsters. During the Mesozoic era, some crocodiles grew so large that they overshadowed even the largest carnivorous dinosaurs in size. In particular, one species of North American Alligator has garnered a mystical reputation over the years as being so enormous that it routinely feasted on dinosaurs. This behemoth Alligator, the aptly named Deinosuchus, did indeed live alongside dinosaurs; but did it really prey upon them? In this article, I will discuss the validity of Deinosuchus’ fame as a dinosaur-eating crocodile, as well as some other cool facts about the “terrible crocodile”.

The Size of a Giant

Just how big was Deinosuchus? While this may seem like a straightforward question, the true size of Deinosuchus had been a mystery to paleontologists for almost a century following its discovery. This is due in large part to the fact that, to this day, no complete skeleton of Deinosuchus has been discovered. Instead, known remains largely consist of teeth, skull and jaw bones, osteoderms (armor on its back) and the occasional vertebrae. This lack of fossil material may seem problematic; however, it is enough to be able to make an accurate figure of Deinosuchus’ size by comparing the fossils to its modern relatives. Modern crocodiles and alligators have an uncomplicated ratio of skull to body size, with larger skulls indicating larger individuals. By using this ratio of skull: body size, paleontologist David Schwimmer has been able to extrapolate the size of Deinosuchus. His findings indicate that the minimum size of Deinosuchus was around 8 meters in length, with the maximum size reaching 12.5 meters in length (Schwimmer 2002). Another method used by Schwimmer was to take Deinosuchus and Alligator vertebrae — the former of which has a vertebrae 1.5 times larger — and multiply the dimensions of large alligators by this figure. His findings once again produced the figure of around 8 meters in length, giving conclusive results to the size of Deinosuchus.

What about weight? By once again comparing the weight of modern Crocodiles and Alligators to their prehistoric cousin, Schwimmer found that Deinosuchus had a minimum weight of around 4 tonnes and a maximum weight of 8.5 tonnes. Allow me to take a moment to put the size and weight numbers of Deinosuchus into perspective. The record-holder for largest crocodile in captivity was a man-eating saltwater crocodile from the Philippines named “Lolong”. At the time of death, Lolong was a monstrous 6.15 meters long and weighed over a tonne (Dell’Amore 2012). The MINIMUM size of Deinosuchus was over two meters longer and weighed three more tonnes than Lolong. The maximum size of Deinosuchus, 8.5 tonnes and 12.5 meters long, is about the same size as the largest known Tyrannosaurus Rex specimen! With size dimensions like these, it becomes clear how Deinosuchus gained a reputation as a killer of dinosaurs.

Lineage of Supercrocs

Even though Deinosuchus may seem to be a sure-fire candidate for the “largest crocodile ever” award, it was far from the only species of giant crocodile. In addition to Deinosuchus, many additional genera of “Supercroc”— most notably Sarcosuchus from North Africa and Purussaurus from South America — exceeded sizes of ten meters or more in length. These Supercrocs were widespread across the world, with individuals known from North and South America, Africa and Asia. Supercrocs weren’t restricted to the Mesozoic period either; some genera thrived long after the K-T extinction, with Purussaurus going extinct shortly before the start of the ice age. The vast reign of the Supercrocs is a testament to the adaptability of crocodilians, as even through catastrophic extinctions, these magnificent animals can still reign supreme.

Were Dinosaurs on the Menu?

To answer the million-dollar question, we must first understand the paleoecology of Deinosuchus. As previously stated, Deinosuchus lived during the late Cretaceous period of what is now the USA. During the Cretaceous, North America was divided into three separate landmasses by a shallow inland sea that covered most of the modern-day American Midwest as well as the areas that would become the Canadian prairies. The western landmass, known as Laramidia, was flourishing with enormous amounts of dinosaur genera. The eastern landmass, Appalachia, still had plenty of dinosaurs, but far less than Laramidia. The fossils of Deinosuchus are widespread amongst both landmasses, which indicates that they were able to traverse the open ocean to migrate in a fashion similar to modern saltwater crocodiles. While their presence on both landmasses indicates the occasional venture into deeper waters, there is a key difference between the eastern and western Deinosuchus: their diets.

The eastern species of Deinosuchus is known as D. rugosus, who can be characterized (relatively speaking of course) as a bit of a light weight. D. rugosus was on the smaller side of the scale for Deinosuchus, topping out at around 8 meters in length and first appearing in the fossil record around 82 million years ago. The western species of Deinosuchus, D. riograndensis, was the true giant. D. riograndensis represents the 12-meter-long individuals of Deinosuchus and evolved about seven million years after D. rugosus, appearing some 75 million years ago in what is now Texas. The vast difference in size between the two species must have been caused by some environmental factor within their respective landmasses. One possible explanation for their inequality is simple: what they ate.

As noted, the dinosaur population to the east was scarce in comparison to that of the west. For a large crocodile to survive, it would have had to prey on the food that was readily available. In the case of Deinosuchus, this entailed preying upon large fish species as well as common turtles. These attacks on turtles are demonstrated in the fossil record, as shells in the east are routinely found with the bite marks of a large crocodile on them, sometimes shattered entirely. With this in mind, it is clear that these eastern Deinosuchus likely fed on a wide variety of food, similar to modern alligators. The lack of consistent, large prey prevented them from exceeding the length of 8 meters, hindering them from becoming massive. On the other hand, their western counterparts experienced no such difficulties. Large herds of Hadrosaurids and Ceratopsians shared the estuaries and river systems that Deinosuchus would have called home. Since there was plenty of dinosaur prey available, it has been theorized that the western Deinosuchus populations became specialists when it came to hunting large dinosaurs. This theory is supported by the larger size of the western populations, due to the larger and more readily available prey, as well as the fact that Hadrosaurid bones have been found displaying evidence of a crocodile attack. The injuries of the bones fit when placed alongside Deinosuchus teeth, giving concrete evidence of a predator-prey relationship between the two species. Some have gone so far as to anoint Deinosuchus the top predator of its western habitats, beating out large carnivorous dinosaurs and possibly eating them as well. In either situation, it’s clear that Deinosuchus would have been a terrifying opponent for any dinosaurs unlucky enough to cross its path.

Based upon the evidence presented, it would seem as though Deinosuchus did in fact eat dinosaurs. For 10 million years Deinosuchus thrived in the shallow seas of North America, only perishing when the waterways it called home eventually receded. While other Supercrocs would come after it, only Deinosuchus can hold the title of the dinosaur-eating alligator.

References:

I do not take credit for any artwork in this article.

Deinosuchus attack courtesy of Andrey Atuchin

The grand Deinosuchus courtesy of Mark Witton, found Here

Deinosuchus skull size found Here

Dell’Amore, Christine. “Giant Crocodile Breaks Size Record-Suspected in Fatal Attacks.” National Geographic, 3 July 2012, http://www.nationalgeographic.com/news/2012/7/120702-biggest-crocodile-lolong-guinness-world-records-animals-science/.

Schwimmer, David R. King of the Crocodylians: the Paleobiology of Deinosuchus. Indiana University Press, 2002.

Witton, Mark P., and Charles Robert Knight. Life through the Ages II: Twenty-First Century Visions of Prehistory. Indiana University Press, 2020.