The ancient crocodile, Deinosuchus riograndensis, had a broad spectrum when it came to feeding on dinosaurs, just like its broad snout, a feature most alligators share. However, one feature that differentiates modern alligators from this apex prehistoric predator is the tolerance Deinosuchus had for salt water, which also indicates why it was such a versatile and dino-devouring predator.
Deinosuchus had a body as large as a bus and teeth as long as bananas, ruling the rivers and estuaries of North America 82 to 75 million years ago. Their scientific name translates to “terror crocodile,” and the name wasn’t too far off either. They had broad, long skulls, tipped with a bulbous lump never seen in other crocodilians. Their toothmarks have been discovered in dinosaur fossils, which suggests that they preyed on dinosaurs.
Although called terror crocodiles, these reptiles were thought to be more akin to alligators and their predecessors. However, newer fossils and DNA studies of modern crocodiles and alligators have uncovered hints that Deinosuchus belonged to a different branch of the crocodilian tree.
Unlike alligatoroids, Deinosuchus retained the salt glands, which are present in modern crocodiles, enabling them to tolerate salt water by collecting and releasing excess sodium chloride.
Tolerance toward saline waters would have helped Deinosuchus navigate the Western Interior Seaway, which once divided North America, during a greenhouse phase characterized by global sea level rise. Deinosuchus could have then spread across the continent to dwell in coastal marshes on both sides of the ancient inland sea, as well as along North America’s Atlantic coast.
The new study sheds new light on the family tree of crocodilians, offering fresh insights into climate resilience within the group and also providing insight into how some species adapted to environmental cooling while others went extinct. With salt glands allowing Deinosuchus to travel where its alligatoroid relatives couldn’t, these crocodilians settled in habitats abundant with large prey. Deinosuchus evolved to become an enormous apex predator that dominated marshy ecosystems, where it fed on anything it chose to consume.
According to senior study author Dr. Márton Rabi, a lecturer at the Institute of Geosciences, University of Tübingen, Germany, no animal was safe in these wetlands, especially when giant, killer crocodiles were present.
Since the middle of the 19th century, Deinosuchus fossils have been found on both sides of the ancient seaway in North America, on the island of Laramidia, and the other island portion called Appalachia. Scientists have been puzzled by the fact that a species that shared more features with alligators, which strictly kept to freshwater, was able to inhabit both sides of the vast seaway. One hypothesis that was rejected due to a lack of evidence is that alligators had tolerance to saltwater, but eventually lost that trait.
Another hypothesis was that Deinosuchus spread across North America before the Western Interior Seaway formed, establishing a divide between western and eastern populations. However, the fossil finds doesn’t support this, as the seaway formed approximately 100 million years ago, making it approximately 20 million years older than the fossils that have been found to date.
The researchers used data from extinct crocodilians that were not sampled for the group’s earlier family trees for the analysis. The team connected species that were not previously recognized as related. These “missing links” helped the team reassemble the order in which specific characteristics emerged in the group.
According to Rabi, saltwater tolerance is a fairly ancient trait that was lost in alligators. Dr. Evon Hekkala, a professor and chair of the Department of Biological Sciences at Fordham University in New York City, states that moderate saltwater tolerance was sufficient to aid in the survival of crocodilian species that were more resilient to climate change and drastic environmental shifts.
The researchers formulated a new crocodilian family tree using molecular data from modern crocodilians to have a clear idea about the traits shared by alligatoroids. The team found that the earliest alligators were smaller than other crocodilians that lived at the same time. After the climate cooled and competition subsided, alligators began to evolve the larger body sizes seen today, about 34 million years ago.
Another clue that giant Deinosuchus was no “greater alligator” is the dwarfism noted in alligators of that era. Deinosuchus likely diverged into a different branch of the family tree before alligatoroids evolved, Rabi said.
This new study shifts the rigid vision of Deinosuchus as an alligatoroid to something more flexible, suggesting that it may represent a distinct branch of crocodilians altogether. This aligns much better with the ecological role that these giant reptiles played, providing a valuable insight into how evolution occurred in crocodilians.
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