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New evidence moves early giant crocodile further from modern alligator on family tree

An international team of paleontologists, geologists, geoscientists and Earth scientists has found evidence that a type of giant crocodile that lived millions of years ago in what is now North America is not closely related to modern alligators. In their study in the journal Communications Biology, the group took a closer look at Deinosuchus fossils and those of other species to determine whether it was saltwater-tolerant.

Prior evidence has shown that Deinosuchus lived approximately 75 million years ago and was quite large. Researchers believe that at least part of its diet included some dinosaurs. They have also assumed that Deinosuchus was closely related to modern alligators. In this new effort, the research team found that not to be the case.

To learn more about Deinosuchus, the research team amassed data from 128 living and extinct crocodilians, including Deinosuchus. They used 219 morphological features to note the differences between the specimens under study. Crocodilians include alligators, crocodiles and caimans. The team used the data to create an evolutionary tree for all of them. The researchers noted that the tree could be used to help make estimates about the sizes of extinct species.

They found that size was not associated with particular periods in time—it was much more tightly tied to opportunity. In places where crocodiles had ample food and plenty of room to roam, they tended to grow bigger. Geography did not seem to matter, either; crocs grew to enormous sizes over the past 130 million years in many parts of the world.

They also found that Deinosuchus was on a distant branch from alligators, and that they were likely at least somewhat tolerant of saltwater. Deinosuchus fossils, the team notes, have been found on both sides of the Western Interior Seaway, suggesting the creature may have swum across—a feat that would have required tolerance of salty seawater.

The research team suggests future studies of Deinosuchus fossils include CT scans to determine if they had salt-excreting glands similar to those in modern crocodiles to prove their tolerance and distance from alligators on the crocodilian family tree.