DNA and Fossil Evidence Reveal That North America’s Ancient ‘Terror Crocodiles’ Were Not Alligators

Photo credit: www.smithsonianmag.com

A new study reveals that the giant reptile Deinosuchus is not closely related to modern alligators as previously believed, and it may have thrived by adapting to saltwater environments.

Sara Hashemi – Daily Correspondent

April 24, 2025 2:17 p.m.

Over 75 million years ago, a massive reptile known as the “terror crocodile,” or Deinosuchus, patrolled the waters of North America. Previously thought to be a close relative of modern alligators, recent research indicates that Deinosuchus occupies a more distant branch on the evolutionary tree.

The research, which focused on the genetic and fossil records of 128 living and extinct crocodilians—including crocodiles, alligators, and caimans—provides new insights into their evolutionary history. The findings, now available in the journal Communications Biology, suggest that Deinosuchus was capable of tolerating saltwater, a trait that sets it apart from contemporary alligators.

This study also challenges previous notions regarding the evolution of large crocodilian species. It mentions other gigantic relatives, such as the South American Purussaurus, which reached lengths double that of a pickup truck, and the immense Sarcosuchus, once found in regions that are now South America and Africa.

“It appears that having giant crocodiles may have been fairly common during certain periods,” noted Márton Rabi, a paleontologist from the University of Tübingen in Germany and the study’s senior author, in an interview. “Giant crocs are not particularly exceptional.”

Nonetheless, Deinosuchus distinguished itself in Cretaceous North America as a formidable apex predator. Known for its voracious appetite, it is believed to have preyed on a wide range of animals, including dinosaurs, using its famously large, “banana-sized teeth” for hunting.

“In the wetlands of its time, Deinosuchus was an absolute nightmare for its prey,” Rabi remarked to CNN’s Mindy Weisberger. “This was an enormous creature, likely measuring over eight meters (26 feet) in length.”

According to the study, Deinosuchus’ ability to prosper as a top predator might have stemmed from its adaptability to saltwater environments. During the Cretaceous period, the Western Interior Seaway divided North America into two landmasses, and fossils of Deinosuchus have been identified on both sides. This raised questions among paleontologists since modern alligators are primarily freshwater inhabitants, leading to inquiries about the migration of a supposed alligator ancestor across saline waters.

The research posits that Deinosuchus may not be an alligator at all, potentially possessing salt glands that enabled it to navigate across the salty sea—capabilities not available to its alligator counterparts. This anatomical feature likely allowed Deinosuchus to inhabit coastal regions rich in large prey, contributing to its vast size.

“The ecological adaptability would have permitted crocodilian lineages to exploit varied niches, especially during significant environmental shifts, such as rising sea levels that led to the decline of less tolerant species,” explained Evon Hekkala, a biologist at Fordham University who was not part of the study.

The researchers reconstructed the evolutionary history of crocodilians, positioning Deinosuchus on a lineage that diverged prior to the most recent common ancestor of modern alligators and crocodiles. The implications of these findings suggest that features permitting salt tolerance were retained in crocodile ancestors but lost in later alligator species.

“With this new perspective on the family tree, we propose that the saltwater tolerance observed in past crocodiles remains evident in the Deinosuchus lineage,” stated lead author Jules D. Walter, a paleontologist at the University of Tübingen. “While Deinosuchus may not have inhabited the ocean full-time, its ability to traverse the Western Interior Seaway suggests a significant geographical spread.”

Not all experts are in agreement with the study’s conclusions, however. Skepticism remains regarding the assertion that Deinosuchus was saltwater tolerant. Adam Cossette, a vertebrate paleobiologist at the New York Institute of Technology, expressed doubt, suggesting that while Deinosuchus may have used saline waters opportunistically, it preferred freshwater habitats.

Cossette further questioned the evidence supporting the idea that Deinosuchus could easily cross the Western Interior Seaway, pointing out that distinct species of the reptile have been found on either side of the waterway. If frequent crossings were possible, the likelihood of interbreeding would increase.

In defense of their findings, Rabi countered, “Crossing [the sea] once does not necessarily indicate a species’ continuous ability to traverse saline environments. It might have been an isolated incident.”

Conversely, Hekkala remarked that the new research aligns well with our understanding of the ecological flexibility among both extinct and extant crocodilian species. “The study effectively illuminates the evolutionary and ecological significance of this remarkable animal,” she added.

Source
www.smithsonianmag.com