‘Shieldcroc’: The Prehistoric Crocodile With a Bump On Its Head

MU assistant professor Casey Holliday nicknamed Aegisuchus witmeri “Shieldcroc” because of its thick skinned shield. (Henry Tsai/University of Missouri)

MU assistant professor Casey Holliday analyzed a portion of a fossilized crocodile skull to identify a new species, Shieldcroc. Analyzing scarring and ridges on the skull, he identified a thick-skinned “shield” on top of the skull. (Casey Holliday/University of Missouri)

The remains of a new species of ancient crocodilian have been unearthed in Morocco that date back to the Late Cretaceous Period, around 95 million years ago.

The now-extinct crocodile is named Aegisuchus witmeri and has been nicknamed “Shieldcroc” due to the shield-like layer of thick skin on its head. The new species was identified from the remnants of a fossilized skull.

Study co-author Casey Holliday at the University of Missouri noticed blood vessel scarring on the surface of the skull bones, indicating that the croc had a circular mound-like structure on top of its head. This is unknown in any other crocodile species. He believes it could have been used in breeding displays or to scare off enemies, and may also have been involved in temperature regulation.

Comparison of the skull with other crocodile species revealed that Shieldcroc had a flatter head.

“We believe Shieldcroc may have used its long face as a fish trap,” said study co-author Nick Gardner at Marshall University in the release. “It is possible that it lay in wait until an unsuspecting fish swam in front of it. Then, if it was close enough, Shieldcroc simply opened its mouth and ate the fish without a struggle, eliminating the need for strong jaws.”

The researchers determined that this particular croc was about 30 feet long with a 5-foot-long head.

“Scientists often estimate body size of crocodilians based on the size of the skull,” Gardner said. “However, estimating the body size of Shieldcroc was difficult, due to the enormous size of the skull compared to other crocodilians. To make a size estimate, we compared several features of the bone to many different species.”

Despite living almost 100 million years ago, Shieldcroc can help scientists understand how to protect the ecosystems of modern crocodiles from the damaging effects of human activities.

“Today’s crocodiles live in deltas and estuaries, the environments put under the most stress from human activity,” Holliday said, adding that understanding how ancient crocs went extinct can help preservation of modern crocs’ habitats.

The findings were published in the journal PLoS-ONE on Jan. 31.