An enormous prehistoric crocodile-like creature called "Shieldcroc," so named because of a shield-like bony plate on its head, could be the last common ancestor of animals related to crocodiles and alligators.
Shieldcroc lived during the Late Cretaceous approximately 93 to 99 million years ago. Its skull was discovered in continental freshwater deposits from what is now Morocco, and researchers think that modern crocs may have first evolved near the Mediterranean Sea.
But Shieldcroc then and now is capturing greater interest due to its hard-to-miss "shield," a raised mound of tissue packed with blood vessels and likely covered by a thick sheath, similar to what is seen in the frill of horned dinosaurs. It might have helped to regulate body temperature, but probably served a flashier purpose.
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"There is anecdotal evidence that modern horned crocs will raise the back of their heads to show off their horns during courtship and territorial disputes," Casey Holliday told Discovery News. "We think this shield served a similar purpose, as a means to show off."
Holliday and co-author Nick Gardner analyzed the remains of Shieldcroc, which have been housed at the Royal Ontario Museum of Canada since the early 2000's. The researchers examined the skull in detail, and also compared it to other crocodyliformes from the same time period in Africa.
They determined a sister taxon to Shieldcroc is Aegyptosuchus, but this animal possessed a poorly defined "shield."Given its impressive shield and size, Shieldcroc would have been hard to miss back in its day. Holliday and Gardner estimate that the ancient croc measured over 33 feet long and potentially had a 6.5-foot-long head. Shieldcroc appears to have had a very long, flat face, a rounded nose, small teeth and surprisingly weak jaws.
"Like most of today's crocs, it was likely opportunistic, feeding on whatever it could, however, it was likely not capable of wrestling large vertebrate prey given the slenderness of its jaws," Holliday said.
The Mediterranean Sea at this time was part of the Tethyan Sea that opened into both the Atlantic and Indian Oceans. The Middle East, he explained, hadn't fully formed, "nor had India rammed into Asia yet." Europe then was a cluster of islands.
The area seems to have been ground zero for crocs, leading some researchers to even rename this Age of Dinosaurs time to the Age of Crocs.
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"The Cretaceous is full of giant crocs including Sarcosuchus, Dyrosaurus, Deinosuchus, Shieldcroc and others," Holliday said. "There was likely ample food and a warm climate facilitating their ability to reach large sizes. There are fossils of very large fish from the region, so there were certainly large prey to catch as well."
Huge fish called coelacanths were probably front and center on Shieldcroc's menu, the researchers suspect. They presented their work today at the Society of Vertebrate Paleontology's 71st Annual Meeting in Las Vegas.
Christopher Brochu, an associate professor in the University of Iowa's Department of Geoscience, told Discovery News that Shieldcroc "really is a cool crocodyliform" and he admires the authors' "careful comparative work," but he doesn't "buy the taxonomic conclusions." Brochu thinks "the origins of Crocodylia are almost certainly Laurasian in origin and probably not Mediterranean."
Brochu, however, added that Shieldcroc is a significant fossil, with its importance lying "in revealing the diversity and flat-out bizarreness of crocodyliformes during the Cretaceous, especially in the Southern Hemisphere. There was something different about that region at that time -- many of the roles played by dinosaurs in the Northern Hemisphere were played by crocodyliformes in the south."
Hans Larsson, chair of Vertebrate Paleontology at McGill University, told Discovery News, "This specimen sheds more light and shadow on the origins of living crocodiles."
"There is just enough information in the specimen to help clarify some issues, such as the possible Mediterranean origin of living crocs," Larsson continued. "But the species adds another bizarre piece of anatomy, the strange bony plate on its skull, to an already wildly diverse group of Cretaceous crocodyliformes."
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