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Feb. 8, 2012 Volume 33, No. 19

MU researcher identifies new prehistoric crocodile species

Casey Holliday

CROCS Scientist Casey Holliday holds the Shieldcroc skull roof, which helped identify a new species of crocodile that lived 95 million years ago in Africa. Rob Hill photo


Creature had glowing spot on skull roof, perhaps to convey mood

Imagine a hot and humid misty delta of streams and rivulets green with vegetation and low-hanging trees. Imagine a flying reptile gliding across the sky, a titanosaurus grazing on treetop leaves and crocodiles up to 40 feet long — some running on land, some with flippers paddling in the water, others dining on carcasses, plants or gulping down giant fish.

This was North Africa 95 million years ago, a region that had at least eight species of crocodiles of stunning variety. Last week, an MU paleontologist announced discovering yet another species from the Late Cretaceous period. Nicknamed “Shieldcroc,” the animal was perhaps 25 feet long with a pancake snout and, most remarkably, a glowing raised surface on its skull.

“The fossils we’re finding from this period indicate that the crocodiles we have today are really more boring than those living in the Age of Dinosaurs,” said Casey Holliday, co-researcher and an assistant professor of anatomy at the School of Medicine. “In fact, there is such amazing diversity then that it might be better to call the period the Age of Crocs.”

The discovery was published last week in the journal of the Public Library of Science, PLoS-ONE.

Identifying Shieldcroc

Holliday has studied crocodiles since 2000, but it wasn’t till 2005 that he began the process that led to identifying Aegisuchus witmeri, or Shieldcroc.

Holliday was working at Royal Ontario Museum in Toronto and completing his dissertation on comparative anatomy of skulls of crocodiles and dinosaurs, when one day he opened a drawer to find two specimens tagged “Unidentified.” The specimen that excited him was a 95 million-year-old skull roof, which he could hold in his palms, dug up years earlier in Morocco.

Immediately he knew he had something special. “I recognized it as being from a crocodile, but it had features I had never seen on a crocodile skull before,” Holliday said.

Croc Illustration
Henry P. Tsai illustration

Despite the extraordinary find, Holliday couldn’t thoroughly examine the skull for two years because of other pending projects.

Finally, in 2008, he got down to business.

On modern-day crocodiles and alligators, the skull roof between the ear cavities is about a half-inch. On Shieldcroc, that space is about three inches wide.

But rather than have uniform skull dimples, typical of the genus, Shieldcroc, Holliday discovered, had on its skull ridges, canals and smooth areas. Holliday said the anomalies are blood vessel scarring on the bone. This suggests blood circulated in a rise, or shield, atop the skull.

Many animals signal intimidation, territorial displays and mating desires through a surge of blood into a specific part of the body. Holliday suspects Shieldcroc’s shield was used similarly, or perhaps to regulate brain temperature.

But we’re not talking Rudolph the Red Nosed Reindeer here.

“We think it looked like an eye spot in the middle of the head,” Holliday said. “The region probably had a different color, dark green as opposed to the light green of the rest of the body.”

Holliday set out to identify Shieldcroc’s species. He sent pictures of its skull cap to a colleague at Iowa State, who said it looked a lot like that of Aegyptosuchus, or Egyptian crocodile. As with Shieldcroc, Aegyptosuchus was discovered in North Africa and is about the same age.

After Holliday and other researchers examined Shieldcroc and the Egyptian crocodile, whose specimen is at BSPG (Bayerische Staatssammlung für Paläontologie und Geologie), it was decided that, while similar, Shieldcroc had enough unique attributes to declare it a new species.

“It was a good-news-kind-of day,” Holliday said.

A fish eater, not a fighter

Shieldcroc probably had small teeth and a gaping, pelican-like mouth, researchers say. It lived mostly in the water and would be awkward on land.

Shieldcroc was no SuperCroc, or Sarcosuchus, both of whom lived in North Africa at the same time. At perhaps 40 feet in length and with more than 100 sharp massive teeth, Super Croc had the goods to prey on small- and medium-sized dinosaurs, most likely by dragging them into the delta waters where it drowned, crushed and ripped them to shreds.

Nick Gardner, an undergraduate Shieldcroc researcher at Marshall University in Huntington, W. Va., said Shieldcroc likely hid in underwater foliage or on the sandy bottom lying in wait for fish.

“There were lots of slow moving fish in this environment such as bichirs and coelocanths,” Gardner said.

Neither Shieldcroc nor SuperCroc is a direct ancestor of modern crocodiles and alligators, Holliday said. Shieldcroc and its crocodilian contemporaries were extinct by about 75 million years ago, when the anatomically modern crocodiles and alligators (which are crocodilian forms with differently shaped snouts and rearranged teeth) arrived.

Even so, studying prehistoric crocodiles remains important, Holliday said.

Beside birds, crocodiles are our only living link to dinosaurs and can shed light on those creatures, he said.

Studying them also puts in context the plight of today’s crocodiles as their environments in the Gulf Coast, the Caribbean, the Amazon, Southeast Asia, New Guinea and northern Australia becoms more endangered.

“By understanding how these animals’ ancestors became extinct,” Holliday said, “we can gain insight in to how to protect and preserve the ecosystems vital to modern crocodiles.”

The Shieldcroc fossil will soon be returned to the Royal Ontario Museum, where it will be the centerpiece of a display on Aegisuchus witmeri.