T. rex fossil leads researchers to new species of shark

Scientists examining rock left over from the discovery of afossilizedTyrannosaurus rex recently came across a surprise: shark teeth.

The huge meat-eating dinosaur, the remains of which wereextricated in the1990s,was not killed by a shark. But, scientists said on Monday, when the 12.3-metre beast, known these days as Sue, died some 67 million years ago, it fell into a South Dakota river teeming with sharks albeit small ones thriving in the freshwater environment.

The skeleton of Sue, the largest, most complete and best-preserved T. rex ever unearthed, is displayed at the Field Museum in Chicago, which kept the leftover rock for years in underground storage. That rock has now yielded fossils from other creatures that were Sue's neighbours including a shark species called Galagadon nordquistae.

Galagadon, related to a group called carpet sharks found in Indo-Pacific seas today, measured 0.3 to 0.6 metreslong, with teeth the size of a sand grain, about onemillimetre. Tyrannosaurus teeth were up to 30 centimetres long.

If the sharks ever interacted with Sue, it may have been when the thirsty dinosaur came to the river for a gulp of water.

"It would not surprise me at all if a T. rex individual scared a little Galagadon as it lowered its head to drink," said North Carolina State University paleontologist Terry "Bucky" Gates, lead author of the researchpublished in the Journal of Paleontology.

If the prehistoric shark resembled its existing relatives, it was a blunt-faced bottom-dweller with barbels by its mouth like a catfish and camouflage patterning.

"The teeth have an unusual shape with three unequal points and a wide apron at the root. Some of the teeth bear an uncanny resemblance to the spaceship in the 1980s arcade game Galaga,which inspired the genus name," said co-author Pete Makovicky, a paleontologist and Field Museum dinosaur curator.

Scientists also are studying fossils of at least two other shark species from Sue's river. Virtually all sharks live in the sea, though two freshwater species today reside permanently in rivers and lakes, and some other species venture into freshwater.

"I doubt Galagadon spent its whole life in freshwater habitats," Makovicky said, suggesting its river may have been connected to an inland sea 160 kilometresaway that at the time split North America in half.