Photo by Paul Sereno
The claw on the hand of this predator was probably
10 inches long in life with its horny covering.

Asia's Cretaceous Meat-eaters
Asia's most famous Cretaceous meat-eaters are all tyrannosaurs. And like the most famous North American tyrannosaur, Tyrannosaurus rex, they all lived during the Late Cretaceous. The most common was Tarbosaurus, a huge predator and close cousin of T. rex.

Little is known about the large predators that roamed Asia's Cretaceous world before the "tyrant" meat-eaters rose to dominance. The first clues were unearthed 40 years ago along the eastern edge of the Alashan Desert in Inner Mongolia by the Sino-Soviet Expedition. Jaws and powerfully-built forelimbs with huge sickle-shaped claws were unearthed and named Chilantaisaurus, an Early Cretaceous predator.

Two pieces of the jaw that fit together
and encase several sockets and teeth
of a new, large-bodied predator.

The red and green rocks that compose the buttes and ridges surrounding Camp II date back to the Early Cretaceous.

"There it is, whew!" Paul said as he panted a little from the climb. Paul lifted a 5-inch hand claw from the surface. Brushes and awls whirled, as several team members followed the bones of the forelimb into the rock. This was no Chilantaisaurus. The claw, although robust, was not an enormous, highly recurved, sickle-shaped bone. Yet, it and the other bones of the hand we exposed clearly did not belong to the diminutive forelimb of a tyrannosaur. Was it a relative of North America's high-spined meat-eater Acrocanthosaurus?

Unfortunately, the bones of this new predator were extremely fragile. We could not clean them further in the field without risk of damage. Our curiosity must wait until the jackets are opened and the bones properly exposed in the lab!

This tooth, with serrations on only one of its edges, reveals the presence of a dromaeosaur, a small Deinonychus-like predator.

Small predators were also present in the Early Cretaceous, and we began to find their teeth and fragile limb bones in great numbers. One tooth type was common and peculiar; it had serrations only on one of its edges. That kind of tooth belongs to a dromaeosaur, a family of sickle-toed predators that includes Velociraptor, known from Late Cretaceous deposits elsewhere in the Gobi. Another tooth type from a large predator was also common and similar to that in the jaws of Acrocanthosaurus.

Ancient injury

Unlike 5-toed humans, two-legged dinosaurs stand on only three toes,
the middle one always the longest.

Dave has an extraordinary knack for finding footprints. "Did you just stumble on it? I mean, how did you find it?" we questioned him as we gazed down at the three-toed footprint cast. When you have bones in mind, you can easily walk right over anything else. But Dave often has footprints in mind, especially when he sees a ledge-forming sandstone. He went looking for footprints, overturning heavy slabs of rock.

The footprints he discovered were casts made by sand that infilled a deep trackway in mud made by a large two-legged dinosaur. Compared to a human foot, the print was huge, its three toes broadly splayed. The toes of the print were broader than those commonly made by predators, suggesting that the trackmaker was a large ornithopod, something like Iguanodon . We had one in mind, a large ornithopod called Probactosaurus, first described from similar-aged rocks on the opposite (east) side of the Gobi's Alashan Desert. The space between each print allowed Dave to measure its stride-length.

Not more than a stone's throw away, Andy spied the ribs of a skeleton protruding from the wall of the valley. Soon we had exposed enough of its bones to identify it as an ornithopod, perhaps a close relative of Probactrosaurus. Could it have been the trackmaker? Perhaps. It's rare to find tracks and a potential trackmaker in the same beds, because the conditions for preserving prints and bones can be quite different.

The swollen woven bone on this rib shaft, compared to that of a normal rib, marks the site of an ancient injury which this dinosaur survived.

The ribs grabbed our attention for another reason-a section of the shaft of one of the ribs was swollen. Looking closer, we could see that the enlarged shaft was made of woven bone that forms after an injury. This ornithopod had suffered a broken rib! The natural repair of a broken bone means that the dinosaur survived the accident, dying later for other reasons. The fossils really came alive for us when we saw such vivid evidence of dramatic events in the life of a dinosaur, that took place more than 100 million years ago.

Puzzling turtles
The pea-green color of the rock and the presence of flaky shales gave us the idea that we were about to prospect an ancient swamp or marshland. Shales are made of mud laid down in quiet environments located at some distance from the churning water of a stream. Chipping away at the shale with his rock hammer, Fabrice found twigs that had turned into black coal embedded in the layers.

Minutes after leaving on our first prospecting session, several team members found bones of what we soon would learn was a common swamp inhabitant-turtles. Pieces of shell and limb bones littered the valleys.

Professor Zhao reported finding most of a skeleton. We followed him back to the site, as he quickly scaled a butte more than 100 feet in height. Incredible! The man is 66 years old and is prospecting the top of the tallest butte in the area! His turtle was spread over several square feet. We were amazed at how many bones of the skeleton we were able to find, plucking the tiniest toe bones (called "phlanges") from the eroded surface.

"Here's a claw!" shouted Jeff with delight, holding the quarter-inch long bone between two fingers. All of us had encountered turtle bones, but no one had found one, as it was in life-- shell intact. These turtles were just too delicate, their shells made of dozens of individual plates that seemed to drift apart after death in the mud of the swamp.

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