This data set was compared with modern groupings of animal bones to check what sort of process today "closely mimics" the Utah deposit.

One of the closest analogies he found is "an African water hole during drought."

Many animals gather around water holes in a drought. Elephants will eat all the food in the vicinity and then ingest "dirt and logs and rocks" to keep their stomachs full, without leaving the water hole, he said.

At the end of a bad drought, "you get numerous animals dying." As animals die, carnivores move in and feed on the carcasses. They tear up the remains.

The African water hole site contained a large "disarticulated mass of bones" — similar to what scientists are finding at Cleveland-Lloyd.

Gates thinks the long-necked dinosaurs may have died first in the drought, each leaving "a ton of meat" for the allosaurs.

The allosaurs scavenged and they too died in the drought. Still more of the meat-eaters moved in, apparently not above cannibalism.

"That might be why we ended up with close to 50 allosaurs around this tiny water hole in the Jurassic," Gates said.

He and experts at the Prehistoric Museum in Price are carrying out chemical analyses of teeth found at Cleveland-Lloyd, particularly those of camarasaurus. They want to determine if the teeth recorded a pattern of drought that stressed the big beasts.

Gates stressed that his findings so far are "not the end of the story. There's a lot more information that needs to be found before we come up with a more solid reading."

Meanwhile, scientists and members of the public were delighted with the new visitor center and the improvements at the quarry.

"I think it's (the renovation) overdue," said Scott Sampson, paleontologist for the Utah Museum of Natural History, who now lives in California.

"I think this is a world-class site. It contains by far the largest collection of any large carnivorous dinosaurs in the world. ... There's nothing else like it, and the site needs to be highlighted."

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E-mail: bau@desnews.com