But they are not the only fossil hunters here.

Once a year for the past four years, the quarry has been opened to the public, and citizen paleontologists have come in droves — about 1,500 for the most recent community event last fall.

“I found a pile of rocks,” said Alexandra Hopper of Mantua, one of the participants. “When we rinse them off, we’re hoping some of them are fossils.” The diggers kept the fossils they found, and there are plenty to go around. The doomed creatures in the pit were mostly clams and oysters. But the fossils of animals like crocodiles and sea turtles are here, too, as well as the occasional mosasaur, a ferocious aquatic lizard with two long teeth at the back of its throat that pointed toward its gullet, ensuring that any prey it swallowed would never struggle out.

Fossils are being found throughout the sediment that fills the pit, but the assemblage occupies a single concentrated layer. Bones and shells sometimes pile up when currents sweep dead sea creatures toward a particular eddy, where they accumulate over years or centuries.

But here the skeletons of the larger creatures remain largely intact. That suggests they all died at the same time and then settled gently on the sea bottom.