“We wondered if we did alligator falls, if we’d recover species that haven’t been previously known to science — relics and refugees from a time when marine reptiles dominated the ocean,” he said. “Are we going to be able to uncover an ancient fauna?”

The research, published last month in PLOS ONE, didn’t just turn up a new species that thrives on alligator bones, but also revealed surprises about the food web deep beneath the Gulf of Mexico, including how carbon from Earth’s surface gets recycled in the oceans.

Usually, Dr. McClain’s lab studies how deep-sea creatures feed on trees swept into the Mississippi Delta. But they began wondering what happened to alligators.

“There were three swimming behind my house in the harbor,” Dr. McClain said. “That got my lab thinking about alligators in general as potential food falls.”

Alligators are found in coastal habitats from Texas to South Carolina, and occasionally venture into saltwater. When they die, some must sink into the deep ocean.