Natural selection is a powerful thing and it works. This article is about huge otters who lived 6 million years ago and their favorite meal, big clams.

Digital, 3-D reconstructions show the skulls -- including the jaws -- of the roughly 15-pound common otter Lutra lutra (left), and the roughly 110-pound Siamogale melilutra, a giant prehistoric otter with a surprisingly powerful bite (right).

In this wet and forested environment, the otter's jaw power could have given it an edge over predators that could not hunt in water or smash the shells of aquatic prey.

"Carnivores are known to evolve powerful jaws, often for the purpose of cracking the bones of their prey," said Wang, a curator in the Vertebrate Paleontology Department of the Natural History Museum of Los Angeles County. "In the shallow swamp of South China, it's possible that an abundance of big clams drove these giant otters to acquire their rare traits, including their crushing teeth and robust jaws." Wang, along with Su, White and Ji, was a member of the research team that first reported the discovery of the giant otter's fossils in January.

A giant, prehistoric otter's surprisingly powerful bite. The extinct otter had an unexpectedly sturdy jaw, suggesting that the animal may have been a top predator.