A dolphin captured alive near southwestern Japan on Oct. 28 was found with two short, symmetrical hind fins in addition to the normal front flippers, an anomaly many scientists have called an evolutionary throwback.

The unusual appendages near the dolphin’s tail are shorter and stubbier than its front fins and are about the size of a human hand.

Most biologists say the dolphin’s front fins correspond structurally to the arms and forelegs in other land-based mammals; the back fins found on the animal appear to be homologous to the hind legs of terrestrial mammals.

Fossil evidence indicates that the ancestors of dolphins and other marine mammals had previously walked on land before evolving into ocean creatures, said Dean Adams, associate professor of ecology, evolution and organismal biology.

“It happens a lot, and not just to marine mammals,” Adams said. “Snakes appear to have also lost their legs; we know they’ve lost them because their fossil ancestors had hind legs. Pythons and boas even have nubs, which are what’s left of their femurs.”

Adams said terrestrial mammals such as the hippopotamus may share an evolutionary ancestor with dolphins and whales.

He said changes in genetic silencing could account for the sudden appearance of a long-lost physical trait.

It was unclear whether the dolphin made effective use of the back fins during swimming and maneuvering.

The animal was transported from the southwestern Japanese coast to the nearby Taiji Whaling Museum for further study.

Erin Mugge, junior in zoology and president of the ISU Marine Biology Club, said the discovery demonstrated the progression of scientific knowledge and showed how much there still is for humans to learn about nature in general and the ocean in particular.

“This discovery demonstrates the fact that not only is our knowledge of biology always changing, but especially marine biology,” Mugge said.

“There seems to always be new discoveries made in the ocean, especially because the ocean has such a large biodiversity in general. I think that is what intrigues many biologists and marine biologists – the fact that they could find something never seen before and this creates an exciting career or area of study.”

Mugge said more knowledge about evolution could possibly be gained from this discovery.

“I think this could very well be a factor helping to determine whether marine mammals evolved from terrestrial mammals and whether marine mammals have the same lineage as the hippopotamus,” Mugge said.

Kim McFarland, senior in animal ecology and Marine Biology Club secretary, also said the discovery could have important implications.

“I think this discovery is one that could possibly open many doors to the mystery of the past,” McFarland said.

“There is so much that is unknown that every little bit adds a piece to the puzzle.”