Evolution Of Hips Simpler Than Suspected
May 15, 2013

From Swimming To Walking, The Evolution Of Hips Simpler Than Thought

April Flowers for redOrbit.com - Your Universe Online

The evolutionary path from the bone structure of the fish to the complex, weight-bearing hips of walking animals was a much simpler process than previously thought, according to a new study.

About 395 million years ago, the first tetrapods, or four-legged animals, stepped onto land. This transition was accomplished using strong, weight-bearing hipbones and a connection through the spine via the ilium. These features were not present in the fish predecessors of tetrapods.

An international team of researchers, including Dr Catherine Boisvert of the Australian Regenerative Medicine Institute at Monash University, MacQuarie University's Professor Jean Joss and Professor Per Ahlberg of Uppsala University, examined the hip structures of some of humankind´s closest fish cousins. Their results were published in a recent issue of Evolution and Development.

The team found that the differences between us and them are not as great as they appear. Most of the key elements needed for the transformation from fish hips to human hips were already present in the ancient fish.

To determine this, the team compared the hip development — including both bones and musculature — of the Australian lung fish and the Axolotl, or Mexican Walking Fish. They found that the transition from simple fish hip to complex weight-bearing hip could be done in just a few evolutionary steps.

"Many of the muscles thought to be ℠new´ in tetrapods evolved from muscles already present in lungfish. We also found evidence of a new, more simple path by which skeletal structures would have evolved," Boisvert said.

The sitting bones, according to the study, would have evolved by the extension of the already existing pubis. An genetic process for iliac development already present in fish could have evolved into the connection in the vertebral column in a relatively simple manner.

"The transition from ocean-dwelling to land-dwelling animals was a major event in the evolution of terrestrial animals, including humans, and an altered hip was an essential enabling step," Boisvert explained.

"Our research shows that what initially appeared to be a large change in morphology could be done with relatively few developmental steps."