Evolution Exclusive: Fishy Hips Were Fostered to Become Human Hips
All land-based animals originated from the primordial sea-common knowledge. However, it remains a mystery to scientists. According to a new study, complex, weight-bearing hips in walking animals evolved from the basic skeletons of fish more quickly than previously thought.
In order to find out exactly how fish hips might have evolved into complex, weight bearing hips, Australian researchers examined the bones and musculature of some of humans' closest fish relatives including the Australian lungfish and the Axolotl (known as the Mexican Walking Fish). To their surprise, the differences between human hipbones and fish hips are not nearly as great as they first appeared.
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In fact, it turns out that most of the key elements that are necessary for the transformation to human hips were already present in our fish ancestors. Through the study, they also noticed some rather strong evidence that the structural integrity needed in the hipbone to walk on dry land began forming while tetrapod ancestors were still swimming.
Tetrapods, or four-legged animals, stepped onto land about 395 million years ago. The evolution of strong hipbones and a connection through the spine via an ilium (features not present in the fish ancestors of tetrapods) helped transition from sea to land.
"Many of the muscles thought to be 'new' in tetrapods evolved from muscles already present in lungfish," said Catherine Boisvert of the Australian Regenerative Medicine Institute at Monash University in a news release. "We also found evidence of a new, more simple path by which skeletal structures would have evolved."
So exactly, how would these bones have evolved? Researchers learned that the sitting bones in these fish would have progressively stretched from the pubis already present.
"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," said Boisvert. "Our research shows that what initially appeared to be a large change in morphology could be done with relatively few developmental steps."
The research could have huge implications for the study of evolution and understanding the process by which land mammals came into being.
The research's findings are in the journal Evolution and Development.