Evolution: transition fish to land (Introduction)

by David Turell , Tuesday, September 05, 2017, 00:04 (2433 days ago) @ David Turell

A strange new finding that doesn't really fit previous findings:

https://www.newscientist.com/article/2146256-weird-fish-fossil-changes-the-story-of-how...

"Fossils have revealed many of the stages in this iconic evolutionary event. The evolutionary tree of species involved in the switch from sea to land has remained stable since the late 20th century, even as new fossils have come to light.

"However, a fossil discovered in a quarry in Ningxia, north China, now threatens that stability. It was discovered in 2002 by Min Zhu at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and Per Ahlberg at Uppsala University in Sweden.

"The fossil belongs to a new species of lobe-finned fish, named Hongyu chowi. It was about 1.5 metres long, and lived 370 to 360 million years ago.

"But when the researchers tried to fit H. chowi into the existing evolutionary tree, it didn’t fit easily.

"That’s because in some respects, H. chowi looks like an ancient predatory fish called rhizodonts. These are thought to have branched off from lobe-finned fish long before the group gave rise to four-legged land animals.

"But Ahlberg says H. chowi has aspects that look surprisingly like those seen in early four-legged animals and their nearest fishy relatives – an extinct group called the elpistostegids. These include the shoulder girdle and the support region for its gill covers.

"This implies one of two things, the researchers say. The first possibility is that H. chowi is some sort of rhizodont that independently evolved the shoulders and gill cover supports of a four-legged animal.

"Alternatively, the rhizodonts may be more closely related to the four-legged animals and the elpistostegids than we thought. But this would also imply a certain amount of independent evolution of similar features, because the rhizodonts would then sit between two groups that have many features in common – features the two groups would have had to evolve independently.

"This implies one of two things, the researchers say. The first possibility is that H. chowi is some sort of rhizodont that independently evolved the shoulders and gill cover supports of a four-legged animal.

"Alternatively, the rhizodonts may be more closely related to the four-legged animals and the elpistostegids than we thought. But this would also imply a certain amount of independent evolution of similar features, because the rhizodonts would then sit between two groups that have many features in common – features the two groups would have had to evolve independently."

Comment: Apparently more than one type of fish tried to evolve into a life on land. Appears to be an example of convergence.