Ancient Eel-Like Chordates Linked To Evolution Of Human Skeleton
October 17, 2013

Ancient Eel-Like Chordates Linked To Evolution Of Human Skeleton

redOrbit Staff & Wire Reports - Your Universe Online

An international team of paleontologists has published new research in the journal Nature revealing that the human skeleton did not evolve from ancient predatory fossil fish, as previously believed.

Rather, the human skeleton evolved as a way to protect against predators such as the conodont, extinct eel-like chordates that evolved tooth-like structures and tissues independently of other creatures, according to experts from Bristol University, Peking University, the US Geological Survey and the Paul Scherrer Institute.

Conodonts are an extinct group of jawless vertebrates that lived roughly 500 million years ago. Their tooth-like structures are believed to be the earliest instance of a mineralized skeleton among all vertebrates.

“For decades, it was thought that our skeleton and all its characteristic bony tissues originated” in predators like the conodont. However, the new study shows that those creatures were actually “evolutionary copy-cats who evolved tooth-like structures and tissues independently of other vertebrates,” the UK institute said in a statement.

In work funded in part by the Natural Environment Research Council, the researchers used synchrotron radiation X-ray tomographic microscopy to study the tooth-like skeleton of the eel-like creatures. Those high-energy X-rays revealed that the tooth-like structures evolved as part of a separate evolutionary lineage, rather than originating in a common ancestor that the conodont shared with other vertebrates.

“We were able to visualize every tissue, cell and growth line within the bony teeth, allowing us to study their development,” explained lead author Duncan Murdock of the University of Bristol. “We compared the tooth-like skeleton of conodonts to that of their ‘paraconodont’ ancestors and to teeth in living vertebrates, demonstrating that the tooth-like structure of conodonts was assembled through evolutionary time independently of other vertebrates.”

“This removes a key piece of evidence from the hypothesis that teeth evolved before the skeletal armor, and suggests that the common ancestors of conodonts and other vertebrates likely lacked a mineralized skeleton. Rather, it seems that teeth evolved from the armour of our meek filter-feeding ancestors,” added co-author Philip Donoghue of the University of Bristol’s School of Earth Sciences.

In addition to Murdock and Donoghue, study authors included Xi-Ping Dong of the Peking University School of Earth and Space Science; John E. Repetski of the USGS; and Federica Marone and Marco Stampanoni of the Paul Scherrer Institut and ETH Zurich.