Common ancestor of sharks and humans revealed

Jun 14, 2012

Just when you thought it was safe to go back in the water, researchers find common ancestor

A NEW STUDY suggests that all jawed vertebrates, including humans and sharks, evolved from a shark-like fish that lived about 300 million years ago, Discovery reports.
Scientists came to the conclusion after analysis of a 290-million-year-old fossil braincase. Researchers say the braincase showed the 'shark' belongs to the same group as modern animals with jaws, the study, published in Nature, says.
"The common ancestors of all jawed vertebrates today organised their heads in a way that resembled sharks," study researcher John Finarelli, a vertebrate biologist at University College, Dublin, said in a statement.
"Given what we now know about the interrelatedness of early fishes, these results tell us that while sharks retained these features, bony fishes moved away from such conditions."
Finarelli and his colleagues examined a fish called Acanthodes bronni, part of the acanthodian group of fish, which included the earliest vertebrate animals with jaws.
A. bronni lived about 290 million years ago, during the Paleozoic period. The sharks, whose bodies are supported by cartilage instead of hard bones, split from the bony fishes, which have harder skeletons, about 460 million years ago.
The acanthodian sharks lived before the evolutionary divergence of the earliest cartilaginous sharks and the first bony fishes. Bony fishes eventually gave rise to human beings.
The Acanthodes were relatively large compared with other known "spiny" sharks. They measured about a foot in length, and had gills, large eyes and fed on plankton.
Scientists say the acanthodians became extinct about 250 million years ago. Very little is known about what they looked like, because few fossils have been found.
But after scientists acquired new data, they conducted an analysis of the evidence from the braincase of Acanthodes bronni, the best-preserved of the species within the group.
According to environmental biologist Dr Maureen Kearney of the National Science Foundation in the United States, the new study shows "important evolutionary transitions in the history of life, providing a new window into the sequence of evolutionary changes during early vertebrate evolution".

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