Shark spotted in Karoo

A fossil discovered in the Karoo has led scientists to solve one of the great mysteries of evolution - where the last major surviving vertebrate group sits on the tree of life.

Farmer Roy Oosthuizen's discovery of the fossil in the Prince Albert area in the early 1980s has finally enabled chimaeroids, which are closely related to sharks, to find their place in evolutionary history.

High-definition CT scans of the 280-million-year-old fossilised skull allowed US and South African scientists to reach this conclusion, and their findings were published yesterday in the scientific journal Nature.

"This specimen is the piece of the puzzle that says: 'Ahh right, this is where chimaeroids branch from sharks'," said Rob Gess, of the Albany Museum in Grahamstown, an SA Centre of Excellence in Palaeosciences partner.

An avid fossil hunter, Oosthuizen amassed a collection of more than 3000 specimens. He was with his son when he discovered a slightly flattened egg-shaped rock nodule, which he asked his son to hold so he could hit it with his hammer.

The fossil broke into three, revealing what was thought to be a fossil shark skull.

After being described, the fossil was boxed and archived in the SA Museum in Cape Town, where it remained for decades until 2013, when Gess began scanning Devonian shark fossils.

The scan of the fossil, outwardly that of an extinct symmorid "shark", revealed structures of the brain, cranial nerves, nostrils and inner ear that can be seen in modern-day chimaeras.

"Chimaeroids belong somewhere close to sharks and rays, but there has always been uncertainty when you search deeper in time for their evolutionary branching point," said Michael Coates, professor of organismal biology and anatomy at the University of Chicago, who led the study.

"Chimaeras are unusual throughout the long span of their fossil record," Coates said.

"Because of this it's been difficult to understand how they got to be the way they are. This discovery sheds new light not only on the early evolution of shark-like fishes, but also on jawed vertebrates."

Oosthuizen didn't live to see the impact his fossil would make. Gess said he died in 1999. But the fossil bears his name - Dwykaselachus oosthuizenae.