280 Million-Year-Old-Fossil Reveals How Ghost Sharks Evolved

Posted: Jan 5 2017, 12:54pm CST | by , in News | Latest Science News

 

280 Million-Year-Old-Fossil Reveals How Ghost Sharks Evolved
Reconstruction of Dwykaselachus oosthuizeni (Image: Kristen Tietjen)
 

The fossilized fish skull could be a key evolutionary link between modern-day chimaeroids and their distant relatives

Chimaeroid, also known as ghost shark, is an unusual group of fishes that has been around since Triassic period. But it is poorly understood due to the lack of remains in the fossil record.

Researchers have recently scanned the fossilized skull of a shark-like fish in South Africa and have found that its brain structure is remarkably similar to modern-day chimaeras. 

Dating back to 280 million years, the Dwykaselachus oosthuizeni fish fossil could fill the evolutionary gap between today’s chimaeras and their distant relatives in the past.

“Chimaeroids belong somewhere close to the sharks and rays, but there's always been uncertainty when you search deeper in time for their evolutionary branching point,” said lead researcher Michael Coates, professor of organismal biology and anatomy at the University of Chicago.

“Chimaeras are unusual throughout the long span of their fossil record. Because of this, it's been difficult to understand how they got to be the way they are in the first place. The discovery sheds new light not only on the early evolution of shark-like fishes, but also on jawed vertebrates as a whole.”

Chimaeroid fishes represent one of the four principal divisions of modern vertebrate biodiversity. Despite only 47 known species, chimareoids are a subject of intense research and their ecology has baffled researchers for more than 100 years. 

Chimaeroid are also noticeable for the physical appearance. They have a soft body with distinct location of pelvic fins. Moreover, their skeletons are made of fragments of cartilage instead of bones. Despite being distant relative of sharks and rays, these fishes can be easily separated from them by their anatomic characteristics.

"Chimaeras are ancient specialists, now anchored within a large and very distinctive group of early shark-like fishes that thrived in the late Paleozoic era." Coates said.

The Dwykaselachus fish fossil was originally discovered by amateur paleontologist Roy Oosthuizen in 1980s. However, the detailed analysis of the fossil was done only recently. The shark-like fish was estimated to be 4 feet long and belonged to a bizarre group of ancient sharks, known for their unusual dorsal fin spines. But the most surprising results came from the CT scan of the skull.

The high definition CT scans allowed researchers to reconstruct the structure of its brain case including major cranial nerves, nostrils and inner ear and found that the specimen was actually an early chimaera, not a shark.

“For many years, the relationship of modern chimaeras to the early fossil record of sharks has been a puzzle,” said Coates. “We now have a glimpse of the preconditions from which modern chimaeras evolved.”

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Hira Bashir covers daily affairs around the world.

 

 

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