Ghost Sharks: 280 Million Year Old Skull Explains Origin of the Strange Animal
Ghost sharks, also known as chimaeras, are rarely seen deep sea cartilaginous fish that are actually related to sharks. According to a report from Phys Org, a new study published in Nature International Weekly Journal of Science revealed the ghost shark's place in evolutionary history: they are descended from an ancient creature called Dwykaselachus oosthuizeni.
The scientists used the 280 million year old brain case of Dwykaselachus, a shark-like fossil that was discovered in South Africa in the 1980s. This allowed them to peek into the history of the animal and observe clues on the divergence of the ghost shark from actual sharks.
"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," lead author Michael Coates, PhD, also a professor of organismal biology and anatomy at the University of Chicago, said.
A report from Gizmondo cited unique characteristics of these animals often referred as ghost sharks including large eyes, bird-like fins, tooth plates and boneless bodies. Instead, they are shaped by plates and bone-like bits of cartilage. Although scientists estimate almost 50 species of ghost sharks worldwide, the creatures are rarely seen because they live in deeper waters.
Because they are made up of cartilage instead of bone, ghost sharks rarely leave well-preserved fossils. When Coates and his team used a micro CT scanner to study the Dwykaselachus, the images revealed that it has tell-tale anatomical structures that make it a chimaera instead of a shark.
"Chimaeras are unusual throughout the long span of their fossil record," Coates explained. "Because of this, it's been difficult to understand how they got to be the way they are in the first place. This discovery sheds new light not only on the early evolution of shark-like fishes, but also on jawed vertebrates as a whole."
Roughly 360 million years ago, there was a large-scale extinction of vertebraes that led to the rise of cartilaginous fishes. This study indicates that most of these animals didn't become modern-day sharks - they were actually early chimaeras.
"We can now say that the first radiation of cartilaginous fishes after the end Devonian extinction was chimaeras, in abundance." Coates said. "It's the inverse of what we've got today, where sharks are far more common."