High-definition CT scans of the fossilized skull of a 280 million-year-old fish reveal the origin of chimaeras, a group of cartilaginous fish related to sharks. Analysis of the brain case of Dwykaselachus oosthuizeni, a shark-like fossil from South Africa, shows telltale structures of the brain, major cranial nerves, nostrils and inner ear belonging to modern-day chimaeras. 
 
 This discovery, published early online in Nature on Jan. 4, allows scientists to firmly anchor chimaeroids -- the last major surviving vertebrate group to be properly situated on the tree of life -- in evolutionary history, and sheds light on the early development of these fish as they diverged from their deep, shared ancestry with 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," said Michael Coates, PhD, 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 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." 
 
 Chimaeras include about 50 living species, known in various parts of the world as ratfish, rabbit fish, ghost sharks, St. Joseph sharks or elephant sharks. They represent one of four fundamental divisions of modern vertebrate biodiversity. With large eyes and tooth plates adapted for grinding prey, these deep-water dwelling fish are far from the bloodthirsty killer sharks of Hollywood. 
 
 For more than 100 years, they have fascinated biologists. "There are few of the marine animals that on account of structure and relationships to other forms living and extinct have as great interest for zoologists and palaeontologists as the Chimaeroids," wrote Harvard naturalist Samuel Garman in 1904. More than a century later, the relationship between chimaeras, the earliest sharks, and other early jawed fishes in the fossil record continues to puzzle paleontologists. 
 
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 Chimaeras -- named for their similarities to a mythical creature described by Homer as "lion-fronted and snake behind, a goat in the middle" -- are unusual. Their anatomy comprises features reminiscent of sharks, ray-finned fishes and tetrapods, and their form is shaped by hardened bits of cartilage rather than bone. Because they are found in deep water, they were long considered rare. But as scientists gained the technology to explore more of the ocean, they are now known to be widespread, but their numbers remain uncertain. 
 
 After a 2014 study detailing their extremely slow-evolving genomes was published in Nature, interest in chimaeras blossomed. Of all living vertebrates with jaws, chimaeras seemed to offer the best promise of finding an archive of information about conditions close to the last common ancestor of humans and a Great White. 
 
 Like sharks, also reliant on cartilage, chimaeras rarely fossilize. The few known early chimaera fossils closely resemble their living descendants. Until now, the chimaeroid evolutionary record consisted mostly of isolated specimens of their characteristic hyper-mineralized tooth plates. 
 
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 The Dwykaselachus fossil resolves this issue. It was originally discovered by amateur paleontologist and farmer Roy Oosthuizen when he split open a nodule of rock on his farm in South Africa in the 1980s. An initial description named it based on material visible at the broken surface of the nodule. It was carefully archived in the South African Museum in Cape Town, where its splendor awaited technology able to unwrap its long-shrouded secrets. 
 
 In 2013, when the University of the Witwatersrand Evolutionary Studies Institute obtained a micro CT scanner, Dr. Robert Gess, a South African Centre of Excellence in Palaeosciences partner and co-author of this study, began scanning Devonian shark fossils while he was based at the Rhodes University Geology Department. Coates encouraged him to investigate Dwykaselachus. 
 
 At the surface, Dwykaselachus appeared to be a symmoriid shark, a bizarre group of 300+ million-year-old sharks, known for their unusual dorsal fin spines, some resembling boom-like prongs and others surreal ironing boards. 
 
 CT scans showed that the Dwykaselachus skull was remarkably intact, one of a very few that had not been crushed during fossilization. The scans also provide an unprecedented view of the interior of the brain case. 
 
 "When I saw it for the first time, I was stunned," Coates said. "The specimen is remarkable." 
 
 The images, one reviewer commented, are "almost dripping with data." 
 
 They show a series of telltale anatomical structures that mark the specimen as an early chimaera, not a shark. The braincase preserves details about the brain shape, the paths of major cranial nerves and the anatomy of the inner ear. All of which indicate that Dwyka belongs to modern-day chimaeras. The scans reveal clues about how these fish began to diverge from their common ancestry with sharks. 
 
 A large extinction of vertebrates at the end of the Devonian period, about 360 million years ago, gave rise to an explosion of cartilaginous fishes. Instead of what became modern-day sharks, Coates said, revelations from this study indicate that "much of this new biodiversity was, instead, 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." ||||| The pointy-nosed blue chimaera, or ghost shark, was filmed alive for the first time ever off the coasts of Hawaii and California. The deep-sea fish was previously known only from specimens caught in the southwestern Pacific Ocean. (Jorge Ribas/The Washington Post) 
 
 Like its Greek mythological namesake, the chimaera — or “ghost shark” — is a mysterious, rarely seen creature with a patchwork of bizarre features. 
 
 Dwelling in the depths of the ocean, its eyes are pale and seemingly dead. Where teeth should be, the ghost shark uses tooth plates instead to grind food. 
 
 Their heads are lined with cryptic dots, like the remnant scars of ancient stitches. Male chimaeras have retractable sex organs — on their foreheads. 
 
 Its other nicknames — ratfish, rabbitfish, spookfish — hint at how bizarre chimaeras are in appearance. 
 
 And now, scientists believe they have captured on video a species of ghost shark that had never before been filmed live: the pointy-nosed blue chimaera. 
 
 The actual video was taken in 2009 but was only recently released by the Monterey Bay Aquarium Research Institute, along with a paper by researcher Lonny Lundsten and his colleagues at the institute. 
 
 Six years ago, researchers from the nonprofit sent an ROV, or remotely operated vehicle, on several dives off the waters of central California and Hawaii. 
 
 The ROVs captured footage from depths of up to 6,700 feet. What they returned with surprised researchers: On film was what appeared to be a species of ghost shark previously only caught in the southwestern Pacific Ocean. 
 
 [Record-breaking Maryland fish weighs more than the girl who caught it] 
 
 According to his paper, Lundsten consulted with three chimaera experts who watched the video from the diving expeditions. All believed the fish was, in fact, a pointy-nosed blue chimaera. 
 
 Still, Lundsten and others from the Monterey Bay Aquarium institute can't be 100 percent certain that the fish captured on video is a pointy-nosed blue chimaera, despite their similar physical characteristics. Because of that, the paper refers to the fish they recorded as Hydrolagus cf. trolli, rather than its scientific name, Hydrolagus trolli. 
 
 To be absolutely sure, researchers would have to capture the ghost shark and bring it back to the surface, the institute said. 
 
 “This is much easier said than done, because these fish are generally too large, fast, and agile to be caught,” the institute notes. “If and when the researchers can get their hands on one of these fish, they will be able to make detailed measurements of its fins and other body parts and perform DNA analysis on its tissue.” 
 
 Doing so would either allow them to remove the “cf.” from the species description — or lead to perhaps an even more exciting alternative: that they discovered a new species of ghost shark. 
 
 [This nearly 1,700-pound shark is being tracked off the Virginia coast] 
 
 “If these animals turn out to be the same species as the ghost sharks recently identified off California, it will be further evidence that, like many deep-sea animals, the pointy-nosed blue chimaera can really get around,” the institute said. 
 
 The pointy-nosed blue chimaera was first discovered by researcher Dominique Didier Dagit in 2002, in the deep waters around Australia, New Zealand and New Caledonia. 
 
 Dagit, then an assistant curator of ichthyology at the Academy of Natural Sciences in Philadelphia, told the Associated Press in 2002 that she named her discovery Hydrolagus trolli after Alaskan artist Ray Troll because they shared a love for ratfish. 
 
 ''It's kind of nice to be able to name a species for someone,'' Dagit told the AP. ''I thought, 'Here's my chance to name a fish for someone who's really interested.' . . . It kind of looks like him, [but with] less facial hair.'' 
 
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 Do shark attacks swing elections? ||||| A 280-million-year-old skull of a so-called ghost shark has helped researchers determine exactly how chimaeras — mysterious, mostly deep-sea fish with wing-like fins and pointy snouts — are related to sharks, a new study finds. 
 
 The ancient skull, belonging to the 4-foot-long (1.2 meters) shark-like fish Dwykaselachus oosthuizeni, was a rare find, as this animal's skeleton is made of cartilage, which rarely fossilizes, the researchers said. An anatomical examination showed that the animal had a surprising number of similarities to modern chimaeras — also called ghost sharks for their silvery white exterior and overall appearance — suggesting that the two types of creature are related, the researchers said. 
 
 "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," said the study's lead researcher Michael Coates, a professor in the Department of Organismal Biology and Anatomy at the University of Chicago. "We now have a glimpse of the preconditions from which modern chimaeras evolved, suggesting that the large eyes of these early sharks predisposed chimaeras for low-light, deep-sea habits." [Photos: The Freakiest-Looking Fish] 
 
 A 3D printout of the Dwykaselachus oosthuizeni brain case. Credit: Coates, et al. Nature (2017) 
 
 Little is known about chimaeras, which are also called ratfish. Scientists aren't sure what chimaeras eat, how long they live or how often they reproduce. But based on chimaeras that have washed ashore or been caught as bycatch, researchers know that these fish have cartilaginous skeletons, indicating that the mysterious animals are related to sharks and rays, which also have cartilaginous bodies. 
 
 An artist's interpretation of Dwykaselachus oosthuizeni, a type of symmoriid shark now known to be an early chimaera. Credit: Kristen Tietjen 
 
 But beyond that, the chimaeras' evolutionary origins were a real mystery, the researchers said. 
 
 However, Coates had an inkling that a fossil in South Africa could help solve the mystery, he said. Roy Oosthuizen, an amateur fossil collector, discovered the specimen on his farm in Cape Province, South Africa, in the 1980s, and it had stayed at the South African Museum in Cape Town ever since. 
 
 The specimen had been described on a rudimentary level, but Coates wanted to learn more about it, so he asked his colleague and co-author Rob Gess, of the South African Centre of Excellence in Palaeosciences, to examine it. 
 
 Gess used a micro computed-tomography (CT) scanner (which produces more detailed images than a regular CT scanner) to create a virtual 3D image of the skull and its braincase, the area where the brain sat. 
 
 Intriguingly, some of D. oosthuizeni's braincase structures, including its major cranial nerves, nostrils and inner ear resembled those seen in modern chimaeras, the researchers found. 
 
 The rock nodule containing the fossil that amateur paleontologist and farmer Roy Oosthuizen found in the 1980s in South Africa. Credit: Rob Gess 
 
 For instance, "in all modern sharks and rays, the cartilage roof of the skull is open at the front," Coates told Live Science in an email. "But in chimaeras and Dwykaselachus, this roof is closed. And further details of the labyrinth of tubes and ducts that contain the semicircular canals of the inner ear are also shared." 
 
 The discovery indicates that the evolutionary lineage leading to chimaeras is rooted deeply within this group of early shark-like fishes, of which Dwykaselachus is a late, but anatomically conservative, representative, Coates said. 
 
 "For many years, the relationship of modern chimaeras to the early fossil record of sharks has been a puzzle," Coates said. Now, researchers know that D. oosthuizeni was an early chimaera, he said. 
 
 "Dwykaselachus allows us to connect the pieces and provides a time point for divergences, splits between major vertebrate groups in the tree of life," Coates said. 
 
 The study was published online today (Jan. 4) in the journal Nature. 
 
 Original article on Live Science.
– The chimaera, or so-called "ghost shark," is an elusive deep-water fish that has fascinated biologists for more than a century. Like its relative the shark, however, it's made of cartilage and thus rarely fossilizes, so little is known about its evolutionary past, reports Live Science. Now the blanks have been filled in thanks to a "remarkable" 280 million-year-old fossil found on a farm in Cape Province, South Africa, in the 1980s that was thought to be a symmoriid shark. Researchers at the University of Chicago Medical Center report in a ScienceDaily news release that the specimen—micro CT scan images of which one reviewer describes as "dripping with data"—is actually an early chimaera, not a shark. The specimen offers "a glimpse of the preconditions from which modern chimaeras evolved." Reporting in the journal Nature, the team says the fossil establishes strong links between the brains, major cranial nerves, nostrils, and inner ears of early and modern chimaeras. We're learning more about elusive modern chimaeras, too: Scientists recently said they think they've captured video of a type of ghost shark never filmed before; the Washington Post published the footage of what's believed to be a pointy-nosed blue chimaera last month. Filmed off the coast of central California, it's the first seen outside the Pacific waters of Australia and New Zealand, suggesting widespread populations. Scientists have yet to work out what chimaeras eat, how often they reproduce, or even how long they live. (Researchers who filmed the ghost shark say it came down to "dumb luck.")