Arkansas’ 3D shark fossils have paleontologists calling us Sharkansas
In some circles, Arkansas is known for its sharks.
Their fossilized remains are embedded in the Fayetteville Shale, which was once a muddy sea floor.
These well-preserved fossils prompted one prominent paleontologist to come up with a portmanteau — Sharkansas.
John Maisey, curator emeritus of fossil fish at the American Museum of Natural History in New York City, has said that should be Arkansas’ new name.
“It just struck me as humorous, my English humor,” said Maisey. “Because you do have Arkansas sharks, don’t you? It seems appropriate from my point of view, from a paleontologist’s point of view.”
Maisey grew up in England, spent 39 years with the museum in New York and now lives in Florida.
Maisey believes he was the first person to coin the phrase Sharkansas, although it may have been swimming in the subconscious of other minds.
The term has since been used in a movie title and by some Arkansas Razorback basketball fans who donned shark costumes for the games.
In 2015, a film titled “Sharkansas Women’s Prison Massacre” was released. It’s about Arkansas prison escapees battling prehistoric sharks that erupt from underground after a fracking accident rips open the Earth’s crust.
“You’ve got to be kidding me,” one escapee says just before she’s devoured by a prehistoric shark.
Maisey has encountered no such problems with prehistoric Arkansas sharks.
He said the American Museum of Natural History has dozens of shark fossils from Arkansas — the most extensive collection of Arkansas shark fossils anywhere — thanks to Royal and Gene Mapes, a husband-and-wife team of scientists and professors at Ohio University. They donated their collection of 540,000 marine fossils from Arkansas, Kansas, Oklahoma and Texas to the museum in 2013.
One impressive shark fossil from Arkansas has been named Ozarkus mapesae. The museum’s specimen is about 4 inches long, but that’s only the head minus the snout region, and the gills and pectoral girdle, said Maisey. He estimates the shark would have been about 16 inches long.
“This is a complete head of a little tiny shark,” Maisey said in a video describing Ozarkus. “Inside this rock, there’s every little piece of all these gill arches and all the rest of the skeleton, the jaws and other things. Everything’s preserved in exquisite detail, but you can only see it by scanning it and processing the scan using computer technology. And that’s what we’ve been doing.
“This is one of these fossils from Arkansas, which I think should be renamed Sharkansas, that is so spectacular, even though it doesn’t look like much. In scientific terms it’s really significant. It’s a major discovery.”
About 320 million years ago, Arkansas was covered by a shallow sea. Sharks were the dominant fish back then, and there were a lot of them, said Maisey. When they died, their bodies descended to the sea floor, where oxygen was lacking and conditions were excellent for preservation.
“It’s this unique burial situation that has allowed these fossils to be preserved intact,” he said.
The Fayetteville Shale is a geological formation that stretches across much of northern Arkansas. It’s primarily underground, but there are outcrops in the Ozark Mountains, and the shale layers can be seen in highway road cuts, including one along U.S. 65 near Marshall.
Royal Mapes mostly collected invertebrates, such as ammonites, but he had a “nose for finding shark fossils,” said Maisey.
ARKANSAS SHARK HUNTING
Royal and Gene Mapes were guides several years ago for a trip to Arkansas in which Maisey participated.
Maisey said they searched for shark fossils in the shale along the banks of the White River and tributary creeks. To the average person, these fossils may not look much like sharks, but the experts know what to look for.
“If you’re there at the right time and the river hasn’t washed everything out … you can see the layers and layers of shale, the flat layers, and here and there you’ll see a bulge in the shale,” said Maisey. “It’d be like a lump sticking out … Then you set to with your hammers and chisels and you get that thing out. If you’re lucky, it’s got some fossils in it.
“It’s an awful lot of luck and chance,” he said. “We know where they occur but we can’t guarantee we’re going to find anything. We were out there for three or four days in the White River and we found, like, two sharks. And that’s a team of five people, including Royal.”
But that was actually a successful outing.
“You could go there for a month and not find anything,” said Maisey.
Allison Bronson came to Arkansas in 2015 to search for shark fossils. She was Maisey’s graduate student at the museum’s Richard Gilder Graduate School from 2014 to 2018. She’s now a researcher at California State Polytechnic University, Humboldt.
“We spent most of our time near Fayetteville and east of there, like Marshall and Leslie, and we are really grateful to the landowners there who have allowed paleontologists to collect fossils on their property for many years now,” said Bronson. “Since many of the fossils weather out from riverbeds, summer is the best time to collect, and it’s such a beautiful area.”
THREE-DIMENSIONAL FOSSILS
Because of an unusual combination of biological and geological factors, the Fayetteville Shale shark fossils are three-dimensional.
Shortly after the sharks died, bacteria capable of producing mineral compounds as a by-product of decay accumulated around the remains, and these mineral compounds resisted compaction as the fossil became buried deeper and deeper in sediment, said Maisey.
“This is what sets the Arkansas fossils apart from others,” he said.
“So you can imagine that millions of tons of sediment finally accumulating and burying, sitting on top of these fossils, they’re going to get squashed flat,” said Maisey. “But if you’ve got something in the rock that’s kind of resistant to that, the fossils don’t get quite so badly flattened. That’s what makes these unique.
“If it weren’t for those conditions, we’d never find anything,” he said. “We’d just find maybe a few teeth scattered around or something like that.”
Teeth are the only remains usually found from ancient sharks.
“Shark’s teeth are among one of the most common vertebrate fossils that you can find, but the skeletons are exceptionally rare,” Maisey said in a 2018 video for the museum. “Sharks and their relatives don’t have lots of bones covering the head and the body like a fish you buy at the supermarket.”
Shark skeletons are made of soft cartilage coated with a hard calcium phosphate layer, said Maisey.
“It’s not bone, but it consists of literally hundreds of thousands of little, tiny crystals or fragments of calcite that are held together by collagen fibers,” he said.
SCANNING
Since shark fossils found in the Fayetteville Shale are three-dimensional, researchers can use computed tomography scanning to get a look inside without damaging the fossil, said Maisey.
“Scanning, I think, has been the real modern breakthrough in paleontology in general,” he said. “We’ve been scanning fossils now for 25 years. We want to be able to see stuff that’s very, very difficult to see. We want to see inside fossils. For example, in a shark we want to study the inside the brain case. We want to see what shape was the cavity where the brain was. And scanning can do that.”
The shark fossils found in the Fayetteville Shale represent parts of the head, sometimes with the paired pectoral fins, but no tails, he said.
Maisey said some complete shark fossils have been found in the Bear Gulch limestone in Montana, but they’re completely flattened.
“I suspect that it is only a matter of time before someone finds a complete shark fossil in the Fayetteville Shale,” he said. “Complete fossil sharks are extremely rare in general in the fossil record.
“There are very, very, very few places that have consistently produced fossils. In North America, there are two other places that are well known for the number of fossil sharks. One of them is Bear Gulch. And the other one is the Cleveland Shale in Ohio.”
COSMOS
Last month, an article was published in the journal Geodiversitas describing a newly identified shark that lived about 326 million years ago. It has been named Cosmoselachus mehlingi.
Bronson was the article’s lead author, and Maisey was a co-author.
The fossil specimen was collected in the 1970s by Royal and Gene Mapes from a series of outcrops in the bed of Cove Creek in Searcy County, according to the article.
After being damaged in shipping, the museum’s team spent months reconstructing its anatomy, which included dozens of tiny pieces of cartilage, before it could be CT scanned, according to a summary of the article posted online by the museum.
Maisey said the fossil is 16 to 18 inches long. “But that is just from the snout to just behind the pectoral fins,” he said. “Assuming that the body form was similar to related forms, I would estimate the fish total length would have been about 3 to 4 feet.”
The fossil helps researchers understand the evolution of an enigmatic group called the symmoriiforms, according to the museum post. That group has been linked with sharks and ratfish, with different researchers coming to different conclusions.
“Cosmoselachus has mostly shark-like features, but with long pieces of cartilage that form a gill cover, which is only seen in ratfish today,” according to the post.
Bronson mentioned in a recent post on X, formerly Twitter, that Cosmoselachus came from the “shark-dominated fauna of our beloved Fayetteville Shale! (#Sharkansas)”
“The Fayetteville Shale preserves far more shark cartilage than similar-aged sites around the world, which mostly preserve teeth,” Bronson said in an email. “We think this is partly because of the water and sediment conditions of the site 326 million years ago. The bottom of the ocean there was low in oxygen and very acidic which slowed down decomposition.
“Most of the shark fossil record is teeth, but teeth from very different groups of sharks can look similar, so they aren’t as helpful for understanding shark evolution across very long periods of time. The three dimensionally preserved cartilage from Arkansas is therefore extremely valuable for learning about the anatomy and evolution of early groups of sharks and their relatives.”
The intact fossils raised Maisey’s interest level from the start.
“The Arkansas stuff is remarkably well preserved, which is what really attracted my attention in the first place because it’s not just the diversity and all the abundance, but the preservation,” said Maisey.