A tooth of Cretodus houghtonorum superimposed over an image of a rendering of how the shark might have looked. Image provided by Kenshu Shimada & Michael Everhart. Submitted photo
The chance discovery in Western Kansas of a fossil vertebra turned into an important and unique paleontological find – the remains of the first ever North American occurrence of a large fossilized skeleton of Cretodus, a large prehistoric shark previously known only from isolated teeth.
This remarkable specimen, recently added to the collection at Fort Hays State University’s Sternberg Museum of Natural History in Hays, is the most complete in North America and is one of two best known in the world. The other is in Italy.
Dr. Kenshu Shimada, a paleontology professor at DePaul University, Chicago, and Mike Everhart, adjunct curator of paleontology at the Sternberg Museum, worked for eight years to be able to share the discovery with the world.
The find is especially important because most of what is known about prehistoric sharks is based on finds of individual teeth.
“We found a fairly complete individual with most of its teeth and about half of the vertebral column. It’s quite a major jump from what we knew about this Cretaceous shark,” said Everhart.
The shark was found just south of Tipton, in Mitchell County, at the Ring Neck Ranch, owned by Keith and Deborah Houghton. The Houghton family has been open to scientific collecting trips on their property.
Everhart and a friend, Gail Pearson, had collected fossils from the ranch’s Blue Hill Shale outcrops. On a trip in 2010, they took a friend of Pearson’s who had never before hunted fossils: Fred Smith, editor of The Tipton Times.
Everhart found some broken rib fragments from a plesiosaur and started to recover them.
“While Pearson and I were trying to pick up these little bone fragments, Smith got bored and went further upslope to the east. He came back with this chunk of rock that had this round shape on both ends, and he’s saying, ‘Hey look, I found a piece of petrified wood,’” said Everhart.
While the shape and concentric rings were understandably suggestive of a tree branch, it was not. Smith had found something special.
“I recognized it as a concretion (a rounded mass of mineral matter) containing several vertebrae from a shark. Nothing quite like it had ever been found in the Blue Hill Shale,” said Everhart.
They marked the location and, after several weather delays, came back in the spring and started digging.
“The more we dug, the more we found. We found more concretions, more disc-shaped vertebrae, and lots of shark’s teeth. We got almost a complete mouth,” said Everhart. “It had this whole tooth array, different teeth from all over the mouth of the shark. In shark paleontology, single fossil teeth are mostly what you have to work with. But in this case, these were all from the same individual.”
Everhart got Shimada involved. Shimada, who earned his bachelor’s and master’s degrees from Fort Hays State, is an expert on fossil sharks. He provided on-site direction for the dig, collected material for further study and is credited for measuring and assembling the data so a description of the shark could be submitted for publication.
In the beginning, they thought their shark was a mostly complete specimen of an 1850s English find, which was based on only a single tooth.
“Until now, that discovery from 150 years ago was the only descriptive information we had to work with,” said Everhart.
They discovered that was not the case. The new shark did not match, and the team began to think that it may be the first known, reasonably complete specimen of a different shark – and could be a new species.
“Identifying it involved defining not only descriptions of the individual teeth – height and width and whatever else – but also explaining why they were different in shape from other known specimens,” said Everhart.
Once the dig, research, and extensive descriptions were complete, Shimada and Everhart submitted a comprehensive manuscript documenting their data.
This 91-million-year-old shark was preserved in sediments deposited in an ancient ocean that covered the middle of North America during the Late Cretaceous period. The find consists of 134 teeth, 61 vertebrae and 23 plate-like scales.
From measurements, discovery location and comparison to other sharks of the time, the team determined that at nearly 17 feet long, this shark was a distant cousin to modern great-white and sand tiger sharks.
The shark is estimated to have been 22 years old when it died, but the life expectancy of the species was extrapolated to be a possible 51 years.
From the position of other fossils near the find, it was inferred that the shark’s last meal was a much smaller shark, and after dying, its carcass was scavenged by another large shark.
“This new shark differs from all other known species in the genus by having a distinct array of teeth that are uniquely shaped,” said Everhart. “Our analysis showed that the teeth of this shark are measurably different (size and shape) from any other known species of Cretodus and that justified the naming of the new species.
While preparing all the materials for publication, Shimada and Everhart also had to propose a Latinized name for the species.
That original 1850s tooth was found near Houghton, England. The new shark came from the Houghton family ranch. The coincidence of name struck Everhart and Shimada as the natural choice for the nomenclature.
It was scientifically confirmed that the find was a new species, and the official, published, species name is Cretodus houghtonorum.
The Blue Hill Shale shark now lives in the Sternberg Museum of Natural History collection because the Houghton family wanted it kept in Kansas. An event honoring the donors and participants will be held at the Sternberg Museum at a later date.
“It’s a great addition to the collection. We’re grateful to the Houghton family for donating it to us,” said Everhart.
Shimada and Everhart’s study is titled “A New Large Late Cretaceous Lamniform Shark from North America with Comments on Taxonomy, Paleoecology and Evolution of the Genus Cretodus.” It appears in the forthcoming issue of The Journal of Vertebrate Paleontology. It is available online at https:/doi.org/10.1080/02724634.2019.1673399.
More pictures and information from this dig are posted online