Excavation of a partial skeleton of the newly described, 91-million-year-old fossil shark, 'Cretodus houghtonorum,' in central Kansas in 2010, showing two local residents, Fred Smith (left) and Gail Pearson (right), assisting the lead author of the new study, Kenshu Shimada (middle). Inset shows a tooth of the shark as found. The species name, 'houghtonorum,' is in honor of the landowners Keith and Deborah Houghton, who donated the specimen to the Sternberg Museum of Natural History in Hays, Kansas, for science. (Image provided by Michael Everhart/Sternberg Museum of Natural History)A 91-million-year-old fossil shark, newly named 'Cretodus houghtonorum,' discovered in Kansas joins a list of large dinosaur-era animals. Preserved in sediments deposited in an ancient ocean called the Western Interior Seaway that covered the middle of North America during the Late Cretaceous period - 144 million to 66 million years ago - 'Cretodus houghtonorum' was an impressive shark estimated to be nearly 17 feet or slightly more than 5 meters long based on a new study appearing in the Journal of Vertebrate Paleontology.
The fossil shark was discovered and excavated in 2010 at a ranch near Tipton, Kansas, in Mitchell County by researchers Kenshu Shimada and Michael Everhart and two central Kansas residents, Fred Smith and Gail Pearson. Shimada is a professor of paleobiology at DePaul. He and Everhart are both adjunct research associates at the Sternberg Museum of Natural History, Fort Hays State University in Hays, Kansas. The species name 'houghtonorum' is in honor of Keith and Deborah Houghton, the landowners who donated the specimen to the museum for science.
Although a largely separated and incomplete skeleton, it represents the best 'Cretodus' specimen discovered in North America, according to the researchers. The discovery consists of 134 teeth, 61 vertebrae, 23 placoid scales and fragments of calcified cartilage, which when analyzed by scientists provided a vast amount of biological information about the extinct shark.
Besides its estimated large body size, anatomical data suggested that it was a rather sluggish shark, belonged to a shark group called Lamniformes that includes modern-day great white and sand tiger sharks as distant cousins, and had a rather distinct tooth pattern for a lamniform shark, the researchers say.
“Much of what we know about extinct sharks is based on isolated teeth. An associated specimen representing a single shark provides a wealth of anatomical information that in turn offers better insights into its ecology,” says Shimada, the lead author on the study. “As important ecological components in marine ecosystems, understanding sharks in the past and present is critical to evaluate the roles they have played in their environments and biodiversity through time, and, more importantly, how they may affect the future marine ecosystem if they become extinct."
During the excavation, Shimada and Everhart believed they had a specimen of 'Cretodus crassidens,' a species originally described from England and subsequently reported commonly from North America.
"However, not even a single tooth matched the tooth shape of the original 'Cretodus crassidens' specimen or any other known species of 'Cretodus,'" he says. “That’s when we realized almost all the teeth from North America previously reported as 'Cretodus crassidens' belong to a different species new to science."
The growth model of the shark calibrated from observed vertebral growth rings indicates the shark could have reached up to about 22 feet.
“This also inferred large size at birth, almost 4 feet in length, suggesting the cannibalistic behavior for nurturing embryos commonly observed within the uteri of modern female lamniforms must have already evolved by the Late Cretaceous period,” Shimada adds.
Furthermore, the 'Cretodus houghtonorum' fossil co-occurred with isolated teeth of another shark, 'Squalicorax,' as well as with fragments of two fin spines of a yet another shark, a hybodont shark, the researchers say.
“We think the shark possibly fed on the much smaller hybodont and was then scavenged by 'Squalicorax' after its death,” Everhart says.
Discoveries like this would not be possible without the cooperation and generosity of local landowners, and the local knowledge and enthusiasm of amateur fossil collectors, according to the authors.
“We believe continued cooperation between paleontologists and those who are most familiar with the land is essential to improving our understanding of the geologic history of Kansas and Earth as a whole,” Everhart says.
The new study, "A new large Late Cretaceous lamniform shark from North America with comments on the taxonomy, paleoecology, and evolution of the genus 'Cretodus,'” will appear in the forthcoming issue of the Journal of Vertebrate Paleontology and is currently online.