When Joseph Frederickson and Janessa Doucette-Frederickson began digging in 2010, neither expected to make a discovery of a lifetime.
Three 100-million-year-old fossils found in Tarrant County, Texas, are the remains of a giant Cretaceous era shark. Details of the discovery were published Wednesday and are free at PLOS ONE, an online journal for researchers. Both are doctoral students at the University of Oklahoma.
The fossils are part of a collection for researchers at the Sam Noble Museum of Natural History.
As undergraduates at the University of Wisconsin-Milwaukee, the couple started a paleontology club and set out to dig all over the U.S. They decided to dig at Duck Creek Formation near Ft. Worth for extinct marine creatures, when Janessa ended up in the right place at the right time.
“I tripped over a rock that had a fossil in it,” said Janessa, anthropology doctoral candidate. “We discovered it was something not at all expected. We were really surprised at the size— this is way bigger than it's supposed to be.”
The edge of the fossil that she tripped on, known as lamellae, are lines that helped identify the shark as lamniform, a group of large sharks including the Great White.
With help from shark specialists and their own research, the couple estimates the shark was 20.5 feet, three times larger than a average Great White. They hypothesize, with co-author Scott Schaefer, that the fossils areleptostyrax macrorhiza, the largest of the lamniform shark species living at that time. A 1997 study from the Kiowa Shale of Kansas revealed a 30 foot long shark with similar vertebrae as Fredrickson's discovery. Both sharks lived during the same time period.
“People ask what would it look like,” said Frederickson, a doctoral candidate in ecology and evolutionary biology. “It is a primitive member of its species meaning it doesn't look like a Great White. It looks more like a Sand Tiger or Goblin shark.”
The shark is distinguished by its ragged-teeth and tail fin with a long upper lobe. It likely ate everything in its path, if it was fully grown.
Frederickson said the fossils are somewhere near the back, assuming it is the largest part of the shark's structure. If not, their discovery might have been a growing shark destined to reach massive scales up to 30 feet, that of the largest leptostyrax macrorhiza.
These predators ate “whatever could fit in its mouth,” he said, crabs, invertebrates, marine reptiles and other sharks.
The 1997 giant and the recent fossil discovery both have yet to be "confidently identified," the study states, because shark teeth are yet to be found. Though the findings may change when scientists believe giant sharks evolved.
“People didn't know there were giant predatory sharks during the Early Cretaceous,” Frederickson said. “There is potential that there are giant fossils in our state. Discovering vertebrae with teeth would be great— we could solve this mystery. A lot is left to be done.”