Did the largest prehistoric shark in the world need an orthodontist, or did it just eat badly?
Researchers from North Carolina State University and the North Carolina Museum of Natural Science examined a deformed tooth from an Otodus megalodon shark to find the root cause: was it related to development or food? The work could give paleontologists greater insight into the developmental processes associated with dental injuries in ancient sharks, as well as feeding behavior.
The problem is an abnormality called double tooth pathology, in which a single tooth appears “split”. There are several possible causes: during the development of teeth, two tooth buds can fuse into one or a tooth bud can split into two (a process called gemination). Gemination and fusion can be caused by disease, genetics, or physical injury to the tooth bud.
“We don’t have a lot of data on the pathologies of double teeth in ancient species of sharks,” says Harrison Miller, a former NC State undergraduate student and corresponding author of a paper describing the work. “So it was an opportunity to fill those gaps and maybe learn more about sharks in the process.”
The researchers examined three abnormal teeth: a 4-inch tooth from O. megalodon, an apex predator the size of a school bus that ruled the seas in the Miocene and early Pliocene (11 to 3.7 million years ago); and two from Carcharhinus leucas, a much smaller species of bull shark that lived around the same time and still roams the seas today.
The three oddly shaped teeth exhibited a form of dual dental pathology. The researchers compared the teeth to normal teeth from both species and performed nano-CT imaging of the deformed teeth so they could examine what was going on inside.
While pathological teeth had more internal canals than normal teeth, confirming either incomplete separation or joining of two teeth during development, researchers have not been able to definitively establish a developmental cause.
“Part of the difficulty was applying the terminology of work in humans and other mammals to sharks,” says Haviv Avrahami, North Carolina State doctoral student and co-author of the paper.
“Sharks have cartilaginous skeletons, not bony skeletons, so preservation of their jaws is rare in the fossil record, and typically we only find the individual teeth in isolation. Additionally, sharks have different tooth development mechanisms – they have continuous tooth replacement, so you can’t look at what’s going on in the rest of the jawbone to rule out fusion or gemination.”
Given what researchers know about this type of pathology in modern shark teeth, however, they’re leaning towards feeding-related injuries as a more likely cause.
“With O. megalodon in particular, the current understanding is that they preyed primarily on whales,” says Avrahami. “But we do know that tooth deformities in modern sharks can be caused by something sharp piercing the conveyor belt of developing teeth inside the mouth. From what we see in modern sharks, the wound was probably caused by the bite of a thorny fish or taking a bad stab from a ray.”
“We also know that O. megalodon had nesting grounds around Panama, and that relatives of modern stingray species also inhabited that region,” Harrison said. “And those spines can get really thick. So a tooth injury like that could indicate that O. megalodon was more of a generalist predator — and that this particular O. megalodon just had a bad day.”
Lindsay Zanno, head of paleontology at the NC Museum of Natural Sciences, associate research professor at NC State, and co-author of the research, agrees.
“When we think of predator-prey encounters, we tend to reserve our sympathy for the prey, but the life of a predator, even a gigantic megatooth shark, was no walk in the park either.”
The work appears in PeerJand was made possible by Mark Kostich’s donation of the pathological tooth O. megalodon (NCSM 33639) to the Paleontological Collections of the North Carolina Museum of Natural Science.
“We are extremely grateful to Mark for donating this specimen to the museum so we can learn more about these ancient animals,” Zanno said. “So many important fossils are hidden away in private collections, where they are unable to shed new light on our wonderful world.”
Research reveals how teeth functioned and evolved in giant mega-sharks
Harrison S. Miller et al, Dental pathologies in lamniform and carcharhiniform sharks with comments on the classification and homology of double-tooth pathologies in vertebrates, PeerJ (2022). DOI: 10.7717/peerj.12775
Provided by North Carolina State University
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