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Imagine being a fish swimming in the ocean millions of years ago, when a shark pounces at you, gaping its mouth to bite. The horror of your situation increases as the predator’s lower jaw also stretches downward on both sides, so the new sharper teeth that were previously flat along the jaw now curl.
Scientists recently discovered this nightmarish trait in a fossil of a 370-million-year-old shark that once inhabited the waters near what is now Morocco. The previously undescribed species, nicknamed Ferromirum oukherbouchi, had a jaw that turned inward when the mouth was closed and outward when the mouth was open.
Unlike modern sharks, in which worn teeth are constantly being moved by new teeth, this shark sprouted its new teeth in a row inside the jaw, alongside older teeth. As the new teeth grew, they curved towards the shark’s tongue. When the shark opened its mouth, the cartilage on the back of the jaw flexed so that the sides of the jaw “fold” down and the new teeth turn upward, allowing the shark to bite into its prey with as many teeth as possible, according to a new study.
Related: 8 weird facts about sharks
F. oukherbouchi had a small, slender body about 13 inches (33 centimeters) long, and his muzzle was triangular and short; its eyes were unusually large, the sockets occupying about 30% of the total length of the puzzle, the scientists reported. The shark’s jaw and hyoid arch – the cartilage structures behind the jaw – have been preserved in 3D, offering intriguing clues to the structure and function of the jaw in ancient sharks.
Because the jawbone was so well preserved, the researchers were able to scan it with computed tomography (CT) and then digitally model it in 3D for mechanical testing. They found that the shark’s jaw was not fused in the center, so it was able to bend outward along this flexible seam when the mouth was open.
“Thanks to this rotation, the younger, larger and sharper teeth, which usually pointed inward of the mouth, were placed in an upright position. This made it easier for the animals to impale their prey, ”said Linda Frey, lead author of the study. doctoral student at the Institut für Paläontologie und Paläontologisches Museum at the University of Zurich in Switzerland.
When the shark’s jaw closed, seawater rushed into its mouth to push the prey towards its throat. At the same time, the closing jaw rotated the teeth inward to immobilize and trap the shark’s meal, Frey said. in a report. This pattern of jaw movement is unlike anything known in any living fish, the scientists wrote in the study.
Previous studies of the jaws of the early chondrichthyans – the group that includes sharks, rays, and stingrays – have been hampered by poor preservation of the fossils. But only a few well-preserved 3D fossils like this could help paleontologists piece together a clearer picture of how the jaws of ancient sharks behaved in 3D, even though most of the fossil specimens in existence are incomplete or ‘flattened’. , according to the study.
Understanding how this specialized combination of jaw movement and tooth placement was distributed across the shark family tree could also explain how the ever-growing tooth cluster assembly line in modern sharks evolved, the researchers reported. researchers.
The results were published online Nov. 17 in the journal Communications biology.
Originally posted on Live Science.
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