迄今为止发现的最大的鲨鱼——巨鲨——可能是一种光滑的、身长的利维坦。
研究人员1月22日在《科学》杂志上报告说，对这种已经灭绝的食肉动物化石遗骸的新观察表明，它的身体比以前重建的要长很多米，可能更苗条。这一发现可能会更好地了解巨齿鲨的生物学和生活方式，包括它游得多快或吃什么。
即使有完整的化石遗迹，重建古代灭绝动物活着时的样子也是一项挑战。但是重建巨齿鲨要困难得多。像所有的鲨鱼一样，巨鲨的软骨骨架相对于骨头来说保存得很差。人们主要是从牙齿和许多米长的软骨椎骨化石中知道它的，而骨骼的其余部分仍然是一个谜。
Traditionally, modern great white sharks () have been used as a model for megalodon’s body shape. That’s because great whites are the largest predatory sharks alive today and great whites and megalodons are categorized in somewhat closely related families.
A 2022 reconstruction that extrapolated from great whites caught the attention of Kenshu Shimada, a paleobiologist at DePaul University in Chicago, and his colleagues. That study based its reconstruction on the cartilaginous vertebral column of purported megalodon remains housed in a Belgian museum. Adding together all the vertebrae end-to-end revealed a body length of over 11 meters. But Shimada and his colleagues noticed that older work on that same specimen from the 1990s had calculated the entire animal’s length as about 9 meters. That work was based on the diameters of the vertebrae and how those scale with size in great white sharks, which tops out at around 6 meters long.?But the 2022 study still assumed megalodon was more or less great white-shaped, Shimada and his colleagues argue.
In their reassessment of the Belgian megalodon specimen’s vertebral column and the 2022 reconstruction, Shimada and his team question relying on the shape of great white sharks to build our view of megalodon. Megalodon’s vertebral column is relatively thin compared with the sturdier vertebrae that support the beefy brawn of great whites, makos and other modern relatives, the team notes. The researchers offer a new interpretation: Because such a small vertebral column would make more sense in a longer, leaner body shape, megalodon may have been built more like a bus than a van.?Overall, it may have been an even bigger predator than researchers thought, Shimada says.?
This study was “a major learning moment for both myself and many other scientists in that we need to take a broader perspective when reconstructing extinct animals, especially megalodon,” says coauthor Phillip Sternes, an organismal biologist at the University of California, Riverside.
A slender body may mean that megalodon wasn’t as powerful a swimmer as great whites are. This matches recent research from Shimada and his colleagues on the shape of a megalodon scale that suggested the shark was a slow cruiser capable of short bursts of speed.?This shift in body shape may hint at how it ate or how much it ate, says paleontologist Dana Ehret of the New Jersey State Museum in Trenton, who was not involved in either work.
“When working with extinct species, especially ones that don’t have any close living relatives today, we do our best by estimating what they may have looked like or how they behaved but it is never exact,” he says.
The new study takes an interesting approach, says vertebrate paleontologist Michael Gottfried, but the researchers still rely on great white sharks as a model in some ways, like on patterns of the size of vertebrae in different parts of the shark’s body. Gottfried and his colleagues were the researchers who measured and reconstructed the Belgian specimen as roughly 9 meters long in the 1990s. He says he isn’t sure how accurately the vertebrae can be added up to a total length, because many of the vertebrae are incomplete or fragmentary.?
“Ultimately, we are still speculating on body form and many other aspects of megalodon,” says Gottfried, of Michigan State University in East Lansing. Additional fossil material from the head and fins would be crucial for understanding how the giant shark looked.
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