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正好赶上夏天, 巨齿鲨，古老的, city bus-sized shark known as the “Megatooth”—has reared its ravenous snout.
While the oceans are now safe from the Megatooth, which went extinct an estimated 3.五百万年前 Otodus megalodon has been revealed by new research to have occupied a higher position on the food chain—known as its trophic level—than any other ocean predator, 活着的还是灭绝的.
Megatooth, 可能还有它的一些祖先, at the top step of the prehistoric food chain when it stalked the seas during the Cenozoic era, 从6600万年前开始一直延续到今天, 根据发表在该杂志上的电子游戏正规平台结果 科学的进步 by a team that included 电子游戏软件 Assistant Professor of Earth and Environmental Science Xingchen (Tony) 王.
Cenozoic megatooth sharks occupied extremely high trophic positions, 清晨里, E.R.等人，《电子游戏软件》. 经美国科学促进会许可转载.**
“这不仅仅是把巨齿鲨称为顶级捕食者，”王说. “今天的顶级捕食者可能会吃较小的鱼. Our study suggests that these megalodon were probably pretty picky about their food—they ate mainly other predators or even their own kind.”
The findings drew from a new technique that 王 developed while working on his doctorate at Princeton University. The technique determines trophic level based on nitrogen isotope ratios of trace organic molecules (mostly proteins) in the enamel of shark teeth as large as a man’s hand.
Those ancient proteins preserved in fossil teeth allowed researchers to determine that marine food chains during megatooth sharks’ time were about one to two steps longer than they are today. 换句话说, 巨齿鲨不仅吃食肉动物, 但这些野兽捕食那些看似优势的物种.
电子游戏软件助理教授托尼•王
王 started this project as a young graduate student working in the lab of Princeton Professor Daniel Sigman.
“We had developed a laboratory technique that could analyze the nitrogen isotopic composition of various kind of fossil samples,王说. “然后我在寻找一些化石材料来分析. 普林斯顿大学附近有一个鲨鱼电子游戏正规平台所. One day I visited them and they gave me a box of shark teeth samples from the Caribbean Sea. 这个项目就是这样开始的.”
王 turned his attention to other projects and passed the early work to another graduate student, 艾玛清晨里. 现在是美国剑桥大学的博士后电子游戏正规平台员.K., 清晨里 advanced the work as part of her doctoral dissertation at Princeton and was the lead author of the 科学的进步 报告 “新生代巨齿鲨占据了极高的营养地位”.
卡斯特注意到鲨鱼在漫长的时间里一直存在, existing long before the dinosaurs—for more than 400 million years—and continuing to evolve into the megatooth uber-predator well after the dinosaurs went extinct.
While many iconic big-bodied prehistoric creatures of the sea and land quietly sifted feedstocks from the ocean depths or nibbled on leafy treetops, 巨齿鲨是一种食肉动物. 一个幸存者.
“我们习惯于想到最大的物种——蓝鲸, 鲸鲨, 甚至大象和梁龙——作为滤食性动物或食草动物, 不是食肉动物,卡斯特在新闻发布会上说. “But Megalodon and the other megatooth sharks were genuinely enormous carnivores that ate other predators, 巨齿鲨在几百万年前就灭绝了.”
They say that the length of Megalodon has been estimated at approximately 50 feet—dwarfing modern great white sharks that grow to a maximum length of about 15 feet. 当他们离开大海的时候.五百万年前 they left behind clues in an abundant supply of fossilized teeth divers have culled from the sea floor around the world.
A Megaladon tooth held in the hand of paper co-author Harry Maisch at Florida Gulf Coast University, 谁收集了许多用于分析的样本.
Scientists first described fossil shark teeth the size of human hands about 180 years ago, 根据之前的电子游戏正规平台. But paleontologists were challenged to identify Megatooth’s trophic level. Methods used in modern ecosystems could not be applied to extinct species.
王, 清晨里,and the team 报告 they determined that measurements of nitrogen isotope levels within the enamel of modern shark teeth correspond with the nitrogen isotope levels in their dentin collagen, 哪一种常用来确定现代鲨鱼的营养地位. Animals at higher trophic levels have higher ratios of nitrogen-15 to nitrogen-14 since more nitrogen-15 is retained in their body during metabolism, 根据报告.
When the researchers applied their new technique to fossilized megalodon teeth, they found that Megatooth had significantly higher nitrogen-15 levels than modern white sharks, 北极熊, 和虎鲸. 然而, 这些鲨鱼体内的氮-15含量确实变化很大, indicating that not every large individual fed at the top of the food chain.
因为鲨鱼的牙齿非常丰富，而且保存得很好, the nitrogen signatures in enamel provide a way to measure status in the food web, whether the tooth fell from a shark’s mouth millions of years ago or yesterday. There is still so much to learn about the marine food webs using shark teeth.
“We knew that megatooth sharks went extinct long before human civilization,王说. “But human activities have been causing extinction of many marine species since the industrial revolution, 所谓的“第六次大灭绝”.
“当我手里拿着一颗巨大的牙齿时, 我一直在想:如果它们存在于今天的海洋中, 它们能在“第六次大灭绝”中幸存下来吗??王说.
Since 王’s arrival at BC in early 2020, he has set up a cutting-edge 稳定同位素生物地球化学实验室, which now includes five doctoral students and one postdoctoral scholar. His lab continues to use fossil materials, including teeth, to study ocean chemistry and biology.
“We are one of a handful of labs in the world that could analyze the nitrogen isotopic composition of fossil materials, 包括珊瑚, 贝壳, 和牙齿.王说. “Our students and postdoc are currently working on important questions ranging from climate change and its impacts to ocean pollution and marine food webs. 敬请关注他们的调查结果!”
艾德·海沃德|大学传播| 2022年7月
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