Université de Lyon, ENS de Lyon, Université Lyon 1, CNRS, UMR 5276 Laboratoire de Géologie de Lyon: Terre, Planète, Environnement, 69342 Lyon, France.
Sorbonne Universités - CR2P - MNHN, CNRS, UPMC-Paris 6, Muséum national d'Histoire naturelle, 57 rue Cuvier, CP 38, 75231 Paris Cedex 05, France.
Curr Biol. 2017 Jun 5;27(11):1641-1644.e2. doi: 10.1016/j.cub.2017.04.043. Epub 2017 May 25.
The collapse of marine ecosystems during the end-Cretaceous mass extinction involved the base of the food chain [1] up to ubiquitous vertebrate apex predators [2-5]. Large marine reptiles became suddenly extinct at the Cretaceous-Paleogene (K/Pg) boundary, whereas other contemporaneous groups such as bothremydid turtles or dyrosaurid crocodylomorphs, although affected at the familial, genus, or species level, survived into post-crisis environments of the Paleocene [5-9] and could have found refuge in freshwater habitats [10-12]. A recent hypothesis proposes that the extinction of plesiosaurians and mosasaurids could have been caused by an important drop in sea level [13]. Mosasaurids are unusually diverse and locally abundant in the Maastrichtian phosphatic deposits of Morocco, and with large sharks and one species of elasmosaurid plesiosaurian recognized so far, contribute to an overabundance of apex predators [3, 7, 14, 15]. For this reason, high local diversity of marine reptiles exhibiting different body masses and a wealth of tooth morphologies hints at complex trophic interactions within this latest Cretaceous marine ecosystem. Using calcium isotopes, we investigated the trophic structure of this extinct assemblage. Our results are consistent with a calcium isotope pattern observed in modern marine ecosystems and show that plesiosaurians and mosasaurids indiscriminately fall in the tertiary piscivore group. This suggests that marine reptile apex predators relied onto a single dietary calcium source, compatible with the vulnerable wasp-waist food webs of the modern world [16]. This inferred peculiar ecosystem structure may help explain plesiosaurian and mosasaurid extinction following the end-Cretaceous biological crisis.
海洋生态系统在白垩纪末期大灭绝期间崩溃，涉及食物链的基础[1]，甚至包括普遍存在的脊椎动物顶级捕食者[2-5]。大型海洋爬行动物在白垩纪-古近纪（K/Pg）边界突然灭绝，而其他同期的群体，如Bothremydidae 龟鳖类或 Dyrosauridae 鳄形目爬行动物，尽管在家族、属或种的水平上受到影响，却在古近纪的后危机环境中幸存下来[5-9]，并且可能在淡水生境中找到了避难所[10-12]。最近的一个假设提出，蛇颈龙类和沧龙类的灭绝可能是由于海平面的大幅下降造成的[13]。沧龙类异常多样化，在摩洛哥的马斯特里赫特阶磷矿床中丰富，并且与大型鲨鱼和一种上龙类蛇颈龙一起，导致顶级捕食者过多[3、7、14、15]。由于这个原因，海洋爬行动物的局部多样性很高，表现出不同的体型和丰富的牙齿形态，暗示着这个最新的白垩纪海洋生态系统中存在复杂的营养相互作用。使用钙同位素，我们研究了这个灭绝组合的营养结构。我们的结果与现代海洋生态系统中观察到的钙同位素模式一致，表明蛇颈龙类和沧龙类无差别地属于第三级肉食动物组。这表明海洋爬行动物的顶级捕食者依赖于单一的饮食钙源，与现代世界脆弱的黄蜂腰食物网相兼容[16]。这种推断出的特殊生态系统结构可能有助于解释蛇颈龙类和沧龙类在白垩纪末期生物危机后的灭绝。
