Data from: An ecomorphospace for the Ammonoidea

The fossil conchs of ammonoids provide valuable information about the life habits of this extinct group. A new conch measurement, the apertural surface area, is introduced here along with modelled sizes of the buccal mass and the hyponome, based on ratios of these organs in comparison with the aperture height from the Recent Nautilus pompilius. A principal components analysis was performed using the three main characters (1) apertural surface area index (i.e., the ratio of the apertural surface and the conch diameter), (2) buccal mass area index (i.e., the ratio between the buccal mass area and the apertural surface area) and (3) coiling rate of the conch and reveals an ecomorphospace where life history traits can be tentatively assigned to species of the Ammonoidea. In this morphospace, Recent Nautilus has a marginal position, being one of the ectocochleate cephalopods with best properties for active life (capacity for handling large food items, rather good mobility). In contrast, most ammonoids possessed, at comparable conch sizes, much smaller buccal apparatuses and hyponomes, suggesting a more passive life history with reduced mobility potential and reduced capacities for larger prey items.菊石类（ammonoids）的化石外壳，可为解析这一已灭绝类群的生活习性提供宝贵参考。本文引入一项全新的外壳测量指标——壳口表面积（apertural surface area），并基于现生珍珠鹦鹉螺（Nautilus pompilius）的相关器官与壳口高度的比例关系，推导出吻球（buccal mass）与漏斗（hyponome）的模拟尺寸。研究采用三个核心特征开展主成分分析：(1) 壳口表面积指数（即壳口表面积与外壳直径的比值）、(2) 吻球面积指数（即吻球面积与壳口表面积的比值），以及(3) 外壳旋卷速率；分析结果揭示了一个生态形态空间（ecomorphospace），可据此将生活史特征初步对应至菊石亚纲（Ammonoidea）的各个物种。在该生态形态空间中，现生珍珠鹦鹉螺处于边缘位置，是最适配活跃生活模式的外鳃亚纲（ectocochleate）头足类（cephalopods）之一——其具备处理大型食物的能力，且机动性较强。与之形成鲜明对比的是，多数菊石在外壳尺寸相近的情况下，吻球与漏斗的尺寸要小得多，这表明它们的生活史更为被动，机动性潜力更低，且捕食大型猎物的能力也有所减弱。