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（ammonoids）的化石壳体，可为这一已灭绝类群的生活习性提供极具价值的研究资料。本文引入一项全新的壳体测量指标——口面面积（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，推导得到该类群口球（buccal mass）与漏斗（hyponome）的模拟尺寸。研究选取三项核心特征开展主成分分析（principal components analysis）：（1）口面面积指数（即口面面积与壳体直径的比值）、（2）口球面积指数（即口球面积与口面面积的比值）以及（3）壳体旋绕速率（coiling rate），最终构建出生态形态空间（ecomorphospace），可用于初步判定菊石类物种的生活史特征（life history traits）。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壳头足类（ectocochleate cephalopods）类群之一——其具备处理大型食物的能力，且机动性较为出色。与之形成显著反差的是，多数菊石在壳体尺寸相当的情况下，其口器与漏斗的尺寸均偏小得多，这暗示它们的生活史更为被动，机动性潜力受限，且捕食大型猎物的能力有所减弱。