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（Ammonoidea）的化石壳体可为解析这一已灭绝类群的生活习性提供关键参考信息。本研究引入一项全新壳体测量指标——口面面积（apertural surface area），并基于现生珍珠鹦鹉螺（Nautilus pompilius）的相关器官与口高的比例关系，构建了口球（buccal mass）与漏斗（hyponome）的模拟尺寸。本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（conch diameter）的比值）；2. 口球面积指数（即口球面积与口面面积的比值）；3. 壳体旋卷速率（coiling rate of the conch）。分析结果揭示出一个生态形态空间（ecomorphospace），可依托该空间将生活史特征初步对应至菊石类各物种。在该生态形态空间中，现生鹦鹉螺处于边缘位置，是适配活跃生活的外壳头足类（ectocochleate cephalopods）类群之一——其具备处理大型食物的能力与较为出色的移动性能。与之形成鲜明反差的是，多数菊石类在壳体尺寸相近的情况下，其口器与漏斗的尺寸均显著更小，这暗示它们的生活史更为被动，移动潜力更低，且捕食大型猎物的能力亦有所受限。