Comparing the differential filling of morphospace and allometric space through time: the morphological and developmental dynamics of early Jurassic ammonoids

The evolutionary history of shell geometry of Early Jurassic ammonoids during the Pliensbachian–Toarcian second-order mass extinction is explored at both adult and ontogenetic levels. The ontogenetic approach builds on the concept of allometric space to get insights into the developmental aspects of morphological evolution. Investigation of the deployment of taxa in adult morphospace and allometric space allows the appraisal of the temporal evolution of morphological and allometric disparities. Curves of taxonomic diversity, adult morphological disparity, allometric disparity, and average adult size are contrasted. Results show that during the Pliensbachian–Toarcian interval, ammonoids underwent two successive and drastic declines in taxonomic diversity. Patterns of morphospace and allometric space occupancy suggest nonselective extinction at both morphological and developmental levels. Another measure of allometric disparity suggests the occurrence of two heterochronic trends, a peramo...

本研究针对普林斯巴阶（Pliensbachian）-托阿尔阶（Toarcian）二级集群灭绝事件（second-order mass extinction）期间，早侏罗世菊石（Early Jurassic ammonoids）的壳体几何形态演化历史，从成体与个体发育（ontogenetic）两个层面展开探究。本研究的个体发育分析方法以异速生长空间（allometric space）概念为基础，旨在解析形态演化的发育学维度。通过分析类群在成体形态空间（morphospace）与异速生长空间中的分布模式，可评估形态与异速生长差异度的时间演化规律。研究对分类多样性（taxonomic diversity）、成体形态差异度、异速生长差异度以及平均成体体型的变化曲线进行了对比分析。结果显示，在普林斯巴阶-托阿尔阶时段内，菊石的分类多样性经历了两次连续的大幅下降。形态空间与异速生长空间的占据模式表明，菊石在形态与发育层面均发生了非选择性灭绝。另一项异速生长差异度指标的分析结果则显示存在两起异时性演化趋势，即近于...