Building the trilobite morphospace: the influence of different morphological structures

ABSTRACT The study of morphological disparity is a powerful tool for exploring evolutionary and ecological patterns and processes. Disparity is usually quantified from empirical morphospaces, often constructed from a single anatomically independent structure. However, results can differ depending on the analysed structure, raising the question of whether morphospaces from different structures converge on a common pattern. To address this, we analysed geometric morphometric data of Silurian–Permian trilobites available in TriloMorph, a collaborative database of trilobite morphogeometric information. Trilobites are an ideal model for this question because their segmented body plan is composed of distinct tagmata, offering a unique opportunity to compare morphospaces derived from different morpho-functional structures and landmark configurations. Here, we examined morphospace occupation using alternative morpho-functional configurations of the cephala and pygidia, including both outlines and internal structures. Our results show that the cephalic outline alone captures much of cephalic disparity but fails to reflect the variability revealed by internal cephalic structures, indicating that some aspects of morphological diversity are overlooked when relying exclusively on outlines. Cephalic and pygidial morphospaces are poorly correlated, reflecting that each tagma represents different aspects of biological variation. Our analysis highlights the need to consider multiple aspects of the trilobite body plan to capture the full extent of trilobite disparity. Future methods integrating multiple structures are essential for achieving a more comprehensive understanding of trilobite morphological diversity.