Morphometric and taxonomic analysis of trilobite Acanthopyge haueri (Barrande, 1846) from the Middle Devonian (Eifelian) of the Barrandian area (Czech Republic)

 

Authors: Budil P, Šilinger M, Crônier C, Vokáč V, Frýda J, Chatterton BDE

Published in: Bulletin of Geosciences, volume 101, issue 3; pages: 389 - 420; Received 3 December 2025; Accepted in revised form 16 September 2026; Online 10 October 2026

Keywords: Lichida, Acanthopyge, Devonian, systematics, taphonomy,

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Abstract

A comprehensive study of morphological variability in Acanthopyge haueri (Barrande, 1846), the genotype species of Acanthopyge Hawle & Corda, 1847 from the Middle Devonian (Eifelian) of the Barrandian area (Czech Republic), is presented. Two different methods were used to assess variability: classical biometric analysis and landmark-based morphometrics. The data show notable morphological variability within a supposedly well-defined species. All measured parameters are variable, and some of these characters, previously considered to be of generic significance, show substantial variation. Early holaspid specimens of A. haueri are less variable, whereas larger ones show much greater variability which, however, may partially also reflect diagenetic and tectonic deformation. Prominent allometry is observed during development: early holaspid specimens obviously have less vaulted cephala with less prominent lobation; pygidia are almost sub-circular, with relatively shorter post-axial ridge and relatively long and straight marginal spines. In contrast, large specimens have prominent vaulting of the cranidium (especially median lobe), relatively longer pygidia with often a semi-elliptic to elongate, sub-triangular outlines, relatively shorter marginal spines, a relatively longer (sag.) post-axial ridge, and distinctly vaulted lateral lobes of the pygidium, while the axis is only moderately vaulted. However, the observed variability may reflect the broad stratigraphic range of A. haueri, which may comprise several subspecies or distinct species that cannot yet be differentiated. The new material allows an amendment to the description of Lower Devonian (upper Emsian) Huginarges? pervasta (Přibyl, Vaněk & Hörbinger, 1986), a species previously poorly known. The morphology of H.? pervasta is intermediate between Acanthopyge and Huginarges Basse in Basse & Müller, 2004. Early holaspid specimens of A. haueri are morphologically similar to H.? pervasta, including a relatively shorter postaxial pygidial ridge. The abrupt appearance of abundant Acanthopyge probably reflects the partial release of niche habitats following the extinction of many shallow-water scutelluid trilobites during the early Eifelian Basal Choteč Event. It is possible that A. haueri evolved from the H.? pervasta group through predominant peramorphosis. The decline of Acanthopyge is related to the early Givetian Kačák anoxic Event, although some representatives apparently survived into the early Givetian.