Go large or go conical: allometric trajectory of an early Cambrian acrotretide brachiopod

Zhiliang Zhang*, Timothy P. Topper, Yanlong Chen, Luke C. Strotz, Feiyang Chen, Lars E. Holmer, Glenn A. Brock, Zhifei Zhang

*Corresponding author for this work

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    Abstract

    Acrotretides are extinct micromorphic brachiopods that exhibited considerable morphological variation during their rapid evolution in the early Palaeozoic. The plano-conical shells of acrotretides are distinct in comparison to other brachiopod groups and despite their diversity and abundance in early Palaeozoic communities, their origins, early evolution, life history and phylogeny are poorly understood. Here, we employ advanced geometric morphometrics to quantitatively investigate ontogenetic variation and allometry in the ventral valve of the oldest known acrotretide species from the early Cambrian of South China. Our results identify substantial shape variation for Eohadrotreta zhenbaensis, along with a parabolic morphological trajectory through ontogeny, demonstrating a remarkable reversal to PC1 values equivalent to those obtained for juveniles, during later ontogenetic stages. The evolutionary novel body plan (diminutive and plano-conical) of Acrotretida was established gradually during two phases of allometry, formed initially during the final stage of the Cambrian evolutionary radiation from an ancestral low, equivalved lingulide body plan. The development of a conical shaped valve seems to have resulted in an overall smaller body size, when compared with non-conical forms. The heterochronic processes responsible for generating these ontogenetic modifications at different allometric phases may have facilitated the evolutionary diversification of acrotretide brachiopods during the early Palaeozoic.

    Original languageEnglish
    Pages (from-to)727-741
    Number of pages15
    JournalPalaeontology
    Volume64
    Issue number5
    DOIs
    Publication statusPublished - Sep 2021

    Bibliographical note

    Copyright the Author(s) 2021. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

    Keywords

    • geometric morphometrics
    • ontogenetic trajectory
    • micromorphic brachiopod
    • allometry
    • evolution
    • early Cambrian

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