DOI: 10.5061/dryad.j0zpc86d8
title: Data from: Go large or go conical: allometric trajectory of an early Cambrian acrotretide brachiopod

description: 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 a juvenile morphology 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.
description: SEM images of each specimen were used to digitalize landmarks,
 with digitization performed using TpsDig2 v. 2.25 (Rohlf
 2016<i>a</i>). Due to the simple morphology of the ventral
 valve of <i>Eohadrotreta</i>, we apply a combination of
 landmarks and semilandmarks or sliding landmarks, for analysing homologous
 points locations together with curves measured on a sample of organisms
 (Zelditch <i>et al.</i> 2012; Gunz & Mitteroecker
 2013; Mitteroecker <i>et al.</i> 2013).
description: <b>Appendix S1</b>: Shape variation among ventral
 valve of <i>Eohadrotreta zhenbaensis</i> from the Cambrian
 Series 2 Shuijingtuo Formation at Wanhjiaping section of South China, as
 well as <i>E. zhenbaensis</i> and <i>P.
 zhujiahensis</i> from the Shuijingtuo Formation at Aijiahe and
 Wangzishi sections of South China for comparison, with indication of
 characteristic thin plate splines. All thin plate splines correspond to
 the shapes of 190 specimens in morphospace. The valve length is indicated
 by different colours. <b>Appendix S2</b>:
 Principal components, size information, and GPA data of all the 158
 specimens of <i>E. zhenbaensis. </i>n/a demonstrates that the
 height measurement is not obtained. <b>Appendix
 S</b><b>3</b>: Relative contribution of each landmark
 (1-38) of <i>E. zhenbaensis.</i>
 <b>Appendix S4</b>: Multivariate regression of
 overall shape with centroid size of <i>E. zhenbaensis</i>,
 involving permutation tests on the correlations with 10 000
 replicates. <b>Appendix S5</b>:
 Multivariate regression of overall shape with valve height of <i>E.
 zhenbaensis</i>, involving permutation tests on the correlations
 with 10 000 replicates.