Allometry in Late Devonian Podocopa ostracods (Crustacea) and its implications for Ostracoda ontogeny

Podocopa ostracods abounds in various marine and non-marine habitats since the early Palaeozoic and leave diversified fossil records in strata worldwide. They are particularly useful for stratigraphic correlation and paleoenvironmental and paleogeographical reconstructions. However, being the most numerous ostracods during the Palaeozoic, their origins, evolution, ontogeny and phylogeny remain poorly defined. This paper represents the first study of morphological variation in Devonian Platycopida (an order of Podocopa) ostracods using a geometric morphometric approach. Our results identify substantial shape variation for Cribroconcha honggulelengensis from the Upper Devonian Hongguleleng Formation of western Junggar, NW China, demonstrating a remarkable change to those juveniles between stages A-3 and A-2. Using linear regressions between Principal component scores from right lateral view and carapace length, we demonstrate allometric growth patterns for the species C. honggulelengensis..., SEM images of each specimen were used to digitalize landmarks, with digitization performed using TpsDig2 v. 2.25 (Rohlf 2016a). A combination of landmarks and semilandmarks or sliding landmarks were used for analysing homologous points' locations together with curves measured on a sample of organisms. Principal component analysis (PCA) was subsequently applied to explore the overall diversity of within-sample shape variation using software  PAST v. 2.13 (Hammer et al. 2001)., s1: Size information (length and height) and 74 Principal components (PC) of all the 178 specimens of Cribroconcha honggulelengensis Song & Crasquin, 2017.

自古生代早期以来，尾肢介亚目（Podocopa）介形类广泛分布于各类海洋与非海洋生境，并在全球各地地层中留下了丰富多样的化石记录。该类群尤其适用于地层对比、古环境与古地理重建研究。然而作为古生代最为繁盛的介形类类群，其起源、演化、个体发育与系统发育关系至今仍尚未明确。本研究首次采用几何形态测量法，对泥盆纪平足介目（Platycopida，尾肢介亚目下一目）介形类的形态变异展开研究。研究结果表明，产自中国西北准噶尔西部上泥盆统洪古勒楞组的红果勒伦筛壳介（Cribroconcha honggulelengensis）存在显著的形态变异，其幼体在A-3期与A-2期之间发生了显著的形态变化。通过对右外侧视图主成分得分与壳长进行线性回归分析，本研究揭示了红果勒伦筛壳介的异速生长模式……本研究采用扫描电子显微镜（SEM）成像获取每块标本的图像，并使用TpsDig2 v.2.25软件（Rohlf 2016a）完成标志点的数字化处理。研究结合标志点与半地标点（滑动半地标点），对样本中生物的同源点位位置及测量曲线进行分析。随后采用PAST v.2.13软件（Hammer等，2001）进行主成分分析（PCA），以探究样本内部的整体形态变异多样性。补充数据集1：涵盖178份红果勒伦筛壳介（Cribroconcha honggulelengensis Song & Crasquin, 2017）标本的尺寸信息（壳长与壳高）以及全部74个主成分（PC）得分。