Conodont animals were early jawless vertebrates equipped with a feeding apparatus composed of several tooth‐like elements. The P1 elements, at the rear of the apparatus, were characterized by a robust shape and rapid morphological evolution. Occlusion occurred between paired right and left P1 elements, occasioning some bilateral asymmetry, which, together with allometric growth, may partially obliterate the temporal differences. The present study aims to disentangle these different components of morphological variation in Late Devonian Polygnathus P1 conodont elements. An extensive 2D geometric morphometric analysis of the platform shape was performed through the Famennian record of two outcrops. This analysis was completed by a 3D study on a subset of conodont elements. The 2D and 3D morphometric quantifications provided highly congruent results, showing that the 2D shape constitutes a good approximation of the element geometry. The 3D analysis delivered further insights into the relationship between the geometry of the elements and the constraints related to occlusion. The 2D analysis allowed a quantitative assessment of the variation among species and through time. Allometry and bilateral asymmetry were differently expressed depending on the species considered, suggesting that constraints imposed on pairing by the morphology of the elements varied even among related species. The within‐species variation was so important that it largely obliterated temporal trends; a relationship of Polygnathus shape and conodont biofacies variations through the Famennian nevertheless suggested an evolution driven by ecological interactions between conodont genera.

中文翻译：

---

晚泥盆纪Polygnathus牙形体的双侧不对称和异形的模式

牙形动物是早期的无颚脊椎动物，配备了由几种牙齿状元素组成的喂养装置。装置背面的P1元素具有坚固的形状和快速的形态演变特征。配对的左右P1元素之间发生遮挡，引起一些双侧不对称，再加上异速生长，可能会部分消除时间差异。本研究旨在弄清晚泥盆世Polygnathus形态变化的这些不同组成部分P1牙形元素。通过两个露头的法门尼记录对平台形状进行了广泛的2D几何形态分析。该分析是通过对牙形石元素的子集进行3D研究完成的。2D和3D形态计量学定量提供了高度一致的结果，表明2D形状构成了元素几何的良好近似。3D分析为元素的几何形状和与遮挡有关的约束之间的关系提供了进一步的见解。通过2D分析，可以定量评估物种之间以及整个时间上的差异。异构和双侧不对称性根据所考虑的物种而不同地表达，这表明，即使在相关物种之间，由元素的形态对配对施加的约束也有所不同。种内变异是如此重要，以至于它在很大程度上消除了时间趋势。的关系然而，通过法门尼人时期的gna柏形状和牙形生物相的变化表明，牙形生物属之间的生态相互作用驱动了演化。