Patterns of bilateral asymmetry and allometry in Late Devonian Polygnathus conodonts

Conodont animals were jawless vertebrates equipped with a feeding apparatus composed of several tooth-like elements. The P1 elements, at the rear of the apparatus, are well preserved and abundant in the sediments, and their temporal evolution constitutes a tracer of ecological interactions and/or abiotic changes in the water column. However, occlusion occurred in these animals between paired right and left elements, occasioning bilateral asymmetry, which, together with allometric growth, may obliterate the temporal differences. This study aimed at disentangling these different components of morphological variation in Late Devonian Polygnathus P1 elements. An extensive 2D geometric morphometric analysis of the platform shape was performed and completed by a 3D study on a subset of elements. The 2D and 3D morphometric quantifications provided highly congruent results, showing that the 2D shape provides a good approximation of the element geometry. The 3D analysis, however, provides a more complete description of the geometrical changes involved in growth and bilateral asymmetry, providing insights on the constraints related to occlusion. In complement, the 2D analysis allowed a quantitative assessment of the variation between and within species, showing that allometry and bilateral asymmetry were differently expressed depending on the species considered. This suggests that constraints imposed on pairing by the morphology of the elements, and the pattern of bilateral asymmetry, varied even among related species. The within-species variation was so important that it obliterated temporal trends; a relationship of Polygnathus shape and conodont biofacies variations through the Famennian suggested an evolution driven by ecological interactions between conodonts.Poly3D_with carina_raw .txt file: - 3D morphometric dataset: semi-landmarks along the anterior and posterior margins and along the carina; 34 Po. communis and 30 Po. glaber. Polygnathus_2D_CTBU .txt file: - 2D morphometric dataset: semi-landmarks along the anterior and posterior margins; all species through the Famennian (1564 specimens). SupplementaryTable .xlsx and txt files: Number of Polygnathus per level and per group in the successive levels in Buschteich (BU) and in Col des Tribes (CT). Indet.: indeterminate specimens, lauri.: lauriformis, margar.: margaretae. Ages are given by the conodont zones after Spalletta et al. (2017). The total number of specimens considered for morphometric analyses is provided in the column "total" and corresponds to the sum of entire elements ("entire"), and those for which only the platform was unbroken ("platform"). Supp_Statistics .txt file: provide all the statistical results. Funding provided by: Agence Nationale de la RechercheCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001665Award Number: ANR-13-BSV7-005Poly3D_with carina_raw .txt file: A first set of landmarks was digitized on 3D models extracted from µCT-scans (cubic voxel resolution 1 µm). This dataset includes 34 Polygnathyus communis and 30 Po. glaber. The landmark set comprises three landmarks and 34 semi-landmarks. The three landmarks described (1) the dorsal extremity of the platform, (2) the insertion of the anterior margin of the platform on the free blade and (3) the insertion of the posterior margin on the free blade. Two curves of 13 equally distributed semi-landmarks correspond to the anterior and posterior margins of the platform, from the insertion points to the dorsal extremity of the platform. A third curve of 8 semi-landmarks correspond to the carina. Semi-landmarks are the landmarks #4 to 37. Raw 3D coordinates are columns V1 to V111. Polygnathus_2D_CTBU .txt file: A second set of landmarks was digitized on 2D pictures of the conodont elements, the oral surface facing the camera. This dataset includes 1564 conodonts. The landmark set comprises the three landmarks and two curves of 13 semi-landmarks described above for the 3D surfaces. Semi-landmarks are the landmarks #4 to 29. Aligned 2D coordinates are columns V1 to V48; the centroid size is reported in the column "Centroid_Size.