DOI: 10.5061/dryad.xpnvx0kff
title: Data from: Ontogeny and evolution of the elasmosaurid neck highlight a greater diversity of Antarctic plesiosaurians

description: The Antarctic plesiosaurian record is critical for understanding the
 evolution of elasmosaurids in the southern hemisphere. Elasmosaurids
 exhibit some of the most remarkable modifications of the vertebrate axial
 skeleton given their extreme elongation of the cervical region. Despite a
 considerable amount of information available on vertebral counts within
 Plesiosauria throughout the decades, we have a considerably more limited
 understanding of the diversity of cervical vertebral shapes in
 elasmosaurids and how these have changed throughout ontogeny and
 phylogeny. Here, we compile the largest known morphometric dataset on
 elasmosaurid cervical vertebrae, including data on juveniles and adults,
 to answer some of those long-standing questions. This dataset also
 includes newly recovered materials from Antarctica, which we describe
 herein. Using multivariate statistical approaches, we find that the two
 major elasmosaurid cervical morphotypes, the elasmosaurine
 anteroposteriorly elongate (can-shaped) and the aristonectine
 anteroposteriorly short and dorsoventrally tall (disk-like), evolved
 towards opposite regions of the morphospace from the plesiomorphic
 ‘Cimoliasaurus’-grade condition. We also find a marked ontogenetic shift
 from the disk-like to can-shaped morphologies, which is especially
 pronounced in elasmosaurines, but more limited in aristonectines.
 Furthermore, we find that juvenile aristonectines occupy a specific region
 of the vertebral morphospace, distinct from any other group or ontogenetic
 stage, thus suggesting that reversal to the ‘short-necked’ condition in
 elasmosaurids is mostly characterized by ontogenetic predisplacement in
 aristonectines. Finally, we find that it is possible to discriminate
 between vertebral shapes of distinct taxonomic groups regardless of
 ontogenetic stage, which suggests a greater diversity of Antarctic
 elasmosaurids than previously recognized.
description: <strong>Phylogenetic analysis. </strong>The codification of the specimen in the matrix of O’Gorman (2019a) with the codification of <em>Jucha </em>by Fischer <em>et al.</em> (2021) is available in the files “OG(2019a) & Fischeretal(2021).nex” and “OG(2019a) & Fischeretal(2021).tnt”. <strong>Statistical analyses. </strong>The whole dataset employed in our statistical analyses of cervical and dorsal vertebrae are compiled in the file “Dataset.xlsx”. All the compiled cervical vertebrae specimens are listed in <strong>Supplementary Table 1</strong>. The whole dataset of PAST files to cervical vertebrae are available in the files: “Supp cervical adult morphotypes.dat”; “Supp cervical adult genus level.dat” and “Supp cervical juvenile genus level.dat”. All the analyzed dorsal vertebrae specimens are listed in <strong>Supplementary Table 2</strong>. The whole dataset of PAST files to cervical vertebrae are available in the files: “Supp dorsal adult genus level.dat”.             We plotted the VLI values in histograms and performed the normality test Shapiro-Wilk (<em>W</em>) to determine whether we could perform non-parametric analyses.