DOI: 10.5061/dryad.7wm37pvr8
title: Geometric morphometric analysis of Protoconites minor from the Cambrian (Terreneuvian) Yanjiahe Formation in Three Gorges, South China

description: The Ediacaran to Cambrian transition is a critical interval of time during
 which major evolutionary changes occurred. Recently, abundant Protoconites
 minor have been recovered from the silty shales of the lower Cambrian
 Yanjiahe Formation (Terreneuvian, Fortunian – Stage 2) in the Three Gorges
 area of South China. These fossils represent an important ecological
 diversification of macroscopic organisms at the onset of the Cambrian.
 Protoconites minor is a probable cnidarian-grade organism preserved by
 carbon compression. Herein, geometric morphometric analyses are applied to
 crack out specimens of P. minor to reveal any cryptic morphological
 details that may have implications for their morphological diversity,
 ontogenetic processes, and taxonomic identification. These statistical
 analyses reveal a strong relationship between size and shape, which
 indicates that the overall shape of P. minor was mainly controlled by
 allometric growth. The smaller specimens are generally wider at the
 anterior, and more commonly have straight-sides. Larger individuals tend
 to be narrower at the anterior, with bending more common. Our analyses
 demonstrate that there are transitional forms between larger, strongly
 bent specimens and smaller, straight specimens, suggesting that the
 assemblage likely consists of a single species.
description: All 1048 specimens (see supplementary material) of <em>P.
 minor</em> utilised for this study occur as carbonised films
 preserved on bedding surfaces (Figure 2). Obviously broken or extensively
 damaged specimens have been excluded from the analysis. Collection number
 “CH” indicates fossils from the Dingjiaping section. “Y” indicates fossils
 from the Yangjiachong section. Digital images were taken with a light
 camera (Canon EOS70D) under both natural light and with an external light
 source in Chang’an University, Xi’an, China. Specimens are housed in the
 collections at the School of Earth Science and Resources, Chang’an
 University. Geometric morphometric analyses required
 application of a combination of landmarks and sliding semilandmarks.
 Landmarks were used to cover static homologous anatomical loci that can be
 found unambiguously on every specimen (Zelditch et al., 2004), while
 sliding semilandmarks were used to cover curves where no homologous point
 can be precisely defined (Bookstein, 1997a, b; Gunz et al., 2005;
 Mitteroecker and Gunz, 2009; Gunz and Mitteroecker, 2013). In total, three
 Type II landmarks (Zelditch et al., 2004) and 34 sliding semilandmarks,
 were applied to each specimen using the software TpsDig2 v. 2.26 (Rohlf,
 2010a; Figure 3.1-2). A sliders file was generated using the software
 TpsUtil v. 1.74 (Rohlf, 2011a). Relative Warp (RW)
 analyses were carried out using the software TpsRelw v 1.74 (Rohlf, 2010b)
 using the Generalized Procrustes Analysis superimposition method (Figure
 3.3; Zelditch et al., 2004; Gunz and Mitteroecker, 2013; Chen et al.,
 2016). The centroid is a measure of size that is mathematically
 independent of shape (Zelditch et al., 2004), and was calculated using the
 mean of all the landmarks’ coordinates automatically using TpsRelw v 1.74.
 Multivariable linear regression analyses were conducted using TpsRegr v
 1.45 (Rohlf, 2011b). Data was also transferred to the Palaeontological
 Statistics Program (PAST) (Hammer et al., 2001) for simple linear
 regression. Some specimens exhibit left or right
 curvature. As <em>P. minor </em>was not mineralized, it is
 possible that extent of curvature is a taphonomic artefact. To control for
 bias associated with direction of curvature, we have reflected some of the
 images so all specimens curve in the same direction.
description: The upload files here are the input files used for all the
 analyses used in this manuscript.