DOI: 10.5061/dryad.zs7h44jbv
title: Data from: Morphometric analysis of Skiagia-plexus acritarchs from the early Cambrian of North Greenland

description: The Cambrian evolutionary radiations are marked by spectacular biotic
 turnovers and the establishment of increasingly tiered food chains. At
 their base are primary producers, which in the Cambrian fossil record are
 chiefly represented among organic-walled microfossils. The majority of
 these microfossil remains have traditionally been attributed to an
 informal category of incertae sedis called “acritarchs”, based entirely on
 form taxonomy. Acritarch form-taxa have been intensely used for
 biostratigraphy, and in large-scale studies of phytoplankton diversity.
 However, both prospects have been challenged by cases of taxonomic
 inconsistencies and over-splitting arising from the large phenotypic
 plasticity seen among these microfossils. The acritarch form-genus Skiagia
 stands as an ideal case-study to explore these taxonomic challenges, since
 it encompasses a number of form-species widely used in lower Cambrian
 biostratigraphy. Moreover, subtle morphological differences among Skiagia
 species were suggested to underlie key evolutionary innovations towards
 complex reproduction strategies. Here we apply a multivariate morphometric
 approach to investigate the morphological variation of Skiagia-plexus
 acritarchs using an assemblage sourced from the Buen Formation (Cambrian
 Series 2, Stage 3–4) of North Greenland. Our analysis showed that the
 specific-level classification of Skiagia discretizes a continuous spectrum
 of morphologies. While these findings bring important taxonomic and
 biostratigraphic hurdles to light, the unequal frequency distribution of
 life cycle stages among Skiagia species suggests that certain elements of
 phytoplankton paleobiology are nonetheless captured by Skiagia
 form-taxonomy. These results demonstrate the value of using morphometric
 tools to explore acritarch phenotypic plasticity and its potential
 ontogenetic and paleoecological drivers in Cambrian ecosystems.
description: Three fine-grained samples (labelled 184002, 184003, 184004) from
 the early Cambrian of North Greenland (Brillesø locality,
 <em>Skiagia ciliosa</em>‒<em>Heliosphaeridium
 dissimilare</em> Zone) have been collected by Grønlands Geologiske
 Undersøgelse in 1974. Nine palynological preparations were produced by
 Vidal and Peel (1993) using a standard HF acid maceration procedure (Vidal
 1988). All 9 palynological preparations yielded
 acritarchs attributable to five species (<em>S. scottica</em>,
 <em>S. ciliosa</em>, <em>S. orbiculare</em>,
 <em>S. compressa</em>, <em>S. ornata</em>) that
 were counted and measured from photomicrographs by E. Wallet. A total of
 10 continuous parameters capturing the shape of processes and size of the
 central body were measured for each <em>Skiagia </em>species.
 This dataset was used as a basis for principal component and discriminant
 analyses. A seprate dataset was compiled to include counts of discrete
 features related to various stages in the life cycle of
 <em>Skiagia</em><em>.</em>
 Measurements were performed using the free software Image J; and
 multivariate analyses and plots were computed using the free software
 package PAST. More information on methods and measured
 parameters can be found in Wallet et al. 2022.
 <strong>References</strong>
 Vidal, G. 1988: A
 palynological preparation method. Palynology 12:215–220.
 Vidal,
 G., and J. S. Peel. 1993: Acritarchs from the Lower Cambrian Buen
 Formation in North Greenland. Grønlands Geologiske Undersøgelse Bulletin
 164:1–35. Wallet, E., Willman, S. and Slater, B. J. 2022:
 Morphometric analysis of Skiagia-plexus acritarchs from the early Cambrian
 of North Greenland: towards a meaningful evaluation of phenotypic
 plasticity. Paleobiology.
description: The dataset is divided into two folders: 
 Supplementary files cited in Wallet et al. 2022: 
 [Wallet_et_al._2022_Supplementary_Figure_1.tif]
 [Wallet_et_al._2022_Supplementary_Figure_2.tif]
 [Wallet_et_al._2022_Supplementary_Figure_3.tif]
 [Wallet_et_al._2022_Supplementary_Figure_4.tif]
 [Wallet_et_al._2022_Supplementary_Figure_5.tif]
 [Wallet_et_al._2022_Supplementary_Figure_6.tif]
 [Wallet_et_al._2022_Supplementary_Figure_7.tif]
 [Wallet_et_al._2022_Supplementary_Table_1.xlsx]
 [Wallet_et_al._2022_Supplementary_Table_2.xlsx]
 Captions for these figures and tables can be found in the file
 [Wallet_et_al._2022_Supplementary_Figures_and_tables_captions.docx]. Raw data: [Wallet_et_al._2022_raw_data_measurements.csv] [Wallet_et_al._2022_raw_data_standardization.xlsx] [Wallet_et_al._2022_raw_data_Fig.6.csv] [Wallet_et_al._2022_raw_data_PCA-LDA.csv] Information about raw data, collection/methods data and overall content of the dataset can be found in [README_data_from_Wallet_et_al._2022.txt].