Data from: The middle Smithian (Early Triassic) ammonoid Arctoceras blomstrandi: Conch morphology and ornamentation in relation to stratigraphy ...

• Main Authors: Hansen, Bitten, Bucher, Hugo, Schneebeli-Hermann, Elke, Hammer, Øyvind
• Format: Dataset
• Language: English
• Published: Dryad 2020
• Subjects: Buckman’s law; Smithian; Svalbard; Conch morphology; Arctic; Hyatt; Norway
• Online Access: https://dx.doi.org/10.5061/dryad.vq83bk3qw; https://datadryad.org/stash/dataset/doi:10.5061/dryad.vq83bk3qw

The ammonoid genus Arctoceras (Hyatt, 1900) occurs across all palaeolatitudes, and is a key genus for middle Smithian (Early Triassic) biostratigraphic correlations at a global scale. In this study, intraspecific variations in conch morphology, ornamentation and allometry are examined in relation to stratigraphic position. Arctoceras is the most abundant ammonoid genus in the middle Smithian of Svalbard, Arctic Norway. Originally, seven Arctoceras species were described from Svalbard, but their practical use in fossil identification was questionable. Later, as the importance of intraspecific variation was recognized, six of the Arctoceras species from Svalbard were declared junior synonyms of Arctoceras blomstrandi (Lindström, 1865). Yet, the variations in A. blomstrandi conch morphology remain poorly quantified and the dependence on stratigraphic position unknown. Our research quantifies the intraspecific variation in conch morphology, ornamentation and allometry in relation to stratigraphy of the Svalbard ... : Arctoceras blomstrandi specimens were measured and described following Klug et al. (2015). For each specimen, measurements were taken for the largest preserved diameter d and corresponding whorl width ww, whorl height wh and umbilical width uw. Where the conch was not complete on both sides, the half width was measured on the intact side and the full whorl width inferred. All measurements are available in the online material. In some damaged specimens the best measurements were obtained not on the outermost whorl, but on a younger part of the conch (measurements noted with a ‘*’ in the online dataset). Specimens with diameters below ~10 mm were not included in analyses because of the low measuring accuracy. Qualitative characterization of shell ornamentation (i.e. ribs) is also considered for each specimen (weak/strong/absent). When a specimen was too damaged, the ornamentation was characterised as ‘unknown’. The material is curated at the Paläontologisches Institut und Museum, Universität Zürich, ...