DOI: 10.5061/dryad.bzkh189gp
title: Measurement data for septal spacing and conch morphology in Cretaceous ammonoids

description: We analyzed the ontogenetic trajectories of conch morphology and septal
 spacing between successive chambers in Cretaceous ammonoids (suborders
 Perisphinctina and Ancyloceratina) collected from southern India,
 Madagascar, and Japan. All examined species, except for the family
 Collignoniceratidae, exhibited similar characteristics during early
 ontogeny. The common ontogenetic trajectories of septal spacing show a
 cycle comprising an increase and a subsequent decrease in septal spacing
 during early ontogeny. The conch diameters at the end of the cycle were
 estimated to be 1–4 mm. The conch shape (aperture height and whorl
 expansion rate) covariably changed at this conch diameter. Such covariable
 changes are commonly recognized in the suborders Perisphinctina and
 Ancyloceratina. The similarity in the ontogenetic trajectories of conch
 morphology implies a closer phylogenetic relationship between these
 suborders compared to Lytoceratina or Phylloceratina.
description: Each specimen was polished along its median plane (plane of
 symmetry) using a silicon carbide powder. The septal spacing between
 successive septa was deﬁned as the rotational angle between two
 consecutive septa (i.e., N and N-1 septal numbers) at the positions where
 the septum met the siphuncle and was measured using a digital optical
 microscope (Keyence VHX-900; magnification × 25–175; error &lt;
 0.01°). The center of rotation was defined as the center of the initial
 chamber’s maximum diameter through the base of the caecum (Fig. 3.1). The
 measured septal spacings are shown as graphs of the septal spacing between
 two successive septa (N and N-1) against the phragmocone diameter through
 ontogeny. This is because the septal numbers could not be accurately
 determined in most specimens owing to partial dissolution, especially of
 the earliest whorl. To measure the conch shape, we
 measured the aperture height (Klug et al., 2015) on the median plane,
 every 180° in <em>Cleoniceras</em> sp.,
 <em>Perisphinctes</em> sp., and <em>Yezoites
 puerculus</em> or 45° in the other examined species (regarding
 differences in the accuracy of the resultant growth trajectories, refer to
 Tajika and Klug, 2020). Based on these measurements, scatter diagrams of
 the aperture height and conch diameter were constructed. We discerned the
 critical point(s) at which the slopes of the regression lines (calculated
 by the reduced major axis) changed (statistically significant, <em>p
 </em>&lt; 0.05; Kermack and Haldane, 1950; Hayami and Matsukuma,
 1970). Furthermore, the whorl expansion rate (WER), one
 of the major parameters of ammonoid conchs, was measured on the median
 plane, as a representative parameter of conch shape (Klug et al., 2015).
 In each specimen, the WER on the median plane was measured (the
 measurement intervals were the same as those of the aperture heights), and
 the ontogenetic trajectories of each WER were recorded.
 Ammonitella diameters were measured using an optical microscope
 with a digital measurement tool (Keyence VHX-900; magnification × 25–175;
 error &lt; 0.01 mm). In this study, the ammonitella diameter was
 defined as the maximum diameter of the ammonitella from the primary
 constriction (Landman et al., 1996; De Baets et al., 2015a).
description: # Measurement data for septal spacing and conch morphology in Cretaceous
 ammonoids We analyzed the
 ontogenetic trajectories of conch morphology and septal spacing between
 successive chambers in Cretaceous ammonoids (suborders Perisphinctina and
 Ancyloceratina) collected from southern India, Madagascar, and Japan. All
 examined species, except for the family Collignoniceratidae, exhibited
 similar characteristics during early ontogeny. The common ontogenetic
 trajectories of septal spacing show a cycle comprising an increase and a
 subsequent decrease in septal spacing during early ontogeny. The conch
 diameters at the end of the cycle were estimated to be 1–4 mm. The conch
 shape (aperture height and whorl expansion rate) covariably changed at
 this conch diameter. Such covariable changes are commonly recognized in
 the suborders Perisphinctina and Ancyloceratina. The similarity in the
 ontogenetic trajectories of conch morphology implies a closer phylogenetic
 relationship between these suborders compared to Lytoceratina or
 Phylloceratina. ## Description of the data and file structure Dataset
 included: 1\) Septal spacing 2\) Outer conch morphology 3\) Summary of
 shell morphology In these data, #N/A cells mean that morphological data
 cannot be measured due to poor preservation. ## Sharing/Access information
 Links to other publicly accessible locations of the data: *
 Data was derived from the
 following sources: * Nishino, Y., Komazaki, K., Arai, M., Hattori, A.,
 Uoya, Y., Iida, T., and Wani, R., Covariable changes of septal spacing and
 conch shape during early ontogeny: a common characteristic between
 Perisphinctina and Ancyloceratina (Ammonoidea, Cephalopoda). Journal of
 Paleonotology.