Fig. 15
Volume density diagrams of the variation of spiral height (δX) versus axial length in keel view (δY) through time for G. menardii (yellow), G. limbata (purple, and G. multicamerata (red) at Hole 925B during the past 8 million years. Upper row shows diagrams in side view, lower row shows diagrams in front view. Axes of δX and δY are scaled to values between 0 and 1 (see section about "Materials and methods" section). The time axis shows real ages (from 0 to 8 Ma) and were linearly converted from the ΔZ values in the original Voxler data set. All iso-surfaces represent an arbitrary but constant frequency value of 0.4665 (normalized V i,j , see "Materials and methods" section). Settings for contour construction in Voxler 2: Method = Min, Max, count; Min = 0.5, Max = 10, interval = 1. Red dots represent voxel centers after finer re-gridding was applied to the input data matrix. Superposition of the G. limbata iso-surface (purple in b, e) shows, that there is strong morphological overlap with G. menardii, which makes the two forms virtually indistinguishable by δX and δY alone. Addition of the G. multicamerata iso-surface (red in c, f) shows two separate time-progressive surfaces suggesting gradual size expansion and divergence of G. multicamerata from the ancestral G. menardii–G. limbata. The dotted plane in a represents a diagonal (45°) longitudinal section from 0 to 8 Ma across the density volume, to which Fig. 16 is referred to for a paleoceanographic interpretation of the menardiform density pattern. In the small inset of a the upper cover of the iso-surface is removed to sketch the internal contoured density distribution of specimens through time in the longitudinal section (see Fig. 16 for an enlarged representation of contours in that projection). The data of scaled and normalized volume densities V ij of G. menardii, G. limbata and G. multicarmerata are available from Table 7a–f in the electronic supplementary materials. Table 7g of the electronic supplementary materials provides explanations to Table 7a–f. An animation of the volume density diagram shown in c is available from the electronic supplementary materials (file Supplmentary Video. Due to technical reasons the time-axis in this video is labeled with normalized ages instead of real ages)