Fig. 17

Evolution of spiral height (δX) versus axial length (δY) of G. menardii during the past 8 Ma represented by volume density diagrams at a ODP Site 925B (Ceara Rise), b DSDP Site 502 (Caribbean Sea), and c DSDP Site 503 (eastern equatorial Pacific). Volume density diagrams are involved surfaces of equal specimen frequencies, where rare specimens populate outer surfaces and frequent specimens occur on more inner iso-surfaces. The illustrated iso-surface skins in (a–c) are hulls of the outer tails of skewed frequency distributions through time and thus represent rare forms. The red arrows at 2.58 Ma denote the lower bound of the blue rectangle shown in Fig. 16 (absence of large menardiforms at Site 502). The red arrow at 1.95 Ma in a marks the beginning of immigration of extra-large adults at Site 925. The red arrow at 1.7 Ma indicates the entry of extra-large adults at Site 502 further north in the Caribbean Sea. On the Pacific side (c) the pattern is more continuous. Iso-values are set to 0.4665. Contours in Voxler are set to Method = Min, Max, count; Min = 0.5, Max = 10, interval = 1). Data to draw the diagrams for DSDP Sites 502 (b) and 503 (c) were taken from Knappertsbusch (2007) and Knappertsbusch and Mary (2012)