The performance contours of the three putative tasks for ammonoid shells. (A) Contours for shell economy, defined as the ratio of internal volume to shell volume, with red denoting high values, and blue low values. For gyroconic shells (non-overlapping whorls), this performance function becomes constant, and equal to the lowest contour shown (deep blue). The triangle encapsulating the entire ammonoid dataset is shown in black. (B) Contours for the drag coefficient measured by Chamberlain , red lines denote lower drag or better hydrodynamics. (C) Contours for the growth function defined in the main text, red lines denote quicker growth. (D) The contours of the three tasks give rise to a suite of variation denoted by blue points.