Fig. 4
From: Interpreting drag consequences of ammonoid shells by comparing studies in Westermann Morphospace
Coefficients of drag measured on six casts of fossil shells by Jacobs (1992) are plotted against the log of tested Reynolds number (Re). Least-squares regression lines are shown for each specimen. The more streamlined shells (Cardioceras, Oppelia, Sphenodiscus) produce the highest drag coefficients at Re < 3400, but produce the lowest drag coefficients at Re > 11,200. Regression lines for specimens with similar involution across around Re = 7000 (Cardioceras should produce less drag than Lytoceras when Re = 6816; Sphenodiscus should produce less drag than Scaphites when Re = 7050; Oppelia should produce less drag than Gastroplites when Re = 7515)