Fig. 12

Life reconstruction of Prolobites. Since hardly anything is known about the anatomy of ammonoid soft parts, reconstructions are still largely speculative, two different reconstructions are proposed. On top, a mature female Prolobites carrying an egg sac externally like the Recent decabrachian squid Gonatus, and at the bottom, Prolobites as an active swimmer with the aperture oriented at roughly 40°–50°, due to its body chamber exceeding 360° in length (compare with Saunders and Shapiro 1986; Klug and Korn 2002). We show ten arms because this appears to be the plesiomorphic state in coleoids and perhaps also in nautilids, as indicated by the ten arm-buds displayed by Nautilus-embryos (compare Shigeno et al. 2007)