The heteromorph ammonite Tropaeum (Tropaeum) evolutum sp. nov. from the Hythe Formation, Lower Greensand Group (basal upper Aptian, Lower Cretaceous) of Maidstone, Kent, UK

Tropaeum is a genus of large to very large heteromorph ammonites, typical of the Aptian and among the dominant invertebrate organisms of its time. Here we describe a new species, Tropaeum (Tropaeum) evolutum sp. nov., from the basal upper Aptian Epicheloniceras martinioides Zone of the now back-filled Coombe Quarry at Maidstone, Kent, southern England. The new species is characterised by remarkably evolute coiling, the umbilical diameter exceeding 56% of the total, and by a body-chamber of rather more than half a whorl, which is boldly sculpted throughout with fourteen widely, but equally spaced single primaries. Unlike many early (lower Aptian) Tropaeum species, where the adult body-chamber is uncoiled, it appears that in the upper Aptian T. (T.) evolutum sp. nov., the whorls remained just in contact to the end. This follows the general trend exhibited by other late examples of the genus.