Paleobiological interpretation of the Turonian ammonite species Pseudaspidoceras flexuosum and its epibionts

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Pseudaspidoceras flexuosum is a widely distributed ammonite species and index for an early Turonian (Late Cretaceous) biozone. New material from Vallecillo, northeastern Mexico, shows a possible dimorphism for this species, including long spines, hitherto not recognized for this species. However, the most widely accepted explanation for the presence of such spines, a balancing aid to rest on the sea-floor, cannot be applied here. Previous studies of the palaeoenvironemt at Vallecillo have shown that conditions at the sea-floor were hostile to most organisms preserved. This project is aimed at an intraspecific study of P. flexuosum regarding anatomy and function of the spines, a possible dimorphism, and the possibility to recognize former spines where they are broken away. Spines were described from three other Late Cretaceous ammonite species and may have been a more widespread feature of Late Cretaceous ammonites than hitherto recognized. In addition, study of epibiontic cirripedians (Crustacea) may allow for additional conclusions on the palaeoecology of their host P. flexuosum. This project intends to contribute to further understanding of the hitherto elusive palaeobiology of one of the most popular fossil groups.