Evolutionary patterns–tested with cladistics–and processes in relation to palaeoenvironments of the Upper Barremian genus Gassendiceras (Ammonitina, Lower Cretaceous)

摘要: Phylogenetic reconstruction of the Upper Barre- mian ammonite genus Gassendiceras (Gassendiceratinae) was performed using a cladistic analysis incorporating continuous data. Some morphological features were found to vary identi- cally among all analysed species and therefore carry no phylogenetic information (= symplesiomorphic). The single obtained cladogram allows interpreting evolution as an anagenetic succession eight species, in stratigraphic order appearance, multicosta- tum, G. alpinum, hoheneggeri, rebouleti, bosellii, quelquejeui, coulletae enayi. clade Pseudosh- asticrioceras ⁄Imerites is derived from enayi, so appears be paraphyletic. But here, we accept this fact best evolutive classification. over time modulated by some processes, which could have constrained inferred pat- tern with drift global variability towards most gracile forms time. It tempting interpret evolu- tion constant selection environmental control due eustatic variation across transgressive sequence. Thus, peramorphic (gracile) individuals seemed favoured at expense those robust (paedomorphic).