Intraspecific variability and systematics in South American Syrotrigoniinae (Trigoniida, Bivalvia)

摘要: Abstract The systematics of the genus Syrotrigonia is revised in light intraspecific variability a large sample sigeli from Valanginian Neuquen Basin, Argentina. can be recognized by presence concentric or subconcentric costae surrounding umbo, later on developing an inflection and finally resulting set anterior horizontal to commarginal another posterior sub-vertical costae. part area bears transverse, usually anteriorly concave, which direct towards umbo escutcheon; initially they are continuous with those flank, but alternate. General shell shape, antecarinal sulcus, junction pattern between both sets number relative vertical variable among species, while width density development vs. may vary highly within species. rugae developed whole surface interpreted as result environmental perturbations. A brief biogeographical interpretation family Buchotrigoniidae also outlined. probably originated North America Tithonian, being widespread Pacific coast South Early Cretaceous times; at least six (probably seven) American species could recognized. By Aptian times taxon reached Tethyan realm, its last record Albian age. frequent different marginal marine deposits suggests euryhaline lineage adapted salinity variations, this cause rugae. Considering high displayed analyzed material, samples needed characterize new group.