Early evolution of the Cretaceous serial planktic Foraminifera (late Albian-Cenomanian)

The classification of the late Albian-Cenomanian biserial planktic foraminiferal family Heterohelicidae Cushman, 1927, is reevaluated. This group underwent a period of relatively slow evolutionary change during the late Albian-early Cenomanian followed by rapid evolution in the middle Cenomanian. Three new heterohelicid genera and species in the late Albian-early Turonian are described: Protoheterohelix obscura, Planoheterohelix postmoremani, and Globoheterohelix paraglobulosa. Two reassigned species are also emended: Protoheterohelix washitensis (Tappan) and Planoheterohelix moremani (Cushman). Reassessment of the taxonomic significance of morphological features of the heterohelicid test leads to the conclusion that the most important characters in their taxonomy are test architecture, symmetry/asymmetry of the periapertural structures, nature of periapertural structures, relative size difference of the proloculus and second chamber, test ornamentation, and pore size. Most heterohelicid taxa of the late Albian-Cenomanian display microperforate test walls. Heterohelix Ehrenberg, 1843, which evolved in the early Turonian, is a distinct lineage.