Scanning electron microscopy investigation of monads and tetrads of basal core eudicots from the Upper Cretaceous Vilui Basin, Siberia: Evidence for reticulate evolution

Non-marine Late Cretaceous sediments from the Vilui Basin, Siberia, yield a diverse palynoflora of over 180 taxa, a third of which had a circum-polar distribution. The Vilui palynoflora belongs generally to the northerly Aquilapollenites Province admixed with minute Normapolles types, and comprises about 36–70% angiosperm pollen forms, indicating a late Campanian/early Maastrichtian age. Using a combination of light and scanning electron microscopy we examined well-known stratigraphic taxa such as Aquilapollenites mtchedlishvilii Srivastava, Aquilapollenites decorus Srivastava,Azonia recta Bolkhovitina and Tricerapollis minutus Chlonova. Further we present pollen belonging to early eudicots such as Saxifragales (Cercidiphyllaceae, Altingiaceae and Hamamelidaceae), basal eudicots (? Buxaceae) and basal core eudicots (?Gunnerales) that are preserved as colpate or porate forms, some of which are preserved as obligate tetrads, such as the morphogenera Virgo Ward, Artiopollis (Agasie) Singh, and Senectoteradites Dettmann while others are preserved as single grains or in pollen aggregations, such as Periporopollenites (Potonié) Pflug &Thomson, Retitricolpites (van der Hammen) Pierce and unnamed tricolpate types. The following new species are introduced: Virgo nicholsii, Artiopollis tyungensis, Artiopollis bellus, Periporopollenites sakhaensis, and Senectotetradites viluiensis. Our approach revealed features suggesting that individual grain types exhibit affiliations to more than one extant family. This mirrors trans-familial characters also observed in Late Cretaceous leaf fossils and is typical of reticulate evolution.

► The Late Cretaceous Vilui Basin, Siberia, has a diverse (180 taxa) pollen flora.
► The area spans the overlap between the Aquilapollenites and Normapolles Provinces.
► Five new pollen taxa are described from non-marine sediments.
► Individual basal eudicot grains have characters spanning several extant families.
► Pollen and leaves show reticulate evolution was important in early angiosperm history.