Acta Palaeobotanica 2(Suppl): 111–127, 1999

An angiosperm cradle community and new proangiosperm taxa.

Summary: A few leaves and pollen grains from the Baisa locality in the upper reaches of the Vitim river, Transbaikalia, are recognized as angiospermous. This locality also yielded eight species that are considered proangiospermous, including the derived forms of gnetophytes, bennettites and cycadophytes. The Baisian assemblage is, thus, an example of an arogenic, or type-making, community that gave rise to several lineages trending towards angiosperm morphology. On the basis of ostracod zonation this assemblage is assigned to the Hauterivian or early Barremian. Most proangiosperm remains came from an open wetland vegetation that replaced the typical Mesozoic fern marshes. With the elimination of the latter a new type of wetland community was formed by the ecological expansion of preadapted gymnosperm groups developing new (partly herbaceous) growth forms in which proangiospermous characters appeared in the process. The vegetational change correlates with extensive rifting and basaltic volcanism. Mats of aquatic insects covering bedding planes indicate mass mortality perhaps related to sharp pH fluctuations that might also have affected the wetland plant community. Plant – insect interactions, as evidenced by pollen grains from the gut contents of fossil insects, may have played a significant role in proangiosperm evolution. A new species of Eoantha and four new genera are described, including a bisexual pre-flower Preflosella nathania gen. et sp. nov. [Acta Palaeobot. - Supplementum No. 2]

Keywords: angiosperm origins, proangiosperms, morphological evolution, palaeoecology, Early Cretaceous