In search of the correspondence between in situ and dispersed pollen

Abstract

The amount of information about the diversity of dispersed pollen grains and spores exceeds that about their in situ counterparts by several orders of magnitude. Strangely, there are several finds of in situ pollen types that are thus far unknown from dispersed palynomorph assemblages. Here we provide a brief discussion of this peculiar phenomenon based mainly on two examples from our recent studies, including a late Permian lyginopterid seed fern from Jordan and a Middle Jurassic conifer from Siberia. Several reasons could account for such “in situ only” pollen types, including the scarcity of the parent plants, low pollen productivity, entomophily, or immaturity of in situ pollen, although the last variant seems overestimated. Such pollen grains, when found dispersed, might also be considered as untypical, featureless or inadequately preserved specimens and, as a consequence, be reported without illustrations as undetermined specimens or even ignored altogether; this way, they receive little attention from the authors, remain unregistered, and cannot be analyzed by subsequent researchers. We stress the importance of publication of as complete as possible information about all components of palynological assemblages, including their photos, even if they do not belong to stratigraphically important taxa. We do not attribute the disparity to taphonomic differences between megafossil and microfossil deposition, because the ‘in situ only’ pollen types are absent not only in the same beds where the pollen organs were found, but are unknown from any other deposits.