DEVELOPMENTAL ORIGINS OF FOSSILIZED POLLEN MALFORMATIONS, A POTENTIAL VOLCANOGENIC ENVIRONMENTAL STRESS PROXY

Heightened frequencies of saccate pollen malformations in terrestrial fossil records have been interpreted as a volcanogenic environmental stress proxy for the end-Permian biotic crisis and possibly other Phanerozoic mass extinctions. However, the developmental origins of these morphological deviations are unclear. To determine which types of developmental disruptions may induce teratologies in saccate pollen of the past, we reviewed microsporogenesis and cytology literature on developmental deviations in modern saccate-pollen-producing conifers. Prior studies indicate phenotypic malformations in modern conifers, similar to those known from the end-Permian crisis, are not only associated with a range of irregularities during microsporogenesis, but also production of unreduced (>2n) pollen grains. We describe and diagram a hypothesized framework for the developmental origins of malformation traits, corresponding with irregularities during meiosis and the tetrad stages. With this framework, morphological traits in fossilized palynomorphs may be used to determine which stages of pollen development were most likely disrupted and thus constrain the range of plausible mechanisms behind ecosystem turnovers.