Contributions towards whole-plant reconstructions of Dicroidium plants (Umkomasiaceae) from the Permian of Jordan

Abstract

Four Dicroidium species and associated fertile organs are here described from the late Permian Umm Irna Formation (Dead Sea Region, Jordan). Dicroidium irnense, D. jordanense and D. robustum, which were so far only known from the Wadi Himara locality, are now reported from several other sites, some yielding nearly complete fronds and excellently preserved cuticles; D. hughesii, a species so far only known from the Triassic, is here reported from the upper Permian. The largest species, D. robustum emend. nov., can be correlated with the pollen organ Pteruchus lepidus sp. nov. and the cupulate structure Umkomasia aequatorialis sp. nov. based on repeated co-occurrences and striking similarities in cuticular features. Dicroidium irnense is associated with Pteruchus frenguellii sp. nov. based on consistent co-occurrence. Dispersed Umkomasia seeds are common in all localities where Dicroidium occurs. The here described material comprises some of the most completely reconstructed species of Umkomasiaceae known to date. All Dicroidium plants are characterized by comparatively large fronds and both Pteruchus species have strongly elongate, strap-shaped microsporophylls, similar to Triassic Umkomasiaceae growing under comparable, seasonally dry conditions. Dicroidium first appeared during the late Permian in the paleotropical regions, survived the end-Permian biotic crisis, colonized large parts of Gondwana during the Triassic, and persisted in southern high-latitude refugia into the Jurassic. Umkomasiaceae thus show a remarkable resilience as the group survived two of the most severe mass extinctions in Earth history.