Callospermarion ovules from the Early Permian of northern China: palaeofloristic and palaeogeographic significance of callistophytalean seed-ferns in the Cathaysian flora

Abstract

A distinctive kind of anatomically preserved cardiocarpalean ovule is described from the Early Permian Taiyuan Formation of northern China. Ovules are small, have 180° rotational symmetry, and possess variably thick integuments with prominent secretory cavities that may be empty, filled with resinous materials and in several instances appear to contain animal coprolites. Comparisons show that (where known) these features conform to those of Callospermarion undulatum (Neely) Rothwell, to which they are assigned, previously only known from the Pennsylvanian of Euramerica. These fossils represent the first indisputable occurrence of the genus Callospermarion in the Early Permian Cathaysian floras, and show the presence of callistophytalean seed-ferns in this palaeofloristic realm for the first time. These data combined with results from previous investigations now support the Early Permian northern Cathaysian flora including the Taiyuan Formation having evolved from the Late Carboniferous and earliest Permian Euramerican flora, with which it shares far too many generic level similarities for these co-occurrences to be coincidental. Our hypothesis is therefore that the Early Permian flora of the northern Cathaysian realm represents the continued evolution of wetland Euramerican-type coal-swamp floras, and as such is likely to present a model for evolutionarily driven floral change as opposed to the climatically driven floral changes observed in the Euramerican flora after the demise of coal-swamp environments. The distribution of coprolites in and immediately around glandular cavities in this species suggests specialised syndromes of herbivory existed in Early Permian Cathaysian ecosystems, with herbivores preferentially selecting these areas of the ovule integument.