A permineralized thamnopteroid rhizome (Osmundaceae) with coprolites from the Permian of Heilongjiang Province, Northeast China: The most primitive record of Osmundaceae in Asia

Abstract

The earliest and most primitive fossil trunk or rhizome taxa of the family Osmundaceae, as important evidence for understanding its early evolutionary history, have so far all come from the Permian of the Ural Mountains region of European Russia. In this study, a thamnopteroid rhizome fossil, one of the most primitive members of the Osmundaceae, is reported from the Permian of Heilongjiang Province, Northeast China, based on a permineralized rhizome fragment consisting of the cortex and petiole bases with coprolites. This is the first report of a thamnopteroid rhizome found outside the Ural Mountains region since the previous thamnopteroid rhizome was described more than 90 years ago. Still, all known thamnopteroid trunks and rhizomes, i.e., from the Ural Mountains region and Heilongjiang Province, occurred within the realm of the Angara flora during the Permian. The fossil records suggest that the Angaraland is perhaps the cradle for the early diversification of the Osmundaceae (first family of Osmundales), while the Cathaysia is an important region for the early diversification of the Guaireaceae (another family of Osmundales). The fossil studied herein is the most primitive and earliest record of the Osmundaceae in Asia. For the Mesozoic of Asia, four genera of trunks and rhizomes of Osmundaceae have been found in the Jurassic and Cretaceous of Northeast China and the Cretaceous of the Rajmahal Hills of India. The new fossil serves as crucial evidence for the diversification of the Osmundaceae in Asia from the Paleozoic. The occurrence of coprolites in the parenchyma of the petiole base indicates that Osmundaceae rhizomes were favorable hosts for arthropods and provided a suitable environment for their parasitism