Although approximately 12,000 species of moss make up today’s modern vegetation, this plant group rarely shows up in the fossil record. Bryant’s Biological and Biomedical Sciences professor Qin Leng and a team of outside researchers recently discovered an extraordinarily preserved moss fossil at the Pingzhuang Coal Mine in northern China that dates back to the early Miocene (about 23 to 16 million years ago); this is the first fossil record of Platydictya in Asia, and the group’s findings were recently published in Frontiers of Earth Science.
Platydictya refers to small-sized mosses commonly located in the northern hemisphere’s temperate and subtropical climatic zones. These plants thrive in moist environments — such as dense forests — and are often found on the underside of wet tree trunks or in a tree’s surrounding soil.
“The most surprising and fascinating thing of this research is how well the fossil is preserved,” says Leng. “As a delicate plant, after about 16 to 23 million years it still has its cellular level structure preserved, allowing us to compare most of its morphological and anatomical features with other fossils as well as modern plants.”
The small and slender moss fossil occupies a little more than one square centimeter and has 10 branches, eight attached and two detached. The fossil shows all observable features similar to those of the living species Platydictya jungermannioides but is missing reproductive organs and rhizoids (which help anchor the plant). Therefore, researchers have tentatively named it Platydictya cf. jungermannioides — with cf. meaning to confer.
The study notes how most plants in the fossil record are vascular — unlike moss species which are nonvascular; Leng says vascular tissue is the equivalent to an animal’s skeleton and is meant to support the plant.
“Without the supportive tissue, nonvascular plants — also called bryophytes — are normally small and soft, thus not easy to be preserved as fossils,” Leng says.
Since paleobotanists reconstruct the ecology and environment of ancient forests almost exclusively from vascular plants, this discovery reveals clues about ancient forest microhabitats that rarely left any trace in the fossil record and, in turn, enriches people’s understanding of the early Miocene environment.
Due to the fossil’s excellent preservation and condition, researchers believe the plant was buried with water and rapidly covered by sediments, which was confirmed through a compaction experiment. Since Platydictya currently grows in the Pingzhuang Coal Mine, researchers suggest that this genus may have lived in this area of northern China from the early Miocene to the present. Looking to the future, Leng says researchers may use the moss fossil to explore more paleoenvironmental and paleoclimatic information of this ancient period.
