New Plants from the Lower Devonian Pingyipu Group, Jiangyou County, Sichuan Province, China

Abstract

Descriptions of Lower Devonian plants from Yunnan, South China, have revolutionized concepts of diversity and disparity in tracheophytes soon after they became established on land. Sichuan assemblages have received little attention since their discovery almost 25 years ago and require revision. With this objective, fieldwork involving detailed logging and collection of fossils was undertaken in the Longmenshan Mountain Region, Jiangyou County and yielded the two new taxa described here. They are preserved as coalified compressions and impressions that allowed morphological but not anatomical analyses. Yanmenia (Zosterophyllum) longa comb nov is based on numerous rarely branching shoots with enations resembling lycophyte microphylls, without evidence for vasculature. The presence of sporangia is equivocal making assignation to the Lycopsida conjectural. The plant was recently described as a zosterophyll, but lacks strobili. These are present in the second plant and comprise bivalved sporangia. The strobili terminate aerial stems which arise from a basal axial complex displaying diversity in branching including H- and K- forms. These features characterise the Zosterophyllopsida, although the plant differs from Zosterophyllum in valve shape. Comparisons indicate greatest similarities to the Lower Devonian Guangnania cuneata, from Yunnan, but differences, particularly in the nature of the sporangium border, require the erection of a new species, G. minor. Superficial examination of specimens already published indicate a high degree of endemism at both species and generic level, while this study shows that Yanmenia is confined to Sichuan and Guangnania is one of the very few genera shared with Yunnan, where assemblages also show a high proportion of further endemic genera. Such provincialism noted in the Chinese Lower Devonian is explained by the palaeogeographic isolation of the South China plate, but this cannot account for differences/endemism between the Sichuan and Yunnan floras. Such an enigma demands further integrated geological, palaeobotanical and palynological studies.

Taungurungia gen. nov., from the Lower Devonian of Yea, central Victoria, Australia

“…Zosterophyllopsida have sporangia that have a width to height ratio ≥1 and are reniform, globose or rounded in face view (Banks, 1968(Banks, , 1975. However, some rare exceptions have been noted where the sporangia are longer than wide (Edwards et al, 2016;Edwards and Li, 2018;Hao and Beck, 1991;Hao and Xue, 2013;Wang and Hao, 2002). The specimen described herein augments taxa with longer-thanwide sporangia and is significant because little is known about these aberrations and their taxonomic significance.…”

“…However, the presence of emergences suggests affinities with the Gosslingiales; but Gosslingiales lacks terminal sporangia (Hao and Xue, 2013). Additionally, the sporangia of Taungurangia garrattii are not reinform or globose as in zosterophylls, which precludes assignation to Zosterophyllum (Edwards et al, 2016;Gensel, 1992: 455). Instead, the terminal sporangia are noticeably elongate and lack a thickened zone bounding a dehiscence line as seen in most zosterophylls (Hao and Xue, 2013).…”

Further insights into the Lower Devonian terrestrial vegetation of Sichuan Province, China

“…A detailed account of the Lower Devonian rocks of the east limb of the Tangwanzhai Syncline was presented in Edwards et al (2016). It included the stratigraphic log of the strata in which the new fossils occur in the lower part of the Pingyipu Group exposed near Yanmenba, Jiangyou County.…”

“…The rocks extend from the Lochkovian to the upper Pragian. All specimens were collected from the base of the sequence (Horizons 1 and 2 in Edwards et al, 2016) at the locality from which Yanmenia (Zosterophyllum) longa was described. It was concluded to be of Lochkovian age although a younger basal Pragian age should not be discounted.…”

“…A recent reappraisal of Lower Devonian plant assemblages from the Pingyipu Group, Sichuan (Geng, 1992a,b) indicated that many of the published taxa were incorrectly identified and in Geng's and subsequent collections, there are a number of new taxa requiring description and others in need of revision (Edwards et al, 2016). Our initial investigation concentrated on two new taxa, the endemic Yanmenia (Zosterophyllum) longa and a new species of Guangnania, a genus originally described from the Posongchong Formation, Yunnan Province and endemic to China.…”