Journal of Asian Earth Sciences 76 (2013) 59–69 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Species of the medullosan ovule Stephanospermum from the Lopingian (late Permian) floras of China ⇑ Alan R.T. Spencer a, , Shi-Jun Wang b,c, Michael T. Dunn d, Jason Hilton e a Department of Earth Sciences and Engineering, Imperial College London, London SW7 2BP, UK b State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China c State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, PR China d Department of Biological Sciences, Cameron University, Lawton, OK 73505, USA e School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK article info abstract Article history: The medullosan pteridosperm ovule Stephanospermum Brongniart is a well-known component of Carbon- Received 18 April 2013 iferous aged coal-ball and siderite nodule floras from North America and Europe but also occurs in the Received in revised form 3 July 2013 Permian floras of Cathaysia where it is represented by the Lopingian (late Permian) aged species Stephan- Accepted 22 July 2013 ospermum trunctatum (Li) Wang et al. (2009) from coal-balls in the Wangjiazhai Formation in Southern Available online 7 August 2013 China. We provide a detailed emendation of S. trunctatum and illustrate it comprehensively for the first time, and document an additional specimen from the Wangjiazhai Formation coal-ball assemblage that Keywords: we assign to Stephanospermum shuichengensis sp. nov. S. shuichengensis is distinguished from S. truncta- Gymnosperm tum by the absence of apical teeth in the sclerotesta and non-obovate base. The two species of Stephan- Medullosales Trigonocarp ospermum from the Wangjiazhai Formation are important as they extend the stratigraphic and Coal-ball geographical range of the genus from the Pennsylvanian of Euramerica into the Lopingian of Southern Wangjiazhai Formation China, and demonstrate that the genus persisted in wetland, peat forming environments in the run up Shuicheng to the end-Permian mass extinction event. The 44 MY stratigraphic discontinuity between the Euramer- ican and the Cathaysian species, here named the Stephanospermum gap, leads us to infer that the genus was likely to have occurred in the Pennsylvanian–Permian successions of southern Russia and northern China that are geographically and stratigraphically intermediate to the known occurrences but from which the genus has yet to be discovered. Medullosan pteridosperms appear to have become extinct at or immediately prior to the Permian–Triassic boundary that coincides with the Permo–Trias mass extinction event; although the exact causes of this loss in plant diversity remains unknown, a response to regional climatic drying is likely to have been a contributing factor. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction conform to the traditionally circumscribed trigonocarpalean concept (senus Seward, 1917) and are large, radially symmetrical, Medullosans are a comparatively well characterised group of have the nucellus attached to the integument at the chalaza only, Late Palaeozoic pteridosperms that were widespread in wetland and possess a domed or campanulate pollen chamber (Serbet and and moister parts of seasonal wetland settings in the Pennsylva- Rothwell, 1995; Spencer et al., 2013). In the compression/impres- nian of Europe and North America (DiMichele et al., 2006) and sion record, medullosan ovules are typically placed in the genus the Permian of China (Wang et al., 2009). As a group they exhibit Trigonocarpus Brongniart 1828, whereas those known with ana- a range of growth architectures including trees, vines and liana- tomical preservation are variously assigned to the genera Pachytes- like plants. In addition DiMichele et al. (2006) suggest that some ta Brongiart 1874, Stephanospermum Brongniart 1874, medullosans may have been cormose, acaulescent plants. How- Hexapterospermum Brongniart 1874, Polypterospermum Brongniart ever, currently the evidence is lacking for an evolutionary frame- 1874, Codonospermum Brongniart 1874, Rhynchosperma Taylor work in which to determine the relationships between taxa with and Eggert 1967, and Hexaloba Dunn et al. 2002. different growth architectures (DiMichele et al., 2006; Hilton and The genus Stephanospermum at present includes eight species Bateman, 2006). Where known, ovules produced by medullosans from the Pennsylvanian to earliest Permian floras of Euramerica plus a single species from the Permian of China (see Wang et al., ⇑ Corresponding author. Tel.: +44 07824325531. 2009; Spencer et al., 2013, for a recent review). The species from E-mail address: [email protected] (A.R.T. Spencer). China occurs in Changhsingian (late Permian) aged coal-balls from 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.07.030 60 A.R.T. Spencer et al. / Journal of Asian Earth Sciences 76 (2013) 59–69 the Wangjiazhai Formation and was first documented and partially available, and have the drawback of often forming peels of unequal illustrated by Li (1988) as part of an unpublished PhD thesis. This thickness from which photography of uneven surfaces may be account was subsequently published by Li (1991) who assigned challenging. These limiting factors in addition to non-sequential it to Stephanospermum cf. akenioides noting its similarity with Step- slides, uneven spacing between the peels/film pulls, and with hanospermum akenioides Brongniart 1874 from the Pennsylvanian one specimen only having two peels it has not been possible to of Europe. Li’s (1988, 1991) account was based on a single speci- reconstruct the 3D organisation of the seeds in full. men exposed on the external surface of a coal-ball that was then Mounted slides were photographed with a Cannon EOS 40D cut longitudinally and from which acetate peels were subsequently mounted on a Zeiss Tessovar macro system with illumination pro- made. The same specimen was later included and illustrated with- vided by twin fibre-optic light guides and a ring light. The resulting in an atlas of fossil plant anatomy in China (Li and Cui, 1995, pg. images where processed (cropped, rotated, edge enhanced and 62), although in this account it was erroneously illustrated up- equalised for hue and brightness) in GIMP 2, ImageJ (Abràmoff side-down. In 2009, as part of their revision of the coal-ball floras et al., 2004) and Corel Paint Shop Pro Photo X2 with figures con- of China, Wang et al. reinvestigated the species based on the peels structed in Adobe Illustrator CS4/5 and Inkscape (see Spencer from Li’s earlier investigation, concluding that it was distinct from et al., 2013, for an overview on the software packages used). S. akenioides in having 4 short, triangular apical teeth rather than possessing a conspicuous crown characteristic of S. akenioides 3. Geological information and age (Wang et al., 2009). These distinctions led Wang et al. (2009) to transfer the species into S. trunctatum Wang et al., but other than Specimens occur in coal-balls from the Wangjiazhai Formation the systematic section of that account, the remaining text was pub- in Guizhou Province in South China (Wang et al., 2009). Although lished in the Chinese language so is not available to non-Chinese the full flora has yet to be studied in detail, previous investigations scientists. Furthermore, only key features of S. trunctatum were demonstrate it to include lycopsids (Wang et al., 2009), marattia- emended and illustrated. Here we provide a full systematic ac- lean (He et al., 2006) and osmundalean ferns (Li, 1993; Wang count of S. trunctatum, illustrate it comprehensively and compare et al., 2013), pteridosperms (Seyfullah et al., 2009; Wang et al., it with other species of the genus for the first time. 2009) and cycads (Wang et al., 2011b). In the Wangjiazhai Forma- During the course of our investigation we have also identified tion, peat forming wetland plant communities developed in low- another specimen from the coal-ball assemblage in the Wangjiaz- lying coastal settings with peat formation ceasing with marine hai Formation that conforms to the generic circumscription of Step- incursion, with the onset of marine conditions facilitating the for- hanospermum but is distinct from Stephanospermum trunctatum. mation of coal-balls (Wang et al., 2011a). Coal-balls in these set- This specimen is described and illustrated here for the first time, tings were permineralized by an early diagenetic calcium and comparisons demonstrate it to represent a new species with carbonate cement, but pyritization is also abundant within the a close affinity to species of Stephanospermum from the Pennsylva- coal-balls where presumably it was triggered by early decay of soft nian of Euramerica. We name the new species Stephanospermum tissues in reaction with saline water prior to carbonate mineraliza- shuichengensis Spencer et al. Evolutionary and environmental tion (for overview of coal-ball formation see Scott et al., 1996). implications of the presence of two species of Stephanospermum Wang et al. (2011a) presented a regional stratigraphic correla- in the Lopingian flora of southern China are considered. tion of the Guadalupian–Lopingian aged sedimentary successions in Guizhou Province and