Re-examination of specimens attributed to Sawdonia curstipa Wang and Hao (zosterophyll) from the Middle Devonian of Xinjiang, China

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1 Available online at Palaeoworld 20 (2011) Short communication Re-examination of specimens attributed to Sawdonia curstipa Wang and Hao (zosterophyll) from the Middle Devonian of Xinjiang, China Hong-He Xu State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing , China Received 27 February 2011; received in revised form 12 May 2011; accepted 24 June 2011 Available online 18 July 2011 Abstract Specimens previously attributed to Sawdonia curstipa were re-examined. Some of the specimens are transferred to Serrulacaulis cf. S. furcatus based on axial morphology. Other specimens, including fertile axes with one or two rows of sporangia with curved stalks and sterile axes with cone-shaped spines covering the surface, are of uncertain assignment due to poor preservation. The nomenclature problem of Sawdonia custipa is also noted Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved. Keywords: Sawdonia; Serrulacaulis; Zosterophyll; Devonian; Xinjiang 1. Introduction Zosterophylls, as a group of significant early land plants, are characterized by leafless axes bearing lateral cauline sporangia with distal dehiscence and are common components of Early Mid Devonian flora worldwide (Banks, 1975; Gensel, 1992; Berry and Fairon-Demaret, 2001). However, great care must be taken in assigning fragmentary specimens to specific genera based only on sterile axis with lateral appendages (Hueber and Banks, 1979; Gensel, 1992), as is the case with sterile axes of Sawdonia Hueber (Hueber, 1971; Gensel et al., 1975), Serrulacaulis Hueber and Banks (Hueber and Banks, 1979; Berry and Edwards, 1994) and some species of Zosterophyllum Penhallow (Edwards, 1970). Sawdonia curstipa Wang and Hao (1996), so far the only species of Sawdonia reported from the Devonian of China, was established from materials collected in the Middle Devonian of Hujiersite, Xinjiang. Because the sterile axis of S. curstipa varies widely in appearance (see Wang and Hao, 1996), its identity has been questioned (Xu et al., 2008; C.M. Berry, Pers. Comm., 2010). Here we re-examine original specimens of S. curstipa and give a new identification in light of recent developments in our understanding of the morphology Corresponding author. Tel.: ; fax: address: hhxu@nigpas.ac.cn and distribution of Serrulacaulis (Berry and Edwards, 1994; Xu et al., 2011). The nomenclatural status of S. curstipa is discussed. 2. Materials and methods The study is based on the specimens that were all previously attributed to S. curstipa, including seventeen numbered pieces and one without serial number (Table 1). These specimens were collected from the type section of the Hujiersite Formation (Wang and Hao, 1996), Utubulak, Xinjiang (GPS: N, E; for geological map, see Xu and Wang, 2008). The specimens are preserved as compressions in a green yellow muddy siltstone and sandstone. The geological age of the Hujiersite Formation was regarded as Mid Devonian based on biostratigraphical and lithological studies (Cai and Wang, 1995; Cai, 2000; Wang et al., 2004; Xu et al., 2008). However, a preliminary result from an ongoing palynological study of the plant fossil bearing beds of this locality, the first of its kind, suggests an Eifelian age (J. Marshall, Pers. Comm., 2010). Currently we assign the plant-bearing beds an early Mid Devonian (Eifelian) age. A light dégagement (Fairon-Demaret et al., 1999) was performed to some specimens where necessary. Macro- and microphotography used a Nikon D300 camera with crosspolarized illuminations and Leica MZ 16A microscope equipped X/$ see front matter 2011 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved. doi: /j.palwor

2 358 H.-H. Xu / Palaeoworld 20 (2011) Table 1 Re-assignment to the specimens attributed to Sawdonia curstipa Wang and Hao. Specimen numbers were not mentioned in the caption of Wang and Hao (1996). We here firstly give the correspondence relations between specimens and original figures. ( ) Not illustrated; (?) no number in original paper. Specimens Figure in Wang and Hao (1996) Figure in this study Assignment and brief description XH05A Fig. 1D Serrulacaulis cf. S. furcatus. Axis with emergences on both sides. XH06 pl. II, fig. 2 Fig. 1G Serrulacaulis cf. S. furcatus. Axis with cone-liked, spine-liked or saw-toothed emergences. XH07 pl. I, fig. 4 Fig. 1A Serrulacaulis cf. S. furcatus. Axis with emergences on both sides. XH08 Serrulacaulis cf. S. furcatus. A circinate axis with spine-liked emergences. XH11 pl. II, fig. 8 Fig. 1C, arrow 2 Serrulacaulis cf. S. furcatus. A circinate axis tip. XH11 Fig. 1C, arrow 1 Serrulacaulis cf. S. furcatus. Axis with step-like emergences. XH15 pl. II, fig. 7 Fig. 1E Serrulacaulis cf. S. furcatus. Axis with saw-toothed and obdeltoid emergences. XH16 pl. II, fig. 1 Fig. 1B Serrulacaulis cf. S. furcatus. Axis with saw-toothed emergences. XH18 pl. II, fig. 3 Fig. 1H Serrulacaulis cf. S. furcatus. A circinate axis with emergences on both sides. XH01A pl. I, fig. 3; pl. II, figs. 6 and 9 Fig. 1F and J Unidentified fertile axis. XH01B Unidentified bifurcated fertile axis. XH01C pl. I, fig. 3 Unidentified fertile axis. XH05B pl. I, fig. 2 Fig. 1K Unidentified fertile axis. Sporangia with up curved stalk. XH13B pl. I, fig. 6 Unidentified fertile axis. A down-curved axis with sporangia, no axial spine was seen. XH14 pl. I, fig. 1 Unidentified fertile axis. Poorly preserved.? pl. I, fig. 7 Unidentified fertile axis. Axis probably smooth. XH03 Unidentified, poorly preserved axis. XH10 pl. I, fig. 8 Fig. 1I Unidentified axis. Axis with tightly arranged spines. XH21 pl. II, fig. 4 Unidentified axis. A circinate axis with or without sporangia attached. with a digital camera. All specimens are housed at Peking University. 3. Result 3.1. Specimens of Serrulacaulis cf. S. furcatus Subdivision: Zosterophyllophytina Banks, 1968 Order: Sawdoniales Kenrick and Crane, 1997 Family: Sawdoniaceae Kenrick and Crane, 1997 Genus: Serrulacaulis Hueber and Banks, 1979 emend. Xu et al., 2011 Type species: Serrulacaulis furcatus Hueber and Banks, 1979 Species: Serrulacaulis cf. S. furcatus (Fig. 1A E, G and H) Specimens: XH05A, XH06, XH07, XH08, XH11, XH15, XH16, XH18 Description: Axes consist of both straight and curving stems bearing circinate tips. The longest preserved unbranched axis is up to 6.2 cm (Fig. 1A). The axis is mm wide exclusive of the bilateral emergences (Fig. 1A E and G). Specimens of the axis with circinate apex (Fig. 1H), and isolated circinate apex (Fig. 1C, arrow 2) are common in the collection. Emergences are non-vascularized (Fig. 1A) and seen on the two opposite sides of otherwise smooth axes (Fig. 1A, B and E) or on a single side showing as step-like structure (Fig. 1C and D), indicating that the emergences occur in opposite bilateral rows on the axis. The emergences, depending on their orientation during compression, have a variety of appearances. In lateral view, they appear as a continuous saw-tooth (Fig. 1A and B) or spines (Fig. 1E and G); in sub-lateral view, they give the appearance of obdeltoid (i.e., narrower at the base and expanding distally) (Fig. 1E, arrow) or cone-like structures pointing towards the observer (Fig. 1C and D). The majority of specimens show emergences on two opposite sides of the axis. Emergences on one side of the axis are thought to be a result of unusual compression orientation. In cases such as these, step-like structures are formed, as indicated by Serrulacaulis specimens from Venezuela (Berry and Edwards, 1994) and Xinjiang (Xu et al., 2011). The emergence as a whole is up to 1.4 mm long (Fig. 1E), of which the base is about 0.6 mm wide; the distal end is about 1.3 mm wide (Fig. 1E). The emergences extend to the apex of circinate tip (Fig. 1H). Identity: The axis consisting of bilateral emergences obviously belongs to the zosterophyll group. The Devonian zosterophylls with ranks of saw-toothed emergences (spines) mainly include Crenaticaulis (Banks and Davis, 1969), Sawdonia (Hueber, 1971) and Serrulacaulis (Hueber and Banks, 1979). In Crenaticaulis, one or two rows of single or double, alternate or overlapped, teeth that are usually less than 0.5 mm in height are sparsely arranged on the axis (Banks and Davis, 1969). In Sawdonia, tiny spines with irregular length are arranged on the axis (see Hueber, 1971; Gensel et al., 1975). The present axis shows much more similarities to that of Serrulacaulis, the key character of which is two opposite rows of protruding non-vascularized emergences on Serrulacaulis axes from all known localities (Hueber and Banks, 1979; Berry and Edwards, 1994; Xu et al., 2011). We therefore assign the axis to Serrulacaulis. We also noted that the dimension of the present axis shows great similarity to the type species, S. furcatus from New York State (USA) (see Hueber and Banks, 1979), but it is obviously

3 H.-H. Xu / Palaeoworld 20 (2011) Fig. 1. (A) (E), (G), (H) Serrulacaulis cf. S. furcatus. (F), (J), (K) fertile axes with uncertain affinity. (I) uncertain sterile axes. All from the Middle Devonian of Xinjiang, China. (A) The longest preserved axis with bilateral emergences that appear as saw teeth. XH07. Scale bar = 10 mm. (B) An axis with lateral emergence. XH16. Scale bar = 5 mm. (C) A sub-lateral compressed axis, note the emergences appear as step-like structure (arrow 1). Arrow 2 indicates an isolated circinate apex that probably belongs to Serrulacaulis. XH11. Scale bar = 5 mm. (D) An axis with emergences in sub-lateral view appearing as step-structure. XH5A. Scale bar = 10 mm. (E) A sterile axis with bilateral emergences appearing as spines and obdeltoid shape (arrow). XH15. Scale bar = 5 mm. (G) A sterile axis with emergences appearing as tiny spines. XH06. Scale bar = 5 mm. (H) A circinate apex with spiny, lateral emergences (arrow). XH18. Scale bar = 5 mm. (F) A fertile axis with one or two rows of sporangia by one side. Note every sporangium is higher or lower than its neighbor. XH01A. Scale bar = 5 mm. (J) The enlargement of a sporangium in F (arrow 3). XH01A. Scale bar = 2 mm. (K) Enlargement of the two sporangia on the fertile axis illustrated in pl. I, fig. 2 of Wang and Hao (1996), showing the curved, upward sporangium stalk. XH05B. Scale bar = 2 mm. (I) Axes with spines covering around the surface, spines in face view are cone-shaped (arrow 6) and appear as tightly arranged depression in impression (arrow 5). XH10. Scale bar = 5 mm.

4 360 H.-H. Xu / Palaeoworld 20 (2011) different from the second species of Serrulacaulis, S. spineus (table 1 in Xu et al., 2011). No fertile specimens verify other characters of Serrulacaulis; however, the current morphological observation permits us to assign these axes to Serrulacaulis cf. S. furcatus Specimens of unidentified fertile axis (Fig. 1F, J and K) Specimens: XH01A, XH01B, XH01C, XH05B, XH13B, XH14 Description: The fertile axis is up to 5.6 cm long (Wang and Hao, 1996). Tiny spines are on the axis (Fig. 1F, arrow 4). But the poor preservation does not permit further preparation, and it is difficult to judge whether the spines are borne all around the axis or just on bilateral sides. The spines measure mm long and 0.5 mm wide in the basal portion. Sporangia on the axis form a spike (Fig. 1F). In the fertile axis, all sporangia are borne on one side, and neighboring sporangia are not in the same plane (Fig. 1F). The fertile axis with bilateral sporangia (see pl. I, figs. 1 and 2 in Wang and Hao, 1996) shows that the two rows are always orthogonal, or at least one longitudinal line of sporangia is partially covered by the compressed axis (see pl. I, figs. 1 and 2 in Wang and Hao, 1996). We conclude that the sporangia of these fertile axes are probably arranged in two rows and on one side of the axis, whereas the occasional axis with symmetrical bilateral sporangia is interpreted as a result of compression. Sporangia are oval in lateral view, ca. 5.6 mm long and 3.6 mm wide. Each sporangium is stalked. The stalk curves upward. No spines were observed on the sporangium surface. Identity: The fertile axis consists of two rows of sporangia that were probably borne on the same side of the axis, forming a spike that resembles Serrulacaulis furcatus (Hueber and Banks, 1979). So far fertile specimens of Serrulacaulis are only reported from the type species from New York State (Hueber and Banks, 1979) and the second species S. spineus from Hoxtolgay, Xinjiang (Xu et al., 2011). Sporangia of S. furcatus were thought to be arranged in two rows on one side of the fertile axis (Hueber and Banks, 1979), but can also occur on opposite sides of the fertile axis (see pl. III, fig. 2 in Hueber and Banks, 1979). The sporangia of S. spineus are loosely arranged, no spike can be recognized, and this is an obvious difference from the specimens illustrated here. Additionally, the sporangium of the present fertile axis has a curved stalk, and in this respect shows similarity to that of the Early Devonian zosterophyll Ensivalia from Belgium (Gerrienne, 1996). Curved sporangium stalks do not occur in S. furcatus or S. spineus. Spines on the sporangium were reported by Wang and Hao (1996), but not verified in our re-examination. Based on current preservation and in the absence of preparation, it is impossible to assign these fertile specimens to any known genus but only to the more inclusive zosterophyll group. In order to give further assignation, more specimens from the same locality are needed Specimens of unidentified sterile axes (Fig. 1I) Specimens: XH03, XH10, XH21 Description: The axis is about 4.6 mm wide excluding the lateral spines. Cone-shaped (Fig. 1I, arrow 6) spines are tightly arranged around the surface of the axis, not continuous at the basal portion, and can be seen both in face view and lateral view. On impression specimens, these spines appear as tightly arranged dots or depressions on the axial surface (Fig. 1I, arrow 5). The spines are mm long and 0.4 mm wide at the basal portion. Identity: The spiny axis specimens are fragmentary. No fertile specimens are connected with these axes, making them difficult to be assigned. The spines on the axis are tighter and smaller than those in Sawdonia (Hueber, 1971; Gensel et al., 1975). The axis is also obviously different from that of Serrulacaulis in respect of the axial emergences. However, axes with spines as presumable rhizoid-bases were included in the name Serrulacaulis furcatus, based on a collection of specimens from Belgium (Stockmans, 1968; Xu et al., 2011). Even though, we think it premature to assign these spiny axes to Serrulacaulis for the limited information. The spiny axes probably belong to a new and unidentified zosterophyll or lycopsid. 4. Discussion Based on our new observations, specimens previously attributed to S. curstipa (Wang and Hao, 1996) are recognized to be composed of more than one plant. Some fertile axes and spiny axes cannot be assigned to any know taxon from the limited information we can obtain. Some sterile axes are recognized as Serrulacaulis cf. S. furcatus based on the typical features and information gained from the new morphological study on Serrulacaulis specimens from all known localities (Xu et al., 2011). None of these specimens indicates characters of Sawdonia or S. curstipa (Wang and Hao, 1996) (see Table 1). More specimens from this locality are needed to get a better understanding of Middle Devonian zosterophylls, including the potential new plants. It is worth noting that specimens of Serrulacaulis cf. S. furcatus have been recently reported (Xu et al., 2011) from the locality discussed here. In addition, a second species of Serrulacaulis was reported from a Hujiersite Formation locality that is ca. 70 km to the south. In the study of Serrulacaulis, some questions remain unsolved, including the presence or absence of rhizoids and sporangium arrangement (Xu et al., 2011). All the present specimens are probably related to Serrulacaulis,but further study of new materials is needed. With regard to the nomenclature, S. curstipa was not validly published as no type specimens were designated in original study of Wang and Hao (1996) (Art. 37.1, ISBN, see McNeill et al., 2006). However, we find it unnecessary to select a lectotype (Art. 9.13, ISBN, McNeill et al., 2006) because the original collection clearly comprises specimens assignable to other genera (e.g., Serrulacaulis) or specimens that are too incomplete to warrant a formal nomenclatural treatment.

5 H.-H. Xu / Palaeoworld 20 (2011) Acknowledgements We thank Prof. J.E.A. Marshall (Southampton University, UK), and Dr. C.M. Berry (Cardiff University, UK) for their instructive suggestions; Dr. D.M. Wang and Prof. S.G. Hao, Peking University, China, for their help in re-examining present specimens; Qi Wang and an anonymous reviewer for their careful reviewing and suggestions; and Dr. Miao D.S., Kansas University, for help in English. This study is supported by Chinese Academy of Sciences (KZCX2-EW-QN113) and NSFC ( ). References Banks, H.P., The early history of land plants. In: Drake, E.T. (Ed.), Evolution and Environment: a Symposium Presented on the One Hundredth Anniversary of the Foundation of Peabody Museum of Natural History at Yale University. Yale University Press, New Haven, pp Banks, H.P., Palaeogeographic implications of some Siluro-Early Devonian floras. In: Campell, K.S.W. (Ed.), Gondwana Geology. Australian National University Press, Canberra, pp Banks, H.P., Davis, M.R., Crenaticaulis, a new genus of Devonian plants allied to Zosterophyllum, and its bearing on the classification of early land plants. American Journal of Botany 56, Berry, C.M., Edwards, D., New data on the morphology and anatomy of the Devonian zosterophyll Serrulacaulis Hueber and Banks from Venezuela. Review of Palaeobotany and Palynology 81, Berry, C.M., Fairon-Demaret, M., The Middle Devonian flora revisited. In: Gensel, P.G., Edwards, D. (Eds.), Plants Invade the Land: Evolutionary and Environmental Perspectives. Columbia University Press, New York, pp Cai, C.Y., Non-marine Devonian of China. In: Nanjing Institute of Geology and Palaeontology, Academia Sinica (Ed.), Stratigraphical Studies in China ( ). University of Science and Technology of China Press, Hefei, pp (in Chinese). Cai, C.Y., Wang, Y., Devonian floras. In: Li, X.X. (Ed.), Fossil Floras of China through the Geological Ages. Guangdong Science and Technology Press, Guangzhou, pp Edwards, D., Further observations on the Lower Devonian plant, Gosslingia berconensis Heard. Philosophical Transactions of the Royal Society B: Biological Sciences 258, Fairon-Demaret, M., Hilton, J., Berry, C.M., Surface preparation of macrofossils (dégagement). In: Jones, T.P., Rowe, N.P. (Eds.), Fossil Plants and Spores: Modern Techniques. Geological Society, London, pp Gensel, P.G., Phylogenetic relationships of the zosterophylls and lycopsids: evidence from morphology, paleoecology, and cladistic methods of inference. Annals of the Missouri Botanical Garden 79, Gensel, P.G., Andrews, H.N., Forbes, W.H., A new species of Sawdonia with notes on the origin of microphylls and lateral sporangia. Botanical Gazette 136, Gerrienne, P., Contribution à l étude paléobotanique du Dévonien inférieur de Belgique: les genres nouveaux Ensivalia et Faironella. Académie Royale de Belgique Classe des Sciences Mémoires Collection 3è série 4, Hueber, F.M., Sawdonia ornata: a new name for Psilophyton princeps var. ornatum. Taxon 20, Hueber, F.M., Banks, B.P., Serrulacaulis furcatus gen. et sp. nov., a new zosterophyll from the lower Upper Devonian of New York State. Review of Palaeobotany and Palynology 28, Kenrick, P., Crane, P.R., The Origin and Early Diversification of Land Plants: A Cladistic Study. Smithsonian Institution Press, Washington and London, 441 pp. McNeill, J., Barrie, F.R., Burdet, H.M., Demoulin, V., Hawksworth, D.L., Marhold, K., Nicolson, D.H., Prado, J., Silva, P.C., Skog, J.E., Wiersema, J.H., Turland, N.J., International Code of Botanical Nomenclature (Vienna Code). A. R. G. Gantner Verlag, Ruggell, 568 pp. Stockmans, F., Végétaux Mésodévoniens récoltés aux confins du Massif du Brabant (Belgique). Mémoires Musée Royal d Histtoire Natturelle de Belgique 159, Wang, D.M., Hao, S.G., Report of Sawdonia in China, Sawdonia curstipa sp. nov. Acta Botanica Sinica 38, (in Chinese, with English abstract). Wang, Y., Xu, H.H., Fu, Q., Tang, P., A new diminutive plant from the Hujiersite Formation (late Middle Devonian) of North Xinjiang, China. Acta Palaeontologica Sinica 43, Xu, H.H., Wang, Y., The palaeogeographical significance of specimens attributed to Protolepidodendron scharyanum Krejči (Lycopsida) from the Middle Devonian of North Xinjiang, China. Geological Magazine 145, Xu, H.H., Wang, Y., Berry, C.M., Cai, C.Y., Two species of Haskinsia Grierson et Banks (Lycopsida) from the Middle Devonian of Xinjiang, China, and consideration of their palaeogeographical significance. Botanical Journal of the Linnean Society 157, Xu, H.-H., et al., Morphological study on the Devonian zosterophyll Serrulacaulis Hueber and Banks: New materials and emendation. Palaeoworld, doi: /j.palwor