Restudy of the Early Devonian rugose coral Xystriphylloides from South China

Accepted Manuscript Title: Restudy of the Early Devonian rugose coral Xystriphylloides from South China Author: Chang-Min Yu PII: DOI: Reference:

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Please cite this article as: Yu, Chang-Min, Restudy of the Early Devonian rugose coral Xystriphylloides from South China.Palaeoworld http://dx.doi.org/10.1016/j.palwor.2017.06.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Restudy of the Early Devonian rugose coral Xystriphylloides from South China

Chang-Min Yu

Key Laboratory of Economic Stratigraphy and Paleogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China

E-mail address: [email protected]

Abstract Early Devonian rugose coral Xystriphylloides in South China is restudied from the perspective of its taxonomic definition, biostratigraphy, paleoecology, and implication for the Yujiang Event. The diagnostic characters of the genus are clarified and its taxonomic position is also revised. In particular the septa of Xystriphylloides are shown to be fibrous rather than trabeculate. Xystriphylloides distinctus Yu n. sp. is described. Species of Xystriphylloides are widely distributed in South China and North Vietnam, so they are useful for regional biostratigraphic correlation and regional geological mapping. As an important biostrome builder, Xystriphylloides became extinct below the base of the nothoperbonus Conodont Zone, so it can be considered as one of the important pieces of evidence for recognizing the first episode of the Early Devonian Emsian Yujiang Event, which is also significant for studying paleoecology and event stratigraphy.

Keywords: rugose corals; fibrous septa; Devonian; biostrome; event stratigraphy; Yujiang Event

1. Introduction The generic name Xystriphylloides with its type species X. nobilis was proposed in a paper recording the subdivision of Devonian Yukiang Formation and its underlying Nahkaoling Formation in central-eastern Guangxi (Wang et al., 1964). No systematic 1

description of generic and species characters or illustrations were presented at that time. A brief description with limited illustration of Xystriphylloides nobilis was published in the atlas (Yu et al., 1974), and it was illustrated in another published paper (Yu in Wang et al., 1974). Subsequently, a series of confusing generic and species names and concept of characteristics appeared in the following publications: Jia in Jia et al., 1977; Kuang in Jia et al., 1977; Jia in Lin et al., 1995. Clarification of the characteristics of genus (and species) and its taxonomic position, and comparison with allied genera and species are the aims of the present paper. Further, the wide distribution of biostratigraphically significant species of Xystriphylloides in the Early Devonian of South China and North Vietnam is documented (Fig. 1). Xystriphylloides, with other organisms, is an important biostrome constructor, and disappeared before the nothoperbonus Conodont Zone, signifying the early stage of Devonian Yujiang Event. It is therefore of significance for studying the paleoecology and event stratigraphy.

Fig. 1 here

2. Materials Most of the described material in this paper was collected by Yu and his colleagues during their field work in Guangxi from 1959 to 1961. The number of sections cut from specimen prefixed with “BD”, are mainly from two localities, including Liujing, Hengxian, about 60 km east of Nanning, the capital city of Guangxi Zhuang Autonomous Region (Fig. 2), and Ertang, Wuxuan County in Guangxi (Fig. 1, locality 5). A few specimens were collected by the late Prof. Yu Wang and Dr. Di-Yong Liu from the locality between Nanning and Liujing in 1954 (Wang and Rong, 1986), and by Prof. Han-Kui Xu from Guangnan and Wenshan, Yunnan.

Fig. 2 here

The holotype of Xystriphylloides nobilis and some additional specimens were collected from the Early Devonian Shizhou Member of Yukiang Formation in Liujing, 2

Hengxian, Guangxi. As one of the well-known reference sections of the Devonian in South China, the sequence of the Yukiang Formation is sketched in Fig. 3. Four members of the Yukiang Formation have been recognized in ascending order as the Liujing Member, the Daliancun Member, the Shizhou Member, and the Xiayiling Member (Wang et al., 1964; Kuang et al., 1989).

Fig. 3 here

The Shizhou Member, about 106 m thick, is composed of bedded silty mudstones intercalated with biogenic marls and bioclastic limestones. Representatives of some 13 fossil groups including brachiopods, tabulate and rugose corals, bivalves, gastropods, nautiloids, bactritids, bryozoans, trilobites, ostracods, crinoids, tentaculitids, and conodonts have been found. The characteristic assemblage of fossils dominates the Shizhou Member since the Early Devonian transgression on the South China block. Species referred to Xystriphylloides occur particularly in this member, especially in the lower and middle part, where they coexist with index brachiopods such as Dicoelostrophia crenata, Atrypa variabilis, Rostrospirifer tonkinensis etc.

Fig. 4 here

Abundant Xystriphylloides occur in the calcareous lens, which are intercalated within the sandy deposits in Ertang, Wuxuan County and adjacent localities in Miaohuang, Xiangzhou County in Guangxi (see Fig. 1). They occur with some index brachiopods, such as Rostrospirifer sp. and Dicoelostrophia sp., etc. Overlying strata are 18 m thick marl and mudstone beds and yield rugose coral Breviphrentis angusta together with some index brachiopods, which can be correlated with those from the Liujing Member, the top Member of Yukiang Formation in Liujing, Hengxian, Guangxi. The Emsian deposits with a thickness of about 600 m overlie the marl and mudstone beds (Yu and Yin, 1978). In southeastern Yunnan, the described corals were collected from the Pochiao 3

Formation, which can be correlated approximately with the lower part of the Yukiang Formation (Liao et al., 1979; Jin et al., 2005). Xystriphylloides has been found widely in both outcrops and subsurface drill cores through South China and northern Vietnam (Fig. 1). Biostratigraphically, species of Xystriphylloides have been chosen as the leading taxa of the Xystriphylloides nobilisHeterophaulactis semicrassa Assemblage, and can be regarded as a megafossil marker useful for the regional stratigraphic correlation and regional geological mapping (Yu et al., 1978). The age of the Yukiang Formation (Fig. 4) and its equivalents has traditionally been considered as the Emsian Stage of the Early Devonian, which was based mainly on the conodonts and tentaculitids. The conodonts assigned to the Polygnathus dehiscens and the dacryoconariids referred to the Nowakia subtilis Zone corresponding to the European Nowakia zlichovensis Zone, have been reported from the lower part of the Yukiang Formation (Ruan et al., 1979; Wang et al., 1979; Wang and Rong, 1986). In fact, when the corals and other megafossil groups were collected in the field in those days, the conodonts and some other microfossil groups eluded our attention and hence were not being sampled simultaneously. Recently, restudy of the conodonts from Liujing, Hengxian, Guangxi has proved that the upper part of the Shizhou Member should belong to the excavatus Zone and both the Daliancun Member and Liujing Member of the Yukiang Formation should belong to the conodont nothoperbonus Zone (Yu et al., in press). Although the age of the Xystriphylloides-bearing bed remains uncertain at present, there has been no record of species of Xystriphylloides ranging up to the nothoperbonus Zone.

3. Paleoecology and implications for the Emsian Yujiang Extinction Event Abundant Xystriphylloides were found together with the tabulate corals Favosites, Pachfavosites, Thamnopora, and Cladopora, and bryozoans Semicoscinium striatum, Fenestella cf. elongata, Eridotrypella sinensis, Monotrypa nanningensis, Fistuliramus sp., Leptotrypella sp. (Yang, 1954), etc., all of which are the main constructors in 4

building the biostromes in the Shizhou Member of the Yukiang Formation in Liujing, Hengxian, Guangxi. However, the best exposed biostromes are located at Mengong, Guigang, Guangxi, where the biostromes intermittently range up to 42 m in thickness and may be traced horizontally for 15 km (Wang et al., 2012). The biostromes mostly have a dome or circular disk shape, or sometimes irregular massive form, 10 cm to 40 cm in diameter, and 15 cm to 35 cm in height. The attached organisms include brachiopods, solitary rugose corals, bivalves, gastropods, crinoids, etc. From the paleoecological viewpoint, the biostrome can be regarded as paleocommunity and might indicate peri-reefal environment (Fig. 5).

Fig. 5 here

Corals and other benthic megafossils may play important roles in event stratigraphy. The Xystriphylloides-Favosites biostraome can be named to represent those biostromes occurred in the lower part of the Shizhou Member of the Yukiang Formaion. Those biostromes disappeared after the deposition of dark limestone with pelagic fauna at the base of Daliancun Member, indicating the peri-reefal environment had been destroyed. The extinction event of the biostromes can be recognized as the first episode of the Yujiang Event, or construed as the Early Yujiang Event, which can be dated by conodonts as the early stage of the nothoperbonus Zone. The major episode of the Yujiang Event, also named the Late Yujiang Event, can be recognized by the extinction of the so-called “tonkinensis fauna”, which terminated not only brachiopod communities, but also the coexisting corals and other organisms characteristic of the Yukiang Formation (Yu et al., in press).

4. Systematic paleontology All illustrated specimens are deposited in the House of Collection of Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences with the prefix NIGP attached to the registration numbers of thin sections. 5

Family Columnariidae Nicholson, 1879 Subfamily Paradisphyllinae Jell, 1969 Genus Xystriphylloides Yu, Liao and Deng, 1974

1974

Xystriphylloides – Yu et al., p. 224.

1974

Xystriphylloides – Yu in Wang et al., p. 33.

1977

Neopetrozium – Jia in Jia et al., p. 151.

1977

Petrozium – Jia in Jia et al., p. 144.

pars 1977

Petrozium Smith – Jia in Jia et al., p. 144 (not Smith, 1930, nor the

included upper Devonian species). pars 1977

Petrozium Smith – Kuang in Jia et al., p. 145 (not Smith, 1930, nor the

included upper Devonian species). 1981

Xystriphylloides – Hill, p. 271.

1988

Zelolasma Pedder – Tong-Dzuy and Khoa, p. 140.

1989

Xystriphylloides – Kuang in Kuang et al., p. 38, pl. 9, fig. 1.

1995

Neopetrozium – Jia in Lin et al., p. 347.

1995

Xystriphylloides – Jia in Lin et al., p. 332.

pars 1995

Xystriphylloides Yu, Liao and Deng – Lin et al., p. 332 (not the included

genus Paraspongonaria). 2005

Xystriphylloides – Jin and Xie in Jin et al., p. 124.

Type species. Xystriphylloides nobilis Yu, Liao and Deng, 1974, p. 224, pl. 104, figs. 17-20, from the Yukiang Formation, Liujing, Hengxian, Guangxi, traditionally dated as the conodont dehiscens Zone of the lower Emsian, although not confirmed in the present restudy. Revised diagnosis. Rugose coral with fasciculate, partly cateniform corallum. Increase marginarial and nonparricidal. Septa well developed in two radially arranged orders composed of fibres, major septa continuous, weakly to moderately fusiform at boundary between dissepimentarium and tabularium, being slightly to distinctly carinate in their expanded parts; axial ends of the minor septa reduced in places to fine 6

and short spines. Dissepimentarium continuous, narrow to relatively broad, everted, with moderately to highly inflated flat-lying dissepiments, except for innermost row of dissepiments being steeply inclined adaxially. No horseshoe dissepiment present. Tabulae incomplete, closely spaced, forming periaxially elevated and peripherally outwardly sloping to concave tabularial surfaces. Tabulae may be depressed axially to form a triseriate tabularium. Comparison. Jia in Jia et al. (1977) and Kuang in Jia et al. (1977) in the same atlas respectively described three new species referred to Petrozium, two of which from the Lower Devonian Yukiang Formation in Guangxi are actually synonymous with Xystriphylloides nobilis. Another form from the lower part of the Upper Devonian of Xuan’en, Hubei also has no features comparable to the type species, Petrozium dewari from the British Llandovery, except that they are all colonial rugose corals. In the same atlas, Jia in Jia et al. (1977) erected a new genus, named as Neopetrozium with P. zhongguoensis Jia as the monotypic species from the Early Devonian Yukiang Formation in Guigang (Guixian), Guangxi. She emphasized the presence of horseshoe dissepiments as one of the characteristics of her new genus and later described it again (Jia in Lin et al., 1987). Hill (1981), however, viewed the genus as a synonym of the Russian Eifelian genus Vestigiphyllum Sytova in Sytova and Ulitina, with Thamnophyllum tabulatum Bulvanker, 1958 as the type species. Indeed, horseshoe dissepiments are not present in so-called Neopetrozium, in which rows of dissepiments generally form everted dissepimentarial surfaces, with a few smaller inflated dissepiments locally having their ends based on the larger ones next below and arranged vertically and intermittently in an irregular series. Vestigiphyllum has a distinct pipe of horseshoe dissepiments and mesa-shaped tabular floor and differs remarkably from Neopetrozium.

Therefore,

Neopetrozium

is

considered

synonymous

with

Xystriphylloides. Pedder (1998, p. 237) noted that Neopetrozium, Xystriphylloides, and Ivdelephyllum Spasskiy, 1971 appear to be synonymous and differ from his erected genus Asarcophyllum by having trabeculate septa and fusiform septal dilation. Indeed, the septa in Xystriphylloides are not trabeculate, but are composed of fibres (Fig. 6C), 7

and the dilation of septa is moderately fusiform in Xystriphylloides. The septa of Asarcophyllum are folded and distinctly carinate and the minor septa are continuously lamellar. Ivdelephyllum Spasskiy, 1971 based on Keriophylloides caespitosum Vaganova, 1959 as the type species, occurred in the Upper Emsian of northern and central Urals distinctly differs from Xystriphylloides in the shape and arrangement of tabulae in the tabularium, and in the transverse view of the morphology and arrangement of septa shape, although the microstructure of septa cannot be compared from the illustrations. Regarding the discontinuous character of minor septa in Xystriphylloides, the adult minor septa are mostly thin and consist of an outer lamellar part, confined to the marginarium, and an inner discontinuous part of short to very short strands. It has some similarities with Paraspongonaria Pedder, 1983, which has been considered to be synonymous with Xystriphylloides by Jia (Jia in Lin et al., 1995, p. 332). Judging from the original diagnostic description and illustration, the septa are extremely thin and lack carinae, typically with remarkable ribbon-like septal fragments in the tabularium, and the shape of tabularium of Paraspongonaria delicata Pedder from the serotinus and possibly the topmost inversus zones, in southern Ellesmere Island, Canada, is quite distinguishable from Xystriphylloides. Another species, P. sverdrupi (Loewe) from the Zlichovian part of the Blue Fiord Formation in southern Ellesmere Island, Canada, with larger diameter of corallites and more septa (22 × 2 in a corallite diameter of 14.5 mm) and less segmented septa, can also be distinguished from species of Xystriphylloides in having the extremely thin septa, the inflated dissepiments not forming an inverted dissepimentarium, and the broad tabularium having irregularly arranged tabulae (Pedder, 1983, p. 231). In comparison with Paradisphyllum Strusz, 1965, the septa are non-trabeculate but fibrous, and the dissepimentarium is distinctly narrower with highly inflated and less numerous dissepiments in Xystriphylloides. With regard to the morphology of the dissepimentarium in forms of Xystriphylloides, the Silurian Llandovery (Telychian) rugose coral Shensiphyllum aggregatum Ge and Yu, 1974 occurred in southern Shaanxi and northern Sichuan, 8

China (Ge and Yu, 1974, p. 71, pl. 79, figs. 2, 3) and its allied forms have some similarities. No typical horseshoe dissepiments exist in these genera. Remarks. Hill (1981) placed Xystriphylloides, Ivdelophyllum Spasskiy, 1971, Paradisphyllum Strusz, 1965, Exilifrons Crickmay, 1968, Gurievskiella Zheltonogova in Zheltonogova and Ivaniya, 1961, Martinophyllum Jell and Pedder, 1969, Radiastraea Stumm, 1937, and Xystrigona Yu in Wang et al., 1974 in the subfamily Paradisphyllinae Jell, 1969 of family Disphyllidae Hill, 1939. Most of the above mentioned genera occurred in Lower Devonian (Emsian) strata and are characterized by generally having everted dissepimentarial surfaces formed by flat lying and inflated dissepiments, and having major septa mostly with weak or strong fusiform dilation and carinae. No typical horseshoe dissepiments exist in these genera. To place those Devonian genera in Disphyllidae is not suitable as they do not have distinct parallel trabeculae extending obliquely upward and the dissepimentarium is formed by globose dissepiments inclined adaxially inward. It is appropriate to place Xystriphylloides in the subfamily Paradisphyllinae Jell, 1969 of the Family Columnariidae Nicholson, 1879, as suggested by Pedder (1983).

Xystriphylloides nobilis Yu, Liao and Deng, 1974 (Figs. 6, 7)

1974

Xystriphylloides nobilis – Yu et al., p. 224, pl. 104, figs. 17-20.

1974

Xystiphylloides nobilis Yu, Liao and Deng – Wang et al., pl. 2, figs. 29-32.

1977

Neopetrozium minor – Jia in Jia et al., p. 151, pl. 50, fig. 5a, b.

1977

Neopetrozium zhongguoense – Jia in Jia et al., p. 151, pl. 51, fig. 4a-d.

1977

Petrozium guixianense – Kuang in Jia et al., p. 145, pl. 48, fig. 4.

1977

Petrozium halysiforme – Jia in Jia et al., p. 144, pl. 48, fig. 5.

1981

Xystriphylloides nobilis Yu, Liao and Deng – Hill, p. 275, fig. 175.1a, b.

1982

Xystriphylloides nobilis Yu – Kuang and Wei, pl. 5, figs. 15, 16.

1988

Petrozium halysiforme Jia – Jia in Hou and Wang, p. 250, pl. 9, fig. 1a, b. 9

1988

Zelolasma dongvanensis – Tong-Dzuy in Tong-Dzuy and Khoa, p. 140, pl. 55,

figs. 2-4. 1989

Xystriphylloides nobilis Yu – Kuang and Chi, p. 38, pl. 9, fig. 11a, b.

1995

Neopetrozium zhongguoense Jia – Jia in Lin et al., p. 347, text-fig. 439.

1995

Xystriphylloides nobilis Yu, Liao and Deng – Lin et al., p. 333, text-fig. 414a,

b. 2005

Xystriphylloides nobilis Yu, Liao and Deng – Jin and Xie in Jin et al., p. 124,

pl. 31, figs. 1-4.

Type. Holotype, NIGP18705-18706 (BD47-235), from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi. Additional material. NIGP18709-18710 (BD50-201), NIGP18707-18708 (BD47-231), NIGP152321-152322 (BD47-230), NIGP152319-152320 (BD47-234), NIGP152328152329 (BD52-186), NIGP152338-152339 (BD53-86), all from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi; NIGP152340 (Loc. no. IV2-054), from the Shizhou Member of Yukiang Formation, about 1 km west of Wuhe railway station, Guangxi (courtesy of late Prof. Yu Wang and Dr. Di-Yong Liu); NIGP2251222513, from the Pochiao Formation, Xiyangjie, Guangnan, Yunnan. Diagnosis. A species of Xystriphylloides with typically (19–22) × 2 septa in adult corallites of 5.5–6 mm diameter. Major septa long, continuous, mostly extending near to axis of corallite, moderately fusiform at boundary between dissepimentarium and tabularium, being carinate moderately or distinctly in their expanded parts. Adult minor septa mostly thin and consist of an outer lamellar part, confined to marginarium, and an inner discontinuous part of short to very short strands. No horseshoe dissepiments present, but dissepimentarium continuous, narrowly everted, complete and closely spaced, with moderately to highly inflated flat-lying dissepiments, except for the innermost row of dissepiments being steeply inclined adaxially. Triseriate tabularium with well defined peripheral, periaxial and axial regions, including periaxially elevated and peripherally outwardly sloping to depressed axially tabularial surfaces. 10

Description. Fasciculate corallum, with slender cylindrical and angulo-cylindrical corallites. Mostly one side of the corallite wall is in contact with the adjacent corallites; sometimes a group of three or four corallites is attached to each other and arranged in a chain-like catenoid arrangement. Increase is marginal and nonparricidal; as many as three offsets may bud simultaneously from the dissepimentarium of the parent corallite (NIGP18707). The outer corallite wall is composed of a dark thin epitheca, which is mostly 0.06–0.1 mm thick but in places as thin as 0.02 mm, and a layer of perpendicular fibres, which are contiguous with the slightly expanded peripheral septal ends. The diameter of adult corallites is commonly between 4.5 mm and 6.5 mm, with only a few specimens having corallites up to 6.5–8 mm in diameter. Septa radially arranged in two well differentiated orders, typically with 19–22 × 2 in adult corallites of 5.5–6 mm in diameter. Only a few corallites less than 5.5 mm in diameter have the same septal numbers, and 20–22 × 2 occur in larger corallites of 7–8 mm in diameter. Major septa long, continuous, of which one or two may extend to the corallite axis, although most are withdrawn from it, leaving an axial space ranging from 0.3 mm to 0.45 mm. Typically, major septa are more or less straight near the periphery and slightly crenulate in the tabularium, where the axial ends are generally sinuous and undulant and tend to be slightly rotated or in rare cases directed toward a long and straight major septum on both sides. Although major septa are weakly to moderately fusiform at the boundary between the dissepimentarium and the tabularium, interseptal loculi are consistently wider than their enclosing septa. Major septa are slightly to distinctly carinate in their expanded parts, but smooth elsewhere. Minor septa are variable in length, just projecting a little from the dissepimentarium to slightly over half of the length of majors. They are mostly thin and consist of an outer lamellar part, confined to the marginarium, and an inner discontinuous part of short to very short strands. At some levels in the corallite, the outer continuous parts of the minor septa may be slightly thickened and very weakly carinate.

Fig. 6 here 11

Fig. 7 here

The skeletons of the studied material have suffered from recrystallization or replacement of substances from the eroded matrix to some degree, the least altered parts in the specimen showing that neither the thin nor thick parts of septa reveal any indication of trabeculae (septa incorrectly described as trabeculate by Yu in Yu et al., 1974). Indeed, the septa are completely composed of fibres, represented as tufts or short needles or as the brachycolumns (a term for minute structure of septa established by Wang et al., 1989). The blunt carination of the thicker septal parts is due to the transverse view of the inclination of the innermost dissepiments. In longitudinal section the tufts or brachycolumns, irregular and diverse in shape, are perpendicular to and in fan-like arrangement on the broadly arched dissepimentarial surface. In one longitudinal section of a septum, segments of tufts or brachycolumns with diameters in the order of 0.08–0.10 mm appear in the outermost tabularium/innermost dissepimentarium region. The dissepimentarium is two to four, rarely five, dissepiments wide. Except where corallites expand in preparation for gemmation, there is little variation in the 1.5–1.8 mm width of the adult dissepimentarium. In contrast, the dissepiments show considerable variation as a whole, those centrally situated dissepiments are moderately arched, but have less outward inclination in the outer part of dissepimentarium, and are smaller and vertically inclined in the innermost part of the dissepimentarium, distinct from the very different inclination of the outermost tabulae in longitudinal view. As viewed in longitudinal section, the tabularium is triseriate with well-defined peripheral, periaxial, and axial regions. The overall arrangement of the three series is such that the highest part of the tabularium, which is normally the summit of the periaxial series, is 1.8–2.2 mm above the lowest part of the tabularium, close to its periphery. Concave plates forming the peripheral series may be flat-lying, but more commonly are outwardly sloping. Variably distorted, well inflated vesicles comprise the periaxial series. They may be asymmetric in longitudinal view, and in places plates of the peripheral series are displaced by the lower end of one of the larger sigmoidal 12

plates of the periaxial series. Some of the plates forming the axial series are flat, but most are slightly concave, numbering 5–7 within a distance of 2 mm. A few are continuous with the unrolled end of a periaxial vesicle. Vertical spacing of elements of the tabularium varies depending on the series. Ten to 15 peripheral plates occur over a vertical distance of 5.0 mm; spacing is less crowded in both the axial and periaxial series.

Xystriphylloides distinctus Yu n. sp. (Figs. 8, 9)

1978

Xystriphylloides nobilis Yu, Liao and Deng – Kong and Huang, p. 86, pl. 30,

fig. 8a, b.

Etymology. Latin, meaning distinguishable, gender masculine. Types. Holotype, NIGP152317-152318 (BD47-233); paratype, NIGP152326-152327 (BD53-120); both from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi. Additional material. NIGP152331-152332 (BD380-314), from the correlative bed of the lower part of Yukiang Formation in Ertang, Wuxuan, Guangxi; NIGP152333152334 (BD450-45), NIGP152335-152337 (BD450-44), from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi; NIGP152323-152325 (Loc. no. f8), collected by Prof. Han-Kui Xu from the Pochiao Formation, at Gumo, Wenshan, Yunnan. All above listed slides are illustrated and deposited, except the following listed slides which are only deposited: NIGP152344-152345 (BD52-167), NIGP152346152347 (BD52-168), NIGP152343 (BD380-312). Description. Xystriphylloides with comparatively larger diameter of adult corallites between 6.5 mm and 7.5 mm, with occasionally some around 10 mm in diameter and smaller ones between 5 mm to 5.8 mm. The number of septa is up to 20–22 × 2, being 18 × 2 in smaller corallites. Major septa mostly thin and smooth, not extending to axis of corallite, leaving a more or less distinct axial space mostly 0.6–0.8 mm in diameter, 13

even though within the smaller corallites, the size of the axial space remains the same as that in the larger ones; the dilation and carinae of the major septa at the boundary between innermost dissepimentarium and outer tabularium as a rule are weak; the length of minor septa is variable, just projecting slightly from the wall to slightly through the dissepimentarium, and displaying discontinuous very short strands from the axial ends. Within 0.8 to 1.8 mm width of adult dissepimentarium there are one to four rows of dissepiments. Except for the innermost row of smaller dissepiments being steeply inwardly inclined, the larger inflated dissepiments may be sigmoidal maintaining the asymmetric arching of the dissepimentarium and more rows of dissepiments generally form everted dissepimentarial surfaces, gently inclined outward and inward. The broad, regularly arranged, axial tabulae mostly are flat or slightly convex upward, numbering 4–8, rarely 7–10 within a distance of 2 mm; the periaxial series is mainly represented by moderately uplifted shoulders of tabularium, composed of inflated vesicles, with one or two smaller vesicles sitting on the larger ones; the comparative narrower peripheral series is recognized by continuous outwardly inclined plates, numbering 5–7 within a distance of 2 mm, becoming concave before attaching to dissepimentarium.

Fig. 8 here

Fig. 9 here

Comparison. The characteristic features of the new species, which distinguish it from Xystriphylloides nobilis, are the slightly larger size of corallites with distinct and larger size of axial space, the comparatively less apparent inner wall due to weak dilation and carination of the major septa, the comparatively broad and flat axial tabulae and narrower periaxial and peripheral series of the tabularium. Remarks. Species described by Kong in Kong and Huang (1978) as Xystriphylloides nobilis from the drilling core in Hezhang, Guizhou may well be referred to the present 14

new species. In the same atlas, he also recognized Xystrigona Yu in Yu et al., 1974 as a genus with cerioid colony corresponding to the fasiculate Xystriphylloides and differing from the Australian Emsian Martinophyllum Jell and Pedder, 1969 in lacking the convex upward tabulae and the perforated septa mostly seen in the latter (Jell and Pedder, 1969; Yu in Wang et al., 1974; Kong and Huang, 1978). Kong also suggested removing some forms without perforated septa from Martinophyllum into Xystrigona (Kong and Huang, 1978). This is a question worth discussing in detail but is beyond the scope of the present paper. However, there is no evidence to include Australia in the distribution range of Xystriphylloides as Kong did. The erection of the new species found in Guangxi, Guizhou, and Yunnan increases the distribution range of Xystriphylloides toward the north of South China.

Acknowledgements Many thanks to Dr. Alan Pedder (Geological Survey of Canada in Calgary) for sending and allowing me to share his draft of description and comparison of Xystriphylloides; to Prof. Thanh Tong-Dzuy for kindly informing me about relevant Devonian biostratigraphy in northern Vietnam. I wish to express my gratitude to Dr. Ross McLean (Australia) for critically reading and improving the original manuscript; to Dr. Anthony Wright (Australia) and an anonymous reviewer for critically reviewed the manuscript and provided helpful comments and suggestions that greatly improved this paper. Dr. Guang-Xu Wang (Nanjing Institute of Geology and Palaeontology) helped in making photos and drafting figures; Mr. Jing-Cheng Li (Geological Survey of Guangxi) kindly donated the photos of the biostromes at Mengong, Guitang, Guangxi used in this paper, the assistance they rendered to me is deeply appreciated. This work is financially supported by National Ministry of Science and Technology Foundation Project of China (2013FY111000) and the National Natural Science Foundation (Projects 41521061 and 41290260).

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Fig. 1. Distribution of species referred to Xystriphylloides. 1. Jintang, Kangding, Sichuan Province, two obliquely cut sections sent to me for identification by a geological team from the locality is doubtfully identified as species of Xystriphylloides; 2. Tiekuangshan, Hezhang County, Guizhou Province; 3. Xiyangjie, Guangnan County, Yunnan Province; 4. Gumo, Wenshan, Yunnan Province; 5. Ertang, Wuxuan County, Guangxi Zhuang Autonomous Region; 6. Lantian, Dinbu and Tianpingshan, Guigang City, Guangxi; 7. Menggong, Guigang City, Guangxi; 8. Liujing, Hengxian, Guangxi; 9. Wuhe, Nanning City, Guangxi; 10. Ha Giang, Vietnam.

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Fig. 2. Map showing the location of described material mainly collected from the localities between Nanning and Liujing, Hengxian, Guangxi.

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Fig. 3. The measured section of the Yukiang Formation in Liujing, Hengxian, Guangxi (after Wang et al., 1964).

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Fig. 4. Stratigraphic column of the Early Devonian Yukiang Formation.

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Fig. 5. (a) The outcrop of the biostromes at Menggong, Guigang, Guangxi. (b) A close view of the colony of species of Xystriphylloides at the same locality.

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Fig. 6. Xystriphylloides nobilis Yu, Liao and Deng, 1974. (A, B) NIGP18705-18706 (BD47-235), from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi, holotype; (A) transverse section; (B) longitudinal section. (C–E) NIGP1870718708 (BD47-231), from the Shizhou Member of Yukiang Formation in Liujing, Hengxian, Guangxi; (C) transverse section; (D) enlarged part of (C), showing the interrupted axial ends of minor septa; (E), longitudinal section. (F, G) NIGP2251222513, from the Pochiao Formation, Xiyangjie, Guangnan, Yunnan Province, collected by Prof. Han-Kui Xu; (F) longitudinal section; (G) transverse section. The scale bars represents 5 mm, unless specifically indicated otherwise.

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Fig. 7. Xystriphylloides nobilis Yu, Liao and Deng, 1974. (A, B) NIGP152319-152320 (BD47-234), from the Shizhou Member, Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (A) transverse section; (B) longitudinal section. (C, D) NIGP152321-152322 (BD47-230), from the Shizhou Member, Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (C) transverse section; (D) longitudinal section. (E, F) NIGP18709-18710 (BD50-201), from the Shizhou Member, Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (E) transverse section; (F) longitudinal section. (G, H) NIGP152328-152329 (BD52-186), from the Shizhou Member, Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (G) longitudinal section; (H) transverse section. (I, J) NIGP152338-152339 (BD53-86), from the Shizhou Member, Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (I) transverse section; (J) longitudinal section. (K) NIGP152340 (Loc. no. IV2-054), from the Shizhou Member of Yukiang Formation, about 1 km west of Wuhe railway station, Guangxi (courtesy of late Prof. Yu Wang and Dr. Di-Yong Liu), transverse section. The scale bars represents 5 mm.

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Fig. 8. Xystriphylloides distinctus Yu n. sp. (A–C) NIGP152317-152318 (BD47-233), from the Shizhou Member of Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi, holotype; (A) transverse section; (B) longitudinal section; (C) longitudinal section. (D, E) NIGP152326-152327 (BD53-120), from the Shizhou Member of Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi, paratype; (D) transverse section; (E) longitudinal section. (F–H) NIGP152323-152325 (Loc. no. f8), from the Pochiao Formation, Gumo village, Wenshan, Yunnan Province, collected by Prof. Han-Kui Xu; (F) longitudinal section; (G) transverse section; (H) longitudinal section. The scale bars represents 5 mm, unless specifically indicated otherwise.

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Fig. 9. Xystriphylloides distinctus Yu n. sp. (A, B) NIGP152331-152332 (BD380-314), from the correlative bed of the lower part of Yukiang Formation in Ertang, Wuxuan, Guangxi; (A) longitudinal section; (B) transverse section. (C, D) transverse sections, NIGP152333-152334 (BD450-45), from the Shizhou Member of Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi, transverse sections. (E–G) NIGP152335-152337 (BD450-44), from the Shizhou Member of Yukiang Formation, north of Shizhou village, Liujing, Hengxian, Guangxi; (E) transverse section; (F) transverse section; (G) longitudinal section. The scale bars represents 5 mm.

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