Three rugose species of the family Holmophyllidae Wang, 1947 are described for the first time from the Gionyama Formation of the Kurosegawa Terrane, Southwest Japan. They are Holmophyllum sp., Holmophyllum? sp., and Labechiellata reguloris (Sugiyama, 1939). These species are found in the Middle Member of the Gionyama Formation, which is Late Llandovery to Early Ludlow (Silurian) in age. Holmophyllum and Labechiellata are typical cosmopolitan genera. The compound holmophyllids such as Labechiellata may indicate tropical environments and suggest that ‘Proto-Japan’ was, like other areas that yield these corals, located in subtropical to tropical latitudes during the Silurian.
Introduction
The Silurian to Devonian Gionyama Formation (Saito and Kanbe, 1954) is part of the Kurosegawa Terrane and is exposed around Mt. Gionyama, Gokase-cho, Miyazaki Prefecture in southwest Japan. Lithostratigraphically it was divided into three members by Kido and Sugiyama (2007a): the Lower (Upper Llandovery to Wenlock), Middle (Upper Llandovery to Lower Ludlow), and Upper (Upper Wenlock to lower Middle Devonian). The Middle Member is characterized by a limestone conglomerate intercalated with thin lenticular beds of tuffaceous shale and sandstone. The limestone conglomerate yields abundant corals with various other fossils, such as stromatoporoids, crinoids, bryozoans, and gastropods (e.g. Hamada, 1961; Niko and Adachi, 2002; Kido, 2009). Kido and Sugiyama (2007a) suggested that the limestone conglomerate of the Middle Member might have derived from shallow-water reefal limestone, and was transported and deposited as the result of a debris flow or storm action on a reef slope or along a reef front. Kido (2009) and Kido and Sugiyama (2005, 2007a, b) reported 18 rugose species in 14 genera from the Middle Member and assigned an age of Late Llandovery to Early Ludlow to this member on the basis of rugose corals. Among them, three species of the family Holmophyllidae Wang, 1947 are described in this paper.
Specimens of these species were collected from Loc. KL1 and occur within the limestone conglomerate beds exposed on the southwestern slope of Mt. Gionyama (Figure 1). The stratigraphic position of Loc. KL1 is included within the section in Figure 2. Details on the lithology and stratigraphy of the fossil locality (Loc. KL1) are given in Kido (2009).
The family Holmophyllidae is characterized by having a solitary, fasciculate, and massive corallum with septa which are present as discrete spines, and a clearly differentiated tabularium and dissepimentarium. Two genera of Holmophyllidae, Holmophyllum Wedekind, 1927 and Labechiellata Sugiyama, 1941, have been found in the Gionyama Formation. In Japan, Holmophyllum was formerly listed by Kato et al. (1980), without description, from the Fukata Formation (Late Llandovery to Early Ludlow) of the Yokokurayama Group (Umeda, 1998) of the Kurosegawa Terrane. This paper represents the first detailed study of Holmophyllum since its recognition from the Silurian strata of Japan.
The genus Holmophyllum has been confused in taxonomic definitions with the genus Nipponophyllum as the internal structures in both genera are similar (McLean, 1974, 1975, 1976; Kato, 1982a). However, Holmophyllum is distinguishable by having a solitary form, whereas Nipponophyllum has a fasciculate form with small corallite diameter. Holmophyllum sp. and Holmophyllum? sp. are described in this paper.
The second genus obtained from the section is Labechiellata. It is a rugose coral with a massive, thamnasterioid corallum, though it was considered to belong to another systematic group when the taxon was raised for the first time. Its type species, Labechiella regularis Sugiyama, 1939, from the Kawauchi Formation (Wenlock to Ludlow) of the South Kitakami Terrane in northeast Japan (Sugiyama, 1939), was proposed as a stromatoporoid. However, it turned out that it is identical with Mazaphyllum mirum Kato, 1982b which was described by Kato (1982b) as a holmophyllid rugose coral from the same formation. Mori (1994) clarified that Mazaphyllum Crook, 1955 is a junior synonym of Labechiellata, a fact which is not well known. An overview of the confusion in the history of Labechiellata, together with a description of Labechiellata regularis from the Gionyama Formation, is provided below.
Figure 1.
Index map of the fossil locality. The topography is from the 1:50,000 scale “Kuraoka” map sheet published by the Geographical Survey Institute of Japan.
Holmophyllum and Labechiellata are typical cosmopolitan taxa. The affinities of species and the geographic distribution of genera will help in constructing the paleobiogeographic connections between the areas where they occur.
The purpose of this paper is to provide detailed taxonomic descriptions and to discuss the paleobiogeographic relations of the taxa.
Paleobiogeographic Relations
Kido (2009) indicated that the rugose corals from the Gionyama Formation include both endemic and cosmopolitan genera. Holmophyllum and Labechiellata are typical cosmopolitan genera. Holmophyllum is known from Japan, South China, North China, Tajikistan, Kazakhstan, Kuzbas, Urals, Siberian Platform, Vaygach, Gotland, Podolia, Australia (Queensland and New South Wales), and North America (McLean, 1974; Hill, 1981). Holmophyllum? sp. from the Gionyama Formation seems to show similarities to species from eastern Australia, China, and North America. Labechiellata occurs in Japan, China, Kazakhstan, eastern Australia, and possibly Arctic Canada. Labechiellata regularis from Japan is closely comparable to Labechiellata currani (Wright in Wright and Bauer, 1995) from eastern Australia. The affinities of both species from the Gionyama Formation suggest a paleobiogeographic relationship between ‘Proto-Japan’ and those other areas where similar species occur.
Figure 2.
Generalized columnar section of the Silurian to Devonian of the Gionyama Formation on the western and southern slopes of Mt. Gionyama.
Kato (1990) plotted occurrences of the compound holmophyllids Nipponophyllum and Labechiellata from the Kawauchi Formation of the South Kitakami Terrane on the Wenlock paleogeographic map of Scotese et al. (1979) with the result that the places of occurrence formed a zone parallel to the reconstructed equator. Nipponophyllum occurs in Japan, South China, Tajikistan, Kazakhstan, Urals, Sweden, Great Britain, and Australia (Kato, 1982a). On the Wenlock to Ludlow paleogeographic map of Kiessling et al. (2003), the occurrence of Labechiellata and Nipponophyllum plots in paleoequatorial realms. Tabulate corals like favositids and halysitids commonly occur together with massive and fasciculate holmophyllids in the Silurian of the Kurosegawa and South Kitakami terranes. These compound corals may indicate tropical environments and suggest that ‘Proto-Japan’ was, like other areas that yield these corals, situated in subtropical to tropical latitudes during the Silurian.
Figure 3.
1–3. Holmophyllum sp. 1a, b. Transverse and longitudinal sections of a single corallum. GF. D 25087a, b, respectively. 1c. Longitudinal section showing trabeculae of discrete spine. Same specimen as Figure lb. 2a–c. Transverse sections of a single corallum. GF. D 25085a–c, respectively. 3. Transverse section. GF. D 25084a. (1a, b, 2, 3, ×2, 1c, × 10). 4. Holmophyllum? sp., 4a, b. Transverse and longitudinal sections of a single corallum. GF. D 25088a, b, respectively. (×3.5)
Systematic Paleontology
All specimens of rugose corals reported herein, with the abbreviation “GF. D”, are deposited at Fukuoka University, Japan.
Subclass Rugosa Milne-Edwards and Haime, 1850
Order Cystiphyllida Nicholson in Nicholson and Lydekker, 1889
Family Holmophyllidae Wang, 1947
Genus
Holmophyllum
Wedekind, 1927
Type species.—Holmophyllum holmi Wedekind, 1927, p. 31, pl. 4, figs. 6–8, pl. 29, fig. 16. Late Ludlow, Eke Beds. Lau Backar, Gotland.
Diagnosis.—Solitary Holmophyllidae with septa which are present as discrete spines and a well differentiated tabularium and dissepimentarium.
Remarks.—McLean (1976) considered that the genus Holmophyllum is characterized by having a solitary or fasciculate corallum with septa composed of discrete spines piercing several dissepiments or tabulae, tabularium of flat or concave, complete and incomplete tabulae, and dissepiments. However, Kato (1982a) treated the growth form of corals as an important generic character and separated fasciculate forms which were synonymized with Holmophyllum by McLean (1975, 1976), such as Nipponophyllum Sugiyama, 1940, Baeophyllum Hill, 1940, and Dendroholmia Spasskiy and Kravstov in Spasskiy et al., 1974, from Holmophyllum. Kato (1982a) also placed Baeophyllum and Dendroholmia in synonymy with Nipponophyllum and regarded Nipponophyllum as a distinct genus. Hill (1981) considered that Holmophyllum has only solitary forms and regarded Holmophyllia Sytova, 1970, Gukoviphyllum Sytova, 1968, and Aculeatophyllum Zhavoronkova in Strelnikov and Zhavoronkova, 1972 as synonyms of Holmophyllum. Here, the genus Holmophyllum is considered to include only solitary forms of holmophyllids following the conception of Hill (1981) and Kato (1982b).
McLean (1974) included Holmophyllum in the family Cystiphyllidae Edwards and Haime. Later, McLean (1976) discriminated two subfamilies, Cystiphyllinae M'Coy and Digonophyllinae Wedekind, and put Holmophyllum into the Cystiphyllinae. Hill (1981) and Kato (1982b) divided Cystiphyllidae into two families, Cystiphyllidae and Holmophyllidae, and included Holmophyllum in the latter family. Kato (1982b) regarded “cystiphyllid corals in which tabularium and dissepimentarium are clearly differentiated and septal spines are relatively long to pierce dissepiments” as Holmophyllidae. Here the genus Holmophyllum is regarded as a representative of the family Holmophyllidae as proposed by Hill (1981) and Kato (1982b).
The species described here as Holmophyllum? sp. is identical with Nipponophyllum sp. aff. N. aggregatum (Ge and Yü, 1974) in Kido and Sugiyama (2007a, b) and Kido (2009). It is characterized by a cylindrical corallum of which the average corallum diameter is 16.7 mm with a maximum diameter of 24.5 mm, discrete spines in regularly aligned radial series, a tabularium of incomplete and sagging tabulae, and a wide dissepimentarium. Whether this species has a solitary or fasciculate corallum is unknown because of poor preservation. The author considered that it is internally similar to Nipponophyllum aggregatum from the Upper Llandovery of South China, which has a fasciculate corallum. However, N. aggregatum clearly differs from the described species in having a small corallite diameter (10–12 mm).
The author reexamined the Gionyama species and revised it to Holmophyllum? sp. based on the following reasons: 1) it has no clear evidence of a fasciculate corallum, 2) its corallum diameter is clearly large compared to the corallite diameter in the species of Nipponophyllum and falls within the range of Holmophyllum, 3) there are some species of Holmophyllum which are similar to the Gionyama species in having long series of discrete spines and a wide dissepimentarium.
Kato (1982a) reviewed Nipponophyllum and assigned 14 species to this genus. The corallite diameter in these species reaches up to 13 mm. Three species of Nipponophyllum (N. colligatum Hill, 1940 and N. magnum Cao in Cao and Lin, 1982 from the Silurian of the Bailongjiang Formation, Gansu, China, and N. angustum Cao in Cao and Xuan, 1987 from the Upper Silurian of the Yanglugou Formation, Gansu and Sichuan, China) were described after Kato's (1982a) work. These species from China also have a small corallite diameter of up to 10 mm. Focusing on the incomplete specimens of the Gionyama species, the corallum diameter is assumed to have actually been larger. Therefore, the Gionyama species is distinguishable from Nipponophyllum by its large corallum diameter.
Sytova (1970) recognized a group which is characterized by having long septa and a wide dissepimentarium in Holmophyllum. This group includes H. holmi Wedekind, 1927, H. podolicum Bulvanker, 1952, H. pseudocarinatum Stumm, 1962, and H. wajgatchicum Sytova, 1970. Later, McLean (1974) recognized “Group I” (including forms with long septa and a wide dissepimentarium) in Holmophyllum and put ten species into this group. They are H. podolicum Bulvanker, 1952, H. wajgatchicum Sytova, 1970, H. multiseptatum Hill, 1940, H. wedekindi Lavrusevich, 1968, H. progressivum Lavrusevich, 1971, H. pauciseptatum Frügel and Saleh, 1970, H. gyalophylloides (Wang, 1944), H. conicum Wang, 1944, H. markovskii Lavrusevich, 1968, and H. confertum McLean, 1974. Some species of the group of Sytova (1970) and “Group I” of McLean (1974), such as H. pseudocarinatum, H. multiseptatum, and H. confertum, are similar to Holmophyllum? sp. from the Gionyama Formation in having long septa and a wide dissepimentarium.
Figure 5.
1. Holmophyllum sp. 1a. Transverse section showing fossula-like structure. 1b. Longitudinal section of calicular part of corallum with a flat bottom. GF. D 25086b, c, respectively. (× 2) 2. Holmophyllum? sp., 2a–c. Transverse and longitudinal sections of a single corallum. GF. D 25089a–c, respectively. (× 3.5) 3. Labechiellata regularis (Sugiyama), 3a. Transverse section of thamnasterioid corallum. GF. D 20764a. (×2) 3b, c. Transverse and longitudinal sections. GF. D 20764a, b, respectively. (×6)
Holmophyllum
sp.
Figures 3–1—3; 4–1—3; 5–1
Material.-Four prepared specimens. GF. D 25084-25087 with 8 thin sections from Loc. KL1, Middle Member of the Gionyama Formation, Mt. Gionyama, Gokase-cho, Miyazaki Prefecture.
Description.—Corallum large, solitary. Vertical profile suggests a ceratoid to cylindrical corallum (Figure 3–1c). Specimens incomplete but average corallum diameter 26 mm, maximum 34 mm. Septa present as series of discrete spines which extend to central part of tabularium. Major and minor septa not differentiated (Figures 3–1a, 3–2a, b, 3–3, 4–1, 5–1). Up to one hundred septa at corallum diameter of 31.5 mm and 92 at corallum diameter of 26.6 mm in incomplete specimens, GF. D 25085b (Figure 3–2b) and GF. D 25086b (Figure 5–1a), respectively. Up to 74 septa at corallum diameter of 29.4 mm in incomplete specimen GF. D 25084a (Figure 3–3), and 72 at corallum diameter of 20.9 mm in the younger part of the same specimen, GF. D 25084b. Short discrete spines widely spaced in tabularium (Figures 3–1a, 4–1). In peripheral part of corallum, discrete spines are somewhat thick and some of them appear to be continuous plates. Structure of trabeculae not clear in transverse section, but a radiating arrangement of fibres in discrete spines is observed in longitudinal section (see Figures 3–1c, 4–3). Fossula-like structure developed as shown in Figure 5–1a. Peripheral wall eroded.
In longitudinal section, discrete spines are observed through dissepimentarium to tabularium (Figures 3–1b, 4–2). Calicular floor wide, subhorizontal and dish-shaped (Figure 5–1b). Differentiation between tabularium and dissepimentarium is distinctive. Wide tabularium composed of incomplete tabulae, and width of tabularium three-fourths that of corallum diameter. Diameter of tabularium is 28–30 mm in specimen GF. D 25087c. Tabulae subhorizontal or slightly arched with marginal ends turned up (Figures 3–1b, 4–2). Seven to nine tabulae occur in vertical distance of 5 mm. Dissepiments almost elongated and steeply inclined toward axis (Figures 3–1b, 4–2). Dissepiments composed of four to seven rows in well preserved specimens.
Remarks.—In the present species, some of the discrete spines appear to become continuous plates in the marginal area of the corallum. However, they do not develop to complete septa. Spines which are at a high angle to the corallum wall might give the appearance of forming continuous plates in transverse section.
Hill (1981) defined Holmophyllum as having rhabdacanthine or tufted monacanthine trabeculae. In the present species, a radiating arrangement of fibres in discrete spines is observed in longitudinal section (see Figures 3–1c, 4–3). This may indicate rhabdacanthine trabeculae.
Holmophyllum sp. is characterized by having a large corallum with discrete spines that extend to the center of the corallum and a well defined wide tabularium. It is clearly distinguishable from Holmophyllum? sp. from the same locality (KL1) in having a much larger corallum diameter and wide tabularium composed of subhorizontal or slightly arched, less dense tabulae.
The type species of Holmophyllum (H. holmi Wedekind, 1927) from the Eke Beds (Late Ludlow, McLean, 1976) in Gotland differs from the present species in having a much smaller corallum diameter (12 mm) with septa which withdraw from the center of the corallum and a tabularium composed of deeply sagging tabulae (see Wedekind, 1927).
The Gionyama species is similar to Holmophyllum podolicum tewoense Cao in Cao and Lin, 1982 from the Silurian of the Bailongjiang Group, Wudu, Gansu in possessing discrete spines which are somewhat thicker in the periphery of the corallum and a wide tabularium. However, the latter differs from the former in having discrete spines which appear sparsely within the tabularium and concave tabular floors. The species H. tungchuanense Wang, 1947 from the Silurian of northern Yunnan, China is also similar to the Gionyama species in having discrete spines which are thicker in the marginal area of the corallum and a wide tabularium, but it is distinguishable by discrete spines which appear sparsely in the tabularium. These Chinese species clearly differ from the Gionyama species in having a much smaller corallum.
Figure 6.
Holmophyllum? sp. 1. Transverse section. GF. D 25089a. 2. Longitudinal section. GF. D 25088b.
Holmophyllum?
sp.
Figures 3–4; 5–2; 6–1, 6–2
Material—Two prepared specimens. GF. D 25088, 25089 with 8 thin sections from Loc. KL1, Middle Member of the Gionyama Formation, Mt. Gionyama, Gokase-cho, Miyazaki Prefecture.
Description.—Corallum cylindrical; clear evidence of a solitary or fasciculate corallum lacking because of poor preservation. Specimens incomplete, but average corallum diameter is 16.7 mm with a maximum diameter of 24.5 mm. Calicular floor is the shape of a shallow cup. Major and minor septa not differentiated. Septa consist of discrete spines in regularly aligned radial series (Figures 3–4a, 5–2a, b, 6–1). Total number of septa at corallum diameters of 18.4 mm (GF. D 25088a) and 24.5 mm (GF. D 25089a) is 96. Series of discrete spines are long but withdrawn from center of corallum (Figure 6–1). Discrete spines are somewhat thick in periphery, but become thin toward the axis. In peripheral part of corallum, discrete spines partly appear to be continuous plates. Structure of trabeculae can not be ascertained. Peripheral walls rarely preserved (Figures 5–2a, b).
In longitudinal section, discrete spines present in dissepimentarium and outer part of tabularium (Figures 3–4b, 5–2c, 6–2). Differentiation of dissepimentarium and tabularium is clear. Diameter of tabularium is 5.5 to 6.2 mm in specimen GF. D 25088b. Tabularium composed of incomplete, concave, and closely spaced tabulae. Vertical distance between tabulae approximately 0.3 mm and 12 to 15 tabulae occur in 5 mm. Dissepimentarium composed of five to six rows of elongate and crowded dissepiments. Dissepiments are somewhat convex near periphery, but moderately inclined toward axis (Figures 3–4b, 6–2). Dissepimentarium wider than tabularium and three-fourths width of corallum (Figure 6–2).
Remarks.—Whether the present species has a solitary or fasciculate corallum is unknown because of poor preservation. However, this species is characterized by having a cylindrical form with a corallum diameter that is large compared to the corallite diameter in Nipponophyllum, discrete spines, and a well differentiated tabularium and dissepimentarium. This species possibly belongs to the genus Holmophyllum.
Holmophyllum? sp. is similar to H. confertum McLean, 1974 from the Rosyth Limestone (Upper Llandovery) of New South Wales, H. multiseptatum Hill, 1940 from Cliftonwood Limestone (?Lower Ludlow) of New South Wales, Australia, and H. pseudocarinatum Stumm, 1962 from the Hardwood Mountain Formation (Silurian) of Maine, North America in having long septa represented by radial alignment of discrete spines and a wide dissepimentarium. The species H. confertum also has a similar corallum size (maximum 19 mm) and number of septa (up to 88). However, the present species differs from H. confertum in possessing axially sagging tabulae. H. multiseptatum is distinguishable from the Gionyama species by having a much greater corallum diameter (35 mm) and a larger number of septa (about 180). H. pseudocarinatum is similar to the Gionyama species in corallum size (maximum 22 mm) and number of septa (about 100), but differs in having tabulae which are deeply sagging in the central part of the tabularium.
Three species which are known from the Silurian of China also show similarities to the Gionyama species in having long septa which extend to near the axial part of the corallum, and a wide dissepimentarium. They are Holmophyllum sarburense Cai in Geological Bureau of Xinjiang, 1981 from the Shaerbuer Formation (Wenlock) of Xinjiang, H. zhifaagense Cai in Geological Bureau of Xinjiang, 1981 from the Kaokesaiergai Formation (Upper Silurian) of Xinjiang, and H. preciosum Guo, 1976 from the Xibiehe Formation (Ludlow to Pridoli) and the Chaganhebu Formation (Pridoli) of Inner Mongolia. H. sarburense, however, differs from the Gionyama species in having a larger number of septa (120 at corallum diameter of 17 to 21 mm) and distinct major and minor septa. H. zhifaagense is distinguished by its larger number of septa (114 at corallum diameter of 23 mm), thin septa, and more closely packed, subhorizontal tabulae. H. preciosum differs from the Gionyama species in having a larger number of septa (120 at corallum diameter of 25 mm) and tabulae which are axially convex with the peripheral depression.
Nipponophyllum aggregatum (Ge and Yü, 1974) from the Ningqiang Formation (Upper Llandovery) of Shaanxi and Sichuan is internally similar to the present species. The former species has a fasciculate, cylindrical form with 100 to 110 septa at a corallite diameter of 10 to 12 mm (see Ge and Yü, 1974). N. aggregatum also has a tabularium composed of numerous tabulae with a depressed axial area and a wide dissepimentarium (four-fifths the radius of the corallite). The major difference between N. aggregatum and the Gionyama species lies in their relative sizes.
Genus Labechiellata Sugiyama, 1941
Labechiella Sugiyama, 1939, p. 443; Sugiyama, 1940, p. 111.
Labechiellata Sugiyama, 1941, p. 75; Mori, 1994, p. 677.
? Labechiellata Sugiyama. Sugiyama, 1944, p. 44.
Mazaphyllum Crook, 1955, p. 1052; Cotton, 1973, p. 125; p. 125; McLean, 1976, p. 298; Spassky, 1977, p. 70; Hall, 1978, p. 89; Hill, 1981, p. F107; Kato, 1982b, p. 390; Wright and Bauer, 1995, p. 100; Lin et al., 1995, p. 133.
Aksarlinia Kaplan, 1971, p. 17; Sytova and Kaplan, 1975, p. 67.
? Mazaphyllum Crook. Pedder, 1976, p. 287.
non Mazaphyllum? Crook. Scrutton, 1989, p. 49.
Type species.—Labechiella regularis Sugiyama, 1939, p. 454, pl. 24, figs. 10, 11. Wenlock to Ludlow of the Kawauchi Formation. Higuchizawa Valley, Hikoroichi, Ofunato City, Iwate Prefecture, northeast Japan.
Diagnosis.—Corallum plocoid, thamnasterioid with some tabularia. Septa are long, each septum consists of a single series of discrete spines that pierces several dissepimental layers in the wide dissepimentarium. Narrow tabularium composed of concave tabulae, which is clearly distinguished from dissepimentarium. Dissepimentarium is very wide, composed of small, globose to elongate dissepiments. Trabeculae are rhabdacanthine and holacanthine.
Discussion.—It is not well known that the genus Labechiellata Sugiyama, 1941 is a senior synonym of Mazaphyllum Crook, 1955, and Labechiella regularis Sugiyama, 1939 is the type species of Labechiellata. Mori (1994) reexamined the confusing history of the study of Labechiellata regularis (Sugiyama, 1939).
Yabe and Sugiyama (1930) proposed Labechiella as a subgenus of Labechia, which Milne-Edwards and Haime (1851) described as a stromatoporoid. They chose Labechia serotina Nicholson, 1886 from the Middle Devonian of Devonshire, England (see Nicholson, 1886, p. 162; Webby, 1979, p. 92) as the type species of Labechiella. The name Labechiella was proposed again by Sugiyama (1939) as a stromatoporoid without referring to the previous study. At the same time, Sugiyama (1939) assigned Labechiella regularis from the Silurian deposits of the Kitakami Mountainland in northeast Japan as the type species of his Labechiella. He labeled the holotype of Labechiella regularis as Reg. No. 50595 (Sugiyama, 1939, p. 444). However, he gave another number, Reg. No. 50593, to the holotype specimen figured in the same paper (Sugiyama, 1939, p. 454, pl. 24, figs. 10, 11). One year later, Sugiyama (1940) published the same description of thegenus Labechiella and the species Labechiella regularis, and recorded the holotype number of this species as Reg. No. 50593. Later, in 1941 Sugiyama revised his own proposal, changing Labechiella to Labechiellata, and Labechiella regularis to Labechiellata regularis. His new generic name, Labechiellata, has been considered as a lapsus memoriae for the genus Labechiella. Webby (1979) erected a new name Labechiella sugiyamai for the species described by Sugiyama (1939) as Labechiella regularis to resolve the dilemma of homonymy. However, Mori (1994) addressed the situation by noting that the specimen assigned by Webby (1979) as the holotype of Labechiella sugiyamai (Reg. No. 50593), which was illustrated in Sugiyama (1939, pl. 24, figs. 10, 11), was not a stromatoporoid but a rugose coral that had also been described as Mazaphyllum mirum (compare Kato, 1982b, p. 390, pl. 61, figs. 1, 2; text-fig. 1A–C;). Both specimens were collected from the same locality within the Kawauchi Formation, Higuchizawa Valley, Hikoroichi, Iwate Prefecture. Therefore, based on the International Code of Zoological Nomenclature, Mori (1994) concluded that Labechiellata regularis is a valid name for a rugose coral, and the genus Labechiellata is a senior synonym of Mazaphyllum.
Sugiyama (1944) reported Labechiellata regularis from the Silurian of the Kurosegawa Terrane in the Imose area, Kochi Prefecture and included it within the stromatoporoids. He mentioned that the Imose species had similar features to Labechiellata regularis that he described from the Silurian deposits of the Kitakami Mountainland. The section figured by Sugiyama (1944, pl. 2, figs. 2a, b) is a part of the specimen and does not show the complete features of this species. Therefore, it remains unclear whether his specimen is a stromatoporoid or a rugose coral.
Since Crook (1955) established the genus Mazaphyllum and described the type species M. cortisjonesi that occurred in the ?Wenlock of Palmers Oakey district in New South Wales, Australia, two other species have been described as Mazaphyllum from New South Wales. They are M. acclive Hall, 1978 from the Upper Llandovery of the Woolomin Beds and M. currani Wright in Wright and Bauer, 1995 from the ?Upper Llandovery of the Quarry Creek Limestone. The New South Wales species are characterized by having a plocoid, thamnasterioid corallum with series of discrete spines which arrange radially piercing small dissepimental layers, and sagging tabulae.
Kato (1982b) indicated that the genus Aksarlinia Kaplan, 1971 from the Lower Devonian of Kazakhstan was a junior synonym of Mazaphyllum because the type species of Aksarlinia, A. concavotabulata Kaplan, 1971, has a thamnasterioid corallum with series of discrete spines arranged radially, and sagging tabulae. Lin et al. (1995) also considered Aksarlinia as a junior synonym of Mazaphyllum. According to the synonymy of Labechiellata by Mori (1994), the species reported as Mazaphyllum from New South Wales and Aksarlinia concavotabulata described from Kazakhstan are considered to be representatives of Labechiellata.
Pedder (1976) reported a new species of Mazaphyllum from the ?Pridoli of the Read Bay Formation, Somerset Island, Arctic Canada. This species has a massive corallum with tabularia, which possesses discrete spines penetrating dissepimental layers and a narrow tabularium composed of sagging tabulae (see Pedder, 1976, p. 287). However, this species differs from the Japanese, Australian, and Kazakhstan species of Labechiellata in having discrete spines which do not show radial alignment in its transverse section. Pickett et al. (2000) indicated that the Canadian species differs from Mazaphyllum known from Australia in having dissepiments which are strongly angulated in longitudinal section. Thus, the inclusion of Pedder's (1976) species in Labechiellata remains questionable. Wright and Bauer (1995) indicated that this Canadian form is similar to the arachnophyllid Zenophila Hill, 1940 in many ways.
Scrutton (1989) considered that the species from the Upper Llandovery of the La Vieille Formation, Quebec, Canada which was described as Strombodes approximatus by Parks (1933) and Arachnophyllum approximatum by Northrop (1939) is a representative of Mazaphyllum. This species is characterized by an aphroid corallum with tabularia, discrete spines which are densely developed around the tabularia, and concave tabulae. Scrutton (1989, p. 50) and Pickett et al. (2000, p. 136) indicated the possibility that this species could be a new genus. It is not assigned to Labechiellata here.
Labechiellata was previously compared with some arachnophyllid corals, such as Zenophila Hill, 1940, Arachnophyllum Dana, 1846, Angullophyllum McLean, 1974, and Bungoniella Wright and Bauer, 1995 (see Crook, 1955; McLean, 1974; Kato, 1982b; Wright and Bauer, 1995). Zenophila has an aphroid or in part thamnasterioid corallum with long septa and a tabularium composed of subhorizontal or sagging tabulae, which is clearly separated from the dissepimentarium (see Hill, 1981). Zenophila differs from Labechiellata in having platy septa.
McLean (1974) indicated that Arachnophyllum and Angullophyllum are most closely related to Mazaphyllum. They have septa which developed discretely in common. Arachnophyllum is an asteroid or aphroid corallum and possesses platy or discontinuous septa, a narrow tabularium composed of arched tabulae, and a wide dissepimentarium (see Hill, 1981; Scrutton, 1989). In some species, the peripheral part of the septa develop sporadically in the wide dissepimentarium and intercorallite walls are formed (see Scrutton, 1989). In general, two orders of septa are recognized in this genus. Thus, Arachnophyllum is clearly distinguishable from Labechiellata in many ways. Angullophyllum occurs in the Lower limestone horizon (Upper Llandovery) of Cobblers Creek, Angullong District, New South Wales, Australia (McLean, 1974). The type species Angullophyllum warrisi McLean, 1974 differs from Labechiellata in having a cerioid corallum composed of cup-shaped corallites, discontinuous septa which develop in layers wrapped in sclerenchymal tissue on the dissepimental surfaces, and up-arched tabulae.
Wright and Bauer (1995) established the genus Bungoniella Wright and Bauer, 1995 for materials that occurred in the Lookdown Limestone (?Ludlow), Bungonia, New South Wales, Australia. The type species B. clarkei is characterized by a thamnasterioid corallum with complete, carinate septa, a narrow tabularium composed of arched tabulae, and a wide dissepimentarium. Bungoniella clearly differs from Labechiellata. Wright and Bauer (1995) proposed that Bungoniella and Mazaphyllum are somewhat similar because the two orders of septa are not distinguishable.
Scrutton (1989) postulated that Mazaphyllum has rhabdacanthine and holacanthine trabeculae. Crook (1955) described the trabeculae as rhabdacanths and holacanths. Kato (1982b) stated that the trabeculae in Mazaphyllum mirum which occurs in the type locality might be holacanthine, but initially were possibly rhabdacanthine. As mentioned by McLean (1974), it is likely that the trabeculae of discrete spines in Labechiellata are originally rhabdacanthine, and holacanthine trabeculae represent a reconstitution.
The pattern of septal insertion in Labechiellata is unique. In general, it is difficult to identify orders of septa. Septa in the Gionyama species radiate out from the tabularium and lean on other septa in the dissepimentarium. On average 29 septa, which protrude into or slightly withdraw from the tabularia, are counted. The number of septa becomes larger in the periphery of the corallite where septa are arranged nearly parallel. In general, the septal insertion is not cyclical. Idiophyllum Cao in Li et al., 1975 from the Upper Llandovery of the Ningqiang Formation near the border of Shaanxi and Sichuan occurs both as a solitary and a compound form. Only one species, I. massulatum Chen in He and Chen, 1986, has a compound corallum. This species is similar to Labechiellata in having a thamnasterioid corallum, but clearly differs in having platy septa. I. massulatum has distinct third-order septa which are inserted irregularly between the major and minor septa. Scrutton and Deng (2002) reported a new species from the Ningqiang Formation as a thamnasterioid rugose coral gen. nov. without description. This species is similar to Labechiellata in possessing a thamnasterioid corallum with some tabularia and long septa (see Scrutton and Deng, 2002, p. 118). However, the former differs from the latter in having platy septa. It seems that the pattern of septal insertion is closely related to the growth morphology as observed in Labechiellata, the compound species of Idiophyllum, and the species of Scrutton and Deng (2002).
Kato (1982b) assigned Mazaphyllum to the family Holmophyllidae. In this paper the genus Labechiellata is considered a member of Holmophyllidae as proposed by Kato (1982b).
Included species and their distributions.—Labechiellata acclive (Hall, 1978): Upper Llandovery of the Woolomin Beds which are exposed just east of the Peel Fault System in New South Wales, Australia (Hall, 1978).
Labechiellata currant (Wright in Wright and Bauer, 1995): ?Upper Llandovery of the Quarry Creek Limestone, Quarry Creek in New South Wales, Australia (Wright and Bauer, 1995).
Labechiellata regularis (Sugiyama, 1939): Upper Llandovery to Lower Ludlow of the Middle Member of the Gionyama Formation, Mt. Gionyama, Gokase-cho, Miyazaki Prefecture in southwest Japan, and the Wenlock to Ludlow of the Kawauchi Formation, Higuchizawa, Hikoroichi, Ofunato city, Iwate Prefecture in northeast Japan (Sugiyama, 1939, 1940, 1941; Kato, 1982b).
Labechiellata cortisjonesi (Crook, 1955): ?Wenlock, unnamed strata, Palmers Oakey district, east of Bathurst in New South Wales, Australia (Crook, 1955).
Labechiellata? sp.: ?Pridoli of the Read Bay Formation, east end of main cliff, southeastern Garnier Bay, Somerset Island, Arctic Canada (Pedder, 1976).
Labechiellata concavotabulata (Kaplan, 1971): ?Gedinnian of Central Kazakhstan, near Aksarly (Sytova and Kaplan, 1975).
According to McLean (1974), species assigned to Labechiellata occur in the ?Ludlow of the Borenore Limestone near Borenore and the Yarrangobilly Limestone, New South Wales, Australia. Additionally, there are several thin sections of Labechiellata in the collections of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. These specimens were collected from the Upper Llandovery of the Ningqiang Formation, China. Based on this information, Labechiellata ranges from the Upper Llandovery to Lower Devonian and occurs in Japan, South China, Kazakhstan, eastern Australia, and possibly Arctic Canada.
Figure 7.
Labechiellata regularis (Sugiyama). 1. Transverse section of thamnasterioid corallum. GF. D 25092. 2. Transverse section of an incomplete corallum. GF. D 25096. 3a, b. Transverse and longitudinal sections of an incomplete corallum. GF. D 25097a, b, respectively. (×4).
Labechiellata regularis
(Sugiyama, 1939)
Figures 5–3; 7–1–3; 8
Labechiella regularis Sugiyama, 1939, p. 444, pl. 24, figs. 10, 11; Sugiyama, 1940, p. 111, pl. XXXI (XIX), figs. 1–3.
Labechiellata regularis (Sugiyama). Sugiyama, 1941, p. 75.
? Labechiellata regularis (Sugiyama). Sugiyama, 1944, p. 44, pl. 2, figs. 2a, b.
Labechiella sugiyamai Webby, 1979, p. 92.
Mazaphyllum mirum Kato, 1982b, p. 390, pl. 61, figs. 1, 2, text-figs. 1A–C.
Material.—Twelve prepared specimens. GF. D 20764, 25089-25093 with 13 thin sections from Loc. KL1, the Middle Member of the Gionyama Formation, Mt. Gionyama, Gokase-cho, Miyazaki Prefecture.
Description.—Corallum compound and thamnasterioid. External shape of the complete corallum and surface features are unknown. No outer wall observed. Corallum includes some calices as shown in Figures 5–3a, 7–1, 7–2, 7–3a; in some cases, at least thirteen calices are observed within a space of 42×17 mm in GF. D 25092 (Figure 7–1). Neighboring four calices in this specimen are arranged in line (see lower right part of Figure 7–1), but other corallites are arranged randomly. Interval between calicular pits ranges from 2.2 to 9.5 mm in the same specimen. Four calices are observed within a space of 40×30 mm in GF. D 20764a (Figure 5–3a), the intervals between them range from 3 to 15 mm. In another case only one calyx is developed in GF. D 25097 (Figure 7–3a), with a corallum 20 × 14 mm in size. There are two calices in GF. D 25096 (Figure 7–2), with a corallum of similar size to GF. D 25097. Density of calices in corallum somewhat irregular. Tabularia appear as calicular pits on surface of corallum. Tabularia small with a diameter ranging from 1.2 to 1.5 mm.
Septa present as series of discrete spines; spines pierce several dissepimental layers. Average distance of discrete spines is 0.1 mm. Septa protrude into tabularium, but spaces are retained in central area of tabularia (Figures 5–3b, 7–1, 7–2, 7–3a, 8–1, 8–2). The length and thickness of discrete spines in transverse section are various; in general, spines show as small dots in the plane of each septum through corallites, but locally some spines are linked like beads.
It is difficult to trace series of discrete spines in transverse section. However, 28 to 30 series of discrete spines that protrude into or slightly withdraw from tabularia are counted in GF. D 20764 (Figures 5–3b, 8–1). Twenty-six to thirty series of discrete spines are observed in GF. D 25092 (Figure 7–1). The specimen which includes only one tabularium has about 30 series of discrete spines (Figure 7–3a). Up to 37 series of discrete spines are counted in GF. D 25096 (Figure 7–2). In general, series of discrete spines are long, not separated into two orders.
Septal arrangement of this species currently unknown. Septa lean on other septa in dissepimentarium and lie almost parallel in marginal region of corallite (see Figures 5–3a, 7–1, 7–2, 7–3a, 8–1, 8–2). Average interval between septa is 0.18 mm (measured in section GF. D 20764a). The trabeculae of discrete spines show as a dark, structureless mass.
In longitudinal section, discrete spines occur in both tabularium and dissepimentarium (Figures 5–3c, 7–3b, 8–3); spines in central area of tabularium are short. In contrast, those of dissepimentarium are continuous, piercing several dissepimental layers. Spines are more or less continuous at border of tabularium and dissepimentarium (see Figures 5–3c, 7–3b, 8–3). Differentiation between tabularium and dissepimentarium is distinctive (see Figure 8–3). Narrow tabularium composed of sagging and incomplete tabulae. Intervals between tabulae are approximately 0.4 to 0.7 mm with 10 to 15 tabulae in a vertical distance of 2 mm. Wide dissepimentarium composed of numerous, small, and globose dissepiments (Figures 5–3c, 7–3b, 8–3). Dissepiments somewhat flattened at periphery, but elongate dissepiments appear near the boundary between tabularium and dissepimentarium (Figure 8–3).
Remarks.—According to Mori (1994), the type specimen of Labechiellata regularis consists of a collection of small pieces of a corallum and does not show the complete features of the species. The author compared the Gionyama specimens with specimens from the Kawauchi Formation described as Mazaphyllum mirum by Kato (1982b). The Gionyama species is essentially the same as the species from the Kawauchi Formation. The species from the Kawauchi Formation is characterized by small tabularia (1 to 1.5 mm) and septa that protrude into them. The tabularia of the Gionyama species are similar in size (1.2 to 1.5 mm). Kato (1982b) reported about 93 septa within the Kawauchi specimens. In his text-fig. 1, A–C, 89 to 93 septa are counted in the peripheral parts. This number differs when counting septa that protrude into or slightly withdraw from the tabularia. In that case 24 to 34 septa are counted in the specimen illustrated as pl. 61, fig. 2. The number of septa is similar in the Kawauchi and the Gionyama species. Additionally, the septal arrangement of the Gionyama species is also quite similar to the Kawauchi species.
Labechiellata cortisjonesi (Crook), L. concavotabulata (Kaplan), and L. acclive (Hall) are distinguishable from the Gionyama species in having a much larger diameter of tabularia and a wide open space within the tabularia. The tabularia in L. cortisjonesi are 4–4.5 mm in diameter, in L. concavotabulata 3–3.5 mm, and in L. acclive 2.3–3 mm. Crook (1955) and Hall (1978) reported that the number of septa which are observed near the tabularium in L. cortisjonesi and L. acclive is 40 to 50 and about 40, respectively. The number of septa near the tabularium in these two species is larger than that in the Gionyama species.
Labechiellata currant (Wright) which occurs in the ?Upper Llandovery of Australia is closely related to Labechiellata regularis. Wright and Bauer (1995) wrote that the diameter of tabularia in L. currant is about 1.5 mm and up to 60 septa are developed, including contratingent septa, withdrawn from the axial part of the tabularia. When counting septa around tabularia which protrude into or slightly withdraw from them, 30 to 34 septa are counted in their specimen illustrated as fig. 4, A. The diameter of tabularia and number of septa in this species is similar to the Gionyama species. The corallites in the specimen illustrated by Wright and Bauer (1995) as fig. 4, A are obviously parallel. A similar arrangement of corallites is also observed in the Gionyama species (see lower right part of Figure 7–1). However, L. currant differs from the Gionyama species in having more sagging, complete tabulae.
Acknowledgments
Prof. T. Sugiyama (Fukuoka Univ.) provided encouragement and advice on the classification of rugose corals and Silurian paleobiogeography. Prof. Z.-Q. Deng and Prof. X.-D. Wang (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences) offered much information concerning Silurian rugose corals from South China. Emeritus Prof. R. R. West (Kansas State University) reviewed an early version of the typescript, providing useful suggestions. Two reviewers, Dr. R. A. McLean (Canada) and Dr. G. A. Young (Manitoba Museum), provided detailed critiques on the classification of rugose corals. Associate Editor Prof. Y. Ezaki (Osaka City University) provided constructive comments. This research was funded by the Chinese National 973 Project 2006CB806400, National Natural Science Foundation of China (J0630967), and the CAS Research Fellowship for International Young Researchers. The initial field survey in Japan was supported by the Board of Education, Gokase-cho Town Hall.
