Three species of the Middle Permian echinoconchoide brachiopod Vediproductus from the Kamiyasse area, northeast Japan, V. mugenjin sp. nov., V. punctatiformis, and V. sp., are described, and their paleogeographic significance is discussed. V. mugenjin sp. nov. is characterized as having spine bands on both the outer and inner surface of the valve, showing a strong relief with a comparatively wide interval of each band and a typical sawtooth outline of spine bands in cross-sectional view. The stratigraphic and paleogeographic distributions suggest that the genus flourished in the Tethyan province and was possibly restricted to a lower latitude than warm-cool water transitional environment.
Introduction
Kitakami Mountains represents a variety of sedimentary facies in a relatively narrow area. These facies are characterized by terrigenous deposits in association with lenses of calcareous sediment and are unique in their abundance of various fossils such as corals, fusulines, brachiopods, cephalopods, crinoids, and trilobites (e.g., Onuki, 1969; Choi, 1973; Tazawa, 1973; Ehiro, 1977; Kobayashi et al., 2009). The modes of occurrence of these fossils mostly depend on the lithofacies, except in the case of brachiopods, which occur in all facies types. Using the brachiopod fauna from the Kamiyasse area, Permian paleogeography has been reconstructed, not only of the Southern Kitakami mountains but also on a global scale (e.g., Tazawa, 2002; Shen and Shi, 2004; Shi, 2006; Tazawa and Chen, 2006).
The genus Vediproductus was first described by Sarytcheva in Sarytcheva and Sokolskaya (1965). Despite its occurring less frequently than other Permian brachiopods, this genus has been utilized for paleogeographic reconstruction because of its characteristic distribution in the paleoequatorial region (e.g., Campi et al., 2002; Shen et al., 2002). In order to confirm its effectiveness for reconstruction, further reporting of its occurrence is required. The author recently recovered specimens of Vediproductus from the Middle Permian beds of the Kamiyasse area, Southern Kitakami Mountains. Taxonomic examination of these specimens revealed that they can be assigned to three Vediproductus species, V. punctatiformis, V. sp., and a new species. Their systematic descriptions are given in this paper.
Local geology and stratigraphy
The study site is the Kamiyasse area of the Southern Kitakami Mountains, where the Middle Permian sequence is exposed (Tazawa, 1973; Misaki and Ehiro, 2004; Shiino and Suzuki, 2007; Shiino et al., 2008; Kobayashi et al., 2009). The area is located at latitude 38°58′20″ to 39°0′15″ North and longitude 141°30′20″ to 141°32′55″ East (Figure 1).
The Middle Permian sequence in the Kamiyasse area consists of three formations, in ascending order: the Hoso-o, the Kamiyasse, and the Kurosawa Formations (Misaki and Ehiro, 2004). On the basis of previous biostratigraphic studies using fusulines and ammonoids, each formation is thought to be late Cisuralian to early Guadalupian, middle Guadalupian, and late Guadalupian in age, respectively (e.g., Morikawa, 1960; Choi, 1973; Misaki and Ehiro, 2004). Recently, the upper portion of the Hoso-o and the Kamiyasse Formation were correlated to the Midian on the basis of fusulinid occurrences (Shiino et al., 2008; Kobayashi et al., 2009). The lithostratigraphic columns for the five selected routes and the results of these correlations are shown in Figure 2.
Figure 1.
Geological map along the Shigeji-zawa and Chaya-zawa creeks in the Kamiyasse area showing the fossil localities of Vediproductus.
The Hoso-o Formation consists mainly of alternating beds of mudstone and sandstone/fossiliferous pavement beds in a coarsening and thickening upward sequence. The clastsupported conglomerate beds are locally distributed as lenses. The lower portion of the Kamiyasse Formation is characterized by skeletal packstone and grainstone with medium-to coarse-grained sandstone beds in the basal portion. The poorly sorted fine-grained sandstone beds rest on the skeletal packstone and grainstone with a matrix-supported conglomerate bed in its basal portion. The Kurosawa Formation consists of alternating beds of black mudstone and sandstone beds in a fining and thinning upward sequence. Lenses of matrix-supported conglomerate beds are locally exposed.
The present specimens of Vediproductus were recovered from two stratigraphic horizons of the lower and the upper portion of the Kamiyasse Formation (Figure 2). The lower horizon yielded Vediproductus in a bed of skeletal packstone and grainstone, which contains abundantly an oldhaminid brachiopod Leptodus sp. and fenestrated bryozoans. Vediproductus also occurs in the poorly sorted, fine-grained sandstone beds, the sequence of which represents sense stricto alternating beds of fossil pavement and fine-grained sandstone. The pavement consists exclusively of Waagenoconcha imperfecta (Tazawa, 1973; Shiino and Suzuki, 2007). Vediproductus specimens were rarely found from the sandy portions of the alternating beds.
Systematic description
Repository.—All the specimens described are housed in the collections of The University Meseum, The University of Tokyo, Japan (UMUT PB30075 to PB30078).
Order Productida Sarytcheva and Sokolskaya, 1959
Suborder Productidina Waagen, 1883
Superfamily Echinoconchoidea Stehli, 1954
Family Echinoconchidae Stehli, 1954
Subfamily Juresaniinae Muir-Wood and Cooper, 1960
Genus
Vediproductus
Sarytcheva in Ruzhentsev and Sarytcheva, 1965
Vediproductus mugenjin sp. nov.
Figure 3
Type.—The holotype is a dorsal valve (UMUT PB30075). The specimen consists of two parts, the outer and inner molds.
Diagnosis.—Spine bands on outer surface of the valve are comparatively wide with strong relief that present a typical sawtooth outline in cross-sectional views.
Type locality and age.—The specimen locality is an outcrop of poorly sorted, fine-grained sandstone bed of the upper part of the Kamiyasse Formation in the mountainside along an armlet of Shigeji-zawa creek (Loc. 1 in Figure 1). The stratigraphic horizon is slightly above and/or is included in the upper part of the Waagenoconcha assemblages (see Shiino and Suzuki, 2007); this location correlates with the Upper Midian of the Tethyan stage and with the MiddleUpper Capitanian of the Standard stage (Shiino et al., 2008; Kobayashi et al., 2009).
Etymology.—The species name mugenjin is taken from the name of a Japanese traditional sword with a serrate blade.
Material.—One dorsal valve was collected with outer and inner molds.
Description.—The specimen is 21.3 mm in length and 33.5 mm in width. The dorsal valve and the dorsal disc are slightly subquadrate in outline (Figure 3A, B, C, D) but rounded in comparison with that of Waagenoconcha (see Tazawa, 1974; Shiino and Suzuki, 2007). The dorsal valve is gently concave with a short trail. The trail is half the length of the dorsal disc. The outer surface of the dorsal valve exhibits concentric rugae, called spine bands, of a typical sawtooth shape in a longitudinal cross section, each of which is 2.5 to 3 mm in maximum width (Figure 3E). More than two rows of recumbent spine bases are quincunxially arranged in each valley of the sawtooth (Figure 3F). These spine bases decrease their thickness in the outer row of each band. The spines, about 300 µm in diameter, are radially directed. The ears are fairly small and triangular in shape (Figure 3B: black arrowhead).
The interior surface of the dorsal disc exhibits structures associated with internal systems, such as the median septum, the cardinal process, and two pairs of muscle scars (Figure 3G). A faint thin median septum is tapered anteriorly and grades into the cardinal process posteriorly (Figure 3G). The median septum contains a small tear-shaped alveolus. The cardinal process is trilobate and its shaft is relatively short (Figure 3H, I). The shaft diverges about 30 to 40 degrees dorsally from the dorsal disc and is slightly divided into two lobes by the shallow and narrow myophore (Figure 3H). The length of the cardinal process is about one-eighth relative to the dorsal disc. Paired lateral ridges, which are hemicyclic in cross section, are located in front of the dorsal narrow ginglymus (Figure 3D, G). The ridges are arranged perpendicular to the median septum (Figure 3G). The cardinal ridges laterally extend and bend moderately across the ears. The lateral ends of these ridges taper around the anterior half of the dorsal disc.
Two pairs of muscle scars, though faint, are lateral to the median septum (Figure 3G). The muscle scars of the inner anterior pair, which are longitudinally elongate and elliptical in outline, are situated in the posterior half of the dorsal disc. The inner muscle scar is bordered by an outer posterior scar whose outline is fanlike. Both muscle scars exhibit fairly faint granulated surfaces that seem to have an eclipsed surface form.
On the outside of the muscle scars, the surface has sawtooth ornamentation in a longitudinal cross-sectional view, which corresponds to the counterpart of the exterior sawtooth. The dorsal disc includes the posterior three to four bands of the saw teeth (Figure 3D, J). On each band, strainer spines are arranged, and anteriorly the spines of each band are comparatively short and thin. The strainer spine is small and conically shaped, and its apex slants anteriorly and is directed toward the interior surface of the ventral valve. These spines tend to be larger medially toward the anterior margin. Several long spines extend radially along the dorsal disc only in the posterior bands and reach to the outer end of the dorsal disc. These long spines appear to be conglutinated with the inner dorsal disc (Figure 3G: sp). The long spines are about 300 µm in diameter.
Remarks.—The present species is similar to V. tongluensis (Liang, 1990, p. 187, pl. 29, figs. 1–10) in having several rows of spines on each band of the outer surface, but it is distinguished by having a strong sawtooth-shaped relief in cross sectional outline. In addition, the internal structures of the present species, such as the thin median septum and several rows of strainer spines on each band, are unique characteristics that are not found in the other species.
Figure 2.
Columnar sections along surveyed routes. Correlation with the Tethyan stage shown in the right figure is revised from the work of Kobayashi et al. (2009). Black circles represent horizons of Vediproductus. Each number inside a black circle corresponds with the number plotted in the Middle Permian world map (revised from that of Ziegler et al., 1997).
Figure 3.
Vediproductus mugenjin sp. nov. (UMUT PB30075). A. Outer mold of dorsal valve. B. Silicone rubber cast of A. Black arrowhead shows an ear. C. Inner mold of dorsal valve. D. Silicone rubber cast of C. E. Cross sectional view of outer surface in dorsal valve. Note the sawtooth outline (black arrowhead). F. Magnified outer surface of B. G. Magnified posterior inner surface of D. Note that two pairs of anterior and posterior adductor muscle scars (am and pm) are recognized near median septum (ms). H. Dorsal view of trilobed cardinal process as shown by three black arrowheads. I. Ventral view of H. J. Magnified right side of D. Note that the strainer spines (sp) become smaller in the anterior and lateral direction. Black arrow shows thin lateral ridge (Ir) vents antero-laterally. e: ear, Ir: lateral ridge, av: alveolus, am: anterior adductor muscle scar, pm: posterior adductor muscle scar, ms: median septum, my: myophore, sp: strainer spine.
Figure 4.
Vediproductus punctatiformis (A-H) and Vediproductus sp. (I–M). A. Outer mold of dorsal valve (UMUT PB30076). B. Silicone rubber cast of A. C. Magnified posterior surface of B. D. Magnified anterior surface of B. E. Inner mold of dorsal valve (UMUT PB30077). F. Silicone rubber cast of E. G. Magnified anterior inner surface of F. H. Magnified posterior inner surface of F. Note that two pairs of anterior and posterior adductor muscle scars (am and pm) are recognized bordering median septum (ms). I. Inner mold of ventral valve (UMUT PB30078). J. Magnified inner surface of I. K. Silicone rubber cast of beak in I. L. Lateral view of K. M. posterior view of K. am: anterior adductor muscle scar, pm: posterior adductor muscle scar, ms: median septum, m?: inferred muscle scar, sp: strainer spine, h: hinge.
Vediproductus punctatiformis Chao, 1927
Figure 4A-H
Echinoconchus punctatiformis Chao, 1927, p. 72, pl. 6, figs. 9–12; Zhan and Li, 1962, p. 477, pl. 2, fig. 9.
Vediproductus vediensis Sarytcheva in Ruzhentsev and Sarytcheva, 1965, p. 221, pl. 35, figs. 1–3; Feng and Jiang, 1978, p. 257, pl. 91, fig. 6.
Bathymyonia punctatiformis (Chao); Feng and Jiang, 1978, p. 256, pl. 90, fig. 10.
Vediproductus punctatiformis (Chao); Tong, 1978, p. 225, pl. 79, fig. 16; Zhao and Tan, 1984, p. 27, pl. 1, figs. 21–22; Chang, 1987, p. 759, pl. 2, fig. 4; Liang, 1990, p. 187, pl. 27, fig. 5.
Vedirpoductus sp., Campi et al., 2000, Fig. 4B; Campi et al., 2002, Fig. 6, G-I, L, O; Shen et al., 2002, p. 673, Fig. 3: 19–24.
Locality and age.—The locality yielding the specimens is on the forest road of Chaya-zawa creek (Loc. 3 in Figure 1). The stratigraphic horizon of the fossil occurrence correlates with that of V. mugenjin sp. nov. described above.
Material.—One external (Figure 4A, B, C, D: UMUT PB30076) and one internal (Figure 4E, F, G, H: UMUT PB30077) dorsal valve were collected.
Description.—The specimens had dimensions of 23.4 to 24.7 mm in length and 23.8 to 25.8 mm in width (Figure 4A, B, E, F). The dorsal valve and the dorsal disc are slightly semicircular in outline (Figure 4A, B, E, F). The dorsal valve is gently concave with a short trail. The outer surface in the posterior half of the dorsal disc possesses quincunxially arranged spine bases (Figure 4C), while that of the anterior dorsal disc and trail has concentric rugae, called spine bands, showing a ripple shape in longitudinal profile (Figure 4D). Each band is 0.6 to 1.5 mm in width. Double rows of recumbent spine-bases are quincunxially arranged on each band. The spines, about 300 µm in diameter, are radially directed.
The anterior half of the interior surface has concentric spine bands, while the posterior half accommodates with the muscle system and the median septum. The inner surface of the valve is wave-shaped, except for the muscle scars in cross-sectional view, which, as in the narrow spine bands, correspond to the exterior ripple shape (Figure 4G). A double line of strainer spines is quincunxially aligned on each band. These short spines exhibit a small conical shape whose apex slants anteriorly and is directed toward the interior surface of the ventral valve (Figure 4G). These spines become larger medially toward the anterior margin. The posterior five-spine bands are overlapped by the anterior half of the fairly thin median septum, which is tapered anteriorly (Figure 4E, F).
Two pairs of muscle scars are recognized on the lateral side of the median septum (Figure 4H). The muscle scars of the anterior pair are longitudinally elongate and elliptic in outline. The elliptic anterior scar exhibits several transversal furrows, which are adaxially diverged from the long axis of the elliptic outline. The surface of the posterior muscle scar is comparatively smooth but has several fairly shallow dimples.
Vediproductus sp. indet.
Figure 4I–M
Locality and age.—The specimen was collected from the skeletal grainstone of the Lower Kamiyasse Formation in the mountainside along the armlet of Shigeji-zawa (Loc. 2 in Figure 1).
Material.—One internal ventral valve (Figure 4Q, R, S, T, U: UMUT PB30078) was collected.
Description.—The ventral valve is more or less convex, but it is secondarily deformed from the dorso-ventral direction (Figure 4I). The specimen is 40.2 mm in length and 32.5 mm in width. The median sulcus is shallow and becomes wider and shallower anteriorly (Figure 4I). A narrow and small beak slightly overhangs the ginglymus dorsally (Figure 4J, K, L). The valve is covered by spine bands with comparatively strong relief and a wavy shape in a longitudinal section. Each band is 3 to 4 mm in width. Many delicate spine bases, possibly hairy spines originally, are arranged on the inner surface (Figure 4M). Each of them is 300 to 400 µm in diameter.
Remarks.—The valves are similar to Juresania, but a convex ventral valve whose surface is covered by spine bands of strong relief is identical to that of the genus Vediproductus (e.g., Brunton et al., 2000; Tazawa and Chen, 2006).
Time and space distribution of Vediproductus
Vediproductus has been reported from four provinces, Transcaucasus (Ruzhentsev and Sarytcheva, 1965), South and North China (e.g., Chao, 1927; Liang, 1990; Shen et al., 2002; Tazawa and Chen, 2006), and Malaysia (Campi et al., 2002). Among these occurrences, Vediproductus vediensis from the Transcaucasus and V. punctatiformis from Jiangxi and western Yunnan, south China, are known as older species, both being found from stratigraphic horizons older than the Roadian (see Figure 2: Middle Murgabian in the Tethyan stage). V. punctatiformis is also reported from the Capitanian of Southeast China and Malaysia (see Figure 2: Middle to Late Midian in the Tethyan stage). These fossil records indicate that the genus could be regarded as a new indicator of the Tethyan biota and as possibly indicative of a warm-water and warm-cool water transitional environment, as mentioned previously (e.g., Campi et al., 2002; Shen et al., 2002; Shi, 2006). Regardless of the small number of fossil records that have yet been discovered, these findings suggest the possibility that Vediproductus originated in an inner Tethyan province and radiated inside that province.
On the basis of the occurrence of Vediproductus, the Southern Kitakami Massif during the Permian appears to have been under a warmer water environment such as the Tethyan province and/or paleoequatorial area. Although such a rough conclusion is concordant with previous studies using other fossil organisms such as cephalopods and reef corals (e.g., Kawamura and Machiyama, 1995; Ehiro and Misaki, 2005), the brachiopod fauna reported in previous studies tell us that the paleogeographic and environmental interpretations are not so simply explained (e.g., Tazawa, 1999, 2002, 2003; Tazawa et al., 2000; Tazawa and Chen, 2006). The skeletal packstone and grainstone yielding Vediproductus sp. contains abundant remains of the oldhaminid brachiopod Leptodus, a well known indicator of a warm-water environment. Meanwhile, V. punctatiformis and V. mugenjin sp. nov. from the poorly sorted, fine-grained sandstone beds are accompanied by Waagenoconcha, indicative of a cool-water environment (e.g., Tazawa, 2001; Shen and Shi, 2004). This suggests that the faunal character of brachiopods presumably changed temporally in accordance with the change of sedimentary facies. Further work is needed to understand how the warm and cool faunas mixed in the Southern Kitakami region.
Acknowledgments
I gratefully acknowledge Kazushige Tanabe (University of Tokyo) for his supervision of this work and critical reading of the first draft. I thank Yutaro Suzuki (Shizuoka University) for his encouragement and for offering the opportunity to carry out field investigation. Aoi Sato and Kota Kitazawa kindly provided helpful suggestions. I thank the Board of Education, Kesennuma City, and Hideo Araki for helpful support of our investigations. I thank Guang R. Shi of Deakin University and Shuzhong Shen of the Chinese Academy of Sciences for their helpful comments and constructive suggestions. This study was supported by the Japan Society of the Promotion of Science, Research Fellowship for Young Scientists, and the COE Internship in 2007 granted to the Department of Earth and Planetary Science, University of Tokyo.
