Hexasaturnalis nakasekoi nov. sp., a Jurassic saturnalid radiolarian species frequently confounded with Hexasaturnalis suboblongus (Yao)

Original article Hexasaturnalis nakasekoi nov. sp., a Jurassic saturnalid radiolarian species frequently confounded with Hexasaturnalis suboblongus (Yao) Hexasaturnalis nakasekoi nov. sp., une espèce jurassique de Radiolaires Saturnalidae confondue fréquemment avec Hexasaturnalis suboblongus (Yao) Paulian Dumitrica a,* ,b, Ruth Dumitrica-Jud a a Dennigkofenweg 33, 3073 Gümligen, Switzerland b Institut de Géologie et Paléontologie, UNIL, 1015 Lausanne, Switzerland Abstract Detailed morphological study of the ring of the Jurassic saturnalid radiolarian species frequently cited in the literature as Hexasaturnalis suboblongus (Yao) has proven that it contains two well-defined species: H. suboblongus (Yao), practically ranging within the boundaries of the Bajocian, and Hexasaturnalis nakasekoi nov. sp., ranging within the Bathonian–Kimmeridgian interval. The two species seem to be important stratigraphically because the transition from the former to the latter took place at or around the Bajocian/Bathonian boundary. The phyletic lineage Hexasaturnalis hexagonus (Yao) → H. inuyamaensis (Yao) → H. suboblongus (Yao) → H. nakasekoi nov. sp. → H. minor (Baumgartner) → Dicerosaturnalis angustus (Baumgartner) → D. dicranacanthos (Squinabol) is proposed. © 2005 Elsevier SAS. All rights reserved. Résumé L’étude morphologique détaillée de l’anneau de l’espèce de Radiolaire Saturnalidae jurassique fréquemment citée dans la littérature comme Hexasaturnalis suboblongus (Yao) montre qu’elle est composée de deux espèces bien définies : H. suboblongus (Yao), pratiquement limitée au Bajocien, et Hexasaturnalis nakasekoi nov. sp., dont l’extension recouvre l’intervalle Bathonien–Kimméridgien. Les deux espèces semblent être importantes du point de vue stratigraphique car le passage entre la première et la deuxième a eu lieu au voisinage de la limite Bajocien/Bathonien. La lignée phylogénétique Hexasaturnalis hexagonus (Yao) → H. inuyamaensis (Yao) → H. suboblongus (Yao) → H. nakasekoi nov. sp. → H. minor (Baumgartner) → Dicerosaturnalis angustus (Baumgartner) → D. dicranacanthos (Squinabol) est proposée. © 2005 Elsevier SAS. All rights reserved. Keywords: Jurassic; Radiolaria; Saturnalidae; New species; Systematics; Phylogeny Mots clés : Jurassique ; Radiolaires ; Saturnalidae ; Espèce nouvelle ; Systématique ; Phylogénie 1. Introduction This paper is part of an extended study of the Middle Juras- sic to Early Cretaceous Saturnalidae (Radiolaria) that was pre- sented during the INTERRAD VIII meeting held in Septem- ber 1997 in France (Dumitrica and Dumitrica-Jud, 1997) but not published as yet by present. Since this new species was frequently mistaken for other species in the literature and has an important stratigraphic value we considered that its sepa- rate description and morphological study deserve a special publication. Consequently, it was presented during the INTERRAD X meeting held in Lausanne (Dumitrica and * Corresponding author. E-mail address: [email protected] (P. Dumitrica). Revue de micropaléontologie 48 (2005) 159–168 http://france.elsevier.com/direct/REVMIC/ 0035-1598/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.revmic.2005.03.001 Dumitrica-Jud, 2003) and is described and discussed in extenso in the present article. Hexasaturnalis suboblongus (Yao) is one of the most cited saturnalid species in the Middle and Late Jurassic radiolarian assemblages. According to Baumgartner et al. (1995b) it is a rather long ranging species, its range encompassing the early– mid Bajocian to late Kimmeridgian–early Tithonian strati- graphic interval. Detailed morphological study of its ring has proven that the species, as considered until present by many authors, contains in fact two well-defined species: H. subob- longus (Yao), practically ranging within the boundaries of the Bajocian, and Hexasaturnalis nakasekoi nov. sp., rang- ing commonly within the Bathonian–Kimmeridgian interval. 2. Material The specimens studied for the present paper come from: (a) many localities of Callovian–Oxfordian radiolarites occur- ring in the Eastern Carpathians and Apuseni Mountains (Romania), Kimmeridgian to Lower Cretaceous rocks from Svinitza (SW Romania), many sections of Middle–Upper Jurassic and Lower Cretaceous radiolarian-bearing rocks from the Hawasina Basin (Guwayza, Sid’r, and Wahrah Forma- tions) (Oman) (Blechschmidt et al., 2004), Maiolica Forma- tion from Western Tethys (Switzerland and Italy), upper Bathonian–lower Callovian radiolarites of the Fonsazo For- mation (Belluno Trough, Vajont Dam, N Italy) (Baumgartner et al., 1995a), lower Bajocian limestone nodules from the Warm Springs Member of the Snowshoe Formation, Oregon (USA) (Pessagno et al., 1986), Bajocian manganese carbon- ate nodules from the Inuyama area, Mino Terrane of Central Japan (Yao, 1997), etc. All this material is to be found in the authors’ collection and was collected by the present authors or provided by some colleagues. The specimens illustrated in the literature (see synonymy list below) were also success- fully used. The specimens illustrated or only discussed in the present paper come from the following samples, mentioned in strati- graphic order: OR 555—Warm Springs Member, Snowshoe Formation. Reddish-brown weathering, dark-grey, fissile shale with dark- grey, micritic limestone nodules and lenticular masses of silty limestone. Limestone nodules commonly bear well-preserved Radiolaria dated as early Bajocian (Pessagno et al., 1986). The sample contains Hexasaturnalis hexagonus (Yao), H. suboblongus (Yao), H. tetraspinus (Yao), Hexasaturnalis sp. A of Yao (1997) (with eight spines, a species common in the Aalenian), and other saturnalid species which are out of the object of this paper. IN 7—Manganese carbonate nodule occurring in reddish siliceous mudstone along the Kiso River, east of Unuma, Kag- amigahara City, Gifu Prefecture, Japan (Yao, 1972, 1997). The radiolarian assemblage of this sample belongs to the Unuma echinatus Assemblage (Yao et al., 1980) and has been assigned to UAZ 3, dated as early–middle Bajocian (Yao and Baumgartner, 1995; Yao, 1997). Among other saturnalids the sample contains H. hexagonus (Yao), H. inuyamaensis (Yao), H. suboblongus (Yao), H. tetraspinus (Yao), and Hexasatur- nalis sp. A mentioned above under OR 555 (see Yao, 1997). IN 1—Same location and lithology as IN 7 but about 30 m above the latter (Yao and Baumgartner, 1995). The radiolar- ian assemblage of the sample belongs to the upper part of the U. echinatus Zone and was assigned to the UAZ 4, dated as late Bajocian (Yao and Baumgartner, 1995).Among other sat- urnalids the assemblage contains H. hexagonus (Yao), H. inuyamaensis (Yao), H. suboblongus (Yao), but no Hexasat- urnalis sp. A. (see Yao, 1997). P 621—Red radiolarian chert from the Umar Group, Oman, UTM 0668866/2497253. The sample was collected by Professor Tjerk Peters, Faculty of Geosciences, Univer- sity of Berne. It contains a poorly preserved radiolarian assem- blage that seems to be latest Bajocian–earliest Bathonian in age. Among other saturnalids it contains H. nakasekoi n. sp., H. suboblongus (Yao) and H. tetraspinus (Yao). Vda—Cherty limestone, Fonsazo Formation, Belluno Trough, N Italy (Baumgartner et al., 1995a). The sample was collected from the upper entrance of the road tunnel, next to the Chapel commemorating the catastrophe of theVajont Dam break. The assemblage contains well-preserved radiolarians and can be rather well correlated with the middle part of the listato member of the Fonsazo Formation from Southern Alps (Beccaro et al., 2002) that was assigned to UAZ 7 and dated as late Bathonian–early Callovian. Among other saturnalid species the radiolarian assemblage of the sample contains Dicerosaturnalis angustus (Baumgartner), Hexasaturnalis minor (Baumgartner), and H. nakasekoi n. sp. DR 20—Red radiolarite above the Middle Jurassic ophio- lites, Gomilelor Valley, Tamasesti village, Drocea Moun- tains, southern part ofApuseni Mountains, Romania. The radi- olarian assemblage suggests UAZ 7 and can be dated as late Bathonian–early Callovian. The saturnalids are represented by H. minor (Baumgartner) and frequent H. nakasekoi n. sp. G.17—Red radiolarite, Ghilcos Mt., Haghimas Syncline, Eastern Carpathians, Romania. The sample is part of the so-called Jasper Beds, and its radiolarian assemblage consist- ing of Archaeodictyomitra (?) amabilis Aita (UAZ 4–7), Cin- guloturris carpatica Dumitrica (UAZ 7–11), Eucyrtidiellum ptyctum (Riedel and Sanfilippo) (UAZ 5–11), E. unumaense (Yao) (UAZ 5–8), Gongylothorax sakawaensis Matsuoka (UAZ 6–7), Japonocapsa robusta (Matsuoka) (UAZ 5–7), etc., suggests a UAZ 7, dated as late Bathonian–early Call- ovian age. A single species—Striatojaponocapsa plicarum (Yao) (UAZ 4–5), occurring in this assemblage, would indi- cate an older age. The occurrence of this species would sug- gest either a reworking material or a longer range of this spe- cies. The saturnalids are represented in this sample by only H. minor (Baumgartner) and H. nakasekoi n. sp. SV 16—Radiolarian-bearing carbonate nodule, north of the old church, Svinitza village, Banat, SW Romania.Accord- ing to the radiolarian assemblage and ammonites, occurring several meters above, the age of the sample is early Kim- 160 P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 meridgian. The sample contains H. nakasekoi n. sp., H. minor (Baumgartner), and D. angustus (Baumgartner), but no D. dicranacanthos (Squinabol). POB 1205—Limestone concretion at the base of the Maiolica Formation, Cava Rusconi section, southwest of the small village Cittiglio at about 4 km southeast of the Lago Maggiore, Province Varese, Italy. The sample belongs to the UAZ 7 (Jud, 1994), dated as early Berriasian. It contains many early Cretaceous saturnalid species among which numerous D. dicranacanthos (Squinabol) and extremely rare frag- ments of H. nakasekoi n. sp. BR 860—Wahrah Formation, Wariegated Mudstone Mem- ber, Al Hammah Range, UTM 621930/2494940 (Blech- schmidt et al., 2004: Fig. 2/24, p. 107–108, Appendix). The assemblage, indicating an early Berriasian, contains also extremely rare specimens of H. minor (Baumgartner) sug- gesting that the range of this species should be extended up to this level. 3. Taxonomy Class RADIOLARIA Müller, 1858. Subclass POLYCYSTINA Ehrenberg, 1838, emend. Riedel, 1967. Order ENTACTINARIA Kozur and Mostler, 1982. Family SATURNALIDAE Deflandre, 1953. Subfamily HEXASATURNALINAE Kozur and Mostler, 1983. Genus Hexasaturnalis Kozur and Mostler, 1983. Type species: Spongosaturnalis (?) hexagonusYao, 1972. H. nakasekoi nov. sp. Pl. 1, Figs. 3–13; Pl. 2, Figs. 1–4, 7 and 8. 1978. Acanthocircus sp. cf. Spongosaturnalis (?) subob- longus Yao—Foreman, p. 744, Pl. 1, Fig. 8. 1981. Acanthocircus suboblongus (Yao)—Kocher, p. 52, Pl. 12, Figs. 4 and 5. 1985. Acanthocircus carinatus Foreman—De Wever and Miconnet, p. 383, Pl. 2, Figs. 7 and 8. 1986. A. suboblongus—Kishida and Hisada, Fig. 2/21. 1987. A. suboblongus (Yao)—Aita, p. 63, Pl. 8, Fig. 9. 1987. A. suboblongus (Yao)—Ozvoldova and Peterca- kova, p. 118, Pl. 31, Fig. 3. 1989. A. suboblongus (Yao)—Danelian, p. 132, Pl. 1, Figs. 12 and 13. 1990. Acanthocircus variabilis (Squinabol)—Yang and Wang, Pl. 2, Fig. 8. 1991. A. suboblongus (Yao)—Widz, p. 243, Pl. 1, Fig. 3. 1992. A. suboblongus (Yao)—Ozvoldova, Pl. 2, Fig. 2. 1993. Acanthocircus sp. aff. A. carinatus Foreman—Pessagno et al., p. 124, Pl. 2, Fig. 11. 1994. A. suboblongus Yao—Chiari, p. 382, Pl. 1, Figs. 3 and 4. 1994. A. suboblongus (Yao)—Aubrecht and Ozvoldova, Pl. 2, Fig. 2. 1995b. A. suboblongus minor Baumgartner n. ssp.—Baumgartner et al., p. 66, Pl. 3085, Fig. 4, non 1–3. 1995b. A. suboblongus suboblongus (Yao)—Baumgartner et al., p. 68, Pl. 3088, Fig. 1, non 2–4. 1995. A. suboblongus (Yao)—Kiessling, p. 269, Pl. 6, Fig. 21. 1996. A. variabilis (Squinabol)—Kozur et al., Pl. 4, Fig. 3, non 1. 1997. A. suboblongus suboblongus (Yao)—Chiari et al., Pl. 1, Fig. 2. 1997. A. suboblongus (Yao)—Hull, p. 31, Pl. 1, Figs. 16 and 20. 1997. ?Acanthocircus sp. aff. A. suboblongus Foreman (sic)—Hull, p. 31, Pl. 9, Fig. 19. 2001. A. suboblongus (Yao)—Hori, Pl. 5, Fig. 5. 2002. Hexasaturnalis sp. aff. H. suboblongus (Yao)—Beccaro et al., Pl. 3, Fig. 26. 2003. Acanthocircus cf. suboblongus (Yao)—Suzuki and Gawlick, p. 173, Fig. 6:11. 2003. Acanthocircus cf. suboblongus suboblongus (Yao)—Suzuki and Gawlick, p. 173, Fig. 5:8. 2003. H. nakasekoi Dumitrica and Dumitrica-Jud—Chiari et al., Pl. 1, Fig. 11. 2003. H. suboblongus (Yao)—Chiari et al., Pl. 1, Fig. 12. 2004. H. suboblongus suboblongus (Yao)—Chiari et al., Pl. 1, Fig. 8. 2004. H. suboblongus (Yao)—Beccaro, Pl. 2, Fig. 11. 2005. H. suboblongus ssp. A—Smuc and Gorican, Pl. 2, Figs. 3–5. Description: Ring elliptical with two spines at each end. All spines three-bladed but at each end, on the same face, the left spine shows two blades and the right spine one blade. This blade is thicker and usually shorter than the other two blades and results from the fusion of the external blade of the right portion of the ring with the external blade situated between the two spines. In order to fusion, the right portion of the ring twists slightly sinistrally so that the external blade becomes almost perpendicular to the plane of the ring. Simi- larly, the portion of the ring situated between the two spines twists in the same sense so that the external blade lies approxi- mately in the plane of the ring. As a result of this rotation and disposition of the blades the ring is not bilaterally symmetri- cal neither relative to the longitudinal nor to the transversal axis; it has symmetry of rotation of 180°, and the spines are similar along diagonals. Holotype: Plate 1, Fig. 5, coll. Musée Cantonal de Géolo- gie, Lausanne, No. 74391. Etymology: The species is named for Dr. Kojiro Nakaseko to honour his valuable contributions to the study of radiolar- ians of Japan. Dimensions: Length of ring without spines 320–420 µm, width of ring 205–275 µm. Remarks: H. nakasekoi nov. sp. was very frequently con- founded with H. suboblongus (Yao) (Plate 1, Figs. 1 and 2) because of the resemblance of the shape of the ring and of the similar number of spines. However, H. suboblongus has all spines four bladed and longer, its ring is usually slightly nar- rower, and the species is older than this new species. It 161P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 Plate 1. Figs. 1 and 2. H. suboblongus (Yao). 1, OR 555, × 115; 2, IN 7, × 115. Figs. 3–13. H. nakasekoi nov. sp., VDa, specimens with more or less sinistrally twisted spines. 3, holotype, × 130; 4, paratype, × 140; 5, same, slightly oblique view showing details of the morphology of spines, × 230; 6, paratype, × 170; 7, same, lateral view showing details of the morphology of spines, × 207; 8, oblique apical view of the spines of Fig. 9, × 183; 9, paratype, × 135; 10, paratype with very twisted spines and a specimen of Eucyrtidiellum cf. unumaense (Yao) attached to the ring, × 164; 11, same, apical view of spines, × 164; 12, same, oblique lateral view of ring, × 164; 13, paratype, × 164. Planche 1. Figs. 1 and 2. H. suboblongus (Yao). 1, OR 555, × 115 ; 2, IN 7, × 115. Figs. 3–13. H. nakasekoi nov. sp., VDa, exemplaires avec des épines plus ou moins torsadées. 3, holotype, × 130 ; 4, paratype, × 140 ; 5, même, détail, vue un peu oblique montrant la morphologie des épines, × 230 ; 6, paratype, × 170; 7, même, vue latérale, × 207 ; 8, vue apicale-oblique du paratype illustré dans Fig. 9, × 183 ; 9, paratype, × 135 ; 10, paratype avec des épines très torsadées et un exemplaire d’Eucyrtidiellum cf. unumaense (Yao) attaché à l’anneau, × 164 ; 11, même, vue apicale des épines, × 164 ; 12, même, vue latérale-oblique de l’anneau, × 164 ; 13, paratype, × 164. 162 P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 co-occurs usually with H. hexagonus (Yao) (UAZ 1–4) and partly with H. tetraspinus (Yao) (UAZ 1–6) (Yao, 1972, 1997; Wakita, 1982; Kishida and Sugano, 1982; Gorican, 1987; Kito, 1989; Yao and Baumgartner, 1995) and biostratigraphi- cally occurs in the U. echinatus Zone, correlative to UAZ 3 and 4 that practically comprise the whole Bajocian (Yao and Baumgartner, 1995). From A. carinatus Foreman (Aurisaturnalis carinatus according to Dumitrica and Dumitrica Jud, 1995) and A. vari- abilis (Squinabol), with which H. nakasekoi was sometimes confounded, it differs essentially in having the odd blade on the inner side of the ring, which is a characteristic of the sub- family Hexasaturnalinae (De Wever et al., 2001). Moreover, these two species are early Cretaceous taxa, the former appear- ing in the upper Hauterivian, the latter in the lower Valangin- ian. H. minor (Baumgartner) (Plate 2, Figs. 5, 11–18), origi- nally described as A. suboblongus minor Baumgartner (in Baumgartner et al., 1995b), is also a species very close to H. nakasekoi from which it differs in having the spines laterally flattened and H-shaped in transverse section, consisting of only one blade perpendicular to the plane of the ring and, sometimes, two narrow blades or a thickened margin on each face of the ring, especially on the proximal portion. Variability: In most cases the spines of H. nakasekoi nov. sp. are short, straight and pointed (Plate 2, Figs. 3, 4, 7 and 8). In some populations (samples) they are very short and highly divergent (Baumgartner et al., 1995b: p. 67, Pl. 3085, Fig. 4; similar specimens also occur in some Callovian– Oxfordian samples from the Drocea Mts., Romania), or rela- tively long and subparallel (Plate 2, Figs. 1 and 2). In some populations from the Fonsazo Formation (Vajont Dam, Bel- luno Trough, N. Italy) (Plate 1, Figs. 3–13) and from Oman most specimens may have sinistrally twisted spines and very high external blades between the two spines. Despite this populational variability, all specimens show the same three- bladed character of the spines and the same rotational sym- metry of 180° as mentioned above. This symmetry will be inherited by some species of the genus Dicerosaturnalis Dumitrica and Dumitrica Jud (in O’Dogherty, 1994; Dumi- trica et al., 1997). Evolutionary relationships: H. nakasekoi nov. sp. is part of a phyletic lineage H. hexagonus (Yao) → H. inuyamaen- sis (Yao) → H. suboblongus (Yao) → H. nakasekoi nov. sp. → H. minor (Baumgartner) → D. angustus (Baumgartner) → D. dicranacanthos (Squinabol) (Fig. 1). Along this lin- eage there was a trend toward elongated ring in a perpendicu- lar direction to polar rays and, as a consequence, a reduction of the spines situated at the two ends of the ring. A trend toward reduced number of blades of the spines from four to two took also place at a latter stage along this lineage. Hexa- saturnalis tetraspinus (Yao), a species co-occurring in the Bajocian with H. hexagonus, H. inuyamaensis and H. sub- oblongus, is not part of this lineage. It seems to have appeared in early–middle Aalenian according to Yao (1997) as a result of a trend towards widened ring. Its forerunner seems to have been the same as that of H. hexagonus as suggested by the late middle/early late Toarcian Mesosaturnalis sp. cf. M. sep- tispinus illustrated by Carter et al. (1988). Fossil record suggests that the reduction of the axial spine of the six-spined H. hexagonus started in late Aalenian (see Yao, 1997), and the first step along this lineage is represented by H. inuyamaensis (Yao), a species with two very short or practically absent axial spines but with a still broad ring. The disappearance of the axial spines of this species combined with the lengthening of the ring gave rise to H. suboblongus (Plate 1, Figs. 1 and 2), quite probably during the early Bajo- cian (see Yao, 1997). Fossil record proves that the latter spe- cies makes its first appearance in UAZ 3, dated as early–mid Bajocian (Baumgartner et al., 1995b). The morphology of the peripheral ring and the fossil record prove that H. nakasekoi appeared undoubtedly from H. sub- oblongus. The exact moment of this change is unknown at present because we found no continuous stratigraphic sec- tion where this evolutionary change could have been recorded. Most samples we studied, from Oman or from elsewhere, con- tain either only H. suboblongus, usually associated with H. hexagonus (Yao) and/or H. tetraspinus (Yao), or only H. nakasekoi. Usually, H. nakasekoi is single or associated with H. minor (Baumgartner) or/and D. angustus (Baumgartner) in the Bathonian–Kimmeridgian interval, depending on the sampled stratigraphic level. In several samples from Oman we found H. nakasekoi associated also with H. tetraspinus, and in a single sample (P 621) we found it associated with both H. tetraspinus and H. suboblongus. The latter case records, in our opinion, the oldest occurrence of H. nakasekoi, very close to the FAD of the species, which we situate around the Bajocian/Bathonian boundary or in the earliest Batho- nian. The former case we consider to be above the LAD of H. suboblongus, somewhere in the early or middle Bathonian taking into account that according to Baumgartner et al. (1995b) H. tetraspinus ranges up to the middle Bathonian (UAZ 6). Based on the morphology of its ring and the number of spines we consider that H. nakasekoi gave rise, at its turn, to H. minor (Baumgartner) (Plate 2, Figs. 5, 11–18). The type of spines of this latter species resulted from the continuation of the trend, manifested in H. nakasekoi, toward reduced num- ber of blades. If in the latter species only on a face of each spine the two blades are fused and reduced to one, in H. minor the blades of the spines are fused on both faces (Plate 2, Figs. 11 and 12). As a result, in face view all spines of H. minor resemble the upper margin of the right spine of H. nakasekoi. Moreover, the ring of H. minor is usually asym- metrical relative to a plane passing through the polar rays, one half being smaller than the other half. In this case the spines of the larger half are as described above whereas the spines of the smaller half still preserve, at least partly, the morphology of the spines of H. nakasekoi. This asymmetry of the spines is very clearly expressed with the specimen of H. minor illustrated by Pessagno (1977: Pl. 3, Fig. 6) as A. variabilis, and it also seems to exist with the holotype of H. 163P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 Plate 2. Figs. 1–4, 7 and 8. H. nakasekoi nov. sp., specimens with untwisted spines. 1, fragment of distal end of ring, POB 1205, × 145; 2, SV 16, × 87; 3, fragment of ring, DR 20, × 97; 4, fragment of distal end of ring, VDa, × 97; 7, fragment of distal end of ring with details of morphology of spines, face view, G 17, × 207; 8, same, oblique view showing the two external blades, × 207. Figs. 6, 9–13. H. minor (Baumgartner). 6, holotype, × 82; 9, normal specimen, SV 16, × 87; 10, specimen with only one spine at one end, SV 16, × 87; 11, fragment of distal end showing the two spines, face view, G 17, × 173; 12, same, oblique view, × 225; 13, specimen with only one spine at one end, VDa, × 97. Figs. 5, 14–20. D. angustus (Baumgartner). 5, 15–18, specimens with slightly twisted spines, VDa; 5, × 106; 15, × 101; 16, same, lateral view, × 101; 17, × 120; 18, same specimen, oblique view, × 120; 19, detail of spine, × 230; 20, same, oblique view, × 230; 14, specimen with untwisted spines, SV 16, × 87. Planche 2. Figs. 1–4, 7 and 8. H. nakasekoi nov. sp., exemplaires avec des épines droites (non torsadées). 1, fragment de l’extrémité distale de l’anneau, POB 1205, × 145 ; 2, SV 16, × 87 ; 3, fragment de l’anneau, DR 20, × 97 ; 4, fragment de l’extrémité distale de l’anneau, VDa, × 97 ; 7, fragment de l’extrémité distale de l’anneau avec des détails de la morphologie des épines, G 17, × 207 ; 8, même, vue oblique montrant les deux lames externes, × 207. Figs. 6, 9–13. 164 P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 minor (Plate 2, Fig. 6 of the present paper), although the left spine of the smaller half is covered by a radiolarian fragment. H. minor appeared probably very soon after the appear- ance of H. nakasekoi, in the middle Bathonian. We suppose that the record of its appearance in the early–mid Bajocian and the entire range of H. minor as mentioned in Baumgart- ner et al. (1995b), are wrong and resulted from a misdetermi- nation of this species in some of the samples included in the program Biograph to construct Unitary Associations. Its appearance in the early–mid Bajocian, before H. nakasekoi, is impossible because: (a) the morphology of its spines proves that H. nakasekoi is intermediate between H. minor and H. suboblongus, and (b) we never found this species associated with H. suboblongus that practically is a Bajocian species. H. minor (Baumgartner). 6, holotype, × 82 ; 9, exemplaire normal, SV 16, × 87 ; 10, exemplaire avec une seule épine à une extrémité, SV 16, × 87; 11, fragment de l’extrémité distale montrant les deux épines, G 17, × 173 ; 12, même, vue oblique, × 225 ; 13, exemplaire avec une seule épine à une extrémité, VDa, × 97. Figs. 5, 14–20. D. angustus (Baumgartner). 5, 15–18, exemplaires avec des épines faiblement torsadées, VDa ; 5, × 106 ; 15, × 101 ; 16, même, vue laté- rale, × 101 ; 17, × 120 ; 18, même, vue oblique, × 120 ; 19, détail de l’épine, × 230 ; 20, même, vue oblique, × 230 ; 14, exemplaire avec des épines droites, SV 16, × 87. Fig. 1. Dendrogram illustrating the approximate ranges and probable phylogenetical relationships between species along the phylogenetical lineage H. hexagonus– Dicerosaturnalis dicranacanthos. Fig. 1. Dendrogramme illustrant les extensions stratigraphiques approximatives et les relations phylogénétiques probables entre les espèces au long de la lignée phylogénétique H. hexagonus–Dicerosaturnalis dicranacanthos. 165P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 As regards the upper limit of the range of H. minor, it is con- sidered late Kimmeridgian–early Tithonian in Baumgartner et al. (1995b).Although this level is practically exact, it seems that the species still survived until the latest Tithonian–early Berriasian because we found extremely rare specimens of it in a sample from Oman (BR 860) having this age according to its radiolarian assemblage. H. minor is the last representative of the genus Hexasat- urnalis and the forerunner of the middle Bathonian–Albian genus Dicerosaturnalis Dumitrica and Dumitrica-Jud (in O’Dogherty, 1994; Dumitrica et al., 1997: p. 18). Dicerosat- urnalis differs from the former genus by only having a single spine at each end of the ring. The transitional position of H. minor results not only from its FAD relative to the FAD of the other species of Hexasaturnalis but also from its morphol- ogy, because it contains frequently specimens having at one end a single spine (evolutionary character) and at the other end two spines (atavistic character) (Plate 2, Figs. 10 and 13). The oldest species of the genus Dicerosaturnalis is D. angustus (Baumgartner) (Acanthocircus trizonalis angustus Baumgartner in Baumgartner et al., 1995b) that first appeared in the middle Bathonian (UAZ 6) according to Baumgartner et al. (1995b). This species has very broad spines in vertical plane, with thickened upper and lower margins, and in many populations, as for example in that from the Fonsazo Forma- tion (Plate 2, Figs. 5, 15–20), it has slightly sinistrally twisted spines with rather broad blades on both sides of the ring. In face view these twisted spines resemble the left spines of H. nakasekoi from which they differ in having the same shape on both sides (upper and lower) of the ring. This character is also exhibited by the holotype and paratypes (Baumgartner et al., 1995b: p. 71, Pl. 3082), both of Kimmeridgian age, proving that there is no structural difference between the older and the younger members of the species. This sinistral twist- ing will be inherited by Dicerosaturnalis dicranacanthos (Squinabol) and farther on by other few species of this genus. Range: According to Baumgartner et al. (1995b) H. nakasekoi nov. sp. [H. suboblongus suboblongus (Yao) in the cited publication] became extinct in the late Kimmerid- gian–early Tithonian. Without denying this extinction data it is to mention that we found a (reworked?) specimen of H. nakasekoi (Plate 2, Fig. 1) in the lower Berriasian sample POB 1205 from the Cava Rusconi section (see Jud, 1994: p. 16, for the position of the sample in the stratigraphic col- umn). In the interval of its range (Bathonian–late Kimmeridgian/early Tithonian) the species is one of the most common saturnalid. Occurrence: Cosmopolitan in the Tethys area. 4. Conclusions The morphologic study of the ring of the species fre- quently cited in the literature as H. suboblongus (Yao) has a systematic, biostratigraphic and evolutionary importance: (a) it allowed us the distinction of two successive and closely related species (H. suboblongus and H. nakasekoi) in what was considered until present a long-ranged species; (b) H. suboblongus becomes a rather good biostratigraphic indica- tor for the Bajocian; (c) H. nakasekoi has a longer range encompassing the Bathonian–Kimmeridgian interval, and the LAD of the former and the FAD of the latter species seems to correspond practically to the Bajocian/Bathonian boundary. Discrimination of these two species is very easy even in poorly preserved faunas because the distal fragments of their ring are easily determinable and usually sufficiently well- preserved; (d) H. nakasekoi nov. sp. becomes an evolution- arily intermediate species between H. suboblongus (Yao) and H. minor (Baumgartner). Acknowledgements The authors wish to thank Dr. Spela Gorican (Institute of Paleontology, Ljubljana, Slovenia) and Dr. Atsushi Mat- suoka (Niigata University, Japan) for reviewing the manu- script and valuable suggestions. References Aita, Y., 1987. Middle Jurassic to Lower Cretaceous radiolarian biostratig- raphy of Shikoku with reference to selected sections in Lombardy Basin and Sicily. Science Reports of the Tohoku University, Series 2. Geology 58, 1–91. Aubrecht, R., Ozvoldova, L., 1994. Middle Jurassic–Lower Cretaceous development of the Pruské Unit in the western part of the Pieniny Klippen Belt. Geologica Carpathica 45, 211–223. Baumgartner, P.O., Martire, L., Gorican, S., O’Dogherty, L., Erba, E., Pillevuit, A., 1995a. New Middle and Upper Jurassic radiolarian assem- blages co-occurring with ammonites and nannofossils from Southern Alps (Northern Italy). In: Baumgartner, P.O., O’Dogherty, L., Gori- can, S., Urquhart, E., Pillevuit, A., De Wever, P. (Eds.), Middle Jurassic to Lower Cretaceous Radiolaria of Tethys: Occurrences, Systematics, Biochronology. Vol. 23. Mémoires de Géologie, Lausanne, pp. 737–750. Baumgartner, P.O., O’Dogherty, L., Gorican, S., Dumitrica-Jud, R., Dumi- trica, P., Pillevuit, A., et al., 1995b. Radiolarian catalogue and systemat- ics of Middle Jurassic to Early Cretaceous Tethyan genera and species. In: Baumgartner, P.O., O’Dogherty, L., Gorican, S., Urquhart, E., Pille- vuit, A., De Wever, P. (Eds.), Middle Jurassic to Lower Cretaceous Radiolaria of Tethys: Occurrences, Systematics, Biochronology. Vol. 23. Mémoires de Géologie, Lausanne, pp. 37–685. Beccaro, P., 2004. Upper Jurassic radiolarians from Inici Mt. Area (north- western Sicily, Italy): biochronology and calibration by ammonites. Rivista Italiana di Paleontologia e Stratigrafia 110, 289–301. Beccaro, P., Baumgartner, P.O., Martire, L., 2002. Radiolarian biostratigra- phy of the Fonsazo Formation, Middle–Upper Jurassic, Southern Alps, Italy. Micropaleontology 48 (Suppl. 1), 43–60. Blechschmidt, I., Dumitrica, P., Matter, A., Krystyn, L., Peters, T., 2004. Stratigraphic architecture of the northern Oman continental margin– Mesozoic Hamrat Duru Group, Hawasina complex, Oman. GeoArabia 9, 81–132. 166 P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 Carter, E.S., Cameron, B.E.B., Smith, P.L., 1988. Lower and Middle Juras- sic radiolarian biostratigraphy and systematic paleontology, Queen Charlotte Islands, British Columbia. Geological Survey of Canada, Bul- letin 386, 1–109. Chiari, M., 1994. Radiolarian assemblage from ophiolite sequence of North- ern Apennines: 2-Sasso di Castro sections. Ofioliti 19, 377–395. Chiari, M., Baldanza, A., Parisi, G., 2004. Integrated stratigraphy (radiolar- ians and calcareous nannofossils) of the Jurassic siliceous sediments from Monte Kumeta (western Sicily, Italy). Rivista Italiana di Paleonto- logia e Stratigrafia 110, 129–140. Chiari, M., Bortolotti, V., Marcucci, M., Photiades, A., Principi, G., 2003. The Middle Jurassic siliceous sedimentary cover at the top of the Vouri- nos ophiolite (Greece). Ofioliti 28, 95–103. Chiari, M., Cortese, G., Marcucci, M., Nozzoli, N., 1997. Radiolarian biostratigraphy in the sedimentary cover of the ophiolites of south- western Tuscany, Central Italy. Eclogae geologicae Helvetiae 90, 55–77. Danelian, T., 1989. Radiolaires jurassiques de la zone Ionienne (Epire, Grèce). Paléontologie-Stratigraphie, implications paléogéographiques. Ph.D. Thesis (no. 89-25), Université Pierre et Marie Curie, Paris (unpublished). Deflandre, G., 1953. Radiolaires fossiles. In: Grassé, P.-P. (Ed.), Traité de Zoologie. Masson, Paris, pp. 389–436 1. De Wever, P., Dumitrica, P., Caulet, J.P., Nigrini, C., Caridroit, M., 2001. In: Radiolarians in the Sedimentary Record. Gordon and Breach Science Publishers, pp. 1–533. De Wever, P., Miconnet, P., 1985. Datations directes des radiolarites du bassin du Lagonero (Lucanie, Italie méridionale). Implications et con- séquences. Revista Española de Micropaleontología 17, 373–402. Dumitrica, P., Dumitrica Jud, R., 1995. Aurisaturnalis carinatus (Foreman), an example of phyletic gradualism among saturnalid-type radiolarians. Revue de Micropaléontologie 38, 195–216. Dumitrica, P., Dumitrica-Jud, R., 1997. 1997. Upper Jurassic and Lower Cretaceous Saturnalidae from Western Tethys. Abstracts INTERRAD VIII 1997. Eighth Meeting International Association of Radiolarian Paleontologists. Paris-Bierville 8–13, 48. Dumitrica, P., Dumitrica-Jud, R., 2003. Hexasaturnalis nakasekoi n. sp., a saturnalid radiolarian species usually confounded with Hexasaturnalis suboblongus (Yao). In: Diserens, M.-O., Jackett, S.-J. (Eds.), Abstracts and Programme. Tenth meeting of the International Association of Radi- olarian Palaeontologists, September 7–12, 2003. University of Lau- sanne, pp. 53–54. Dumitrica, P., Immenhauser, A., Dumitrica-Jud, R., 1997. Mesozoic radi- olarian biostratigraphy from Masirah Ophiolite, Sultanate of Oman. Part I: Middle Triassic, Uppermost Jurassic and Lower Cretaceous spumel- larians and multisegmented nassellarians. Bulletin of the National Museum of Natural Science 9, 1–106. Ehrenberg, C.G., 1838. Über die Bildung der Kreidefelsen und des Kreide- mergels durch unsichtbare Organismen. Abhandlungen der königlichen Akademie der Wissenschaften zu Berlin. Jahrg. 1838, 59–147. Foreman, H.P., 1978. Mesozoic Radiolaria in the Atlantic Ocean off the northwest coast of Africa, Deep Sea Drilling Project, Leg 41. In: Lance- lot, Y., Seibold, E., et al. (Eds.), Initial Reports of the deep Sea Drilling Project. Vol. 41. US Government Printing Office, Washington, DC, pp. 739–761. Gorican, S., 1987. Jurassic and Cretaceous radiolarians from the Budva zone (Montenegro, Yugoslavia). Revue de Micropaléontologie 30, 177–196. Hori, N., 2001. Triassic and Jurassic radiolarians from the chert–clastic sequence of the Takatori Unit in the Torinoko Block,Yamizo Mountains. News of Osaka Micropleontologists (NOM). Special 12, 159–180. Hull, D.M., 1997. Upper Jurassic Tethyan and southern Boreal radiolarians from western North America. Micropaleontology 43 (Suppl. 2), 1–202. Jud, R., 1994. Biochronology and systematics of Early Cretaceous Radi- olaria of the Western Tethys. Mémoires de Géologie, Lausanne 19, 1–147. Kiessling, W., 1995. In: Oman, Südalpen (Eds.), Palökologische Verwert- barkeit oberjurassisch-unterkretazischer Radiolarienfaunen mit Beispielen aus Antarktis. Universität Erlangen unpublished Ph.D. Kishida, Y., Hisada, K., 1986. Radiolarian assemblages of the Sambosan Belt in the western part of the Kanto Mountains, central Japan. In: Ichikawa, K. (Ed.), Recent Progress of Research on Radiolarians and Radiolarian Terranes of Japan. News of Osaka Micropaleontologists. pp. 25–34 Special Volume 7. Kishida, Y., Sugano, K., 1982. Radiolarian zonation of Triassic and Jurassic in outer side of southwest Japan. In: Nakaseko, K. (Ed.), Proceedings of the First Japanese Radiolarian Symposium. News of Osaka Micropal- eontologists, pp. 271–300 Special Volume 5. Kito, N., 1989. Radiolaires du Jurassiques Moyen et Supérieur de Sicile (Italie): Biostratigraphie et Taxonomie. Ph.D. Thesis (no 89-7), Univer- sité Pierre et Marie Curie, Paris (unpublished). Kocher, R.N., 1981. Biostratigraphische Untersuchungen oberjurassischer Radiolarien führender Gesteine, insbesondere der Südalpen. Mitteilun- gen aus dem geologischen Institut der Eidgenossischen Technischen Hochschule und der Universität Zürich. NF 234, 1–184. Kozur, H., Mostler, H., 1982. Entactinaria subordo nov., a new radiolarian suborder. Geologisch-Paläontologische Mitteilungen Innsbruck 12, 399–414 11/. Kozur, H., Mostler, H., 1983. The polyphyletic origin and the classification of the Mesozoic saturnalids (Radiolaria). Geologisch-Paläontologische Mitteilungen Innsbruck 13, 1–47. Kozur, H.W., Mock, R., Ozvoldova, L., 1996. New biostratigraphic results in the Meliaticum in its type area around Meliata village (Slovakia) and their tectonic and paleogeographic significance. Geologisch- Paläontologische Mitteilungen Innsbruck 21, 89–121. Müller, J., 1858. Über die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres. Abhandlungen der königlichen Akademie der Wissen- schaften zu Berlin. Jahrg. 1858, 1–62. O’Dogherty, L., 1994. Biochronology and paleontology of Mid-Cretaceous radiolarians from Northern Apennines (Italy) and Betic Cordillera (Spain). Mémoires de Géologie, Lausanne 21, 1–413. Ozvoldova, L., 1992. The discovery of a Callovian radiolarian association in the Upper Posidonia Beds of the Pieniny succession of the Klippen Belt (Western Carpathians). Geologica Carpathica 43, 111–122. Ozvoldova, L., Petercakova, M., 1987. Biostratigraphic research of Upper Jurassic limestones of the Cachtice Carpathians (locality Bzince pod Javorinou). Zapadné Karpaty, Seria Paleontologia 12, 115–124. Pessagno, E.A., 1977. Upper Jurassic Radiolaria and radiolarian biostratig- raphy of the California Coast Ranges. Micropaleontology 23, 56–113. Pessagno, E.A., Blome, C.D., Dull, D.M., Six, W.M., 1993. Jurassic Radi- olaria from the Josephine ophiolite and overlying strata, Smith River subterrane (Klamath Mountains), northwestern California and south- western Oregon. Micropaleontology 39, 93–166. Pessagno, E.A., Whalen, P.A., Yeh, K.-Y., 1986. Jurassic Nassellariina (Radiolaria) from North American geologic Terranes. Bulletins of American Paleontology 91, 1–75. Riedel, W.R., 1967. Subclass Radiolaria. In: Harland, W.B., et al. (Eds.), The Fossil Record. Geological Society of London, Burlington House, Lon- don, pp. 291–298. Smuc, A., Gorican, S., 2005. The Jurassic evolution of carbonate platform into a deep-water basin, Mt. Mangart (Slovenian–Italian border). Rivista Italiana di Paleontologia e Stratigrafia 111 (in press). Suzuki, H., Gawlick, H.-J., 2003. Biostratigraphie und Taxonomie der Radi- olarien aus den Kieselsedimenten der Blaa Alm und nördlich des Loser (Nördliche Kalkalpen, Callovium–Oxfordium). Mitteilungen der Gesellschaft der Geologie und Bergbaustudenten in Österreich 46, 137– 228. Wakita, K., 1982. Jurassic radiolarians from Kuzuryo-ko-Gujo-hachiman area. In: Nakaseko, K. (Ed.), Proceedings of the First Japanese Radiolar- ian Symposium. News of Osaka Micropaleontologists, pp. 153–171 Spe- cial Volume 5. Widz, D., 1991. Les Radiolaires du Jurassique supérieur des radiolarites de la zone des Klippes de Pieniny (Carpathes occidentales, Pologne). Revue de Micropaléontologie 34, 231–260. 167P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 Yang, Q., Wang, Y.J., 1990. A taxonomic study of Upper Jurassic radiolar- ians from Rutog county, Xizang (Tibet). Acta Micropaleontologica Sinica 7, 195–218. Yao, A., 1972. Radiolarian fauna from the Mino Belt in the northern part of the Inuyama area, Central Japan. Part I: Spongosaturnalids. Journal of Geosciences, Osaka City University 15, 21–65. Yao, A., 1997. In: Faunal change of Early–Middle Jurassic radiolarians. Proceedings of the Fifth Radiolarian Symposium. News of Osaka Micro- paleontologists, pp. 155–182 Special Volume 10. Yao, A., Baumgartner, P.O., 1995. Radiolarian occurrence data from the Middle Jurassic manganese carbonates of the Inuyama and Kamiaso areas, Japan. In: Baumgartner, P.O., O’Dogherty, L., Gorican, S., Urqu- hart, E., Pillevuit, A., De Wever, P. (Eds.), Middle Jurassic to Lower Cretaceous Radiolaria of Tethys: Occurrences, Systematics, Biochronol- ogy. Vol. 23. Mémoires de Géologie, Lausanne, pp. 967–976. Yao, A., Matsuda, T., Isozaki, I., 1980. Triassic and Jurassic radiolarians from the Inuyama area, central Japan. Journal of Geoscience, Osaka City University 23, 135–154. 168 P. Dumitrica, R. Dumitrica-Jud / Revue de micropaléontologie 48 (2005) 159–168 Hexasaturnalis nakasekoi nov. sp., a Jurassic saturnalid radiolarian species frequently confounded with Hexasaturnalis suboblongus (Yao) Introduction Material Taxonomy Conclusions Acknowledgements References