RESEARCH ARTICLE
Hauterivian corals from Oshima Island (Japan) revised
2026 年 30 巻 p. 77-98
詳細
2026 年 30 巻 p. 77-98
The Hauterivian coral fauna of Oshima Island (Miyagi, Japan) is taxonomically revised on the basis of the type and additional materials. The fossil localities are no longer accessible. Sixteen species from 13 genera and seven families are described. Not all originally described species could be revised either because the type material could not be found or owing to the poor state of preservation of the corals. The coral fauna from Oshima shares most species with the species-rich Hauterivian coral fauna of the Paris Basin (France). Four genera undergo a range extension: Calamophylliopsis, ?Eohydnophora, Siderohelia and Palaeosiderofungia.
The earliest Cretaceous (Berriasian and Valanginian) was a time of falling sea level (Haq, 2014). The most recently deposited sedimentary rocks become exposed and are eroded as sea level falls, so coral faunas from this time are poorly known because they were effectively removed from the fossil record. Löser et al. (2021b) showed that the composition of coral faunas is comparable to that of the Latest Jurassic, but the reduction of the available area of shallow marine environments also reduced the richness in genera and led to the extinction or strong reduction of various families.
A remarkable sea-level rise at the beginning of the Hauterivian again resulted in the formation of large epicontinental seas (e.g. Husinec and Jelaska, 2006; Marzouk and Ben Youssef, 2008; Gréselle and Pittet, 2010). The basal Hauterivian marks the beginning of a faunal recovery and the origination of coral associations that were typical from the Early Cretaceous and persisted until the end of the Albian (Löser, 2016b; Löser and Callapez, 2022). Hauterivian coral faunas are well known, and most are rich in species despite being concentrated in certain areas and not distributed worldwide. Figure 1 shows the following Valanginian to Hauterivian coral faunas with more than 10 species reported in the literature (from west to east):
Jamaica—A Hauterivian coral fauna (18 species) was described by Löser et al. (2009).
Mexico—The coral faunas of the San Juan Raya Formation in Puebla were formerly assigned to the Aptian (Löser et al., 2013) but are stratigraphically older and have to be assigned to the upper Valanginian to lower Hauterivian (González León et al., 2015). This coral fauna is under revision.
Argentina—The upper Valanginian to Hauterivian coral faunas of the Neuquén Basin are under revision (Garberoglio et al., 2020, 2021, 2022).
Spain, Cazorla/Larga—The lower Valanginian coral fauna of the Sierra de Cazorla (51 species) was described by Löser et al. (2021b), and the coral fauna from the upper Valanginian to lower Hauterivian of the Sierra Larga in Murcia (34 species) was described by Löser et al. (2019a).
Spain, Catí—A Hauterivian coral fauna (14 species) was described by Götz et al. (2005).
France, Paris Basin—The lower Hauterivian coral fauna of Dept. Aube, Haute Marne, Yonne was first described by Fromentel (1857, 1862–1887) but never revised (Löser, 2013). This coral fauna is very rich in species and under revision.
Poland—The Hauterivian coral fauna of Wieliczka (12 species) was described by Morycowa (1964).
Bulgaria—A Kimmeridgian to Valanginian coral fauna (72 species for the whole section) was described by Roniewicz (2008).
Crimea—Hauterivian coral faunas from the Crimea area were described by Kuzmicheva (1960, 1966, 2002).
Georgia—Hauterivian coral faunas (48 species) were described by Sikharulidze (1985).
Japan, Oshima—The first coral species from Oshima was reported by Eguchi (1942), and a greater abundance of material was illustrated and described by Eguchi (1951) in his revision of Japanese Cretaceous corals. Eguchi described 18 species from Oshima, 17 of them as new (one species was not described and remains nomen nudum). Although he applied the use of thin sections, the Japanese species remained poorly known because of the poor printing quality of the 1951 monograph, and the absence of morphometric data that could make a comparison with materials from other areas possible. The aim of the present paper is to reevaluate these materials for the first time using modern comparative methods. The principal aim of the study is the comparison of the coral fauna from Oshima with other Hauterivian coral faunas, which are concentrated in two broad areas (the Eastern Pacific and the Tethys; Figure 1). The fauna from Oshima was located a great palaeogeographic distance from those areas, and the question is whether this is expressed in the faunal composition.
The Hauterivian corals all derive from the island Oshima in Kesennuma, Miyagi, Japan (Figure 2). The literature and specimen labels give three coral fossil localities on Oshima: Kazamatsu, Nagasawa and Yogai. Only the location of Yogai, which lies in the western part of the island, could be verified based on the literature and maps, so the other localities are not shown in Figure 2. The corals derive from the Yokonuma Formation of the Oshima Group, which belongs to the Karakuwa–Oshika sub-belt that mainly crops out on Oshima. The Yokonuma Formation is mainly composed of sandstone alternating with mudstone, rare limestone and tuffaceous sandstone (Moreno et al., 2016). The ammonite Crioceratites ishikawai (Yabe and Shimizu, 1926) constrains the age of the Yokonuma Formation to the Lower Hauterivian (Iba and Sano, 2007). The known outcrop area is now almost completely covered by buildings, and the former fossil bearing sites are no longer accessible. For this reason, no details on the sedimentology, microfacies, or other faunal elements could be determined. It is also unknown whether the coral association formed small reefs or mounds.
The studied material comes entirely from the Institute of Geology and Paleontology, Tohoku University Museum in Sendai, Miyagi (acronym IGPS). It encompasses the material studied by Eguchi (1942, 1951) and additional material. The Eguchi collection is not complete, with some of the type material missing (see Löser et al., 2002a, b for more details). The revision of the Japanese Cretaceous corals was originally envisaged to be realised by Irene Bugrova (St. Petersburg, Russia) during a research stay in 1999. Since this work never appeared after 25 years, I feel free to publish my own result.
The corals are poorly preserved. The fine skeletal structure is often not conserved. Corals without existing thin sections were polished, and more thin sections were prepared when preservation allowed. A total of 54 specimens were available for study, of which 17 are included in this study. All other specimens did not allow identification.
Thin sections were scanned by passing light through them using an Epson Photo Perfection 750 flatbed scanner with an optical resolution of 6,400 dpi. Some coral surfaces were scanned with reflected light with varying resolution. Scanned images were then transferred to grey scale bit maps. Their quality was amended by histogram contrast manipulation (contrast stretching) where possible using Aldus PhotoStyler 2.0.
To gain more insight into the intraspecific variation of fossil corals and obtain a better strategy for comparing species, calicular dimensions of each species were systematically measured from each thin section. To achieve statistical significance, the largest number of possible measurements was taken. This number was mainly determined by the size and quality of the thin section and the size of the single corallites in relation to the size of the thin sections.
For each type of measurement (calicular diameter and distance; width and distance of calicular row), the following values were obtained:
n number of measurements
min–max lowest and highest measured values
μ arithmetic mean (average)
s standard deviation
cv coefficient of variation according to K. Pearson
μ±s first interval
Thin sections were measured and values were calculated using the PaleoTax/Measure module of the Palaeontological Database System PaleoTax (version 1.8; https://www.paleotax.de/measure). For details on the mathematical background, see Löser (2012). Characters visible on the fossils were compared against characters on specimens in worldwide fossil coral collections, and an associated image database (29,240 specimens, 17,200 illustrated, located in the Estación Regional del Noroeste (ERNO), Sonora, Mexico). Data storage and processing were carried out using the PaleoTax database program (version 2.6; Löser, 2004).
To compare the studied fauna with other coral faunas, a computer database of about 3,600 Jurassic to Palaeogene coral localities worldwide was used. To simplify the analysis, localities of the same age and located in the same basin, on the same continental margin, or the same interoceanic platform were grouped together into one palaeo-province (a type of large faunule, sensu Johnson, 2007). Altogether, this produced 550 provinces. Only firmly dated localities were assigned to a province to ensure that the following analysis was valid, and the studied locality was not included in any existing province. For the study area, an independent province was created to allow a clear comparison between the existing provinces and the new material. Interregional comparisons were carried out between the new province and existing provinces having at least three species in common with the fauna of the studied area. For details, see also Löser (2008) and Löser and Minor (2007).
The preliminary classification system introduced in Löser (2016b) is used here. It does not apply suborders, but superfamilies that group families together. Practically, suborders are for the moment replaced by superfamilies. Twenty-seven superfamilies with 56 families (or informal groups) that have a range in the Cretaceous were distinguished. In contrast to the former classification system based on suborders, the superfamilies may constitute monophyletic groups. The basic characteristic that distinguished superfamilies is the size of the trabeculae relative to the septa. Further distinction was made based on the presence or absence of synapticulae and the septal perforation. A brief modern description of the morphology of the coral skeleton is provided by Löser et al. (2019b).
The distribution data (as reflected in the synonymy lists) are almost entirely based on well-examined material. Materials only mentioned in the literature, not available for study or insufficiently described and illustrated in the literature were not considered. To obtain better insight into the distribution patterns of the studied coral fauna, additional unpublished material was included. For example, this is the case for the Hauterivian corals from the Paris Basin: rich collections were brought together by the author and much material was examined using thin sections. Rich historically collected materials from San Juan Raya (Puebla, Mexico; upper Valanginian to lower Hauterivian) were also included. Therefore, distribution areas indicated under ‘Other occurrences’ may encompass more areas than reported in the synonymy lists.
The abbreviations used in the synonymy lists follow Matthews (1973): *, earliest valid publication of the species name; ?, the assignation of this description to the species is doubtful (so marked quotations are not reflected in the stratigraphic and palaeobiogeographic distribution); p, the described material belongs only in part to the species concerned; v, the specimen was observed by the author.
Collection abbreviations as follows: GPI, Geological Survey of India, Kolkata, India.
The following abbreviations are used describing the dimensions of the corals:
ccd, distance between calicular centres;
cdw, distance between calicular centres within calicular series;
clmax, large lumen;
clmin, small lumen;
cmax, larger outer calicular diameter;
cmin, smaller outer calicular diameter;
crd, distance of calicular series;
crw, width of calicular series;
md, distance between monticule in a hydnophoroid colony;
ml, length of monticules in hydnophoroid colony;
sd, density of septa (number of septa counted along a defined distance, such as two or five millimetres);
septa, number of septa in the adult corallite (in corals with a regular septal symmetry, the septa per septal cycle are given).
All measurements are given in millimetres, except septa and sd that are counts.
Order Scleractinia Bourne, 1900
Superfamily Cyclolitoidea Milne Edwards and Haime, 1849
Diagnosis.—Solitary and colonial corals. Septa either with regularly distributed perforations, with perforations only in certain parts of the septa, or almost compact. Septa generally thick, without notable symmetry (except Negoporitidae). Septa often connected to each other. Septal lateral faces with pennulae and thorns. Septal distal margin with large granulae. Both lonsdaleoid septa and main septum absent. Microstructure of large trabeculae. Synapticulae present. Pali in some genera probably present but difficult to distinguish from the perforated inner margins of the septa. Columella poorly defined. Endotheca present or absent. When present, mostly thin tabulae. Marginarium absent. Wall poorly developed. Coenosteum varies depending on the organisation type. Budding varies.
Family Dermosmiliidae Koby, 1889
Diagnosis.—Phaceloid corals. Septa occasionally with few perforations at their inner margins. Pennulae not very pronounced. Synapticulae present. Septa fuse together in the centre of the corallite to form a columella. Wall septothecal.
Genus Calamophylliopsis Alloiteau, 1952
Type species.—Calamophyllia flabellata Fromentel, 1861.
Diagnosis.—Phaceloid coral with parallel growing branches. Corallite outline elliptical. Septa almost compact, thicker in the centre and fused together to form a kind of columella.
Calamophylliopsis sp.
Material.—IGPS coll. cat. no. nn; one thin section.
Dimensions.—(IGPS coll. cat. no. nn)
cmin 5.6–6.9
cmax 6.7–9.1
septa 50
Description.—The available transverse thin sections correspond well to the diagnosis of the genus. The corallites are elliptical, the septa are nearly compact and fused in the corallite centre. A septal symmetry cannot be recognised.
Remarks.—This specimen probably came later into the IGPS collection; it has no collection number and was not mentioned by Eguchi (1951). It constitutes, for the moment, the last known occurrence of the genus. Younger material from the Cretaceous assigned in the literature to Calamophylliopsis belongs for the larger part to Latohelia Löser, 1987 (see discussion in Samaniego-Pesqueira et al., 2023).
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi).
Family Latomeandridae Fromentel, 1861
Diagnosis.—The family encompasses numerous solitary and colonial coral genera that show septa with perforations which are concentrated on the inner margin of the septa. The septa are thinner than in the Synastraeidae and less perforated than the Microsolenidae. The thickness of septa and the space between them is similar.
Genus Astraeofungia Alloiteau, 1952
Type species.—Astrea decipiens Michelin, 1846.
Diagnosis.—Thamnasterioid colony, with mostly only at the inner margin perforated septa, that differ hardly in length and thickness. The corallites are regularly distributed, generally not in rows, or only when juvenile. Costae run between all corallites. There is no wall.
Astraeofungia diversisepta (Hackemesser, 1936)
*v Thamnastraea diversisepta. Hackemesser, 1936, p. 48, pl. 6, fig. 5.
v Thamnasteria crespoi (Felix, 1891). Reyeros Navarro, 1963, p. 4, pl. 1, fig. 1, 4.
Material.—IGPS coll. cat. no. nn; one thin section.
Dimensions.—(IGPS coll. cat. no. nn)
n min–max μ s cv μ±s
ccd 6 6.53–8.25 7.19 0.65 9.0 6.55–7.84
septa 5 31–38 35.20 3.42 9.7 32–39
Description.—Thamnasterioid colony, with mostly only at the inner margin perforated septa, that differ hardly in length and thickness. The corallites are regularly distributed and do not form rows. Costae run between all corallites. There is no wall. The columella is poorly defined.
Remarks.—This specimen probably came later into the IGPS collection; it has no collection number and was not mentioned by Eguchi (1951).
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Kimmeridgian of the Central Tethys (Poland), Valanginian to Aptian of the Western Atlantic (Mexico), Hauterivian of the European Boreal (France), lower Albian of the Western Atlantic (Mexico) and the Western Tethys (Spain), upper Cenomanian of the European Boreal (Germany), Cretaceous of the Central Tethys (Greece).
Astraeofungia hieroglyphica (Stoliczka, 1873)
*v Thamnastrea hieroglyphica. Stoliczka, 1873, p. 41, pl. 8, fig. 5,
v Thamnasteria rikuzenica. Eguchi, 1951, p. 48, text-fig. 4, pl. 16, fig. 5.
v Astraeofungia hieroglyphica (Stoliczka, 1873). Löser and Wilmsen, 2023, p. 283, fig. 3.7–3.9 [here more synonymy].
Material.—IGPS coll. cat. no. 39732.
Dimensions.—(IGPS coll. cat. no. 39732, holotype of Thamnasteria rikuzenica)
ccd 4–6
sd 12/5 mm
septa 40–48
Remarks.—The original type specimen is cut into small pieces, which makes a comparison to the figure in Eguchi (1951) difficult. Thin sections could not be found, and from the remaining pieces alone corallite dimensions and septal counts could hardly be obtained. The above measurements were taken from the largest remaining piece of the type specimen. Moreover, the specimen is poorly preserved. It is not possible to give an updated description that would go beyond a generic diagnosis. The measurements compare very well with the holotype of Thamnastrea hieroglyphica (GPI, 1803).
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrence.—Tithonian to lower Berriasian of the European Boreal (Czech Republic), Valanginian to Aptian of the Western Atlantic (Mexico), upper Aptian to lower Albian of the Western Tethys (Spain), upper Kimmeridgian of the Central Tethys (Germany), lower Albian of the Western Tethys (Spain), upper Albian of the Southern Tethys (India), lower Cenomanian of the Western Tethys (Spain), upper Cenomanian of the European Boreal (Germany).
Astraeofungia nagaoi (Eguchi, 1951)
*v Kobya ragaensis var. nagaoi. Eguchi, 1951, p. 35, pl. 4, figs. 6, 7, pl. 6, figs. 6, 8, pl. 7, figs. 4, 5, pl. 10, figs. 6–8.
v Meandrarea nipponica. Eguchi, 1951, p. 51, pl. 16, figs. 9, 10.
v Fungiastraea cf. conferta (Milne-Edwards and Haime, 1849). Löser, 1994b, p. 64, text-fig. 51.
v Astraeofungia ragaensis var. nagoi (Eguchi, 1951). Löser and Ferry, 2006, p. 483, fig. 5.6.
v Astraeofungia siva (Stoliczka, 1873). Löser, 2014, p. 38, fig. 5k.
v Astraeofungia decipiens (Michelin, 1841). Löser, 2015, p. 281, fig. I.
v Astraeofungia sp. Löser et al., 2015, p. 55, fig. 6g–6i.
Material.—IGPS coll. cat. no. 39735; two thin sections.
Dimensions.—(IGPS coll. cat. no. 39735, holotype of Meandrarea nipponica)
n min–max μ s cv μ±s
ccd 10 3.50–5.49 4.43 0.67 15.1 3.76–5.10
septa 5 35–37 36.0 0.71 2.0 35–37
Description.—The small thin section shows closely spaced corallites with sub-confluent to confluent septa. The septa are connected to each other in the corallite centre and show only few perforations at their inner margins. The columella is styliform and small.
Remarks.—The specimen shown in Figure 3.6 is the holotype of Meandrarea nipponica Eguchi, 1951. The small thin section shows that the coral has almost compact septa and therefore cannot be referred to Meandrarea. Since the holotype of Kobya ragaensis nagaoi Eguchi, 1951 (IGPS coll. cat. no. 65320) is much better preserved than the present material, and since both specimens are conspecific, the specific epithet nagaoi is preferred. The sub species is elevated into the level of a species. Compared to the holotype of Kobya ragaensis nagaoi, the present specimen shows more sub-confluent septa due to the position where the thin section was taken: it is the margin of the colony where corallites are more closely arranged.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrence.—Tithonian to lower Berriasian of the European Boreal (Czech Republic), lower Hauterivian of the Western Tethys (France) and the European Boreal (France), upper Barremian of the Western Tethys (France), upper Aptian of the Western Pacific (Japan), lower Albian of the Western Atlantic (Mexico), Albian of the Western Tethys (Spain), upper Cenomanian of the European Boreal (France, Germany).
Genus Dimorphastrea Orbigny, 1850
Type species.—Dimorphastrea grandiflora Orbigny, 1850.
Diagnosis.—Thamnasterioid colony with corallites arranged in concentric rows. The colony surface is plane, the corallite centres may be slightly depressed. Septa are much more connected between corallites of neighboured rows than with corallites of the same row. No wall. Dimorphastrea is similar to Astraeofungia and juvenile colonies of Astraeofungia and Dimorphastrea are difficult to distinguish.
Dimorphastrea meandra (Orbigny, 1850) sensu Koby, 1898
v Thamnastraea maeandra. Koby, 1898, p. 80, pl. 18, fig. 1. 2.
v Thamnasteria cotteaui Fromentel, 1857. Turnšek and Mihajlovic, 1981, p. 35, pl. 39, figs. 1, 2.
Material.—IGPS coll. cat. no. 56506; two thin sections.
Dimensions.—(IGPS coll. cat. no. 56506)
n min–max μ s cv μ±s
crd 10 4.40–8.23 6.29 1.33 21.1 4.96–7.62
cdw 10 2.28–4.66 3.56 0.72 20.1 2.84–4.27
septa 8 19–25 21.25 2.38 11.2 19–24
Description.—The corallites form more or less regular rows around a central corallite (that is not visible in the thin section). The septa are confluent between corallites of neighboured rows but not between corallites of the same row. The septa are slightly perforated at the inner margins, but they are not connected to each other in the centre of the corallite. The columella is small and styliform.
Remarks.—When Koby (1898) described and illustrated Thamnasteria meandra, he clearly referred to Synastrea meandra Orbigny, 1850. Morycowa (1964) considered the material described by Koby different from Synastrea meandra Orbigny, 1850 and applied the species name with Koby as author. She was followed by several authors. A new name should be established for this group, but the Japanese material is too poorly preserved for that.
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi ).
Other occurrence.—Upper Kimmeridgian of the Central Tethys (Germany), lower Hauterivian of the European Boreal (France), Hauterivian to lower Aptian of the Central Tethys (France, Serbia), uppermost Aptian of the Western Tethys (Spain).
Genus Periseris Ferry, 1870
Type species.—Agaricia elegantula Orbigny, 1850.
Diagnosis.—Thamnasterioid coral with corallites arranged in rows. Septa run not only between neighbouring rows but also between corallites of the same row. Septa nearly compact, few in number. Columella styliform.
Periseris elegantula (Orbigny, 1850)
*v Agaricia elegantula. Orbigny, 1850, p. 293.
v Microsolena sp. Löser and Ferry, 2006, p. 484, fig. 5.7–9.
v Periseris? crassisepta (Sikharulidze, 1985). Löser, 2013, figs. 3, 5.
v Periseris elegantula (Orbigny, 1850). Löser et al., 2021b, p. 22, fig. 23.1–3.
Material.—IGPS coll. cat. no. 65384; one thin section.
Dimensions.—(IGPS coll. cat. no. 65384)
n min–max μ s cv μ±s
crd 8 2.93–4.51 3.71 0.56 15.1 3.15–4.26
cdw 8 1.89–3.04 2.39 0.40 16.6 2.00–2.79
septa 8 17–23 20.0 2.20 11.0 18–22
Description.—The corallites are arranged in irregular rows. The number of septa is low. The septa seem to be compact. The columella is large and styliform. The endotheca seems to be absent but the thin sections are poorly preserved and do not allow recognising fine structures.
Remarks.—The distance of corallite rows and septal counts compare well to the type material of Periseris elegantula.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Bajocian of the European Boreal (France), Tithonian of the Western Pacific (Japan), Kimmeridgian of the European Boreal (Germany), lower Valanginian of the Western Tethys (Spain), lower Hauterivian of the European Boreal (France), upper Barremian of the Western Tethys (France).
Family Microsolenidae Koby, 1889
Diagnosis.—Solitary and colonial (cerioid, hydnophoroid, meandroid, phaceloid, plocoid, thamnasterioid) colonies. Septa completely and regularly perforated. Interseptal space larger than or equal to septal thickness.
Genus Polyphylloseris Fromentel, 1857
Type species.—Polyphyllastrea convexa Orbigny, 1850.
Diagnosis.—A thamnasterioid coral like Microsolena, but the corallites are slightly erected and the coenosteum is more developed. Since the radial elements are running straight from the centre of the corallites, they are subconfluent. The trabeculae close to the centre of the corallites are inclined and, therefore, pennulae appear at the surface of the colony.
Polyphylloseris icaunensis (Orbigny, 1850)
*v Polyphyllastrea Icaunensis. Orbigny, 1850, (2), p. 94.
v Mastophyllia japonica Eguchi, 1951, p. 52, pl. 17, fig. 5.
v Polyphylloseris icaunensis (Orbigny, 1850). Bonilla González, 2015, p. 100, pl. 12, figs. 4–6.
v Polyphylloseris icaunensis (Orbigny, 1850). Samaniego-Pesqueira et al., 2023. p. 130, fig. 9A–C [here more more detailed synonymy]
Material.—IGPS coll. cat. no. 39729.
Dimensions.—(IGPS coll. cat. no. 39729, holotype of Mastophyllia japonica)
n min–max μ s cv μ±s
cmin 7 4.22–5.61 4.80 0.47 9.9 4.33–5.27
cmax 7 4.43–6.45 5.40 0.67 12.4 4.74–6.07
ccd 6 4.90–6.10 5.48 0.46 8.4 5.02–5.94
septa 4 47–52 49.5 2.38 4.8 47–52
Description.—The corallites are circular and well marked. The septa are regularly perforated. They are subconfluent between the corallites. The columella is not well defined; in some corallites a substyliform columella seems to exist.
Remarks.—The specimen shown here is the holotype of Mastophyllia japonica Eguchi, 1951.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Lower Hauterivian of the European Boreal (France), Hauterivian to Barremian of the Central Tethys (France), lower Barremian of the Western Tethys (France), lower Aptian of the Central Tethys (Greece) and the Western Tethys (Spain), middle Albian of the Western Atlantic (Mexico), upper Albian of the Western Tethys (Spain).
Superfamily Eugyroidea Achiardi, 1875
Diagnosis.—Colonial (cerioid, flabelloid, hydnophoroid, meandroid, phaceloid, plocoid) corals. Septa compact. Septal symmetry regular and in various systems, in size orders or irregular. Septa poorly ornamented. Microstructure poorly known, probably of small trabeculae. Lonsdaleoid septa only in the felixigyrids; main septa absent. Synapticulae and pali absent. Columella rare. Endotheca well-developed, generally as dense, thick, and regular tabulae. Marginarium absent. Wall compact and tabulothecal or septothecal formed by thickening of septa. Coenosteum and budding varies.
Family Eugyridae Achiardi, 1875
Diagnosis.—Colonial (cerioid, flabelloid, hydnophoroid, meandroid, or hybrid) corals. Septa in size orders. Columella rare. Wall compact and septothecal by thickening of septa.
Genus Eohydnophora? Yabe and Eguchi, 1936
Diagnosis.—The informal genus presents a structure identical with Eohydnophora but the crests are always conical. In Eohydnophora? the number of septa per crest can be counted and always results in a value of low variation. Conical and polygonal crests occur together only rarely.
Remarks.—Eohydnophora, based on E. tosaensis, is a hydnophoroid coral with polygonal crests. Material with conical crests was formerly assigned to Hydnophora, but this genus differs in many characteristics from similar Cretaceous material. For the moment, this material is, therefore, questionable and tentatively referred to Eohydnophora.
Eohydnophora? picteti (Koby, 1897)
v Lobophyllia Requienii Mich. Toula, 1877, p. 538.
*vp Hydnophora Picteti. Koby, 1897, p. 45, pl. 8, figs. 1, 2.
v Eohydnophora cf. picteti (Koby). Eguchi, 1951, p. 45, pl. 15, figs. 2–4.
v Eohydnophora picteti (Koby, 1897). Turnšek and Mihajlovic, 1981, p. 18, pl. 12, figs. 4–6.
v Eohydnophora picteti (Koby, 1896). Masse and Morycowa, 1994, p. 435, text-fig. 3, pl. 1, figs. 1–5.
v ?Eohydnophora picteti (Koby, 1896). Löser and Wilmsen, 2024, p. 75, fig. 3.8–3.9.
Material.—IGPS coll. cat. no. 65902; one thin section.
Dimensions.—(IGPS coll. cat. no. 65902)
n min–max μ s cv μ±s
ml 10 0.89–1.42 1.16 0.19 16.1 0.97–1.34
md 10 1.44–1.92 1.69 0.19 11.0 1.50–1.87
septa 10 6–10 8.50 1.27 14.9 7–10
Description.—The thick polygonal crests are closely spaced. The corallites are indistinct. The septa are thick and compact. There are possible remains of a lamellar columella. The endotheca is well preserved with thin, regularly spaced tabulae.
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi).
Other occurrence.—Lower Barremian of the Western Tethys (France), Barremian to lower Aptian of the Central Tethys (Switzerland, Serbia), Aptian of the Southern Tethys (China) and the Eastern Tethys (Iran), lower Cenomanian of the Western Tethys (Spain).
Remarks.—This material was collected from the Nagasawa locality, the whereabouts of which are unknown.
Genus Diplogyra Eguchi, 1936
Type species.—Diplogyra lamellosa Eguchi, 1936.
Diagnosis.—Meandroid coral with mostly straight rows. In places distinct corallites can be seen. A broad coenosteum is developed, so all corallite rows have their own walls. No columella.
Diplogyra sp.
Material.—IGPS coll. cat. no. 65901; one thin section.
Dimensions.—(IGPS coll. cat. no. 65901, paratype of Eugyra oshimaensis)
n min–max μ s cv μ±s
crw 6 1.60–1.95 1.81 0.15 8.2 1.66–1.96
crd 4 2.29–2.81 2.61 0.23 8.9 2.38–2.84
sd/2 mm 5 7–9 8.0 0.71 8.8 7–9
Description.—The corallite rows are parallel. There is a wide ambulacrum. The corallites are mostly indistinct; only in places corallites can be identified. The septa occur in two generations that differ in length and thickness. They are not connected to each other. No columella.
Remarks.—The specimen compares to D. arasensis (Alloiteau, 1946), but this species has larger dimensions and lower septal density.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Remarks.—Some of this material was collected from the Nagasawa locality, the whereabouts of which are unknown.
Genus Eugyra Fromentel, 1857
Type species.—Meandrina cotteaui Orbigny, 1850.
Diagnosis.—Meandroid colony with straight and parallel rows. Corallites indistinct. No coenosteum, no columella. Corallite rows share the wall.
Eugyra cotteaui (Orbigny, 1850)
*v Meandrina Cottaldina. Orbigny, 1850, (2), p. 94.
Eugyra cuyleri. Wells, 1932, p. 237, pl. 35, fig. 4.
v Eugyra oshimaensis. Eguchi, 1951, p. 45, pl. 15, fig. 5, pl. 16, fig. 12.
v Eugyra besavotrensis. Alloiteau, 1958, p. 111, pl. 17, fig. 4m pl. 25, fig. 1.
v Eugyra aff. digitata Koby, 1898. Morycowa, 1971, p. 56, pl. 9, fig. 2.
v Eugyra lanckoronensis (Morycowa, 1964). Turnšek and Buser, 1976, p. 13, 39, pl. 3, figs. 1–4.
v Eugyra cotteaui (d’Orbigny, 1850). Schöllhorn, 1998, p. 83, pl. 19, figs. 1–4, pl. 26, fig. 3.
v Eugyra pontica hydnophoroides Bendukidze, 1961. Baron-Szabo and González León, 2003, p. 200, fig. 5A.
v Felixigyra patruliusi patruliusi Morycowa, 1971. Baron-Szabo and González León, 2003, p. 199, fig. 5D.
v Pseudomyriophyllia carpathica Morycowa, 1971. Baron-Szabo and González León, 2003, p. 198, fig. 5H.
v Pseudomyriophyllia sp. 1. Löser, 2008, p. 46, pl. 2, fig. 8,
v Meandrina cotteaui Orbigny, 1850. Löser, 2016b, fig. E30a–d.
Material.—IGPS coll. cat. no. 39725-1; three thin sections.
Dimensions.—(IGPS coll. cat. no. 39725, holotype of Eugyra oshimaensis)
n min–max μ s cv μ±s
crw 15 1.11–1.59 1.41 0.13 9.1 1.28–1.54
crd 10 1.69–2.21 1.93 0.15 7.7 1.78–2.08
sd/5 mm 5 8–10 9.0 1.0 11.1 8–10
Description.—The coral shows long and parallel rows of corallites. Corallites can be only rarely distinguished. The septa occur in two generations and are not connected to each other. No columella.
Remarks.—The distance of corallite rows and septal density compares very well to the type material of Eugyra cotteaui. There are rarely isolated corallites visible.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Hauterivian to Albian, worldwide.
Superfamily Montlivaltioidea Felix, 1900
Diagnosis.—Solitary and (astreoid, cerioid, flabelloid, meandroid, phaceloid, thamnasterioid) colonial corals. Septa compact. Septal thickness regular, septa in an irregular radial symmetry, but septal generations can be distinguished. Septa not connected to each other. Septal lateral faces with vertical keels, upper margins with granulae. Lonsdaleoid septa and main septum absent. Microstructure of large trabeculae. Synapticulae absent. Pali rarely present. Columella in some genera, generally lamellar. Endotheca well-developed. Marginarium absent. Wall poorly defined, generally only with an epitheca. Coenosteum present, depending on the organisation form. Budding generally extracalicinal.
Family Montlivaltiidae Felix, 1900
Diagnosis.—The ornamentation of septal lateral faces is more pronounced in this family. Generally no columella.
Genus Dimorphocoenia Fromentel, 1857
Type species.—Dimorphastrea crassisepta Orbigny, 1850
Diagnosis.—Thamnasterioid colony with corallites arranged in rows. Often a central corallite exists. Septa in a low number. No columella.
Dimorphocoenia maxima (Eguchi, 1951)
vp Dimorphastraea rudis. Fromentel, 1886, p. 588, pl. 171, figs. 1, 2.
*v Thamnasteria maxima. Eguchi, 1951, p. 47, pl. 16, figs. 2–4.
Material.—IGPS coll. cat. no. 39731; one thin section.
Dimensions.—(IGPS coll. cat. no. 39731, holotype of Thamnasteria maxima)
n min–max μ s cv μ±s
crd 10 9.49–13.4 11.1 1.31 11.9 9.74–12.4
cdw 15 5.97–10.5 8.20 1.47 17.9 6.73–9.67
septa 8 24–29 26.3 1.91 7.3 24–28
Description.—The corallites are loosely arranged in rows. The septa are compact and not connected to each other. They are only running between neighboured rows, not between corallites of the same row. The septa generally occur in two generations. No columella.
Remarks.—The specimen cannot be assigned to Dimorphocoenia rudis because this species is based on two syntypes which vary in their dimensions and belong probably to different species. A lectotype has so far not been selected for D. rudis.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrence.—Lower Hauterivian of the European Boreal (France), uppermost Barremian of the Central Tethys (Bulgaria), lower Aptian of the Central Tethys (Greece), Aptian of the southern Tethys (China).
Superfamily Rhizangioidea Orbigny, 1851
Diagnosis.—Solitary and colonial (astreoid, cerioid, plocoid, reptoid, and thamnasterioid) corals. Septa almost not perforated. Normal septal thickness, septal symmetry regular radial or irregular, septa often and regularly connected to each other. Upper septal border and lateral faces with granulations. No lonsdaleoid septa, no main septum. Microstructure of medium-sized trabeculae. Synapticulae present. Pali absent. Columella present, styliform or by septal fusion. Endotheca present. Marginarium absent. Wall absent or present. Coenosteum depending on the colony type. Budding extracalicinal.
Family Rhizangiidae Orbigny, 1851
Diagnosis.—Astreoid, cerioid, plocoid, reptoid, and thamnasterioid colonies. The symmetry is regular or subregular radial in varying systems, or irregular. The columella is formed by septal fusion.
Genus Palaeosiderofungia Löser, 2016a
Type species.—Thamnasteria exigua Reuss, 1854.
Diagnosis.—Thamnasterioid colony where the corallites are arranged in rows. A septal symmetry does not exist. Columella small.
Palaeosiderofungia mabutii (Eguchi, 1951)
*v Meandrarea mabutii. Eguchi, 1951, p. 51, pl. 17, fig. 8.
v Palaeosiderofungia sp. 3. Löser, 2016a, p. 9, fig. 2f.
Material.—IGPS coll. cat. no. 65388; one thin section.
Dimensions.—(IGPS coll. cat. no. 65388, holotype of Meandraraea mabutii)
n min–max μ s cv μ±s
crd 5 3.70–4.90 4.36 0.43 9.9 3.93–4.79
cdw 5 2.41–4.86 3.36 0.98 29.1 2.38–4.34
septa 36–46
Description.—The corallites are embedded into a wide coenosteum. They form irregular rows. The confluent septa are nearly compact and connected to each other close to the centre of the corallites. There does not exist a septal symmetry. The columella is formed by septal fusion. Synapticulae are present, mostly in the space between the corallites.
Remarks.—The type specimen was originally attributed to the genus Meandraraea. The type specimen does not show pennulae (balcon-like ornamentations of the septal blades) and cannot be assigned to the Microsolenidae family. Moreover, there are almost no septal perforations. The amount of synapticulae and the septa connected in the corallite centre clearly assigns it to the Family Rhizangiidae (formerly Siderastraeidae).
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi).
Other occurrences.—Lower Aptian of the Central Tethys (Greece), Aptian of the Western Atlantic (Mexico).
Remarks.—This material was collected from the Kazamatsu locality, the whereabouts of which are unknown.
Genus Siderohelia Löser et al., 2021a
Type species.—Siderohelia aquilai Löser et al., 2021a
Diagnosis.—Phaceloid colony. Corallite circular to elliptical. Septa in a regular radial symmetry and varying systems. Younger septa attached to older septa in a regular plan. Costae short. Columella by septal fusion. Synapticulae rare, only close to the wall. Wall compact, septothecal. Endotheca absent.
Siderohelia sp.
Material.—IGPS coll. cat. no. 6004286#1; one thin section.
Dimensions.—(IGPS coll. cat. no. 6004286)
n min–max μ s cv μ±s
cmin 5 5.11–7.69 6.05 1.00 16.5 5.05–7.05
cmax 5 4.88–8.09 6.78 1.40 20.7 5.38–8.18
septa 4 39–44 41.5 2.38 5.7 39–44
Description.—Phaceloid colony with irregular circular corallites. The corallites are densely arranged and partly attached with their walls. Septa nearly compact, in an irregular decameral symmetry. The columella is formed by septal fusion.
Remarks.—This species in open nomenclature is characterised by a decameral septal symmetry. To date, it is the first known occurrence of the genus. The dense arrangement of the corallites that questions the phaceloid arrangement is typical for the genus (see the illustrations of the holotype of the type species in Löser et al., 2021a).
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi).
Superfamily Stylinoidea Orbigny, 1851
Diagnosis.—Solitary and colonial corals. Septa compact. Septal symmetry mainly regular, radial, or bilateral. First septal cycle (or cycles) generally thicker than later cycles. Septal lateral faces ornamented. Septal inner margins with auriculae. Lonsdaleoid septa present in two families. No main septa. Microstructure of small trabeculae. Synapticulae and pali absent. Columella present in two families. Endotheca well-developed. Marginarium absent. Wall compact, septothecal. Coenosteum present in some genera. Budding varies depending on the colony type.
Family Stylinidae Orbigny, 1851
Diagnosis.—Colonial (phaceloid, plocoid) corals. Septal symmetry radial, in varying systems, bilateral in one genus. Lonsdaleoid septa absent. Columella well-developed, styliform or lamellar.
Genus Enallhelia Milne Edwards and Haime, 1849
Type species.—Lithodendron compressum Goldfuss, 1829.
Diagnosis.—Plocoid colony growing in the form of branches which show corallites on only one face. Corallite outline circular. Symmetry of septa radial and regularly hexameral, rarely octameral. Pali absent. Costae present, non-confluent. Columella styliform. Endotheca consists of thin tabulae. Wall compact, probably septothecal. Coenosteum broad.
Enallhelia nipponica Eguchi, 1942
*v Enallhelia nipponica. Eguchi, 1942, p. 138, pl. 6, figs. 4–7.
v Enallhelia nipponica somaensis. Eguchi, 1942, p. 139, pl. 6, figs. 8–11.
v Enallhelia nipponica Eguchi. Eguchi, 1951, p. 44.
Material.—IGPS coll. cat. no. 39726, nn; seven thin sections.
Dimensions.—(IGPS coll. cat. no. 39726, holotype of Enallhelia nipponica)
n min–max μ s cv μ±s
clmin 7 0.87–1.25 1.03 0.14 13.5 0.90–1.17
clmax 1.4
septa 6+6
(IGPS coll. cat. no. nn)
n min–max μ s cv μ±s
clmin 15 0.85–1.22 1.06 0.11 10.8 0.95–1.17
clmax 15 0.89–1.59 1.32 0.20 14.8 1.12–1.52
ccd 12 1.31–3.87 2.49 0.85 34.1 1.64–3.34
septa 6+6
Description.—The coral formed densely packed dendroid colonies covered with corallites in a plocoid arrangement. Septa thin and compact, not connected to each other, with auriculae at their inner margins. Septal symmetry regularly hexameral with two septal cycles. Columella styliform and strong.
Remarks.—The species shows two septal cycles in a hexameral septal symmetry and the beginning of a third with a total of up to 18 septa. It never completes the third septal cycle. Enallhelia occidentalis Wells, 1944 shows three complete septal cycles.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Oxfordian to Tithonian of the Western Pacific (Japan), Kimmeridgian of the European Boreal (Germany), upper Kimmeridgian of the Central Tethys (Germany), lower Albian of the Western Atlantic (Mexico).
Remarks.—Some of this material was collected from the Nagasawa locality, the whereabouts of which are unknown.
Genus Stylina Lamarck, 1816
Type species.—Stylina insignis Fromentel, 1861.
Diagnosis.—Plocoid colony. Corallite outline circular. Symmetry of septa regular radial. Costae non-confluent. Columella styliform. Endotheca consists of thin tabulae. Wall compact, septothecal. Coenosteum broad, consisting of costae and exothecal dissepiments.
Stylina higoensis Eguchi, 1951
*v Stylina higoensis. Eguchi, 1951, p. 74, pl. 12, figs. 6–9.
*v Stylina higoensis Eguchi. Löser and Mori, 2002, p. 83, fig. 2.3 [here more synonymy].
Material.—IGPS coll. cat. no. 6004286#2.
Dimensions.—(IGPS coll. cat. no. 6004286#2)
n min–max μ s cv μ±s
clmin 4 0.57–0.74 0.67 0.07 11.1 0.59–0.74
clmax 4 0.98–1.11 1.04 0.06 5.4 0.98–1.09
septa 6+6
Description.—Plocoid colony with very small corallites. Septa thin, in a regular hexameral symmetry with two septal cycles. Auriculae at the septal inner margins. Columella styliform.
Remarks.—Stylina higoensis has smaller dimensions than Stylina japonica.
Occurrence.—Lower Hauterivian of Japan (Oshima, Kesennuma, Miyagi).
Other occurrences.—Callovian to lower Kimmeridgian of the Western Pacific (Japan), Kimmeridgian of the European Boreal (Germany).
Stylina japonica Eguchi, 1951
*v Stylina ? japonica. Eguchi, 1951, p. 46, text-figs. 2, 3, pl. 16, fig. 1.
v Stylina cf. regularis de Fromentel. Liao and Xia, 1994, p. 147, pl. 39, fig. 5.
v Stylina micropora Koby, 1896. Baron-Szabo et al., 2003, p. 208, pl. 36, figs. 1, 2.
v Stylina japonica Eguchi, 1951. Löser et al., 2019a, p. 281, fig. 11.4–6.
Material.—IGPS coll. cat. no. 39730; one thin section.
Dimensions.—(IGPS coll. cat. no. 39730, holotype of Stylina japonica)
n min–max μ s cv μ±s
clmin 15 0.78–1.11 0.93 0.11 11.9 0.82–1.04
clmax 15 1.08–1.41 1.27 0.11 8.7 1.16–1.38
ccd 15 1.10–2.13 1.66 0.33 20.2 1.33–1.99
septa 6+6
Description.—Plocoid colony with small corallites. Septa thin, in a regular hexameral symmetry with two septal cycles. Auriculae at the septal inner margins. Columella styliform.
Occurrence.—Lower Hauterivian of Japan (Yogai, Oshima, Kesennuma, Miyagi).
Other occurrences.—Upper Oxfordian to lower Kimmeridgian of the Central Tethys (Poland), lower Kimmeridgian of the Western Tethys (Spain), upper Kimmeridgian of the Central Tethys (Germany), Tithonian of the Western Pacific (Japan) and the Central Tethys (France), Berriasian to Valanginian of the Southern Tethys (China), upper Valanginian to lower Hauterivian of the Western Atlantic (Mexico), lower Hauterivian of the European Boreal (France) and the Western Tethys (Spain), lower Aptian of the Central Tethys (Greece), upper Aptian to Albian of the Eastern Tethys (Iran).
Table 1 compares the results of this study to the data on the corals from the Oshima area published by Eguchi (1951). However, the results are limited because several type specimens were not available and much of the material is poorly preserved.
| Eguchi, 1951 | Comments |
|---|---|
| Centrastrea japonica Eguchi, 1951 | Only the poorly preserved paratype IGPS 65389 is available that may belong to Ahrdorffia. |
| Enallhelia nipponica Eguchi, 1942 | = Enallhelia nipponica |
| Eohydnophora cf. picteti (Koby, 1897) | = Eohydnophora? picteti |
| Eugyra oshimaensis Eguchi, 1951 | = Eugyra cotteaui |
| Mastophyllia japonica Eguchi, 1951 | = Polyphylloseris icaunensis |
| Meandrarea mabutii Eguchi, 1951 | = Palaeosiderofungia mabutii |
| Meandrarea nipponica Eguchi, 1951 | = Astraeofungia nagaoi |
| Microsolena japonica Eguchi, 1951 | Type specimen not available. |
| Microsolena shimizui Eguchi, 1951 | Nomen nudum. Very possible an objective synonym of Microsolena japonica because it has the same type number. Type unavailable. |
| Microsolena subexcavata Eguchi, 1951 | Type specimen not available. |
| Rhabdophyllia osimaensis Eguchi, 1951 | Type material poorly preserved. |
| Stylina? japonica Eguchi, 1951 | = Stylina japonica |
| Thamnasteria cycloides Eguchi, 1951 | Type specimen not available. |
| Thamnasteria komagataensis Eguchi, 1951 | Type material poorly preserved. |
| Thamnasteria maxima Eguchi, 1951 | = Dimorphocoenia maxima |
| Thamnasteria protoserioides Eguchi, 1951 | Type material poorly preserved. |
| Thamnasteria rikuzenica Eguchi, 1951 | = Astraeofungia hieroglyphica |
| Trochosmilia? orientalis Eguchi, 1951 | Type material poorly preserved. |
Figure 7A shows the stratigraphic distribution of the species in the study area in other areas. It can be observed that there are less species that already occurred in the Jurassic, and more species that continued into the Lower Cretaceous.
As the stratigraphic distribution of the genera (Figure 7B) shows, there are four range extensions. The known last occurrence of the genus Calamophylliopsis was previously the Kimmeridgian (Upper Jurassic). Previous purported Cretaceous occurrences of Calamophylliopsis were misidentified (see Samaniego-Pesqueira et al., 2023), but the results of this study represent a true range extension into the Lower Cretaceous. The first appearance of ?Eohydnophora was extended from the upper Hauterivian to the lower Hauterivian. The first appearance of the genus Siderohelia was extended from the upper Barremian to the lower Hauterivian. The first appearance of Palaeosiderofungia was extended from the Aptian to the Hauterivian. All other species were already known in Hauterivian or older strata.
Figure 8 shows the correlation of palaeo-provinces (faunules) based on 16 species within the study area that have a distribution in other areas. Sixteen species for the study area is a very low number. Other Hauterivian coral faunas have many more species: the literature reports 159 species of lower Hauterivian coral from the Paris Basin (Löser, 2013), nearly 80 species from the Puebla Basin in Mexico (Löser, 2002; Löser et al., 2013), 48 species from Georgia (Sikharulidze, 1985), and nearly 80 species from the Crimea area (Kuzmicheva, 1960, 1966, 2002). The coral fauna from Oshima is probably more diverse than it seems, but the poor state of preservation precludes identification of all materials. Because of the low number of recognized species, the number of species shared with other faunas generally low, and no clear pattern could be observed. The very species-rich coral fauna of the Paris Basin (lowest Hauterivian) shares the highest number of species (eight out of 16) with the fauna from Oshima. Correlations with other areas are low. Correlations of other fossil invertebrate groups within the examined time period are unknown.
Except for the range extensions discussed above, the coral fauna from Oshima does not show any peculiarities. The generic inventory compares well to other coral faunas of the same age. For instance, the abundance of genera of the families Eugyridae (Diplogyra, Eugyra), Latomeandridae (Astraeofungia, Periseris), Microsolenidae (Polyphylloseris), Montlivaltiidae (Dimorphocoenia), and Stylinidae (Enallhelia, Stylina) compares well to the Hauterivian faunas from the Paris Basin and the Puebla Basin.
As already discussed by Löser et al. (2021b), there is no turnover from Jurassic to Cretaceous faunas. The change from Late Jurassic to Early Cretaceous coral faunas was a smooth transitional process that started with the reduction of taxonomic diversity during the Berriasian and Valanginian, times of a falling sea level. With the sea level rise during the Hauterivian, niches were quickly filled again. As pointed out by Löser et al. (2021b), the Early Cretaceous was not so much a time of recovery, it was more a time of an increasing number of taxa (Figure 9). Whereas the number of genera increased around 60% in the Aptian compared to the upper Berriasian, the number of families experienced an increase of 85%. This increase in the number of families is substantial. In comparison, 16 new families appeared from the Valanginian to the early Aptian. This increase continued through the Cretaceous (Löser, 2016b, fig. 6.1.5) and can be explained by several factors. Most probably, the Cretaceous corals are much better investigated than the Jurassic corals. During the past 50 years, there were 490 publications with taxonomy and illustrated material on Cretaceous corals (Löser, 1994a and later updates) but only around 350 publications on Jurassic corals. Whereas Cretaceous corals have been systematically revised (Löser, 2016b), Jurassic corals have not. Because they are older, more Jurassic faunas may have been eroded and lost than Cretaceous faunas. Because the global sea-level was higher during the Cretaceous than the Jurassic, a greater area was available for colonisation,which may have triggered the increase in diversity (also shown in Löser, 2016b, fig. 6.4.4B).
During a visit (October 1999–March 2000) as guest-professor at the Tohoku University Museum in Sendai, I had the opportunity to study the Mesozoic corals of the collection of Motoki Eguchi. I am very grateful for the invitation. During a second short visit in 2007, I was able to scan all thin sections. During both visits I received abundant support from the Tohoku University Museum staff, which is greatly acknowledged. I also thank my colleague Noritoshi Suzuki (Sendai) who supported my second visit. A grammatical check was carried out by Matthew Copley (Barcelona). Reviews by Ricardo Garberoglio, three anonymous reviewers, the editor in chief Yuta Shiino, and the associate editor helped improve the manuscript.
