THE FIRST RECORD OF THE ORECTOLOBIFORM SHARK GENUS CEDERSTROEMIA (ELASMOBRANCHII, ORECTOLOBIDAE) IN ASIA (KASHIMA FORMATION, UPPER CRETACEOUS; OYUBARI AREA, HOKKAIDO, JAPAN)

: We described fossil teeth assigned to the orectolobiform shark genus, Cederstroemia collected from the tuffaceous sandstone of the Kashima Formation (Santonian) in the Oyubari area, Hokkaido, Japan. This is the first report of fossil remains of Cederstroemia from Asia. Due to the small number of specimens and their poor preservation, we left the studied material in open nomenclature as Cederstroemia sp. At the same time, the studied material may belong to a new previously undescribed morphology of Cederstroemia . The occurrence of Cederstroemia fossils in Japan indicates that this genus dispersed to the northwestern part of the Pacific Ocean in the Late Cretaceous, which considerably extends the range and previously known

In recent decades, the Upper Cretaceous Yezo Group, which is broadly exposed on the Hokkaido Island, has become one of the most important units for studying and understanding the elasmobranch assemblages in the Northwest Pacific region during the Late Cretaceous.A number of elasmobranch taxa have been reported from these successions, including one hybodontiform, three ptychodontiforms, seven hexanchiforms, one squaliform, five lamniforms, and two echinorhiniforms (e. g.Goto et al. 1996;Tomita & Kurihara 2011;Kanno et al. 2017Kanno et al. , 2022)).
In the present paper, we describe in detail the first occurrence of the orectolobiform shark genus Cederstroemia in Asia, based on isolated teeth from the Santonian Kashima Formation (Yezo Group) in Yubari City, Hokkaido, Japan.
The studied Cederstroemia material from the Kashima Formation provides us with important information for discussing the paleogeography of the genus Cederstroemia and its dispersal process in the Late Cretaceous.

GeoloGIcal settInG
The tuffaceous sandstone bed where the fossils were obtained is exposed on the riverbed of the Shuparo River near Titose-cho, Kashima District, Yubari City (Fig. 1).This area has been submerged by a lake due to the completion of the Yubari Shuparo Dam in 2015.
The geologic exposures at the riverbed of the Shuparo River near Titose-cho, Kashima District, Yubari City consist of the Upper Cretaceous Kashima Formation.In the river bed around this area, a dark gray mudstone bed with an almost vertical inclination direction is exposed, and a turbidite tuffaceous sandstone bed with parallel lamination is observed.Fossils shark teeth, including Cederstroemia, were found in a dense bed of shell bioclasts contained in a medium-grained sandstone bed with a thickness of about 1 m.
The dense layer is about 20 cm thick and consists mainly of bivalves and small gastropods presumed to be species of Inoceramus, Ostrea, and Na-nonavis, and many glauconite particles less than 0.2 cm in diameter.It also contains sporadically flat mudstone pseudo-pebbles of 2-20 cm in length.
Fragments of Inoceramus are usually less than 5 cm in size, but include relatively large fragments identified as Inoceramus amakusensis Nagao et Matsumoto, 1940, which are more than 20 cm in rare cases.
Fossilized shark teeth are scattered in this dense layer and are mostly well preserved without significant wear.
The Kashima Formation, named by Motoyama et al. (1991), is mainly composed of dark gray massive mudstone that has undergone strong bioturbation with numerous tuff sandstone beds or tuff layers with a thickness of less than 1 m (Takashima et al. 2004(Takashima et al. , 2018)).
The age of the Kashima Formation has been the subject of debate for several decades (Motoyama et al. 1991;Toshimitsu et al. 1995;Takashima et al. 2004).Traditionally, the age of this formation is considered as Turonian to the Campanian based on microfossils (Takashima et al. 2004).However, a number of studies consider the age of the Kashima Formation as Coniacian (Yamada 2009), as Coniacian -Santonian (Tanaka et al. 2017), or as the Santonian-Campanian boundary (Matsui & Karasawa 2020).In addition, Kaneko et al. (2012Kaneko et al. ( , 2015) ) found I. amakusensis in rocks where fossilized shark teeth were collected, which has been correlated with the Santonian (Toshimitsu et al. 1995).Following this, we consider the age of the sedimentary rocks of the Kashima Formation exposed on the riverbed of the Shuparo River near Titose-cho, Kashima District, Yubari City where the described material was collected as Santonian.
According to Kaneko et al. (2012) the fossil-dense layer in which the shark teeth were discovered is considered to be an allochthonous fossil group assemblage, with transported shells and other materials entwined in turbiditic sandstone.Based on the benthic foraminiferal assemblages the depositional environment of the Kashima Formation reflects the upper part of the upper bathyal environment with medium-to relatively high-oxygen levels (Takashima et al. 2004).

MaterIal and Methods
All of the specimens documented here were collected from the riverbed of the Shuparo River basin in the Kashima district of Yubari City, Hokkaido (Japan).This collection consists of four specimens in total, each comprising a slightly damaged to incomplete tooth.All specimens (MCM-A2575 to MCM-A2578) are housed in the Mikasa City Museum.The topographical map of «Shuparo lake» scale 1:25000 published in 1989 by the Geospatial Information Authority of Japan.
Formic acid treatment was carried out in order to extract the specimens from the host rock.Formic acid was used in a fume hood after diluting 78% industrial grade (Mitsubishi Gas Chemical Co., Ltd.) into a 5-7% aqueous solution.Kaneko et al. (2015), Kaneko and Fujimoto (2022) were used as references for the process of treatment with formic acid.The main component of the gas generated during the acid treatment work is carbon dioxide, but it also contains trace amounts of harmful components such as sulfur dioxide, so it was discharged through a water tank as a trap.
Photographs of the specimens were taken with a Nikon D300S DSLR mounted with an 80-400 mm lens as an imaging lens and a Mitutoyo M Plan Apo 5X as an objective lens.Illustrative drawings, images of the specimens and graphics were prepared using the Combine ZM stacking software, NX Studio (Ver.1.3.2Nikon Corporation) and Adobe Photoshop CC 2017(v. 2017.04.25.r.252).
Description.The teeth have a maximum height of up to 2.75 mm and a width of up to 5.12 mm (in anterior tooth MCM-A2575).The teeth have a low cusp with high shoulders in MCM-A2575 and relative low shoulders in MCM-A2576-MCM-A2578.The cusps are slightly inclined distally.In comparison, the mesial shoulder is high and the distal shoulder is low.The cusp is thick labiolingually in lateral view and divided labiolingually by a clear cutting edge.The cutting edge does not form a blade.There are mesial and distal heels.The heels are very high and strongly inclined.There is a wide centrally located apron which extends beyond the base of the tooth root, with a missing lower part in MCM-A2575 and MCM-A2578.Both sides of the apron are concave in MCM-A2575 and rectangular in MCM-A2576-MCM-A2577 with slightly concave center of the apron's extremities.The enameloid of the crown is generally smooth, but in MCM-A2576 there are several rough, short, linear ornaments situated at the base of the lateral heels on lingual and labial sides (Fig. 3, 2c, 2f-g).An indistinct uvula that is not covered by enameloid from the lower center of the cusp to the end of the root.The root is thick in lingual view.Multiple lingual marginal foramina are situated between the border with the crown and the lingual protuberance, and a median lingual foramen opens at the lingual protuberance.The basal surface of the root is sub-rectangular, with a small centrally located foramen (hemiaulacorhize vascularization) and multiple small scattered foramina across the basal surface.
Remarks.The combination of morphological features of the fossil teeth described above allow us to attribute them to a species of Cederstroemia.The distinctive features of teeth of this genus are presented in detail below (see «Morphological features of Cederstroemia, Cretorectolobus and Squatina teeth» and Tab. 2).The specimens described here closely resemble the type material of late Campanian C. havreensis from Belgium and early Campanian C. nilsi from Sweden.Fossils of these chondrichthyan taxa are to date only known from Europe.C. havreensis mainly differs from C. nilsi in exhibiting a labial, rarely also lingual, ornamentation on the tooth crown, whereas C. nilsi is lacking any ornamentation on the crown (Guinot et al. 2013;Jambura et al. 2024, see «Distinctive features of the teeth of valid Cederstroemia species», and Tab.3).The available Cederstroemia material is limited to four incompletely preserved teeth, three of which are lacking any ornamentation and are similar to C. nilsi.However, some subtle features, including ornamentation, may have worn away on these teeth.In addition, one tooth (MCM-A2576) is similar to C. havreensis in that it has a linear ornamentation on the tooth crown (Fig. 3, 2f-g).At the same time, it may be a previously undescribed new Asian species of this genus.Further detailed studies may confirm or refute this hypothesis.Due to the small number of specimens and poor preservation, we tentatively left this material in open nomenclature.

Morphological features of Cederstroemia, Cretorectolobus and Squatina teeth
Squatina-type (Squatiniformes) morphology teeth have a main cusp that is triangular in labial view with lateral shoulders extending mesially and distally and with well-developed lateral heels, an apron on the labial side, a wide lingual protuberance, and a transversely elongated root with a flat and wide root base (Siverson 1995).This type is characteristic of the teeth of orectolobiform shark genera, Cretorectolobus and Cederstroemia in addition to those of the genus Squatina (Squatiniformes) (see Tab. 2).
Due to the high degree of similarity, teeth of Cederstroemia are often mistakenly attributed to the Squatina (e.g.Ebersole et al. 2022).This is particularly probable if fossil teeth come from the same locality, and it is highly likely that Cederstroemia tooth fossils are included in the reported Squatina tooth fossil record.Identification is possible, although extremely difficult, especially when considering incomplete specimens.
In the current paper we have summarized the data on the tooth characteristics of the three genera, Squatina, Cretorectolobus, and Cederstroemia, based on available literatures sources and personal observations.
The combination of features described below allows us to identify these taxa more confidently.In basal view, the root of the Squatina teeth are more often triangular to diamond-shaped with a clear central foramen on basal face.The root has a large depression from the center to the labial side with hemiaulacorhize vascularization but never holaulacorhize vascularization.The root of the Cretorectorobus and Cederstroemia teeth on the other hand is triangular to rectangular in shape, with holaulacorhize or hemiaulacorhize vascularization with a strongly oblique profile.The teeth of the Cederstroemia and Cretorectolobus have the low cusps, relatively high and more oblique lateral shoulders and more elongated and parallel-sided labial protuberance, whereas the cusps of the Squatina teeth is high and the lateral shoulders relatively low and straighter.In addition, some teeth of Cretorectorobus have lateral shoulders with cusplets.The cuspidate lateral shoulders are missing in Squatina and Cederstroemia teeth (Case 1978;Siveson 1996;Cappetta 2012;Guinot et al. 2012;Guinot et al. 2013;Siverson et al. 2016;Hoganson et al. 2019;Ebersole et al. 2022;Jambura et al. 2024).It should be underlined that a combination of a number of the characteristics listed above is required for reliable identification.

Distinctive features of the teeth of valid Cederstroemia species
As mentioned above, the genus Cederstroemia, consists of five valid species: Cederstroemia siverssoni, C. ziaensis, C. nilsi, C. triangulata and C. havreensis.However, with the exception of C. havreensis, which was described based on the examination of about one hundred fossil teeth, each description was based on a small number of specimens, including incomplete specimens.Consequently, identification is potentially open to consideration.
In this paper, we compared the morphological characteristics of the five species based on comprehensive literatures sources and personal observations and summarized their distinguishing features (see Tab. 3) that are described below.
Teeth of C. siverssoni and C. havreensis are large in size, with a maximum width of 13-15 mm, and their teeth have the vertical ridges on the lateral extremities of the lingual face of the heels or rarely also on the labial face in C. havreensis (Guinot et al. 2013).However, the maximum size of the other three species is less than 10 mm, and the crown surfaces of all tooth types are smooth (Siverson 1995;Bourdon et al. 2011;Guinot et al. 2013).Meanwhile the medio-lingual foramen of C. siverssoni is wide and oval, whereas the medio-lingual foramen of C. havreensis is small and round (Guinot et al. 2013).Additionally, teeth of the C. havreensis can be separated from C. siverssoni on the basis of their lingually oriented lateral extremities of the cutting edges, less densely arranged and less organized marginolingual foramina, more elongate lingual protuberance of the crown and generally more bulky and shorter apron (Guinot et al. 2013).Teeth of C. havreensis and C. nilsi closely resemble each other.Nevertheless, C. havreensis mainly differs from C. nilsi in exhibiting a labial, rarely also lingual, ornamentation on the tooth crown, whereas C. nilsi is lacking any ornamentation on the crown (Guinot et al. 2013;Jambura et al. 2024).Teeth of the C. triangulata and C. ziaensis have a basal face of the root that is subtriangular in outline with a straight labial bord, thereby differentiating this taxon from other species.However, in the teeth of C. ziaensis the cusp and mesial shoulders of lateral positions merge much more smoothly than those of C. triangulata or C. nilsi (Bourdon et al. 2011).
The variation of the root vascularization seems to be a poor character to distinguish species (Jambura et al. 2024).Nevertheless, we will briefly note this in order to have a comprehensive understanding of morphological features and variability.The holotype anterior tooth of C. havreensis is intermediate between the hemiaulacorhize and holaulacorhize stage, with a labiolingually very elongated central foramen (Siverson 1995).The root vascularization of C. triangulata is at the hemiaulacorhize or at the holaulacorhize, but the furrows are very deep, making it clearly distinguishable from the other four species.The root vascularization in C. nilsi teeth is characterized by a hemiaulacorhize stage in all teeth, with a small circular central foramen located slightly lingually of the center of the root (Siveson 1995).C. ziaensis has a hemiaulacorhize root in all specimens and a large central foramen located labially at the base of the tooth, whereas the other four species have numerous scattered foramina (Bourdon et al. 2011).

dIscussIon
Palaeobiogeographic implications and significance of the occurrence of Cederstroemia in the Asian North Pacific region.
There are still few reports of fossil occurrences for Cederstroemia, of which all previous reports were limited to Europe and North America (Fig. 4 and Tab. 1) forming many gaps in the spatiotemporal and geographical distribution of this genus.Fossil teeth of this genus have only been found at relatively high paleolatitudes between 30° and 65° north latitude, including the Anglo-Paris Basin (UK and France), the peri-Tethys sea (Ukraine, Russia), the Western Interior Seaway (New Mexico, Wyoming, Montana), and presently the Asian North Pacific (Japan) (e.g., Siverson 1995; Bourdon et al. 2011;Guinot et al. 2013;Ebersole et al. 2022;Solonin et al. 2023).In addition, the fossil teeth of Cederstroemia sp.described in this paper of this genus from Japan (Hokkaido) were discovered at approximately 43°N, and as mentioned above, the paleoenvironment between 30° to 65°N palaeolatitudes is suitable for this genus to live.The origin of this genus is unknown, but there are clues to its origin from the Anglo-Paris Basin to the peri-Tethys sea in Russian platform area.The oldest known fossils of this genus are from Albian of France (Grand Est), Ukraine (Cherkasy Oblast) and Russia (Kursk Oblast) (Guinot et al. 2013;Sokolsky & Guinot 2021;Solonin et al. 2023).The position of the epicontinental seas from the Anglo-Paris Basin to the western part of Russian platform area during the Late Cretaceous would have greatly favored a subsequent spread of elasmobranchs throughout the entire peri-Tethys (Amadori et al. 2022).In the Late Cretaceous Cederstroemia, like other elasmobranchs (e.g., Ptychodus), probably exploited this epicontinental seaway to migrate along the peripheral areas of the Neo-Tethys Ocean (e.g., Asian peri-Tethys) and to access the northwestern margin of the paleo-Pacific Ocean.At the same time, the dispersal of the fish fauna was not restricted exclusively to this route.Biogeographic trends for dispersal between northeast Asia and North America were previously reported for bony fishes (Cavin 2008).Therefore, the dispersal of elasmobranchs may have a similar biogeographic trend in the most favorable periods, when elasmobranchs could disperse between epicontinental seas of Northeast Asia and North America.This hypothesis though needs further detailed study and verification.
As previously reported by Kitamura (2019), the characteristics of the Late Cretaceous shark fauna of the Japanese Islands are similar to those of the contemporaneous Southern Hemisphere fauna (e.g.Angola, Australia, and Antarctica).Kitamura (2019)  tatus (Woodward, 1886), Chlamydoselachus sp.) had the opportunity to spread to the middle latitudes of the Northern Hemisphere by the Late Cretaceous (Kitamura 2019).At the same time, based on the currently available data, the north-south distribution of elasmobranchs faunas was not predominant and taxonomic coincidence between elasmobranchs fauna of the Japanese Islands and assemblages of elasmobranchs of the Southern Hemisphere is less pronounced.In particular, previous studies of elasmobranchs of the Japanese Islands (e.g.Goto et al. 1996;Kaneko et al. 2015Kaneko et al. , 2019;;Kanno et al. 2022) show a significant taxonomic overlap between the Upper Cretaceous elasmobranchs of Europe, North America and Japanese islands, which may indicate a practically unhindered dispersal between these regions of the Northern Hemisphere in the Late Cretaceous, meanwhile apparently in different directions.
Further detailed studies of marine faunas, including elasmobranchs, in Northeast Asia and in the whole paleo-Pacific region will help to clarify and improve our understanding of these events.

conclusIon
This report results from the examination of four fossil teeth recovered from the Kashima Formation (Santonian) of the Upper Cretaceous Yezo Group, Hokkaido, belonging to the orectolobid shark genus, Cederstroemia.This study represents the first report of the occurrence of this genus in Asia and in the Western Pacific region as a whole.Due to the small number of specimens and poor preservation, we left this material in open nomenclature as Cederstroemia sp.At the same time, the material described here may belong to a new previously undescribed morphology of Cederstroemia, although further materials is needed to test this hypothesis.
Following Cappetta (2012), Ebersole et al. (2022), andJambura et al. (2024), we currently consider Cederstroemia as belonging to the family Orectolobidae.The teeth of the orectolobid shark genera, Cretorectolobus and Cederstroemia are characterized by a Squatina-type morphology, which is observed in the squatiniform shark genus Squatina.Meanwhile, the teeth of the orectolobid shark genera Cederstroemia and Cretorectolobus differ from the teeth of Squatina in a number of distinctive features as a higher and more oblique lateral shoulder, much lower cusps, a strongly oblique root profile, and more elongated and parallel-sided labial protuberance.
Here, we have examined the distinctive features of five valid Cederstroemia species, although we identify problems with differentiating between certain species if in the absence of well-preserved material.
The Japanese Cederstroemia fossils record fills the gap between its European and North American contemporaries, further improving our understanding of the distribution of Cederstroemia in particular, and of elasmobranchs in general in the Late Cretaceous seas of the Northern Hemisphere.
Further sampling of the fossil teeth of Cederstroemia from Kashima Formation will improve and clarify the identification of the fossil material, including the one we described in the present paper.

Fig. 1 -
Fig. 1 -Geographic maps of Japan.Map A) map of Japan showing the location of the Yubari City (a black asterisk).Map B 1 ): map of the region around Yubari City showing the position of the studied locality where the fossils of Cederstroemia were collected. 1

Fig. 2 -
Fig. 2 -Dental terminology used for the morphological description of the teeth of Cederstroemia.The graphic drawings used here are modified from Cappetta (2012, fig.144ac) for A -C, and Siverson (1995, fig.2) for D, E.Not to scale.
concluded that the typical Southern Hemisphere shark taxa (e.g.Notidanodon den-Features C C. .s si iv ve er rs ss so on ni i C C. .n ni il ls si i C C. .h ha av vr re ee en ns si is s C C. .t tr ri ia an ng gu ul la at ta a C C. .z zi ia ae en ns si is s