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岩手県久慈市の上部白亜系久慈層群玉川層より 産出した板鰓類化石群の予察的検討 宮田真也 * ・平山 廉 ** ・中島保寿 *** ・前川 優 **** ・ 大倉正敏 ***** ・佐々木猛智 **** A preliminary report of elasmobranch fossils from the Upper Cretaceous Tamagawa Formation(Turonian-Santonian) , Kuji Group, Iwate Prefecture, Northeast Japan

Authors:

Abstract

Elasmobranch fossils have been found from the upper part of the Late Cretaceous Tamagawa Formation(Turonian- Santonian/Coniasian)of the Kuji Group, Iwate Prefecture, Northeast Japan. Teeth belonging to Cretoxyrhinidae(Cretalamna), Mitsukurinidae(Scapanorhynchus), Odontaspididae, and Sclerorhynchidae were identified. All of these elasmobranch fossils have been assumed to be marine species. However, it is thought that their habitat reached to the estuary environment, because the estimation of the sedimentary environment of the stratigraphic horizon of the fossils based on the sedimentary facies analysis is like that. The present study shows implications for the paleoecology of possible non-marine, brackish or euryhaline elasmobranchs from the North Pacific area in the Late Cretaceous.
[原著]
化石研究会会誌 JournalofFossilResearch,Vol.51(2),68-75(2019)
岩手県久慈市の上部白亜系久慈層群玉川層より
産出した板鰓類化石群の予察的検討
宮田真也・平山 廉**・中島保寿***・前川 優****
大倉正敏*****・佐々木猛智****
A preliminary report of elasmobranch fossils from the Upper Cretaceous Tamagawa
Formation(Turonian-Santonian), Kuji Group, Iwate Prefecture, Northeast Japan
ShinyaMiyata*,RenHirayama**,YasuhisaNakajima***,YuMaekawa****,
MasatoshiOkura*****andTakenoriSasaki****
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はじめに

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

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[原著]
      
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
岩手県久慈市の上部白亜系久慈層群玉川層より
産出した板鰓類化石群の予察的検討


A preliminary report of elasmobranch fossils from the Upper Cretaceous Tamagawa
Formation(Turonian-Santonian), Kuji Group, Iwate Prefecture, Northeast Japan


Abstract


CretalamnaScapanorhynchus

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

 
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

󰎪
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󰎪
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󰎪
 


化石産地および地質概説


  





 Fibulapollis  Aquillapollenites 

  



  

Inoceramus naumanni, Linuparus japonicus,
Texanites collignoni, Polyptychoceras subundulatum 

  


  

    

󰎪


   
    


図 1 .岩手県久慈市の久慈層群玉川層における板鰓類化石の産出地点.地質図は梅津ほか(2013)を改変.
󰐸󰐸
久慈層群の板鰓類化石
󰎪




          

 


SYSTEMATIC PALEONTOLOGY 古生物学的記載



󰎪








Cretalamna

Cretalamna


 

図 2 玉川層の模式柱状図(梅津ほか2013を改変).板鰓類化石は上位の中粒砂岩中のボーン
ベッドから産出した.ボーンベッドは河川―河口の堆積物であると考えられる.
󰐸󰐸
   







図 3 .岩手県久慈市の上部白亜系久慈層群玉川層より産出した板鰓類化石.
    1 . クレタラムナ属未定種 Cretalamna sp., OSD525.a 舌側面,b 唇側面,c 外
側面.
    スカパノリンクス Scapanorhynchus cf. raphiodon, OSD629.a 舌側面,b
唇側面,c 外側面.
    3 オオワニザメ科の一種 Odontaspididae gen. et sp. indet., OSD570.a 舌側
面,b 唇側面,c 外側面.
    4 .スクレロリンクス科の一種 Sclerorhynchidae gen. et sp. indet., OSD1380.
      a 頭側面,b 後側面,c 頭側面(CT 画像),d 背側面(CT 画像)e 後側面(CT
画像)CT 画像の撮影は東京大学総合博物館.
    5 .板鰓亜綱科属種未定.Elasmobranchii fam., gen. et sp. indet, KAM030.
   スケールバー= 5 mm( 1 , 1 mm(2-5).
󰐸󰐸









 C. appendiculata 
   C.
appendiculataC. sarcoportheta, C. borealis, C.
gertericorum, C. ewelli, C. hattini, C. deschutteri, C.
catoxodon 

 Cretalamna


Scapanorhynchus

Scapanorhynchusraphiodon

 




















 S. lewisii 
   S. texanus

S. rapax 
       
    S. raphiodon 


 S. raphiodon 


 S. raphiodon
 Sraphiodon 





 











 Odontaspis
aculeatus  Carcharias 











 


 



󰐸󰐸





Ischyrhiza iwakiensis 
Sclerorhynchus
   




Ischyrhiza I. schneideri, I.
texana, I. mira   
  

Micropristis
    



󰎪

󰎪

 




󰎪
議論
 Cretalamna
 Scapanorhynchusraphiodon

    




󰤂󰠭
    



Scapanorhynchus raphiodon     
         
 


  

󰎪
 Scapanorhynchus
raphiodon 

󰎪


󰎪


  
   

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
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謝辞

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
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
󰤂󰠭


引用文献

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󰐸󰐸

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Scapanorhynchus raphiodon
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󰎪
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Mitsukurina owstoni
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Muscites kujiensis
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




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     
 
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appen-diculata
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
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 Squalicorax 
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
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... Since 2010, a joint excavation of Kuji Amber Museum and Waseda University has been conducted at the bank of a tributary of Osawada river that is located about 70 m north of the amber digging experience site (Fig. 1). From this site, more than 2000 vertebrate fossils, including diverse freshwater turtles such as Adocus kohaku Hirayama et al., 2021, elasmobranch that belong to Cretalamna, Scapanorhynchus, Sclerorhynchidae, and Odontaspididae (Miyata et al., 2019), crocodilian, and dinosaurian fossils have been excavated. Sauropod teeth are the most abundant material among dinosaur remains recovered from this site. ...
... Sedimentary environments were estimated as fluvial to nearshore, nearshore to inner shelf, and fluvial for Tamagawa, Kunitan, and Sawayama Formations, respectively (Terui and Nagahama, 1995;Umetsu et al., 2013). Sauropod teeth studied here were excavated at the outcrop along the tributary of Osawada river ( Fig. 1), where the uppermost part of Tamagawa Formation has become exposed (Arimoto et al., 2018;Miyata et al., 2019;Umetsu et al., 2013). The uppermost Tamagawa Formation comprises conglomerate, sandstone, and amber-rich and tuff-intercalated siltstone. ...
... Sauropod teeth were excavated from a coaly mudstone bed, which is rich in amber and has a thickness of about 1 m (Umetsu et al., 2013). This mudstone bed is overlaid by a sandstone bed which frequently yields elasmobranch fossils (Miyata et al., 2019). An autochthonous tuff bed that changes its thickness horizontally exists between these sandstone and mudstone beds, from which radiometric age was determined (Fig. 2;Hirayama et al., 2021). ...
Article
Full-text available
Sauropod teeth from the Tamagawa Formation of Kuji Group, northeastern Japan, were described and diet of the Kuji sauropod was inferred by dental microwear texture analysis (DMTA). The morphology and slenderness index (SI) of Kuji sauropod teeth indicate they belong to a titanosauriform somphospondyli sauropod and thus confirm the existence of a titanosauriform sauropod at the coastal area of East Asia during the late Turonian. Dental microwear texture (DMT) of the Kuji sauropod is compared with extant lepidosaurs with known dietary preferences, indicating a higher degree of oral food processing in the Kuji sauropod than to extant lepidosaurs. The Kuji sauropod fed on materials less resistant and softer than molluscan shells or exoskeletons of insects and likely relied on plant materials. Considering paleoflora of the Tamagawa Formation, the most likely diet was ferns and gymnosperms. These initial results encourage future applications of DMTA to various sauropods, which could help to reveal the evolution of their feeding ecology and whether the increase of SI is associated with dietary change.
... Cretaceous locality in the Tamagawa Formation (Kuji Group), Iwate Prefecture, northeast Japan. This formation was already well known for amber, but has recently yielded a diversity of vertebrates including fishes, crocodilians, turtles, dinosaurs, and pterosaurs (Hirayama et al., 2010(Hirayama et al., , 2015(Hirayama et al., , 2021Miyata et al., 2019). Here we report the discovery of isolated choristoderan vertebrae from this locality, representing the first choristoderan record from the lower Upper Cretaceous of Asia. ...
... Of these localities, the Zhirkindek Formation in Kazakhstan is similar to the Tamagawa Formation, with several horizons that mark marine transgressions and yield vertebrates such as fish, squamates, turtles, salamanders, crocodilians, pterosaurs, and dinosaurs (Averianov et al., 2016). Some of these vertebrates are shared with the Tamagawa Formation, such as adocid turtles (Hirayama et al., 2010;2021), and the marine-to-brackishwater shark Scapanorhynchus (Miyata et al., 2019). In addition, the age of Zhirkindek Formation is considered to be Turonian (Nesov, 1993), similar to that of the Tamagawa Formation. ...
Article
Choristoderes are freshwater diapsid reptiles that are distributed through Laurasia in Jurassic–Miocene deposits. The group shows great diversity in the Early Cretaceous of Asia, with all recognized morphotypes recorded from that region. However, there is then a substantial gap in the Asian record until choristoderes are reported from the Paleocene of Kazakhstan. This gap has raised questions as to whether the group became extinct in Asia during the Late Cretaceous, with subsequent reinvasion from either North America or Europe. Here we report the discovery of vertebrae attributable to Choristodera indet. from the lower Upper Cretaceous (Turonian) of the Tamagawa Formation, Kuji City, Iwate Prefecture, Japan. This is the first record of Choristodera from the Upper Cretaceous of Asia, and may imply that the group persisted in this region from the Jurassic to the Paleocene. The challenge for the future will be to recover a more complete record of Choristodera in the Upper Cretaceous of Asia.
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