Elasmobranch fauna from the upper most part of the Cretaceous Bagh Group, Narmada valley, India

• Published in: The island arc 2017-09, Vol.26 (5), p.n/a
• Main Authors: Prasad, Guntupalli V. R., Verma, Vishal, Sahni, Ashok, Lourembam, Ranjit S., Rajkumari, Priyadarshini
• Format: Article
• Language: English
• Subjects: Bagh Group; Composition; Cretaceous; Cretalamna; Cretodus; Cretodus crassidens; Elasmobranchii; Fauna; India; Limestone; Marine animals; Marine fishes; Marine molluscs; Narmada valley; New records; Ptychodus; Sandstone; Scapanorhynchus; Scapanorhynchus raphiodon; Sedimentary rocks; Sequencing; Sharks; Squalicorax; Squalicorax falcatus; Teeth; Valleys
• ISSN: 1038-4871; 1440-1738
• DOI: 10.1111/iar.12200

In India, Cretaceous elasmobranchs are known from the uppermost Cretaceous Deccan intertrappean sedimentary sequences of peninsular India and the lower Upper Cretaceous (Cenomanian) Karai Formation of the Cauvery basin, South India. The intertrappean elasmobranchs are represented mainly by rays and skates, whereas the Karai fauna is known by hexanchiform, squaliform, and lamniform sharks. The latter assemblage is dominated by cool temperate water forms in addition to some cosmopolitan forms. Here new shark teeth recovered from the upper part of the marine Cretaceous Bagh Group, in the lower Narmada valley, Western India are described. This is the first detailed description of sharks from the Bagh Group and the first record of sharks from the youngest horizons (Coniacian to Late Maastrichtian) of this marine sedimentary sequence. The fauna, recovered from an oyster shell‐rich green sandstone at the top of the youngest geological unit (the Coralline Limestone) of the Bagh Group, is assigned to Ptychodus sp., Scapanorhynchus sp. aff. S. raphiodon (Agassiz, 1844), Cretodus sp. aff. C. crassidens (Dixon, 1850), Cretalamna sp., Squalicorax sp. aff. S. falcatus Agassiz, 1843, and Elasmobranchii indet. This assemblage, previously widely documented from the Cretaceous deposits of North and South Americas, Europe, North and West Africa, Far East and Near East, demonstrates that there is a clear change in elasmobranch faunal composition of India from cool temperate water forms in the early Late Cretaceous to essentially cosmopolitan forms in the Late Cretaceous. インドの白亜紀サメ類は, インド半島デカントラップ挟在層の最上部白亜系とインド南部のカーヴィリ堆積盆の上部白亜系下部(セノマニアン)カライ層から知られている. デカントラップ挟在層のサメ類は主にエイ, ガンギエイで特徴付けられるのに対し, カライ層フォーナではカグラザメ目, ツノザメ目, ネズミザメ目が知られている. 後者のフォーナでは, いくつかの汎世界的な種類に加えて, 冷温帯水域の種が卓越する. この論文ではインド西部ナルマダ川下流域の海成白亜系バグ層群上部から採取されたサメ類歯化石について報告する. 本論はバグ層群からのサメ化石の初となる詳細な記載であり, この海成層の最も新しい層準(コニアシアンからマストリヒシアン後期)からの最初のサメ化石記録である. バグ層群最上位層準のユニット(サンゴ石灰岩)の最上部にある カキ殻多産緑色砂岩から採取されたフォーナからは, Ptychodus sp., Scapanorhynchus sp. aff. S. raphiodon (Agassiz, 1844), Cretodus sp. aff. C. crassidens (Dixon, 1850), Cretalamna sp., Squalicorax sp. aff. S. falcatus Agassiz, 1843と板䚡亜綱の不明種に同定された. この群集は, 以前より南北アメリカ, ヨーロッパ, 北・西アフリカ, 極東, 近東域の白亜紀堆積物から広く記録されているが, インドのサメ類群集構成において,  後期白亜紀前期の冷温帯水域の種類から後期白亜紀の本質的に汎世界的な種類へと, 明瞭な変化があったことを示している. An elasmobranch assemblage consisting of Ptychodus sp., Scapanorhynchus sp. aff. S. raphiodon (Agassiz, 1844), Cretodus sp. aff. C. crassidens (Dixon, 1850), Cretalamna sp., Squalicorax sp. aff. S