The Himalayan connection of the Middle Triassic brachiopod fauna from Socotra (Yemen)

The brachiopod fauna from the Middle Triassic beds of the Socotra Island, collected along the Ras Momi log, consists basically of four species, here described: Nudirostralina mutabilis (Stoliczka, 1866), Lepismatina lilangensis (Stoliczka, 1866), Spirigerellina stoliczkai (Bittner, 1899), Adygella socotrana sp. nov. Additional, very rare, species are Koeveskallina sp. and an undescribed very large dielasmatid. This fauna is arranged in three assemblages, with different age. The older is represented by Adygella socotrana and dated as Bithynian according to the presence of the conodonts Neogondolella regalis and Paragondolella bulgarica. The middle one is the richest in specimens, with lumachelle of Spirigerellina stoliczkai and rare specimens of other species. Its age is Illyrian on the base of several species of Paragondolellids and Neogondolellids, The younger one contains rare very large dielasmatid, Nudirostralina mutabilis, and Spirigerellina stoliczkai, which continues to be fairly abundant. The age of this assemblage is an indefinite Ladinian, due to the presence of Budurovignathus sp. This fauna is compared with a few specimens from Himalaya (G. lilangensis, S. stoliczkai, and “Dielasma” himalayanum), which were collected from the sections of Muth (Spiti), Phugtal (Zanskar), and Tulong (South Tibet). The brachiopod fauna of Socotra has an obvious counterpart with the Himalayan fauna, indicating a strong connection during the Middle Triassic. Our palaeobiogeographic interpretation is that Socotra was a part of the Indian Plate fringe or lying nearby during the Triassic. In the latest Triassic–Jurassic it was detached from the Indian margin with the Gondwana fragmentation, and then with the subsequent opening of the Indian Ocean in the Late Cretaceous. Socotra remained attached to the Arabian Peninsula until the opening of the Gulf of Aden in the Miocene. This separated Socotra from the Arabian Peninsula and left it as the easternmost tip of the Somali Plateau.