Tithonian brachiopods from the Kachchh and Jaisalmer basins, India
Mukherjee, Debahuti; Shome, Sabyasachi
published: Aug 1, 2017
Brachiopods are common in the Middle Jurassic in the Kachchh and Jaisalmer basins of India but show a decline at the Oxfordian-Kimmeridgian boundary. After an absence in the Kimmeridgian, two brachiopod taxa suddenly appear in the Tithonian in both areas but does not continue afterwards. The two species, Somalithyris lakhaparensis n. sp. and Acanthorhynchia multistriata are the first records of Tithonian brachiopods from the Indo-Madagascan and Ethiopian biogeographic Provinces. The present study describes these two species from Kachchh and Jaisalmer on the basis of numerous specimens collected from the Upper Tithonian. The presence of the two brachiopod genera in the Tithonian in large numbers but their complete absence thereafter in the Berriasian, in India, as well as globally, is probably the result of the J-K boundary mass-extinction. Somalithyris, is an important genus in the Ethiopian Province in the Upper Jurassic, having endemic species in both Saudi Arabia and Somali Republic and it has also been recorded from Tunisia and Iran. The new species, S. lakhaparensis, is formally described establishing its taxonomic affinities by comparison with similar taxa. The dominance of specimens resembling the pre-adult stage of Somalithyris in the assemblage is interpreted as resulting from paedomorphosis or selective size reduction due to an unstable environment.