Paleoecology and paleobiogeography of Early Miocene bivalve fauna from Kerala, India

Venu Gopal, K. Srinivasa (2019) Paleoecology and paleobiogeography of Early Miocene bivalve fauna from Kerala, India. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The effect of tectonic reconfiguration of the seaways on marine organisms is of great interest to paleontologists. Northern hemisphere witnessed one such major event in Miocene where the Tethyan seaway closed due to the collision of the African Plate with the Eurasian plate leading to the event of development of the Gomphotherium land bridge. Formation of this landbridge acted as a geographic barrier for marine biotic community. Consequently, the eastern and the western part of Tethyan seaway became disconnected. Although, this process started during late Oligocene, Early Miocene, especially Burdigalian (20.4-16Ma) is an important time due to the estimated time of closure (~19Ma). It also marks the period of transition of the marine biodiversity hotspots from the proto-Mediterranean to Indo-Australian Archipelago (IAA). To assess the effect of Tethyan closure on the marine fauna of the eastern Tethyan region, we evaluated the microscopic and megascopic bivalve assemblage of Quilon Limestone recovered from Padappakkara village (N 08⁰58ˊ36ʺ, E 76⁰3ˊ08ʺ), Kerala. The assemblage shows limited taphonomic alteration, preserving original aragonitic shells. The fauna is diverse and comprised of molluscs (bivalve, gastropod, scaphopod), foraminifera, arthropod (malacostraca, ostracod). We found a total of 52 species of bivalves; many of them are reported in previous literature. We have documented 13 species of bivalves in extremely small size, representing nine families including Arcidae, Limopsidae, Cardiidae, Lucinidae, Corbulidae, Kelliellidae, Tellinidae, Chamidae, and Anomiidae. These microscopic individuals show high degree of ornamentation, well developed dentition – features that are not commonly found in juveniles. The fauna is dominated by infaunal bivalves. The proportion of deposit feeders are very low, compared to suspension feeders and chemosymbionts. The fauna also shows predatory traces in the form of drillholes. Based on gastropod and foraminiferal assemblage, this fauna has been interpreted to represent a seagrass habitat. Dominance of infauna, suspension feeders and chemosymbionts (Lucinids) in our study also supports this interpretation. The comparison of generic association of the fauna with coeval fauna of Proto-Mediterranean to Indo Australian Archipelago (IAA) revealed a higher degree of biogeographic connectivity with IAA. This points to a lack of exchange with the western Tethys, probably due to the complete seaway as an aftermath of Gomphotherium landbridge development.

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