Late Oligocene dugongid remains from India: insights into past seagrass-sirenian associations in the eastern Tethys

Abstract

Sirenians, or sea cows, were among the first mammals to become fully aquatic and are closely tied to seagrass ecosystems in shallow seas. Establishing direct links between fossil sirenians and seagrass habitats, however, is challenging due to the poor preservation potential of seagrass leaves. Here we report sirenian rib remains from a newly identified late Oligocene (24.37 Ma) shell bed in the Bermoti Member of the Maniyara Fort Formation, Kutch Basin, western India. Morphological comparisons indicate a dugongid affinity. The ribs were preserved in situ with minimal transport, as suggested by their taphonomic features. Sedimentological characteristics, together with an associated marine invertebrate assemblage of mollusks, coral, and foraminifera, indicate an inner ramp setting in the vicinity of patch reef environment, a setting capable of supporting seagrass habitats. The co-occurrence of Amussiopecten subpleuronectes with sirenian remains further parallels assemblages reported from the Oligo-Miocene Qom Formation of Iran that have been interpreted as associated with seagrass environments, suggesting possible ecological similarities across the Tethyan seaway. Together, these findings are consistent with the possibility of long-term seagrass-sirenian associations in the eastern Tethys and provide additional context for interpreting their paleoecology and paleobiogeography.