Tracing Back the Origin of the Indo‐pacific Mollusc Fauna: Basal Tridacninae From the Oligocene and Miocene of the Sultanate of Oman

Two new tridacnine species are described from the Chattian and Aquitanian of the Arabian Peninsula. For these, the new names Omanidacna eos gen. et sp. nov. and Tridacna evae sp. nov. are erected. Omanidacna is interpreted as an Oligocene ancestor of Hippopus, being the oldest record of this tridacnine lineage. The Aquitanian Tridacna evae is the first occurrence of the genus Tridacna. These Arabian taxa imply that the modern tridacnine lineages are rooted in the Palaeogene and early Neogene of the East African‐Arabian Province, although their Eocene ancestors, such as Byssocardium, are Western Tethyan taxa. During the Neogene they successfully settled the Indo‐Polynesian Province and became typical elements of the entire Indo‐West Pacific Region. The tridacnines are thus an example of a successive transformation and gradual eastward dispersal of an originally Tethyan element contributing to late Neogene diversity in the Indo‐West Pacific.