From Late Miocene (Toronian, 8 - 9Ma) till Late Pliocene (Piacenzian, 2.5 Ma) times, a gigantic lake, Palaeolake Obweruka, extended in the Albertine Basin. This palaeolake was geomorphologically identical to Modern L. Tanganyika and in addition shares the occurrence of thallasoid (marine-like) molluscan faunas. Former research on this palaeolake revealed that evolution gave rise to 3 different thalassoid malacofauna’s, each preceded by an extinction. Over the last years fossil bearing deposits were discovered north of L. Albert, dating from the earliest lake stage (8-9 Ma), from which evidence had been missing. In the present study, the fossil molluscan assemblages from these deposits were treated. They yielded a diverse mollusk community (15 species) dominated by viviparids (Neothauma) and unionids (Coelatura), that lived in a vast but relatively shallow lake. About half of the species are new to science. Assemblages from the subsequent deeper lake stage (7 – 4.5Ma) contain species that were also found during earlier investigations in other parts of the basin. The major scientific importance of the earliest assemblages is that they consist for a large part of thalassoid endemics, new to science, representing evidence for a first thalassoid evolutionary escalation at the very onset of the lake. It is clear that the four thalassoid molluscan faunas of L. Obweruka represent rapid escalatory punctuations, each preceded by a major environmental shift and an extinction.