During its history it lost its connections with the neighbouring seas and became a lake.
The Pannonian Sea existed from about 10 Ma (million years ago) until 1 Ma, during the Miocene and Pliocene epochs, when marine sediments were deposited to a depth of 3–4 km (1.9–2.5 mi) in the Pannonian Basin.
Through the Đerdap Strait, the Pannonian Sea was linked to the Paratethys in the Wallachian-Pontic Basin.
Its last remnant, the Slavonian Lake, dried up in the Pleistocene epoch.
The remnants of the former islands of the Pannonian Sea are the modern Pannonian island mountains (Mecsek, Papuk, Psunj, Krndija, Dilj, Fruška Gora, and Vršac Mountains).