The Ural Ocean was a small, ancient ocean that was situated between Siberia and Baltica. The ocean formed in the Late Ordovician epoch, when large islands from Siberia collided with Baltica, which was now part of a minor supercontinent of Euramerica. The islands also caused Ural Ocean's precursor, Khanty Ocean to close. By the Devonian Period, however, Ural Ocean begins to shrink because the Siberian continent and Kazakhstania microcontinent were closing in to Baltica. In the Late Devonian to Mississipian periods, Ural Ocean became a seaway. Until the three collided in the Carboniferous, it created the Ural Mountains, completely closing the ocean, and forming the Pangaea supercontinent.