The Palaearctic and Oriental (Indomalayan) biogeographic regions are separated by the:

The Himalayas serve as a crucial biogeographic barrier, effectively separating the Palaearctic region (which includes Europe and much of Asia) from the Oriental (Indomalayan) region (covering South and Southeast Asia). This massive mountain range creates distinct climatic zones and physical obstacles, leading to unique evolutionary paths and species distributions on either side.

• The Indus River is a significant waterway but does not define this major biogeographic boundary.
• The Ural Mountains separate Europe from Asia within the Palaearctic realm.
• The Suez Canal is a man-made waterway separating Africa from Asia, relevant to the Afrotropical and Palaearctic regions, not the Oriental.