Consider the following assertion:
In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa.
Which of the following is/are the basis of the above assertion?
1. The Nadi-Sukta of the Rigveda
2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
3. The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below:

The assertion relates to the Indo-Brahm (or Shiwalik) River hypothesis proposed by geologists E.H. Pascoe and G.E. Pilgrim, which suggests that a mighty river once flowed longitudinally along the Himalayas during the Pleistocene epoch, connecting the present-day Indus and Ganga systems.

• Statement 1 is incorrect: The Nadi-Sukta of the Rigveda describes the river systems as they existed during the Vedic period (Holocene epoch), not the Pleistocene epoch.
• Statement 2 is incorrect: Robert Bruce Foote is renowned as the father of Indian prehistory for discovering Paleolithic tools (e.g., at Pallavaram). The geological explorations regarding the Indo-Brahm river and the shifting of the Sutlej/Yamuna were conducted by Pascoe and Pilgrim.
• Statement 3 is correct: A major biological evidence supporting the past connection between the Indus and Ganga river systems is the presence of the South Asian river dolphin (Platanista gangetica) in both basins. Since these dolphins are strictly freshwater species and cannot survive in the sea, their distribution indicates that the Indus and Ganga systems were once interconnected.

Thus, only statement 3 provides a valid basis for the assertion.