Which animal did Harappan people worship?

From evidence of seals unearthed in Harappa, it is believed that the Harappan people worshipped both plants and animals. Among the animals they particularly worshipped, the bull, the rhinoceros, the tiger, and the crocodile. As for plants, the pipal tree was considered a symbol of wisdom

However, it should be noted that the religious beliefs of the Harappans and by extension the entirety of the Indus Valley Civilisation is a matter of debate and speculation that continues to this day. 

For further reading check the following articles:

• Prehistoric Age in India
• Indus Valley Civilization
• Prehistoric Rock Painting