Complex sentence: The first objects unearthed from Harappa and Mohenjo-Daro, major sites of the Indus Valley Civilization, were small stone seals inscribed with elegant depictions of animals, including a unicorn-like figure, and marked with Indus script writing which still baffles scholars.
Split into simpler sentences: The first objects unearthed from Harappa and Mohenjo-Daro, major sites of the Indus Valley Civilization, were small stone seals. The seals are/were inscribed with "elegant" depictions of animals, including a unicorn-like figure, and marked with Indus script writing which still baffles scholars.