All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Archaeology has proven that these huge skeletons of animals existed; this is an evidence that these animals lived during a given time period. The fact that the Qur'aan has not mentioned them does not mean that they did not exist. The Qur'aan was not revealed as a textbook on the kinds of creatures, and the reason for their creation. Rather the Qur'aan was revealed to clarify matters of religion, the Oneness of Allaah's Lordship and the Oneness of His Worship (that None has the right to be worshipped but Allaah), and related stories of those previous nations that denied their Prophets, so that mankind would take a lesson from them. As regards the saying of Allaah (interpretation of meaning): {We have neglected nothing in the Book}[6:38], the Book here means the Preserved Book, as Ibn 'Abbaas interpreted this verse by saying: 'We have not left anything except that we have recorded it in the preserved Book.'
Allaah knows best.