If you wana find this guy there is a metal structure to the west of the sanctuary and I found like 4 there
Dreadnoughtus
The Dreadnoughtus is a large sauropod added in Extinction for ARK: Survival Ascended. This creature won in ARK's Community Creature Vote and was announced on September 23, 2023.

How to survive, fight, and kill a wild Dreadnoughtus, from players who have done it.