Go to the rightmost part of the southern islets. The river that flows next to the green obelisk, the southern part especially, is where I have found most of my spinos. If there are none there, kill all of the swimming creatures (barrys, carbys, fish, otters, ducks, etc). Then go away to the redwoods and come back. If there is a spino, great, if not then just kill all the water creatures off again, leave, and come back. Repeat as necessary.