You can still ride a Spino if you don't have a saddle yet by hopping on their tail and walking to where you want to stay. It's similar to the Sarco's "living raft" ability. Just whistle to where you want your Spino to run or swim, and they will carry you. How do I get onto their back, you ask? I make sure the front paws are higher than the rear paws so I can jump onto their spiky tail. Position yourself right, and set them to Aggressive, and you can watch one of nature's ultimate predators hunt everything around it.