To be strictly honest the spinosaur is one of the best mounts in game if you are even wble to obtain one be sure to make it a high level one they are very squishy at first so go around killing small dinos before attacking big prey
TLC patch coming in March 2018 to add the ability to swap between 2 legged mode (faster attacks and ability to attack with claws) and 4 legged mode (Faster movement), as well as increased turning radius, movement speed, damage, and health regen while in water and for a short time after leaving it. Like so people can see!
When in water, the spino can move without using stamina, this means that in a fight, if you run into a deep water source, you don't need to worry about stamina if you need to retreat. Has an oxygen bar so you can't dive forever sadly, very fast in water though.
Perfect for under water drops. If for any reason you disconnect down there (and you will) it will float to the surface. To get the drop just jump off and whistle follow all straight away and you'll be fine. These can take on all sea creatures with ease.
With a higher damage output and more stamina than a rex, the spino is an excellent alternative. The turning radius and hit box of spino makes it easier to hit targets as well, much easier than a rex. Not to forget the spino also shines in water, moving faster than it does on land and consuming no stamina while swimming, it makes for great escape route.
Overall the only negative thing I can say about it is that it's speed on land is slightly slower than a rex. If youre keeping it inland, consider putting a few points in speed.