You can't tame these guys by knocking them out. Instead, you need to steal their fertilised eggs (just like wyverns and rock drakes), hatch them and raise them, just a bit harder than knocking them out. The eggs can, of course, be found in their nests and do be careful while trying to steal one as the Deinonychus is very territorial. Hope this helps :)
Here's how to steal one early game: If you spawn in at chalk hills 3 and spawn next to a pond walk opposite to the pond. There are some nests right there. Snatch one quickly and run off the cliff next to the pond. Be careful and make sure to fall into the water. From there make a left and you should get to a beach area. From there it should be easy to find your base.
1. Tame a kangaroos 2. Have a tribe mate with a whip in the pouch 3. Quickly jump on a nest and have your tribe mate whip the egg into his inventory 4. Jump away! No one has to dismount so there’s basically no risk