Tame them by getting their eggs. Use a whip while you're grappled to a flyer. They need five fireplaces to hatch. It doesn't take that long for them to grow, but to hatch them it's thirty minutes. They can be found easily on the white cliffs along with their eggs. I don't care if you like this or not I just wanna give tips.
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 :)
Take any creatures with platform saddle and build a wall around its legs so that the Deimos cant attack(preferably stone) then walk in on them and watch them try to attack you. Use your protected creatures and go walk on top of a nest. Jump of and under the creatures quickly and u will be safe. Then grab the egg and get out. Very simple. Preferable creature quetzal or paracerithium.
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
My base is at the lake in chalk hills, and one day I found this tunnel that went through the rock. I came out on the other side of a cliff and there is a nest like 10 yards away.
I got an egg without seeing a single deinonychus!
Have a great day! 👍🏼