My Carno was 1 hit killed by stego, I had only just tamed it, waited for it to get get back to 100% health. It was as if its health regen from taming was actually a lot slower than the graphic showed, and that it kept the 1/4 health from when unconscious. Carno was lvl 6, stego 26
Also one of my friends ptera got killed by a t rex spawning in the sky