The thing I found easiest is to use a distraction dino, such as a few dodos, and just set them in front of you so the agrent will agro on it for a moment. Maybe not long, but it did long enough for me to be able to knock it out
An argentavis can't fit through a ceiling with one tile missing, but a pteranadon or lymantria can. Build a trap with one corner ceiling missing, aggro the argentavis, fly in one side and out the missing ceiling tile, and land. Dismount, run around, and close the entry door. Tame safely at your leisure.