I've had Dino's disappear like that but they usually glitch under the map... Haven't played official in a while so that might be fixed but I went to where my bronto used to be after it disappeared and layed down hit whistle follow all in the ground (didn't even hear the whistle above ground) and when I flew up in the air on a pterra I watched the bronto walk up from under the map so that might be a option but like I said it's been about 7 months since I've played official so they might have fixed that bug