You are making two great assumptions at the same time, neither of them have certain answers. First that PTSD as a condition makes sense out side of our cultural context. We have not proved this. Second that PTSD exists in other species. We do not know this either.

You are asking people to come down on this by looking at the written record, while most professionals need to talk to a patient and make their own observations to establish a diagnosis. This isn't going to happen. We are not going to get anything other than speculation, because that is all there can be.

You're assumptions seem to rest on an unspoken question. Is PTSD a real thing, a piece of reality defined by science, or a convenient shorthand for a set of correlated observations. This question can be asked for most of our scientific entities, like species or even such things as gravity. If you want to talk about something universal and eternal, like PTSD in long dead dogs, then that thing should be more than a good correlation, but a part of reality.