Dinosaur cloaca

As Cecil explained in http://www.straightdope.com/columns/read/2357/how-did-dinosaurs-have-sex , the urinary, digestive, and reproductive tracts of dinosaurs meet in a chamber called the cloaca, from which the appropriate excretions and secretions leave the body.

My question: is the actual opening also called the cloaca, or is it something else, such as cloacal opening, anus, or anal opening? I’m writing a short story which is narrated by a palentologist, and I need to make him sound like he knows what he is talking about.

Forgive me if I do not acknowledge any answers right away. I am about to log off until tomorrow (or later).


“Cloaca” applies to both the chamber and the opening. However, the opening is also referred to a the “vent” in birds and reptiles. You could use either term.

To be completely accurate, unless there’s some fossil with soft tissue preserved that I have not encountered, we do not know what the urogential-excretory outlet(s) of dinosaurs in the classic sense (Ornithischia and non-avian Saurischia) were. However, the surviving dinosaurs (Aves) the other surviving archosaurs (Crocodylia), and the other reptle-grade surviving forms (lizards, snakes, turtles, tuatara) all have cloacas, as do the Monotremes (hence their name). So it is a very reasonable conclusion that dinosaurs had them as well. But, of course, it’s not proven.

Colibri, thank you, that is what I needed to know.

Polycarp, I already made that assumption, and I’m hardly the first. Read Cecil’s column referred to in my original post.


Polycarp, I’m sorry. What I said to you was rude. Your answer was correct, but it was not the answer to my question.


It’s no problem, and I took no offense. Colibri had already answered the question quite well; I supplemented it with the point that it was an almost-certain assumption, not something definitively known to have existed, for anyone who might otherwise draw an erroneous conclusion.