Someone on talk.origins asked how dinosaurs had sex. One of the replies pointed to
this Straight Dope column, which mentions
a painting by Luis Rey of carnotaurs having sex, which I’ve reproduced here for your enjoyment and edification. (See also this article in Cosmos.)
Apparently the late paleontologist Beverly Halstead did some research in the area of dinosaur sex, but apparently he couldn’t come up with anything conclusive. A major problem is that animals’ naughty bits also tend to be soft bits, which means they don’t fossilize easily, so we’re not sure what dinosaurs’ reproductive organs looked like. The best guess I’ve seen is that, like birds, they had a cloaca, basically an all-purpose rear orifice for eliminating urine and feces, laying eggs, and emitting sperm. So most likely dinosaurs didn’t distinguish between “regular” sex and anal sex.
(Update: PZ Myers informs me that like Carol, Chris, and Leslie, Beverly is a man’s name. Thanks for the correction.)