in my opinion the only cocks that look good on animals are the cocks that are large enough to do some good penetration, some good pussy stretching. otherwise it is pointless to put realistic cocks on the animals that comes with them naturally.
Take a Goat for example. I live on a farm and we have a Goat here, He is a really tough and rough animal with large horns, so everyone on our farm stays away from him otherwise he will but you. But he has a very very long and super thin cock, kind of like a thin stick. it is about 1 foot long or 12 inches long and to imagine him fucking something with it, you would think it would break off.
He constantly pees on everything and loves the taste of his own piss.
Honestly the only animals worth having to fuck girls, are a Horse, or a Cow or a donkey, or a large Dog, or Wolf. Im sure there are other animals out there with large and fat cocks. but you would have to do a google search.
About dinosaurs, well scientists can only guess about their dimentions and size and so it really is up to you what their cocks look like, however they are really big lizards, so I dont know what a lizard cock would be.