Third party reference
Why imagine how dinosaurs could breed? Is mating like any other animal as we know it today? Yeah just the same, like a bird, only bigger. But this answer is not satisfactory enough.
With the same idea of a mating as a bird, there will be more questions like, for example, the usual mating position that the birds do, what does it incriminate the opposite sex? Given the size is very large and of course very heavy.
Third party reference
Paleontologists try to simulate this. Experts believe that dinosaurs have the same "spare parts" as the birds of today. These ancient giant reptilian males and females have one hole for urination (though not small), defecation, and for reproduction, something called the cloaca. As quoted from typepad.com.
Furthermore, you may be able to imagine how much a male dinosaur reproduction might have reached 12 feet or 3 meters more. So how can this great tool reach the cloaca of female dinosaurs?
Dr. Halstead, one of the paleontologists from England, argues that the poses that male dinosaurs used to reach the females were backwards. This is actually the same theory presented by many other paleontologists, but Halstead seems quite popular with this theory, especially after his article on the marriage of dinosaurs in Omni science magazine.
According to him, all dinosaurs use nearly the same position to mate. Get her partner from behind, put her arms in front of her partner's shoulders, lift one leg behind her back and twist her tail down to show her the cloaca.
Third party reference
The same is also said by Dr. Gregory M Erickson, an evolutionary biologist at Florida State University told The Huffington Post. There is no doubt about it, he says, but it is a very bad scene to see or imagine
