What are you using as the basis for that statement?
People think of dinosaurs as huge animals that could peer over the tops of tall trees. But many dinosaurs were small. Some were about the size of young chickens, and some were not much bigger than the dinosaur tooth pictured at right. Obviously Noah wasn't going to stuff a pair of 30-meter high dinosaurs in the Ark. So what did he do?
Small dinosaurs would fit on the Ark easily. And remember that even the largest dinosaurs started their lives as younger and smaller babies. In the late 1970s, skeletons and eggs of some tiny juvenile Mussaurus dinosaurs were found in Patagonia in southern Argentina. Mussaurus means “mouse reptile”, and the name is apt because the best-preserved Mussaurus skeleton is so small it fits comfortably in a human hand.
New Scientist of 6 December, 2000 announced the discovery of fossils of the smallest known adult dinosaur. These “microraptors” were only 39 centimeters (15 inches) long — 24 centimeters (9½ inches) of which were its tail.
We don't know how many species of dinosaur that God sent to Noah to take on the Ark. If the largest types were included, it is possible they were taken when they were still youngish but able to mate. Many animals can mate long before they are fully grown. </sarcasm>