No one really knows the sleeping habits of the dinosaurs. It is not easy to infer such activities based on just the fossil record, as sleeping leaves no definitive physical trace. After all, no one knew sharks slept until just a few decades ago, and sharks are common in today’s oceans.

Still, scientists have inferred the sleeping habits of some of the dinosaurs. For example, most of the smaller animals probably slept like modern reptiles, just flopping down on the ground like a crocodile. Others, such as the huge Tyrannosaurus, probably had a much harder time sleeping lying down. Once it laid down, it would be difficult to get up using its small arms. Other larger dinosaurs would probably find their enormous weights would get in the way. Thus, the only way larger dinosaurs could sleep was by standing up. It is interesting to note that modern birds (close relatives to the dinosaurs, or maybe even dinosaurs themselves) sleep standing up.