To keep warm.
Yes. Here's a definition:den: a cave. Dinosaurs sleep in dens.
True. During winter, they have to sleep in dens to keep warm.
Yes they do.
Beavers create little dens where they sleep and hibernate.
No, they sleep in dens which may be covered with snow.
No they only sleep in trees
Porcupines typically sleep in dens or burrows in the wild.
yes. all animals sleep
Yes they only sleep in trees they do not have dens tree holes or a nest
Yes.
Bears do not really hibernate. They will fall into a deep sleep, but vital signs remain near normal. They sleep in dens they find or dig themselves. Females give birth in these dens over winter.
All terrestrial vertebrates require some form of sleep. We can't learn about how dinosaurs slept from their fossils, but because birds and crocodiles, their closest relatives, sleep, it is safe to assume all dinosaurs did, too.