He explained it was a group evolutionary advantage - if one of them wakes up because of a predator attack, for example, they’d all be woken up and hopefully most of them would manage to get away. I specifically remember him mentioning that dogs and puppies still have a slight preference for sleeping the same way.

I haven’t for the life of me been able to remember the word (or phrase?) he used to describe the behavior and every so often I Google in vain for more information. I can’t even recall whether the term he used was in english or german. Perhaps someone here can point me in the right direction?