Reptiles Have the Same Sleep Cycles as Ours

"Australian bearded lizards"

Australian bearded lizards

BEACON TRANSCRIPT – We certainly think a lot about dinosaurs. This mostly goes back to our childhoods and Jurassic Park, but even if the movie hadn’t come out I like to think that people would still have an interest in the giant reptiles. Because, after all, they were still reptilian giants roaming the planet.

So it should come as no big surprise that scientists are still looking into the past, attempting to learn as much as possible about the gigantic creatures and to relate them to their evolutionary counterparts. Of course, birds are these evolutionary descendants, while other modern day reptiles are great-great-cousins of sorts.

This is because at one point mammals, reptiles, and birds all had a common ancestor which lived some 300 million years ago. Part of the amniotic family, all three have a protective membrane around their eggs (for mammals it’s the placenta). At some point, the three families were born, with birds evolving out of certain species of dinosaurs after the great extinction.

And so far, so good; we’ve talked about the common ancestor, but what does it have to do with sleeping lizards? Well, the way lizards sleep is actually a confirmation that that common ancestor actually exists. And the whole affair is a bit complicated, so let’s dive right in.

What basically happened was that so far it was assumed that the states of sleep were only typical of mammals and birds. But it turns out that reptiles have  the same sleep cycles as ours, albeit lasting far less than they do in humans. Both REM sleep and slow-wave sleep are part of the sleep cycles of mammals, birds, and reptiles.

According to Daniel Margoliash, a professor of anatomy and organismal biology at the University of Chicago, this study offers

[…]extremely strong evidence that the patterns of structure of sleep that we’ve seen in a broad range of species is reflective of something that evolved very early in vertebrate evolution and is shared across many – perhaps all – vertebrates. It forces us to think about the earliest evolution of these phenomena. When did these aspects of sleep start, and what were they for?

Now, there are two possible explanations for the discovery. Either the families evolved the exact same sleeping patterns independent form one another, or we actually had a common ancestor. The common ancestor theory is more likely for a number of reasons.

One of these reasons is actually the fact that lizards go through the same sleep cycles for us, but shorter. While in humans a regular sleep cycle last around an hour or an hour and a half, in lizards it last around a minute or a minute and a half. This is an indicator that reptiles indeed separated from the common ancestor before the dinosaurs, and it might actually be a much closer sleep cycle to that of prehistoric times.

Image source: Wikimedia