The farther back you go on the mammal family tree, the more likely you are to run into some sets of cousins that you just would not expect.

It seems absurd to me that whales and hippos are among each other’s closest living relatives. And that goes double for hyraxes and elephants.

These two? Like how? Why?

And what about this guy? I’m not even sure what it is, let alone what it’s related to. So, it came as a surprise to me to find out that the next branch over from it on the family tree might be us.

And by “us,” I mean, primates. [♪♪ Intro ♪♪] This is a colugo, sometimes called a flying lemur – even though it does not fly and it’s not a lemur. If it was a lemur, this video would be over – there would be no question about whether or not it’s one of our relatives, because lemurs are definitely primates, like us. Colugos live in the forests of southeast Asia, from parts of Vietnam, Laos, and Thailand, down through Malaysia, Indonesia, and the Philippines.

They stay out of sight in tree holes and among patches of dense foliage during the day, and come out at night to snack on the soft parts of plants, like young leaves and flowers. And they rarely, if ever, come down from the trees – to move between them, they glide instead. They can glide for distances of over 100 meters.

The two species of colugos are the only living members of an order of mammals called Dermoptera – which comes from the Greek words for “skin” and “wing.” For comparison, in the Primate order, the International Union for Conservation of Nature recognizes over 500 species. Now, back before we knew about DNA and using genes to group animals with shared evolutionary histories together, we used to do it based on how they looked. Which, for some groups, works really well.

Take rodents, for example. There are big ones and small ones, and yes, some weird ones, but they all have four furry limbs and incisors used for gnawing. But for colugos.

Well, what do you think it looks like? I think it has wings made of a stretched-out membrane of skin, kinda like a bat, but not quite. Much of a bat’s wing is supported by their elongated finger bones, and they’re the only mammal capable of what’s called ‘powered flight’ – they actually flap their wings to generate thrust.

Colugos don’t do that – they leap from trees and just glide. And instead of having their gliding membrane stretched between extra-long fingers, it’s supported by all four limbs and their tail, kind of like a flying squirrel But they are the only mammal other than bats whose collarbone articulates with their first ribs, so they have that in common. Colugos have some traits of their foot bones in common with tree shrews, too, which are a separate taxonomic group from terrestrial shrews.

And, like lemurs, colugos also have a thing called a “tooth comb,” that’s used for grooming and feeding. In lemurs, it’s made up of their narrow lower incisors and canines, packed together closely like the teeth of a comb. But in colugos, their individual lower incisors each look like little combs, with multiple comb-teeth on each regular tooth!

And when you look at the rest of their skeleton, some researchers have said that colugos have features of their ankle and elbow joints in common with other primates in addition to lemurs. Basically, these guys sit in the middle of the anatomy Venn Diagram made up of bats, tree shrews, and primates. And because of these similarities in anatomy, over the last 200-plus years, scientists have proposed three different hypotheses about where they belong on the family tree of mammals.

They are either in a group with bats, a group with tree shrews, or in a group with us. And that’s part of what makes the enduring nature of this 200-year-old-mystery so weird. Colugos could be the other kind of mammal that’s most closely related to our own order, but we just didn’t know it, and we’re pretty notoriously self-centered about studying ourselves.

And if they are, this might tell us something about the origins of all primates and what the first primates might’ve been like. It would take modern genetic methods to sort this relationship out – and even DNA doesn’t always paint the clearest picture. For example, one study from 2001 compared 18 segments of genes from 64 different species of placental mammals representing all the orders of mammals alive today from aardvarks to rhinos.

And the researchers built three big mammal family trees from those genes using three different mathematical methods. In one tree, colugos sit smack in the middle of primates, a place that we know they don't belong We are definitely more related to lemurs than we are to colugos. And in the other two, they’re the closest relatives of tree shrews, with that combined group being the next branch over from primates.

So, we’re done here, right? DNA says we have two closest relatives: tree shrews and colugos. Well, no.

Molecular family trees are only as good as the DNA samples they’re based on – and this study only used genes from one species of colugo and one species of tree shrew. A more recent study from 2016 took a deeper dive into colugo genetics. The researchers included both species of colugos and two different tree shrews, and it looked at more of their genomes.

And they found pretty good support for the hypothesis that colugos are, indeed, the closest relatives of primates – a result that several other studies since then have also supported. So, it looks like these strange, nocturnal gliding mammals may actually be our long-lost cousins after all, found again by the wonders of modern genetics. And maybe that should make them seem less weird to us – after all, they’re family.

The Bizarre Beasts pin club subscription window is open from now through the end of September 12th, giving you a little extra time to snag one of these adorable colugo pins for yourself. When you sign up, you’ll get the colugo pin in the middle of the month, and the pins after that around the time each new video goes live. And, in case you missed this, we’ve also just printed a limited run of Bizarre Beasts calendars, featuring some of our favorite critters.

You can order yours at ComplexlyCalenders.com or click the link in the description! Because you’re gonna need a calendar, might as well support one of your favorite YouTube channels while you know what date it is. And, as always, profits from the pin club and all of our merch go to support our community’s efforts to decrease maternal mortality in Sierra Leone. [♪♪ Outro ♪♪]