When Bats Took Flight

A bat fluttered through the sky above what’s
now Wyoming some 52 million years ago. But it wasn’t like the bats you and I know. It was small, like most modern bats, but it
had claws on the tips of all five digits that supported each wing. And its wings were a bit shorter, while its
hindlegs were a little longer. With those claws and long hindlimbs, it was
a better climber than most modern bats. And its teeth suggest that it ate insects,
but it probably didn’t use echolocation to find and catch them. This little flying mammal was Onychonycteris
and it was definitely a bat – the most primitive bat that we have good fossil evidence of,
and also one of the oldest. And on the Mammal Family Tree, it sat on the
next-closest branch to all other bats, living and extinct. But when you trace that branch back…well,
it’s a mystery. Bats pretty much appear in the fossil record
as recognizable, full-on, flying bats. And they show up on all of the continents,
except Antarctica, around the same time, in the early Eocene Epoch. However, the very earliest fossils consist
only of teeth and limb bones, which don’t give us many clues about what the ancestors
of today’s bats looked like. So where did bats come from? And which of the many weird features that
bats have, showed up first? Like, did these mammals learn to fly first? Or echolocate first? Or … both? And how do they fit into the mammal family
tree? We used to think that — based on their skeletal
structure — bats were closely related to primates: like…us! Which is kind of strange, when you think about
it. But once we were able to study their genetic
history, their DNA revealed something much weirder. Instead of being closely related to the mammals
that they kinda look like, bats turn out to be much more closely related to the ones that
they … don’t. The fossil record of bats is both great and
terrible – which is why we’ve waited so long to do this episode. It’s great, in that, several of the earliest
fossil bats we have are exquisitely preserved. They’re basically complete, because they
were buried in an ancient lake deposit. The best bat fossils come from these types
of lagerstatten, or fossil sites with exceptional preservation. On the other hand, the fossil record of bats
is also terrible, because it’s either that or nothing. Most bats are small and have thin, fragile
bones. This keeps them light, which makes flight
easier, but it also means they don’t preserve well. But we are lucky enough to have a few specimens
of very old bats. Flying around at the same time as Onychonycteris,
and likely sharing the skies with it, was Icaronycteris index. This species also comes from Wyoming, and
for a long time it held the title of earliest known definitive bat, since it was first described
in 1966. Like Onychonycteris, which was published in
2008, Icaronycteris dates to around 52.5 million years ago. And because these two were already distinct
from each other, we know that bats must’ve evolved sometime before this. Both bats were clearly capable of powered
flight and also looked a lot like most modern insect-eating bats. But modern bats only have claws on one or
two of their digits — and Onychonycteris had claws on all five digits, while Icaronycteris
had a well-developed claw on its second digit and bony tips on three others.. And this ancient bat was probably capable
of echolocation, because it had specialized features on one of the inner ear bones — called
the malleus — and in the base of its skull that are linked to echolocation in living
bats. Also early bats weren’t restricted to North
America. There are at least four more spectacularly
preserved taxa of bats from just a bit later, around 47 million years ago, from the Messel
Pit in Germany, a site we’ve talked about before. These are also complete or nearly complete
skeletons, and in some of them you can even see the outlines of their soft tissues! And, like Icaronycteris, they’ve got all
the hallmarks of modern bats, and several of them seem to have been able to echolocate,
too. But all of these fossil bats had already mastered
powered flight: So how did their ancestors make it into the air in the first place? The answer to that question is tied up with
the evolution of another one of the defining features of most bats: echolocation. And among the experts, there are three competing
hypotheses for how bats evolved: either echolocation came first, or flight came first, or the two
developed together. All three hypotheses start with the same basic
assumptions based on the traits that are most common in bats today. These are that the bat ancestor was arboreal,
or lived in trees; it was insectivorous, or ate insects; and it was probably nocturnal. In the echolocation-first hypothesis, the
bat ancestor would’ve already had ultrasonic capabilities to start off with. This seems like it could be a possibility,
because there are modern insectivores, like some species of shrews, that use ultrasound
for communication or navigation. So the thinking here goes that this ancestral
bat might have reached out from tree branches to snatch passing insects. Over time, the super high-pitched calls would’ve
evolved into sonar that it could use to track its prey. And, being arboreal, its digits would’ve
been selected to get longer, with a membrane stretched between them, to more effectively
capture food. Those long, webbed hands would’ve then been
co-opted for gliding, when the animal started leaping to get at insects that flew further
and further from its perch. And eventually, it acquired adaptations for
powered flight. But the main problem with this hypothesis
is that this kind of hunting behavior — catching insects that just happen to fly where you
can reach — hasn’t been observed in the wild. Plus, weirdly enough, it turns out that it
takes a lot of energy to echolocate — especially when you’re stationary – so this whole feeding
strategy seems pretty inefficient. So what if they flew first, instead? In this model, powered flight evolved from
a gliding ancestor, which had originally started by leaping between trees or branches. This arboreal creature would’ve developed
longer digits and a membrane between them as part of its gliding phase, eventually transitioning
into powered flight. Once this proto-bat was flying around, it
likely encountered insects, possibly scooping them up with its wings or catching them out
of the air. And from there, an energy-efficient form of
echolocation developed, with bats exhaling – and squeaking – in time with their wingbeats. Some researchers have argued against this
idea, saying that a leaping or gliding nocturnal animal without specialized senses – either
vision or echolocation – wouldn’t be able to see where it was trying to land. But here at least, the fossil record can tell
us something: the skeleton of Onychonycteris shows that it was definitely capable of powered
flight, but it didn’t have the cranial features that are linked to echolocation. Because the skull was partially crushed, we
can’t tell if it had large eyes like many nocturnal gliding and leaping creatures do,
such as flying squirrels, but it’s still good evidence that flight likely came first. But there’s still the third option to consider:
that maybe echolocation and flight evolved in tandem. In this hypothesis, the bat-ancestor originally
used ultrasound to communicate and was able to start using it like basic sonar to help
it plot its nighttime leaps between branches. As its ability to echolocate evolved in power,
so too did its ability to make longer jumps, which eventually turned into gliding and powered
flight. And those two adaptations — stronger echolocation
and powered flight — made bats the stealthy aerial predators of insects that many still
are today. The problem with this model is: Onychonycteris
didn’t echolocate, but it did fly. Okay, so it seems that the fossil evidence
we have is in favor of the flight-first hypothesis. So that’s one piece of the puzzle of bat
origins that we can kinda snap into place. But it still doesn’t tell us where bats
came from! To figure out where bats truly fit in the
mammal family tree, paleontologists have teamed up with geneticists to study the DNA of living
bats. For a long time, bats were thought to be part
of the superorder Archonta — the group that includes treeshrews, colugos, and primates,
because those are the mammals they look the most like. Now, superorders are, by their very nature,
incredibly diverse. But members of Archonta do share a lot of
the same skeletal features, from the presence of a tiny bone in the inner ear to the particular
way their ankle bones fit together. And some studies even suggested that bats
and colugos were more closely related to each other than to the rest of the group, based
on some features of their hands, elbows, and feet. Colugos are nocturnal, arboreal, and they
glide using a membrane of skin stretched between their limbs – like the transitional pre-bat
is hypothesized to have done. So it’s easy to see why scientists thought
they were closely related. And in the 1980s and ‘90s, an Australian
neuroscientist even suggested that the fruit bats evolved from primates, based on similarities
in the pattern of connections between the retina and the brain. But in more than two dozen molecular studies
carried out since the early 1990s, bats have never grouped with Archonta. Instead, all of these studies put bats into
a totally different superorder, one known as Laurasiatheria. This includes a number of the placental mammals
that are thought to have originated on the supercontinent Laurasia during the Late Cretaceous
Period. And this group is also very diverse, including
the orders containing moles, camels, horses, whales, pangolins, and bears – most of which
look /nothing/ like bats. So that’s right. It turns out that bats are more closely related
to whales than they are to us. Within this group, analyses usually place
bats with a clade that contains pangolins, carnivores, and ungulates, or as the sister
group of shrews, moles, and maybe hedgehogs. But it’s still really unclear who within
Laurasiatheria bats are most closely related to and how. They seem to have come from some very primitive
mammal near the base of Laurasiatheria that also gave rise to one or more of the other
groups in the superorder. Another benefit of all these genetic data
is that they can give us a sense of when bats became a thing. According to studies based on that model known
as the molecular clock, bats seem to have originated around 65 million years ago, just
after the extinction of the non-avian dinosaurs. So where does that leave us in understanding
bat origins? Well, we seem to be getting closer to figuring
out the order in which bats evolved their most distinctive traits. It looks like flight came first, followed
closely by echolocation. And we’re still digging up wonderfully preserved
early bat fossils. As genomics continues to grow as a field,
we will hopefully be able to zero in on exactly what group bats are closest to. And this might be able to tell us what kinds
of traits to look for in a bat ancestor. It may end up looking totally different from
what we expected. After all, it’s happened before. But for the moment, the lack of enough evidence
— both in the ground and in their DNA — is keeping the true origins of bats in the dark. So what do you think? Did bats evolve flight or echolocation first,
or did it evolve in tandem? Let us know in the comments which hypothesis
you support and why! Also thanks to this month’s Eontologists:
Patrick Seifert, Jake Hart, Jon Davison Ng, and Steve! Be sure to go to patreon.com/eons and pledge
your support! And thanks for joining me in the Konstantin
Haase Studio. If you like what we do here, then subscribe
at youtube.com/eons.

100 thoughts on “When Bats Took Flight

  1. What if there were two species of early bats, one that could use echolocation & one that couldn't, that lived side by side & evolved from a single common ancestor? Maybe one species developed flight and echolocation simultaneously, while the other only developed flight. That would explain the differences in claws and limbs.

  2. What if flight developed first, but it was because they didn't start out nocturnal? What if they started out eating bugs that came out during a time in the day where the batcestors (bat ancestors) could still be reaching, hopping, gliding, and then flying from branch to branch without worrying about how they'd see the next branch? But you see the buggy bois didn't wanna be snacks, so they started coming out later and later. AHAH, but look who will become the squeak in the night! (SPOILER ALERT: It's the bats) So the bats (Spoiler over) started hunting later and later in the day. But it is becoming harder to see them buzzy buggos…(hangry acquired) WAIT Buzzy buggos? BUZZ-y! That's it! Bat-eureka! (This is all in various squeaks, but I'm translating for you). We must hear the buzz feel the buzz, become the buzz! martial arts training montage with bats throwing stuff at other bats that are blindfolded while they try and catch them or something The first to master this was Batt Murdock, who became Bat-Daredevil after losing his sight in a squeak, uh I mean in a freak accident. And like the bats slowly evolved to have better hearing for echolocation, because them buzzy buggy bois were partying all night long, but oops that really messes with your sleep cycle bro. Guess we're nocturnal now too? but idk

  3. If the avian dinosaurs declined when their non avian kin died out (makes sense they would have shared traits thus been affected by many of the same things) bats may have evolved to fill the niche left by them, and not been nocturnal at all but simply winged hunters who became nocturnal when the ancestors of modern birds reentered the scene at a later date.

  4. Your content is always great! Thank you for that! Minor complaint: "Lagerstätten" is quite correctly pronounced but the "ä" is more like the "e" in "led" or "ea" in the element lead. Or, closer to the topic, the "a" in "bats". 🙂

  5. I think they bats developed echolocation at the same time as flight, from an evolutionary timeline; however, if you want to get really down to it, the flapping motion making them exhale and squeak would have been a more refined 'flight,' but it wouldn't have taken any of them long to realize their food makes an interesting sound.

  6. bats despise running into things bc of their fragile bones. I'm no scientist but my personal theory is that bats developed echolocation after flight, as bats that could avoid obstacles lived longer than bats that couldn't

  7. 1:18 You literally answered this question like 30 seconds earlier? This bit doesn't make sense. I don't see why it's even a question lmao

  8. My understanding of Quantum biology,is that DNA is mutated by errors created in the DNA string when quantum powered proteins get stuck in a receiver slot there by denying its pair. In this hypothesis the mutant gene results in an immediate benefit to its owner. Therefore the mutation is not informed by the environment, but is amplified by its superior nature and quickly fills it’s niche.

  9. I think it’s the first hypothesis or the third one not sure ?? I do know that they only catch food with their mouth not their hands so I’m thinking the third is the correct answer. The reason I don’t support the second option because they are nocturnal an they would need ecolocation first to see which would give them a reason to fly??

  10. Is the fact that they evolved right after the KT extinction because niches were now opened up, or was that coincidental?

  11. Hello EONS!
    My husband and I would like to know more about the migration from salt water to freshwater, when did the freshwater get colonized? How did it happen?

  12. Experiencing flight development before my internal sonar and GPS lends me to assume that bats developed in a similar fashion, as fashions go.
    Flying without sonar and GPS was quite distressing until it finally developed. Whew.
    Leg hanging never worked out, but nocturnal does, especially when using a daytime pine box. ;>))

  13. i think flight came first but early bats wasn't nocturnal.
    i believe the first bats was like fruit bats and was day hunters.

  14. I'm surprised there aren't any ground dwelling mammals that evolved from bats on islands, especially in New Zealand.

  15. More or less in tandem, I would guess, with echo location becoming more refined as their flight also became more refined. I would also guess that they started out gliding, probably as jumping and gliding insectivores. Actually, I wonder when vampire bats and fruit bats deviated from insectivorous bats, assuming they all started out as insectivores. I suppose populations grew, migrated, got isolated and eventually developed different lifestyles due to differences in environments, so I would have to guess that fruit bats and vampire bats had problems catching insects or simply developed to take advantage of other food sources that were relatively easily available.

  16. Echolocation may have been developed later, due to the nocturnal habits to find nocturnal insects, not necessarily ancient bats were already nocturnal creatures.

  17. There are bats that act like Mols in australia or New zealand right that makes a lot more sense now
    thanks .

  18. Could they be ancesors of Yi qi or Ambopteryx longibrachium? Maybe they seperated from other mammals much earlier. Even their parasites (bat-flies) are very special and their high resistance to many of pathogens and zoonotics. How is this possible? Maybe their immune system evolved alongside this plagues so the evolutionary arms race between them made bats almost immune to most of plagues but is although unable to "kill" it.

  19. I live in a downtown area with lots of tiny bats. I can walk right through them when they are hunting insects, and they never touch me. Amazing!

  20. I used to think they were related to mouses, the Swedish word for bat literally translates into flutter-mouse.

  21. I feel inclined to agree with echolocation coming later.
    All that made me wonder tho, if it could be possible to find out this answer based on DNA archeology.

  22. I think they started flying first if I'm wrong it could be these little guys might be a small group depending on what social animal it is

  23. I just can't get over how smooth and exciting she makes her topics sound. (I had to pause in the middle of this video to make this comment.)

  24. I was once attacked by a bat. It was resting like a corpse on top of a kitchen door. The first footsteps I made at the kitchen immediately aroused and energized it, so that it launched two well-cordinated, sniper-style attacks at my face. Echo navigation should have come first because these little guys are just too lethargic and are normally drunk in total inertia, but they turn into missiles once provoked by even very small sounds, like those made by the soft footsteps I took in slippers at the kitchen.

  25. Great episode! German: raus, maus, fledermaus – I always thought bats where flying rodents. This was fascinating and well-presented. We need more YouTube channels like this!

  26. Hey, you could make a video about the modern raccoon evolution. I love your videos! And all the eontologists in the show!

  27. The conundrum assailing my puzzler, here is something you don't touch on, to wit: megapteran v. micropteran bats. This split alone suggests flight first, and echolocation second and possibly twice. Makes sense that chiropterans split early, just after the laurasiaotheria and Boreoeutheria split, as all stem mammals at that point would have been rather similar, having just passed a mass extinction favoring small, generalist burrowers.

  28. Echo location first, because they originated as small aquatic mammals in shallow fresh water habitats. Their echo location was used to hunt low flying insects at night and they would leap from the water to catch them or escape predators. Gradually, bats with the ability to leave the water longer to glide escaped predators and eat more evasive prey. Eventually the water dried up or the insectivores left the water for trees and caves. There's just as much evidence for that as anything presented in the video.

  29. The fact that bats suddenly exist with no progression in the fossil record could be used to bolster fictive vampirism in novels and movies.

  30. Perhaps echolocation developed in bats not as a way to find food, but a way to communicate with the colony/mates and avoid midair collisions. Then bats would be active in the day, still need echolocation, and achieve flight fairly closely together. Any animal that lives in a 4 dimensional field has to develop an extra sense of z axis space, like starlings or sardines, as well as an extra sense of space within a large group. Unlike sardines, bats still regularly crash into each other, which means bats rely wholly on sound for spatial recognition and not motion-based patterned reflex. As tree-dwelling climber bat colonies grew larger, identifying individual mates on far away branches, like penguins in an ice field except in x, y, and z axis space, would have required specialized hearing. As they developed the sense of 4th dimensional space from mating pressures, gliding from branch to branch, they then developed echolocation to help find food as well, and to disseminate warnings from all of the various directions they could be attacked from. As their sight grew less necessary, they became more nocturnal in order to avoid competition or loss from other day dwellers, like predatory birds. Their echolocation would give them an edge over sight-based predators during the night.

  31. I think it glides on a tree to get a food and evolve wings but maybe there's something makes them nocturnal maybe predator or climate where they evolve echolocation. Flying would've help them to wander at night because insects.

  32. If we saw fossils of these ancestral bats without having extant bat species we would have be comically confused trying to figure out what they look like. Almost makes you wonder what we’ve gotten wrong and just don’t know and maybe never will.

  33. Would you guys please do a video about megabats and microbats and whether they share a common phylogentic origin or are simply analogous? I feel like this video didn't really touch on that question much. It would be easy to assume that they share the same origin but I'm not sure whether or not the science supports that. I heard many different things back in the 90s when I was learning about this topic with microbats being said to come from insectivore ancestors related to rodents and shrews and megabats coming from a colugo-like lineage. Or is there already a video touching on this?

  34. So basically Bats originally came from a very old family tree that diversified so much that now they don't look very much alike?….oh wait we even came from there lol, that explains our similar looking skeletons.

  35. With the flight first scenario, maybe as they were moving around faster, they need a way to detect things further away, thus they developed a primitive form of sonar.

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