Obligatory disclaimer: real life sucks. So, let us talk
about some real life animals, the bats. Why? Because the YouTube channel PBS
Eons have started a discussion on them, or rather – on their evolutionary
history, as to how they have evolved, as well as from what ancestor, and what
other mammals did they share their ancestor with. Those are some genuinely
interesting questions, so let us begin.
First, what has evolved… well, first: the bats’
echolocation, their power of flight, or both? That is an interesting question,
made complex further by the fact that there is a group of bats, the so-called
megabats or flying foxes that do not really use echolocation at all. Why?
Because they do not need it – they are fruit-eating mammals, as well as
nectar-eating. What next?
Well, the tricky thing is that if previously megabats were
something of a sister group to all the other bats, (which do use echolocation, in one way or another), now they are proven to
be close relatives of false vampire bats, (which are called that because they don’t suck blood, but are active
carnivores instead) and of horseshoe bats and their relatives, all of which
have elaborate nasal leaves or similar structure that they use in echolocation
instead. The rest of the bats mostly lack such elaborate nasal structures and even if they do, they still echolocate
using their mouths instead. So what?
…Well, it can mean that echolocation could have evolved in
the bat order at least twice, following two different evolutionary lines. Is it
a stretch? No more so than the theory that states that the pinnipeds consist of
two mammal superfamilies, each with its own affiliation – true or earless seals
one way, the walrus and the eared seals another – instead, but we digress. Even
professional scientists aren’t entirely sure as to how echolocation has evolved
– as it is usual with fossils, fossil bats lack soft tissues, and without them
it’s hard to trace the anatomical evolution of bats’ echolocation, as well as
the bats’ evolution properly – the first bat fossils appear to be largely
similar to the modern species, and their differences (that people can see) aren’t connected to echolocation.
Therefore, let us turn to the evolution of flight.
How did the bats’ flight evolved? Was it from the ground
level up or from the tree tops down? Here, we can safely say that it was the
former. Why? Because it is active, or true flight. …As opposed to the passive
or the gliding flight, utilized by the flying squirrels, the colugo, the
marsupial gliders and so on. Those animals do not have front legs modified into
wings, what they have instead is an organ named the pataglia that connects
their front and back legs; it isn’t exactly a handicap, but all of the gliding
animals – mammals, reptiles, amphibians, etc. – live in tree tops, or in case
of the flying fish – in the water instead…
Wait. Don’t bats live there too? (Just not in the water?)
Well yes, which brings us to the matter of the bat evolution in general – until
recently, they were considered the members of the so-called Archonta group that
includes primates, tree shrews, colugos or flying lemurs (but they are
certainly not lemurs at all) and etc., but now that group is obsolete, (it has
expanded and now includes also rodents and lagomorphs, aka rabbits, hares and
pikas as well), and bats, instead, belong to the Laurasiatheria clade instead.
This means that they are more closely related to European insectivores like
shrews and hedgehogs, as well as to the true carnivores such as cats and dogs,
as well as hooved mammals and cetaceans, among others. Pause.
…A while back I came across the concept of Afrotheria – a
clade of mammals that includes elephants and their cousins – sea cows and
rodent-like hyraxes, as well as the various African insectivores, (which are
not related to their European counterparts at
all) and the aardvark. It is a motley group of mammals, but still nowhere
as motley as the Laurasiatheria clade instead. The Afrotheria clade appeared in
the Palaeocene, the very beginning of the Cenozoic, the Age of Mammals. The
Laurasiatheria again has done one better – scientists claim that it arose 99
MYA, which puts into the Cretaceous, aka the Mesozoic, the age of the dinosaurs
and various other reptiles, extinct and extant. A second pause.
One of the initial advantages
of science over religion, (we are talking eighteenth/nineteenth/early twentieth
centuries here), was its’ clarity and straightforwardness. Just how good this
quality is is another question, true,
but the thing is that those days science seems to be going too far in the other
direction instead. In particular, most scientists themselves differentiate the Mesozoic
mammals from their Cenozoic cousins and keep them separate; to pronounce that
at that time – aka the Mesozoic, 99 MYA – bats had a common ancestor with
European hedgehogs (plus gymnures), shrews, whales, and hooved animals, for
example, is simply pretentious and deliberately obscure, nothing good can come
out of this take on science. But we have digressed.
…The evolutionary origins of bats are obscure, no matter
what the keen scientific minds behinds the Laurasiatheria and the Afrotheria
and the other such clades (whatever they are) might proclaim. However, we can
safely assume that the evolution of the bats’ wings came from the ground level
upwards, just as the birds’ did. In the first half of the twentieth century and
beyond there were plenty of arguments regarding the birds’ evolution, there
were many people claiming that the ‘protobirds’ had been tree-dwelling animals
that learned to glide first and then to glide; Zdenek Burian, who was the
founding father of paleoart in Europe, (that’s my opinion, and I’m sticking to
it), has even painted a, well, painting, of this theoretical animal; the result
was… a more subdued version of the real life Microraptor. If anyone doesn’t
know yet, this was a tree dwelling dinosaur with a gliding flight, wings on its
front and rear legs, and though it
was a ‘raptor’ it wasn’t a close relative of either the ‘true’ raptors –
Velociraptor, Deinonychus, Utahraptor and etc. - or the first birds. Yes, the evolution of
birds itself is still a tangled mess, for example Archaeopteryx, which, for a
long time, had been something of a canon ‘first bird’, has now been rather
demoted or sidelined… but regardless, Microraptor wasn’t a part of it, it wasn’t,
or isn’t, the ancestor of modern avians – but it glided, it lived in trees, and
by now scientists are certain that the various family branches of theropod
dinosaurs evolved various versions of flight several times throughout the
Mesozoic. Period. Where does it leave bats?
Well, basically, lucky that they were able to evolve at all –
Bruce Wayne might be their mascot, but birds are still the true masters of the
sky that bats are not. There is a reason as to why almost all bats are active
at night, (except for the fruit bats aka flying foxes, again, which can be
active around the clock), and it’s because otherwise they’d be outcompeted by
birds. This raises a question again as to how did the bats evolve their wings,
as well as why. Possibly, because they could not compete with other small
insect-eating mammals of the early Cenozoic, and birds, seeing how they are
real life modern dinosaurs do not function so well at night. All birds are
theropod dinosaurs, baseline daytime hunters as their cousins the raptors did,
(by contrast, tyrannosaurs had a very evolved sense of smell, so maybe they
could hunt at night as well), so at night they are at a disadvantage; the
proverbial owl hunts during the day as well as at night, (it might be a case of
case by case preference of when to hunt, because there’s plenty of footage
showing owls not being intimidated by falcons and hawks and similar birds of
prey at all), and the other birds that are active at night are oilbirds,
nighthawks and their relatives… essentially, bird counterparts of bats. Nature
does love its’ ironies, it appears. The ancestral bats found an ecological niche
in the early Cenozoic ecosystem – the same one that they are still occupying in
modern times, that of a flying mammal – and have stuck with it. That is the
generalization; the details still must be hammered out and uncovered, which
brings us back to echolocation.
…We have no idea per se just how and when did echolocation
evolve in bats, as fossils so far haven’t yielded a clear-cut answer to the
scientists, and neither do the modern bats – as we’ve discussed, they can be
grouped into two major groups: bats that echolocate using their mouths…and those
bats that don’t. This raises the possibility that echolocation evolved in
different ways in different bat groups and that complexes the picture further. Ah
well, this is what science is for – to give us the common folk answers to
question that we did not know about. Good luck to them and good luck to PBS
Eons with their thought-provoking videos! (Seriously, check out their YouTube
channel. It is truly impressive!)
… This is it for now, see you all soon!
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