Many theories and hypothesis arise about where first mammals came from.
The general accepted main-stream theory claims that mammals evolved from reptilians and that reptilians, in turn, evolved from amphibians.
This blog post presents an alternative theory better matching many experimental facts.
I will try to convince the reader that "mammals evolved directly from amphibians, and the first mammal to arise in planet Earth was no other than a tiny 'not so cute' bat"
First of all, a warning. The reader might be convinced that the established theories about the evolution of mammals are beyond any doubt or dispute.
Absolute truths set in stone, similar to Newton's laws in classical mechanics or the Dirac equation for relativistic quantum fields.
Nothing could be further from the truth. We know for certain that evolution is real, but the sequence of events that led from one species to another
is based on evidence with little scientific rigor. Not because scientists lack rigor, but because of the limited tools and resources available to them.
A few bones hidden underground for thousands or millions of years and carbon-14 dating are all the available tools.
Add to this the fact that paleontology is not a science of great interest to industry, and so with scarce fundings.
Only museum exhibitions, some occasional Hollywood movie about dinosaurs, and some optimistic and curious researcher
in a dimly lit room sustent this area of reseach.
Big mistakes and pitfalls are the rule and advances "accidental".:
Today we know that dinosaurs were covered in feathers, but for decades this was not the case.
More notably is the recent discovery that placental mammals, which for over a century were considered "incomplete" mammals, are actually
"evolved" mammals (Females evolved to be able to abandon the gestating offspring in case of an attack by a predator, so that they could at least have a new opportunity in the future.).
**Theories about evolution cannot be replicated in a laboratory**. We only have a few samples buried millions of years ago underground. We cannot repeat millions of years of random evolution of species that we don't even know existed under habitat conditions that we can only guess at. In this sense, it is more like theorical work on the String theory used to unify Quantum Theory and Einstein's curved space ("gravity"). We do not have a laboratory to test it, and no matter how exact and precise theoretical physics is, even the brightest theorists end up lost in a sea of doubts. Perhaps it is just a crazy theory, and the correct explanation will come from a theory of quantum gravity loops. Without a laboratory to confirm the theory, we are only talking about more or less intelligent assumptions. (even if theorical physicists counts with many more tools, funds and budgets than paleontologists!!)
Today we know there was a mass extinction of dinosaurs due to the impact of a large meteorite, but for decades, it wasn't even clear if it was due to a meteorite, an epidemic, invasive mammals, or an ice age. Again, the fortuitous discovery of the remains of a large crater in Chicxulub, Yucatán, provided the definitive clue. If this crater had been hidden underwater, NASA satellites would not have been able to locate it, and we would still be lost in a pit of mystery.
Now, let's come back to the theory of bats as the first specie of mammals in Planet Earth. Where this arbitrary claim come from?. Do I have some rests of bones or some DNA analysis to probe it?. Of course, not. To arrive to it I just support myself in spots of deductive and inductive reasoning and starting with some evidence nobody will deny.
Simply put: "Bats fly!".
It could look a curiosity at first sight, but a very weird one. It's weird because there is no doubt than
flying is something hard. Flying is difficult, very difficult. Flying requires lot of energy, lot of changes in the brain and lot of physiological changes in the body of a bat. It's also weird, extremely weird that bats are the only mammals that can fly.
Bats are closely related to rodents and in particular to their mouse cousins, up to the point that is quite normal to associate bats to flying mouses (at least for all of us not working in a Museum or Research Center). This is where some deductive reasoning takes place.
Darwin's theory of evolution explains how living beings evolve through
*small changes*. Random
*small changes* in the ADN provides some
*adaptive advantage* that makes the new specie to survive. The words
*small changes* and
*adaptive advantage* are highlighted because here is where things starts to fail with the current theories:
According to established theories bats evolve from rodents but this is very hard to explain with Darwin's theory of evolution. There is no small change that suddenly allows a mouse to start flying. There is no single change in the ADN that magically lets a rodent fly. Even if magically a mouse would be born with wings, its brain would not be adapted to flying. Even if magically a mouse would be born with wings and also magically its brain would change to let him fly its digestive system will not be adapted to consume all the energy needed to fly. Even if magically a mouse would be born with wings, with an adapted brain and a digestive system allowing it to fly, it will need changes to its breathing system, and some sort of mechanism not to loose heat throught its wings, and many other adaptations just because as already said, flying is hard to achieve, even for human engineers designing an airplane it's very, very complex (and humans count with the advantage of being able to burn tons of petrol to make an airplane fly, something forbidden to living beings).
Could it be the case that through thousands or hundreds of thousands or millions of years some species of rodents could evolve through small changes until, at some point, they were able to fly?
The problem with that hypothesis is that it goes directly against Darwin's theory of evolution. All the
*small changes* required for a bat to fly provide no
*adaptive advantage* until such a bat actually flies. Quite the opposite a mouse with "big wings" but unable to fly will be doomed to die. It will not be able to move and will loose heat very fast. This is exactly the same for many other adaptive changes.
And so, if the evolutionary step driving from rodents to bats are hardly difficult to explain, what about the opposite? What if rodents evolved from bats?
Curiously this question is much easier to defend while respecting Darwin's theory of evolution of species. Maybe just at some point the bat's wings started to become atrophied or the bat augmented its weight or its metabolism didn't allow them to consume as much energy as needed to keep flying. Not being able to fly will be a disadvantage that could be *immediately* be compensated by the fact that such a bat will waste much less energy by just "walking". This is something we have already observed in birds and specially in the now famous Albatross in the Galapagos Islands.
So let's assume the arrow of time moved forward from bats to rodents. What then?
Where do bats came from, if not from rodents? What other mammal could evolve to the point of creating such curious flying mammal? They easy answer is: NONE.
The same arguments that lead us to the conclusion that rodents can't be the parents of bat would apply to any other mammal.
There is no such mammal. Bats are actually the first mammals living in Planet Earth.
Who was them the parent of first bats? Well, I have not a answer to this question. My time machine to travel 50 millions back in time and check for a definitive answer broke last week. Intuitions tells me that, with (high?) probability, some sort of flying frog were the direct ancestors of bats. I base this hyphotesis on the next matches:
- Both frogs and bats emit sound and they do with similar patterns (note: this claim was written around 2017, check for updates later on a few years a few paragraphs down for key discoveries around this). No other amphibian or reptilians have such a feature. Emitting sound as frogs and bats do require important changes and new "modules" in the brain to be able to control it. This is an extremely sound coincidence for such small primitive creatures with small brains and in fact the audible sound emitted by
bats resembles to a certain point to that of frogs (
https://www.youtube.com/watch?v=ppLsu5Z2Np0)
- In general both species are much more active during the night.
- The physical appearance of flying frogs and bats have many coincidences, specially their "hypertrophied" hands-wings.
- Both have insects as main source of proteins.
- Size and weight match.
To hypothesize that a flying frog could at some point be able to "just fly" is not hard to believe and there are adaptive advantages in passing more and more time flying. It could be that at some point this flying frog could pass most of the time flying. This would trigger many fast evolutionary steps. It will first allow that flying amphibian to traverse many distances in search of food or just escape from predators with easy favoring their flying skills. Its lungs will grow fast to allow to breath more oxygen from the air and pass more time flying. Greater capacity to absorve great quantities of oxygen from air will quickly favor warm-blooded metabolism (Curiously the other warm-blooded species in animal kingdom apart from mammals are birds who also fly). With wam-blooded metabolism, carrying the foetus inside protected will provide another adaptive adavantage.
The animal's fur would protect it from the wind. At some point this flying frog changed and a first mammal, a primitive bat, was born!.
If a theory is to be taken seriously it must also have some predictive power. Let's examine what this theory can predict:
- If bats were actually the first mammals on Earth there must be many different subspecies of them after so many years of evolution. This is in fact true, and as today bats is the second more diversified specie in the mammal kingdom living in all sort of climates and places. Curiously they are only surpassed by rodents, that will be nothing more than adapted bats.
- If bats were actually the first mammals there must exists fossils where no other o very few other species of mammal actually exists. This is actually true, and fossils of bats have been found in places where other mammals were difficult to find.
- If all mammals come from bats there must be some trace easy to identify. This is not so evident, but in fact bats needs lot of brain power to control their wings. Curiously bats wings are nothing more than hands in newer mammals, and curiously many mammals have extraordinary skills to control their hands than no other terrestrial specie do have. Mammals brain also have a great power to understand the world in "three dimensions", something that could have appeared while bats learned to move in three dimensions.
And finally, as a gift for curious researches with no plans for the weekend, this is a non-yet-proved predictive fact of this theory. It's well known that bats use sound to localize and hunt insects. My hypothesis is that some (or many) species of frogs could be using that same mechanism to localize insects, and not just as a way for males to get the attention of females. It's even possible that they will be using the same frequencies and we were not noticing it just because we didn't even thought about it. The inflated vocal sac of the frog, full of sensory nerves, can be a very good tool to detect the echo of the croaking just put your hands in an inflated balloon to feel the sound with the touch.
Could it be that the bat's wings (their fingers with big membranes full of sensity nerves) are also used as part of their echolocalization system? I guess this is the case. Why settle just for the ears, when their finger-wings are some excellent parabollic (aka "directional") antennas.
Update 1, 2017-08-09:
I'm enjoying summer's holidays now. Time for beach and caipirinhas in the sunny coast.... or even better, time for updating my theory on bats and mammals evolution.
I just landed by pure chance to a web page with
a complete collection of bat-faces. The first thing that anyone will notice is how many distinct bat faces can be. But more interestingly and related to this post is the fact that many of those faces resemble many other different branches of mammals. Some fruit-bats clearly resemble to a lemur, an sub-specie of primate, that curiously have the same feeding habits that the bat it resembles to.
Please, I'm a bat! not a lemur
Then we have the Hammer-headed bat whose aspect is quite close to a primitive ruminant and again, another "random" coincidence, I read that those species of male bats
"possesses an enormous head for producing loud honking calls" like ruminants, and that they live in zones of Africa that match those of African ruminants with similar
lek mating habits !!!
Why not speaking about the naked buldog bat,
whose movements resemble those of a feline. Again new coincidences. Those naked bats are typical of Asia, where the first skulls of felines were found.
The face difference between some other bats and hedgehog (who are also insectivore) are hardly to distinguish.
In conclusion, we have a family of mammals, the bats, that share many physiological and behavioral characteristics with many other family of mammals (primates, ruminants, felines, rodents), with little resemblance between them. This point outs to bats as common denominator (or in evolution terms, as the root of evolution for mammals).
Update 2, 2017-08-09:
I also read on page 67 of
this book that
"the earliest known fossil of a primitive bat, an insectivorous species from the Eocene period was found in America. Bats had certainly existed for the previous 50 million or more years, but their evolutionary history is poorly known since their small, fragile skeletons do not lend themselves well to fossilization". This "fragile skeletons" explanation is difficult to sustain, considering that fossils for much more fragile structures have been found, even
for bacteria.
I have a much simpler explanation. Fossils were in fact found, but they were confused with those of an amphibian (a frog or similar), since by just looking at the skeleton it would be impossible to know whether it was still a "frog" or a primitive "mammal"
.
Update 2, 2021-12-30:
More than 4 year ago I predicted that if bats had evolved from frogs it could also be possible for some type of frog to be using sounds to hunt their preys. Today I just got aware of
this link speaking about a weird Torrent frog, able to listen sounds in the 128 kHz ultrasonic frequency, raising the question of whether frogs might use ultrasonics for echolocation, the method bats and dolphins use to find their way around.
Digging a little bit further I found
this other link where it is written """(Torrent frog) Males have ear canals with recessed tympanic membranes at the end of the canals, like mammals but unlike all other anurans except for Huia cavitympanum (Feng et al. 2002).
""" (yet another curious coincidence with mammals), ...
"Vomerine teeth are present " (like in bats),
...
Update 3, 2024-04-21:
Yet more "matches". A new
article published by Ubiratã Ferreira Souza, Guilherme Augusto-Alves, Mariana Retuci Pontes, Lucas Machado Botelho, Edélcio Muscat & Luís Felipe Toledo, mention the discovery of a frog using ultrasounds as a defensive strategy. My guess is that such frog is just hunting "a la bat".
Update 4, 2025-05-03:
An article was recently published in the
Proceedings of the Royal Society by Logan S. James, M. Teague O'Mara, Justin C. Touchon, Michael J. Ryan, Ximena E. Bernal and Rachel A. Page titled "The ontogeny of decision-making in an eavesdropping predator". They present their findings of fringe-lipped bats (Trachops cirrhosus) capacity to detect the acoustic advertisement calls of co-occurring anurans (frogs and toads!!!). Bats are able to learn, through the time, to detect the type of frog and choose to attach to palatalbe frogs while rejecting poisonous toads, based on the type of sound or acoustic cues emitted. The results offer the first evidence of developmental changes refining decision-making in an eavesdropping predator in the wild.
"It's truly remarkable that
these bats hunt using the calls of an entirely different group of animals (frogs) in the first place, and we have wondered for a long time how these bats acquire this unusual skill," said Logan James, STRI postdoctoral researcher and lead author of the study.
... (A little bit less remarkable after reading this blog post).
