Alien Biosphere Evolution #4: Constraints Shape Animal Phyla

[@Alteori]

I love alien biology and scifi but I love how you present this as a ground-up science series 😀

[@geheimest4781]

How can it be that I find you under every video that I watch.

[@jaysonklein6018]

"I like to poop out one end." "I like to poop out the OTHER end." Brilliant. 👏👏👏👏

[@pigcatapult]

I was like, "Is that baby horseshoe crab having a seizure?" but no, they were just molting.

[@p00bix]

That was a Tadpole Shrimp (Order Notostraca), not a Horseshoe Crab.

[@quentenwalker1385]

I am just loving this series - especially as I like to design reasonable alien plants and animals, let alone sentients

[@Phrenotopia]

Thanks and stay tuned! I will get into more detail and starting speculating more and more as the series progresses.

[@ImpossibleEvan]

This man has helped me so much with my speculative evolution project

[@mechd3stroy3r63]

RNG is the rule of life

[@yanberry846]

Loving the osomatsu-san comparison xD

[@Woodledude]

You know, I've always been curious - We see both a through-gut and a blind gut throughout evolutionary history and into today, but have there ever been, or could there be, a "through-lung"? Basically, a respiratory system where air goes in one end and out the other? I must wonder what modes of life such an origin body plan might enable... Could it be more efficient at absorbing oxygen? Store carbon dioxide temporarily the way our body does with other waste products, to be disposed of at opportune times?

[@Phrenotopia]

Yes, there is, more or less. Birds actually have a unidirectional lung, which makes sense with their need for a sustained oxygen-supply during high-powered flight. Although, they still need to breathe in and out through the throat, in the lungs themselves the air can only go one way. Also, pumping action is provided by air sacs permeating the body meaning that the harder they flap their wings, the more air is forced through. So birds are a pretty alien alternative to mammals as a highly advanced vertebrate and a close match to your question.

[@Woodledude]

@@Phrenotopia Aha! So it can be more efficient, and is actually used in nature to an extent... Obviously, a true through-lung would have some issues that need to be solved, such as immune response for any invasive organisms within it, maintaining movement of air through itself, and the most obvious one - Air circulation is a far more time-sensitive need than something like digestion of food. Any active systems involved in moving air through the through-lung need to be worth the extra payoff, and this all needs to happen very quickly... Perhaps not having to process and filter outgoing air provides enough benefits? I could imagine a through-lung could work very similarly to a mammalian lung, actually. All you'd need is a set of valves like the ones in the heart, which prevent air from back-tracking as the lung inflates and deflates. You could even have multiple lungs, each taking in air while others aren't, achieved by very simple "rotary" actuation, say of a band of cartilage being bent into each lung successively to help deflate it, actuated by muscles near the base. So many possibilities! And I imagine at least some forms of life would really appreciate the extra potential of this body plan, too. It's probably a lot of work to make something like this really, properly plausible, but dang if it isn't fun coming up with ideas like this.

[@Phrenotopia]

@Woodledude - I don't think a through-lung in itself is harder to evolve per se. It all comes down to the developmental constraints imposed by ancestral adaptations and the resulting body plan like I explain in the video. Vertebrate lungs were presumably initiated by early fish swallowing air bubbles from the surface either for extra oxygen, increased buoyancy or both. This then led to the development of an outpouching of the throat and eventually the (dead-ended) sac-like structure that in time turned into the tetrapod lungs and the osteichthyan swim bladder, respectively. However, a different initial strategy may well have led to through-lungs. After all, fish gills are unidirectional themselves, so these could also have been evolved into lungs somehow. In fact, mudskippers come very close to a scenario like this. At some stage, I want to dedicate a whole video to lung varieties and speculate on unseen alternatives.

[@Tann114]

Hey this is really awesome, exactly the sort of stuff I've been thinking about recently! Great job : )

[@Dragrath1]

Fairly good it did bother me that you used some well outdated scene for the Ediacaran but it is quite fascinating the role luck plays in evolution or how some niches are way more vulnerable to environmental perturbations while some are highly resilient to one sort of catastrophe but others seem to just wipe them out despite other creatures getting spared. The Cambrian explosion is interesting in while there were clearly major changes it is hard to pin any one of them as the cause, You had glaciations the decline of microbial mat based ecosystems the latter of which had a disproportionate effect on fossilization that makes it hard to identify creatures before and after. I wonder if the ice age conditions led to a spike in oxygen which allowed more active animals to out compete microbial mats in a way they hadn't before. And then there is a lot of details revealed in recent years about the causes and factors involved in various "major" and "minor" mass extinctions. Did you see the Science advances paper(open access) on how a major collision out in the asteroid belt likely drove the onset of the previously confounding Ordovician Ice age that blew my mind and serves as a cross discipline solution to an existing mystery found by looking for planets around other stars and study of meteorites on Earth.

[@Phrenotopia]

Well spotted, and not to worry! I will make up for this minor sleight of hand in the next installment. Here I will dive into the nature of the Ediacara biota in more detail and try to go through some of the factors that could have played a role in initiating the Cambrian "Explosion" for as far as my research went. You have to keep in mind that these videos are for a general audience and I don't have ample time and resources, so corners have to be cut, if I am to get anything out at all. One thing that you missed was that I allowed an illustration of a multituberculate to pose as marsupial ancestor. Still, these visuals are there merely to illustrate a point to the average viewer and not to be parsed for details like a true scientific publication. BTW I haven't seen that paper in Science (I barely have time to just make videos), but thanks for the tip and it does indeed sound fascinating!

[@JontyLevine]

"Fixing something as fundamental as a body plan will almost inevitably break it." This is true, but it doesn't really explain why it would break it. I like to think of it this way: adding, say, an extra pair of limbs to a four-limb body plan may indeed be an improvement in the long run, but limbs are complex parts that require many smaller changes in order to work properly. And a half-formed proto-limb is not going to offer any immediate benefit to a creature that already has limbs. So these sorts of changes are therefore selected against. It's easier for a creature to _lose_ a pair of legs if it no longer has a good use for them, such as in snakes and cetaceans. But in order for a complex feature like a leg to arise out of nothing, it has to offer benefits at all stages of its development, as indeed it did with the evolution of eyes, or the evoluton of limbs for the limbless sea creatures that may not have depended on walking on them right away.

[@definitivamenteno-malo7919]

I love this series. For real. I love Science fiction even in fantasy settings.

[@GubekochiGoury]

Where is the advanced polychaetes video? I'm really intrigued by the idea...

[@idle_speculation]

5:37 There was actually one hoofed marsupial, the pig-footed bandicoot of the genus Chaeropus. They were able to get around the constraint of having to climb into the pouch by giving birth while laying on their sides, which made the process much easier.

[@Phrenotopia]

Interesting! That adaptation would certainly open a pathway to ungulate analogues.

[@erisstewart4236]

Yes.

[@dklowpoinde9239]

Phrenotopia

[@idaileb5246]

This was super interesting

[@thekingofnipples9806]

I really enjoy the images you have next to the evolutionary vocabulary makes it very easy to understand. I also thought the bit about imagining alien biospheres, can't wait for the next episode!

[@Phrenotopia]

Thanks for letting me know! I sometimes feel I spend way too much time on the visuals, so very nice to hear it's not for naught!

[@kayseek1248]

5:33 Australia is my home.

[@juanjoaniortemontoya8257]

very interesting!

[@danielwols]

when does the actual evolution stuff going to happen? like how biblaridion did?

[@Phrenotopia]

I want to get a better grasp on the theoretical foundation first, but will get eventually to a point where I will do my own speculative biospheres.

[@lexibyday9504]

Well the marsupial horse doesn't need to have hooves it just needs to resemble a horse or be usable as a horse. The marsupial horse would most likely be a large quadrupedal herbivorous marsupial that can be ridden or used to pull things. it's strong climbing front claws allow it to scale mountains better than a horse but it's lack of hooves limit it's carrying capacity and mean it needs more frequent breaks. Australia's inhabited area is predominantly mountains though so it would be more practical than a horse for this country as travel times would be shorter. The ability to just scale steep slopes could even make it a more practical means of travel than cars resulting in gradual but drastic changes to Australian cities. But how does this benefit the animal? That's what evolution wants to know. Herbivores only need to get big to avoid predators and only can get big when competition is low. The niche for a marsupial horse just isn't available. Or is it? Any suggestions?

[@annawing770]

If those really big eagles (like, big enough to carry off a 5-year-old child) lived on mainland Australia instead of New Zealand, and if they never got wiped out by human tribes living there, then that could be a possible trigger for a lineage of kangaroos in the mountainous regions frequented by large birds of prey to possibly grow to around the size attained by the small, stocky breeds of ponies bred in some cold, rocky regions of Europe. The pony-kangaroos would possibly be worth keeping as livestock by aboriginal peoples recognizing a reliable source of food when they see one, bringing these tribes into an age of pastoralism that was never achieved in Australia in the real world.

[@lexibyday9504]

@@annawing770 I hope you realise that you've painted a beautiful setting for an australian fantasy novel that either I or someone else is now going to write.

[@annawing770]

@@lexibyday9504 If you write it, I hope to be among the first to read it.

[@fishyfishyfishy500akabs8]

Didn’t megalania live in Australia? Also komodos

[@annawing770]

@@fishyfishyfishy500akabs8 Yes, but giant lizards don't do as well up mountains as birds of prey do, so competition with aforementioned giant eagles would probably have kept them to flatter ground for the most part.

[@balazsvarga1823]

Polycete worms? Star wars benis worm.

[@cameoshadowness7757]

:0 What if an insect becomes hollowish to help with the air situation? Will that ever be possible? Also did you ever saw my alien tree? I can't remember if you did or didn't?

[@Dragrath1]

Hollow insects wouldn't help as that is basically their current solution to get over their size constraints a closed circulatory would be the most effective way to get around their limitation by allowing them to concentrate oxygen rather than relying on ambient gas levels

[@cameoshadowness7757]

@@Dragrath1 ooooh! Got ya!

[@Phrenotopia]

@Cameo Shadowness - Yes, wasn't that the tree I told you was like a phenogram? :) For the rest I concur with Dr A Grath here. The biggest constraint is the exoskeleton. Spiders e.g. have lung-like organs which in theory could have been coupled to a circulatory system. But the exoskeleton becomes increasingly massive in comparison to endoskeletons and leaves too little space for muscles above certain sizes.

[@cameoshadowness7757]

@@Phrenotopia Sorry I couldn't remember. I couldn't find my comment in your other video either so I didn't knew if I told you! Super sorry! Also, I didn't know that about spiders?! That is yet another epic fact about them :3.

[@parmaxolotl]

But there are land polychaetes! Earthworms!

[@Hilja1suus]

Earthworms aren‘t polychaetes, though they are also annelids. They are oligochaete annelids, more closely related to leeches. They do share some features with arthropods and vertebrates, but lack the more complex limbs and movement system of some of their polychaete relatives

[@parmaxolotl]

@@Hilja1suus "In 2007 Torsten Struck and colleagues compared three genes in 81 taxa, of which nine were outgroups,[9] in other words not considered closely related to annelids but included to give an indication of where the organisms under study are placed on the larger tree of life.[63] For a cross-check the study used an analysis of 11 genes (including the original 3) in ten taxa. This analysis agreed that clitellates, pogonophorans and echiurans were on various branches of the polychaete family tree." "Also in 1997 Damhnait McHugh, using molecular phylogenetics to compare similarities and differences in one gene, presented a very different view, in which: the clitellates were an offshoot of one branch of the polychaete family tree; the pogonophorans and echiurans, which for a few decades had been regarded as a separate phyla, were placed on other branches of the polychaete tree.[61] Subsequent molecular phylogenetics analyses on a similar scale presented similar conclusions.[62]" From Wikipedia, earthworms are clitellates btw

[@adrianokury]

@@Hilja1suus -- parmaxolotl wasn't referring to the traditional Linnean ranks, but to the cladistic approach. As he elegantly put, the polychaetes would only be monophyletic if they also included some non-polychaetes as the Oligochaeta.

[@titanomachy2217]

I believe arthropods evolved from polychaetes. I don't care if they aren't both in the proposed clade Ecdysozoa, I believe moulting is a more derived trait in the Panarthropoda, which wouldn't have characterized the original lobopods. I think the clade Ecdysozoa is invalid. Who says everything that sheds its skin is related? Reptiles shed their skin, and yet they are chordates like us, not Ecdysozoans. I think it's the same thing going on with roundworms and arthropods, they convergently evolved to shed their skin. I mean, look at the early lobopods. Many fossils from the Cambrian cannot even be distinguished between polychaetes and lobopods, it is nearly impossible to tell where one ends and the other begins. I am surprised the hypothesis that arthropods are derived polychaetes hasn't gained more traction, I mean I do see some pop science articles that talk about this connection but it looks like the general consensus within the scientific community itself sides against my position and with the validity of Ecdysozoa. If arthropods did evolve from within that clade, what the hell would they have evolved from specifically? Roundworms? The mud dragons? The Loricifera? I just don't see it.

[@idle_speculation]

There are a lot of other anatomical similarities between ecdysozoans, such as amoeboid sperm and an absence of spiral cleavage in embryonic development, which sets them apart from all other protostomes, annelids included. There’s also the internal throat teeth and oral cone.

[@titanomachy2217]

@@idle_speculation So you think lobopodians evolved from nematodes of all things? Why do we see no polychaete-looking transitional forms between roundworms and panarthropods? Some Cambrian polychaetes are so similar to lobopodians anatomically that paleontologists first assumed certain lobopodian worms were polychaetes before resolving their true affinity to arthropods, but the confusion is understandable as one seems to bleed into the other, much like how eurypterids segway into early scorpioform arachnids so seemlessly that species like brontoscorpio are sometimes referred to as eurypterids and sometimes referred to as scorpions, and yet if you ask the average paleonerd, they'll tell you the two groups are only distantly related, as though arachnids evolved from some yet to be discovered group of Silurian chelicerate arthropods, when the morphological similarities are just too striking to be ignored. I know convergent evolution can be misleading, but I feel like I am just applying Occam's Razor and concluding that, for instance, apes are mammals and not some kind of weird arthropod that just convergently evolved to look like mammals. Unless there is some other likely lineage for panarthopods to have descended from, I don't feel convinced that these distinctly similar-looking groups are not closely related. If something as specific as a body plan of repeating similar segments with limbs or pseudopods combined with oral tentacles or antennae and chitinous claws could convergently evolve in both annelids and lobopodian worms at the same time as you allege, then why would it be far-fetched to suggest that molting, oral cones, and an absence of spiral cleavage as is seen in spiralians like annelids could evolve in the various ecdysozoa separately, or at least between the more primitive ones and the panarthropoda. I feel like reproductive methods and embryonic development isn't really a great way of discerning or grouping taxonomy. Very closely related organisms reproduce and develop in vastly different ways. Some fish have penises, most don't. Some reptiles have penises, some don't. Some sharks are oviparous, some are viviparous, and some are ovoviviparous. Some plants are unisexual, some are bisexual. Some echinoderms can reproduce through splitting, some cannot. Hell, there's a species of cave-dwelling insect in South America in which the females have spiky penises and the makes have vaginas. Evolution produces some drastically different reproductive methods from closely related groups. Wuthering placental mammals like humans are quite unique in embryonic development because we form the blastocyst, while almost all other animals form only a blastosphere, and yet that doesn't mean eutherians aren't mammalian animals, it just means they have a unique quirk, and I see no reason why two groups couldn't independently evolve the same mutations. I don't see why the gene mutation that causes spiral cleavage or switches off spiral cleavage couldn't exist independently in any two or more groups of organisms. And at the end of the day, I trust morphological analysis slightly more than genetic testing. If a genetic test says I'm a banana tree, and I somehow rule out human error, I'm going to believe I'm a human nonetheless, one with banana genes that have magically wound up in my genome somehow, like a banana retrovirus. Similarly, I see no evidence in the fossil record or in anatomical structure of modern roundworms and arthropods to hint at any close evolutionary relationship, it is only a matter of RNA studies performed in the 90s. Scientists get stuff wrong, actually more often than they get it exactly right. And the convergence of genomes is a thing too, it's not just external appearance but also the very genes that can be similar to genes in other organisms for a variety of reasons other than divergence. Some organisms and viruses even alter the genes, so perhaps both groups were impacted by the same viruses. And some features can be switched off for millions of years and then get switched on again, like primates being able to see in full color like our reptilian ancestors, unlike other mammals. I realize lots of early animal forms had to take a basic bilaterian shape, which is pretty much a worm shape, but I think the lobopodians and polychaetes have a lot more in common than just general body shape. It would be fine if the ecdysozoa clade were a hypothesis among many and scientists admitted we don't know what arthropods evolved from, but for some reason it is treated like some kind of certainty, you don't see science communicators telling the layperson that it's an open-ended question that we are still investigating, you see arthropods listed as ecdysozoa in the textbooks with no addendum about how certain we are about it, like they would do with turtle evolutionary affinity. Convergent evolution usually results in only superficial similarities, and when you look at the actual morphological structures that are being used to ID the group of organisms in question and its cladistic relationships to other groups, you can see that they are not homologous to the structures in another group which look similar at first and serve the same purpose in a similar niche. Something like an oral cone, molting, or non-spiral cleavage in embryonic development seems pretty superficial to me. We should be able to look at the overall body plan and see some connections, but it seems to me that they go "Look, these both have mouths and RNA studies say they're related." Well, RNA studies would show we're all related, but it doesn't make you my mom or dad. Those RNA patterns could have evolved in their pre-Phanerozoic metazoan ancestors or early bilaterians, before they branched off, and they could have simply mutated out of the genome of annelids since then.

[@titanomachy2217]

@@idle_speculation And oddly enough, some annelids actually DO shed their skin. Are they suddenly ecdysozoans now? Leeches shed their skin to grow, and many polychaetes shed their chitinous claws and pharyngeal jaws to grow bigger ones as they age. And could the oral cone not simply be a general, simple structure for feeding in primitive animals? I think some scientists have become too reliant on sophisticated technology and have lost the ability to see the forest for the trees, like a woman that won't believe her child is actually her baby until it is DNA tested, even though she just gave birth to it. Oh, the Hox gene shows up tardigrades and nematodes, guess that means insects are highly derived roundworms. It just seems like quite a leap of logic to make. Tardigrades aren't the entire panarthropod phylum anyways. There have been various slightly arthopod-like organisms that are unrelated to them, like the mud dragons for instance, with their chitinous exoskeleton over a body of repeating segments, or stylophorans, those bizarre echinoderm things that we couldn't place for a long time that some scientists thought were chordates or ancestral to chordates. When it comes to clades as broad as the ecdysozoa, we are very hazy on the legitimacy of such a grouping, and we will almost certainly have to adjust our understanding over time to the point that what we believe in the future becomes unrecognizable compared to the popular beliefs on the subject of today. If I had Hox genes, would I then be an ecdysozoan? Of course not. Genetics isn't everything.

[@titanomachy2217]

@@idle_speculation I also disagree with the placement of nectocaris within the Cephalopoda, as it is often claimed to be. Early cephalopods had shells, resembling snails with tentacles around their mouths, kind of like conchs. I think nectocaris is possibly some kind of crazy flatform or maybe even a lanclet-like chordate. I doubt it was an arthropod or dinocaridid. Are there any popular ideas in taxonomy that you disagree with? I think the definition of "species" needs to be cleaned up, simplified, and test it more rigorously. Just because two supposed species live in different areas and don't breed with each other because of geographic separation doesn't necessarily mean they are distinct species. Subspecies perhaps, but not species. So long as any two organisms can bring forth offspring that is viable more than 50% of the time, I consider those organisms to be the same species. I think it is absurd to be so specific about naming distinct species without ever even checking whether a male-female pair made of individuals from either group can conceive and carry to term a hybrid offspring, especially when all of humanity is lumped into not just the same species but the same subspecies, pretty much arbitrarily so as to not be "scientific racists" or whatever. Making it more complicated than whether or not viable offspring can result from a coupling just muddles the concept, making it inconsistent. At least more and more scientists are starting to acknowledge that Homo neanderthalensis is really more accurately referred to as Homo sapiens neanderthalensis, as is the case with Homo denisova. It's weird how it is socially acceptable to dehumanize people groups so long as they are extinct. Neanderthals were just as human as you or I, and yet they were maligned as barbaric cavemen, inferior to the supposedly more intelligent and graceful Homo sapiens. We're a culture that doesn't fear speaking ill of the dead, but quakes with fear over the possibility of being socially ostracized and character assassinated for saying something that could be construed as offensive to groups with lots of social capital. Hybridization isn't only common in nature, it's basically the norm, and the concept of a "pure" species is erroneous, as all species are mutable. Humans aren't just Homo sapiens sapiens, we have a variety of different admixtures from other archaic Homo species depending upon what racial background you have. Somehow, according to the politically correct, different races having DNA from different Homo groups like Neanderthals, Denisovans, Homo erectus and Homo naledi, still doesn't undermine their dogmatic belief that "race is only a social construct", which they will juggle with the knowledge of human biodiversity with impressively flexible mental acrobatics. Franz Boas completely ruined anthropology, turning it from a dispassionate and analytical science into a pseudo-religious litany of rules. You can't get an "is" from an "ought", but they certainly try. They insist that because denoting extant human biodiversity could potentially be seen as a means to justify racism, they have to disavow the concept of human biodiversity existing anywhere but in the prehistoric past. I don't think so lowly of mankind as them, I believe we are mature enough to know the truth without taking it to an illogical place of value judgments of entire groups of people and acts of oppression or violence against them. Evolution never actually suggests that any species could be "superior" or "inferior" to another.

[@ferencgazdag1406]

I think evolution is slow, because if there was some gene what enhanced the evolutionary potential of an organism, it would be relatively quickly mutated to be disfunctional, and will thus be expected to be less frequent. Because of this, after enough itterations, the only genes still common would be ones that minimize the chances of their own mutations.