Dude you're an amazing explainer!! If I had had a science teacher like you I would have been a biologist instead of a lowly mathematician!! Thanks for sharing your insights and reasoning!! Prester Bob
I feel the internal skeleton would be the major sticking point for alien vertebrates: It seems that, for the intial function of holding the gills open, it would be just as good to have external valves, which would also provide further advantage in the form of armour. While it might be workable before predation is common, it'd have to be quite advanced (and the alternatives being less advanced) by the time predation comes on the scene to have a good chance
I don't know but the resource economy is very important when depredation begins. Does an armour deserve all the energy an resources when you can run and hide? Gills seems to be the winning choice. Plus, a mouth. But I can be wrong.
@@DrNova-hj6co Slower/Sessile armoured creatures are quite a common type of animal, so don't be so quick to discount it Furthermore, there's no reason a primitive creature couldn't have small light valves, similar to gill supports but in the exterior: This wouldn't slow them down any worse than internal supports, but would still be better as armour in the case it gets caught
In regards to gills and the internal structures which supported them it's worth noting they also appear to have played an important role in the development of gnathostomes as the genes involved in the formation of gill arches in jawless fish coupled with one of the preserved molecular fossils of polypoidal hybridization seems to have lead to the parts of the duplicated genome involved in this secondary gill arch structure becoming repurposed into jaws. Polypoidal hybridization events are rare in animals but when they do occur they lead to some of life's most dramatic morphological developments in body plans. Incidentally the evolution of jaws was a major innovation as it made the armored slow moving/sessile lifestyle much harder by allowing gnathostomes to bite through and crush shells or exoskeletons, once gnathostomes appeared invertebrates were forced to adapt or go extinct. Among arthropods for example some got spiny or even more heavy duty armor, some got fast and streamlined, some even moved into freshwater and eventually into land to escape... only for jawed vertebrates to follow course several hundred million years later.
I wonder if life evolving on an alien world in which the life forms don't have access to a substrate would evolve a central notochord and are not bilateral. For example evolving in an ocean without access to the bottom or evolving in a thick atmosphere?
@@AnarchicMakotoI always enjoy it cuz then I immediately know most of all I need to know about a person empathy and morals-wise, especially given the left libertarian skew of the compass.
I once conceived of a kind of plant like alien that developed seed capable of active flight to spread, which eventually evolved into a non-sessile species. Turns out that's just us, who would've thought...
also, i wonder if the flipping of the nerve cord has something to do with how our nervous system undergoes torsion and results in the left brain hemisphere controlling the right side of the body and vice versa? perhaps instead of having to restructure the entire creature nervous system to essentially operate upside down, it wouldve been 'easier' evolution-wise to just twist the rest of the body below the head 180° so that the notochord is dorsal, yet the brain is still in the correct orientation.
@@Phrenotopia From what I can tell at least in cephalopods and arthropods the brain/nerve clusters are centralized/focused around the mouth. I far as I can tell don't believe they do a similar flip reversal so you might be onto something since their neural structure is as a whole simpler with a more direct connection to their limbs than is seen in vertebrates though cephalopods in particular have a consequential problem with their mouth going through their brain which limits their ability to swallow large pieces of food.
One interesting theory I picked up is that it may have to do with the fish-like habitus of early cephalochordates, as visual systems became more advanced and sideways eyes developed. There could have been an advantage of having muscles on one side of the body respond quickly to whatever happened on the opposite side of the body, by contracting abruptly thus veering the body away from danger.
from an engineering perspective, it makes a lot of sense to have a rigid compressive element in the center (bone) surrounded by tensile elements (muscles). for example, a tent, a yacht mast with rigging to hold it up. buckminster fuller called it a tenseigrity. it can get quite large but also be very light weight. 10 steps is quite a long list, but do they need to happen in that order? Maybe they could occur in a different order, but on earth, once vertibrates existed, they moved into any niche they could effectively blocking out any convergent design approaching from a different direction
This was an absolute blast to watch! I especially like the idea of dual spine, one of the lineages in my project incorporates it. Also the bench to coatrack analogy was hilarious lol.
Wow. I must watch this awesome video again because my English is not good enough yet. But something I read time ago came back to my mind: It seems one more purpose of the skeleton was to store phosphorus. Anyway. It's interesting.
I think it was a mix of both a need for a _support structure_ and a _storage system_ for calcium and phosphorus. Just the prior led to cartilaginous and chitinous skeletons. Just the latter would likely lead to a single large mass of highly porous bone.
I love this video! After the last video, I was worried this video would support the tunicate ancestor hypothesis. The idea that ancestral chordates were tunicates, whose larvae underwent paedomorphosis and became cephalochordates and vertebrates. I still see people support this hypothesis, which drives me up a wall because Tunicates are no longer considered basal chordates.
Thank you and Yeah don't worry 😄 I've been scouring the literature to get a grip on the latest insights. Neoteny did occur but presumably in a enteropneust stage
@Phrenotopia Yea, I find that interesting. I always thought the ancestors of deuterostomes were pelagic filter feeders; ambulacraria evolved as an adaptation to a benthic lifestyle, chordates evolved as an adaptation to a pelagic filter feeding lifestyle. I did a little bit of research after watching your video, and really I believe no interpretation is wrong at the moment. Some authors support a pelagic ancestor of deuterostomes, others a deposit feeding ancestor. (At least as far as I can tell) There’s really not enough genetic data to fully reconstruct the ancestors of deuterostomes at the moment.
I recently stumbled upon some of your amazing videos and am super impressed. Might you consider doing an "About me" video, giving your background, CV, etc?
Double spines with a ventral and dorsal branch would be a difficult fluke. First: Why double this structure? Second: How to keep them synchronized while swimming? However: would a central spine be a possible outcome - maybe the digestive system placed at the ventral side of it and other organs at the dorsal part of the body? It could work in the end (at least with ribs curving upward to suspend the upper organs from), but which steps could lead to it? A ventral spine would mean the digestive system about it, which would probably exclude some kinds of feeding. It could work in the water (more or less), but on land it would become a challenge, all the organs pressing on each other, so a land-going species would probably have to flip over to get a dorsal spine again where all the organs can be suspended from.
This is a lot of great food for thought; excellent speculation and coverage of the known elements; and many thanks for including some of the lesser-known members of the chordates & family. I just have one question, @phrenotopia - the Micrognathozoa have a large number of bones in their heads, but not in their bodies, and they are in the other side of the animal kingdom from chordates...they're closer to arthropods and molluscs. Do you think that they developed their skulls in the same way chordates did, or is another strategy in play there? Regardless, great work!
How did Deuterostomes disentangle the anterior gut from the ancestral neural ring? Do you see it as being as simple as opening a new mouth and closing the old one? Are there relics of the ring in the nervous system of any living Deuterostomes?
It depends on whether the mouth was formed through amphistomy too or formed anew. Interestingly, they found out that the lancelet"s mouth is not homologous with vertebrates but a novel formation, apparently derived from an anterior gill slit.
'Lancelets can swim' - Lancelet smashes headfirst into the seafloor
bonk 😂
@@Phrenotopia Lol, you never said they could swim *well*!
@@Cranberrie123 I mean they swim quite OK, but they're basically blind 😁
In order to crash, they have to first be moving...I learned that firsthand. :)
They don't have a head
Dude you're an amazing explainer!! If I had had a science teacher like you I would have been a biologist instead of a lowly mathematician!! Thanks for sharing your insights and reasoning!! Prester Bob
I feel the internal skeleton would be the major sticking point for alien vertebrates: It seems that, for the intial function of holding the gills open, it would be just as good to have external valves, which would also provide further advantage in the form of armour. While it might be workable before predation is common, it'd have to be quite advanced (and the alternatives being less advanced) by the time predation comes on the scene to have a good chance
I don't know but the resource economy is very important when depredation begins. Does an armour deserve all the energy an resources when you can run and hide? Gills seems to be the winning choice. Plus, a mouth.
But I can be wrong.
@@DrNova-hj6co Slower/Sessile armoured creatures are quite a common type of animal, so don't be so quick to discount it
Furthermore, there's no reason a primitive creature couldn't have small light valves, similar to gill supports but in the exterior: This wouldn't slow them down any worse than internal supports, but would still be better as armour in the case it gets caught
In regards to gills and the internal structures which supported them it's worth noting they also appear to have played an important role in the development of gnathostomes as the genes involved in the formation of gill arches in jawless fish coupled with one of the preserved molecular fossils of polypoidal hybridization seems to have lead to the parts of the duplicated genome involved in this secondary gill arch structure becoming repurposed into jaws.
Polypoidal hybridization events are rare in animals but when they do occur they lead to some of life's most dramatic morphological developments in body plans.
Incidentally the evolution of jaws was a major innovation as it made the armored slow moving/sessile lifestyle much harder by allowing gnathostomes to bite through and crush shells or exoskeletons, once gnathostomes appeared invertebrates were forced to adapt or go extinct. Among arthropods for example some got spiny or even more heavy duty armor, some got fast and streamlined, some even moved into freshwater and eventually into land to escape... only for jawed vertebrates to follow course several hundred million years later.
I wonder if life evolving on an alien world in which the life forms don't have access to a substrate would evolve a central notochord and are not bilateral. For example evolving in an ocean without access to the bottom or evolving in a thick atmosphere?
Excellent question
I would imagine there would be a lot of jelly creatures
We're back baby! So psyched for this
Hmph, a political compass pfp. Good thing you're a Libertarian-socialist.
@@AnarchicMakotoI always enjoy it cuz then I immediately know most of all I need to know about a person empathy and morals-wise, especially given the left libertarian skew of the compass.
I once conceived of a kind of plant like alien that developed seed capable of active flight to spread, which eventually evolved into a non-sessile species. Turns out that's just us, who would've thought...
also, i wonder if the flipping of the nerve cord has something to do with how our nervous system undergoes torsion and results in the left brain hemisphere controlling the right side of the body and vice versa?
perhaps instead of having to restructure the entire creature nervous system to essentially operate upside down, it wouldve been 'easier' evolution-wise to just twist the rest of the body below the head 180° so that the notochord is dorsal, yet the brain is still in the correct orientation.
Interesting question.... I wonder what the situation is in protostomes like arthropods
@@Phrenotopia From what I can tell at least in cephalopods and arthropods the brain/nerve clusters are centralized/focused around the mouth. I far as I can tell don't believe they do a similar flip reversal so you might be onto something since their neural structure is as a whole simpler with a more direct connection to their limbs than is seen in vertebrates though cephalopods in particular have a consequential problem with their mouth going through their brain which limits their ability to swallow large pieces of food.
One interesting theory I picked up is that it may have to do with the fish-like habitus of early cephalochordates, as visual systems became more advanced and sideways eyes developed. There could have been an advantage of having muscles on one side of the body respond quickly to whatever happened on the opposite side of the body, by contracting abruptly thus veering the body away from danger.
Weird to think about the biomechanics of vertebrates with the spinal column having formed along the animals' undersides. Bone Tacos
from an engineering perspective, it makes a lot of sense to have a rigid compressive element in the center (bone) surrounded by tensile elements (muscles). for example, a tent, a yacht mast with rigging to hold it up. buckminster fuller called it a tenseigrity. it can get quite large but also be very light weight.
10 steps is quite a long list, but do they need to happen in that order? Maybe they could occur in a different order, but on earth, once vertibrates existed, they moved into any niche they could effectively blocking out any convergent design approaching from a different direction
This was an absolute blast to watch! I especially like the idea of dual spine, one of the lineages in my project incorporates it. Also the bench to coatrack analogy was hilarious lol.
I love documentaries talking about the evolution of early life.
Wow. I must watch this awesome video again because my English is not good enough yet. But something I read time ago came back to my mind: It seems one more purpose of the skeleton was to store phosphorus. Anyway. It's interesting.
I think it was a mix of both a need for a _support structure_ and a _storage system_ for calcium and phosphorus.
Just the prior led to cartilaginous and chitinous skeletons.
Just the latter would likely lead to a single large mass of highly porous bone.
I remember seeing this on scishow
I love this video!
After the last video, I was worried this video would support the tunicate ancestor hypothesis.
The idea that ancestral chordates were tunicates, whose larvae underwent paedomorphosis and became cephalochordates and vertebrates.
I still see people support this hypothesis, which drives me up a wall because Tunicates are no longer considered basal chordates.
Thank you and Yeah don't worry 😄 I've been scouring the literature to get a grip on the latest insights. Neoteny did occur but presumably in a enteropneust stage
@Phrenotopia Yea, I find that interesting.
I always thought the ancestors of deuterostomes were pelagic filter feeders; ambulacraria evolved as an adaptation to a benthic lifestyle, chordates evolved as an adaptation to a pelagic filter feeding lifestyle.
I did a little bit of research after watching your video, and really I believe no interpretation is wrong at the moment. Some authors support a pelagic ancestor of deuterostomes, others a deposit feeding ancestor. (At least as far as I can tell)
There’s really not enough genetic data to fully reconstruct the ancestors of deuterostomes at the moment.
Love this series. Hope this gets a million views
Great videos and really well explained! Keep up the good work!
i second this
Brilliant work. Really loved this one.
LOVE this series so much like genuinely, so excited to watch it!
Another fascinating video!!!
I recently stumbled upon some of your amazing videos and am super impressed. Might you consider doing an "About me" video, giving your background, CV, etc?
5:50 the great anus debate
What is your stance, virus first or cell first
cell first
i love this amazing video i learned a lot of things thank to your video.
Amazing video
I think it's not too out there to call the Phylliroe shown in the video a "snailfish".
YESS! IVE BEEN LOOKING FOR YOU!!!
*HELL YE!!!!!!!*
I've been waiting so long for this and I just know it'll be great :3
Double spines with a ventral and dorsal branch would be a difficult fluke. First: Why double this structure? Second: How to keep them synchronized while swimming?
However: would a central spine be a possible outcome - maybe the digestive system placed at the ventral side of it and other organs at the dorsal part of the body? It could work in the end (at least with ribs curving upward to suspend the upper organs from), but which steps could lead to it? A ventral spine would mean the digestive system about it, which would probably exclude some kinds of feeding. It could work in the water (more or less), but on land it would become a challenge, all the organs pressing on each other, so a land-going species would probably have to flip over to get a dorsal spine again where all the organs can be suspended from.
Starfishes often have bilateral symmetry. If you split 1 in half down 1 of its legs, there would be symmetry.
Their radial symmetry is more blatant.
I know this is gonna be good!
I started reading Across the bridge by Henry Gee a few days ago, very timely 😀
This is a lot of great food for thought; excellent speculation and coverage of the known elements; and many thanks for including some of the lesser-known members of the chordates & family.
I just have one question, @phrenotopia - the Micrognathozoa have a large number of bones in their heads, but not in their bodies, and they are in the other side of the animal kingdom from chordates...they're closer to arthropods and molluscs. Do you think that they developed their skulls in the same way chordates did, or is another strategy in play there?
Regardless, great work!
very interesting
where you got the ending music from any links?
I usually try to put credits in the description including music
How did Deuterostomes disentangle the anterior gut from the ancestral neural ring? Do you see it as being as simple as opening a new mouth and closing the old one? Are there relics of the ring in the nervous system of any living Deuterostomes?
It depends on whether the mouth was formed through amphistomy too or formed anew. Interestingly, they found out that the lancelet"s mouth is not homologous with vertebrates but a novel formation, apparently derived from an anterior gill slit.
I want to know how the vertebrate eye developed and got our blind spot.
I would just say that we are very fortunate as sentient beings.
Yes
This video was amazing! Now when I see a worm I think about anus, bilateral simmetry, filter-feeding, early chordate evolution. Thank you!
The thumbnail 😮
Alt Title: How to Literally Grow a Spine.
makes you wonder how echinoderms evolved. Their ancestors looked like worms.
That thumbnail could get you demonetized! lol 😝