Dimetrodon's sail

[andrewsaurus rex]

What is the most agreed upon purpose for Dimetrodon's sail?  Thermoregulation?   That is the one I favour.  An older theory that I still like is that it was used to warm Dimetrodon up quickly in the morning, so it could be active before most other reptiles and simply go around and eat them while they are in their torpid state.  An easy way to make a living.  The only flaw I can see with that theory is that it would be such easy hunting, that it would drive into extinction many of its prey items.  Which didn't happen.

I also wonder about the sail's colouration.  Brightly coloured for display to rivals or mates, or camouflaged to hide it more effectively while hunting?  It might be tough to sneak up on prey with a bright red billboard on your back.  And what would be the effects of light shining through it?  Would it glow brightly when backlit, due to the translucence of the skin covering it?

Another thing I wonder about is what did it do on windy days?   Strong winds blowing from its side would cause the sail to flex badly, being at the very least painful and perhaps greatly hindering its ability to function.  So what did it do?  Stand facing the wind, or with its back to it until the wind subsided?

[JPuggy]

maybe the sail had a simple form of color change, so it could be bight sometimes for mating, or more basic colors for camouflage?

[Newt]

Most Dimetrodon fossils come from swampy or deltaic environments which would have been pretty thickly vegetated. Dimetrodon was, by early Permian standards, pretty fleet of foot. These two facts make the visual impact of the sail relatively unimportant - prey animals would not have seen Dimetrodon until it was quite close, and then would be hard-pressed to outrun it. This environment was probably also fairly protected from strong winds. I imagine if a Dimetrodon were buffeted by a strong gust it would simply flop over, willy-nilly. Which would have been pretty funny to see.


There's nothing exactly like Dimetrodon's sail among extant animals, but the closest analogs are the vertebral crests of various lizards. These seem to be primarily display structures. I think that's the most likely explanation for Dimetrodon's sail as well.


The equatorial swamps of the Permian would have been pretty warm all night and all day, so it wouldn't make much evolutionary sense for Dimetrodon to expend a lot of energy growing a thermoregulatory sail. The advantage it gained would have been negligible compared to the cost. Also arguing against Dimetrodon's sail having much utility is the fact that its otherwise very similar cousin Sphenacodon got along just fine without one, even in environments where Dimetrodon was also present.


Vertebral sails on land vertebrates have an odd history in the fossil record; they seem to come in waves. You had sailed sphenacodontids, edaphosaurids, and dissorophids in the Late Pennsylvanian/Early Permian, then a long gap until Lotosaurus and the ctenospondylids (and Longisquama, if you want to call that a sail) in the Triassic, then another gap until sailed theropods and ornithopods pop up in the Cretaceous, then yet another gap until modern sailed lizards appear (pretty recently, I think). Probably just coincidence, but it is striking.

[andrewsaurus rex]

thanks for the responses..

Newt, especially thanks to you for a very informative post.  I am repainting my Safari Dimetrodon's sail and was unsure which approach to take, but now i'm going to make it for display and (somewhat) colourful and eye catching.  The only thing about the sail is that females had them too, albeit slightly different in shape, iirc.  To me that flies in the face, somewhat, for it being for display...that's a big piece of hardware to grow just for species recognition and really even for sexual display...but I guess if it gets the ladies, it's worth it.  Maybe as JPuggy suggested it conveyed various moods: anger, warning, come hither etc with simple colour changes and thus would be multi-purpose. .

One of the things I like about the Collecta Edaphosaurus, is the pinkish tone of the sail.....to me that could be a warning signal to others that danger is near, like a warthog sticking its tail straight up in the air.

[stargatedalek]

Most animals with similar displays are not gender specific. Based on sailfish, basilisks, and crested water dragons, Dimetrodon would be unusual if it did have displays that varied from male to female.

Birds are a rare exceptions in the degree to which they can vary in their displays. This is a combination of how comparatively easy it is to make feathers alter the animals overall appearance with surprisingly little underlying difference, and the necessity of dull colours in many species because of nesting behaviour (IE, cavity nesting birds like parrots and toucans are equally vibrant in both genders, while peafowl aren't).

Displays can be used for a lot more than mating and species recognition. They can be used to intimidate predators or even to confuse or herd prey (IE sailfish).

[andrewsaurus rex]

great info, thanks. 

[Halichoeres]

Most animals with similar displays are not gender specific. Based on sailfish, basilisks, and crested water dragons, Dimetrodon would be unusual if it did have displays that varied from male to female.

Birds are a rare exceptions in the degree to which they can vary in their displays. This is a combination of how comparatively easy it is to make feathers alter the animals overall appearance with surprisingly little underlying difference, and the necessity of dull colours in many species because of nesting behaviour (IE, cavity nesting birds like parrots and toucans are equally vibrant in both genders, while peafowl aren't).

Displays can be used for a lot more than mating and species recognition. They can be used to intimidate predators or even to confuse or herd prey (IE sailfish).

Gender isn't a synonym of or euphemism for sex. In this context, sex is the most appropriate word to use.

[stargatedalek]

Most animals with similar displays are not gender specific. Based on sailfish, basilisks, and crested water dragons, Dimetrodon would be unusual if it did have displays that varied from male to female.

Birds are a rare exceptions in the degree to which they can vary in their displays. This is a combination of how comparatively easy it is to make feathers alter the animals overall appearance with surprisingly little underlying difference, and the necessity of dull colours in many species because of nesting behaviour (IE, cavity nesting birds like parrots and toucans are equally vibrant in both genders, while peafowl aren't).

Displays can be used for a lot more than mating and species recognition. They can be used to intimidate predators or even to confuse or herd prey (IE sailfish).

Gender isn't a synonym of or euphemism for sex. In this context, sex is the most appropriate word to use.

Even sex is an incredibly complicated concept to try and objectively measure. It can be defined at a bunch of different levels and all of them are far more complex than they traditionally appear. Chromosomes? All kinds of weird combinations can happen (without someone being intersex). Hormones? Even worse! Even going to a genetic level things only continue to get more and more varied and arbitrary.

I know for a fact you mean it in the opposite connotation, but the idea of "sex = anatomy" is one that itself is often used with transphobic intentions. Defining sex is just as complicated as defining gender, and if you start to use it rigidly to avoid using gendered terms you still run the risk of offending people and if you were to truly define it and take outliers seriously you will find yourself with a lot of cisgendered people who now no longer fit into their "biological" sex qualifiers.

"Binary formatted gendered traits" is perhaps the best technical term you're going to get to describe the phenomena. Anything more specific and the terms usage in a scientific context becomes muddied, whether with controversy or just with logistics.

[HD-man]

An older theory that I still like is that it was used to warm Dimetrodon up quickly in the morning, so it could be active before most other reptiles and simply go around and eat them while they are in their torpid state.

Dimetrodon is a synapsid, not a reptile. As for this thread, to quote Bakker, "things that stick out of your head or stick out of your back are nearly always used first to intimidate...sexual rivals...second maybe as a radiator, but the main reason for moose antlers or fin backs is to intimidate your rivals" (See 6:10-40): https://www.youtube.com/watch?v=2bQ3OHvLHCM&t=388s

[Faelrin]

@stargatedalek FYI, unless this is a typo (or well even if), the correct term would be cisgender, not "cisgendered". The word cis is an adjective, and when used otherwise (such as a noun) can be dehumanizing (rather with ill intent or not). Same goes with transgender, or any other adjective used as such.

On the subject at hand I agree with Newt's and HD-man's take. To add another animal example that may have been similar in the level of being fixed for the spectrum of physiological characteristics, ceratopsians and hadrosaurs, despite not occupying the same niche, are now most likely thought to have evolved their frills, crests, etc to be used as display devices as well, which can also extend beyond sexual selection purposes, such as recognition of individuals (if not herds). Spinosaurus could be another such example (up in the air as far as its remains goes, particularly for its back vertebrae, on rather a sail or hump is more apt, and how the bones should be restored until more discoveries are made).

Additionally the consensus on how Dimetrodon is restored has changed a lot. It is now seen as a more active animal without sprawling legs like a lizard (gone are the days of it being called a "mammal-like reptile" as well), which would also probably make thermoregulation even less needed. There are also numerous species of Dimetrodon, existing at a vast array of sizes as well, likely living in different or similar niches, throughout the Permian. I can only wonder if it could have served as intra-species recognition as well, depending on when, what, and where different species may have been contemporaries. Guess I'll have to look into this more.

[Stegotyranno420]

H @HD-man I guess it depends on your definition of reptile
If dimetrodon, which had reptile ancestors, is not a reptile, by that logic, birds are not reptiles or vice versa, it also depends your idea of what defines as a reptile, or reptilomorph.
But just for now I'm gonna say dimetrodon is a reptilomorph, but not a true reptile.

Also, intimation or dimorphision are my favorite theories

[Lanthanotus]

Most animals with similar displays are not gender specific. Based on sailfish, basilisks, and crested water dragons, Dimetrodon would be unusual if it did have displays that varied from male to female.

[...]

Male Plumed Basilisk


Female Plumed Basilisk


...and to stay with the species with true bone supported sails (the crested water dragons, Physignathus sp., do only have enlarged scales)...

Male Sailfin Lizard


Female Sailfin Lizard

[andrewsaurus rex]

interesting examples.

I've swung around to the thinking that the sail was for display.  However iirc, it is believed that both males and females had very similar sails.  Which is fine, lots of male and female antelope species have the same horns.  But it does fly in the face a bit of the theory the sail was to intimidate sexual rivals.  In the case of Dimetrodon, only adornment/colouration could be the differentiating factor between male and female sails and I guess that can make a sail scarier or sexier, but it does at least suggest there was some other purpose to the sail.

Whatever its use, it is odd that it has so rarely evolved, if it was truly useful and functional in some way.....especially if its function was to intimidate sexual rivals.  If a sail was useful in making you look bigger and scarier, to your rival, or sexier to a potential mate, you'd think they would have been popping up all over the place, including today.  But yet they remain pretty rare, compared to the number of reptile and reptile like animals that have existed.

So, perhaps it had a wide variety of functions, pertinent to a specific ecological niche, that caused it to evolve in rare instances.

[Faelrin]

@Stegotyranno420 Dimetrodon did not have reptile ancestors, as Dimetrodon is a synapsid. Synapsida is the sister branch to Sauropsida, which true reptiles (anything in the clade Eureptilia qualifies) fall under. Birds are maniraptoran theropod dinosaurs, and dinosaurs are archosaurs, and archosaurs fall within clade Eureptilia, so that isn't a good example. While synapsids have traditionally been called "mammal-like reptiles", which you may be familiar with, the term is antiquated as it doesn't reflect the current scientific understanding. "Stem-mammal" might be a more appropriate alternate term these days, when describing any non-mammalian synapsid.

I'm not sure how up to date they are, but it may be worth taking a look at and reading the various wikipedia articles covering these topics as a starting point, as they do cover the various classification systems that have been proposed over the years for synapsids and other amniotes, including true reptiles.

[Stegotyranno420]

@Faelrin eureptilia is true reptiles, the crown group if you will, just like there are crown-group birds and crown-group mammals, so the general term reptile(not eureptile) is very flexible. I agree that birds are reptiles, 100%. It is undoubtedly true that Dimetrodon did evolve from Reptilomorph(the group that contains amniotes), which has been unofficially and inaccurately used as a euphemism for reptiles for new members to the subject(I started learning about synapsids in-depth during the 4th and 5th grades, and early on, i kept saying reptile, although that is not true). So i was just pointing out that going by the vernacular form/word, it could really change definitions. Looking back, it looked more argumentive than passive, so sorry if i gave you the wrong idea. I prefer calling them Early Synapsids rather than mammal-like reptiles.

[HD-man]

@Stegotyranno420 Dimetrodon did not have reptile ancestors, as Dimetrodon is a synapsid. Synapsida is the sister branch to Sauropsida, which true reptiles (anything in the clade Eureptilia qualifies) fall under. Birds are maniraptoran theropod dinosaurs, and dinosaurs are archosaurs, and archosaurs fall within clade Eureptilia, so that isn't a good example. While synapsids have traditionally been called "mammal-like reptiles", which you may be familiar with, the term is antiquated as it doesn't reflect the current scientific understanding. "Stem-mammal" might be a more appropriate alternate term these days, when describing any non-mammalian synapsid.

To add to the above quote: https://www.geol.umd.edu/~tholtz/G104/lectures/104land.html

To add to my previous post, I just read the Dimetrodon section of Witton's Life through the Ages II: Twenty-First Century Visions of Prehistory, which sums up what we currently know about "the function of the Dimetrodon sail". Basically, the evidence "implies a social selection pressure...over a mechanical one": https://books.google.com/books?id=PL_VDwAAQBAJ&pg=PA50&dq=dimetrodon+sociosexual

[Halichoeres]

@stargatedalek Yes, I think we share the goal of trying to be as respectful and inclusive as possible, but what I'm saying is that gender and sex are distinct phenomena. Sex is actually pretty easy to define in terms of gamete size, but obviously there's a lot more variety in how that manifests than you'd conclude based on the chromosomal determination found in humans and fruit flies. All those complications aren't really at issue here. Gender is a social or psychological phenomenon that has to do with how somebody experiences the world, and it may or may not correlate with sex in any particular individual. In nonhuman animals, we aren't really equipped to evaluate whether they experience gender at all. All we know is how the bearers of different gametes vary (or not) in phenotype. In no sense does this make it sensible to slap the word gender on any variation that might exist, because that assumes insight into their experience that we simply don't have. Sex isn't an inherently problematic term, and gender isn't an inherently unproblematic one. They're different things.

[stargatedalek]

@stargatedalek Yes, I think we share the goal of trying to be as respectful and inclusive as possible, but what I'm saying is that gender and sex are distinct phenomena. Sex is actually pretty easy to define in terms of gamete size, but obviously there's a lot more variety in how that manifests than you'd conclude based on the chromosomal determination found in humans and fruit flies. All those complications aren't really at issue here. Gender is a social or psychological phenomenon that has to do with how somebody experiences the world, and it may or may not correlate with sex in any particular individual. In nonhuman animals, we aren't really equipped to evaluate whether they experience gender at all. All we know is how the bearers of different gametes vary (or not) in phenotype. In no sense does this make it sensible to slap the word gender on any variation that might exist, because that assumes insight into their experience that we simply don't have. Sex isn't an inherently problematic term, and gender isn't an inherently unproblematic one. They're different things.

Many animals have behavioural characteristics that vary by sex/gender, and sometimes those behavioural traits don't match up with the animals expected anatomy. This means there are transgender animals (not including things like clownfish, for obvious reasons). If animals can be transgender, that means they have gender identities that are not inherently linked to their sex. Are they always genuinely analogous to ours as humans? Perhaps not, especially given that isn't even true for all human cultures, but it means they do have gender identities of some form.

The ways we express, expect, and experience gender are cultural elements, but the existence of gender identities in general seems to be a biological phenomena based on its presence in non-human animals.

Additionally, trying to use sex as the "scientific version of gender" plays directly into transphobic arguments and sentiments. Calling a transwoman "male" is derogatory, and presenting things as if there is a distinction between sex and gender is something transphobes use heavily to justify their actions and statements, TERFs in particular.

https://blogs.scientificamerican.com/voices/stop-using-phony-science-to-justify-transphobia/

Most animals with similar displays are not gender specific. Based on sailfish, basilisks, and crested water dragons, Dimetrodon would be unusual if it did have displays that varied from male to female.

[...]

Spoiler

Male Plumed Basilisk


Female Plumed Basilisk

[close]

...and to stay with the species with true bone supported sails (the crested water dragons, Physignathus sp., do only have enlarged scales)...

Spoiler

Male Sailfin Lizard


Female Sailfin Lizard

[close]

I stand corrected! I wonder if I was thinking of some reference that had a female of one species and male of another, as I was thinking crest length was the difference between plumed and green basilisks. My bad.

@stargatedalek FYI, unless this is a typo (or well even if), the correct term would be cisgender, not "cisgendered". The word cis is an adjective, and when used otherwise (such as a noun) can be dehumanizing (rather with ill intent or not). Same goes with transgender, or any other adjective used as such.

I guess that was a typo, sorry. I was under the assumption that transgender and cisgender were adjectives rather than nouns, and the extra "ed" at the end was something to be tacked on or not arbitrarily.

[Halichoeres]

If you want to call males that masquerade as females to avoid aggression, or to sneak matings, 'trans,' I think that does more harm than good.

Additionally, trying to use sex as the "scientific version of gender" plays directly into transphobic arguments and sentiments. Calling a transwoman "male" is derogatory, and presenting things as if there is a distinction between sex and gender is something transphobes use heavily to justify their actions and statements, TERFs in particular.

This is exactly the opposite of what I'm doing. They're different things, not versions of each other. This discussion is pointless.

[bmathison1972]

This discussion is pointless.

Agreed! On so many levels!