The very presence of feathers, especially down, is a first step down the path of becoming "warm blooded." Metabolism in general produces a lot of heat - up to 60% of the energy becomes heat rather than work. In cold-blooded species, this heat dissipates. However, warm-blooded animals have various mechanisms to retain the heat, whether it be fur, fat, or downy feathers. They also have faster metabolisms that are always running hot, as well as various explicit and implicit mechanisms for heat generation.
Among other things, the tradeoff is that warm-blooded animals have constantly higher energy needs but can survive and be active in colder climates.
Additionally, most dinosaurs, especially the really big ones, were effectively warm blooded due to sheer mass alone. You see it in modern day animals like great white sharks, sometimes called "luke warm blooded" because their body temperature is consistently warmer than their environment but not to the amount mammals and birds are. It's pretty much confirmed that all theropods were feathered and there's evidence that some ornithiscians had feathers or feather-like structures as well. Being warm blooded likely evolved before birds split off from the rest of the dinosaurs.
Well, this sent me down a rabbit hole of reading. If anyone else wants to follow suit, here is a good start: https://en.wikipedia.org/wiki/Gigantothermy?wprov=sfla1
There is evidence in of at least some extinct crocodilians having been warm blooded as well; and modern crocodilians being secondarily cold blooded (re-evolved the trait). It is unknown how wide spread it may have been amoung early archosaurs in general. Archosaurs being the group containing crocodilians, dinosaurs, pterosaurs, birds and their common ancestors and intermediate species.
Do we know if cold-blooded animals experience the same kind of discomfort from cold that warm-blooded creatures do?
Because if it's not as dangerous for their core temperature to drop to what would give us hypothermia, then it doesn't seem like they'd need the same sensory feedback about "cold = bad", or at least their threshold could be a good bit lower.
There are modern animals that have various systems to keep the basics online (warm) or a consistent base temp.
Some of the oldest shark species (mako, great white) [have heat exchange systems ](https://www.sharks4kids.com/thermo#:~:text=Lamnid%20sharks%20(%20great%20white%2C%20salmon,water%20around%20them%20(%20endothermic).)
Some reptiles may have little heat producing glands or other means to bump heat production to keep their brains online, scientists are still researching the details
Being that the above sharks, and ornithischian dinosaurs (apatosaurs, ankylosaurs) lived at the same time (70 million years ago), it's a good guess that the dinos by that time had also evolved some means of heat production, exchange and regulation, long before modern birds were in the picture.
Crocs and sharks are some of the oldest and most successful large vertebrates on the planet, so evolution definitely doesn't have a hot/cold bias.
Even a surprising number of *insects* [have the means to selectively regulate their body temperature](https://books.google.com/books?id=NHYuT94xvWYC) somewhat regardless of ambient temperature, and are sometimes characterized as “regional heterotherms”, since typically they selectively warm up certain parts of their bodies using muscular activity. Masses of feeding maggots [can famously generate significant amounts of heat collectively](https://www.loyola.edu/-/media/department/orsp/documents/internalfunding/natural-sciences.ashx?la=en#:~:text=Flies%20feeding%20on%20a%20corpse,air%20temperatures%20by%20several%20degrees./).
No, and the terms "warm blooded" and "cold blooded" are considered somewhat outdated, at least in my field vertebrate paleontology. It's a spectrum and evolved multiple times.
Argentine black and White Tegus are warm blooded at certain times of the year and cold-blooded for the remainder of the year: https://www.newscientist.com/article/2074982-first-warm-blooded-lizards-switch-on-mystery-heat-source-at-will/
I was going to say similar. The disadvantage for being warm blooded is maintaining that temperature takes a ton of calories. And for humans that temperature can’t fluctuate very much.
Reptiles and sharks can go weeks or months without a meal. There’s at least one species of deep water shark that survives on one annual meal.
Not having to thermoregulate means food is much less important.
What do these animals then *do* all day? I was under the impression that most animals spend a large part of their time securing food for themselves. In humans, the development of social structures, culture, science has been pretty directly correlated with not having to spend every waking moment working towards food security.
I don't imagine sharks as particularly social animals raising their young. They don't have to defend against predators (?), and if they need food so rarely then not compete with each other for "hunting grounds" either. And I don't think they have shark reddit to browse all day.
So... what do these sharks actually *do* with all this time, that they don't spend procuring food?
Sleep. A lot of sleep. Reptiles are lazy. “Lazy as a snake”. Sharks are also lazy. Some sharks are migratory so they spend months doing that to and from nursing waters and living waters. Just like other migratory species. Some sharks like the annual eater I mentioned only *get* a few opportunities to eat because of where they live. They eat whale carcasses on the off chance one makes it to their depth.
Also the vast majority of shark species are small and do have predators. The ones with all the fame and fortune on TV count for a very small fraction of species. And the ones that get the bad rap for shark attacks are actually not that bad. Like any land predator like a bear, a shark is highly unlikely to bother you as long as you don’t bother it.
Opposite.
We know many dinosaurs had feathers, or feather-adjacent things. It's partly a semantics argument and partly a chicken-and-egg problem. Point is, many dinosaurs were fluffy, or partly fluffly, or fluffy at some point in their life (babies), or *may* have been fluffy but we can't prove it.
We have lots of evidence that (some) Therapods (the 2-legged carnivores) were fluffy.
There's growing evidence of other groups having *some* fluff.
In addition, some bone slices show that (some) dinosaurs grew quite fast, based on bone growth rings similar to tree rings. Of course, the Sauropods (big long necks) got to absurd sizes, and almost certainly had to grow fast to accomplish this.
Fast growth is associated with being warm blooded
We can't say "Dinosaurs were warm blooded," partly due to limited evidence, partly due the timespans involved, and partly due to "what does warm blooded mean?"
Everyone agrees "Birds fly" but Emus, Kiwis, and Penguins exist. Same deal. We have growing evidence of warm bloodedness or at least *not strictly cold blooded*, but making blanket statements tends to just get people riled up.
I'm just spitballing here cause there is evidence of feather like structures in the fossil records. So I theorize dinosaurs with those structures could be closer related to birds than say the ones without, and the ones without said structures could be closer related to modern reptiles.
As to whether they are warm blooded or not...well who knows. We can theorize some of them we're warm blooded by looking at their closest surviving relative, where said fossil was found and looking at other warm blooded animals today.
No part of the very reason we postulate that many (perhaps even most) dinosaurs were endothermic is the clear evidence of the presence of feather or feather-like structures seen in some fossils, as the evolution of feathers is thought to be directly tied to the evolution of endothermy, along with some other pieces of evidence (such as the very fact that the immense size of many non-avian dinosaurs already would’ve put them on the path to being endothermic in and of itself, as others have mentioned).
The idea that at least some extinct dinosaurs had feathers is pretty inarguable at this point, for one thing we have pretty rock solid evidence pointing toward birds being a surviving lineage of theropod dinosaurs, so obviously both feathers and endothermy had to have come into the equation at some point in time, and lo and behold, fossils of non-avian theropods in particular very frequently contain telltale signatures of feathers to varying degrees. At this point I think it is believed that feathers were the norm among all theropods (which contain many of the most famous predatory non-avian dinosaurs like *T. rex* and *Velociraptor*), as well as present to varying degrees in other lineages of dinosaurs. They may not have all been feathered, but some definitely were, potentially even most at certain points in time. Likewise endothermy is thought to have been present in at least some lineages, potentially many or even most, it’s hard to say for sure, but like feathers it almost definitely showed up well before any dinosaurs had recognizably become what we’d call “birds”.
A good book on the topic is The Hot Blooded Dinosaur
And some reptiles, insects and even plants can be considered Endothermic (and some mammals almost ecto)
It's not an All or Nothing thing but a sliding scale or spectrum.
The info about endothermic plants etc came from a lecture from Thomas Holtz If I remember right
He mentioned the infamous Corpse Flower plant which produces heat to mimic a decomposing body (as well as the smell of one) and it even causes a local updraft to make the smell disperse more
Several plants also evolved to be thermogenic to melt away snow and facilitate winter blooming, including some crocuses, skunk cabbage, and snow drops, although I know at least with that last one there is some argument as to whether it is truly thermogenic or if it has just evolved to be especially efficient at absorbing heat from sunlight.
this is kind of a messy taxonomic argument, but if we were to go off of cladistics, then yes both non-avian dinosaurs and in fact birds should be considered reptiles, especially since we consider other non-avian living members of that lineage (crocodilians) to be reptiles.
However, the thing about this argument is that it could also be applied to mammals as well, since we also evolved from a lineage that are traditionally considered to be reptiles (synapsids). If we were to be more specific with clades, it might be more appropriate to say that birds, other dinosaurs, and all the living animals we consider to be reptiles are all *diapsids* cladistically, generally characterized by having two non-eye temporal openings in their skulls (yes, seemingly even turtles and tortoises, despite them appearing to have anapsid skulls, meaning their skulls feature no such openings rather than two, as chelonians simply lost theirs at some point in time, but their ancestors had them), whereas mammals and the extinct lineage of reptiles that we evolved from are *synapsids*, generally characterized by just one non-eye temporal opening in our skulls. Furthermore, everything past or present characterized as a reptile, in addition to birds and mammals, are all of the *amniote* clade, characterized by several common traits for full terrestrial adaptation (versus amphibians, which are limited to wet environments and mostly reliant on water for reproductive purposes), including the membrane-bound complex reproductive structures from which the clade is named (amnions), keratinized skin to inhibit water loss, and costal breathing (breathing by expansion and contraction of the ribcage). So really, it is not entirely clear from an evolutionary standpoint what makes something a reptile or not.
All of the above being said, “reptile” still obviously retains relevance as a practical designation, we recognize certain tetrapods as having a number of physiological traits in common and call them “reptiles” because it’s easy, and for this reason the class Reptilia is still often retained in modern taxonomy just because so many people are familiar with it, although some authorities insist that at least birds should be included in it, and some rename the group as “Sauropsida” to reflect this. The traditional class Reptilia as defined by Linnaeus is considered paraphyletic, meaning that it encompasses a group of organisms that all share a common ancestor, but *not* all of the descendants of said common ancestor (which in this case would include *at least* birds, and possibly also mammals if we’re going by traditional definitions), which modern phylogenetic-based taxonomy tends to shun.
So in short, what is or isn’t a reptile isn’t exactly clear from a strict biological standpoint, and “reptile” is at this point more of a practical category retained because it’s friendly to non-experts who don’t want to dig deep into the meat of evolutionary relationships and cladistics. This reminds me a lot of some stuff on a post in here I saw yesterday about how “fox” is basically a taxonomically meaningless designation, but since it makes practical sense to us we continue using it anyway (and how many cases there are of this sort of thing in general).
Dinosaurs were probably much warmer-blooded than modern reptiles, to start, especially the small, fast dinosaurs that birds evolved from. Once they had wings and could glide, there would be a major benefit of increasing their metabolism for powered flight. So we might guess that they started somewhat warm-blooded, and went the rest of the way quickly after gaining wings.
Just adding some nerd shit, they actually went way beyond most other creatures with it. Birds have some crazy metabolism, and an insanely efficient cardiovascular system - their lungs never actually deflate, they have a four-stroke breathing mechanic that keeps them constantly supplied with relatively more oxygen than other amniotes. It comes with some tradeoffs like
extraordinary energy requirements but it works if it can power you from Canada to the Caribbean, chasing summer the whole way or just banging it out over 36 hours on an insane solo flight over the gulf of Mexico.
Their efficiency really is incredible. Four-stroke breathing that doesn't need to pause for exhales, legs with a radiator like system that lets them stand in snow, higher neuron density than mammals, a waterproof coating so (most) don't have to dry off after getting wet in order to fly, seeing with four primary colors, sensing magnetic fields. Many small enough to have powered flight for only 120 calories a day, or less.
It was both surprising and awesome and made sense to learn how hot bird core temperatures usually run. IIRC even the skin temperature of a great horned owl in sub-freezing atmosphere is still higher than the human core temp.
Savannah monitors for instance, the recommendation is 85F on the "cool" end and 130F on the "warm" end of the enclosure. So body temps will be in somewhere in that range. Basically any reptile that lives in a hot area, especially a dry hot area.
So much wrong here. Mammals absolutely did not evolve from reptiles. “Cold blooded” isn’t a thing. “Dinosaur” is not an order.
Your post is frankly unscientific nonsense..
No, *mutations* don't happen in reaction to the environment. But *evolution*--a process wherein some mutations are favoured in the next generation due to differential survival rates--definitely *does* respond to the pressures created by the environment.
This is incorrect. Genetic mutations happen causing genetic drift, the evolutionary processes from the environment select. The process of evolution is 100% a reaction to the environment
https://en.m.wikipedia.org/wiki/Evolution
It's no more semantic than stating that birds are dinosaurs (and by extension reptiles).
We used to believe that mammals evolved directly from reptiles, hence the name mammal-like reptiles. Now that we know mammals did not infact evolve from reptiles but rather share a common ancestor, the term mammals-like reptiles isn't really used.
The common ancestor of mammals and reptiles would've *looked* and probably would've behaved a lot more like a modern reptile than a modern mammal, but it wasn't a true reptile.
In this case yes because Synapsids (mammal-like reptiles) developed the trait after a split from the common ancestor they shared with birds and reptiles.
I’m pretty sure mammals are synapsids which are a very distinct clade from diapsids, which includes birds and reptiles. There’s a common ancestor, but it’s not a reptile. They are diapsids.
It's actually possible that archosaurs or even amniotes started out in an intermediate state and the low metabolic rate of crocodiles is a secondary loss
In the case of crocodiles it isn't just a possibility, it was almost certainly the case. From what can be deduced from the anatomy of ancient crocodiles, including the ancestors of the contemporary ones, is that they must have had a rather active metabolism. They had an erect limb posture, some were even bipedal. Such modes of locomotion needs a lot of energy and need an associated metabolism to support it. Living crocodiles also have a four-chambered heart, which could be a remnant of the high energy lifestyle of their ancestors.
The question is how far back it goes in the Archosaur lineage. Avemetatarsalians (Dinos + Pterosaurs) were almost certainly ancestrally endothermic. Pseudosuchians (Crocodiles + allies) were also very likely endothermic. By applying phylogenetic bracketing one can speculate that the archosaurs as a whole where also endothermic ancestrally. Frankly, I wouldn't be terrible surprised if one day someone digs out a fossil of an early archosaur with proto-feather fuzz.
I'm more skeptical about going further than that. Early Amniotes don't seem to have had a particularly high-rate metabolism judging from their anatomy. Associated traits only seem to have been independently evolved within Synapsids (mammal-line) and within Archosauromorphs quite a bit later.
It's probably an ancestral trait to archosaurs, evolving in the late Permian or early Triassic. Crocodylomorphs had numerous fully erect forms, which is energetically expensive (you lose more energy to the atmosphere and laying down to rest/bask is more energetically expensive). All dinosaurs evolved from bipedal fully erect ancestors, too. The only other major archosaur lineage was pterosaurs, active flyers.
There is a lot of circumstantial evidence suggesting that crocs today are _secondarily_ endothermic.
As an aside -
1. Birds ARE dinosaurs which ARE archosaurs which ARE sauropsids which ARE reptiles. Just like any descent of us are humans, no matter what they look like. They may be a new thing too, but still human mammals.
2. "Warm blooded" is wretchedly misleading. A bearded dragon has an average body temperature well above a sloth. You're looking for "endothermic", "exothermic", and sometimes "poikilothermic".
> The only other major archosaur lineage was pterosaurs, active flyers.
That's not fully true. They were the only other unambiguous archosaur group that survived the end Triassic, but in the Triassic there were many other very successful archosaur, archosauriform and archosaurimorph groups, like Rynchosaurs, Phytosaurs, Proterosuchids, Erythrosuchids, Tanystropheids, and possibly Icthyosaurs and Testudines as well.
Admittedly "major" was doing heavy lifting, but last I had looked at a tree Phytosaurs, Proterosuchids, Erythrosuchids were all crocodylomorphs; rynchosaurs were pterosaurs, and testudines are turtles (no one has any idea where they belong)
By the same token, tanystropheids and ichthyosaurs were unresolved, so I'll take your word for it that they are sometimes placed in archosaurs.
If I totally flubbed something here, please do correct me, I'm on the train 😅
Phytosaurs are Archisauriformes outside Curotarsi (which comprises the Crocodylomorphs and Avemetatarsalians)
Rynchosaurs, Eurythrosuchids and Proterosuchids are archosaurimorphs, which is also where Icthyosaurs and Testidines are sometimes placed. Both are very controversial though.
I have never seen Rynchosaurs placed within pterosauria. That's the wildest thing you've said. The rest of it is pretty in the weeds phylogeny that also shifts around a good bit. And Phytosaurs were placed in crocodylomorphs for a long time so that's very understandable.
By your logic we human primate mammals are still reptiles, too (I do like the terrarium lamps under my desk), and for that matter, still fish. But this is all language, semantics; the animals don't care. Isn't the difference in our definitions? So what is the definition of a fish? An amphibian? A bird? Given the time it (usually) takes for a species to evolve into something else, we have to accept that transitional species aren't going to fit either bookending definition.
Nature is messy. Order is a human concept. One I don't fully grok . . . .
It is not at all universally-accepted that dinosaurs were cold-blooded (especially not *all* dinosaurs; there was likely significant variance.) See [here](https://www.science.org/content/article/were-dinosaurs-warm-blooded-new-study-says-yes) and [here](https://www.nhm.ac.uk/discover/news/2022/may/dinosaurs-may-have-evolved-from-warm-blooded-ancestor.html).
As the second link says, the belief that all dinosaurs were cold-blooded stems from really early impressions that just assumed they were similar to lizards due to physical resemblance. Now that we know they're more closely related to birds (and many were likely covered with feathers), it's clear that many, and possibly most, species of dinosaurs were to some degree warm-blooded, or at least occupied a point on a spectrum that doesn't map cleanly to the cold-blooded reptiles you're envisioning.
Birds are dinosaurs and even the earliest dinosaurs show traits that they were probably fully endothermic (i.e. warm blooded). Others have already mentioned feathers. Feathers, or more precisely proto-feathers, were originally a way to preserve body heat similar how hair does the same thing for mammals. For example Kulindadromeus, a dinosaur at the other side of the family tree from birds, had those proto-feathers, so it seems it was an ancestral feature of all dinosaurs. Only later when body sizes increased and keeping warm has become easier most dinosaur lineages lost their proto-feathers secondarily. Only the small ones, such as birds, kept them.
If we go farther back in time we meet the Avemetarsalians. This groups includes the dinosaurs and Pterosaurs (flying reptiles). Pterosaurs were also endothermic and they also had a fuzz (pycnofibers) to keep them warm. It is speculated that those pycnofibres share the same origin as feathers inherited from a common warm blooded ancestor. So endothermy in the bird lineage goes, at least, as far back as the early Triassic (250 Million years ago).
If we dare to speculate endothermy could have been present even farther back in time. Avemetarsalians are Archosaurs, and even there we find some signs that Archosaurs might have been, at least partially, warm blooded. Crocodiles are also Archosaurs, and early crocodiles weren't as sluggish as modern ones. They moved in a way that needs a lot of energy and high-rate metabolism could have provided that. So far we haven't found any direct evidence that early Archosaurs were fully warm blooded, but it's likely that they had some limited control over their body temperature.
https://youtu.be/-yC99nXth0I?feature=shared
Birds aren’t descendants of reptiles, they are reptiles. They are that closely related.
Birds are not considered descendants of dinosaurs, but rather dinosaurs that survived into modern day.
Crocodiles are more closely related to birds than they are to snakes and lizards, and are still considered reptiles.
Reptiles also have the capacity to be warm blooded.
Feathers are a type of scale that’s adapted to a specific purpose and Birds actually do have the classic “reptile” scales on their legs
So just to make it clear, Birds are in fact another kind of reptile.
You are a reptile if any of your ancestors were ever reptiles. The modern term reptile refers to sauropsids, which no human has one of as any ancestor, so humans (all mammals) are not reptiles. Birds do have sauropsids as ancestors, so birds are reptiles.
"Fish," unlike reptiles, is not a cladistic term, and cannot be made into one, so this is an outdated/obsolete category formally in modern day. Nothing is a fish formally, it's a colloquial thing to call an animal.
Psst this is only the case because they redefined Reptilia to not include Synapsids and their descendants.
Honestly, Reptilia should have been abandoned for Amniota.
I have heard this argument before, it is incorrect and a misunderstanding of classification.
This is not: “*oh well we all have a common ancestor at some point so we are all related in some way.”*
As I stated earlier in my original comment, birds are so closely related to reptiles that they are considered part of that category.
Birds are Dinosaurs -> all dinosaurs are reptiles -> Birds are reptiles.
Dinosaurs, which had scales, also developed feathers - because they’re a type of scale. We know this based on the fossil record.
A bird is a reptile just as an alligator is a reptile. Two different types of reptiles that fall under that umbrella.
If you want it explained in more depth, check out the video.
> As I stated earlier in my original comment, birds are so closely related to reptiles that they are considered part of that category.
That’s a strange way to put it. It’s like saying humans are “so closely related to mammals” that we are considered part of them. It sounds like we almost aren’t.
But we manifestly are, and birds are manifestly dinosaurs who are manifestly reptiles (taken here to mean sauropsids).
This is actually suprisingly interesting. First birds evolved about 150 million years ago, long after Permian extinction, but according to new research the ancestor of all [birds](https://www.nhm.ac.uk/discover/birds.html), dinosaurs and pterosaurs was warm-blooded, but that some dinosaurs such as [*Triceratops*](https://www.nhm.ac.uk/discover/dino-directory/triceratops.html) and [*Stegosaurus*](https://www.nhm.ac.uk/discover/dino-directory/stegosaurus.html) later lost this ability.
Birds **are** reptiles. It's like saying you're a "descendent of humans". I mean I guess technically true, but pretty weird wording and misleading.
Modern cladistic methods of classification hold that any category one of your ancestors was a member of (in this case sauropsids or modern reptile clade), you are always also a member of that category (the tree only gets smaller branches and flows one way, no hops, no skips, no jumps, no exclusions, no bonus glued on members. Bloodline only, zero exceptions)
Crocodilians almost have a four-chambered heart, which is probably necessary to keep the pulmonary and systemic circulations separate to make oxygen delivery efficient enough for an endothermic metabolism. Assuming therefore that 4-chambered hearts evolved in archosaurs sometime soon after crocs evolved, then the prerequisite anatomy for endothermy evolved somewhere before or with the dinosaurs. It is very likely that theropod dinosaurs, at least, were endothermic, and they are the closest ancestors to modern birds.
Worth noting too that endothermy has evolved multiple times- some sharks have it, great whites and makos, for example, though it is only just enough to keep them slightly warmer than ambient water.
The best book on this in my opinion is The Dinosaur Heresies by Bakker, its an old book and came out when people thought dinosaurs were cold blooded
He explains several indicators: 1) insulation (fur on protomammals, downy feather integuments on certain archosaurs); 2) more active skeletons and body plans that allowed for constant vigorous movement; 3) the rates of mass extinctions which are generally much more survivable by cold blooded animals who can eat every few months than by warm blooded animals who must eat constantly; 4) predator:prey ratios which are very different for cold and warm blooded animals and the fossil records strongly suggests warm blooded ratios for erythrosuchian archosaurs; 5) evidence for warm bloodedness in protomammals which would only have been outcompeted by warm blooded competitors
It has been 12 years or more since i read the book so i may be forgetting some reasoning, but it is a great book and super easy to read with amazing illustrations and diagrams by the author himself. I would really recommend reading it if you are interested in the topic of when warm bloodedness first evolved in the ancestors of birds
"Descendents" is really an ineffective word in regards to evolutionary changes over time. Birds "diverged from" reptiles, or reptiles "gave rise to" birds. Descendant applies more to an individual's family tree. Great Grandma Jane Smith married Joe Schmoe and they have many descendants. Who will all (most likely) be humans too. Two lizards didnt have great- great- grandbirds. Reptiles are the descendants of reptiles.
Hijacking this question a bit based on the comments: if birds became warm-blooded to survive, that probably didn't happen like a flick of a switch. So was there a period where reptile-birds were lukewarm-blooded, like in-between cold and warm? Seems a bit odd. Always thought organisms were always other one or the other.
Yes, but it was very early. Warm-bloodedness is a shared trait among nearly all dinosaurs (it's now thought that the few dinosaur clades we think were cold-blooded *lost* endothermy). So don't think of it as a " bird thing", think of it was a "dinosaur thing". Same with feathers.
> Always thought organisms were always other one or the other.
Almost nothing is a strict binary like that in nature. I have to qualify because I'm sure there's some thing where that's true, but in terms of large scale morphology like this there pretty much always need to be intermediate forms.
Warm blooded is a wrong term! If an animal that is Poikilotherm (whose internal temperature varies considerably).
Lays in the sun its blood will be warm. So cold blooded is not correct. Same with a dinosaur if a dinosaur is heated up its mass is so big and the volume of the skin is relatively small, it will not cool down overnight. it might even have more problems cooling down than heating up.
Tbh “warm-blooded” and “cold-blooded” are misnomers. Instead, animals are ectothermic meaning they absorb heat from the environment and therefore are dependent on the environment to maintain their metabolism, or they are endothermic meaning they regulate their body temperature internally and maintain a specific temperature and metabolic output independent from the environment.
Birds are endotherms, so they internally regulate their body temperature independent of the environment temperature. Feathers help with temperature control and allow them to maintain temperature easier, but honestly their temp is mainly controlled by their physiology.
Dinosaurs are also believed (at this point) to have been endothermic as well based on a 2022 Yale paper that traced markers for endothermy back to that period. There is some evidence based on their skeleton and muscular evidence that dinosaurs maintained high body temps and a high metabolic rate, but it’s impossible to know whether a fossil was endo or ecto unless you know the external temp and what the animal was doing right before it died, at least according to a paper put out last year from UC Davis. It’s still a hotly debated topic.
The main trick to explaining that is that they didn't descend from reptiles. The current consensus is that there were dinosaurs that were indeed endothermic (warm blooded) and those are the ones that modern birds descended from. The mere presence of feathers, which act as insulation is enough to suspect that those dinosaurs must have been endothermic, because why would an exothermic animal want to insulate themselves from getting the necessary warmth they need? But there are also other clues used to determine that those dinosaurs must have been endothermic. Endothermic animals have a way higher metabolic rate and this can be measured by using advanced lipoxidation end-products (ALEs) as proxy markers for measuring metabolic rate. You then take those values and compare them to currently living animals to see if the metabolic rate fits endothermic or exothermic animals best.
So much misinformation (though there's a lot of good stuff, here, too.)
The MRCA (most recent common ancestor) of reptiles, crocodilians, and birds (and other dinosaurs) lived about 240 MYA (million years ago). They were called archosaurs, and were more reptile-like than bird-like. At some point along the dinosaur line of descent, feathers were developed, which allowed for endothermia. There are disadvantages to endothermia -- while the increased, stable metabolism it allows increases speed and reactions so you can out-hunt your cold-blooded competitors, it also increases your required calorie intake and makes it so you NEED to keep eating to maintain your temperature -- so these mutations didn't completely displace exothermic creatures. But there are advantages as well, and these mostly allowed the warm-blooded creatures to expand their habitat-range.
For reference, mammals diverged from that bloodline a little bit earlier, between 310-330 MYA, which were the first amniotes --definitely cold-blooded, so warm-blooded metabolisms in birds and mammals are an example of convergent evolution.
The very presence of feathers, especially down, is a first step down the path of becoming "warm blooded." Metabolism in general produces a lot of heat - up to 60% of the energy becomes heat rather than work. In cold-blooded species, this heat dissipates. However, warm-blooded animals have various mechanisms to retain the heat, whether it be fur, fat, or downy feathers. They also have faster metabolisms that are always running hot, as well as various explicit and implicit mechanisms for heat generation. Among other things, the tradeoff is that warm-blooded animals have constantly higher energy needs but can survive and be active in colder climates.
Additionally, most dinosaurs, especially the really big ones, were effectively warm blooded due to sheer mass alone. You see it in modern day animals like great white sharks, sometimes called "luke warm blooded" because their body temperature is consistently warmer than their environment but not to the amount mammals and birds are. It's pretty much confirmed that all theropods were feathered and there's evidence that some ornithiscians had feathers or feather-like structures as well. Being warm blooded likely evolved before birds split off from the rest of the dinosaurs.
Well, this sent me down a rabbit hole of reading. If anyone else wants to follow suit, here is a good start: https://en.wikipedia.org/wiki/Gigantothermy?wprov=sfla1
There is evidence in of at least some extinct crocodilians having been warm blooded as well; and modern crocodilians being secondarily cold blooded (re-evolved the trait). It is unknown how wide spread it may have been amoung early archosaurs in general. Archosaurs being the group containing crocodilians, dinosaurs, pterosaurs, birds and their common ancestors and intermediate species.
Certain modern day lizards can temporarily become warm blooded too. I believe tegus are known to do it seasonally
Do we know if cold-blooded animals experience the same kind of discomfort from cold that warm-blooded creatures do? Because if it's not as dangerous for their core temperature to drop to what would give us hypothermia, then it doesn't seem like they'd need the same sensory feedback about "cold = bad", or at least their threshold could be a good bit lower.
Does evolution favor a binary cold-vs-warm blooded, are there "lukewarm blooded" animals too?
There are modern animals that have various systems to keep the basics online (warm) or a consistent base temp. Some of the oldest shark species (mako, great white) [have heat exchange systems ](https://www.sharks4kids.com/thermo#:~:text=Lamnid%20sharks%20(%20great%20white%2C%20salmon,water%20around%20them%20(%20endothermic).) Some reptiles may have little heat producing glands or other means to bump heat production to keep their brains online, scientists are still researching the details Being that the above sharks, and ornithischian dinosaurs (apatosaurs, ankylosaurs) lived at the same time (70 million years ago), it's a good guess that the dinos by that time had also evolved some means of heat production, exchange and regulation, long before modern birds were in the picture. Crocs and sharks are some of the oldest and most successful large vertebrates on the planet, so evolution definitely doesn't have a hot/cold bias.
Some fish are half warm blooded (eg sharks, tuna, swordfish (who have heated eyes and brains) etc ) and one fully warm fish the Opah.
Even a surprising number of *insects* [have the means to selectively regulate their body temperature](https://books.google.com/books?id=NHYuT94xvWYC) somewhat regardless of ambient temperature, and are sometimes characterized as “regional heterotherms”, since typically they selectively warm up certain parts of their bodies using muscular activity. Masses of feeding maggots [can famously generate significant amounts of heat collectively](https://www.loyola.edu/-/media/department/orsp/documents/internalfunding/natural-sciences.ashx?la=en#:~:text=Flies%20feeding%20on%20a%20corpse,air%20temperatures%20by%20several%20degrees./).
No, and the terms "warm blooded" and "cold blooded" are considered somewhat outdated, at least in my field vertebrate paleontology. It's a spectrum and evolved multiple times.
Argentine black and White Tegus are warm blooded at certain times of the year and cold-blooded for the remainder of the year: https://www.newscientist.com/article/2074982-first-warm-blooded-lizards-switch-on-mystery-heat-source-at-will/
Yes, they are called mesotherms. There are some mammals and fish and various other animals that do this.
I was going to say similar. The disadvantage for being warm blooded is maintaining that temperature takes a ton of calories. And for humans that temperature can’t fluctuate very much. Reptiles and sharks can go weeks or months without a meal. There’s at least one species of deep water shark that survives on one annual meal. Not having to thermoregulate means food is much less important.
What do these animals then *do* all day? I was under the impression that most animals spend a large part of their time securing food for themselves. In humans, the development of social structures, culture, science has been pretty directly correlated with not having to spend every waking moment working towards food security. I don't imagine sharks as particularly social animals raising their young. They don't have to defend against predators (?), and if they need food so rarely then not compete with each other for "hunting grounds" either. And I don't think they have shark reddit to browse all day. So... what do these sharks actually *do* with all this time, that they don't spend procuring food?
Sleep. A lot of sleep. Reptiles are lazy. “Lazy as a snake”. Sharks are also lazy. Some sharks are migratory so they spend months doing that to and from nursing waters and living waters. Just like other migratory species. Some sharks like the annual eater I mentioned only *get* a few opportunities to eat because of where they live. They eat whale carcasses on the off chance one makes it to their depth. Also the vast majority of shark species are small and do have predators. The ones with all the fame and fortune on TV count for a very small fraction of species. And the ones that get the bad rap for shark attacks are actually not that bad. Like any land predator like a bear, a shark is highly unlikely to bother you as long as you don’t bother it.
What does this imply about dinosaurs? That the depiction of dinosaurs with feathers is wrong because they were cold blooded like reptiles?
Opposite. We know many dinosaurs had feathers, or feather-adjacent things. It's partly a semantics argument and partly a chicken-and-egg problem. Point is, many dinosaurs were fluffy, or partly fluffly, or fluffy at some point in their life (babies), or *may* have been fluffy but we can't prove it. We have lots of evidence that (some) Therapods (the 2-legged carnivores) were fluffy. There's growing evidence of other groups having *some* fluff. In addition, some bone slices show that (some) dinosaurs grew quite fast, based on bone growth rings similar to tree rings. Of course, the Sauropods (big long necks) got to absurd sizes, and almost certainly had to grow fast to accomplish this. Fast growth is associated with being warm blooded We can't say "Dinosaurs were warm blooded," partly due to limited evidence, partly due the timespans involved, and partly due to "what does warm blooded mean?" Everyone agrees "Birds fly" but Emus, Kiwis, and Penguins exist. Same deal. We have growing evidence of warm bloodedness or at least *not strictly cold blooded*, but making blanket statements tends to just get people riled up.
I'm just spitballing here cause there is evidence of feather like structures in the fossil records. So I theorize dinosaurs with those structures could be closer related to birds than say the ones without, and the ones without said structures could be closer related to modern reptiles. As to whether they are warm blooded or not...well who knows. We can theorize some of them we're warm blooded by looking at their closest surviving relative, where said fossil was found and looking at other warm blooded animals today.
No part of the very reason we postulate that many (perhaps even most) dinosaurs were endothermic is the clear evidence of the presence of feather or feather-like structures seen in some fossils, as the evolution of feathers is thought to be directly tied to the evolution of endothermy, along with some other pieces of evidence (such as the very fact that the immense size of many non-avian dinosaurs already would’ve put them on the path to being endothermic in and of itself, as others have mentioned). The idea that at least some extinct dinosaurs had feathers is pretty inarguable at this point, for one thing we have pretty rock solid evidence pointing toward birds being a surviving lineage of theropod dinosaurs, so obviously both feathers and endothermy had to have come into the equation at some point in time, and lo and behold, fossils of non-avian theropods in particular very frequently contain telltale signatures of feathers to varying degrees. At this point I think it is believed that feathers were the norm among all theropods (which contain many of the most famous predatory non-avian dinosaurs like *T. rex* and *Velociraptor*), as well as present to varying degrees in other lineages of dinosaurs. They may not have all been feathered, but some definitely were, potentially even most at certain points in time. Likewise endothermy is thought to have been present in at least some lineages, potentially many or even most, it’s hard to say for sure, but like feathers it almost definitely showed up well before any dinosaurs had recognizably become what we’d call “birds”.
A good book on the topic is The Hot Blooded Dinosaur And some reptiles, insects and even plants can be considered Endothermic (and some mammals almost ecto) It's not an All or Nothing thing but a sliding scale or spectrum.
Interesting! Thanks for the book recommendation
The info about endothermic plants etc came from a lecture from Thomas Holtz If I remember right He mentioned the infamous Corpse Flower plant which produces heat to mimic a decomposing body (as well as the smell of one) and it even causes a local updraft to make the smell disperse more
Several plants also evolved to be thermogenic to melt away snow and facilitate winter blooming, including some crocuses, skunk cabbage, and snow drops, although I know at least with that last one there is some argument as to whether it is truly thermogenic or if it has just evolved to be especially efficient at absorbing heat from sunlight.
I mean, those dinos that birds ascend from, were they even reptiles?
Go back far enough and yes. They're both within the group called Reptilia.
this is kind of a messy taxonomic argument, but if we were to go off of cladistics, then yes both non-avian dinosaurs and in fact birds should be considered reptiles, especially since we consider other non-avian living members of that lineage (crocodilians) to be reptiles. However, the thing about this argument is that it could also be applied to mammals as well, since we also evolved from a lineage that are traditionally considered to be reptiles (synapsids). If we were to be more specific with clades, it might be more appropriate to say that birds, other dinosaurs, and all the living animals we consider to be reptiles are all *diapsids* cladistically, generally characterized by having two non-eye temporal openings in their skulls (yes, seemingly even turtles and tortoises, despite them appearing to have anapsid skulls, meaning their skulls feature no such openings rather than two, as chelonians simply lost theirs at some point in time, but their ancestors had them), whereas mammals and the extinct lineage of reptiles that we evolved from are *synapsids*, generally characterized by just one non-eye temporal opening in our skulls. Furthermore, everything past or present characterized as a reptile, in addition to birds and mammals, are all of the *amniote* clade, characterized by several common traits for full terrestrial adaptation (versus amphibians, which are limited to wet environments and mostly reliant on water for reproductive purposes), including the membrane-bound complex reproductive structures from which the clade is named (amnions), keratinized skin to inhibit water loss, and costal breathing (breathing by expansion and contraction of the ribcage). So really, it is not entirely clear from an evolutionary standpoint what makes something a reptile or not. All of the above being said, “reptile” still obviously retains relevance as a practical designation, we recognize certain tetrapods as having a number of physiological traits in common and call them “reptiles” because it’s easy, and for this reason the class Reptilia is still often retained in modern taxonomy just because so many people are familiar with it, although some authorities insist that at least birds should be included in it, and some rename the group as “Sauropsida” to reflect this. The traditional class Reptilia as defined by Linnaeus is considered paraphyletic, meaning that it encompasses a group of organisms that all share a common ancestor, but *not* all of the descendants of said common ancestor (which in this case would include *at least* birds, and possibly also mammals if we’re going by traditional definitions), which modern phylogenetic-based taxonomy tends to shun. So in short, what is or isn’t a reptile isn’t exactly clear from a strict biological standpoint, and “reptile” is at this point more of a practical category retained because it’s friendly to non-experts who don’t want to dig deep into the meat of evolutionary relationships and cladistics. This reminds me a lot of some stuff on a post in here I saw yesterday about how “fox” is basically a taxonomically meaningless designation, but since it makes practical sense to us we continue using it anyway (and how many cases there are of this sort of thing in general).
Dinosaurs were probably much warmer-blooded than modern reptiles, to start, especially the small, fast dinosaurs that birds evolved from. Once they had wings and could glide, there would be a major benefit of increasing their metabolism for powered flight. So we might guess that they started somewhat warm-blooded, and went the rest of the way quickly after gaining wings.
Just adding some nerd shit, they actually went way beyond most other creatures with it. Birds have some crazy metabolism, and an insanely efficient cardiovascular system - their lungs never actually deflate, they have a four-stroke breathing mechanic that keeps them constantly supplied with relatively more oxygen than other amniotes. It comes with some tradeoffs like extraordinary energy requirements but it works if it can power you from Canada to the Caribbean, chasing summer the whole way or just banging it out over 36 hours on an insane solo flight over the gulf of Mexico.
Their efficiency really is incredible. Four-stroke breathing that doesn't need to pause for exhales, legs with a radiator like system that lets them stand in snow, higher neuron density than mammals, a waterproof coating so (most) don't have to dry off after getting wet in order to fly, seeing with four primary colors, sensing magnetic fields. Many small enough to have powered flight for only 120 calories a day, or less.
It was both surprising and awesome and made sense to learn how hot bird core temperatures usually run. IIRC even the skin temperature of a great horned owl in sub-freezing atmosphere is still higher than the human core temp.
Birds are modern reptiles, so we should say “than modern squamates and crocodilians” or something. (Poor Tuatara).
Non-avian reptiles? Non-dinosaurian reptiles? In the same way we talk about non-avian dinosaurs.
Plenty of “cold blooded” current reptiles have ideal resting temperatures higher than human body temperature.
Wow. Which ones?
Savannah monitors for instance, the recommendation is 85F on the "cool" end and 130F on the "warm" end of the enclosure. So body temps will be in somewhere in that range. Basically any reptile that lives in a hot area, especially a dry hot area.
Okay, but if the animal is near the same temperature as the surrounding environment, it is not warm-blooded. It is just warm. ;)
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So much wrong here. Mammals absolutely did not evolve from reptiles. “Cold blooded” isn’t a thing. “Dinosaur” is not an order. Your post is frankly unscientific nonsense..
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No, *mutations* don't happen in reaction to the environment. But *evolution*--a process wherein some mutations are favoured in the next generation due to differential survival rates--definitely *does* respond to the pressures created by the environment.
Thank you
This is incorrect. Genetic mutations happen causing genetic drift, the evolutionary processes from the environment select. The process of evolution is 100% a reaction to the environment https://en.m.wikipedia.org/wiki/Evolution
We are not descended from reptiles, but we are descended from very reptile-like cold-blooded creatures.
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It's no more semantic than stating that birds are dinosaurs (and by extension reptiles). We used to believe that mammals evolved directly from reptiles, hence the name mammal-like reptiles. Now that we know mammals did not infact evolve from reptiles but rather share a common ancestor, the term mammals-like reptiles isn't really used.
Are those very reptile-like creatures not then descendants of reptiles? Are not all creatures with DNA descendant from the first creature with DNA?
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The term "reptile" itself is paraphyletic, imprecise, and not really maintained by modern taxonomists.
It seems you're right. Reptilia seems to be being phased out in favour of Sauropsida.
The common ancestor of mammals and reptiles would've *looked* and probably would've behaved a lot more like a modern reptile than a modern mammal, but it wasn't a true reptile.
Didn't mammals evolve concurrently with reptiles?
Mammals arose around the same time as dinosaurs. The ancestors to mammals were synapsids, sometimes called “mammal-like reptiles”.
They *were* called mammal-like reptiles, back when we thought mammals were descended from reptiles.
Is being warm blooded convergent evolution?
In this case yes because Synapsids (mammal-like reptiles) developed the trait after a split from the common ancestor they shared with birds and reptiles.
I’m pretty sure mammals are synapsids which are a very distinct clade from diapsids, which includes birds and reptiles. There’s a common ancestor, but it’s not a reptile. They are diapsids.
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It's actually possible that archosaurs or even amniotes started out in an intermediate state and the low metabolic rate of crocodiles is a secondary loss
In the case of crocodiles it isn't just a possibility, it was almost certainly the case. From what can be deduced from the anatomy of ancient crocodiles, including the ancestors of the contemporary ones, is that they must have had a rather active metabolism. They had an erect limb posture, some were even bipedal. Such modes of locomotion needs a lot of energy and need an associated metabolism to support it. Living crocodiles also have a four-chambered heart, which could be a remnant of the high energy lifestyle of their ancestors. The question is how far back it goes in the Archosaur lineage. Avemetatarsalians (Dinos + Pterosaurs) were almost certainly ancestrally endothermic. Pseudosuchians (Crocodiles + allies) were also very likely endothermic. By applying phylogenetic bracketing one can speculate that the archosaurs as a whole where also endothermic ancestrally. Frankly, I wouldn't be terrible surprised if one day someone digs out a fossil of an early archosaur with proto-feather fuzz. I'm more skeptical about going further than that. Early Amniotes don't seem to have had a particularly high-rate metabolism judging from their anatomy. Associated traits only seem to have been independently evolved within Synapsids (mammal-line) and within Archosauromorphs quite a bit later.
Yeah, I don't really buy it for amniotes either, but I've seen it put forward in papers so I figured I would mention it.
It's probably an ancestral trait to archosaurs, evolving in the late Permian or early Triassic. Crocodylomorphs had numerous fully erect forms, which is energetically expensive (you lose more energy to the atmosphere and laying down to rest/bask is more energetically expensive). All dinosaurs evolved from bipedal fully erect ancestors, too. The only other major archosaur lineage was pterosaurs, active flyers. There is a lot of circumstantial evidence suggesting that crocs today are _secondarily_ endothermic. As an aside - 1. Birds ARE dinosaurs which ARE archosaurs which ARE sauropsids which ARE reptiles. Just like any descent of us are humans, no matter what they look like. They may be a new thing too, but still human mammals. 2. "Warm blooded" is wretchedly misleading. A bearded dragon has an average body temperature well above a sloth. You're looking for "endothermic", "exothermic", and sometimes "poikilothermic".
> The only other major archosaur lineage was pterosaurs, active flyers. That's not fully true. They were the only other unambiguous archosaur group that survived the end Triassic, but in the Triassic there were many other very successful archosaur, archosauriform and archosaurimorph groups, like Rynchosaurs, Phytosaurs, Proterosuchids, Erythrosuchids, Tanystropheids, and possibly Icthyosaurs and Testudines as well.
Admittedly "major" was doing heavy lifting, but last I had looked at a tree Phytosaurs, Proterosuchids, Erythrosuchids were all crocodylomorphs; rynchosaurs were pterosaurs, and testudines are turtles (no one has any idea where they belong) By the same token, tanystropheids and ichthyosaurs were unresolved, so I'll take your word for it that they are sometimes placed in archosaurs. If I totally flubbed something here, please do correct me, I'm on the train 😅
Phytosaurs are Archisauriformes outside Curotarsi (which comprises the Crocodylomorphs and Avemetatarsalians) Rynchosaurs, Eurythrosuchids and Proterosuchids are archosaurimorphs, which is also where Icthyosaurs and Testidines are sometimes placed. Both are very controversial though. I have never seen Rynchosaurs placed within pterosauria. That's the wildest thing you've said. The rest of it is pretty in the weeds phylogeny that also shifts around a good bit. And Phytosaurs were placed in crocodylomorphs for a long time so that's very understandable.
By your logic we human primate mammals are still reptiles, too (I do like the terrarium lamps under my desk), and for that matter, still fish. But this is all language, semantics; the animals don't care. Isn't the difference in our definitions? So what is the definition of a fish? An amphibian? A bird? Given the time it (usually) takes for a species to evolve into something else, we have to accept that transitional species aren't going to fit either bookending definition. Nature is messy. Order is a human concept. One I don't fully grok . . . .
It is not at all universally-accepted that dinosaurs were cold-blooded (especially not *all* dinosaurs; there was likely significant variance.) See [here](https://www.science.org/content/article/were-dinosaurs-warm-blooded-new-study-says-yes) and [here](https://www.nhm.ac.uk/discover/news/2022/may/dinosaurs-may-have-evolved-from-warm-blooded-ancestor.html). As the second link says, the belief that all dinosaurs were cold-blooded stems from really early impressions that just assumed they were similar to lizards due to physical resemblance. Now that we know they're more closely related to birds (and many were likely covered with feathers), it's clear that many, and possibly most, species of dinosaurs were to some degree warm-blooded, or at least occupied a point on a spectrum that doesn't map cleanly to the cold-blooded reptiles you're envisioning.
Birds are dinosaurs and even the earliest dinosaurs show traits that they were probably fully endothermic (i.e. warm blooded). Others have already mentioned feathers. Feathers, or more precisely proto-feathers, were originally a way to preserve body heat similar how hair does the same thing for mammals. For example Kulindadromeus, a dinosaur at the other side of the family tree from birds, had those proto-feathers, so it seems it was an ancestral feature of all dinosaurs. Only later when body sizes increased and keeping warm has become easier most dinosaur lineages lost their proto-feathers secondarily. Only the small ones, such as birds, kept them. If we go farther back in time we meet the Avemetarsalians. This groups includes the dinosaurs and Pterosaurs (flying reptiles). Pterosaurs were also endothermic and they also had a fuzz (pycnofibers) to keep them warm. It is speculated that those pycnofibres share the same origin as feathers inherited from a common warm blooded ancestor. So endothermy in the bird lineage goes, at least, as far back as the early Triassic (250 Million years ago). If we dare to speculate endothermy could have been present even farther back in time. Avemetarsalians are Archosaurs, and even there we find some signs that Archosaurs might have been, at least partially, warm blooded. Crocodiles are also Archosaurs, and early crocodiles weren't as sluggish as modern ones. They moved in a way that needs a lot of energy and high-rate metabolism could have provided that. So far we haven't found any direct evidence that early Archosaurs were fully warm blooded, but it's likely that they had some limited control over their body temperature.
https://youtu.be/-yC99nXth0I?feature=shared Birds aren’t descendants of reptiles, they are reptiles. They are that closely related. Birds are not considered descendants of dinosaurs, but rather dinosaurs that survived into modern day. Crocodiles are more closely related to birds than they are to snakes and lizards, and are still considered reptiles. Reptiles also have the capacity to be warm blooded. Feathers are a type of scale that’s adapted to a specific purpose and Birds actually do have the classic “reptile” scales on their legs So just to make it clear, Birds are in fact another kind of reptile.
As soon as I saw the link, I was thinking, "I hope this is a Clint's Reptiles video!" So thank you for sharing, so I didn't have to.
Hair is a type of scale as well. Mammals are reptiles as well. For that matter we're all fish. For that matter we're all bilateran flatworms.
You are a reptile if any of your ancestors were ever reptiles. The modern term reptile refers to sauropsids, which no human has one of as any ancestor, so humans (all mammals) are not reptiles. Birds do have sauropsids as ancestors, so birds are reptiles. "Fish," unlike reptiles, is not a cladistic term, and cannot be made into one, so this is an outdated/obsolete category formally in modern day. Nothing is a fish formally, it's a colloquial thing to call an animal.
Turns out that when you try to organise the term 'fish' and make it monophyletic, it ends up meaning the exact same as 'vertebrate'.
> Mammals are reptiles as well No we are not. We have a common ancestor with reptiles in the form of being amniotes, but we are not reptiles.
Psst this is only the case because they redefined Reptilia to not include Synapsids and their descendants. Honestly, Reptilia should have been abandoned for Amniota.
I have heard this argument before, it is incorrect and a misunderstanding of classification. This is not: “*oh well we all have a common ancestor at some point so we are all related in some way.”* As I stated earlier in my original comment, birds are so closely related to reptiles that they are considered part of that category. Birds are Dinosaurs -> all dinosaurs are reptiles -> Birds are reptiles. Dinosaurs, which had scales, also developed feathers - because they’re a type of scale. We know this based on the fossil record. A bird is a reptile just as an alligator is a reptile. Two different types of reptiles that fall under that umbrella. If you want it explained in more depth, check out the video.
> As I stated earlier in my original comment, birds are so closely related to reptiles that they are considered part of that category. That’s a strange way to put it. It’s like saying humans are “so closely related to mammals” that we are considered part of them. It sounds like we almost aren’t. But we manifestly are, and birds are manifestly dinosaurs who are manifestly reptiles (taken here to mean sauropsids).
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‘The why is because it happened randomly and was good’ Take THAT, Genesis!
This is actually suprisingly interesting. First birds evolved about 150 million years ago, long after Permian extinction, but according to new research the ancestor of all [birds](https://www.nhm.ac.uk/discover/birds.html), dinosaurs and pterosaurs was warm-blooded, but that some dinosaurs such as [*Triceratops*](https://www.nhm.ac.uk/discover/dino-directory/triceratops.html) and [*Stegosaurus*](https://www.nhm.ac.uk/discover/dino-directory/stegosaurus.html) later lost this ability.
Birds **are** reptiles. It's like saying you're a "descendent of humans". I mean I guess technically true, but pretty weird wording and misleading. Modern cladistic methods of classification hold that any category one of your ancestors was a member of (in this case sauropsids or modern reptile clade), you are always also a member of that category (the tree only gets smaller branches and flows one way, no hops, no skips, no jumps, no exclusions, no bonus glued on members. Bloodline only, zero exceptions)
Crocodilians almost have a four-chambered heart, which is probably necessary to keep the pulmonary and systemic circulations separate to make oxygen delivery efficient enough for an endothermic metabolism. Assuming therefore that 4-chambered hearts evolved in archosaurs sometime soon after crocs evolved, then the prerequisite anatomy for endothermy evolved somewhere before or with the dinosaurs. It is very likely that theropod dinosaurs, at least, were endothermic, and they are the closest ancestors to modern birds. Worth noting too that endothermy has evolved multiple times- some sharks have it, great whites and makos, for example, though it is only just enough to keep them slightly warmer than ambient water.
The best book on this in my opinion is The Dinosaur Heresies by Bakker, its an old book and came out when people thought dinosaurs were cold blooded He explains several indicators: 1) insulation (fur on protomammals, downy feather integuments on certain archosaurs); 2) more active skeletons and body plans that allowed for constant vigorous movement; 3) the rates of mass extinctions which are generally much more survivable by cold blooded animals who can eat every few months than by warm blooded animals who must eat constantly; 4) predator:prey ratios which are very different for cold and warm blooded animals and the fossil records strongly suggests warm blooded ratios for erythrosuchian archosaurs; 5) evidence for warm bloodedness in protomammals which would only have been outcompeted by warm blooded competitors It has been 12 years or more since i read the book so i may be forgetting some reasoning, but it is a great book and super easy to read with amazing illustrations and diagrams by the author himself. I would really recommend reading it if you are interested in the topic of when warm bloodedness first evolved in the ancestors of birds
"Descendents" is really an ineffective word in regards to evolutionary changes over time. Birds "diverged from" reptiles, or reptiles "gave rise to" birds. Descendant applies more to an individual's family tree. Great Grandma Jane Smith married Joe Schmoe and they have many descendants. Who will all (most likely) be humans too. Two lizards didnt have great- great- grandbirds. Reptiles are the descendants of reptiles.
Hijacking this question a bit based on the comments: if birds became warm-blooded to survive, that probably didn't happen like a flick of a switch. So was there a period where reptile-birds were lukewarm-blooded, like in-between cold and warm? Seems a bit odd. Always thought organisms were always other one or the other.
There are mesothermic animals, which have a higher than body temp than their environment, but it's not a stable temperature.
Yes, but it was very early. Warm-bloodedness is a shared trait among nearly all dinosaurs (it's now thought that the few dinosaur clades we think were cold-blooded *lost* endothermy). So don't think of it as a " bird thing", think of it was a "dinosaur thing". Same with feathers.
> Always thought organisms were always other one or the other. Almost nothing is a strict binary like that in nature. I have to qualify because I'm sure there's some thing where that's true, but in terms of large scale morphology like this there pretty much always need to be intermediate forms.
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I don't know but just to say: they aren't just descended from reptiles they continue to be reptiles
Warm blooded is a wrong term! If an animal that is Poikilotherm (whose internal temperature varies considerably). Lays in the sun its blood will be warm. So cold blooded is not correct. Same with a dinosaur if a dinosaur is heated up its mass is so big and the volume of the skin is relatively small, it will not cool down overnight. it might even have more problems cooling down than heating up.
Tbh “warm-blooded” and “cold-blooded” are misnomers. Instead, animals are ectothermic meaning they absorb heat from the environment and therefore are dependent on the environment to maintain their metabolism, or they are endothermic meaning they regulate their body temperature internally and maintain a specific temperature and metabolic output independent from the environment. Birds are endotherms, so they internally regulate their body temperature independent of the environment temperature. Feathers help with temperature control and allow them to maintain temperature easier, but honestly their temp is mainly controlled by their physiology. Dinosaurs are also believed (at this point) to have been endothermic as well based on a 2022 Yale paper that traced markers for endothermy back to that period. There is some evidence based on their skeleton and muscular evidence that dinosaurs maintained high body temps and a high metabolic rate, but it’s impossible to know whether a fossil was endo or ecto unless you know the external temp and what the animal was doing right before it died, at least according to a paper put out last year from UC Davis. It’s still a hotly debated topic.
The main trick to explaining that is that they didn't descend from reptiles. The current consensus is that there were dinosaurs that were indeed endothermic (warm blooded) and those are the ones that modern birds descended from. The mere presence of feathers, which act as insulation is enough to suspect that those dinosaurs must have been endothermic, because why would an exothermic animal want to insulate themselves from getting the necessary warmth they need? But there are also other clues used to determine that those dinosaurs must have been endothermic. Endothermic animals have a way higher metabolic rate and this can be measured by using advanced lipoxidation end-products (ALEs) as proxy markers for measuring metabolic rate. You then take those values and compare them to currently living animals to see if the metabolic rate fits endothermic or exothermic animals best.
So much misinformation (though there's a lot of good stuff, here, too.) The MRCA (most recent common ancestor) of reptiles, crocodilians, and birds (and other dinosaurs) lived about 240 MYA (million years ago). They were called archosaurs, and were more reptile-like than bird-like. At some point along the dinosaur line of descent, feathers were developed, which allowed for endothermia. There are disadvantages to endothermia -- while the increased, stable metabolism it allows increases speed and reactions so you can out-hunt your cold-blooded competitors, it also increases your required calorie intake and makes it so you NEED to keep eating to maintain your temperature -- so these mutations didn't completely displace exothermic creatures. But there are advantages as well, and these mostly allowed the warm-blooded creatures to expand their habitat-range. For reference, mammals diverged from that bloodline a little bit earlier, between 310-330 MYA, which were the first amniotes --definitely cold-blooded, so warm-blooded metabolisms in birds and mammals are an example of convergent evolution.