Why Is It So Hard to Tell the Sex of a Dinosaur?
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- Опубликовано: 19 фев 2024
- While we think we know a lot about dinosaurs - like how they moved and what they ate - for a long time, we haven’t been able to ID one seemingly basic thing about their biology...
Which are males and which are females?
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References:
docs.google.com/document/d/14... 
Развлечения
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I saw that my friend had “dinosaur sex” on his google search history a lot so I sent him this because I thought he’d be interested.
It makes sense that sex of dinosaurs would be hard to distinguish. One being bird and reptile related, without colour patterns and feathers or eggs, theres no identifying features to base any differences on. Adding to this, some species of reptiles are very prone to hormonal changes and genetics designating sex in eggs or amphibians, and the existence of reproduction like parthogenisis.
Interesting side note - in mammals (such as humans) the sex chromosomes are X and Y, males are XY females are XX. In birds (and presumably dinosaurs) it's a different set of chromosomes, Z and W. The male is ZZ, the female is ZW.
I wonder if reptiles go through hormone washes that develope varying sexual characteristics and variations after birth like humans
@@stewberryexpress Clearly not binary, gametes aren't the end of it
"No [other] identifying features"? My person, multiple other features, including /body size/ were mentioned. There are plenty of features we probably could use. We just can't use them effectively yet because we don't have enough specimens to perceive patterns. Don't make the mistake of thinking "we don't have enough data to see the pattern" is the same as "there is no pattern".
@@ajchapeliere MANY other identifying features. While a tall female with short hair and higher than average bone density isn't a male. A female with short hair, deliberately deepened voice, chosen name, and adopted masculine social behavior could be a Man. T
Two distinct species could actually be sexual dimorphism and we would have no idea
Angler fish lore
This has actually happened with EXISTING Extant species where we thought two specimen were different species, but it turned out they just had extreme sexual dimorphism and were actually the same species.
So if that can happen with Extant species, its not too far fetched to think it could happen with extinct ones too.
This also applies to adults vs juveniles as well. These can also sometimes appear like different species even when they arent.
@@eragon78What species?
@@eragon78 Our knowledge of sexual dimorphism within extant species is probably exactly the reason for the original comment.
@@MelyssaAKASkittlez I don't know which ones eragon was thinking of, but one famous example is the eclectus parrot. The males and females are completely different colours, and people thought they were two species. They were trying to breed them in captivity by putting males with males and females with females. At least, that's the story I heard
Grew up on a farm. "Sexing chicks" was bad enough. (To tell male from female chicken chicks.) Do that a few years as a kid, and the thought "sex the dino" is basically a NO WAY!
Lift the baby dino by the feet. If it just hangs there passively it’s female, if it fights you it’s male. Supposedly works for chicks, just need to locate a nest of dinosaur hatchings
Do an episode about prehistoric India when the subcontinent was an island before it crashed into Asia.
This would be great!
Oooh that'd be cool.
Adding agreement to this request!
That'd be amazing
If i remember right, it will involve discussions of lemurs.
It’s sometimes difficult to tell the sexes of reptiles to this day, much less from (often incomplete) fossils. One has to be an expert, often probing the cloaca for bumps, counting them for male or female. Those bumps are soft tissue & internal, thus are rarely preserved
Setting aside how cool it is that we can (potentially) tell something like this about a creature that's been dead for over 65 million years, can I just say that I love how well this showcases the scientific process? Someone finds some interesting technique or concept, and backs it up with evidence. Someone else is skeptical, and provides their own evidence as to why. The first person goes out and (maybe?) conclusively backs up their points with brilliant evidence. This is fundamentally what science is about, and I love seeing it on full display here.
Wait! Wait just a second! Are you telling me that the T-Rex in Chicago might be a "boy named Sue?"
Great post!
The Johnny Cash Song !!
Yup,daddy T-Rex knew the world was tough,so to make his son T-Rex strong enough to get through it,he named him "Sue"......
How do you do?
If Steve is still alive and watching, we appreciate you too
Steveeeee you there?
We miss you Steve!!!
The museum I intern at here in Wyoming, has the 1st and only T-rex to stay in Wyoming. We don't know if its male or female; the body is small but a tail section is broken and healed over so maybe mated? The femur size is also small. Our rexes name is Lee :)
I was always told that fossils are essentially "casts" of the original bones in rock.
I wouldnt think that anything inside the bones could have ever been preserved. Thats amazing!
I love the scientific process so much. It's so exciting when scientists think of new ways to test a hypothesis and potentially learn something new.
I first read about medullary bone from a compilation of _Scientific American_ vertebrate articles that I bought, but I didn't realize at the time that it could be discerned in fossils until much later.
This is such a great overview of the scientific process, and an awesome video!
My favorite channel!
Love the face-tickling turtles!
Ugh… I love dinosaurs sooooo much 🦖 never get tired of this!
Something I'm surprised this video didn't touch on is that we do have other animals we've been able to reasonably extrapolate the sex of! Specifically pterosaurs, which aren't dinosaurs themselves but their closest relatives. Pteranodon is famous for having two different size morphs, the larger of which has a big sweeping crest whilst the smaller one has basically a nub. Considering they had been found together, and all other characteristics of their skeletons pointed to them being the same species, we already had some decent evidence of sexual dimorphism. This is further reinforced by immature specimens of both the large AND small morphs being present, indicating that the small morph itself wasn't just an immature version of the larger morph.
Figuring out which is male and which is female specifically is still far from an exact science because of how much dimorphism can vary between species as touched on in this video, but it's fairly universally assumed that the large morph is the male, while the small one is the female. While females can be larger in dimorphic species, males being the larger one is more common among tetrapods, particularly so for males with a display structure just like in Pteranodon. Animals in which females are larger rarely also have display features, and vice versa. Additionally the smaller females seem to outnumber the larger males, which is also consistent with most modern day animals. While there are cases in which females take on multiple males (polyandry) it is much, much rarer than males taking multiple females (polygyny). Males can mate frequently and easily thus have little need to be as selective when choosing a mate, while females need to be more choosy about who they mate with due to the time and resources they have to put into reproduction, so in the majority of animals there's pressure to evolve a polygynous system rather than polyandrous. Again, this isn't universal, but it is by far the more common method of mate selection.
Additionally, the smaller females seemed to have wider-set pelvic bones, likely to pass eggs more easily. It isn't reliable as the sole way to sex a skeleton because many species don't seem to have wider hips when you'd think it advantageous, plus it can vary a lot between individuals within a species (including us, hence why archaeologists try to use cultural signifiers such as what a person was buried with to determine sex rather than features of their skeleton). But with everything else in mind it's a pretty safe assumption that Pteranodon's have sexual dimorphism in which males are larger with big crests, while females are smaller with tiny crests.
It crossed my mind that _T. rex_ evolved from much smaller ancestors so if it did use those bone deposits it could be vestigial
Something of that nature likely wouldnt be vestigial though since it requires a lot of resources to maintain. Producing new bone formations during egg production just to get rid of them later is expensive and would likely have pressure against it from happening if its no longer necessary.
So it COULD be vestigial, but its likely not. Most vestigial traits are more or less benign and dont really help or hurt the creature's survival which is why they stick around.
But it could also still just be used. Its very possible that the trait isnt vestigial at all and was still helpful to some degree which is why it stuck around.
@@eragon78 I mean, vestigial bones are very common in general. We humans have vestigial tail bones.
@@Ezullof Yea, but vestigial bones dont require as much energy to produce and maintain unlike a process that happens regularly.
These types of bone formations form during the reproductive cycle for birds, they dont always exist in the bird's skeleton, only during a certain part of the reproductive cycle.
This means it takes a lot of extra energy every reproductive cycle to both form, and then remove these formations. While its technically possible for something like this to be vestigial, its highly unlikely that such an energy wasteful process that isnt being used anymore would stick around. There would be a heavy selection bias against it.
Compare that to a vestigial bone which usually shrink massively in size, and only form during fetal development, and the distinction is huge. The energy a fetal bone requires is a one time cost, and far lower than that of forming deposits in all your bones during every reproductive cycle.
And even with that, the vestigial parts are almost always significantly smaller as a result of no longer being used. There is no sign of such a thing in dinosaurs. If this really was a vestigial trait, it would likely be far less of the bone structure, and would likely only exist in trace amounts.
So its not IMPOSSIBLE that its vestigial, but its very unlikely that it is. Thats all im really saying.
@@eragon78 would it require extra resources or would it act as a redundant surplus that gets used regardless? Any trait that doesn't cause too severe of a hindrance tends to stick around
@@M_Alexander It might still get used back up and recycled, but im not sure. It still would be a net negative of energy though because changing the states of chemicals is always going to lead to a net loss of energy. No process is 100% efficient. Building those structures just to recycle them still has some energy cost, although if they are efficiently recycled, it may not be AS extreme which may allow them to stick around as vestigial.
But its still going to have a negative energy cost associated with it, so if it is vestigial, then there would be signs of it becoming less and less extreme even if it still ends up existing. (Similar to how a vestigial limb or organ may shrink over time as a species evolves even if it still ultimately sticks around.).
So if it is vestigial, there would probably be some evidence of that in the fossil record from dinosaurs that lived later on compared to those that lived earlier on.
It also means that an ancestor of dinosaurs, or at least the ancestor of the TRex in this case, would have had to have that trait actually being used for it to become vestigial to begin with.
So more archeological evidence should eventually turn up a more definitive answer. But im still pretty sure a system like this would likely be too energy intensive to stick around as a vestigial process, at least to the degree its found in fossils. I could be wrong though.
I’m confused. Aren’t fossil bone molecules different from those of regular bone? Like totally different minerals? How is it then possible to compare staining between the two?
not all molecules are mineralized
Mostly, yes - but fossilization is a haphazard process that is unlikely to replace every single molecule. For the stain to work, there just needed to be enough of the molecules to start a chemical reaction (it's fine if they're mixed in with a lot of other minerals that weren't originally part of the bone tissue).
The structure stays the same
Some proteins stay in fossils for hundreds of millions of years.
If the minerals do not interfere with the binding site of the stain, it would still work.
Great question, and a fortunate test type!
Interesting that the tissue was still preserved after all those millions of years.
I would love to see you guys do a video on the soft tissue that was also found within B-rex and other fossils since
Will you guys be uploading to your podcast anytime soon?
Absolutely fascinating debate and ace work by Schweitzer and her team! The new paper should have tested the large population sample for medulary bone tissue to see if it matched with the dimorphism characteristics! And always appreciate the mention of thanks for indigenous land and community help!
Fascinating episode. Well-explained research.
Thank you for so often acknowledging native land where fossils are found, and where episodes take place. ❤️
Paleontology is so full of unresolved and troubling questions that causes scientists to argue about.
The reason why i love palaeontology. So many mysteries waiting to be unsolved
science lore
Yeah it makes it interesting!
... thanks captain?
The dinolore is a hot topic for discussion I’ll never get tired of
I'm so stupidly excited when a new Eons is posted. Always informative, great art, new ideas.
As always, thank you for your enjoyable & enlightening episodes. 👏🖖
Happy 200 years of Dinosaurs 🦖
Its been 200 years since Megalosarus was named…
I LOVE this cutting-edge paleonthology episodes. only PBS Terra brings this for us.
thanks guys!
I always learn from your videos
It's an interesting question bc well we don't even really know what to base speculation on. As mentioned, many reptile species have larger females. They also do need quite a lot of calcium after laying, so much so that some species can die if they "double clutch" in a season. And then there's some reptiles that are viviparous or oviviviparous. But in any of the cases idk how we'd know for sure that was their method without finding a gravid female. And then there are crocs (yes ik they're a reptiles, but they do it a bit different) and birds.
Love this very interesting content Thank you!!
Oh, this is fascinating!!
The picture at 5:54 almost looks like a Magic Eye illusion.
Enjoyed the video! I prefer the slightly longer approach work more details
We need more investigation into the egg laying cycles of Emos. 😅
00:32 THIS CAUGHT ME OFF GUARD
very intresting as always
I would love to see a study on the evolution of the humming bird!
Was listening along and got to the section on the study that theorized the structure was a more general bone disease and I'm like, "Well, can't tell the sex but might have found evidence of dinosaur syphilis." LOL
Because it's hard to hold their trails up!
I watched you guys back in 2017 i love dinosaurs
Please do an episode on the Livyatan and other macroraptorial sperm whales
Did Dinos also lay unfertiliezed eggs?
I think the likely answer is yes. The more recent findings in paleontology have really been pointing towards modern birds really being a form of dinosaur, with many dinosaurs having bird like traits and habits.
@@prophetofthe8th Just the mere connection of dinosaurs and birds aren't always enough to form a conclusion. Mammals today have various ways to reproduce. If, for example, an extinction event happens and only egg-laying monotremes survived, the future paleontologists cannot immediately rule out that all mammals only ever laid eggs.
With how diverse dinosaurs are, I wouldn't be surprised if at least one clade of them gave live birth.
@@prophetofthe8th More than that, reptiles can do this too, which suggest the trait has existed even before dinosaurs did.
Although laying unfertilized eggs is rare in the wild as most females will mate during ovulation. Its mostly common with stuff like Chickens because they were bread to amplify that property taking advantage of their reproductive cycles.
Here, you’ve read a lot of lame comments. Have a bento 🍱
This is interesting
If both pterasaurs and dinosaurs both had this special bone tissue, then shouldnt it be an ancetry trait from a common ancestor? Maybe it didnt develop in birds but instead is a relic of fish transitionint to land. fish dont have high calcium bones, so maybe then needed it first to develop proper eggshells? Or maybe it developed a bit later when terrestrial animals became totally free from water and developed hard shells?
Maybe we could prove this by looking at mososaur bones. If they have this weird bonestructur even tho they werent terrestial but came from terrestial animals, they just kept the trait?
Isn't alluvium always deposited by water? I think material left behind by ice would be glacial till.
I love the Eons content and hosts! Love that plug at the end for emonightbk, these ladies are the coolest!
I think most definitely would have a cloaca, but finding an external structure preserved would also be interesting.
Do mammals have the same bone differences when pregnant too?
Thinking it will take a lot of calcium to build baby bones inside.
Before watching the video, I am guessing they were like birds and had a cloaca
Quick question. Since chickens have insane head stability. (Insert that funny bmw commercial) are there any known dinosaurs that had that ability?
If modern birds are descended from dinosaurs, does that mean they are more related to dinosaurs than modern reptiles are? Also, does that mean that no birds existed when the dinosaurs existed?
Neat
But...grandpa said all the dinosaurs are girls...
That was all so interesting!
yeah dinosaurs 🤘💯
Birds are Dinosaurs. It is difficult to overstate the significance of this fact, for palaeontology. Perhaps the most recognisable group of vertebrates, Dinosaur bones line both displays and drawers in every natural history museum, offering endless fascination for children and adults alike.
Yet, so much about these creatures is lost to history. Think of how little the bones of an animal resemble the living being they once supported. The colour of their eyes, the texture of their skin, the way they moved, the chemistry of their blood; all gone. We take for granted the ability to discern the sex of living creatures, but this is exceedingly difficult in fossil animals.
Anyone who has ever owned a reptile knows the difficulties of discerning male from female. This is because of their lack of external sexual organs, as well as the typically little sexual dimorphism between the sexes of most species. This difficulty is multiplied when looking at (often incomplete) remains of extinct reptiles, like Dinosaurs. Most species of Dinosaur are known only from a single specimen; so we usually don’t even know what the female of an extinct species is supposed to look like!
Exceptionally preserved fossils, and ever-advancing methods of studying them, help fill in some of these gaps. But the closest we will ever come to knowing the living anatomy of these amazing animals, is found in their living descendants, the birds. Despite how unique birds are, even among the dinosaurs, many of their anatomical curiosities are deeply rooted in the Dinosaur family tree. These include feathers, wishbones and even the air sacs of their respiratory systems. Well, it turns out the similarities go even deeper. Down to the bone, in fact.
Dinosaurs lay hard-shelled eggs; these require extra calcium. In female birds, this calcium is laid down and stored in a unique type of long-bone tissue called Medullary bone. Its presence is an indicator of a sexually mature female, about to lay eggs. This tissue has now been found in multiple Non-Avian Dinosaurs,including a T-Rex.
I feel like we need to look at more species. We don't know if this applies to all theropods or even all dinosaurs.
Regarding function in T-Rex, it is possible that this structure evolved in a smaller ancestor and was kept.
I miss Steve :c
I absolutely adore this channel. All of the presenters are very charismatic and the storytelling is perfectly crafted and compelling. I really miss your podcast on Spotify!
I wonder how dinosaurs mated?
Carefully.
Probably like reptiles or birds now a days
bro you LOOK like someone who would wonder how dinosaurs mated
Oh, those are some cool earrings, they aren't amber fossils are they?
Oh, hey, just like birds!
Egg layers are referred to as "gravid," not "pregnant."
Both words are synonyms but you more often hear gravid used for thing that lay eggs and pregnant for thing that give live birth
I've seen a maternity clothing store in Brazil called A Grávida Vaidosa.
Humans, in medicine, ask *para* (children born) *grava* (pregnancies) status.
(I wonder if any gave live birth?)
However, modern birds lay one egg a day. Wouldn't they be pregnant but not carrying eggs?
Sharks are called pregnant, too, right?
I'm definitely used to hearing about gravid reptiles. (Never thought about gravid birds... Much)
@@TragoudistrosMPH some sharks are called pregnant, but those sharks birth live young. The ones that lay eggs are called gravid.
No. Pregnant literally means "before having a child" and gravid means "full with a child". Gravid is just less common and more technical, but the two words are completely synonymous. You invented a distinction that isn't real.
Such a nice video ❤❤❤❤❤
I believe Dr.Malcom asked about this in Jurassic Park
Bobbi Rex
its hard to tell the sex of a dinosaur nowadays because they usually don't fossilize while "Doing the deed".
That also doesn't tell us exactly what we want to know. Dinosaurs have different types of chromosomes as we do so we wouldn't be able to translate our conception of sex to them quite the same either.
@@user-wj1kg8qo3p Quote[Dinosaurs have different types of chromosomes as we do so we wouldn't be able to translate our conception of sex to them quite the same either.]
What do you mean by this? DNA does not fossilize. We do not know what the genome of dinosaurs actually looked like.
Also, this is "sex" in the biological sense. For most species its pretty straight forward. One sex produces eggs, and one sex produces sperm. Thats how it is for most large species. There are other ways reproduction can happen in other types of living things, but these terms are generally pretty well defined.
So our conception of sex applies just fine to dinosaurs. I dont see how it wouldnt.
@@eragon78 Again, you're really trying hard to oversimplify this. Not only are we sure dinosaurs didn't use the same X and Y chromoses we do, neither do many MAMMALS. No, it's not as simple as which produces eggs, we can't take that to the beginning of microbiological life, which does reproduce and isn't always a sexual. They never evolved eggs.
Not only that, but it still is completely ignoring binary sexual examples from numerous species. Including humans, whether they produce eggs or not. You don't get to pretend definitions are objective when we already talk about sex as a spectrum widely in science.
I always get excited when i see Michelle is hosting a video. They're so cool and their presentation style is really friendly and engaging.
I would have thought Terminal moraine but could be wrong been a long time since I studied Physical Geography
On interesting possibility is that both camps of the discussion are right. Evolution works more often than not by adapting a previous trait (say bones grew out of calcium sacs, or dogs got most of its socializing features by keeping their puppy traits, etc.). Thus, I would not be surprised, if the current medullary bone structure was actually an adaptation of a different feature that the Rex lineage used for something else. After all, the rex are just the previous branch theropods to the lineage that evolved into birds. So I would be inclined to assume that the Maniraptoriformes had some special feature in their bones that they adapted later to enable flights, but probably had the original structure shared with Tyrannosauroidea or even earlier ancestors. It would explain both why it did react to the chemical signature but was not necessary given the bone density for egg laying.
Absolutely, I think there's a real possibility that the features may be similar but not analogous.
Steve...
I love your presenters.
A (very old) stereotype about people in science, is that they have very little fashion sense. But I wish I had one tenth of the style the people of Eons (any of them) show in each video.
What happened to the theory proposed a short while ago, that the first lower caudal spine would be reduced or absent (as in female crocodiles) to allow more room for the eggs to pass?
Michelle has really improved as a host, she’s excellent!
Why did the dinosaur cross the road ?
To ask the chicken who lays the eggs lol😂😂
You’re awesome!
🥰🦖
....moraine
This episode was well done and....well presented.
🤙🖤
Ngl I miss the jokes at the end of the episodes 😢
Thanks for the indigenous acknowledgments at the end. It’s good to know the price of some knowledge.
I don’t know why we’d need clarification between female aka egg producing and male aka sperm producing dinos as that’s an obvious. Enjoying the subject though and hope these continue
You know why.
I also rolled my eyes at this part 😂🙄
Not all animals have a male/female distinction. Some are asexual, or they don't have a pure dichotomy like we're used to in most large fauna. Some lizards are asexual, and a lot of fish are hermaphroditic.
In that case the short or long hand would not be relevant and wouldn't be used. That's not an explanation at all, but rather a clever moving of the goal posts. But not clever enough.@@shoeboxbistro
Understanding the sexual dimorphism of species can be a really interesting way of figuring out mating behaviour, in lions, the males are notably larger with manes of varying length and colour as an adaptation for competition between males and protecting offspring from rivals, if dinosaurs had a similar difference, it could suggest similar behaviours. Contrarily, many species of birds of prey have been seen to have larger females that select for smaller males, in owls in particular this is an adaptation for females guarding the nest while the smaller males are out foraging for food, basically the exact opposite of lions, and likewise there are plenty more species of animal where males and females are almost indistinguishable, and that will have implications for how their behaviour during mating works. There is admittedly an emphasis on size in these examples, but the point stands, understanding sexual dimorphism or the lack thereof is a great signpost for understanding behaviours obscured by the limits of the fossil record.
Defining the sexes solely by the type of gamete produced is the only taxon agnostic, and technically correct, method of doing so.
But don't let PZ Myers know that you did so, because he'll have a conniption over it. 😂
I just love Michelle’s style! It’s gothy/punk paleontology!
0:07 This looks very safe!
What about Dinosaur STDs?
They didn't have phones :P
Dinosaur love and Life is war
Well, now you've gotten tRICKy again! The larger accretions left behind upon the retreat of glaciers is called moraine alright! "Terminal" at the glacier's furthest reach, and "lateral" at the sides. Alluvium is usuallly the ground down material from beneath the body of it, though some of that may arrive from (upstream of) the remaining watercourse? Apologies for being a pedant though, but it is high school stuff, so where was that enquirer then, hmm?
Bone density?
With what bones? Were working with fossils
@@Someone-sq8im It's not too hard to infer bone density from fossils, but it won't tell us anything about dino sex unless we make the assumption that one sex had denser bone than the other.
Humans are a species with sexual dimorphism, where males have denser bones on average. But it's not the case for all species, or even all primates.
3:57 *Can I call you "mista"?*
I saw "femora" in one of those headlines. The other plural, "femina", may have been more appropriate. (It's an r/n noun, though it has no known cognates.)
Well have they found Medullary bone from a male bird?
Yeah, as criticizers of the paper have pointed out: there's a widespread disease that causes it in both female and male birds
Think about amount of sperm. Male representative success id to judge how to invest in a certain female and or offspring
That's a nice view that skips a commonly assumed bias.
If you're going to spend a lot, even if you're 'rich', why not spend it all on quality? 🤔😀
Kind of random and unrelated to the video (which is very interesting) but that dress is so stunning! The colour and belt and pleats it’s just 10/10
Michelle has riveting style
Definitely female
@@harrybruijs2614 She's egg-producing?
We call them Eskers…. There’s a bunch here in PG.
It saddens me that we have to say "sperm producing males" and "egg producing females." Saying male and female should be clear cut but we have lunatics running the asylum.