Prehistoric animals/dinosaurs we know the gender/dimorphism of

[Bowhead Whale]

So far i only know about Male Protoceratops being more robust than females, and many of closely related mammals of the past having similar ways to their modern versions(lions, elephants, dogs)

Im also aware of the myth about female dinosaurs being larger than males
And I know about the debate/speculated notion of male stegosaurus being larger and having more larger plates.

So besides all of that mumbo jumbo what else do we know about this subject.

Male dinosaurs being smaller than females may not be a myth. In baleen whales, just like in sharks and birds of prey, females are bigger than males. So, there may have existed dinosaur species where females were bigger than males, just like it happens among modern species today.

[Stegotyranno420]

Correct me if I'm wrong but female baleéis are only larger because of pregnancy?
Also in the majority of large tetrapods males are larger so it's likely they would had been the same

[Newt]

No, female baleen whales are longer as well as heavier than males. On the other hand, male sperm whales are larger than females. Similarly among turtles, females of emydids and trionychids are larger, while among chelydrids males are larger. Different kinds of dimorphism can even be seen within the same genus: American bullfrogs (Lithobates catesbeianus) have larger males, while many other Lithobates species have larger females.


I'm curious now to see if anyone has compiled the distribution of sexual size dimorphism among tetrapods in a rigorous way. I suspect if they did, the supposed "normal" condition of larger-male dimorphism would turn out to be much less prevalent than some think, and is probably mostly based on our mammal-centric view of the animal world.


Something to think about: why should one sex be larger than the other? In strictly reproductive terms, it makes sense for females to be larger. Eggs and babies are energetically expensive to produce and take up space in the mother's body; a larger female can produce more or larger offspring than a small female. Sperm, on the other hand, is energetically cheap and even a small male can easily produce all the sperm he will ever need. So, if males are larger in a given species it tells you something about that species' biology: namely, that the males fight.


They may be fighting other males over access to females, or over territory or resources to attract females; they may be fighting in the sense of actual violent combat, or in a more ritualized way; they may even be fighting the females (looking at you, waterfowl); but big males are definitely fighting. This does not mean that males don't fight in species with larger-female dimorphism, but it seems less common or extreme in those species.

[Bowhead Whale]

No, female baleen whales are longer as well as heavier than males. On the other hand, male sperm whales are larger than females. Similarly among turtles, females of emydids and trionychids are larger, while among chelydrids males are larger. Different kinds of dimorphism can even be seen within the same genus: American bullfrogs (Lithobates catesbeianus) have larger males, while many other Lithobates species have larger females.


I'm curious now to see if anyone has compiled the distribution of sexual size dimorphism among tetrapods in a rigorous way. I suspect if they did, the supposed "normal" condition of larger-male dimorphism would turn out to be much less prevalent than some think, and is probably mostly based on our mammal-centric view of the animal world.


Something to think about: why should one sex be larger than the other? In strictly reproductive terms, it makes sense for females to be larger. Eggs and babies are energetically expensive to produce and take up space in the mother's body; a larger female can produce more or larger offspring than a small female. Sperm, on the other hand, is energetically cheap and even a small male can easily produce all the sperm he will ever need. So, if males are larger in a given species it tells you something about that species' biology: namely, that the males fight.


They may be fighting other males over access to females, or over territory or resources to attract females; they may be fighting in the sense of actual violent combat, or in a more ritualized way; they may even be fighting the females (looking at you, waterfowl); but big males are definitely fighting. This does not mean that males don't fight in species with larger-female dimorphism, but it seems less common or extreme in those species.

That's right. And, as I said, modern birds of prey and modern sharks show females bigger than males.

[Papi-Anon]

No, female baleen whales are longer as well as heavier than males. On the other hand, male sperm whales are larger than females. Similarly among turtles, females of emydids and trionychids are larger, while among chelydrids males are larger. Different kinds of dimorphism can even be seen within the same genus: American bullfrogs (Lithobates catesbeianus) have larger males, while many other Lithobates species have larger females.


I'm curious now to see if anyone has compiled the distribution of sexual size dimorphism among tetrapods in a rigorous way. I suspect if they did, the supposed "normal" condition of larger-male dimorphism would turn out to be much less prevalent than some think, and is probably mostly based on our mammal-centric view of the animal world.


Something to think about: why should one sex be larger than the other? In strictly reproductive terms, it makes sense for females to be larger. Eggs and babies are energetically expensive to produce and take up space in the mother's body; a larger female can produce more or larger offspring than a small female. Sperm, on the other hand, is energetically cheap and even a small male can easily produce all the sperm he will ever need. So, if males are larger in a given species it tells you something about that species' biology: namely, that the males fight.


They may be fighting other males over access to females, or over territory or resources to attract females; they may be fighting in the sense of actual violent combat, or in a more ritualized way; they may even be fighting the females (looking at you, waterfowl); but big males are definitely fighting. This does not mean that males don't fight in species with larger-female dimorphism, but it seems less common or extreme in those species.

It could be that in some where the males are bigger it's a selective pressure based on anatomy. There's a theory, last I checked, that male peacocks that tend to be successful at reproducing are the more ornate and colorful because females are attracted to pairing with such types due to all that showy plumage actually being a huge survival disadvantage (lack of camouflage, etc), and thus if a male can survive to breeding age while still sticking out like a sore thumb for predators then his survival fitness/instincts are likely good.

Larger size may also correlate with sex hormones that increase muscle/bone/etc size that also may lead to behavioral changes such as elevated aggression/territorialness either year-round or during breeding seasons (such as the seasonal musth in extant male elephants). The larger more aggressive males may thus be better suited to surviving harsh conditions, predation, and intraspecific competition that weeds out less-hardy males from the gene pool by pure survival alone. Elevated aggression, territorialness, and size may then lead to females selecting physically stronger males to increase the likelihood of offspring with similar strength and fitness levels and thus ensure survival of the species.

Of course, some species's females like to get the best of both worlds. There's at least some cuttlefish where the dominant males are significant bigger than the females but less dominant males the same size as females also exist in their marine community. The female cuttlefish will opt for being the mate of the large dominant male, but a smaller male (faeder? I think that's the word) will sneak in and change his appearance (color patterns and perceived behavior) to mimic a typical female to covertly mate with the actual female. The dominant male thinks he's simply snagged an extra mate and doesn't bat an eye at the interloper, but before he can mate with the other 'female' that male has already done the deed with the real female and leaves. And said female? She allows the remaining big male to mate with her too and fertilize roughly half of her eggs to get offspring that are either survivalists by brawn or craftiness, getting the best of both types in her descendants. Mind you, cephalopods and dinosaurs are two VASTLY different types of animals, so any chance of similar strategies or cases of sexual dimorphism (multimorphism? Polymorphism?) is possibly nil. But, it could be that perhaps some of the gracile specimens of some species could simply be males with lower dominance/hormone levels and were just less likely to have offspring but could still survive to adult age by just adopting less risky lifestyles.

WHEW!

Mind you I'm no biologist and by no means are the things I've listed universally applicable in every species or groups. Just some speculation on my part.

[Rexy]

What about the apparent discovery of medullary bone in pterosaurs and dinosaurs including T-Rex and Tenontosaurus?

For anyone who doesn't know, medullary bone is a bone tissue that unique to birds, but it's only found in females about to lay eggs. This bone tissue serves as a reservoir for the calcium that's needed to form the eggshell. Since birds and dinosaurs are related, is it possible that female pterosaurs and non-avian dinosaurs formed medullary bone when they were reproductively active?

[Bowhead Whale]

It is a strong possibility indeed.