bfler
Junior Member
Posts: 97
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Post by bfler on Jul 4, 2011 7:53:00 GMT
Maybe a dumb question but in case of new fossils,what are the characteristics which make scientists think that they found a new species and not only the other gender of an already known species?
For example in case of Hadrosauridae. What indicates that Parasaurolophus with the long head adornment isn't male and Prosaurolophus the female.
Or in case of Ceratopsians. How do we know that, as example, Torosaurus isn't a female Triceratops? If we consider the frill one could argue that females didn't do horn-fights in the breeding season and so they didn't need the massive frill without holes against injuries.
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Post by dinoguy2 on Jul 4, 2011 12:55:25 GMT
Well, in the case of lambeosaurines vs saurolophines, there's more than just the crest that differentiates them. There are some cases where different species might be different genders, like Parasaurolophus walkeri (long, straight crest) and P. cyrtocristatus (short, curved crest). P. cyrtocristatus was thought to be the female by some people, but it actually lived at a later time period. So it's more likely to be an ancestor than a gender.
Generally gender differences can only be known with a very big number of samples to compare, preferably of bonebeds where different types of dinosaurs are more likely to really be the same species. It's been suggested that Styracosaurus is a male Centrosaurus, but we have Centrosaurus bonebeds and you'd expect half of them to have spiky frills if that were true.
Other times, different genders probably represent different growth stages instead. Torosaurus and Triceratops could be male and female of the same species, except all Torosaurus are mature adults and all Triceratops are sub-adult in terms of bone growth. That makes it likely that it's an age difference, not gender difference. Similarly, Ornatotholus (a flat-headed pachy) was long thought to be a female Stegoceras (dome-headed). But new studies show Ornatotholus specimens are all juveniles.
Overll, pretty much every piece of evidence for sexual dimorphism in dinosaurs has been shot down. It looks like there simply weren't many gender differences, or only minor ones (big nose bump in male Protoceratops, for example, is one that is still considered an example). Real gender differneces don't seem to show up until birds, with the long tail feathers of some Confuciusornis specimens, though even that may just be due to molting or age.
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bfler
Junior Member
Posts: 97
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Post by bfler on Jul 4, 2011 14:55:58 GMT
Generally gender differences can only be known with a very big number of samples to compare, preferably of bonebeds where different types of dinosaurs are more likely to really be the same species. In other words we don't know what is male and what is female, right? In case of the Centrosaurus, in my opinion, a bonebed could also be interpretated as remains of the sexually mature females of a breeding colony where the females didn't tolerate males until the breed-phase was over. Maybe they where killed by a flood which also destroyed the remains of the nests. For my thesis about Triceratops and Torosaurus I consider Andrew Farke who wrote that it is unlikely that they are different grown up stages. Hm, seems a bit strange to me that nowadays most animals have different visual genders and in case of dinosaurs it wasn't existant. |
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Post by dinoguy2 on Jul 4, 2011 17:00:28 GMT
Generally gender differences can only be known with a very big number of samples to compare, preferably of bonebeds where different types of dinosaurs are more likely to really be the same species. In other words we don't know what is male and what is female, right? In case of the Centrosaurus, in my opinion, a bonebed could also be interpretated as remains of the sexually mature females of a breeding colony where the females didn't tolerate males until the breed-phase was over. Maybe they where killed by a flood which also destroyed the remains of the nests. For my thesis about Triceratops and Torosaurus I consider Andrew Farke who wrote that it is unlikely that they are different grown up stages. Hm, seems a bit strange to me that nowadays most animals have different visual genders and in case of dinosaurs it wasn't existant. Maybe it just didn't usually involve the skeleton. How many modern animals have obvious gender differences that aren't based on color, size, feather display, or other soft tissues? Even in humans, telling the genders apart would be nearly impossible unless you know specifically what to look for based on studying living examples. You'd be able to tell that one 'morph' is generally smaller, but only if you had a big enough sample size. In modern vertebrates with the biggest gender differences based on bone structures, we'd have to look at things like deer, where one gender has horns and the other doesn't. But this isn't related to display, it's related to the head-butting or horn-locking behaviors of males. It looks like the horns and frills of dinosaurs were as much for species-specific display as for mating display or fighting. Otherwise, you'd expect to find female Triceratops with no horns. Another reason why using mammals as a basis for comparison to dinosaurs is a bad idea. Dinosaur (bird) display tends to be much more color based. Obviously this doesn't apply to mammals, most of which are essentially colorblind. It would make sense for dino genders to differ in color primarily, rather than the obvious bony displays mammals need because they can't utilize color. |
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Post by Griffin on Jul 4, 2011 19:48:01 GMT
If there was sexual dimorphism amongst dinosaurs (and lets face it there probably was considering birds and reptiles) it was probably in the form of color more than anything else.
I wouldn't be surprised if there was sexual size dimorphism too. Its just that there isn't enough fossil evidence to confidently support it. Most reptiles are sexually size dimorphic in addition to lots of birds.
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Post by zopteryx on Jul 4, 2011 23:49:38 GMT
^Building on size dimorphism, female birds of prey (or all birds?) are generally larger than the males while the reverse is true of crocodilians. So, unless I'm mistaken, female maniraptors (maybe all therapods?) would be larger while perhaps the males were larger in ornithsochians. For instance, T-rex, a maniraptor, the females are larger on average...I think.
And going back to coloration, am I correct in recalling that hair can only be shades of brown, black, or white; while scales and feathers can aquire any color?
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Post by Griffin on Jul 5, 2011 3:09:30 GMT
Falconiformes and strigiformes (birds of prey) typically are female larger. Galliformes (chickens turkeys...) are male larger. Those are examples of size dimorphism with birds that i know off the top of my head. Some birds the sexes are the same size.
With reptiles its sort of all over the place. Lizards typically are male larger if there is size dimorphism however there are some exceptions. For instance the genus Sceloporus (fence lizards) consists of almost all male larger species. however, Sceloporus undulatus, just one species within that genus, is famale larger.
Crocodillians tend to be male larger.
Many snakes are female larger.
As for fur I don't really know for sure. I know some primates have fur thats almost bluish in color but that could just be a shade of gray.
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Post by eriorguez on Jul 5, 2011 13:34:12 GMT
Accipiterformes, falconiformes seem to be separate and, well, weird parrots rather that small eagles.  Ratites are also male larger, at least the ostrich, but only slighty IIRC. |
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Post by dinoguy2 on Jul 5, 2011 23:47:42 GMT
And going back to coloration, am I correct in recalling that hair can only be shades of brown, black, or white; while scales and feathers can aquire any color? Correct. Feathers and scales contain beta keratin, which folds in such a way to allow more scattering of light, so they can acquire more and brighter colors, and can combine with pigments to create pretty much any color you want. Hair gets all its color from pigments like melanin, which is basically only capable of doing shades of brown. |
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Post by Himmapaan on Jul 6, 2011 0:17:14 GMT
What about pycnofibre colours?
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Post by dinoguy2 on Jul 6, 2011 23:48:54 GMT
What about pycnofibre colours? Unknown, as we currently don't know what pycnofibres were made of. But the safest bet is that single-filament structures, be it hair or pycnofibres or protofeathers or downy feathers, were all colored only by melanin. For example, you'll never see a blue chick of any species. Structural color in modern birds appears to be restricted to feathers with barbules, but I'm not sure if that's a structural or practical contraint. So, I'd say it's likely that pycnofibres were limited to the same colors as mammal hair and the feathers of bay birds and ratites, which all have loose or downy feathers rather than true pennacoues feathers. |
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Post by Himmapaan on Jul 7, 2011 0:22:06 GMT
Aha, thank you.  |
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