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Post by Exalt on Oct 7, 2023 18:22:27 GMT 5
Are there any ideas why synapsids ended up with fur, and dinosaurs ended up with feathers, then?
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Post by theropod on Oct 7, 2023 19:44:31 GMT 5
Are there any ideas why synapsids ended up with fur, and dinosaurs ended up with feathers, then? I think the main reason ties in with some of the previous things we’ve talked about; as I explained above, pennaceous feathers (i.e. what one would probably externally recognize as a feather, even if I may usually refer to hair-like feather homologues/protofeathers as feathers as well) likely first evolved as display structures, and such display structures are of course much more likely to evolve in animals with good color vision, such as dinosaurs, than in animals with poor color vision, like mammals. Synapsids and Sauropsids also evolved different kinds of keratins (if we even consider all of them to be keratins, which apparently strictly speaking is no longer officially correct, but still conforms to the normal usage of the term): Synapsids have α-keratins, whereas sauropsids have β-keratins (or more properly "corneous beta-proteins"). The latter are generally larger molecules and as a material have higher stiffness and strength, probably making them more suitable to evolve rigid structures, like feathers. However, it’s of course not like mammals don’t also some hard and rigid keratinous structures (horns, claws, hooves, nails and quills/spines), so that’s at best an additinal reason that might have favoured the evolution of complex and rigid filamentous structures in dinosaurs. Basically, synapsids are more or less stuck in the first stage of the evolutionary pathway that Sauropsids took to evolve feathers; simple filaments for insulation (sometimes modified into bristles or spines for defense). Sauropsids also went through that stage first (and of course still use feathers for thermoregulation to this day, albeit usually more complex ones), but they had evolutionary prerequisites to favour the evolution of larger, more complex branching structures, which in turn became a prerequisite to then further adapt these structures into wings used for flight.
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Post by creature386 on Oct 7, 2023 19:51:00 GMT 5
Evolutionary contingency. By and large, animals have the structures they have due to a mix of functional adaptations and being constrained by ancestral structures. It can be presumed that, somewhere in the line leading to modern mammals, an animal had a series of genetic mutations that promoted the growth of epidermal follicles from the dermis, enabling the evolution of fur. Dinosaurs had a different history and thus had to grow their body integuments from their epidermis, resulting in feathers.
Of course, there might be different factors at play as well. Birds tend to have good vision (hence our language has idioms such as "eyes like a hawk/eagle"), which might push them towards visually-focused sexual displays, resulting in feathers being more visibly impressive and complex than fur, on average. However, I do think historical circumstance is the predominant factor though, as the primary differences between feathers and fur are structural rather than functional.
EDIT: Since theropod was quicker, this is of course a response to Exalt, in case it wasn't clear from the context.
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Post by Exalt on Oct 7, 2023 19:52:29 GMT 5
This is probably an absurd sounding hypothetical, but if we put these things together, could mammals have ended up with feathers had dinosaurs gone extinct sooner? Conceivably, I mean.
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Post by creature386 on Oct 7, 2023 20:07:26 GMT 5
This is probably an absurd sounding hypothetical, but if we put these things together, could mammals have ended up with feathers had dinosaurs gone extinct sooner? Conceivably, I mean. That depends on what you mean by "feathers". If you mean body integument that is functionally analogous to feathers (e.g. used in visual display and flight), I guess it's not impossible, but probably unlikely, due to previously discussed reasons (less suitable keratins, less initial selective pressure). They would not be structurally homologous to feathers as we know them though.
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Post by theropod on Oct 7, 2023 20:13:18 GMT 5
This is probably an absurd sounding hypothetical, but if we put these things together, could mammals have ended up with feathers had dinosaurs gone extinct sooner? Conceivably, I mean. That depends on what exactly we mean by feathers; creature and I gave you two slightly different answers, because creature is referring to a more strict, scientific definition of a feather that is based on developmental and structural characteristics, while mine was primarily a functional one explaining why dinosaur filaments (feather homologues) evolved into different shapes and functions than mammal filaments (hair homologues). I think mammals could possibly have stood a decent chance at evolving something that is functionally analogous to a feather if dinosaurs hadn’t existed (or gone extinct at the end of the Triassic), so that mammals wouldn’t have gone through their nocturnal bottleneck, would have kept good color vision, and accordingly would have had more use for colorful display structures, thus incentivizing the evolution of pennaceous feathers. That doesn’t mean it would have necessarily happened, but certainly it would have at least made it more likely. However, evolving a feather in the strict sense, with the developmental and structural characteristics of a feather, is much less likely. Firstly because hair probably already existed in the Permian, so this likely wouldn’t have changed its basic developmental pattern. Secondly because such a developmental pattern is less likely to evolve convergently than mere functional and morphological similarity. Thirdly, if we consider the material these structures are made of (α-vs β-keratin) a factor in their definition, the split between sauropsid and synapsid proteins goes back even further, so that’s another thing that differentiates the two groups and is unlikely to be convergently evolved. We also run into a bit of a philosophical question here as to whether we’d even call this a feather if it were convergently evolved, even if it ticked all the developmental, structural and biochemical boxes for what constitutes a feather, or whether we reserve that term exclusively for those structures in sauropsids that are actually homologous to bird feathers.
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Post by Exalt on Oct 7, 2023 21:54:21 GMT 5
I did not know that hair had already evolved in the Permian.
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Post by Exalt on Oct 8, 2023 0:09:47 GMT 5
Are there any theories as to what caused the extinction of Lystrosaurus?
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Post by Infinity Blade on Oct 8, 2023 18:27:23 GMT 5
Are there any theories as to what caused the extinction of Lystrosaurus? This is an older publication, but it's something ( Anderson & Anderson, 1993). " The rise to abundance of the cynodonts in the Spathian [Olenekian] and of the rhynchosaurs in the Anisian coincides closely with the relative decline of the dicynodonts that were overwhelmingly dominant in the later Permian and lowest Triassic [i.e. Lystrosaurus]. The decline of the latter reflects, most likely, both changing vegetation and competitive pressure."
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Post by Exalt on Oct 9, 2023 5:31:55 GMT 5
I've noticed that a lot of Utahraptor reconstructions match a pattern of being partially white, paired with a darker color. (I'm not sure if this qualifies as counter-shading.)
Is there something about it's environment that suggests this coloration, or?
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Post by Infinity Blade on Oct 9, 2023 8:18:35 GMT 5
I've noticed that a lot of Utahraptor reconstructions match a pattern of being partially white, paired with a darker color. (I'm not sure if this qualifies as counter-shading.) Is there something about it's environment that suggests this coloration, or? Nope, pretty sure it's just speculative (and people liking to associate Utahraptor with a certain color scheme, I guess). It's worth noting that Utahraptor didn't seem to live in 100% the same type of environment over its whole temporal range either, being known from the Upper Yellow Cat and Poison Strip Members of the Cedar Mountain Formation. I'm not an expert in determining paleoenvironment, but from those who are more knowledgable than me*, the Upper Yellow Cat environment was a seasonally wet one, with a short wet season and very long dry season. The succeeding Poison Strip environment had even longer dry seasons with sand washing into the ecosystem (it is, in fact, called the Poison Strip Sandstone), making it more scrub-like (and, unsurprisingly, less dinosaur genera seem to be known from it). *I had to consult a blog post about Utahraptor the paleontologist Meig Dickson wrote.
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Post by Exalt on Oct 9, 2023 8:25:05 GMT 5
This response reminds me of a Darren Naish article where he discussed trends in paleoart, and one was Phorusrhacos...having a similar trend to this one, now that I think about it...
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Post by Exalt on Oct 10, 2023 2:57:38 GMT 5
So thanks to Ben G. Thomas, I've learned a bit about the various creatures with mole-style body plans.
Why might Xenocranium or Necrolestes have gone extinct, while talpids, golden moles, and marsupial moles yet live?
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Post by Exalt on Oct 12, 2023 4:36:14 GMT 5
Are there any ideas on why we evolved such strong pattern recognition skills?
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Post by Exalt on Oct 12, 2023 7:50:55 GMT 5
How do insects that undergo complete metamorphosis avoid having their pupas eaten? I thought of this earlier and I'm surprised that I never considered this, seeing as they teach us about these kinds of bugs a fair bit early on in school.
(Speaking of, I feel like the strangeness of such a thing is more appreciable as an adult. Imagine if you learned today what butterflies and moths are, how astonished you might be by how they change. It's an unbelievably costly mechanism, and yet, clearly a successful one. One thing a friend of mine told me that helps it is because of how it causes niche partitioning.)
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